Patent ID: 12201422

DETAILED DESCRIPTION

The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims.

The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the disclosure or the claims. Alternate embodiments may be devised without departing from the scope of the disclosure. Additionally, well-known elements of the disclosure will not be described in detail or will be omitted so as not to obscure the relevant details of the disclosure.

The words “exemplary” and/or “example” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” and/or “example” is not necessarily to be construed as preferred or advantageous over other embodiments.

The word “approximately” as used herein with respect to certain dimensions means within ten percent of the dimension, including within five percent, within two percent and within one percent of the corresponding dimension.

Conventional methods for obtaining biological samples from a subject are invasive, uncomfortable, and painful. For example, conventional glucose biosensors require that diabetics obtain blood samples by puncturing or lacerating their skin using a sharp blade or pin. The blood sample may then be collected and delivered to a biosensor which detects glucose levels of the sample blood. While such biosensors are often marketed as being “pain-free,” users often experience some degree of discomfort that they may become inured to over repeated samplings. Regardless, conventional biosensors may cause discomfort, pain and may increase the chances of infection or bleeding.

Another disadvantage of the conventional biosensors is that they require several steps before they can analyze a biological sample. Conventional biosensors require breaching the skin, collecting the biological samples (e.g., blood), and delivering the obtained samples from the site of collection to the analyzing device. This multi-step process is time consuming and may cause contamination or loss of the biological sample during the collection and/or delivery. Additionally, if the sharp instruments that are used to breach the epithelium are not disposed of properly, cross-contamination of diseases, such as hepatitis, may result when other persons come in contact with the contaminated sharp instrument. A further disadvantage of the current biosensors is that they require relatively large sample volumes to provide accurate results.

Thus, various embodiment methods and apparatus are disclosed which provide for a safe and non-invasive transdermal sampling, and analysis of biological samples. The various embodiment methods and apparatus obtain and analyze transdermally extracted biological samples with minimal injury or sensation. In addition, the various embodiments obtain biological samples and deliver the samples to a biological sensor in a single step. Thus, potential risk of contamination may be minimized. In an embodiment, a voltage (or current) may be applied to a disruptor unit creating a localized heat that may be applied to the epithelium (i.e., skin) of a subject. The applied localized heat has been found to alter the permeability of the cells at a disruption site in the stratum corneum layer of the epithelium such that channels for fluid flow are created.

Interstitial fluid may permeate from these capillary-like channels and may be collected. The collected fluids may be tested for an analyte, such as glucose, by reacting the collected fluids with a biologically reactive element, such as an enzyme. The products of the biochemical reaction between the biological sample and the biologically reactive element may be analyzed electrochemically to deduce the concentration of the reactant from either a potential or an electrical current. The amount of potential or current that is detected may be mapped to determine levels of analytes or characteristics of the biological sample. Once the disruptor unit is removed from the skin, stratum corneum cells become impermeable again by returning to their original formation and closing the capillary-like channels.

The various embodiment methods and apparatus further allow for accurate real-time analysis of very small amounts of biological samples. In an embodiment, minute quantities of the interstitial fluid collected from the capillary-like channels of the stratum corneum may be used to determine various analyte levels.

The various embodiment methods and apparatus further enable the entire process of analyzing a biological sample including disrupting the skin cells, collecting biological samples, reacting the biological sample with a biologically reactive element, and sensing the signals generated by the reaction in singular device. By incorporating a sampling device and analyzing device in a singular package, a smaller biological sample may be required and the potential for contamination of the biological sample may be dramatically reduced. The time required to obtain a sample and perform an analysis of the sample may be also reduced.

Transdermal extraction of biological samples may require accessing body fluid that may be located under an intact skin surface. The skin is a soft outer covering of an animal, in particular a vertebrate. In mammals, the skin is the largest organ of the integumentary system made up of multiple layers of ectodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs. Skin performs the following functions: protection, sensation, heat regulation, control of evaporation, storage and synthesis, absorption and water resistance.

Mammalian skin is composed of three primary layers: the epidermis, which provides waterproofing and serves as a barrier to infection; the dermis, which serves as a location for the appendages of skin; and the hypodermis (subcutaneous adipose layer).

Epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina. Epidermis is divided into several layers where cells are formed through mitosis at the innermost layers. They move up the strata changing shape and composition as they differentiate and become filled with keratin. They eventually reach the top layer called stratum corneum and are sloughed off, or desquamated. The thickness of the epidermis is about 0.5 to 1.5 mm.

As illustrated inFIG.1, epidermis is divided into the following five sub-layers or strata: Stratum corneum102which consists of 25 to 30 layers of dead cells and has a thickness between 10 μm and 50 μm; Stratum lucidum103, Stratum granulosum104, Stratum spinosum105, and Stratum germinativum106(also called “stratum basale”).

The apparatus of the various embodiments may be placed in direct contact with the skin100and held in position by pressure or an adhesive. A precisely determined and controlled series of electrical pulses may be applied to one or more disruptor units disposed in or on the apparatus in order to produce localized heat and electrical fields that disrupt the cells of the stratum corneum layer102of the skin100without damaging the skin cells. The application of the precision controlled heat alters the permeability characteristic of the stratum corneum and produces capillary-like channels in the skin which allow interstitial fluid to flow out of the subject's body. The interstitial fluid may be collected and directed across the surface of the apparatus. On the surface of the apparatus, the interstitial fluid may come into contact with a sensor to determine composition or presence of a certain analyte(s). One such sensor may utilize a biologically reactive element, such as an enzyme. One or more pairs of electrochemical electrodes may be positioned in a manner to measure one or more biochemical analyte or physic-chemical properties of the interstitial fluid sample after the interstitial fluid reacts with the biologically reactive element. For sake of discussion, the dramatic increase in the permeability of the stratum corneum due to the localized application of heat may be referred to as a disruption process. The element which produces the localized heat may be referred to as a disruptor202. During the disruption process the skin cells remain intact.

FIG.2illustrates the functional components of a transdermal sampling and analysis device200according to an embodiment. A transdermal sampling and analysis device200may include a disruptor202connected to the positive and negative electrical poles204a,204bof a signal generator. In an embodiment, the disruptor202may function as a resistive element. After a brief period of increased permeability due to the application of localized heat, the cells return to their normal function. In an embodiment, a disruptor202produces heat as electrical current is passed through it. When placed on the skin, the localized heat generated by the disruptor element may cause disruption to the skin cells facilitating the flow of interstitial fluid onto the surface of the transdermal sampling and analysis device200. The disruptor202may be made from a variety of materials which exhibit the appropriate heating and control properties to provide the precise heating control properties required to disrupt the skin cells without damaging them. In addition, the materials used to create the disruptor202may be selected for relative ease of manufacture as well as cost considerations. Materials such as titanium, tungsten, stainless steel, platinum and gold may be preferably used to form the disruptor202. In a preferred embodiment, gold may be used to form the disruptor202.

A transdermal sampling and analysis device200may further include a sensing element comprised of counter electrode208and working (or sensing) electrode210. The electrodes208,210may be coated with a biologically reactive element and coupled to electrically conductive paths206a,206b. In an embodiment, the counter and working electrodes208,210form anode and cathode of an electrolytic cell. The counter electrode208may be coated with a biologically reactive element to facilitate the conversion of signals generated by a chemical reaction between the biological sample and the biologically reactive element to electrical signals.

Many different analysis techniques may be incorporated into the transdermal sampling and analysis unit to determine the levels and concentrations of various analytes in a biological sample. For example, amperometric, coulometric, potentiometric techniques may be each alternative techniques which may be incorporated into the transdermal sampling and analysis device to determine levels or concentrations of analytes in a biological sample. In addition, electrochemical impedance analysis techniques may be incorporated to detect the presence of particular antibodies in a biological sample.

As an illustration, amperometric techniques may be employed to detect the level or concentration of glucose in a fluid sample. Two electrodes may be separated and insulated from each other and have a voltage potential applied across the electrodes. Because the electrodes are physically decoupled, no current flows from one electrode to the other. The electrodes may be treated with a reactive agent, which in the presence of a particular analyte produces ions through a chemical reaction. The produced ions facilitate the flow of electrical current between the electrodes as the biological sample containing the analyte may be allowed to flow over the surface of the both electrodes. The relative number of ions produced in the reaction may determine the relative ease in which electrical current may flow. In other words, as a higher concentration of the detected analyte is present in the biological sample, the relative current flowing between the electrodes will increase. Thus, the relative concentration of a particular analyte may be calculated based upon the magnitude of current or voltage drop detected between the two electrodes.

Similarly, coulometric methods use analytical chemistry techniques to determine the amount of matter transformed during an electrolysis reaction by measuring the amount of electricity (in coulombs) conducted or produced. Transdermal sampling and analysis devices incorporating potentiometric methods measure potential under the conditions of no or low current flow. The measured voltage potential may then be used to determine the analytical quantity of the analyte of interest. Transdermal sampling and analysis devices incorporating electrochemical impedance method measure the dielectric properties of a medium as a function of frequency.

In an exemplary embodiment, when analyzing concentrations of glucose in a biological sample, enzymatic conversion of glucose to gluconolactone may yield electrons which may be captured to generate anodic current between the counter and sensing electrodes208,210, also referred to as counter electrode208and working electrode210. Electrical impedance sensing electrodes, such as electrodes208,210, may be configured to determine an electrical impedance spectroscopy across the sensing electrodes208,210. The magnitude of the electrical current generated as a result of the chemical reaction may be proportional to the amount or concentration of glucose contained in the obtained biological sample. In an embodiment, a voltage potential may be applied to the counter and working electrodes208,210using a power generator (not shown). Once the biological sample reacts with the reactive biological element coating the electrodes208,210, the ions that may be released from the conversion of glucose to gluconolactone facilitate generation of a current across the working and counter electrodes. In such a scenario, the working electrode may function as an anode and the counter electrode may function as a cathode or vice versa. The level of the current may depend on the amount of glucose that is in the biological sample and is converted to gluconolactone. The current that may be generated may be measured by an ammeter, the measurement of which may directly correlate to the level of glucose in the collected biological sample.

The counter and working electrodes208,210may be made from any of a variety of materials which exhibit satisfactory conductivity characteristics and appropriate to the specific measurement used. In addition, the materials used to create the electrodes may be selected for relative ease of manufacture as well as cost considerations. Examples of materials exhibiting satisfactory conductivity characteristics for use as the counter and working electrodes208,210may include platinum, silver, gold, carbon or other materials.

A transdermal sampling and analysis device200may further include a reservoir212for collecting and containing biological samples such as interstitial fluids that flow from capillary-like channels in disrupted stratum corneum. As interstitial fluid may be released and begins to flow over the transdermal sampling and analysis device200, the reservoir212provides a volume for the interstitial fluid to collect within. By collecting within the reservoir212, the interstitial fluid may be contained while the analysis of the sample by the electrodes proceeds. The reservoir212may be formed under the disruptor202and electrodes208,210. When the transdermal sampling and analysis device200is place on the subject's skin with the disruptor202contacting the skin, the reservoir may effectively be positioned above the disruptor202and electrodes208,210to contain the released fluid sample. The reservoir212may include a cover or lid to more effectively contain the fluid. A cover or lid is discussed in more detail below with respect toFIGS.14A and14B. A reservoir212may be created using conventional methods known in the art. For example, a reservoir212may be created by the buildup of material such as ceramic or polymer on the first side of a supporting base (e.g., substrate214) in the non-reservoir area either by additive process or by a subtractive process such as photolithography. Alternatively, a spacer material, discussed in more detail below, may be disposed between the lid and substrate214to create a cavity for fluid to collect.

A substrate214may form the support on which other transdermal sampling and analysis device200components may be positioned or attached. The substrate may be formed of a flexible material such that the substrate and components built thereon may deform to conform to the contours of the user's skin. Alternatively, the substrate may be formed of a rigid material such that the user's skin may be forced to deform to conform to the shape of the substrate. The substrate214may include a first or top side and a second or back side. The transdermal sampling and analysis components may be attached to the first side of the substrate214. The substrate214may include certain characteristics to accommodate all the functions of the transdermal sampling and analysis devices200of the various embodiments. For example, a substrate214may have to withstand various etching and or photo-lithography processes which deposit materials to form the disruptor202and electrodes208,210without being damaged. In addition, the first side of the substrate214may undergo an etching process to create the reservoir212. In addition, it may be desirable for the substrate214to exhibit certain thermal conductivity properties. For example, it may be desirable for the heat generated by the disruptor unit202to remain localized and concentrated. Accordingly it may be desirable for the substrate to have a high thermal resistivity such that heat generated by the disruptor is not conducted by the substrate214to areas other than those directly in contact with the disruptor unit202. Additionally, it may be desirable for the substrate to possess a resistance to thermal expansion.

Different substrates214may be used as a base in a transdermal sampling and analysis device200. Substrates214with high coefficient of thermal expansion may flex or buckle as voltage (or current) is applied to the disruptor202and heat is generated. The flexing or buckling action may displace the disruptor unit202away from the surface of the skin100, resulting in an insufficient heating of the stratum corneum. Consequently, the permeability of the stratum corneum may not be altered sufficiently to allow for the flow of interstitial fluid. The end result being that the volume of the obtained biological sample is not sufficient to adequately analyze. The disruptor202may be required to continuously contact the skin100to create the capillary-like channels in the stratum corneum which may allow interstitial fluid to flow from the body of the subject onto the transdermal sampling and analysis device200. Thus, a low thermal modulus substrate214may be selected that does not displace the disruptor202from the skin100.

Further, repeated heating and cooling of the substrate214may damage components of the transdermal sampling and analysis device200that may be attached to the substrate214. For example, differences in thermal expansion characteristics between the materials used for the disruptor202and the substrate214may result in separation of the disruptor202from the substrate214. In other words, the disruptor may begin to peel away from the substrate after repeated heating and cooling cycles. Accordingly, in a preferred embodiment the substrate may exhibit high thermal resistivity (low thermal conductivity) properties while mirroring the low thermal expansion characteristics of the disruptor202material. Different substrates214may have different thermal expansion properties. For example, most metals substrates214have coefficient of thermal expansion of about 5˜10 ppm/° C.; glass has a coefficient of thermal expansion of ˜8 ppm/degF; common plastics have coefficient of thermal expansion of 20˜30 ppm/° C.

