Abstract:
A system and method of indirectly modifying an environmental condition at a test site in one embodiment includes providing a test site on a substrate, providing a hydrogel composition loaded with a chemical factor at the test site, providing an actuator configured to activate the hydrogel composition to release a chemical factor at the test site, controlling the actuator to activate the hydrogel composition to release a chemical factor at the test site, and modifying the local chemical environment at the test site with the chemical factor.

Description:
PRIORITY 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/580,113 to Lang et al. and entitled “MULTISITE BIOSENSOR AND ASSOCIATED METHOD”, filed Oct. 15, 2009, the entirety of which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This patent relates generally to controlling assay conditions in diagnostic tests and more specifically to multiplexed measurement platforms and diagnostic tests. 
       BACKGROUND 
       [0003]    Personalized, preventative, predictive medicine demands diagnostic tests that can be performed at the point of care of an individual, with extreme fidelity that allows a caregiver or researcher to identify specific biomolecules even if those biomolecules are in low concentrations. While multiplexed measurement platforms, such as protein arrays, are utilized in research, there is a need in the art for a point of care platform that operates not only simply, but with great fidelity, as the concentration of different biomolecules in the blood can vary by more than ten orders of magnitude. As such, the identification of low concentration biomolecules, such as biomarkers of interest in certain diagnostic tests, requires that the affinity of the capture molecule to the low concentration biomolecule be orders of magnitude higher than any other molecule in the sample. 
         [0004]    It will be appreciated that, depending upon the particular diagnostic test or assay, the substance tested may be human body fluids such as blood, serum, saliva, biological cells, urine, or other biomolecules. Additionally, testing may be further desired on consumables such as milk, plant tissues or extracts, baby food, or even water. As such there is a need in the art to provide a low cost multiplexed assay for target molecules with sufficient sensitivity and specificity. 
         [0005]    Current attempts to provide such an assay or diagnostic test utilize affinity based sensors. Affinity based sensors function according to a “key-lock” principal in which a molecule with very high association factor to the marker of interest is used for detection. For example, a pregnancy test kit may incorporate a monoclonal antibody specific to a β-subunit of hCG (βhCG). The antibody is conjugated with a tag, e.g., gold, latex, or fluorophore, which is used for detection. If the targeted molecule binds with the conjugated antibody, the tagged pair is detectable such as by a visible test line. 
         [0006]    Similarly, molecular tests based upon enzyme-linked immunosorbent assay (“ELISA”) techniques utilize an antibody or antigen bound to a substrate to immobilize a target molecule. For example,  FIG. 1  depicts an ELISA assay  10  wherein antibodies  12  are immobilized on a substrate  14 . The substrate  14  may be positioned within a well (not shown). A blocker  16  is provided to cover the surface of the substrate around the antibody  12 . In a typical ELISA assay, a sample is then added to the well in which the primary antibody  12  is immobilized. Next, the sample is incubated for some time. During incubation, the blocker  16  prevents the target molecules in the sample from binding to the surface of the substrate  14  in order to avoid false binding. During incubation, some of the target molecules  18  become bound with some of the antibodies  12  as depicted in  FIG. 2 . After incubation, the remaining sample is washed to remove the unbound primary antibodies  18 . 
         [0007]    Subsequently, a secondary antibody  20  with a bound label  22  is added to the well, incubated, and washed resulting in the configuration of  FIG. 3 . As depicted in  FIG. 3 , the labeled secondary antibodies  20  are bound to the target molecules  18  that are in turn bound to the antibodies  12 . Accordingly, the number of labels  22  bound by the antibodies  20  to the antigen  18  is proportional to the concentration of the target antigen. Depending on the label used, the number of labels can be finally detected using colorimetry, amperometry, magnetometry, voltammetry, luminescence, or fluorescence detection. Other label-free antibody processes such as surface plasmon resonance may alternatively be used. 
         [0008]    It will be appreciated that the reliability and minimum detectable concentration of a target molecule are directly related to the sensitivity and cross-reactivity of the detection assay. Indeed, as the cross-reactivity of the assay increases, the minimum detectable concentration and the diagnosis error rate increase. The sensitivity in such tests is generally limited by label detection accuracy, association factor of the antibody-antigen pair, and the effective density of the probe antibody on the surface. 
