Abstract:
A method for performing a blood assay is disclosed. The method includes the steps of: positioning an acoustic biosensor in fluid communication with a blood vessel of the patient whereby blood from the blood vessel contacts the biosensor. The biosensor includes at least one material adapted to bind to an analyte. The method also includes the steps of detecting a change in at least one of an electrical and mechanical property of the biosensor indicative of a mass change resulting from binding of the at least one material with the analyte and transmitting a real time signal representative of mass change to a display module to provide real time analysis by a clinician.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a system and method for performing blood assays. In particular, the present disclosure is directed to in vivo acoustic biosensors configured to continuously monitor blood to detect presence and/or concentration of an analyte of interest. 
         [0003]    2. Background of Related Art 
         [0004]    Various types of blood analyzers for detecting specific analytes of interest (e.g., proteins) are known in the art. A conventional blood analyzer utilizes a sensor to detect the presence of the analyte and optionally determines the concentration thereof. In vitro methods are usually utilized to obtain a blood sample from a blood vessel and subsequently provide the sample to the blood analyzer for analysis. 
         [0005]    However, known blood analyzers of the type aforementioned present a major drawback which detracts from their overall usefulness and effectiveness. In particular, the conventional blood analyzer is incapable of providing real or present time data of the analyte of interest present in the blood stream. Moreover, the conventional blood analyzer is limited in that it can only indicate the presence of the analyte at the moment when the sample of blood was drawn. In many applications, the amount of analyte present does not exhibit elevated concentrations in the bloodstream until several hours after the biological event. 
         [0006]    One conventional solution involves performing multiple in vitro assays to periodically screen the blood for elevated concentration of the analyte. However, performing multiple assays is overly invasive to the patient. In addition, this solution is also imperfect since there is a possibility that occurrence of the biological event may be missed. 
         [0007]    This particular problem is acutely prevalent in the field of monitoring of acute myocardial infarction patients. Biochemical markers associated with myocardial infarction (e.g., cardiac troponin) are detectable in the patient&#39;s blood stream about 3 to 8 hours from the onset of the condition. In the absence of other indications of the condition (e.g., electrocardiogram indicators, acute distress, etc.) a patient complaining of physical conditions associated with myocardial infarction (e.g., chest pain) is typically observed for up to 12 hours to rule out the infarction as the cause of the symptoms. Conventionally, cardiac marker assays are typically performed serially at 6-8 hour intervals in order to detect a recent infarction. Due to the relatively long time periods between assays, a true infarction patient with biological signs of infarction may, as a result, wait for many hours before the signs are detected. Consequently, there is a delay in providing therapy to the patient. 
         [0008]    Therefore it would be desirable to provide a blood analyzer that continuously detects the presence of an analyte in a bloodstream to allow for instantaneous and continuous detection of elevated analyte concentration. 
       SUMMARY 
       [0009]    The present disclosure relates to a system and method for performing in vivo blood assay to detect the presence and concentration of an analyte. The system includes an acoustic biosensor having an antibody material adapted to bind to the analyte of interest. The biosensor is in fluid communication with a blood vessel such that blood continuously contacts the biosensor and the analyte binds to the antibody material. The biosensor is repeatedly excited and the biosensor&#39;s resonant frequency is repeatedly monitored, therefore approximating a continuous measurement. Changes in the resonant frequency are recorded and analyzed by a detector device which calculates the concentration of the analyte in the bloodstream. 
         [0010]    According to one aspect of the present disclosure a method for performing a blood assay is disclosed. The method includes the steps of: positioning an acoustic biosensor in fluid communication with a blood vessel of the patient whereby blood from the blood vessel contacts the biosensor. The biosensor includes at least one material adapted to bind to an analyte. The method also includes the steps of detecting a change in at least one of an electrical and mechanical property of the biosensor indicative of a mass change resulting from binding of the at least one material with the analyte and transmitting a real time signal representative of mass change to a display module to provide real time analysis by a clinician. 
         [0011]    According to another aspect of the present disclosure a medical analyzer to assay blood for an analyte is disclosed. The analyzer includes an acoustic biosensor adapted to be in fluid communication with a blood vessel whereby blood from the blood vessel contacts the biosensor. The biosensor includes at least one material adapted to bind to an analyte in the blood. The analyzer also includes an oscillator for generating a mechanical wave form in the biosensor and a detector adapted to detect a change in resonant frequency of the mechanical wave form indicative of a mass change resulting from the binding of the at least one material of the biosensor with the analyte of the blood. The detector is also adapted to generate a real time signal representative of the mass change of the biosensor to provide real time analysis by a clinician. 