However, in some alternative embodiments, the thermal expansion characteristics of the materials used in both the substrate214may be manipulated to advantageously result in a mechanical movement of the substrate. This mechanical movement of the substrate214may cause a break, disruption, or dislocation of bonds in the lipid barrier membrane, further enabling or assisting in the displacement of biological fluid out from the interstitial region, over and through the transdermal sampling an analysis device200. For example, as electrical current is applied through the disruptor202heat may be generated. The heating of the disruptor202causes the substrate214housing the disruptor202to also heat. This heating results in an expansion of the substrate214material in accordance with coefficient of thermal expansion. As the current applied to the disruptor202is disengaged, both the disruptor202and the surrounding substrate214will cool. This cooling results in a contraction of the substrate214material. As discussed in more detail below, current to the disruptor202may be pulsed. The pulsing on and off of the applied current may cause in a rhythmic expansion and contraction cycle of the substrate214to result in a mechanical movement of the substrate, perpendicular to its plane to enhance flow of biological fluid out of the interstitial region. Materials having a sufficient coefficient of thermal expansion may result in a translation of the substrate214, perpendicular to its plane, of between 0.05 μm and 3.0 μm. In a preferred embodiment, materials having a coefficient of thermal expansion are selected to result in a translation of the substrate214, perpendicular to its plane, of between 0.1 μm and 0.6 μm.

In an embodiment, the substrates214may include physical and/or chemical properties to accommodate certain temperatures without being damaged or cause damage to the components of the transdermal sampling and analysis device200. In an embodiment, a disruptor202generating temperatures as high as 200° C. may be attached to the substrate214. Thus, the substrate214may have to withstand such high temperatures without melting, permanently deforming or conducting the heat to other components of the transdermal sampling and analysis device200.

Even if a substrate214does not melt or permanently deform under high temperatures, the substrate214may expand or contract due to varying temperatures. Because components of the transdermal sampling and analysis device200may be fixedly attached to the substrate214, expansion and contraction of the substrate214may cause the attached components to detach and cause damage to the configuration of the transdermal sampling and analysis device200.

To reduce or eliminate the size variation of the substrate214under varying temperatures, different substrates214may be considered. In an embodiment, a substrate214made of a material with a coefficient of thermal expansion of about 10 to 20 ppm/degF may be used to reduce the expansion/contraction effects of the substrate214when exposed to high heats of about 100° C. to 200° C. In a further embodiment, a substrate214made of a material with a coefficient of thermal expansion of about 10 to 12 ppm/deg F. may be used. In a further embodiment, a substrate214may have a coefficient of thermal expansion that may be within a 20% deviation from the CTE of the disruptor202material.

To reduce or eliminate conduction of heat from the disruptor202attached to the substrate214to other components of the transdermal sampling and analysis device200, alternative materials may be considered for the substrate214. In an embodiment, the substrate214may be formed from a material having a coefficient of thermal conductivity of about 0.1 to 1.1 W/m*K to reduce the conduction of heat from the disruptor202to other components of the transdermal sampling and analysis device200or to other unintended areas of the skin of the subject beyond the portion directly in contact with the disruptor202. In a further embodiment, the substrate214may be made from a material having a coefficient of thermal conductivity of about 0.1 to 0.2 W/m*K. In a further embodiment, a substrate214may be made from a material having a coefficient of thermal conductivity of about 0.13 W/m*K or lower.

In an embodiment, selection of a substrate214for the transdermal sampling and analysis device200may depend on the coefficient of thermal expansion and conductivity of the material used to make the disruptor202of the transdermal sampling and analysis device200. For example, the substrate214may be made of a material which has a coefficient of thermal expansion that deviates from the CTE of the material used in the disruptor202by less than 50%, and preferably by less than 20%. In a further embodiment, the substrate214may be made of a material which has a coefficient of thermal conductivity (CTC) that is lower than 0.5 W/(m·K)

In an embodiment, the substrate214suitable for use in the transdermal sampling and analysis device200of the various embodiments may be made of a variety of materials such as glass, plastic, metal or silicon.

In an embodiment, the substrate214may be made of plastic. When heat is applied to plastics, the plastic material typically shrinks in size before expanding in size. Because of this unique characteristic of plastic, application of heat to a substrate214made of plastic may cause damage to the components of the transdermal sampling and analysis device200attached to the plastic substrate214. To prevent the initial contractions, the plastic material used to make the substrate214may be annealed plastics (i.e., plastics which have been previously heated to remove or prevent the internal stress caused by the initial shrinkage). Annealed plastics are known in the art and may be produced by annealing a plastic material to cause a change in its properties.

In a further exemplary embodiment, the substrate214may be made of a polyimide such as Kapton“. Kapton” is a polyimide film developed by DuPont′ which can remain stable in a wide range of temperatures, from −273 to +400° C. (0-673 K).

A biologically reactive element, such as an enzyme, may be applied to the first side of the substrate. For example, the biologically reactive element may be applied to the working electrode210, the counter electrode208or both. As the stratum corneum is disrupted and interstitial fluid begins to flow through the stratum corneum into the reservoir212by capillary action of the structure. The interstitial fluid may be directed to flow into the reservoir212and specifically over the surface of the counter and working electrodes208,210. The obtained fluid may come into contact with the biologically reactive element on the surface of the counter and working electrodes208,210causing a chemical reaction that releases energy in the form of electrons. The counter and working electrodes208,210may form anode and cathode of an electrolytic cell, enabling current flow through a device which can measure the current at a controllable potential. Thus, the electrons (ions) released from the chemical reaction between the biological sample and biologically reactive element may be converted into electrical signals. The electrical signals generated by the chemical reaction may be measured to determine the amount of a target analyte in the obtained biological sample.

Excessive thickness of the biologically reactive elements on the first side of the substrate may cause certain problems during the manufacturing process or during the operation of the device. For example, greater thickness of the biologically active layer requires greater depth of channels to allow space for the biological sample to flow over the electrodes. If the applied biologically reactive element layer is too thick, greater than 10 micrometers for example, such as common in commercial glucose transdermal sampling and analysis devices, it may clog or fill the channels222that may be configured to guide the biological sample over the electrodes rendering the transdermal sampling and analysis device200dysfunctional, or causing the need for increased channel thickness at increased cost. Channels222are discussed in more detail below. In an exemplary embodiment, to avoid clogging the channels222and blocking the movement of the biological sample over the electrodes, the biologically reactive element may be applied in such a way as to result in a thickness of less than 5 micrometers, and preferably less than 1 micrometer. This can be accomplished by the use of a system such as described by Eugenii Katz, biochemistry and bioenergetics 42 (1997) 95-104 or other known method of thin sensor layer deposition. By reducing the thickness of the biologically reactive element, potential clogs to the channels222in the transdermal sampling and analysis device200may be prevented without the additional cost of increased channel depth.

One example of a commonly used biologically reactive element may be the enzyme Glucose Oxidase (GOD). Another example of a commonly used biologically reactive element may be the enzyme glucose dehydrogenase. In an exemplary embodiment, GOD may be applied to cover the surface of the working electrode210. To determine a subject's glucose levels, a transdermal sampling and analysis device200with a disruptor202may be applied in direct contact with the skin cells. By applying a voltage (or current) across the terminals of the disruptor202, a precision controlled heat may be produced and localized to the disruptor202site. The localized heat may be applied against the skin to alter the permeability of the skin cells and consequently creates capillary-like channels. Interstitial fluid may flow out of the capillary-like channels into the reservoir212and over the counter and working electrodes208,210. The glucose molecules in the interstitial fluid may react with GOD covering the surfaces of the working electrode210. Glucose oxidase catalyzes a breakdown of glucose in the interstitial fluid to gluconolactone, releasing electrons to a mediator such as K3Fe[CN]6. The electron mediator (or electron shuttle) may transfer electrons to the working electrode210, where anodic potential has been applied such that the mediator may be oxidized. The oxidized mediator may be then able to accept another electron from the glucose conversion reaction to repeat the process. The electrons released in this oxidation reaction may travel through the working electrode210towards the counter electrode,208generating a current. The magnitude of the sensed electrical current generated by this reaction may be proportionally related to the concentration levels of glucose in the interstitial fluid. Thus, by determining the magnitude of current generated across the working and counter electrode, one may determine the relative amount of glucose in the obtained sample.

FIG.3illustrates a top view of a transdermal sampling and analysis device200showing an embodiment orientation and configuration of the functional components of the transdermal sampling and analysis device200. The transdermal sampling and analysis device200may include a disruptor202connected to two electrically conductive paths204a,204b. The conductive paths204a,204bmay be coupled to the positive and negative nodes of a power source (not shown). The disruptor202may be placed adjacent to a working electrode210and counter electrode208. The counter and working electrodes208,210may be connected to electrical conductive paths206a,206b, respectively.

The surface of the counter and working electrodes208,210may be patterned with support structures220which displace the electrodes208,210from the surrounding skin of the subject. As the transdermal sampling and analysis device200may be pressed against the subject skin, it may be necessary to displace the electrodes208,210from the surrounding skin in order to allow the free flow of obtained interstitial fluid over the surface of the electrodes208,210. The surrounding skin100may deform across the surface of the electrodes208,210, effectively preventing the biological sample from coming into contact with the electrode surfaces. By placing support structures220over the electrodes, the surrounding skin may be effectively lifted off the surface of the electrode. The various patterns of support structure220may also create channels222which direct the biological samples over the entire surface working and counter electrodes208,210due to capillary action. These patterns may be of any shape or arrangement. For example, the counter and working electrodes208,210may be configured to include star shaped channel supports220to manipulate the movement of biological sample over the entire surface of the counter and working electrodes208,210.

Because the amount of biological sample required is minute and the surface area of the counter and working electrodes208,210may be relatively small, a uniform coverage of the counter and working electrodes208,210by the biological sample may enhance the accuracy of the final analysis of analytes. Results obtained from a transdermal sampling and analysis device200in which the entire surface of a counter and working electrodes208,210are covered require less time and volume of biological sample for analysis and may be more accurate.

FIG.4illustrates a top view of another embodiment transdermal sampling and analysis device200. The functional elements of the transdermal sampling and analysis device200may be disposed upon the surface of a substrate214and may be configured to include counter and working electrodes208,210that may be inter-digitated. In such a configuration, more than one counter and working electrodes208,210may be used to create the inter-digitated configuration. For example, a total of three electrodes may be used to create the inter-digitations; two counter electrodes208aand208bas well as one working electrode210. The counter and working electrodes208,210may be coupled to a current or sensing unit via electrically conductive paths206a,206b. Elongated channels222may be formed using long channel supports220. The channels222may cover the entire surface of the counter and working electrodes208a,208b,210. A disruptor202configured in a serpentine shape may be positioned adjacent to the counter and working electrodes208a,208b,210. A reservoir212may be created to surround the disruptor202and the counter and working electrodes208a,208b,210. The disruptor202may be connected to the positive and negative electrical poles204a,204bof a signal generator.

A biological sample, such as interstitial fluid, may flow from capillary-like channels created by the disruptor202into the reservoir212through capillary action. As the biological sample flows into the reservoir212, the channels222and channel supports220may assist the movement and direction of the biological samples in the reservoir212to disperse the biological sample over the entire surface of the counter and working electrodes208a,208b,210through further capillary action caused by the relative hydrophilic properties of the selected channel support220material, as described in more detail below.

Exhaust ports or vents224may be present on the side of the reservoir212towards which the biological sample may move. The exhaust ports/vents224may relieve any air pressure that would otherwise be caused by air trapped within the reservoir212and prevent the biological sample from moving towards the far side of the reservoir212. In the embodiment shown inFIG.4, the reservoir212may be in a shape of a trapezoid to allow biological samples to flow from the disruptor202over the working and counter electrodes208,210using the channels222and the channel supports220. In alternative embodiments, the exhaust vent224may be configured to direct the vented gases back toward the disruptor202so that the gases may be recirculated back through a hole in a lid1302(seeFIG.14Band discussion below regarding lid). Embodiments utilizing exhaust ports224may be referred to as vented embodiments, whereas embodiments that do not utilize exhaust ports may be referred to as unvented or non-vented embodiments.

FIGS.5A-5Dillustrate top views of various embodiment transdermal sampling and analysis devices421-424each having a different configuration of the functional components. The embodiments shown in each ofFIGS.5A-5Dpossess different disruptor202(5A)-202(5D) configurations, but assume for purposes of this discussion that disruptors202(5A)-202(5D) may be formed of the same material. Moreover, for purposes of this discussion it may be assumed that the same voltage (or current) may be applied across each of disruptors202(5A)-202(5D).

Similar to the transdermal sampling and analysis device shown inFIG.4,FIG.5Aillustrates a transdermal sampling and analysis device421including interdigitated counter and working electrodes208a,208b,210and a disruptor202(5A) with a serpentine configuration. In the embodiment shown inFIG.5Athe cross section of disruptor202(5A) has a relatively small wire gauge (i.e., larger cross section diameter). The smaller gauge may result in a disruptor202(5A) having a relative lower resistive value and thus a lower localized heat as compared to a disruptor202having a higher resistive value where the same voltage may be applied.

FIG.5Billustrates a top view of another embodiment transdermal sampling and analysis device422. The functional components of the embodiment shown inFIG.5Bare similar to those shown inFIG.5A. In particular, the total length of the disruptor202(5B) shown inFIG.5Bmay be the same disruptor202(5A) shown inFIG.5A. In addition, the total area covered by the disruptor202(5B) shown inFIG.5Bmay be the same as disruptor202(5A) shown inFIG.5A. However, the gauge of the serpentine coils of disruptor202(5B) shown inFIG.5Bmay be shown to be larger (i.e., smaller cross sectional dimension) than the disruptor202(5A) shown inFIG.5A. Consequently, when the same voltage (or current) applied to the disruptor202(5A) inFIG.5Amay be applied to the disruptor202(5B) inFIG.5B, a higher temperature localized heat may be generated due to the increased resistive value. Since the higher temperature produced by the disruptor202(5B) shown inFIG.5Bmay be distributed over the same relative area as that produced by the disruptor202(5A) shown inFIG.5A, the power density of the disruptor202(5B) shown in the embodiment ofFIG.5Bmay be much higher relative to the disruptor202(5A) shown inFIG.5A.

FIG.5Cillustrates a top view of another embodiment transdermal sampling and analysis device423. In contrast to disruptor202(5A) shown inFIG.5A, disruptor202(5C) shown inFIG.5Chas a larger gauge than disruptor202(5A), but has fewer windings and covers a smaller total area than disruptors202(5A) and/or202(5B). As compared to disruptor202(5A), because disruptor202(5C) has a smaller gauge than disruptor202(5A), disruptor202(5C) will typically have a higher resistive value than disruptor202(5A). However, because disruptor202(5C) also has fewer windings than disruptor202(5A), the total length of disruptor202(5C) may be shorter than disruptor202(5A). As a result, the increase in resistive value of disruptor202(5C) over disruptor202(5A) due to the larger gauge may be effectively negated and the resistive value of disruptor202(5C) may be the same as disruptor202(5A). However, because disruptor202(5C) covers a significantly smaller total area as compared to disruptor202(5A), the power density of disruptor202(5C) may be significantly greater relative to that of disruptor202(5A). As compared to disruptor202(5B), disruptor202(5C) has the same gauge value as disruptor202(5B) but has fewer windings. As a result, the total length of disruptor202(5C) may be less than disruptor202(5B). Consequently, disruptor202(5C) will have a lower resistive value relative to that of disruptor202(5B). However, since disruptor202(5C) covers a significantly smaller total area as compared to disruptor202(5B), the power density of disruptor202(5C) may effectively be the same relative to that of disruptor202(5B).

