Abstract:
The present invention relates generally to the field of chemical and biological sensors and in particular to micro electro-mechanical systems (MEMS) sensors for measuring fluid viscosity and detection of minute amounts of chemicals and biological agents in fluids. It is an object of the present invention to provide a sensor that will work in disposable cartridges with remote sensing that can measure dynamic changes of the functionalized cantilevers in liquid and gas environment.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of chemical and biological sensors and in particular to a micro electro-mechanical systems (MEMS) sensors for measuring fluid viscosity and detection of minute amounts of chemicals and biological agents in fluids. 
     BACKGROUND 
     Detecting small amounts of chemicals and substances in liquids have many applications in chemistry and biology. In medicine, for example, one can diagnose many diseases by detecting chemicals (sodium, nitrides, calcium, potassium, cardiac markers, etc.) and their concentrations in bodily fluids such as blood, urine, saliva etc. Detecting pathogens (Tuberculosis, Hepatitis, HIV viruses, etc.) in bodily fluids as well as in the environment is also area of active research and development. 
     Similarly measuring fluid viscosity has also great interest in industrial applications and medicine. The ability to gather data on viscosity gives manufacturer important information on how to design fluidic systems. Especially in microfluidic systems viscosity determines the pumpability of the fluids and pressure drops across the channels. For example, viscosity of inks is very crucial for inkjet printing systems. In automotive industry, it is necessary for lubricant manufacturers to know the viscosity of their lubricants developed for different parts of the car engine and hydraulic systems. 
     In medicine, blood viscosity and coagulation time measurements are used for the diagnosis of several diseases such as cardiovascular disorders, rheumatoid arthritis, and certain autoimmune diseases. Patients who use blood thinners need to monitor their blood viscosity and coagulation time continuously. 
     The sensor requirement for the above sensing areas can be addressed by vibrating mechanical structures. Especially microcantilevers find various applications based on advantages such as lower detection limits due to miniaturization, the ability of shape optimization of cantilevers, the ability to selectively place functionlized regions on the these cantilevers (also interchangeably called “microcantilevers”), and the possibility of working on large arrays which can be integrated with optics and electronics. 
     When these cantilevers are placed in liquid, the dynamics of the vibration (phase and amplitude) are influenced by the viscosity of the liquid and the mass accumulation on the cantilevers. By measuring the vibration phase and/or amplitude one can detect liquid viscosity and minute amounts of chemicals and substances that may exist in the liquid. Furthermore, the cantilevers can be set into oscillation using a feedback circuitry. In this case, frequency measurement can be used to monitor dynamic changes of the cantilever vibration. 
     To address the measurement needs for viscosity and mass, various methods have been proposed. Some of the disadvantages of these currently known types of sensors are; that they require electrical connections (also called electrical conductors) to couple the sensor to a detector, limited optical detection options, limitations to gas phase detection, sensors that use frail readout components (for example, Doppler vibrometry), readouts that can be affected by refractive index variations due to monitoring of the deflection, sensors with no immunity against environmental noise, and the inability to heat the cantilever/samples during sensing. Further, it is believed that current alternatives to parallel sensing are limited to laboratory use only. It is therefore desirable to have a fieldable, label-free demonstrator, which is missing due to the lack of various components including a suitable readout mechanism that can be utilized in an array setting, a package that would protect functionalized surfaces during shelf life, which usually requires handling of liquids, and an integrated approach that would allow disposal of certain components, whereas others remain for the next use (for example, disposable cartridges containing the MEMS sensor array). 
     One objective of this invention is to enable a MEMS sensor array having a sensor array that is miniaturized, highly selective, highly sensitive, parallel, label-free and/or portable. Such a sensor array will provide a valuable tool for point-of-care diagnostics, and chemical sensing with its capabilities of a single analyte or a multianalyte screening and data processing. In addition such a sensor can measure dynamic properties of bodily fluids such as viscosity, fluid damping and chemical changes of the liquid. It is a further objective of these sensor arrays to increase sensitivity and specificity to possibly increase the likelihood of early diagnosis as well as the suitability of treatment assistance, such as dosage advice. It is envisioned that this may lead to increased effectiveness of doctor-patient interaction and personalized guidance. It is believed that such systems that meet the demands of parallel, label-free, and highly selective sensing do not exist today as microsystem technologies and readout methods cannot meet expectations for various reasons including: robustness issues associated with functional surfaces and the lack of a truly integrated, array-compatible readout techniques. Alternatively, it is believed that microarray technologies can offer parallel and selective detection, but are not fieldable as they require expertise to run and maintain and require expensive infrastructure due to complex labeling and sensing methods. While many fieldable applications, such as pregnancy test kits or the glucose sensor exist, these applications are limited to one kind of species and lack parallel detection capability. 