         [0012]    According to an additional embodiment of the present disclosure, a medical analyzer to assay blood for an analyte is disclosed. The medical analyzer includes an acoustic biosensor adapted to be in fluid communication with a blood vessel whereby blood from the blood vessel contacts the biosensor. The biosensor includes at least one material adapted to bind to an analyte of the blood and is adapted to transmit a mass change resulting from the binding of the at least one material of the biosensor with the analyte of the blood in response to a change in at least one of an electrical and mechanical property of the biosensor. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Various embodiments of the present disclosure are described herein with reference to the drawings wherein: 
           [0014]      FIG. 1  is a view of a blood analyzer according to the present disclosure accessing a blood vessel; 
           [0015]      FIG. 2  is a cross-sectional view of the entry end of the probe of the blood analyzer illustrating the biosensor within the probe; 
           [0016]      FIG. 3  is a cross-sectional view of another embodiment of the probe according to the present disclosure; and 
           [0017]      FIG. 4  is a flow diagram of a method for performing a blood assay according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
         [0019]    Referring now to  FIGS. 1-2 , the blood analyzer  10  in accordance with the principles of the present disclosure is illustrated. Generally blood analyzer  10  includes an access member or a probe  12  and a monitor  20  in electrical communication with the probe  12 . The probe  12  has a proximal end  14  and a distal end  16 . The probe  12  may be any tubular structure (e.g., a catheter or a cannula) having a housing  13  and a lumen  22  defined therein and one or more ports  24  at the distal end  16  thereof adapted to provide fluid access to the lumen  22 . The distal end  16  of the probe  12  is inserted into a blood vessel “V” to allow for the blood to flow into the lumen as illustrated by directional arrows  26 . It is envisioned that the distal end  16  may be configured for penetration and insertion into the blood vessel “V.” Alternatively, a tissue-penetrating device may be utilized to create an orifice in the blood vessel “V” into which the probe  12  is later inserted. The blood flows into and through the lumen  22  through the ports  24 . 
         [0020]    Probe  12  includes an acoustic biosensor  30  disposed within the lumen  22  which is in fluid communication with the blood flowing through the blood vessel “V.” This allows for the blood analyzer  10  to continuously monitor the blood stream for analyte  34  of interest. The acoustic biosensor  30  may be a piezoelectric material (e.g., quartz crystal) and includes a capture agent  32  disposed on the surface thereof. The capture agent  32  may be, for example, specific antibodies adapted to bind to an analyte  34  of interest. Analytes of interest include cardiac troponin, myoglobin, creatinine kinase, creatine kinase isozyme MB, albumin, myeloperoxidase, C-reactive protein, glucose and the like. The capture agent  32  may be bound to the surface of the acoustic biosensor  30  using any number of conventional deposition techniques, such as covalent bonding, physical absorption, cross-linking to a suitable carrier matrix. During operation, the biosensor  30  is in fluid communication with the blood. If analyte  34  is present in the blood, the analyte  34  binds to the capture agent  32  to form a bound complex  36 . As the capture agent  32  continuously binds to the analyte  34  to form the complex  36 , the effective mass of the biosensor  30  increases. Thus, the acoustic biosensor  30  detects the amount of the analyte  34  by measuring changes in the mass. The mass change is measured by measuring changes in electrical and mechanical properties of the biosensor  30 . Passing an electrical current through the biosensor  30  and measuring changes in the electrical current or the electrical potential allows for measuring changes in effective mass of the biosensor  30 . The change in mass of the biosensor  30  may also be determined by exciting the biosensor  30  and measuring the change in resonant frequency of the biosensor  30 . 
         [0021]    The biosensor  30  is coupled to the monitor  20  via two or more wires, such as an excitation wires  38 ,  50  and a detection wire  39 ,  51 . The probe  12  at its proximal end  14  includes a cable  18  which encloses the wires  38 ,  39 ,  50 ,  51 . The monitor  20  includes an oscillator, a detector, input controls, and a display (not explicitly shown). The oscillator and the detector are coupled to the biosensor  30  via the excitation wires  38 ,  50  and the detection wires  39 ,  51  respectively. The wires  38 ,  39 ,  50 ,  51  include one or more electrodes in electrical communication with the biosensor  30 . The oscillator provides an electrical signal to the biosensor  30  which drives the biosensor  30  at the corresponding resonant frequency. The frequency is transmitted along the detection wire  39 ,  51  to the detector wherein the change in mass of the biosensor  30  is determined. 