FIG.5Dillustrates an embodiment transdermal sampling and analysis device424including counter and working electrodes208,210with large smooth surfaces. In contrast to the configurations shown inFIGS.5A-5C, the reservoir212and the disruptor202(5D) may be rectangular in shape as opposed to serpentine. In addition, the electrodes208,210may be shown as rectangular electrodes that are not interdigitated. The relative resistive value of disruptor202(5D) may be much lower than that of disruptors202(5A)-202(5C) as its gauge may be nearly that of disruptor202(5A) but total length may be nearly that of202(5C). In addition, because disruptor202(5D) covers approximately the same total area as disruptor202(5C), the power density of disruptor202(5D) may be less relative to that of disruptor202(5A), disruptor202(5B) and disruptor202(5C). The various embodiments may be designed to deliver heat to the subject's skin with a power density of 1-10 W per mm2. In a preferred embodiment the disruptor delivers heat to the subject's skin with a power density of 2-5 W per mm2.

As shown inFIGS.5A-5D, the transdermal sampling and analysis devices421-424of the various embodiments may be made using a variety of different disruptor202(5A)-202(5D) configurations. As discussed above, the size and shape of the disruptor may affect its resistive characteristics and consequently, its ability to generate a localized heat. In addition, the material selected to form the disruptor may also affect its resistive characteristics and consequently, its ability to generate a localized heat. As with electrode material selection, disruptor materials may be selected from a wide variety of materials exhibiting satisfactory electrical conductance/resistive properties such that sufficient heat may be generated when specific voltages are applied to the disruptor leads. In addition, thermal conduction and resistance characteristics should be observed in an optimal disruptor material. Finally, ease of manufacturing processing and cost may determine the final selection of disruptor material. For example, a disruptor202may be made of nichrome, titanium, tungsten, or gold. In a preferred embodiment, the disruptor202may be made from gold.

As discussed above with reference toFIGS.5A-5D, the disruptor202may be formed in a variety of configurations.FIGS.6A-6Eillustrate additional shapes that the disruptor202may be formed. For example, a disruptor202may be formed in serpentine, circular, crescent, semi-circular, linear, square, rectangular, trapezoidal, hexagonal and triangular shapes. Each unique shape may impact the manner in which the generated heat may be localized. Studies have shown that that the resulting sensation experienced by the subject induced by the varying disruptor shape also varies. By varying the shape of the disruptor202, the sensation or discomfort experienced by the subject may be increased or decreased.

FIG.6Aillustrates a top view of an embodiment disruptor202with a linear shape.FIG.6Billustrates a top view of an embodiment disruptor202formed in the shape of the Greek letter omega.FIG.6Cillustrates a top view of an embodiment disruptor202formed in a serpentine shape.FIG.6Dillustrates a top view of an embodiment disruptor202formed in a rectangular shape. Disruptor shape configuration may affect the relative sensation or discomfort experienced by the subject from which the biological sample may be drawn. In a preferred embodiment, the disruptor unit may be formed such that the perimeter of the disruptor preferably forms a rectangle. Such preferred disruptor units may be formed from solid disruptors202such as that shown inFIG.6Dor in alternative serpentine configurations such as shown inFIG.6C. The serpentine configuration has some advantages. For example, because the serpentine disruptor may be formed by a long, thin coil (as compared to a solid rectangle), the resistive characteristic of the disruptor may be much larger (assuming similar or same material). In addition, the thinner cross section of each coil also contributes to a higher overall resistive value of the disruptor unit. In this manner, the serpentine shaped disruptor may occupy a generally rectangular area, while providing sufficiently high resistance to produce the required localized heating levels to obtain a transdermal biological sample with minimal sensation and discomfort to the subject.

In an embodiment, the area determined by the perimeter surrounding a disruptor202may affect the amount of biological sample that may be collected or the amount of sensation or sensation that may be experienced by the subject. In addition to absolute area, the aspect ratio of the disruptor202may impact sensation versus fluid generation level. Aspect ratio is a ratio of the area of the skin100that a disruptor202may cover as compared to the parameters of the disruptor202, such as the disruptor's length and cross-sectional area. Different aspect ratios may affect the process of disruption of the skin cells and levels of sensation differently. For example, if the skin area that the disruptor202may cover is of excessive aspect ratio (e.g., a long and thin disruptor such as shown inFIG.6A), the use of the disruptor202may cause high levels of sensation without obtaining a sufficient amount of biological sample. A preferred aspect ratio has been found to be about 2:1. A more preferred aspect ratio may be 1:1 (i.e., a square or circular)+/−50%. At such preferred aspect ratios, subjects have exhibited the least sensation or discomfort while obtaining a sufficient amount of biological sample.

In an embodiment, where the aspect ratio may be about 2:1, the disruptor202may cover a rectangular area with a length of about 150 μm-400 μm and width of 50 μm-200 μm. In a further embodiment, the disruptor202may have a length of about 200 μm-400 μm and a width of 100 μm-200 μm.FIG.7illustrates an exemplary serpentine disruptor202with a length of 200 μm and a width of 100 μm. In a preferred embodiment, the dimensions of the disruptor202may include a length of 120 μm and width of 60 μm. By minimizing the size of the disruptor unit, the relative sensation and discomfort may be likewise minimized. However, limits on manufacturing processes as well as the need to disrupt a large enough area of stratum corneum to obtain a sufficiently large enough sample of biological material may dictate the minimal effective size of the disruptor unit. The disruptor202with dimensions of 120 μm×60 μm may obtain a sufficient amount of biological sample while causing a negligible sensation or discomfort to the subject.

In a further embodiment, other aspect ratios less than 2:1 may also be used. For example, a disruptor202may have a length of 100 μm and a width of 60 μm. In a further embodiment, where the aspect ratio may be about 1:1, the disruptor202may cover a square area with a length and width of about 50 μm-400 μm. In a further embodiment, the disruptor202may have a length and width of about 100 μm-400 μm. In an exemplary embodiment, a serpentine disruptor202with a length and width of 200 μm may be used. In a preferred embodiment, the dimensions of the disruptor202may have a length and width of about 120 μm. In a preferred embodiment, the disruptor202may have the dimensions of 200 μm×200 μm. In a more preferred embodiment a disruptor202may have the dimensions of 60 μm×60 μm.

Electrical resistance of a disruptor may be calculated using the following equation:
R=ρL/Awhere,R is the electrical resistance of a uniform specimen of the material (measured in ohms, Ω)ρ is electrical resistivity of the material (measured in ohm-meters, Ω-m)L is the length of the piece of material (measured in meters, m); andA is the cross-sectional area of the specimen (measured in square meters, m2).

By varying the value of each of these parameters, different electrical resistances may be achieved. For example, the thinner the cross-section of the specimen used in the disruptor, the greater the electrical resistance of the disruptor. Similarly, the longer the length of the material used in the disruptor202, the greater the electrical resistance of the disruptor. Conversely, a wider cross section or shorter disruptor may result in a lower electrical resistance of the disruptor.

The higher the electrical resistance, the greater the heat generated given a constant current applied through the disruptor202. Thus, to obtain a desired heat level, the material used in the disruptor202should achieve a desired electrical resistance. Because electrical resistivity of a material may be constant, the length and cross-sectional area of the material may be adjusted to achieve a desired electrical resistance which in turn may generate a desired heat level. For example, to achieve high electrical resistance in a disruptor202which employs a short piece of gold material, the cross-section area of the gold material may be reduced. Likewise, to achieve high electrical resistance in disruptor202which uses a gold material with a large cross-section area, the length of the gold material may be increased.

While the serpentine configuration of the disruptor creates multiple sites for heat production on the skin, the constructive interference of the heating generated effectively applies a singular source of heating to the subject skin.FIG.8illustrates a cross-sectional view of an embodiment serpentine disruptor202positioned next to the skin100. For example, each coil802may generate heat resulting from the resistance to electrical current applied to the leads of the disruptor202. The generated heat may be conducted through the layers of the skin. The discrete heating from each coil802may constructively interfere with the heating generated from other neighboring coils802to create a uniform heat gradient804. A uniform, continuous heating gradient804may cause uniform and effective disruption to the skin cells. In this manner, the serpentine configuration of the disruptor provides the same uniform heating as can be achieved through use of a solid rectangular configuration for the disruptor. Moreover, the serpentine configuration may provide a disruptor with greater electrical resistance as compared to a solid rectangular disruptor confined to the same area.

In a serpentine disruptor202, the distances of the coils802from one another may determine whether uniform heating gradient804may form as discrete heat sources as they travel through the stratum corneum. If the distances between the coils802are too large, a uniform and continuous heating gradient804may not form at all or may form at a skin level below the stratum corneum, thus, failing to effectively and uniformly disrupt the cells of the stratum corneum. In an embodiment, the coils802of the serpentine disruptor202may be about 5 μm to 40 μm apart. In a preferred embodiment, the coils802—of the serpentine disruptor202may be about 15 μm apart.

Given the variety of disruptor properties that may be varied (e.g., size, shape, gauge, material, current applied, etc.) a disruptor may be formed and implemented that exhibits the desired electrical characteristics to generate a sufficient fluid sample while imparting negligible sensation and/or discomfort to the patient. For example, assuming no other changes, as the size (area) of the disruptor increases so does the amount of fluid extracted. However, again assuming no other changes, as the size (area) of the disruptor increases so does the amount of sensation and discomfort experienced by the patient. Thus, certain proportional relationships may be known. The amount of sensation or discomfort a patient may experience may be proportionally related to the area of the disruptor, the aspect ratio of the disruptor, and the power density that applied. Likewise, the amount of fluid that can be extracted may be proportionally related to the area of the disruptor and the power density that applied. Tests have indicated that an applied power density of 1 W per mm2may be the minimum amount of power required to disrupt a patient's stratum corneum.

In practice a disruptor may be constrained by a number of other factors. For example, in a portable application there may be voltage/current constraints resulting from the use of a particular battery, thus, dramatically impacting the power density requirements. Economic or manufacturing constraints may limit the materials from which the disruptor may be manufactured. When faced with any of these constraints, a disruptor may still be designed by varying the combination of disruptor properties so that each of the constraints is met.

As previously discussed, the disruptor202may essentially operate as a resistor which, when a voltage (or current) is applied to the leads of the disruptor202creates a localized heat source. The amount of heat required to disrupt the skin cells to obtain sufficient amounts of biological samples and cause the least discomfort or sensation may depend on different variables, such as the thickness of the skin100and the concentration of nerve endings on the skin100. Furthermore, sensation and discomfort are subjective to each individual subject. However, the stratum corneum is generally about 50 μm in thickness. It may be thicker or thinner at various locations of the subject. For example, it is thicker at the palm of the hands and soles of the feet and thinner on the eyelids. In an embodiment, the heat generated by the disruptor may result in a heater temperature of about 100° C. to 200° C. The lower temperatures may cause less sensation while higher temperatures may produce larger amounts of biological sample. A desired location for applying the heat to disrupt the skin cells may be on the medial surfaces of the forearm. Given the relative thickness of the stratum corneum at this location as well as the relative number of nerve endings at this location, it may be preferable to apply at 50° C. to 150° C. from the disruptor to cause the disruption in the stratum corneum. In a more preferred embodiment, the temperature of the disruptor may be about 90° C. to 110° C.

In an embodiment, since different subjects may have different skin thickness levels, calibration of the transdermal sampling and analysis device200of the various embodiments may be required to generate sufficient heat for obtaining the most amounts of biological samples with the least amount of sensation. Thus, the level and duration of the temperature of the disruptor202may be adjusted for different subjects.

In an embodiment, the disruption of the skin100may occur when heat of about 85° C. to 140° C. from the disruptor202may be applied to the skin surface for durations of about 100 ms to 200 ms. In a further embodiment, the disruption of the skin may occur when heat of 140° C. from the disruptor202may be supplied to the skin100surface for durations of about 120 ms to 160 ms. In a preferred embodiment, the disruption of the skin100may occur when heat of 140° C. from the disruptor202may be supplied to the skin100surface for duration of about 140 ms.

In order to safely operate on and around the subject, lower voltages and currents may be desirable. Voltages of 10 V or higher may be detected by the body and have been observed in encephalograms. Thus, to reduce the effects of the voltage on the body, it may be preferable to use voltages lower than 10 V. Since there may be a limit on the amount of voltage that may be safely applied to a subject, the electrical resistance of the disruptor202may be adjusted based on the desired voltage. Likewise, there may be a limit on the amount of current that may be safely applied to a subject, the electrical resistance of the disruptor202may be adjusted based on the desired current. In an embodiment, the voltage supplied to the disruptor202may be about 1 V to 10 V. In a preferred embodiment, the voltage supplied to the disruptor202whose area is about 2×10−8m2may be about 2 V. In another embodiment where a current source applies a current, the current supplied to the disruptor202may be about 35 mA to 145 mA. In another embodiment where a current source applies a current, the current supplied to the disruptor202may be about 20 mA to 120 mA. In a preferred embodiment, the current supplied to the disruptor202may be about 100 mA, preferably about 70 mA. For this preferred embodiment, the corresponding power density per unit area of the disruptor on the skin may be about 5×106W/m2, the energy per pulse may be about 65 mJ, and the energy per unit area of the disrupter on the skin may be about 3×106J/m2. Since the amount of heat generated by a resistive element is dependent upon the resistive value of the resistive element and the amount of voltage (or current) applied across (through) the resistive element, the disruptor202suitable for use in the various embodiments may include an electrical resistance of about 1 Ohm to 100 Ohm. In a preferred embodiment, the electrical resistance may be about 5 Ohm to 50 Ohm. In a preferred embodiment, the disruptor may have an electrical resistance of about 15 Ohm. In another embodiment, the disruptor may have an electrical resistance of about 22 Ohm. One of skill in the art would recognize that voltage and current may be proportionally related to one another by Ohm's law. Much of the discussion herein may discuss the application of voltages to the disruptor202. One of skill in the art would recognize that analogous current source limitations may apply.

To generate the desired heat at the disruptor202, electrical current may be applied to the conductive paths204a,204bhaving a duty cycle that may vary from 0 to 100 percent. The electrical current applied to a disruptor202may be a direct or alternate current. A duty cycle is the fraction of time that the electrical current is being applied to the disruptor202and may be static (100%) or pulsed (<100%). It has been found that by pulsing the electrical current effective heating of the stratum corneum may be achieved while mitigating any sensation or discomfort experienced by the subject. In a preferred embodiment, a pulsed direct current may be applied to the disruptor202. The pulsed direct current may be applied to the conductive paths204a,204bof a disruptor202using a duty cycle of about 80 percent.

In an exemplary embodiment, current may be applied for a period of 200 ms. If the duty cycle is about 80 percent, the direct current may be turned on to apply electrical current to the disruptor202for about 160 ms and turned off for 40 ms during the 200 ms period.