     The sensor array platform is highly innovative and versatile and has inspired by the novel uses. For example, for the point-of-care diagnostics applications it is envisioned that a microsystem-based sensors or parallel sensor array (2 to 64 channels and more); can be used for various species for shifts in resonance frequency of an array of cantilevers will be monitored as an indication of mass accumulation. In this example, detection of frequency shifts will be carried out through a novel integrated optoelectronic chip. Sensitivity in the range of 0.1 to 1000 ng/ml with better than 25% reproducibility is aimed. In addition to resonance frequency, one can measure the phase difference between the drive signal and the micro-cantilever motion. Cantilevers can be functionalized with various chemicals and can be placed in different channels. The same fluid can be applied to the channels where the effect of the chemicals is measured on fluid viscosity by monitoring the phase difference between the excitation signal and mechanical vibration waveform of the cantilevers in the array. Typical sensitivity of 0.001 cps is possible to achieve using cantilevers. 
     Additionally, possible use of this invention include liquid phase detection of disease from body fluids (e.g., blood, serum, urine, or saliva), and a detector to detect pathogens that may exists in environmental water supplies. Additionally, it is believed that in an aqueous medium, the invention will allow parallel, fast, real-time monitoring of a large number of analytes (e.g., proteins, pathogens, and DNA strands) without any need for labeling, and, therefore, be ideal for the targets screening in drug discovery process, or as a promising alternative to current DNA and protein micro array chips. Using such a label-free device may decrease the number of preparation stages and shorten diagnosis time. It is proposed that one can investigate DNA sequences, successful results will be the positive detection of various mutations in human DNA (e.g., sickle cell anemia, -thallesemia) in parallel. 
     This invention demonstrates a highly parallel detection of changes in the dynamics of a cantilever array. The proposed sensor can be used for label-free detection of (bio/chem) agents as well as liquid viscosity measurement in a robust, miniaturized package using multiple disciplines including integrated photonics, VLSI, and Micro/Nano system technologies to develop a versatile sensor array with breakthrough performance. 
     Each sensor is typically located on a MEMS sensor array operates by monitoring the resonant frequency, amplitude and/or phase of the vibrating mechanical structures (also called cantilevers or microcantilevers). Output of a sensor is the change in resonant frequency, amplitude and/or phase in response to accumulated mass on the cantilever due to a specific binding event or changes in the viscosity of the liquid. The array of cantilevers may be actuated by an actuating means, for example, electromagnetic force means; piezoelectric force; electric force; electrostatic force means and combinations thereof. The most preferred actuating means is a single electro-coil that carries a superposed drive current waveform. Preferably optical feedback from a mechanism to sense light coupled with each sensor is used for detection of specific binding events and also for closed-loop control of the cantilevers at resonance. More preferably, damping can be tuned by closed-loop control electronics allowing sharp resonance peaks (high-Q) even in liquid media. In a preferred embodiment, frequency resolution is inherently higher compared to other read-out techniques such as the piezoresistive or capacitive methods. 