         [0009]    As noted above, one issue that arises with affinity based sensors is the cross-reactivity of the sensor to other biomolecules. Indeed, in cross-reactive assays, a sensor tends to also sense biomarkers other than the biomarker of interest. The cross-reactivity issue is depicted in  FIG. 4  wherein an ELISA assay  30  includes antibodies  32  immobilized on a substrate  34  to act as a capture molecule with a blocker  36  covering most of the substrate surface  34 . Additionally, a labeled secondary antibody  38  is bound to a target molecule  40  which is in turn bound by the primary antibody  32 . The labeled secondary antibody  38  has also bound to a molecule  42  which exhibited an affinity for the primary antibody  32  and was labeled by a secondary antibody  38 . The sensitivity to a broad range of biomarkers thus increases the false negative/positive rate of diagnostic tests at clinical level as reported, for example, by P. A Benn et al., “Estimates for the sensitivity and false-positive rates for second trimester serum screening for Down syndrome and trisomy  18  with adjustment for cross identification and double positive results,”  Prenatal Diagnosis, Vol.  21, No. 1, pp 46-51, 2001. The presence of other molecules (secondary molecules or antigens) in the sample thus affects the minimum detectable concentration by binding to the primary antibody. 
         [0010]    The accuracy of the assay may further be affected by physiosorption. As further depicted in  FIG. 4 , some features  44  present in the ELISA assay  30 , either contaminants or simply an incongruity, may also be bound to a labeled secondary antibody  38 . The physiosorbed labeled secondary antibody  38  thus causes an increased background signal. 
         [0011]    Provision of diagnostic tests with a high fidelity is further complicated by the relative scarcity of the target molecules in a particular sample. As reported by Robert F. Service, “PROTEOMICS: Proteomics Ponders Prime Time,”  Science  321, no. 5897 (Sep. 26, 2008): 1758-1761, the concentrations of different proteins in blood varies by more than 10 orders of magnitude. Thus, to ensure a desired level of fidelity, the affinity of the capture molecule to the biomarker of interest must be orders of magnitude higher than the affinity of the capture molecule to any other molecule in the sample. 
         [0012]    Overcoming the cross-reactivity and background problems can significantly delay development of a new assay test and can increase the cost and complexity of the overall test. For example, in an effort to mitigate the various sensitivity and interference issues involved with affinity based testing, a particular assay is typically optimized by finding a combination of reagents and environmental conditions that maximizes the binding of the target molecule to the antibody. Thus, optimization can entail incorporating highly selective antibodies. Accordingly, a typical development of an ELISA assay requires several scientists working for more than a year to identify an acceptable antibody. Cross-reactivity of proteins is a common source of the failure of such development efforts. 
         [0013]    Another approach for optimizing the diagnostic test for a particular target molecule entails controlling the test conditions locally at different sites of the platform to increase the specificity of the tests. One such approach is described in U.S. patent application Ser. No. 12/580,113, filed on Oct. 15, 2009, the entire contents of which are herein incorporated by reference. Control of the test conditions locally at different sites of the platform can also be used to increase the dynamic range of the assay as described in U.S. patent application Ser. No. 12/688,193, filed on Jan. 15, 2010, the entire contents of which are herein incorporated by reference. 
         [0014]    Control of the test conditions locally at different sites of the platform has generally been attempted by electrically influencing biochemical reactions. Various attempts at such electrical control have been reported by R. G. Sosnowski et al., “Rapid determination of single base mismatch mutations in DNA hybrids by direct electric field control,”  Proceedings of the National Academy of Sciences of the United States of America  94, no. 4 (Feb. 18, 1997), Ian Y Wong and Nicholas A. Melosh, “Directed Hybridization and Melting of DNA Linkers using Counterion-Screened Electric Fields,” Nano Letters 0, no. 0 (January), Ian Y Wong, et al., “Electronically Activated Actin Protein Polymerization and Alignment,”  Journal of the American Chemical Society  130, no. 25 (Jun. 1, 2008): 7908-7915, and Ulrich Rant et al., “Switchable DNA interfaces for the highly sensitive detection of label-free DNA targets,”  Proceedings of the National Academy of Sciences  104, no. 44 (Oct. 30, 2007): 17364-17369, among others. 