In an embodiment, the frequency of a pulsed duty cycle may be about 1 Hz to about 1 kHz. In a preferred embodiment, the frequency of the pulsed duty cycle may be about 1 Hz to about 10 Hz. In a more preferred embodiment, the frequency of the pulsed duty cycle may be about 5 Hz.

For example, the frequency of the pulsed duty cycle may be 5 Hz for a duty cycle at 80 percent with a period of 200 ms. The pulsed duty cycle may have period of about 0.5 second to 5 seconds. In a preferred embodiment, the pulsed duty cycle may have a period of about 3 seconds to collect a sufficient amount of biological sample for testing. In a preferred embodiment, the voltage may be applied for a duration of 1 to 20 seconds.

In an exemplary embodiment, an electrical voltage of 2.2 V may be applied to the disruptor202with pulsed duty cycle of 80% for 3 seconds to generate temperature of 140° C. If disruptor202has the dimensions of about 100 μm×200 μm and electrical resistance of 22 Ohm, the power (P) over Area required to generate the required heat may be 5 W/mm2which may be calculated using the following equations:
P=I2R=V2/R=2.2V/22 Ohm=0.1 WwhereR=V/I and where,Power P is in Watts;Voltage V is in volts; andResistance R is Ohms.A=100 μm×200 μm=0.02 mm2P/A=0.1 W/0.02 mm2=5 W/mm2where,P is power; andA is area of the disruptor.

The energy (E) per unit area required to generate 140° C. of heat in the disruptor202may be measured by the following equations:
E/A=Pt/A=1 J/mm2where,Energy is measured in Joules,t is time at 0.2 s of one pulse; andA is the area of disruptor.

The amount of biological sample required to be obtained by the transdermal sampling and analysis device200to accurately determine levels of an analyte may be about less than 40 nl. In a preferred embodiment, the amount of biological sample obtained by the transdermal sampling and analysis device200may be about less than 10 nl. In a more preferred embodiment, the amount of biological sample obtained by the transdermal sampling and analysis device200may be about 5 nl.

In an embodiment method, voltage may be applied to the disruptor202in a manner to reduce the amount of sensation felt by the subject. One method of reducing sensation may be to gradually and in a stepwise manner raise the level of the voltage applied to the disruptor202until it reaches a desired voltage. For example, if 1.8 V produces the most amount of fluid, to reduce sensation the voltage may be pulsed at different intervals before reaching 1.8 V. For instance, the voltage may be pulsed five times at 1.2 V, five times at 1.4 V, and five times at 1.6 V before applying 1.8 V to the disruptor202. In this embodiment method, the pulses at lower voltages may cause some biological sample fluid to flow from the skin100. Even though this small amounts of the biological sample obtained at the lower voltages may not be enough to determine the levels of an analyte, the small amount of the biological sample may act as a thermal conductor to render the disruptor202more efficient and reduce the level of sensation felt by the subject at higher volts (i.e., 1.8 V). Thus, by increasing the voltage in a stepwise manner over a period of time, instead of applying the maximum voltage immediately, the same amount of biological samples may be obtained in the same amount of time while the amount of sensation may be reduced.

In addition, it may be noted that the application of electrical energy to the disruptor202may result in the formation of electrical fields surrounding the disruptor202. The formed electrical fields may also alter the permeability characteristics of the stratum corneum. By increasing the localized electrical field formed by applying electrical energy to the disruptor202, the permeability of the stratum corneum may also be increased. The increase in the permeability of the stratum corneum may require less heat imparted upon the stratum corneum to release a sufficient amount of biological fluid needed for an accurate analysis. Consequently, a lessening of the sensation or discomfort may be experienced by the subject.

FIG.9illustrates a top view of an embodiment transdermal sampling and analysis device200using more than one disruptor202. To increase the amount of disruption to the skin100, a transdermal sampling and analysis device200may employ more than one disruptor202. The disruptors202may be configured in a way to disrupt the skin cells and allow the flow of biological samples over the counter and working electrodes208,210of the transdermal sampling and analysis device200. By increasing the number of disruptor202sites, a larger volume of biological sample may be obtained in a shorter amount of time. This may result in a lessening of the experienced sensation or discomfort experienced by the subject. Additional biological samples obtained from the subject may enable a transdermal sampling and analysis device200to more accurately analyze the biological samples.

In the various embodiments, the transdermal sampling and analysis device200may include a reservoir212used to collect the biological samples that flow from the capillary-like channels of the skin. The reservoir212may be created by using processes and methods know in the art, such as by etching or arranging the transdermal sampling and analysis device200components in a manner to create a reservoir212. For example, to create the reservoir212, photoresist material may be applied to the first surface of the substrates214and patterns may be etched into the photoresist material to form the reservoir212. Photoresists and their uses are well known in the art.

In an embodiment, the reservoir212may have a depth of about 20 μm to 100 μm. In a further embodiment, the reservoir212may have a depth of about 50 μm to 100 μm. In a preferred embodiment, the reservoir212may have a depth of about 30 μm. In a more preferred embodiment, the reservoir212may have a depth of about 60 μm.

The reservoir212may be created in a location where it can collect the biological samples that flow out of the capillary-like channels of the disrupted skin100. Since the disruptor202creates the capillary-like channels in the skin100from where biological samples flow, the reservoir212may be positioned under or near the disruptor202to enable the transdermal sampling and analysis device200to collect the flowing biological samples. The reservoir212may comprise a collection reservoir212aformed generally to surround the disruptor202and a sensing chamber212bformed generally to contain the biological sample around the sensing elements such as counter and working electrodes208,210. The sensing chamber212bportion of the reservoir212may contain the biological samples at one location where the samples may be analyzed by reacting with a biologically reactive element and interacting with the electrodes208,210. The reservoir212may further prevent the biological samples from flowing to other components of the transdermal sampling and analysis device200not configured to analyze the obtained samples.

To further guide the movement of the biological samples in the reservoir212and over the counter and working electrodes208,210, channels222may be created. In an embodiment, channels222may be formed using channel support structures220positioned in the reservoir212to facilitate and optimize the movement of the biological sample and the interactions of the sensors with the collected biological samples. The reservoir212and channels222may be created in a variety of shapes. For example, the reservoir212may be square, triangle, trapezoid, rectangle or circle and the channels222may be linear or circular.

FIGS.10A-10Eillustrate top views of embodiment transdermal sampling and analysis devices200with different reservoir212and channel222shapes and configurations.FIG.10Aillustrates a top view of an embodiment transdermal sampling and analysis device200with a square shaped reservoir212, wherein the counter and working electrodes208,210may be positioned within reservoir212and one disruptor202may be also positioned within reservoir212.FIG.10Billustrates a top view of an embodiment transdermal sampling and analysis device200with a trapezoid shaped reservoir212, the inter-digitated counter and working electrodes208,210and disruptor202may be all positioned within the trapezoidal shaped reservoir212.FIG.10Cillustrates a top view of an embodiment transdermal sampling and analysis device200with a rectangular shaped reservoir212, the inter-digitated counter and working electrodes208,210and disruptor202may be all positioned within the rectangular shaped reservoir212.FIG.10Dillustrates a top view of an embodiment transdermal sampling and analysis device200with a narrow rectangle shaped reservoir212, the inter-digitated counter and working electrodes208,210and disruptor202may be all positioned within the narrow rectangular shaped reservoir212.

FIG.10Eillustrates a top view of an embodiment transdermal sampling and analysis device200with a rectangular shaped reservoir212, two counter electrodes208and one working electrode210with inter-digitations and positioned in the reservoir212and a disruptor202also located in the reservoir212. Long narrow channels222may be formed using several long channel supports220arranged in a parallel orientation with one another. The long channels222may function to facilitate the flow from where the biological samples away from the disruptor202and over the counter and working electrodes208,210via capillary action.

Channel supports220may be employed for different purposes. For example, since a subject's skin comes into contact with the side of the transdermal sampling and analysis device200on which biological samples may be collected, the skin100may flex and dip in to the reservoir212and prevent the flow of the biological samples to the counter and working electrodes208,210. Channel supports220may be used to prevent the skin from blocking the flow of the biological sample to the counter and working electrodes208,210by physically lifting the subject's skin100off of the transdermal sampling and analysis device200surface. Channel supports220may further facilitate an even flow of the biological sample over the entire surfaces of the working and the counter electrodes208,210.

In addition, the capillary force imparted by the channel supports220may be adjusted by varying the shape, structure, and hydrophilicity of the constituent materials of the channel supports. By selecting different materials from which to form the channel supports220, the rate of flow of biological sample across the reservoir and surface of the counter and working electrodes208,210may be altered. By selecting materials having greater hydrophilic characteristics the rate of flow across the reservoir may be augmented by the increase in surface tension between the biological sample and the supports of the hydrophilic channel supports220. Thus, by choosing a material with a greater hydrophilic property from which to form the channel support220, the flow rate of the biological sample to cover the counter and working electrodes208,210may be increased, which in turn minimizes the volume of biological sample needed to complete an accurate analysis. The relative hydrophilic characteristic of a material is measured by its wetting angle. Materials suitable for the channel support220may have a wetting angle of less than 40° and more preferably less than 20°. By using materials having such hydrophilic characteristics, the sampled fluid may be drawn by capillary action and hydrophilicity along the channel supports220and to the back of the sensing chamber. Consequently, any trapped air within the sensing chamber or along the channels222formed between channel supports220may be directed back toward the disruptor202.

Moreover, alternative configurations of the channel supports may increase the surface area of the channel support220support that comes into contact with the biological sample. By increasing the surface area of the channel support220support, an increase on the hydrophilic action may be realized.

In still further alternative configurations, by reducing the space between channel supports220at a desired location within the sensing chamber, capillary action may be increased. Consequently, the sampled fluid preferentially fills the sensing chamber. Capillary forces between structures within the remainder of the sensing chamber subsequently draw fluid from the first reservoir until the remainder of the sensing chamber is filled.

FIG.11Aillustrates an alternative embodiment of the transdermal sampling and analysis device200. Similar to the embodiment shown inFIGS.10A-10E, the embodiment transdermal sampling and analysis device200shown inFIG.11Aincludes a disruptor202having a serpentine configuration. The disruptor202may be positioned within a collection reservoir212a. Leads capable of coupling the disruptor202to a voltage/current source may be extended to the corners of the transdermal sampling and analysis device200. The disruptor202may be also positioned within an opening1304in a lid layer so that the disruptor202may be exposed to and may directly contact the subject's skin for disruption of the stratum corneum and the production of a biological fluid sample. The collection reservoir212aportion of reservoir212may be interconnected with a sensing chamber212bportion of reservoir212. The sensing chamber212bportion contains the produced biological fluid sample over counter and working electrodes208,210. The produced biological fluid sample may be directed over the entire surface of counter and working electrodes208,210via channels222formed between channel supports220. An optional reference electrode211may be also shown inFIG.11A. The disruptor202, counter and working electrodes208,210and optional reference electrode211may be all formed on a substrate layer214(not shown inFIG.11A). Channel supports220may be formed above the counter and working electrodes208,210and optional reference electrode211in a spacer layer. The lid layer may be then adhered to the space layer above the channel supports220.

As discussed above, the channel supports may be formed of hydrophilic materials having a wetting angle of less than 40° and more preferably less than 20° to induce a capillary action force and draw the generated fluid sample to the upper regions of the sensing chamber212bportion. In addition, by varying the dimensions along the vertical axis of the channels222, the capillary action may be increased, further forcing the generated fluid sample to the upper regions of the sensing chamber212bportion. As shown inFIG.11A, the dimension of channels222may be smaller in section A as compared to the dimension of channels222in section B. Consequently, a greater capillary action force may be imparted on the generated fluid sample due in large part to the increased contact with the constituent hydrophilic material of channel supports220. Optimal channel222widths have been found to range from 70 μm to less than 50 μm, and most preferably less than 30 μm.

FIG.11Billustrates another alternative embodiment of the transdermal sampling and analysis device200, wherein the dimensions of each of the channels222along the horizontal axis may be varied. As shown inFIG.11B, the channels222shown between channel supports220in region A may be narrower than the channels222shown between channel supports220in region B. In doing so, the generated fluid sample may be directed up through the channels222in region A on the left of the device200faster than the channels in region B on the right of the device200. Thus, any trapped air in the channels222that might prevent the generated fluid sample from completely covering the electrodes208,210in sensing chamber212bmay be effectively systematically pushed from one side of the sensing chamber212bportion to the other so as to avoid trapping the air. Since a larger volume sensing chamber212bportion requires a relatively large fluid sample to completely fill the sensing chamber212bportion and ensure complete coverage across counter and working electrodes208,210, the volume of the sensing chamber212bportion may be varied. Moreover, larger volumes of fluid samples require more time to generate. Thus, optimal volumes for the sensing chamber212bportion have been determined to be approximately less than 100 nanoliters (nl), and more preferably less than 20 nl, and most preferably 1 nl. Sensing chamber212bportion widths may be smaller than 500 μm wide×1 mm long. Preferable dimensions may be below 250 μm wide, 500 μm long. Similarly, the size of the collection reservoir212aportion may also impact the ability to obtain a viable fluid sample. The diameter of the collection reservoir212amay be less than 1 mm and preferably between 500 and 800 μm.

FIGS.12A-12Cillustrate different embodiment channel support220support configurations which offer varying amounts of surface area.FIG.12Aillustrates a cross-sectional view of several channel supports220(12A) arranged in parallel orientation. The channels supports220(12A) may form a contact angle of 90° with the substrate214. The space between two channel supports220(12A) may create the channels222. As the transdermal sampling and analysis device200comes into contact with the skin100, the skin may rest on top of the channel supports220(12A) and dip into the channels222. If the distance between the two channel supports220(12A) is too large, skin100may block the channel222by dipping far into it and touching the surface of the reservoir212. If the distance of the channel supports220(12A) is too small, the channel supports220(12A) may effectively block a sufficient flow of the biological sample to the counter and working electrodes208,210.

FIG.12Billustrates a cross-sectional view of several channel supports220(12B) arranged in parallel orientation. The channels supports220(12B) may form a contact angle greater than 90° with the substrate214. The angled nature of the channel support220(12B) supports increases the surface area channel support220(12B) support, relative to channel supports220(12A) shown inFIG.12A. As discussed above, the increased surface area increases the amount of interaction between the channel support220(12B) hydrophilic material and the biological sample. As a result, the flow of biological sample may be increased through the channels222relative to the configuration shown inFIG.12A.

FIG.12Cillustrates an alternative cross-sectional view of several channel supports220(12C) which increases, relative to channel supports220(12A) shown inFIG.12A, the surface area of the channel support220(12C) material that may come into contact with the biological sample, which providing increased support to prevent the subject's surrounding skin from occluding the flow of the biological sample from the counter and working electrodes208,210. However, the configuration shown inFIG.12Cmay decrease the volume of biological sample allowed to flow in each channel222(12C), unless the distance between channel supports220may be increased as the volume of the channels222(12C) may be decreased relative to the volume of the channels222(12A) shown inFIG.12A.