     Preferably, the MEMS chip contains the functionalization layer on magnetic structural layer (for example, Nickel). More preferably, the location on the cantilever of the functionalized layer can be chosen to maximize the resonant frequency shift per added unit mass or the phase shift. In a preferred embodiment, the novel structure of the cantilevers includes a diffraction grating in the form of simple slits and/or heating elements. The light reflected from the diffraction grating can be collected by optical fibers. In another arrangement, diffraction gratings can be omitted and flat surface of the cantilevers can be used to reflect the light. In this case, light can be still collected using optical fibers where the cantilever vibration determines the amount of light coupling to the optical fibers and hence, the photodetector output that the fibers are coupled represents the cantilever vibration amplitude and phase. The MEMS sensor array (also called a MEMS chip) is preferably envisioned to be disposable and replaceable in future products; for example, as a disposable cartridge containing a MEMS sensor array to be coupled with a detector apparatus containing an actuating means (also sometimes called an actuator). This preferred embodiment would leave the actuator and electronics layers intact for reuse. Preferably, the MEMS chip is a passive component with no electronic link (also called an electrical conductor) to the detector apparatus. In this preferred embodiment this will facilitate work in fluidic environments, since less isolation, coupling, and stiction issues need to be considered. Furthermore, the preferred embodiment includes the integration of electronics and optics coupled with a passive component to provide ease and flexibility of use compared to a direct integration of the MEMS layer with IC detection apparatus. Finally in a preferred embodiment, magnetic actuation can be carried out remotely through an external electromagnetic coil on the MEMS chip. It is believed that sensitivity levels achieved in mass measurements will directly be reflected by detection sensitivity of the analytes of interest. Additionally, the type of surface functionalization utilized on the cantilever surfaces will determine the field of application, e.g., Human Kappa Opioid receptor (HKOR) is utilized for the detection of narcotics. In a preferred embodiment it is believed that a minimum mass detection limit of 500 femtograms or less may be achieved through discrete optics, electronics, and an electromagnet. Also the same system can achieve a low as 0.001 cps viscosity measurement sensitivity. Preferably, integration of discrete components and further miniaturization will substantially improve the minimum detection limit, sensitivity, parallelism, and robustness of the device and will meet the challenges of label-free and parallel detection in a portable device. 
     SUMMARY 
     It is an object of the present invention to provide a sensor that will work in disposable cartridges with remote sensing that can measure dynamic changes of the functionalized cantilevers in liquid and gas environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a preferred embodiment of a system concept for the reader, cartridge and sensor with optical readout illustrating operation for liquid-phase sensing. 
         FIG. 2  is a diagram of one preferred embodiment of microcantilever array placed in a system of microfluidic channels including optical light collectors, actuation means and control electronics. 
         FIG. 3  is a diagrammatic view of one preferred embodiment of the invention including disposable cartridge. 
         FIG. 4  is a diagrammatic top view of one preferred embodiment of the invention including MEMS sensors placed in microfluidic channels. 
         FIG. 5  is a diagrammatic to view of one preferred embodiment of the invention where MEMS microcantilevers have diffraction gratings at one end of the microcantilevers that are placed in microfluidic channels. 
         FIG. 6  is a diagrammatic view of one preferred embodiment of the cantilever where the tip of the cantilever is selectively functionalized with chemicals. 
         FIG. 7  is a diagrammatic view of a preferred embodiment of a system concept for an optical readout diagrammatically includes a cantilever having gratings. 
         FIG. 8  is a diagrammatic view of a preferred embodiment of a concept using optical lever method to detect cantilever deflection where reflected light is collected by an optical fiber. 
         FIG. 9  is a diagrammatic view of a preferred embodiment of a concept illustrating optical illumination method where a fan-out diffraction grating is used to illuminate an array of microcantilevers. 
         FIG. 10  is a diagrammatic view of a preferred embodiment showing the details of the parallel optical readout for cantilevers with diffraction gratings. 
         FIG. 11  is a diagrammatic view of a preferred embodiment of process layers for cantilever array, sensing layer, and local microheaters for the invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In a preferred embodiment the key areas of the system can be listed as follows: (1) A detector chip preferably including a silicon based novel integrated optoelectronic chip utilizing die-bonded laser diode array (1D VCSEL array), photodetectors  13 , and CMOS readout electronics with wafer thinning and Si via technology; (2) A MEMS chip  1  (also called a MEMS sensor array) with micro/nano resonant cantilevers  10  with integrated grating 24 structures, heating elements  47  and, remote electromagnetic actuator for a disposable chip; (3) 3D integration of integrated optoelectronics chip and MEMS chip with hybrid-stacking, (4) Functionalization of MEMS cantilevers  10  with different specific recognition molecules (proteins, oligonucleotides, chemical assemblies) with focused immobilization methods addressing only one individual cantilever  10  from the array; (5) Demonstration of parallel sensor array operation (from 2 up to 64 parallel channels 16) for highly selective and accurate recognition of chemical and biological agents. 