         [0015]    Controlling test conditions by electrically influencing biochemical reactions, while promising, has proven problematic to researchers. For example, while influencing test conditions locally at different sites of the platform can increase the specificity of the tests or increase the dynamic range of the assay, most of the electrical potential is dissipated at the electric double layer formed over the electrode surface. Therefore, the electrical influence has a limited range of effectiveness. 
         [0016]    A need exists for a device and method of performing an assay incorporating low cost antibodies. A further need exists for tests such as multiplexed assays, e.g., protein arrays, competitive assays, or bead based arrays, as well as low cost devices, e.g., lateral flow devices, or other biochips. Furthermore, methods and compositions for implementing these assays and arrays with higher fidelity would be appreciated. Additionally, methods and devices which provide more accurate results than previous assays would be a further benefit. 
       SUMMARY 
       [0017]    In accordance with one embodiment of the disclosure, a system and method of indirectly modifying an environmental condition at a test site includes providing a test site on a substrate, providing a first activatable stimulant at the test site, providing an actuator configured to activate the first activatable stimulant at the test site, controlling the actuator to activate the first activatable stimulant, and modifying the local chemical environment at the test site with a chemical factor released by the activatable stimulant. 
         [0018]    In accordance with another embodiment, a system for controlling an environmental condition at a test site includes a substrate including at least one test site, at least one activatable stimulant on the substrate and configured for use at the at least one test site, and at least one actuator positioned to actuate at least one of the at least one activatable stimulant at the at least one test site. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  depicts a schematic of a prior art test site within an ELISA array with an antibody and blockers formed on a substrate as a sample is added to the test site; 
           [0020]      FIG. 2  depicts the test site of  FIG. 1  with a target molecule bound to some of the antibodies of  FIG. 1  after the test site has been incubated and washed; 
           [0021]      FIG. 3  depicts the test site of  FIG. 2  after a labeled secondary antibody has been added and the test site has again been incubated and washed so that the labeled secondary is bound to the bound target molecules; 
           [0022]      FIG. 4  depicts a schematic of a prior art test site within an ELISA array wherein a labeled secondary is bound to interfering molecules due to cross-reactivity and also physiosorbed to the surface of the substrate raising the background noise level of the test; 
           [0023]      FIG. 5  depicts a multi-site biosensor system configured to control chemical environmental conditions at various test sites to modulate the affinity at the test sites for a target molecule; 
           [0024]      FIG. 6  depicts a platform for providing a number of different test sites in the form of a microarray; 
           [0025]      FIG. 7  depicts a procedure that can be used to indirectly establish different test chemical environments at various test sites on a platform so as to expose a sample to multiple test environments; 
           [0026]      FIG. 8  depicts a schematic of a test site wherein a labeled secondary is bound to target molecules, to interfering molecules due to cross-reactivity, and also physiosorbed to the surface of the substrate raising the background noise level of the test; 
           [0027]      FIG. 9  depicts a schematic of a test site formed identically to the test site of  FIG. 8  and exposed to the same sample to which the test site of  FIG. 8  was exposed, but maintained at a pH different from the pH of the test site of  FIG. 8  during incubation, resulting in different binding efficiencies for the different signal contributors; and 
           [0028]      FIG. 10  depicts a procedure that can be used to indirectly establish different test chemical environments at various test sites on a platform to optimize a test environment for detecting a target molecule. 
       
    
    
     DESCRIPTION 
       [0029]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0030]    Referring to  FIG. 5 , there is depicted a representation of a multisite biosensor system generally designated  100 . The biosensor system  100  includes an I/O device  102 , a processing circuit  104  and a memory  106 . The I/O device  102  may include a user interface, graphical user interface, keyboards, pointing devices, remote and/or local communication links, displays, and other devices that allow externally generated information to be provided to the biosensor system  100 , and that allow internal information of the biosensor system  100  to be communicated externally. 
         [0031]    The processing circuit  104  may suitably be a general purpose computer processing circuit such as a microprocessor and its associated circuitry. The processing circuit  104  is operable to carry out the operations attributed to it herein. 
         [0032]    Within the memory  106  are various program instructions  108 . The program instructions  108 , some of which are described more fully below, are executable by the processing circuit  104  and/or any other components of the biosensor system  100  as appropriate. Affinity databases  110  are also located within the memory  106 . 