Another parameter of the channel supports220that may affect the functionality of the transdermal sampling and analysis device200may be the height of the channel supports220as compared to the distance the channel supports220may be positioned from the disruptor202. If long channel supports220may be positioned too close to the disruptor202, the height of the channel support220may prevent the skin100from coming into contact with the disruptor202when the transdermal sampling and analysis device200may be placed next to the skin100. If short channel supports are positioned too far from the disruptor202, the deformable subject's skin100may dip into a gap1202created between the channel support220and disruptor202and block the flow of the biological samples to the sensor electrodes.

FIG.13illustrates a cross-sectional view of an embodiment transdermal sampling and analysis device200, showing a preferred method of determining the ratio between the height of a channel support220and its distance from the disruptor202. The preferred distance to height ratio between the disruptor202and the channel supports220may be determined by using the ratio of the sides of a 30°-60°-90° triangle1204. The 30°-60°-90° triangle1204side “a” may be used to determine the height of the channel support220. The 30°-60°-90° triangle1204side “b” may be used to determine the distance of the channel support220to the disruptor202. In an embodiment, the side “b” (i.e., the distance of the channel supports from the disruptor202) may be about 0 μm to 30 μm. In a preferred embodiment, the side “b” may be about 30 μm and side “a” may be about 50 μm.

The biological sample collected by an embodiment transdermal sampling and analysis device200may escape from the reservoir212before it comes into contact with the counter and working electrodes. To ensure that the transdermal sampling and analysis device200has sufficient sample to perform the required analysis, different methods may be employed. For example, channels222may be used to facilitate the movement of the biological sample over the counter and sensing electrodes; hydrophilic channel support220material may be used to hold the biological samples attached to the channel supports220for a longer period of time; the disruptor202may apply heat to the skin for a longer period of time to keep the capillary-like opening of the skin open longer to obtain a larger amount of the biological sample; and/or a lid may be placed over the reservoir212to keep the biological sample from evaporating.

In an embodiment, to more efficiently collect and maintain the biological fluid from the subject, a lid may be placed on the exposed side of the transdermal sampling and analysis device200.FIG.14Aillustrates a top view of an embodiment transdermal sampling and analysis device200before a lid1302may be placed over the transdermal sampling and analysis device200. The transdermal sampling and analysis device200includes counter and working electrodes208,210, a disruptor202, and a reservoir212encompassing the disruptor202and counter and working electrodes208,210. Air vents224may be shown coupled to the reservoir212to allow air to escape as the biological sample flows to fill the reservoir from the disruptor202site to the top of the reservoir212. A spacer layer1408may be formed over portions of the counter and working electrodes208,210. The spacer layer1408may effectively form the walls of reservoir212.

FIG.14Billustrates the same transdermal sampling and analysis device200after a lid1302may be placed over the elements of the transdermal sampling and analysis device200and spacer layer1408. The lid1302partially covers the reservoir212to encapsulate the obtained biological sample. The lid effectively creates a closed volume defined by the reservoir212and the lid1302. Without the use of a lid, the biological sample may be contained within the reservoir212by applying sufficient pressure to the transdermal sampling and analysis device200against the subject skin. In effect the subject skin acts as a lid to contain the biological sample within the reservoir212. When a lid1302is placed over the reservoir212, it may be necessary to include air vents224to allow air from escaping as the biological sample flows from one side of the reservoir212to another.

The lid1302may cover the entire surface of the transdermal sampling and analysis device200with the exception of the disruptor202. In an embodiment, a hole1304may be carved in the lid1302to allow the disruptor202to be exposed while the other parts of the transdermal sampling and analysis device200may be covered. The hole may allow the disruptor202to come into contact with the skin100thus effecting adequate heating of the stratum corneum to cause disruption. The hole1304may also guide the biological fluid to flow into the reservoir212. In a preferred embodiment, the hole1304has a diameter (or width) dimension of about 500 μm.

The lid1302that may be placed over the reservoir212may be made of a material such as plastic, metal, ceramic, or polymer. In a preferred embodiment, the lid1302may be made from a polymer. The lid1302thickness should be minimal to enable contact between the user's skin and the disruptor202with a minimal first reservoir212adiameter. However, the lid1302should be thick enough to maintain chamber integrity in the presence of the pressure required to achieve intimate contact between the user's skin and disruptor. The lid1302(and adhesive layer adhering the lid1302to the spacer layer1408discussed in more detail below with respect toFIGS.15A-15C) may have a thickness of about 10 μm to 75 μm. Preferably, the lid1302may have thickness of about 15-30 μm. The inner surface of the lid1302may be hydrophilic, preferably having a wetting angle of less than 50°, and more preferably less than 20°.

In an embodiment, instead of creating the channels222in the reservoir212, channels222may be formed on the side of the lid1302that may be closer to the substrate when the lid1302is placed on the transdermal sampling and analysis device200. In such a configuration, the reservoir212may be constructed without channels222. The lid1302may include channel supports220and channels222. Once the lid1302is positioned on the transdermal sampling and analysis device200, the channels supports220of the lid1302may create channels222in the reservoir212. This may be useful in the manufacturing process, where channels222created in the reservoir212may clog when the biologically reactive element is applied to the surface of the electrodes208,210. By including the channel supports220in the lid1302, the biologically reactive element may be applied to the surface of the reservoir212. The channels222may then be formed on top of the biologically reactive elements in the reservoir212once the lid1302is positioned on the transdermal sampling and analysis device200.

FIG.15Aillustrates a top view of an embodiment transdermal sampling and analysis device200. The transdermal sampling and analysis device may include a substrate214(shown inFIGS.15B and15C), a disruptor202located within a collection reservoir212aportion, a reservoir connector channel1402which connects the collection reservoir212aportion to a sensing chamber212bportion. The sensing chamber212bmay be disposed over (or under) one working electrode210and two counter electrodes208. The sensing chamber212bmay allow the biological sample to collect over the counter and working electrodes208,210, respectively. A biologically reactive element (not shown) may also be applied in the sensing chamber and over the counter and working electrodes208,210. The counter and working electrodes208,210may be connected to electrical conductive paths206a,206b, respectively. A vent hole224may be present at the distal end of the sensing chamber212bto allow air to escape as the biological sample moves from the collection reservoir212ato the sensing chamber212bthrough the reservoir connector channel1402.

The width of the reservoir connector channel1402may affect the distance between the disruptor202and the counter and working electrodes208,210. For example, a narrow reservoir connector channel1402may allow small amounts of fluid to be directed from the collection reservoir212ato the sensing chamber212b. A wide reservoir connector channel1402may be used for directing larger amounts of biological sample from the collection reservoir212ato the sensing chamber212b. Thus, to direct small amounts of fluid from the first to sensing chamber in a transdermal sampling and analysis device200with a wide reservoir connector channel1402, the distance between the disruptor202and the counter and working electrodes208,210may be minimized as compared to a transdermal sampling and analysis device200with a narrow reservoir connector channel1402. In a preferred embodiment, the reservoir connector channel1402may be 30-100 μm wide and 200-500 μm long.

As mentioned above, the transdermal sampling and analysis device200may further include a lid1302with a lid opening1304. The lid opening1304may be located over the disruptor202to allow the disruptor202to come into direct contact with the subject's skin and as well as provide an open path for interstitial fluid to flow out of the stratum corneum and into the collection reservoir212a. The disruptor202may be coupled to a signal generator (not shown). The opening1304in the lid1302exposes the disruptor202and allow contact between the disruptor202and the users' skin should be smaller in diameter than the collection reservoir212ato enhance the collection of the fluid sample. For a 750 μm collection reservoir212adiameter, the lid opening1304should be between 200 μm and 1 mm, preferably between 300-700 μm, and most preferably 500 μm.

FIG.15Billustrates a cross-sectional view of the transdermal sampling and analysis device200along reference points AA′ and reference line1404. The arrows on the cross-section reference line1404shows the direction of the cross-sectional view. The transdermal sampling and analysis device200may be comprised of several layers including a substrate layer214, a spacer layer1408and a lid layer1302. Referring toFIG.15B. the lid1302may be adhered to the spacer layer1408using an adhesive layer1303. The total thickness of the lid1302with adhesive layer1303should be between 10-75 μm, and preferably between 15-30 μm. The lid adhesive layer1303may itself have a thickness of between 5-20 μm, and preferably between 3-10 μm. If the thickness of the adhesive layer is too thick, the adhesive may flow into the first reservoir212aand sensing chamber212b, as well as reservoir connector channel1402when applied. However, if the thickness of the adhesive layer1303is insufficient, it may not flow and completely seal the lid1302to the spacer1408. In addition, the adhesive layer1303should be sufficiently flat when applied so as to seal the surface of the spacer layer1408with minimal flow upon application. The surface of the adhesive layer should have an RMS roughness value of Ra below 3 μm, and preferably below 1 μm. The adhesive layer1303should exhibit hydrophilicity, having a wetting angle below 40° and preferably below 20°. The adhesive layer1303material should exhibit flow characteristics having Tg between 0 and 50° C., preferably between 0 and 30° C., and most preferably between 10 and 20° C.

The spacer layer1408may separate the substrate layer214and the lid layer1302. The first reservoirs212aand sensing chamber212band the reservoir connector channel1402may be created by the spacer layer1302using methods as described above. The spacer layer1408may be 10 and 70 μm thick and may be selected from a material such as polymer or ceramic. It should be noted that if the thickness of the spacer layer1408is too thick, the user's skin will be effectively spaced away from the disruptor202formed on a substrate214. As the diameter of the first reservoir212amay be decreased, it becomes increasingly difficult for the user's skin to deflect into the first reservoir212aand come into contact with the disruptor202. Accordingly, as the diameter of the first reservoir212amay be decreased, the thickness of the spacer layer1408must also be decreased. The thickness of the spacer layer1408may be between 10 and 50 μm, and most preferably between 15 and 30 μm for a first reservoir having a diameter of 750 μm.

The collection reservoir212amay be located within the hole1304and surrounding the disruptor202to allow the biological sample to collect in the collection reservoir212a. As shown inFIG.15B, the width of the collection reservoir212amay be slightly larger than the width of the hole1304in the lid1302. Electrically conductive paths206a,206bmay be located between the substrate layer214and spacer layer1302. The electrically conductive path206aconnects to the counter electrode208and the electrically conductive path206bconnects to the working electrodes210. It may be noted that the thickness of the electrically conductive paths206aand206bmay be such that in comparison to the thickness of the substrate214, spacer1408and lid1302layers, the conductive path layers may not be seen in the cross sectional view.

FIG.15Cillustrates a cross-sectional view of the transdermal sampling and analysis device200along reference points BB′ and reference line1406. The arrows on the cross-section line1404shows the direction of the cross-sectional view. At this cross-section, the transdermal sampling and analysis device200may include a substrate layer214, a spacer layer1408and a lid layer1302. The spacer layer1408may form the boundaries of the sensing chamber212b. By adhering the lid1302fully over the sensing chamber212b, the biological sample may be prevented from evaporating or pouring out of the transdermal sampling and analysis device200and adequately react with the biologically reactive element in the sensing chamber212b.

FIG.16is a perspective view of an embodiment transdermal sampling and analysis device200using a raised disruptor202. The transdermal sampling and analysis device200shown inFIG.16is shown without a lid. The transdermal sampling and analysis device200is shown to have a raised disruptor202. Raising the disruptor202may assure good contact of the disruptor202to the skin100, which may be advantageous with increasing channel support220height. Another advantage of using a raised disruptor202may be that it acts much like the channel supports which displace the skin100from the surface of the electrodes so that the biological sample may flow freely over the surface of the electrodes. This configuration may also allow for creation of channels in the gap between the coils802of serpentine disruptors202which assist in increasing the flow of the obtained biological sample. A spacer layer1408may disposed on the substrate214to form a reservoir212encompassing the counter and working electrodes208,210so that a biological fluid sample generated when the disruptor202disrupts the subject's skin may be contained within the reservoir212and over the counter and working electrodes208,210. Any of a variety of manufacturing techniques may be employed to form the raised disruptor surface. For example, the layer of material used to form the disrupter may be deposited in a series of deposition steps to build up a sufficient layer before excess material may be etched away in a photolithography process. Alternatively, the deposition process itself may be used to continuous deposit material in the form of the disruptor to build up the raised disruptor structure. As discussed above, a biological sample may be tested for presence of an analyte (e.g., glucose) by applying a biologically reactive element to the sample (e.g., an enzyme). In the various embodiments, the biological sample (e.g., interstitial fluid) may react with a biologically reactive element on the surface of the counter electrodes208and working electrodes210. When interstitial fluid contacts a biologically reactive element on the surface of the counter and working electrodes208,210, it causes a chemical reaction that releases electrons. The products of the biochemical reaction between the biological sample and the biologically reactive element may be analyzed by the magnitude of the current that may be generated when the released electrons are transferred to the sensing electrode by the electron mediator.

Example biologically reactive elements may include, but are not limited to, glucose oxidase (GOD), glucose dehydrogenase, etc. In addition, in order to transfer released electrons to the one or both of the working and counter electrodes208,210, an electron mediator may be deposited in conjunction with the biologically reactive element. The electron mediator and biologically reactive element may be linked with a polymer to form a matrix, and the three materials together may constitute a sensing reagent. Example mediators that may be used include ferrocene, i.e., “Fc” (Fe(C5H5)2), potassium ferrocyanide (K3Fe(CN)6), ferrocenecarboxaldehyde (C11H10FeO), etc. Thus, in an embodiment device that uses interstitial fluid to test for glucose, the biologically reactive element glucose oxidase (GOD) may be applied to at least one sensing electrode in a matrix with the electron mediator ferrocene (Fc) and a polymer linear polyethyleneimine (I-PEI) to form the sensing reagent (I-PEI-Fc/GOD matrix).

As discussed above, various embodiments may implement narrow channels formed in the sensing chamber between several channel supports aligned in a parallel block. The channels may facilitate flow of the biological sample away from the disruptor202and collection reservoir212aand over the counter and working electrodes208,210.

In the various embodiments discussed above, channel supports220may be tapered such that the channels222formed between the channel supports220are narrower at the end of the sensing chamber that is farthest from the collection reservoir212a. The channel supports220may be formed using hydrophilic materials, which promote adhesion forces between the biological fluid and the channel supports220. The adhesion forces may increase as the taper of the channel supports220increases such that the channel supports220get thicker. Coupled with the fact that surface tension of the biological sample (i.e., cohesive forces of the fluid) increases with narrower channels, the farthest end of the sensing chamber212bmay exert strong capillary force on the biological sample. The capillary action may force the interstitial fluid to fill the sensing chamber212bfrom the farthest end of the sensing chamber212btoward the collection reservoir212ato avoid trapping bubbles.