     In a preferred embodiment involves the design and fabrication of the MEMS chip on SOI wafer with nickel cantilevers  10 . The idea of an integrated diffraction grating 39 has already been demonstrated to provide extremely high-resolution displacement detection (with demonstrated sub-angstrom average detection limit) for Atomic Force Microscope (AFM) and other applications with simple fabrication and good immunity to environmental noise. In the preferred embodiment microcantilevers  38  can be replaced by membrane devices and in a preferred operation mode, cantilevers  10  or membranes can be coupled with an actuator to adjust the gap  26  to selectively tune the responsivity. 
     A preferred embodiment also involves optical fibers  32  to collect light. If the cantilevers  10  have gratings  24  than fibers  32  will collect light from the diffracted orders and couple it to photodectectors. For flat cantilevers  10 , fibers  32  are also part of the detection mechanism. In this case, cantilever 10 vibration changes the direction of the light and hence affects the light coupled to the optical fiber  32 . 
     A preferred embodiment also involves the design and fabrication of a detection apparatus comprising a detection chip and a control electronics  14  that functions independently of the MEMS layer. Preferably the detection apparatus is a universal read-out with no physical connection or electrical conductors to MEMS chip such that there is no electrical connection for electrons to flow from the detector chip or detector apparatus to the MEMS chip  1  and vice-versa. While VCSEL array technology is commercially available, it cannot be placed on the same side with the photodetectors  13  due to high packing density in the parallel sensor array and can be vertically integrated with flipchip bonding. Silicon via technology developed for 3D hybrid chip stacking will be utilized to channel  16  the VCSEL or other laser  27  onto MEMS chip. The preferably envisioned platform is versatile and can be utilized for optical interconnects and other photonics applications. 
     Preferably the detection apparatus includes a control electronics  14  involving closed loop control of MEMS cantilevers  10  using the detector chip with optical feedback at resonance, noise cancellation, and precise frequency measurement to detect dynamic changes. The detecting apparatus is preferably designed to be able to handle vapour phase and aqueous phase samples. The detector chip, preferably an optoelectronic chip, and the disposable MEMS layer are preferably aligned with good precision. Preferably this can be realized through mechanical guides machined in the package  2 , and more preferably active alignment can be used to achieve few microns precision. 
     Preferably, control electronics  14  will drive the actuation means at a single frequency and the phase difference between the drive signal and the photodetector  13  signal will be measured. 
     Preferably, the individual components of the sensor array can each be optimally designed and manufactured and various noise reduction techniques can be implemented to achieve sensitivities approaching the fundamental limits. Developing compact, highly functional, portable and disposable sensors for bio-sensing, gas sensing, thermal sensing using an absorption area and thermal isolation legs, and spectroscopic devices using grating and selective absorbing materials with this sensor array technology. Hence, realization of the proposed ideas will contribute to a personal health system through multi-analyte diagnostics capability, increased effectiveness in doctor-patient interaction, early detection of diseases and their recurrence including cancer, and detection of hazardous substances for security. 
     Further exemplary embodiments are described below. 
       FIG. 1  shows a preferable disposable package  2  concepts and illustrates that there may be no electrical conductors (also called electrical connections) to the disposable cartridge  100 . Likewise, microfluidics handling can be integrated (e.g., simple filtration can be used) with the disposable package  2  to separate serum from a drop of blood and then drive the serum onto the cantilevers  10  for measurement. The preferable reader  4  shown in  FIG. 1  includes a detector apparatus and an actuating means  15  preferably an electromagnet  46  used for AC (alternating current) actuation and, preferably, a permanent magnet for magnetic field enhancement. The disposable package  2  shown in  FIG. 1  also preferably includes a disposable cartridge  100  including a MEMS chip  1  coupled to a fluid contacting system preferably comprising a fluid chamber  5  (also sometimes called “a reaction chamber”), a fluid inlet coupled to the fluid chamber  5  and a fluid outlet also coupled to the fluid chamber  5 . In some instance the fluid inlet and the fluid outlet may occur through the same space designated as a fluid inlet/outlet  8 . The preferable reusable reader  4  also includes a mechanism to sense light which preferably is optoelectronic readout to measure the MEMS chip  1 . The reader  4  also includes a pump that couples to fluid ports  8 . The reader  4  also includes a temperature controller system to keep the cartridge at a desired temperature during testing. Further, the preferable reader  4  in  FIG. 1  also preferably includes control electronics  14  and a user interface  9 . 