         [0033]    The biosensor system  100  further includes chemical environment actuator equipment  112  and chemical environment detector suite  114 . The chemical environment actuator equipment  112  is configured to activate an activatable stimulant that affects the chemical environmental conditions at a test site, in this example, within a microarray  120  depicted in  FIG. 6 . By way of nonlimiting example, one such activatable stimulant is a hydrogel such as those described in Linden, et al., “Stimulus-sensitive Hydrogels and Their Applications in Chemical (Micro)Analysis,”  The Analyst, no.  128 (2003): pp. 325-331, which is incorporated herein by reference in its entirety. It will be appreciated that hydrogels, and particularly biocompatible hydrogels, can be utilized as a selective carrier for a chemical factor selected for its ability to elicit an environmental response that can, for example, increase the sensitivity of a target molecule to a capture molecule. It will be appreciated that various methods may be used to form the microarray platform  120  depicted in  FIG. 6 , including those methods disclosed in U.S. Pat. No. 5,807,522, incorporated herein by reference in its entirety. 
         [0034]    As shown in  FIG. 6 , a microarray platform  120  includes a number of different subarrays  122   X . The subarrays  122   X  include a number of test sites  124 . Each of the subarrays  122   X  is associated with a respective actuator  126   X . The number and layout of subarrays  122   X  and associated actuators  126   X , as well as the number of test sites  124  within each of the subarrays  122   X  may be varied within the scope of the invention. It will be appreciated that an actuator  126   X  comprises one or more electrodes, integrated heater, Peltier device, LASER, light source, liquid crystal diode, CMOS, or other device operable to activate a selected activatable stimulant. 
         [0035]    According to one embodiment, the selected activatable stimulant comprises a hydrogel operable to selectively retain and release a selected chemical factor. Those chemical factors selected may, by way of nonlimiting example, include biomolecules, pH-altering compounds, buffers, enzymes, antigens, drugs, or other compositions selected for the specific environmental response desired by the practitioner. Alternatively, a hydrogel may be selected for its ability to create bulk fluid flow upon stimulation by the actuator, thereby influencing the flow of components within microarray platform  120 . 
         [0036]    For example, it will be appreciated that the chemical environment actuator equipment  112  is operable to establish a voltage profile within the microarray platform  120  using electrode pairs as actuators  126   X . By way of example, the chemical environment actuator equipment  112  is thus used to electrically stimulate one or more hydrogel compositions bonded to a test site  124 , and thereby release a chemical factor loaded therein, thereby altering the chemical environment at test site  124  to optimize the conditions for sensing a target molecule. For instance, a chemical factor released by the hydrogel upon stimulation by the electrode pairs as actuators  126   X  may be a buffer solution operable to modulate the pH of a test site  124  within an ideal affinity range of a target molecule to a capture molecule at test site  124 . In practice, stimulation of actuators  126   X  results in the conformational change of the hydrogel, causing it to deswell and release the buffer solution at a predetermined rate to modulate the pH at each of test site  124 . Optionally, the precise pH at test site  124  is detected by a detector suite  114 , allowing for feedback to the operator or actuator equipment  112 , and further allowing for the modulation of the release of the chemical factor by altering the stimulation presented to the hydrogel. Sensors may be provided on the microarray platform  120  to assist in determining the precise pH within each of the test sites  124 . 
         [0037]    Referring back to  FIG. 5 , the system  100  further includes a label reader  116 . The label reader  116  may be included in a single device along with the other components of the system  100 . Alternatively, one or more of the components of the system  100  may be provided as a separate device which may be remotely located from the other components of the system  100 . 
         [0038]    As noted above, according to one embodiment, test sites  124  are prepared with a capture molecule effective for selectively binding with a target molecule under preselected environmental conditions. Further details regarding the biosensor system  100  are provided with reference to the procedure  130  of  FIG. 7 . The processor  104  executes the program instructions  108  to execute at least some of the procedure  130  of  FIG. 7 . In different embodiments, the procedure  130  may be modified to include more or fewer steps depending upon the specific criterion. 