The various embodiments shown inFIGS.10F and10Ghave exhibited excellent characteristics in directing the flow of generated biological fluid samples in the collection reservoir212aacross the entirety of the counter and working electrodes208,210in the sensing chamber212b. However, in some instances it has been observed that when the sensing reagent is applied to the counter and working electrodes208,210, the addition of the sensing reagent causes the formation and collection of air bubbles in the sensing chamber212b. These air bubbles prevent the generated biological fluid from completely covering the counter and working electrodes208,210in the sensing chamber212b. One reason for this result may be that the sensing reagent causes a greater hydrophilic environment in the sensing chamber212b. Consequently, the generated biologic fluid may tend to bridge across the channel support members220instead of following the edge of the sensing chamber212band up each of the channels222. The bridging of the fluid over channel support members220may permit an air bubble(s) to form, thereby blocking the flow of biological fluid across the entirety of the counter and working electrodes208,210and signal therefrom.

Multiple design configurations, illustrated inFIGS.17A-17Gmay be used in the various embodiment transdermal sampling and analysis devices to mitigate against the formation of air bubbles in the sensing chamber212bwhen a sensing reagent is employed. By measuring parameters such as fill rate, sensation, and bubble formation for each embodiment design, it may be determined that shortening the height of each channel222relative to its width may mitigate bubble formation. For example, the six channels222shown inFIGS.11A and11Bmay each have a height of about 500 μm, and may each have an average width of about 30 μm. In order to prevent bubble formation, the aspect ratio of channel height to width may be decreased in various embodiments by shortening the heights of the channels222to about 250 μm. Thus, in an embodiment, the aspect ratio of each channel222may be less than 10:1. In a preferred embodiment, the aspect ratio of each channel222may be about 5:1, and more preferably 2:1. In this manner bridging of biological fluid may be prevented, since the distance the biological fluid travels in the sensing chamber212b(i.e., down channels222) may be a much shorter path as compared to previously described embodiments. Embodiment designs configured using these aspect ratios of channel222height to width may therefore significantly lower the formation of air bubbles that prevent the biological fluid sample from flowing over the entirety of the sensing chamber212b.

FIG.17Aillustrates an embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. As shown inFIG.17A, the sensing chamber212bmay contain parallel channel supports220a horizontal configuration. Consequently, the sensing chamber may include a central channel222c, and edge channels222aand222b. In addition, due to the horizontal configuration of the channel supports220, additional horizontal channels1704may be formed between the channel supports220. Each of the central channel222cand edge channels222aand222bmay be configured with an aspect ratio that is less than or equal to approximately 10:1. For example, the height of edge channels222aand222bmay be about 250 μm, and the width of each channel may be about 30 μm. The height of the central channel222cmay be about 250 μm, and the width of the central channel222cmay be about 90 μm. Thus, the aspect ratio of the central channel222cmay be about 3:1 (i.e., less than 10:1). As with other embodiments, the channel supports220may prevent a lid1302from being deformed and encroaching into the sensing chamber212b. The channel supports220may further possess hydrophilic properties which aid in the dispersion of the generated biological fluid across the entire surface of the sensing chamber212b.

FIG.17Billustrates another embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. As shown inFIG.17B, the sensing chamber212bmay contain channel supports220, with channels222between adjacent channel supports220. As shown inFIG.17B, the channel supports220may be configured in a vertical formation with the channel supports220largely parallel to one another. The channel supports220may be divided into four groups configured to form a central channel222cand vertical channels222between the channel supports220. The channel supports220may also be configured to define edge channels222aand222b. Each of the channels222, central channel222cand edge channels222aand222bmay be configured with an aspect ratio that is less than or equal to approximately 10:1. For example, the height of channels222as well as edge channels222aand222bmay be about 250 μm, and the width of each channel may be about 30 μm. Thus, the aspect ratio of the channels222as well as edge channels222aand222bmay be about 10:1. The height of the central channel222cmay be about 250 μm, and the width of the central channel222cmay be about 90 μm. Thus, the aspect ratio of the central channel222cmay be about 3:1 (i.e., less than 10:1). The configuration of channel supports220being divided into four groups may also provide the sensing chamber212bwith a horizontal channel1704. The embodiment shown inFIG.17Bmay also include a space1706between the channel supports220and end1702.

FIG.17Cillustrates another embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. The sensing chamber212bmay contain channel supports220, with channels222between adjacent channel supports220, with a central channel222cand edge channels222aand222b. As shown inFIG.17C, the channel supports220may be configured in a vertical formation with the channel supports220largely parallel to one another. The channel supports220may be divided into two groups forming a central channel222cbetween a group on the left side of the sensing chamber and a group on the right side. Each of the channels222, central channel222cand edge channels222aand222bmay be configured with an aspect ratio that is less than or equal to approximately 10:1. For example, the height of channels222as well as edge channels222aand222bmay be about 250 μm, and the width of each channel may be about 30 μm. Thus, the aspect ratio of the channels222as well as edge channels222aand222bmay be about 10:1. The height of the central channel222cmay be about 250 μm, and the width of the central channel222cmay be about 90 μm. Thus, the aspect ratio of the central channel222cmay be about 3:1 (i.e., less than 10:1). The configuration of channel supports220being divided into four groups may also provide the sensing chamber212bwith a horizontal channel1704. The embodiment shown inFIG.17Cmay also include a space1706between the channel supports220and end1702.

FIG.17Dillustrates another embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. The sensing chamber212bmay contain channel supports220, with channels222between adjacent channel supports220. As shown inFIG.17D, the channel supports220may be configured in a vertical formation with the channel supports220largely parallel to one another. In contrast to embodiments illustrated inFIGS.17A-17C, the channel supports220may be tapered such that the width of each channel support220may be wider at the top and narrower at the bottom. Consequently, the channels222formed between the channel supports220are wider at the bottom and narrower at the top. Each of the channel supports220may be configured with a bulbous shape at the wider end at the top. In an example embodiment, the height of each channel222may be about 250 μm, while the distance between inner channel supports1708a,1708bmay be about 23 μm near end1702, and may be about 33 μm near the end closest to the collection reservoir212a. Thus, the aspect ratio of each channel222may be less than or equal to 10:1. The sensing chamber212bin this configuration may also have edges1710a,1710bthat taper, and form a smooth surfaces at the intersection of the sensing chamber212band the collection reservoir212a. As a result, the distance between the two outer channel supports1712a,1712band edges1710a,1710bmay be greater at the lower end nearest the collection reservoir212aand less at the top end nearest end1702of the sensing chamber212b. In one example, the distance between outer channel supports1712a,1712band edges1710a,1710b, respectively, may be about 38 μm.

FIG.17Eillustrates an alternative embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. The embodiment illustrated inFIG.17Emay be significantly similar to the embodiment illustrated inFIG.17D. However, in the embodiment illustrated inFIG.17E, the sensing chamber212bin this configuration may also have edges1710a,1710bthat do not taper. Thus, the edges1710a,1710bmay form a sharp corner at the intersection of the sensing chamber212band the collection reservoir212a. As a result, the distance between the two outer channel supports1712a,1712band edges1710a,1710bmay be consistent throughout the edges.

FIG.17Fillustrates an alternative embodiment transdermal sampling and analysis device that may have a long sensing chamber212bthat may be divided into two areas, and long channels222. In the embodiment shown inFIG.17Fthe aspect ratio of channel height to channel width may be less than 20:1. For example, each channel222may be approximately 500 μm in height and approximately 30 μm in width. Each of the sensing chamber212bareas may be formed with tapered outer edges1710. In addition, each of the sensing chamber212bareas may contain a singular channel support220. The singular channel support contained in each of the sensing chamber212bareas may be configured in a similar shape as the sensing chamber212bareas in which it may be contained.

FIG.17Gillustrates an alternative embodiment transdermal sampling and analysis device wherein the aspect ratio of the height of each channel to the width of each channel is less than 10:1. The embodiment illustrated inFIG.17Gmay be significantly similar to the embodiment illustrated inFIG.17D. However, as shown inFIG.17G, the channel supports220may be configured without the taper or bulbous shape at the top of the channel supports220. In the configuration, the width of the channel support220and the channels222formed between the channel supports220may be constant. In an example, the width of the channels222formed between inner channel supports1708a,1708bmay be about 35 μm. The width of the channels222formed between outer channel supports1716a,1716band edges1710a,1710bmay be about 40 μm. The height of all channels222may be about 250 μm. Thus, the aspect ratio of each of the channels222inFIG.17Gis less than or equal to 10:1.

Each of the embodiment configurations shown inFIGS.17A-17Ghave been observed to provide satisfactory fill rates as well as sensation levels experienced by the subjects. In addition, each of the embodiment configurations shown inFIGS.17A-17Ghave been observed to mitigate bubble formation even in the presence of a biologically reactive element applied to the counter and working electrodes. While the fill rates vary among the embodiment configurations, embodiments wherein the edges of the sensing chamber may be tapered and intersect the collection reservoir with a smooth surface may be observed to be the most successful in mitigating the formation of air bubbles.

In some embodiments, various compounds in the biological sample in the sensing chamber212band/or collection reservoir212amay create interference by directly reacting with the mediator of the sensing reagent. For example, when a mediator with ferrocene is applied in the sensing chamber212b, various reducing species in interstitial fluid may transfer their electrons to the mediator, thereby significantly reducing the effectiveness of the sensing reagent. To address this issue, a barrier layer may be applied over the sensing reagent film so that interaction between the extraneous redox species and the sensing reagent is substantially decreased. Example barriers may include, but are not limited to, I-PEI, bovine serum, poly(carboxybetaine methacrylate) (pCBMA), GOD, etc. The barrier may be a monolayer of a suitable material, and may effectively reduce the undesirably interactions between ISF and glucose, and improve signal to noise ratio.

Despite the benefit of using a barrier layer to solve the issue of interference, when used in the embodiments discussed above with respect toFIGS.17A-17G, the barrier layer may impede the flow of the biological sample throughout the entirety of the sensing chamber212b. Consequently, interstitial fluid may remain in the collection reservoir212ainstead of being drawn by capillary force to flow over the counter and working electrodes.

In exemplary embodiments shown inFIGS.18A-18D, the configuration of the sensing chamber212bmay prevent bubble formation while allowing proper flow of the interstitial fluid even when a barrier is used over the sensing reagent.FIGS.18A and18Billustrate an embodiment transdermal sampling and analysis device. InFIG.18A, the sensing chamber212bmay form a circular shape surrounding the periphery of the collection reservoir212a. The sensing chamber212bmay contain circular channel supports1801which may form circular sensing channels1802. The circular channel supports1801and circular sensing channels1802may guide the flow of a biological sample through the circular-shaped sensing chamber212b.FIG.18Billustrates a view of the embodiment shown inFIG.18Awithout the circular channel supports1801and circular sensing channels1802. Working electrode1804a, counter electrode1804band reference electrode1806, may be provided in various configurations around the periphery of the collection reservoir212asuch that the sensing chamber212bdirects the flow of interstitial fluid over the entirety of the working and counter electrodes,1804a,1804b.

FIGS.18C and18Dillustrate an alternative embodiment transdermal sampling and analysis device that is substantially the same as the embodiment shown inFIGS.18A and18B. However the embodiment illustrated inFIGS.18C and18Dmay implement a reference electrode1808in a slightly different configuration as compared to reference electrode1806inFIGS.18A and18B.

The circular sensing chamber212bconfiguration shown inFIGS.18A-18Dprovide a sensing chamber212bwith an increased circumference surrounding the collection reservoir212a. In contrast to the embodiment configurations shown inFIGS.11A,11B,17B-17EandFIG.17Gwhich may contain six channels222that may each be approximately 30 μm wide and 250 μm to 500 μm high, the circular sensing chamber configuration shown inFIGS.18A-18Dmay contain, for example, twenty-four circular sensing channels1802formed between circular channel supports1801. Each of the circular sensing channels1802may be approximately 80 μm in height, while still retaining a width of approximately 30 μm. Thus, the aspect ratio of height to width of the embodiment circular sensing channels1801may be less than 3:1. In a preferred embodiment the aspect ratio of height to width of the embodiment circular sensing channels1801may be approximately 1:1. Because the overall width (circumference) of the circular sensing chamber may be increased, the height (radius extending from the center of the collection reservoir212a) of the circular sensing chamber212bmay be decreased while keeping the overall area of the sensing chamber212bconstant. Thus, the same amount of biological fluid may be directed to cover the counter and working electrodes1804a,1804bwhile requiring the biological fluid to travel a shorter distance from the collection reservoir212a. In addition, the circular shape of the sensing chamber212bmay allow the biological fluid that is generated by the disruption of the stratum corneum to more evenly disperse radially outward in manner which further mitigates the creation of air bubbles or zones of fluid bridging across channel supports1801contained within the sensing chamber212b. Embodiment transdermal sampling and analysis devices implementing the circular sensing chamber configuration as shown inFIGS.18A-18Dhave been observed with satisfactory fill rates and sensation levels as well as the absence of air bubble formation even when biologically reactive elements and barrier layer elements have been applied.

The transdermal sampling and analysis devices200of the various embodiments may be manufactured using different methods and materials. Manufacturing methods for an embodiment transdermal sampling and analysis device200may be disclosed in the related International Application Number PCT/US2006/023194, filed Jun. 14, 2006, entitled “Flexible Apparatus and Method for Monitoring and Delivery,” which claims priority to the International Application Number PCT/US2005/044287, entitled “Apparatus and Method for Continuous Real-Time Trace Bimolecular Sampling, Analysis and Deliver,” filed on Dec. 9, 2005, which are attached hereto as Appendices A and B. The manufacturing of an embodiment transdermal sampling and analysis device200is also disclosed in the publication entitled “Novel Non-Intrusive Trans-Dermal Remote Wireless Micro-Fluidic Monitoring System Applied to Continuous Glucose and Lactate Assays for Casualty and Combat Readiness Assessment” by John F. Currie, Michael M. Bodo and Frederick J. Pearce, RTO-MP-HFM-109:24-1, Aug. 16, 2004. A copy of the publication is attached hereto as Appendix C. The entire contents of all of the related applications and publication are incorporated by reference herein.

An embodiment device may be manufactured using materials and equipment commonly used in the micro-fabrication and bio-sensing industries. Formation of the conductive material layer on the substrate may be accomplished using any of the various deposition techniques known in the art. For example, thin film deposition (e.g., evaporation) may be used to form a conductive material layer on the substrate.

FIG.19is a process flow diagram illustrating an example method1900for manufacturing a transdermal sampling and analysis device. In step1902, a conductive material, from which the disruptor, at least two electrodes, and the interconnects may be formed, may be deposited on a base substrate. The substrate layer may be made of a variety of materials such as glass, plastic, metal or silicon. In an embodiment, the substrate may be made of a polyimide such as Kapton™. Kapton™ is a polyimide film developed by DuPont™.