       FIG. 2  shows details of a preferred embodiment of an optical readout and actuation means dramatically includes a disposable cartridge having cantilever  10  and fluid chambers  5 , light collector  12 , photodetector  13  and control electronics  14 . An actuating means  15 , preferably an electromagnet  46  and most preferably an electro-coil as shown, is placed below the cartridge that holds the microfluidic channels  22 . The actuator may cause the cantilevers  10  to vibrate at certain frequencies. Also shown is a preferable laser  27  which couples to the cantilevers  10  and reflects from the cantilever  10  surface. The reflected light can be coupled to light collectors  12  which are coupled to photodetectors  13  for the detection of the reflected light. The signal output from the photodiode  33  is modulated by the cantilever  10  vibration. The cantilever  10  surface may have a grating  24 . In this case the fibers  32  will collect the diffracted light from the gratings  24 . 
       FIG. 3  shows a disposable cartridge. The cartridge may have one of more channels  16  as shown in the figure. The channels  16  may have a fluidic chamber  5  where the width and/or height of the channel  16  are different from the rest of the channel  16 . The cantilever  10  sensor can be placed in this portion of the channel  16 . The cartridge material could be preferably plastic, epoxy glass, Plexiglas or acrylic. The channels  16  can be made by machining the disposable cartridge by mechanically, chemically or by molding techniques. A closed channel  16  can be obtained by gluing a cover plate  17  on the substrate  25  that holds the channels  16 . The cartridge may have an inlet  18  and an outlet  19  coupled to the channels  16 . The fluid can be applied through these openings as well as fluid motion can be achieved by coupling a pump to the inlet  18  or outlet  19 . Inlet  18  and outlet  19  can be also placed on the cover. The cartridge may have alignment or guide cutouts  20  for easy placement of the cartridge into the reader  4 . The cover may have the corresponding cutouts  21 . 
       FIG. 4  shows top view of fluid channels  5  with MEMS chips  1 . In a preferred embodiment, at least one MEMS chip can be placed in each fluid chamber  5 . The MEMS chip is composed of the base  23 , preferably silicon, and the cantilever  10 , preferable a magnetic material. 
       FIG. 5  shows the top view of MEMS chip  1  with gratings  24  at the end of the cantilevers  10 . The cross section image shows the substrate  25  under the cantilever  10 . This part is used for interference. 
       FIG. 6  shows a functionalized cantilever  10 . The sensing surface of individual cantilevers  10  can be appropriately activated (self-assembled monolayer, hydrophilic polymer coating) for covalent immobilization of recognition molecules. In one embodiment, precise addressing of reagent solutions can be achieved using ink-jet deposition system, dip coating, microspotting, or using microfluidic channels  16  for each analyte; alternatively, photoactivation-based chemical reactions will be employed providing reactive groups only in the light-activated surface zones. It is envisioned that model (bio)ligands for covalent immobilization can include antibodies (immunosensing), oligonucleotide probes (hybridization assays) and chemical assemblies (nanotubes, nanoparticles, supermolecular complexes, lipid bilayers). It is believed that surface density of binding sites will be determined using enzyme labeling, fluorescent microscopic imaging and/or atomic force microscopy) 
       FIG. 7  shows details of a preferred embodiment of an optical readout diagrammatically includes a cantilever  10  having grating  24  coupled to a substrate  25  to form a gap  26 . An actuating means  15 , preferably an electromagnet  46  and most preferably an electro-coil as shown, is placed below the substrate  25  which may cause the cantilever  10  to vibrate at certain frequencies. Also shown is a preferable laser  27  which couples to the grating  24  and forms refracted orders  28 : 0 th  order refraction, 1 st  order retraction  30  and 3 rd  order refraction  31  as preferably shown. The refracted orders  28  are collected by a combination of fiber optic cables  32  and photodetectors  13 . The signal output from the photodiode  33  is represented by diffracted order intensities for the 0 th  order refraction and the 1 st  order refraction. 