         [0039]    At block  132  of  FIG. 7 , a target molecule is identified and then a capture molecule, described herein as an antigen, with an affinity for the target molecule is identified (block  134 ). A binding efficiency coefficient for the target molecule (α i ) with the identified antibody is then identified for at least two different chemical environmental conditions (block  136 ) and stored in one of the affinity databases  110  (block  138 ). 
         [0040]    Potential sources of test signal interference or noise likely to be present in a tested sample are then identified (block  140 ). The identification of signal interference may include, for example, an identification of likely or potential molecules within a sample that also have an affinity for the identified capture molecule. A binding efficiency coefficient for each source of noise (α n ) with the identified capture molecule is then identified for each of the different chemical environmental conditions (block  142 ) and stored in one of the affinity databases  110  (block  144 ). 
         [0041]    At block  146 , the microarray platform  120  is prepared by depositing the desired amount of the selected capture molecule in each of the test sites  124 . In alternative embodiments, a subset of the test sites  124  may be prepared with a first capture molecule while another subset of the test sites  124  may be prepared with a second capture molecule so as to allow two separate tests to be conducted within a single microarray platform  120 . Additional configurations within a single microarray platform  120  may also be used. By way of example, each of the test sites within one of the subarrays  122  may be prepared with the same capture molecule while each of the subarrays  122  includes a different capture molecule. The number of test sites  124  prepared with a particular capture molecule in this embodiment is selected to be at least the same as the number of noise sources identified above plus the target molecule. 
         [0042]    Once the microarray platform  120  is prepared, a chemical factor is selected for effectuating a selected environmental condition, and a hydrogel for selectively dispersing the chemical factor is loaded with the chemical factor and bonded to microarray platform  120  (block  148 ). Thereafter, a sample is introduced to microarray platform  120  (block  150 ), and chemical environment actuator equipment  112  is then controlled to actuate the actuators  126   x , thereby stimulating the selected hydrogel to release the chemical factors and regulate the environment of the test sites  124  (block  152 ). 
         [0043]    The sample is then incubated at the established test environment for a predetermined time (block  154 ). During the incubation, the actual test environment within each of the selected set of test sites  124  is monitored by the environment detector suite  114  and data indicative of the established test environment is provided to the processing circuit  104  (block  156 ). 
         [0044]    In one embodiment, data obtained at block  156  is passed to the processing circuit  104  (block  158 ). Under control of the processing circuit  104 , the actuators  126   x  can be controlled to further modulate the sensed environment at each of the test sites  124 . Alternatively, lookup tables may be stored in the memory  106  wherein particular values are associated with electrode voltages for particular concentrations of chemical factors. 
         [0045]    When the sample has been sufficiently incubated, the test sites  124  are washed (block  160 ) and a labeled secondary antibody is introduced into the selected set of test sites  124  (block  162 ) and incubated (block  164 ). The selected set of test sites  124  are then washed (block  166 ) and the labels remaining in the test sites  124  are detected by the label reader  116  (block  168 ). Based upon the signals associated with the number of labels remaining in the selected set of test sites  124 , the concentration of one or more target molecules within the sample is calculated by the processing circuit  104  (block  170 ). 
         [0046]    Calculation of the concentration of one or more target molecules is possible since the signal obtained by the label reader  116  for a particular one of the selected set of test sites  124  is the summation of the contributors to the signal including the target molecule, and each of the noise sources such as interfering molecules. By way of example,  FIG. 8  depicts a test site  180   1 , which, according to certain embodiments, corresponds to test sites  124  described above. As shown herein, a test site  180   1 , includes capture molecule  182  bonded to a substrate  184 . In this exemplary embodiment, certain capture molecules  182  have selectively bound to target molecule  186 , which is further bound to labeled secondary antibody  190 . As shown herein, some interfering antigen  188  has also bound to some of the antibodies  182 . A labeled secondary antibody  190  has bound to each of the bound antigens  186  and each of the bound interfering antigens  188 . Further, a portion of the labeled secondary antibody  190  has physiosorbed to the blocked surface of the substrate  184 . 