In an embodiment, the conductive material may be gold. In alternative embodiments, the conductive material may be one or more other metals, such as one or more of nichrome, titanium, and tungsten. Deposition of the conductive material layer on the substrate may be accomplished, for example, by evaporating a thin layer of conductive material on the substrate. In other embodiments, deposition of the conductive material may be performed using any of a variety of other techniques known in the art. Such techniques may include, but are not limited to, sputter deposition, vacuum deposition, ion plating, ion beam assisted deposition (MAD), pulsed laser deposition, etc. In alternative embodiments, the conductive material may be applied by other coating techniques, such as spin coating, electroplating, spraying, etc.

In step1904, the conductive material layer may be patterned to create the disruptor, at least two electrodes (e.g., a counter electrode and a working electrode), and interconnects of the device. Patterning may be performed according to a basic photolithographic process known in the art, the steps of which may include applying a photoresist, drying, exposing and patterning in the photoresist, developing the photoresist, etching the conductive material (e.g., metal), and stripping the photoresist.

In step1906, a photo-sensitive polymer may be applied onto the surfaces of the counter and working electrodes. The photo-sensitive polymer may be patterned using photolithographic techniques known the art to create channel support structures forming a spacer. In one embodiment, photolithographic techniques may include steps such as applying a photo-sensitive polymer coating to an underside of the lid, applying a positive resist pattern to the photo-sensitive polymer coating, exposing the photo-sensitive polymer coating to a light source, and using developer solution to remove any photo-sensitive polymer that was exposed to the light source.

The photo-sensitive polymer may be, for example, a material with a low wetting angle (e.g., less than 40 degrees) in order to promote capillary action by the channels that are formed between the channel support structures. In an embodiment, the photo-sensitive polymer may include a ceramic.

In step1908, any residue of the photo-sensitive polymer remaining on electrodes between the channel support structures may be removed by oxygen plasma treatment well known in the art. In step1910, an analyte sensing layer, for example may be selectively deposited on the conductive material layer in conjunction with an electron mediator. In an embodiment, the analyte sensing layer may be a film disposed on the surface of the sensing electrode(s), forming a solid state mediated sensor. In an embodiment, the film may be formed by a polymer (e.g., linear poly(ethyleneimine)), a mediator (e.g., ferrocene) covalently bonded to the polymer, and a biologically reactive element such as an enzyme (e.g., (e.g., glucose oxidase, glucose dehydrogenase, etc.) that is immobilized by the polymer with covalently-bonded mediator.

In step1912, a lid for the device may be created by applying a thin layer of adhesive to a polymeric substrate such as polyester, polycarbonate, acetate, or the like, then cutting to size and shape by IR or excimer laser as well known in the art. The lid may be positioned and attached to the device on top of the spacer (i.e., above the channel support structures).

While method1900may be an effective way to manufacture a transdermal sampling and analysis device, it has also been observed that the analyte sensing reagent deposited in step1910may tend to form a non-uniform layer over the counter and working electrodes due to the presence of channel support structures in the spacer. For example, using method1900to create a device with a desired glucose oxidase layer on the electrodes of around 1 μm, the actual resulting layer may measure around 15 μm toward the edges and around 0.1 μm near the center of the reservoir. Since interstitial fluid collected for analysis may be blocked from channels by an excess of glucose oxidase toward the edges, overall performance of the device may be significantly decreased due to this non-uniform distribution.

As discussed above, and as shown inFIGS.21A-21C(discussed in further detail below), an alternative process for manufacturing a transdermal sampling and analysis device may involve constructing the reservoir without attached channel supports (and therefore without channels), and instead forming channel support structures of the spacer as part of the lid (i.e., attached to a first side of the lid). Thus, once the lid is attached onto the transdermal sampling and analysis device, the channels supports of the lid may create channels in the reservoir. This alternative embodiment may substantially decrease or even prevent uneven distribution of the analyte sensing reagent due to clogging of the channels in the reservoir. Consequently a more uniform layer of analyte sensing reagent may be formed.

FIG.20Ais a process flow diagram illustrating an alternative method2000for manufacturing a transdermal sampling and analysis device. In the alternative embodiment method2000, steps1902and1904of method1900may be performed in the same manner as discussed above. In step2002, an analyte sensing layer (i.e., a layer of the analyte sensing reagent) may be applied to the surface of the reservoir (e.g., by deposition, coating, etc.).

In steps2004-2008, a lid for the device may be created with a spacer layer of integrated channel support structures. Specifically, in step2004, a photoresist coating material may be to the surface of the lid substrate, and in step2006the photoresist coating material may be patterned to form the channel support structures.

In step2008, an adhesive material layer may be applied to the top surfaces of the channel support structures. The formation of the adhesive layer is described in further detail below with respect toFIG.20B. In this manner, channels may be created over the counter and working electrodes and the analyte sensing reagent in the reservoir once the lid with the channel support structures is attached to the base, step2010.

WhileFIG.20Aillustrates the lid formation steps (steps2004-2008) as occurring after the conductive material layer is patterned (step1904) and after the analyte sensing reagent is applied to the reservoir (step2002), in alternative embodiments the lid may be formed with the channel support structures (steps2004-2008) at any time before the lid is attached on the device to form channels in the reservoir (step2010). Thus, in some embodiments, a supply of lids with integrated channel support structures may be pre-formed. In other embodiments, the lid with integrated channel support structures may be formed in parallel with some or all of steps1902-2002of method2000. An adhesive layer, formed by applying a layer of adhesive material in step2008, may provide a way of attaching the spacer on the lid to the base. In an embodiment, such attachment may require selectively applying a layer of an adhesive material to the tops of the channel support structures, preventing adhesive material from getting in the channels between the support structures. Therefore, selection of an appropriate adhesive material may be important for proper operation of the device.

FIG.20Bis a process flow diagram illustrating a method of applying the adhesive material layer in step2008ofFIG.20Aaccording to an embodiment. In method2050, a release liner substrate may be coated with an adhesive material to a desired thickness, step2052. In step2054, the adhesive material may be applied as a liquid, and allowed to dry on the release liner substrate to a desired thickness. In step2056, the exposed side of the adhesive layer may be applied to the surfaces of the channel support structures. In step2058, the release liner may be removed to expose the opposite side of the adhesive layer, which may adhere to the base upon attaching the lid to the base to form the device. Notably, the adhesive material may be selected such that the adhesive forces between the material and the channel support structures is stronger than the adhesive forces between the material and the release liner substrate. This may ensure that the release liner is removable from the adhesive layer without pulling it off of the channel support structures. However, the adhesive material selected should also have properties such that the adhesive forces between the material and the release liner substrate are stronger than the cohesive forces of molecules of the adhesive material itself. This may ensure that, in areas between the channel support structures (i.e., in the channels), adhesive material will remain on the release liner and will not adhere to the space between the channels formed between the channel support structures.

Example structures that may be formed in steps1902-2002of method2000are further shown by the progression illustrated inFIGS.21A-21C.FIG.21Aillustrates a clean base substrate layer2102.FIG.21Billustrates the substrate layer2102with a conductive material layer2104, such as a thin metal layer, deposited on the substrate layer2102, corresponding to step1902of method2000.FIG.21Cillustrates the substrate layer2102, with the conductive material layer2104, and a layer2106of an analyte sampling reagent that has been deposited on the conductive material layer2104, corresponding to step2002of method2000. In various embodiments, the layer2106may have an electron mediator in addition to the analyte sampling reagent, and may be further covered with an optional anti-interferent barrier layer (not shown).

FIG.22illustrates an example lid structure that may be formed as a result of steps2004-2008of method2000. Lid2200may include a lid substrate material2202, on which a photoresist coating material may be applied, corresponding to step2004of method2000. The photoresist coating material may be patterned to create channel support structures2204in a spacer layer, corresponding to step2006of method2000. An adhesive material layer2206may be applied to only the top surface of the spacer layer (i.e., the tops of the channel support structures2204) corresponding to step2008of method2000.FIG.23illustrates components that, when joined together, form a device2300. Device2300may have a base with the layers shown inFIG.21C(i.e., base substrate2102, conductive material layer2104, and analyte sensing layer2106), and may have a lid2200shown inFIG.22. In an embodiment, the device2300may be manufactured according to method2000shown inFIG.20A. Once the channel support structures2204on the underside of the lid attach to the base of the on the device2300, the channels support structures2204may create channels in the reservoir.

As discussed with respect toFIGS.20A,21A-21C,22and23, forming a spacer with channel support structures on the lid in method2000may provide an effective way to avoid channel blockage due to non-uniform distribution of the analyte sensing reagent in the reservoir (i.e., excess collection toward edges). However, the spacer may be relatively thick (e.g., around 30 μm) compared to the lid, which may be optimally thin to facilitate disruption. Since photoresist material, from which the channel support structures may be patterned, is typically coated on as a liquid and later dried, forming the spacer may cause internal stress to the thin lid structure (i.e., causing the lid to bend).

FIG.24is a process flow diagram illustrating an example method for manufacturing a transdermal sampling and analysis device according to an alternative embodiment. In particular, method2400may create a configuration in which channel support structures are formed on the base of the device, yet still ensuring uniform distribution of the analyte sensing reagent in the reservoir. Method2400may begin with the same first step as in step1902of method1900. In step2402, a first layer of conductive material may be patterned to form the disruptor, interconnects, and at least a first electrode (e.g., the counter electrode, or counter and reference electrodes). In step2404, a photoresist layer may be applied to the base substrate over the at least first electrode, which may be patterned to form channel support structures, step2406. In step2408, a layer of adhesive material may be applied to only the top surfaces of the spacer channel support structures. In an embodiment, the layer of adhesive material may be applied using a technique similar to method2050, discussed above with respect toFIG.20B.

In step2410, a second layer of conductive material may be deposited on a lid substrate. In step2412, the second layer of conductive material may be patterned to form a second electrode (e.g., the working electrode) on the lid substrate. In step2414, a layer of analyte sensing reagent may be applied to the second electrode. In step2416, the lid may be positioned on the device, attaching to the channel support structures on the base.

Separating the counter and working electrodes may enable the analyte sensing reagent to be applied to the lid surface in a thin, uniform coating. Additionally, separating the electrodes by forming one electrode on the lid may allow for configurations that produce stronger, and therefore more a more accurate and reliable electrodes. In one example, the additional space provided by separation may allow formation of larger electrodes. In another example, since the electrodes are not on the same plane, a larger exposure area over which the biological sample may flow may be available for each electrode.

FIG.25illustrates example components that may be formed as a result of method2400and that, when joined together, create a device2500. Device2500may include a base substrate2502and a first conductive material layer that is patterned to form components including at least a first electrode2504, corresponding to step2402. Device2500may also have a photoresist material applied to the base substrate2502, corresponding to step2404, which may be patterned to form channel support structures2506, corresponding to step2406. An adhesive material2508may be selectively applied to the top surfaces of channel support structures2506, corresponding to step2408. In an embodiment, the adhesive material may be applied using method2050discussed above with respect toFIG.20B.

In the lid structure, a lid substrate2510may have a second conductive material layer, corresponding to step2410, which may be patterned to form at least a second electrode2512, corresponding to step2412. A layer of the analyte sensing reagent2514may be applied to the at least second electrode2512, corresponding to step2414.

As discussed with respect toFIGS.24and25, forming a first electrode (e.g., counter electrode) and a spacer layer with channel support structures on the base of the device, and forming a second electrode (e.g., working electrode) on the lid of the device may enable a thin, uniform coating of the analyte sensing reagent to be applied to the reservoir, thereby avoiding buildup from non-uniform distribution in the channels, and may avoid causing internal stress (and therefore bend) to the relatively thin lid structure. However, another consideration that arises as a result of separating the counter and working electrodes onto different planes is the amount of area of each electrode that is exposed, particularly the electrode on the lid. In the embodiment illustrated inFIG.25, for example, by forming channel support structures2506of a spacer layer over the first (i.e., counter) electrode2504on the base of the device, the portion of the second (i.e., working) electrode2512that is exposed to the channel is defined and limited by the channel support structures2506of the spacer layer. However, similar to the first (i.e., counter) electrode2504, the surface area of the second (i.e., working) electrode2512in device2500may be limited by the channel support structures2506. That is, by applying the adhesive material2508to the top surfaces of the channel support structures2506, once the lid structure is set in place, a portion of the second electrode2512that is exposed to the channel may be defined and limited by the channel support structures2506of the spacer layer.

This effect of the spacer layer channel support structures on the working electrode of the device2500configuration is further illustrated inFIG.26. A device2600(not drawn to scale) may be formed using techniques similar to those discussed above with respect toFIGS.24and25. Representative components of the device2600may include a base structure2601that includes a spacer layer of channel support structures2602formed over a counter electrode2604, which are formed over a base substrate2606. An adhesive (not shown) may be applied to the top surface2603of the channel support structures2602. A lid structure2607of the device2600may have a working electrode2608patterned onto a lid substrate2610. A layer of analyte sensing reagent (not shown) may have been applied to the surface of the working electrode2608. The base structure and lid structure shown in device2600illustrate representative cross-section segments of a larger, three dimensional device2600, and are not meant to limit the device2600based on size or shape. Further, while the base structure2601is shown with two spacer layer channel support structures2602, they are representative of any of a plurality of sets of channel support structures that may be formed across a larger base structure.

As the lid structure2607is brought down into position over the channel support structures2602, the adhesive on the channel support structures2602may secure the lid structure2607by contacting the working electrode2608. In this manner, channels2612may be formed between exposed areas2614of the counter electrode2604and exposed areas2616of the working electrode2608. However, device2600shows that such exposed areas on both electrodes are defined by the channel support structures2602. That is, the direct contact by the top surface2603of the spacer layer channel support structures2602may “block” a corresponding contact area2618of the surface of the working electrode2608. Moreover, if any of the adhesive material used to secure the working electrode2608to the channel support structures2602in device2600is pushed out (e.g., extruded) once the lid2607is secured in place, additional surface regions of the working electrode2608may be effectively blocked from coming into contact with the fluid sample as well.

Therefore, in an alternative embodiment, an additional spacer layer may be applied atop the channel forming spacer layer (i.e., channel support structures). In the various embodiments, the second spacer layer may be recessed back from the channel support structures in order to provide lift space between the channel support structures and a substantial portion of the working electrode surface.

While not limited to particular dimensions, in some embodiments the second spacer layer may be approximately the same thickness as the channel forming spacer layer. In an embodiment, the total thickness of the channel forming spacer layer and second spacer layer may be approximately the same as that of the single channel forming spacer layer, such as that of channel support structures2506,2602inFIGS.25and26respectively. In this manner, the depth of the sensing channels (i.e., vertical space between the counter and working electrodes) may remain the same to avoid requiring a greater amount of fluid to fill.