       FIG. 8  shows details of a preferred embodiment of optical lever readout diagrammatically includes a cantilever  10  with a flat surface. An actuating means  15 , preferably an electromagnet  46  and most preferably an electro-coil as shown, is placed below the disposable cartridge which may cause the cantilever  10  to vibrate at certain frequencies. Also shown is a preferable laser  27  which reflects back from the cantilever&#39;s  10  flat surface. The reflected beam is collected by an optical fiber  32 . The vibration of the cantilever  10  changes the direction of the reflected light and hence changes the amount of light that couples to the fiber optic cable  32 . The fiber optic cable  32  is coupled to photodiode  33  for detection. The signal output from the photodiode  33  is then modulated by the cantilever  10  vibration. 
       FIG. 9  shows details of a preferred embodiment of an optical lever readout implemented for detecting vibration of an array of cantilevers  10  where cantilevers  10  are placed in a system of fluid chambers  5 . A fan-out diffraction grating  34  can be used to generate multiple beams from a single light source  35 , preferably a laser  27 . A focusing optics  36  directs the generated beams onto cantilevers  10 . The reflected light is collected byoptical fibers  32  which are couple to an array of photodiodes  33 . 
       FIG. 10  illustrates the details of another preferred embodiment of electronics system  37  (may be part of the control electronics  14  and user interface  9  shown in  FIG. 1 ) and the optical readout system (may also be known as the optoelectronic readout; for example as in  FIG. 1 ), where the amplitude or the phase of the microcantilever  38  vibration of the microcantilever  38  is the desired sensor output. In this preferred embodiment, the optical readout system includes a laser  27 , preferably a red laser diode, a diffraction grating  39 , a first lens  40 , a beam splitter  41  a second lens  42  and a photodetector  13 , which can be coupled to a fiber  32 , wherein the beam splitter  41  can interact with an individual grating  24  or the flat surface of the cantilever  10 . In this preferred embodiment the microcantilevers  38  can be vibrated at a specific frequency at the vicinity of their resonances. The electronics system  37  includes a preamplifier  48  coupled to the photodetector  13  output, a signal generator  43  coupled to drive amplifier  44  and also coupled to phase and amplitude detection electronics  45 , an electromagnet  46  that couples to the MEMS chip  1 . In a preferred embodiment MEMS cantilevers  10  can be illuminated with a laser beam that is generated from a laser  27  using a fan-out diffraction grating  34 . In the case of cantilevers  10  with gratings  24 , reflected light from the substrate  25  and the sensor surface interfere and create diffraction orders. 1st diffraction order is monitored to avoid large bias in the 0th order direct reflection beam. The 1 st  diffracted order is collected by a system of fiber cable  32  and photodiode  33 . The photo diode signal is fed into a detection circuitry along with the reference drive output of the signal generator  43 . The phase and amplitude detection electronics  45  then outputs the phase difference between the drive signal and the photodetector  13  output as well as the amplitude of the photodetector  13  signal. In the case of flat cantilevers  10 , the optics is aligned such that the fibers  32  collect the reflected light from the cantilever  10  surface. The direction of the reflected light is determined by the cantilever  10  vibration therefore amount of coupled to the fiber  32 . 
     The preferred embodiment shown in  FIG. 11  includes embedding heating element  47  in the cantilever  10  structure allows for local-heating on the cantilevers  10 . This can be especially important for analyzing chemicals and biological samples as each reagent can have different adsorption and desorption rates at different temperatures. This can be used to improve specificity for selectivity) of detection against different chemical and biological binding events. Localized heating can be to create temperature dependent spectra, DNA melting curves, and to increase specificity by introducing multi-modal detection capability.