         [0047]    The relative proportion of the signal attributable to each of the contributors is dependent upon the concentration of the particular contributor, the concentration of the other contributors, and the relative affinity to the initially deposited capture molecule of each of the contributors. The relationship is reflected in the following equation: 
         [0000]        S   1 =α 1-1   C   1 +α 1-2   C   2 + . . . α 1-x   C   x  
 
         [0000]    wherein
       S 1  is the signal associated with the detected label in the spot  122   1 ,   α 1-x  is the binding efficiency proportional to affinity for the identified contributor (1 through x) at the environment established in spot  122   1 , and   C X  is the concentration in the sample of the identified contributor (1 through x).
 
Accordingly, because the number of the selected set of test sites  124  is equal to at least the number of interfering contributors plus one, the number of detected signals will correspond to the number of identified interfering contributors plus the target molecule. The contribution of the various sources to the overall signal, as well as the value of the overall signal, will vary from test site to test site.
       
 
         [0051]    By way of nonlimiting example,  FIG. 9  depicts a test site  180   2  which was prepared identically to the test site  180   1  and exposed to a sample identical to the sample used with the test site  180   1 . The test environment in each of the test sites  180   x  was different. Accordingly, the labeled secondary antibody  190  bound to the target molecule has increased from two in  FIG. 8  to four in  FIG. 9 . Additionally, the labeled secondary antibody  190  bound to the interfering antigen  188  increased from two in  FIG. 8  to three in  FIG. 9 . 
         [0052]    Thus, if three noise contributors are identified in a sample, such as analytes that bind non-specifically to capture molecules sites and prevent the target molecule from binding, analytes that produce erroneous signals, and analytes that physisorb to the surface of the test site and produce erroneous signals, along with the target molecule, four test sites, such as four of the test sites  124 , are the minimum number of cells prepared at block  144 . Therefore, four signals will be obtained, as reflected in the following equations: 
         [0000]        S   1 =α 1-1   C   1 +α 1-2   C   2 +α 1-3   C   3 +α 1-4   C   4  
 
         [0000]        S   2 =α 2-1   C   1 +α 2-2   C   2 +α 2-3   C   3 +α 2-4   C   4  
 
         [0000]        S   3 =α 3-1   C   1 +α 3-2   C   2 +α 3-3   C   3 +α 3-4   C   4  
 
         [0000]        S   4 =α 4-1   C   1 +α 4-2   C   2 +α 4-3   C   3 +α 4-4   C   4  
 
         [0053]    Each term is thus proportional to a binding efficiency factor, α, which is a function of the molecule affinities and other assay conditions, e.g., mass transport. Accordingly, because the same sample is used in each of the test sites  124 , and because the binding efficiency of the target molecule and the interfering antigens for the specific chemical environment in each of the test sites  124  is known, the procedure  130  provides four equations and four unknowns. The concentrations of each of the contributors can thus be ascertained in a known manner. Accordingly, the concentrations of multiple target molecules within a sample can also be ascertained. In practice the signals are noisy and linear estimation algorithms may be used to estimate the value used for any particular signal. Additionally, one or more sensor sites may be used as a control site to improve the accuracy of the procedure  130 . 
         [0054]    Accordingly, a chemical factor can be loaded within a hydrogel and included into a bulk solution that includes a sample. When desired, an actuator can then be controlled to trigger the release of the chemical factor from the hydrogel, thereby releasing the chemical factor into the bulk solution so as to modify the chemical environment at a test site. 
         [0055]    If desired, the chemical factors loaded into varying hydrogels may be of varying types, each type loaded within a hydrogel with a different activation characteristic. For example, pH buffers of increasing acidity can be loaded within hydrogels having different activation energies. Thus, by changing the activation level of the actuator, a different pH buffer is introduced to the system. 
         [0056]    Additionally, other actuators may be used with hydrogel actuators. For example, a LASER or integrated heater can be used to heat thermoresponsive hydrogels, thereby causing the hydrogel to deswell and release a chemical factor preloaded therein. By way of nonlimiting example, a thermoresponsive hydrogel comprising poly(N-isopropylacrylamide) (PNIPAAm) may be selected and loaded with a chemical factor by placing a dried version of the hydrogel in a solution containing the chemical factor in an acetone solution. Thereafter, the chemical factor and hydrogel are allowed to equilibrate for a preselected time—approximately three (3) days according to one embodiment. Thereafter, the hydrogel is prepared according to Dinarvand, “The Use of Thermoresponsive Hydrogels for On-Off Release of Molecules,”  Journal of Controlled Release , vol. 36 (1995), pp. 221-227. Thereafter, according to one embodiment, the chemical factor loaded hydrogel is optionally bonded to a test site  124  in close proximity to an actuator such as a LASER or an integrated heater. It will be appreciated that upon heating of the hydrogel to a lower critical solution temperature by the actuator, the hydrogel releases the loaded chemical factor, thereby modulating the environment of test site  124 . As noted previously, the precise environmental condition effectuated by the chemical factor at test site  124  is detected by a detector suite  114 , allowing for feedback to the operator or actuator equipment  112 , and further allowing for the modulation of the release of the chemical factor by altering the stimulation presented to the hydrogel. 
         [0057]    A multisite biosensor can thus be implemented on a printed circuit board, glass, plastic substrate, or on a CMOS chip with gold, glass, epoxy, polymer, or gel coating, or even in a well plate such as a 96 well plate. If desired, control, readout, and also sensing for the control can be provided in the printed circuit board or CMOS chip. CMOS technology allows multiple sensing sites to be fabricated in close proximity. This assists in maintaining uniformity of non-controlled environmental factors amongst the test sites. The chip can be part of a system using stand alone microfluidics or a capillary principle or may be used with a separately provided device. The signal estimation and the assay data can be hard coded on the CMOS chip if desired. 
         [0058]    Moreover, the activatable stimulant may be provided on the same substrate as the test site and mixed with the sample as the sample is transported to the test site. For example, a substrate may include a sample receiving area that is linked to a test site by a fluid path. The activatable stimulant may be prepositioned at a location on the fluid path such that the activatable stimulant releases a chemical factor in a manner such that it mixes with the sample as the sample moves toward the test site. 
         [0059]    The biosensor system  100  may thus incorporate a variety of activatable stimulants which, when activated, release a preselected chemical factor that modifies the chemical environment of a test site. The particular chemical factor will vary depending upon the particular embodiment and the target molecule selected. Likewise, the type of sensor or sensors incorporated into the label reader  116  will vary depending upon the particular label used. Various embodiments may thus use luminescence, fluorescence, colorimetric, electrochemical, impedance (including electrochemical impedance spectroscopy sensors), and magnetic sensors. The sensors can be configured to allow isolation of the signal produced by a selected one or more test sites Likewise, the sensors incorporated into the environment detector suite  114  may include IR sensors, and Hall sensors. AMR sensors or GMR sensors may be provided to monitor the density of magnetic beads on a test site surface. ISFETs or CMOS based charge detection circuits may be used in electrochemical embodiments. 
         [0060]    The procedure  130  can thus be used in a variety of test site platforms including 96-well plates, plates with fewer or additional wells, microarray platforms, printed circuit board platforms, CMOS chip platforms, multiplexed assays, protein arrays, lateral flow devices, sandwich assays, competitive assays, bead based arrays or other appropriate platforms. The procedure  130  may further be used for the detection of a variety of target molecules as well as different types of molecules in addition to antibodies. By way of example, the procedure  130  may also be used for the detection of nucleic acid, protein, or small molecules. The procedure is not limited to binding processes, and can thus be extended to enzymatic reaction studies including phosphorylation studies, protein-protein interactions, protein nucleic acids interactions, and competitive assays. 
         [0061]    By way of nonlimiting example, an alternative embodiment utilizing biosensor system  100  is provided in  FIG. 10 . Therein, controller or processor  104  is activated and executes the program instructions  108  (block  210 ), wherein processor  104  signals the actuator to activate the activatable stimulant (block  220 ). In this instance, activatable stimulant is a hydrogel loaded with a chemical factor operable to influence the chemical environment at a test site  124 . Upon activation of the hydrogel by actuator, the hydrogel releases the chemical factor into the environment surrounding test site  124  (block  230 ). Thereafter, sensors located near test site  124  sense the chemical environment near test site  124 , and send the sensed value to processor  104  (block  250 ), where processor  104  compares the sensed value to a preselected value correlating to an ideal chemical environmental value for a target molecule&#39;s affinity to a capture molecule (block  260 ). Upon comparing the sensed value to the preselected value or range of values, the processor determines whether additional activation of actuators are necessary (block  210 ), or whether no further action should be taken other than continued evaluation of the chemical environment. 
         [0062]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.