FIG.27is a process flow diagram illustrating an example method for manufacturing a transdermal sampling and analysis device according to this alternative embodiment. In particular, method2700may create a configuration in which a channel forming spacer layer is formed on the base of the device, over which a second, recessed spacer layer is formed to prevent the channel supports from directly contacting (and blocking) portions of the working electrode. Method2700may begin with the same first steps as in steps1902and2402of method2400. In step2702, a photoresist layer may be applied to the base substrate over the at least first electrode (e.g., the counter electrode). In various embodiments, the photoresist layer may be around half of the thickness of the photoresist layer applied in step2402of method2400. In step2704, the photoresist layer may be patterned to form channel support structures of a channel forming spacer layer. In step2706, a second spacer layer material may be applied over the channel forming spacer layer. In various embodiments, the second spacer layer material may be approximately the same thickness as that of the photoresist layer applied to the base substrate in step2702. In one embodiment, the second spacer layer material may be a double sided adhesive that has been pre-cut to be recessed from the channel support structures, thereby removing the need to pattern the material and to apply a separate adhesive layer. Alternatively, the second spacer layer material may be another photoresist layer, similar to the photoresist layer applied over the counter electrode in step2702. In this case, the photoresist layer may be patterned in optional step2708to form the second spacer layer that is recessed from the channel forming spacer layer, and a layer of adhesive material may be applied to the top surface of the second spacer layer in optional step2710. In an embodiment, the layer of adhesive material may be applied using a technique similar to method2050, discussed above with respect toFIG.20B. Formation of the lid structure in method2700may involve the same steps2410-2414as in method2400, discussed above with respect toFIG.24. In step2712, the lid may be positioned on the device, attaching to the recessed second spacer layer that has been formed over the channel forming spacer layer.

FIGS.28A and28Billustrate different views of example components that may be formed as a result of method2700and that, when joined together, create a device2800.FIG.28Ashows a three-dimensional cross-section of a base structure of the device2800. In device2800a first conductive material layer may be applied to a base substrate (not shown), and patterned to form components including at least a counter electrode2802, corresponding to step2402. Device2800may also have a photoresist material applied over the counter electrode2802, corresponding to step2702, which may be patterned to form channel support structures2804in a channel forming spacer layer, corresponding to step2704.

A second spacer layer material may be applied over the channel forming spacer layer to form a recessed second spacer layer2806, corresponding to step2706and, depending on the particular second spacer layer material, to optional step2708. The degree to which the second spacer layer2806may be recessed back from the edge of the channel support structures2804in the channel forming spacer layer is shown by arrow2808. The distance of arrow2808may be variable according to different embodiments. Also depending on the type of material used to create the second spacer layer2806, an adhesive material may be selectively applied to the top surface2810of the second spacer layer2806, corresponding to optional step2710. For example, the second spacer layer material may be a double sided adhesive, thereby making an additional adhesive layer unnecessary. In various embodiments, the second spacer layer2806as well as the channel forming spacer layer may each be around 10-20 μm thick.

FIG.28Billustrates a lid structure of device2800as well as the base structure2801, and effect of the recessed second spacer layer in device2800compared to device2600discussed above with respect toFIG.26. A lid structure2807may have a lid substrate2812to which a second conductive material layer may be applied, corresponding to step2410. The second conductive material layer may be patterned to form a working electrode2814, corresponding to step2412. A layer of the analyte sensing reagent (not shown) may be applied to the surface of the working electrode2814, corresponding to step2414.

As shown by the base structure2801of device2800, while the exposed areas2614on the counter electrode2802are still defined by channel support structures2804, similar to device2600, such channel support structures2804do not limit the exposed areas of the working electrode2814. Rather, the recessed second spacer layer2806serves to raise the working electrode2814off of the channel support structures2804, thereby providing an exposed area2816on the working electrode that is much larger than exposed area2616of device2600. For example, in comparison to the direct contact between the top surface2603of the channel support structures and the working electrode in contact area2618of device2600, the only direct contact to the working electrode2814of device2800is by the top surface2810of the recessed spacer layer2806. As a result, device2800may have a smaller corresponding contact area2818on the working electrode2814. The larger exposed areas of the2816of the working electrode may provide a stronger signal and/or allow for use of a smaller working electrode to produce the same level of result.

Glucose oxidase (GOD), an enzyme prototype, may be absorbed electrochemically onto a polypyrrole (PPy) layer using a potentiostat together with an electrolyte solution consisting of 0.1 M, each, of PPY and KCl at 0.8 V for 2 minutes. 0.1 M Ferricyanide and 8001 units/ml of GOD (18 μl GOD and 48 μl K2FeCN6in 10 ml phosphate buffer solution) may be further added in the electrolyte solution for the deposition of GOD. Selective deposition of PPy+GOD may be then done on one of the exposed electrodes of the transdermal sampling and analysis device200. Chronoamperometric dose responses may be recorded and the results reveal that the sensor has a good linearity from 0 to 10 mM glucose with the sensitivity of 2.9 mA/mM. For the lactate sensor chips, the same process may be used except lactate oxidase was substituted for the GOD.

In an embodiment the transdermal sampling and analysis device200may be used to deliver substances into the capillary-like channels of the skin100. A substance may be loaded on the transdermal sampling and analysis device200, preferably in an encapsulation. Heat applied to the skin creates capillary-like channels in the stratum corneum. The substance may then be delivered transdermally into the body through the capillary-like opening in the skin. Positive pressure may be required to deliver the substance into the body as interstitial fluid exits the body.

The transdermal sampling and analysis device200of the various embodiments may be packaged in a sealed and sterile container without any contaminants. The seal may be broken to access one transdermal sampling and analysis device200using an applicator. Once the transdermal sampling and analysis device200is taken out of the sealed packaging, it may be used as described above. The transdermal sampling and analysis device of the various embodiments may be disposable or reusable.

The transdermal sampling and analysis device200of the various embodiments may have a variety of different uses including monitoring for viability and functionality of organs and tissues prepared and stored for surgical implantations; monitoring entire chemical panels for individuals, patients, or populations at risk; monitoring for critical care, shock, trauma and resuscitation; monitoring for chronic critical diseases; monitoring for early detection of diseases; monitoring for response to therapeutic treatments; and gene therapy.

The transdermal sampling and analysis device200of the various embodiments may also be used to analyze biological samples that have already been collected from samples such as food, water, air, whole blood, urine, saliva, chemical reactions or cultures.

The transdermal sampling and analysis device200of the various embodiments may be applied to the skin100of a subject using an applicator device. The applicator device may be configured to take different shapes and designs. In an exemplary embodiment, as illustrated inFIG.29A, the applicator device2960may be configured to have a cylindrical design with a head2962and a body2964. The head2962may be configured to engage an embodiment transdermal sampling and analysis device200and couple it to both a voltage source as well as to a sensing unit and display. A voltage source2978may be provided in the form of a battery or an alternating current adapted to accept an alternating current voltage signal. For example, a user may load the applicator device2960by picking-up a transdermal sampling and analysis device200for measuring body parameters and unloading by discarding the transdermal sampling and analysis device200when the required parameters may be obtained or when the transdermal sampling and analysis device200is no longer functional.

The body2964may include a processor2966coupled to a display monitor2968for displaying data to the user, a memory2970for storing processed data received from the transdermal sampling and analysis device200, and a transceiver2972for transmitting information from the applicator device2960or for receiving data. The processor2966may also include a digital signal processor which modifies the voltage source to produce a voltage signal having the appropriate duty cycle before application across the terminals of the embodiment disruptor. The body2964may also include an antenna2974, used to transmit and receive radio frequency signals, coupled to the transceiver2972. Alternatively, the applicator2960may include a data communication port2976such as USB or FireWire® which enables the applicator to transfer data over a communication cable to another device.

The processor2966may be configured by software to receive signals from the transdermal sampling and analysis device200and convert the signals to user ascertainable information. The user ascertainable information may be displayed on the display monitor2968. The processed data may be stored in memory2970. For example, if the transdermal sampling and analysis device200is configured to determine blood glucose levels, the applicator device2960may be configured to receive electrical signals generated by the transdermal sampling and analysis device200and convert the signals, using the processor2966, to user ascertainable information such as a numeric glucose level. The information may be stored in the memory2970. The numeric glucose level may be displayed on the display monitor2968. In this example, the blood glucose levels are measured to be “97” which is displayed in the display monitor2968.

The body2964may further include a transceiver2972coupled to the processor2966and an antenna2974to wirelessly transmit data to other devices or receive data. For example, the applicator device2960may transmit data obtained from a subject to a remote server. The applicator device2960may store the processed data in memory2970and transmit the data either continuously or intermittently to other devices.

FIG.29Billustrates a component block diagram for a transdermal sampling and analysis device system2980according to an embodiment. Once the data is collected by the transdermal sampling and analysis device and the applicator device2960, the data may be transmitted to the other components of the transdermal sampling and analysis device system2980for storage/analysis. For example, the data may be transmitted to an external transceiver2982which in turn may relay the data to a remote server2984for storage and/or analysis. The remote server2984may receive and store the transmitted information as part of the subject's records, such as medical records; or the server2984may be configured to receive the data for conducting research. In an alternative example, the server2984may include a built-in transceiver using which it may receive and/or transmit data wirelessly.

In a further embodiment, data received and stored by an applicator device2960may be transmitted to a remote computing device2986. The remote computing device2986may receive and store the transmitted data and display it on the monitor and/or perform further analysis of the data.

The remote devices (i.e., server2984and computing device2986) may communicate with other remote devices, such as server2990by using different communication means such as the Internet2988. For example, information received from the transdermal sampling and analysis device200may be transmitted to the remote devices using the applicator device2960. The remote devices may in turn transmit data to other devices via the Internet2988for storage or further analysis.

In an exemplary embodiment, as illustrated inFIG.29C, several transdermal sampling and analysis devices200may be arranged in a sterile kit2902. In this example, the transdermal sampling and analysis devices200may be arranged next to one another, each in a sterile compartment, in the kit. The applicator device2960may be configured to load one transdermal sampling and analysis device200at a time from different compartments of the kit2902to ensure that the additional transdermal sampling and analysis devices200remain sterile and ready for future use.

In a further embodiment, as illustrated inFIG.29D, the transdermal sampling and analysis devices200may be arranged in a sterile stack in a kit2904that may be cylindrical in shape. In this example, the applicator device2960may be configured to load by contacting the applicator device2960to the transdermal sampling and analysis device200which may be at the top of the sterile stack in the kit2904. The transdermal sampling and analysis devices200may be stacked directly on top of one another in the kit2904or may be separated by a separator material. As transdermal sampling and analysis devices200may be used to obtain a biological sample, the transdermal sampling and analysis device200may be ejected from the applicator device and disposed above.

FIG.29Eillustrates a further embodiment method for loading and unloading transdermal sampling and analysis devices200on the applicator device2960. In this embodiment, a kit cartridge2906including several transdermal sampling and analysis devices200stacked in a vertical configuration may be loaded on to the applicator device2960. The applicator device2960may have a lever2908which may allow the user to load or unload transdermal sampling and analysis devices200onto the tip2912of the applicator device2960. For example, once the kit cartridge2906is may be loaded onto the applicator device2960, the user may push down the lever2908in the direction of the arrow2910to load the tip2912of the applicator device2960with a transdermal sampling and analysis device200. Once the transdermal sampling and analysis device200is used up, it may be unloaded by simply pushing it out of the applicator device2960by pushing the lever2908in the direction of the arrow2910and discarding it. This process may continue until the last transdermal sampling and analysis device200is used. Once the last transdermal sampling and analysis device200is used, the kit cartridge2906may be changed with one that includes new transdermal sampling and analysis devices200.

In an embodiment illustrated inFIG.30, after loading an applicator device2960with a transdermal sampling and analysis device200from a kit2902,2904,2906the applicator device2960may apply the transdermal sampling and analysis device200to the skin100of a subject. The transdermal sampling and analysis device200may be applied to the skin100by moving the applicator device2960in the direction of the arrow3004towards the skin100. Once in contact with the skin100, the transdermal sampling and analysis device200may draw interstitial fluid and generate signals which may be transmitted to a processor.

A number of the embodiments described above may be implemented with any of a variety of remote server devices, such as the server3100illustrated inFIG.31. Such a server3100typically includes a processor3101coupled to volatile memory3102and a large capacity nonvolatile memory, such as a disk drive3103. The server3100may also include a floppy disc drive and/or a compact disc (CD) drive3106coupled to the processor3101. The server3100may also include a number of connector ports3104coupled to the processor3101for establishing data connections with network circuits3105.

The embodiments transdermal sampling and analysis device data described above may also be transmitted or coupled to any of a variety of computers, such as a personal computer3200illustrated inFIG.32, for further monitoring, storage or manipulation. Such a personal computer3200typically includes a processor3201coupled to volatile memory3202and a large capacity nonvolatile memory, such as a disk drive3203. The computer3200may also include a floppy disc drive and/or a compact disc (CD) drive3206coupled to the processor3201. Typically the computer3200will also include a pointing device such as a mouse3209, a user input device such as a keyboard3208and a display3207. The computer3200may also include a number of network connection circuits3204, such as a USB or FireWire®, coupled to the processor3201for establishing data connections to the applicator2960. In a notebook configuration, the computer housing includes the pointing device3209, keyboard3208and the display3207as is well known in the computer arts.

The processor2966,3101,3201may be any programmable microprocessor, microcomputer or multiple processor chip or chips that can be configured by software instructions (applications) to perform a variety of functions, including the functions of the various embodiments described herein. In some mobile devices, multiple processors2966,3101,3201may be provided, such as one processor dedicated to wireless communication functions and one processor dedicated to running other applications. Typically, software applications may be stored in the internal memory2970,3102,3202before they are accessed and loaded into the processor2966,3101,3201. In some mobile devices, the processor2966,3101,3201may include internal memory sufficient to store the application software instructions. The internal memory of the processor may include a secure memory (not shown) which is not directly accessible by users or applications and that may be capable of recording MDINs and SIM IDs as described in the various embodiments. As part of the processor, such a secure memory may not be replaced or accessed without damaging or replacing the processor. In some devices200,3100,3200, additional memory chips (e.g., a Secure Data (SD) card) may be plugged into the device and coupled to the processor2966,3101,3201. In many devices, the internal memory2970,3102,3202may be a volatile or nonvolatile memory, such as flash memory, or a mixture of both. For the purposes of this description, a general reference to memory refers to all memory accessible by the processor2966,3101,3201, including internal memory2970,3102,3202, removable memory plugged into the device, and memory within the processor2966,3101,3201itself, including the secure memory.

The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality may be implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some steps or methods may be performed by circuitry that is specific to a given function.

In one or more exemplary aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium. The steps of a method or algorithm disclosed herein may be embodied in a processor-executable software module executed which may reside on a tangible non-transitory computer-readable medium or processor-readable medium. Non-transitory computer-readable and processor-readable media may be any available media that may be accessed by a computer or processor. By way of example, and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used store desired program code in the form of instructions or data structures and that may be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and/or instructions on a non-transitory processor-readable medium and/or computer-readable medium, which may be incorporated into a computer program product.

The preceding description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

While the invention has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various alterations, modifications and other changes may be made without departing from the scope of the embodiments described herein. It is therefore intended that all such modifications, alterations and other changes be encompassed by the claims. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular.