Abstract:
An agitated flow cell had a micro/miniature vibrator device such as pager motor to agitate the flow cell and its associated sensor to bring fresh analyte to the sensor surface without the need for microfluidic channels, pumps or valves. The agitated flow cell improves the confidence measure of a given sample reading by directing the flow of sample to the sensor/sample interface in a substantially shorter period of time than that required by flow cells that rely on diffusion of analyte molecules through the liquid depletion region in order to bring the sample reliably in contact with the sensor&#39;s biosensing film.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates generally to analytical testing instrumentation, and more particularly to an agitated well or fluid chamber having a micro/miniature vibrator device such as a pager motor to agitate the well/fluid chamber, its contents and its associated sensor to enable mixing of dehydrated reagents and bring analyte to the sensor surface without the need for microfluidic channels, pumps or valves.  
         [0003]     2. Description of the Prior Art  
         [0004]     Most analytical measurements have historically been made in a central laboratory, on sophisticated equipment by highly trained personnel. Modern trends have demonstrated a need for a more de-centralized testing methodology where analytical measurements are actually made at the sample collection site, since this is generally the place where the results are needed.  
         [0005]     One miniaturized sensor platform with integrated channels for controlling the flow of sample over a sensor/sample interface that is available from Texas Instruments Incorporated of Dallas, Tex., provides one low-cost, portable electronic biosensor platform that accommodates such de-centralized testing. This sensor platform incorporates a miniature surface plasmon resonance (SPR) sensor. By measuring the light reflection properties of a gold surface as targeted molecules bind to it, real-time detection of these targeted molecules is possible. This sensor platform is described in detail in U.S. Pat. No. 6,183,696, entitled Optically based miniaturized sensor with integrated fluidics, issued on Feb. 6, 2001 to Elkind et al., assigned to the assignee of the present invention, and is incorporated in its entirety by reference herein.  
         [0006]     While miniaturized sensors are becoming available for use in a wide range of field applications, their effectiveness as an analytical tool is largely determined by the properties of the sample analyte of interest, including molecular weight, concentration, sample matrix, isoelectric point, solubility and stability. Fluctuations in sample concentration, temperature and other environmental conditions affect the reactive properties of film deposit in the presence of the sample. Ideally, a controlled amount of the sample with uniform properties is brought in contact with the sensor/sample interface during the sampling process. With larger systems, a flow cell may be used to control the flow rate of the sample.  
         [0007]     In general, analyte molecules that are dissolved or suspended within the liquid must make contact with the sensing surface of the biosensor in order to provide accurate measurements of any analyte. Usually, this process requires that the analyte molecules diffuse to the surface of the biosensor interface making contact with the liquid. This can be a very slow process, depending on the size of the analyte particles. Smaller molecules move faster through the liquid, while protein molecules, for example, move more slowly. Molecules having beads attached for amplification, or microorganisms such as  E. coli  are comparatively large, and therefore move more slowly through the liquid by a process known as shear-enhanced diffusivity. This slow transport process has been addressed in the prior art by use of high flow rates to accelerate the mass transport flux of analyte to the biosensor surface, rather than relying simply on the diffusion process, alone. In addition, recirculation of the sample can accommodate testing of small sample volumes. Although such flow systems have improved the sensitivity and reliability of biosensor measurements, these flow systems have been problematic. This is because these known flow systems use tubular flow structures that are characterized by a center region where liquid is flowing and an outer (edge, or depletion) region that can be several microns thick where there is no flow. Since this depletion region is static (has no laminar flow), the diffusion process described above must still be relied upon in order to ensure that reagents pass through the depletion region to make contact with the sensing surface of the biosensor. This diffusion process can be undesirably time consuming. In addition, these peripheral technologies add a great deal of bulk and cost to the instrument.  
         [0008]     In view of the foregoing, a need exists for an inexpensive or ultra-low-cost analytical instrument that employs a compartmentalized fluid chamber with an associated biosensor that is both accurate and user-friendly (i.e. easy to use) but that does not rely on complex peripheral technologies. The analytical instrument enables sample/reagent mixing and high mass transport of analyte to the sensor surface within an agitated compartmentalized fluid chamber that incorporates features necessary for temperature compensated, multichannel detection, including memory to hold specific test protocols.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention is directed to an agitated well or fluid chamber having a micro/miniature vibrator device such as pager motor to agitate the well/fluid chamber and its associated sensor to enhance mass transport of analyte to the sensor surface without the need for microfluidic channels, pumps or valves. The agitated well/fluid chamber improves the sensitivity and reduces sampling time by accelerating the mass transport flux of analyte to the sensor surface. Flow cells that rely on convective and diffusional mass transport of analyte suffer from poor sensitivity and extended sampling times.  
         [0010]     According to one aspect of the invention, an agitated well/fluid chamber is implemented to eliminate the need for pumps and other peripheral technology thereby being inexpensive and easy to use.  
         [0011]     According to another aspect of the invention, an agitated well/fluid chamber is implemented to enable rapid mass transport of analyte to maximize sensitivity and reduce sample time.  
         [0012]     According to yet another aspect of the invention, an agitated well/fluid chamber is implemented to allow analytical measurements to be made at the site where samples are collected by exploiting simplified assay methodologies.  
         [0013]     According to still another aspect of the invention, an agitated well/fluid chamber is implemented without use of microfluidic channels, pumps or valves to ensure the instrument is fully portable and easily held in hand so as to allow analytical measurements to be made at the site where liquid samples are collected.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Other aspects, features and advantages of the present invention will be readily appreciated, as the invention becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing figures wherein:  
         [0015]      FIG. 1  illustrates a prior art SPR miniaturized sensor package;  
         [0016]      FIG. 2  illustrates a perspective view of a prior art flow channel sensor; and  
         [0017]      FIG. 3  is a diagram illustrating a pocket analyzer having an agitated well/fluid chamber and associated biosensor platform that brings fresh analyte to a biosensor surface without the need for microfluidic channels, pumps or valves, according to one embodiment of the present invention. 
     
    
       [0018]     While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]      FIG. 1  illustrates a prior art integrally formed optically based Surface Plasmon Resonance (SPR) sensor  50  in close proximity to a sample  25  analyte of interest that is a liquid. The sample  25  may be any liquid (bio)chemical substance for which an indicator interaction is known and which can be formed into thin biosensing layer  61 . The film is deposited on a surface  63  of the sensor and exposed to the sample  25  during analysis. Various ways of bringing the sample  25  in contact with the surface  63  may be employed such as by dipping, dropping or by using a flow cell.  
         [0020]     As shown, a substrate  52  forms a device platform to which a light transmissive housing  56  is coupled. The housing material can be plastic, glass or other similar optic coupling substance. A light source is preferably located above or within the substrate  52  and has an aperture  58  there over allowing light to pass. In one embodiment, the light source is a single high intensity light emitting diode. A polarizer  62  is located near the aperture  58  to polarize passing light which, in turn, continues through housing  56  and strikes a SPR layer  64  which is preferably formed on an exterior surface of the housing  56 .  
         [0021]     The SPR layer  64  may be deposited directly or placed on a glass slide or the like. This configuration achieves an optical surface phenomenon that can be observed when the polarized light is totally internally reflected from the interface between the layer  64  and the sample of interest. This principle is well understood by those skilled in the art and discussed by Ralph C. Jorgensen, Chuck Jung, Sinclair S. Yee, and Lloyd W. Burgess, in their article entitled  Multi - wavelength surface plasmon resonance as an optical sensor for characterizing the complex refractive indices of chemical samples , Sensors and Actuators B, 13-14, pp. 721-722, 1993.  
         [0022]     Analysis is permitted by using a mirrored surface  66  which directs the reflected light onto a detector array  68 . The detector array  68 , in turn, senses illumination intensity of the reflected light rays. For optical radiation, a suitable photodetector array  68  is the TSL213, TSL401 and TSL1401, with a linear array of resolution n times 1, consisting of n discrete photo sensing areas, or pixels. In the detector array  68 , light energy striking a pixel generates electron-hole pairs in the region under the pixel. The field generated by the bias on the pixel causes the electrons to collect in the element while the holes are swept into the substrate.  
         [0023]     Each sensing area in the photodetector array  68  thereby produces a signal on an output with a voltage that is proportional to the intensity of the radiation striking the photodetector  68 . This intensity and its corresponding voltage are at their maxima in the total internal reflection region. Electrical connections  54  are coupled to one end of the substrate  52  and provide signal pathways from the detector  68  output to the external world.  
         [0024]     As stated herein before, the sensing approach illustrated in  FIG. 1 , wherein the sample  25  is brought in contact  30  with the SPR layer  64  for analysis, may lead to unreliable results since analysis is influenced primarily by the properties of the sample  25 . The sample concentration, for example, may vary throughout the sample mass or with time. Likewise, movement of the sensor  50  during analysis changes the orientation of layer  64  with respect to the sample  25 . This is especially true in portable hand held applications where the sensor  50  is brought to the sample.  
         [0025]      FIG. 2  illustrates a perspective view of a prior art flow channel sensor  100  that addresses many of the problems associated with the approach discussed above with reference to  FIG. 1 . Sensor  100  is similar to sensor  50  in most respects, but differs primarily by the integrally formed flow channels  105  and  110  inside the housing structure  56 . As shown, the channels  105 ,  110  extend inside the housing  56  from a first surface  120  to a second surface  125  and pierce the platform  52  to the outside. This permits the sample to flow inside the sensor housing  56  through channel  105  and enter the cavity  115  via the opening  107 . The sample flows over the metal film  117  which is deposited by known means on the bottom surface of the cavity  115 . A more detailed discussion of sensor  100  including its principles of operation is set forth in the &#39;696 patent referenced herein before, and so will not be discussed in further detail herein to preserve clarity and brevity.  
         [0026]     Looking now at  FIG. 3 , a perspective diagram illustrates a pocket analyzer  150  having an agitated well/fluid chamber  155  and a micro/miniature vibrator device  175  such as pager motor to agitate the well/fluid chamber  155  and its associated biosensor  100  to enhance both mixing and mass transport of the analyte  25  to the sensor  100  surface without the need for microfluidic channels, pumps or valves. A sample dispenser may be used to place the particular sample analyte  25  of interest into the well/fluid chamber  155  of the analyzer  150 . Other methods and means of introducing the sample analyte  25  to the analyzer  150  are also contemplated.  
         [0027]     In one embodiment, the fluid chamber  155  is open at end  160 . This allows the sample analyte  25  to be gravity guided to the sensor  100 . Alternatively, a pressure or vacuum means can be provided inside the instrument  150  to direct the sample to the sensor  100 .  
         [0028]     As shown, analyzer  150  has a base  165  which houses a sensor socket  162  inside. In some contemplated applications, the sensor  100  is housed inside the base  165 .  
         [0029]     In one contemplated use of the analyzer  150 , the sensor  100  is plugged into the sensor socket  162  prior to use. The sample analyte  25  is then introduced into the well/fluid chamber  155  and analysis of the sample  25  is then performed according to well-known methods. Following analysis, the sensor  100  can be removed, replaced or optionally disposed of.  
         [0030]     The analyzer  150  can also be seen to have a miniature electromechanical vibration device  175  attached to the sensor socket  162  that can be, for example, a pager motor (commonly used in cellular telephones and pocket pagers), to rigorously vibrate the well/fluid chamber  155  and/or the sensor  100  during the sample analysis process. The present invention is not so limited however, and it will be appreciated that other vibration means such as, for example, a piezo-electric crystal can just as easily be used to implement the requisite agitation. This agitation of the well/fluid chamber  155  and/or the sensor  100  provides a very simple and cost effective way to accelerate the reaction or binding process taking place in the sample  25  such that the reaction or binding process is no longer dependent upon convective and diffusional transport to deliver. The vibration device  175 , in the embodiment shown, is attached to the sensor socket  162  inside the analyzer  150  such that when the vibration device  175  is energized, the socket will then shake the attached well/fluid chamber  155  and/or its associated sensor  100  depending upon the mechanical arrangement of the well/fluid chamber  155  and the sensor  100 . The well/fluid chamber  155  and sensor socket  162  can be formulated as a unitary device such that the vibration device  175  will shake both the well/fluid chamber  155  and the sensor  100  when activated. The well/fluid chamber  155  can also be distinct from the sensor socket  162  such that only the sensor  100  will shake when the vibration device  175  is activated. More than one vibration device  175  can also be employed such that a well/fluid chamber  155  that is physically separated from the sensor  100  can be shaken independently.  
         [0031]     With continued reference to  FIG. 3 , the well/fluid chamber  155  can be seen to have a hinged cap  180  that can be opened to allow filling the well/fluid chamber  155  with the sample solution  25  of interest that contains a suspended analyte. The hinged cap  180  may optionally have secondary analytes  182  embedded in storage compartments such that when the hinged cap  180  is closed to seal the sample solution  25 , the secondary analytes  182  will be released into the sample solution  25  during the agitation process. Such secondary analytes  182  can be, for example, reagents such as biomolecular reagents that are useful to amplify, sensitize and help specify the analyte(s) during the analysis process. The present invention is not so limited however, and it shall be understood that other means for selectively sealing the fluid chamber  155  can also be effectively employed. The cap  180 , for example, could instead be a septum with a rubber cap that can be temporarily punctured with a needle so that sample(s) can be injected; then upon removing the needle from the septum, the septum self-seals. If the fluid chamber  155  is evacuated, that vacuum could be used to draw liquid sample(s) into the fluid chamber  55  through the septum. Further, it is contemplated that one or more extra reagents may just as well be hid within the fluid chamber  155  such as, for example, embedding the reagent(s) within one or more of the chamber walls, or putting one or more solid samples in the fluid chamber  155 .  
         [0032]     The analyzer  150  further includes the requisite data processing device such as, for example, a DSP or microprocessor, appropriate input/output devices such as A/Ds and D/As, and data storage devices such as RAM to accommodate data storage and ROM to accommodate storage of the algorithmic software that is employed for hardware control and to perform the desired sample analysis. The flow of the sample solution  25  and other instrument functions may be controlled with user input keys  185  that can be used to implement modifications to the algorithmic software.  FIG. 3  depicts a computer system  200  that is internal to the analyzer  150  and includes a data processing device (CPU/DSP), a data input device (A/D) in communication with the data processing device, an algorithmic software directing the data processing device, and a data storage unit (RAM Databank), wherein discrete analyte data associated with the liquid sample  25  is stored and supplied to the data processing device such that the data processing device, directed by the algorithmic software, will automatically determine bioanalytical data associated with the liquid sample, wherein predetermined parameters associated with the bioanalytical data are determined via the user input keys  185 . It is also contemplated the analyzer  150  is capable of wireless connectivity/data transmission using conventional data communication techniques well-known in the art. The analyzer depicted in  FIG. 3 , for example, can be seen to have an RF receiver  202  and RF transmitter  204 , both in communication with the computer system  200 . An antenna  206  is used to both receive and transmit the desired information.  
         [0033]     It can be appreciated the sensor  100  surface  102  can be covered with a bio-film, customized for essentially any molecule for which detection is desired. This bio-film provides the analytical specificity. There are a wide variety of bio-film attachment methodologies to choose from and most preferably the sensor  100  is compatible with all assay formats, including direct binding, sandwich, competition, inhibition and displacement assays.  
         [0034]     In view of the above, it can be seen the present invention presents a significant advancement in the art of low-cost, portable electronic biosensor platform technology. Further, this invention has been described in considerable detail in order to provide those skilled in the biosensor art with the information needed to apply the novel principles and to construct and use such specialized components as are required. In view of the foregoing descriptions, it should be apparent that the present invention represents a significant departure from the prior art in construction and operation. However, while particular embodiments of the present invention have been described herein in detail, it is to be understood that various alterations, modifications and substitutions can be made therein without departing in any way from the spirit and scope of the present invention, as defined in the claims which follow.