         [0022]    Mass calculation is performed by using a Sauerbey relationship wherein a change in the measured frequency of the piezoelectric crystal is expressed as a change in mass thereof. The resulting increase in the mass produces a decrease in the resonant frequency of the biosensor  30 . The detector includes programmable instructions (e.g., algorithm) adapted to calculate the change in mass of the biosensor  30  as a function of the change in the measured frequency. The instructions may include the Sauerbey formula as well as any required constants describing the piezoelectric material. Such constants include piezoelectrically active area, density and shear modulus of the crystal. 
         [0023]    An increase in mass of the biosensor  30  signifies that the analyte  34  has been captured by the capture agent  32  to form the complex  36 . The data describing the calculated mass changes is formatted for output on the display. This step may include displaying that the analyte  34  is present in the blood stream (e.g., displaying text “analyte detected.”). It is further contemplated that the detector is configured to calculate a derivative of the change in mass. The rate of change in the resonant frequency correlates to the changes in the mass of the analyte in the blood stream. This relationship allows for determination of concentration and change in concentration of the analyte  34 . In particular, the rate of increase of the mass of the biosensor  30  allows for determination of the concentration of the analyte  34 . Taking a second time derivative of the measured mass allows for calculation of the rate of change in the concentration of the analyte  34 . It is within the purview of those skilled in the art to provide programmable instructions to the detector to enable calculation of derivatives. The data relating to the concentration of the analyte  34  in the bloodstream allows for a more detailed analysis of the test results. In particular, as opposed to simply outputting whether the analyte  34  is present in the bloodstream, knowing the concentration of the analyte  34  and the rate at which the analyte  34  is being generated provides health professionals with a tool to determine the severity of the condition (e.g., myocardial infarction). The detected concentration or the change in concentration of the analyte  34  may be outputted as grams per liter of blood (e.g., μg/L). 
         [0024]    The blood analyzer  10  allows for continuous monitoring of the analyte  34 . During operation, the probe  12  is inserted into the blood vessel such that the biosensor  30  is in fluid communication with the blood and the monitor  20  is calibrated. Calibration includes acquiring the fundamental frequency of the biosensor  30  which corresponds to zero net mass gain, such that any subsequent mass gain detected by the monitor  20  is indicative of the presence of the analyte  34 . 
         [0025]    The oscillator and the detector operate in sequence, such that when the oscillator transmits an excitation pulse to the biosensor  30  the detector is activated to receive the frequency signal. It is contemplated that the monitor  20  interrogates the biosensor  30  on a periodic basis (e.g., every minute) wherein the oscillator and the detectors are activated for relatively short periods of time with pauses between interrogations, therefore approximating a continuous measurement. Those skilled in the art will understand that various proteins indicative of specific biological conditions are generated at different rates, therefore the length of interrogation period may be adjusted based on the type of analyte. 
         [0026]    The biosensor  30  ceases to function when all of the antibodies are bound to the analyte  34  and no more analyte  34  can be bound thereto. Therefore, the duration of the functionality of the biosensor  30  varies with the concentration of the analyte  34  in the patient&#39;s blood. It is preferable that the duration of operation about 8 hours with patients having low analyte concentration to ensure proper detection. 
         [0027]      FIG. 3  shows another embodiment of the probe  12  which includes the biosensor  30  disposed within a chamber  40  of the lumen  22 . The biosensor  30  includes an extension member  41  having the capture agents  32  disposed at a distal end thereof. During operation, the blood flows into the lumen  22  through the ports  24  carrying the analyte  34  which then binds to the capture agents  32 . The biosensor  30  is excited by the monitor  20  in the manner discussed above to determine the change in mass. Since the extension member  41  is coupled to the biosensor  30  the changes in mass caused by the binding of the analyte  34  to form the complex  36  are detected by the monitor  20 . 
         [0028]    The extension member  41  may be a cantilever beam manufactured from a medical grade material (e.g., stainless steel) or a suture filament. Optionally, the chamber  40  may be separated from the rest of the lumen  22  via a seal  42 . The seal  42  may be formed from hydrogel and other materials which do not affect acoustic properties of the biosensor  30 . This prevents the blood from flowing into the chamber  40  and contacting the biosensor  30  further isolating the biosensor  30 . 
         [0029]    The biosensor  30  of the embodiment shown in  FIG. 2 , must be removed after the blood analysis is complete since the biosensor  30  includes bound complexes  36  on the surface thereof. In contrast, the biosensor  30  of the embodiment shown in  FIG. 3  may be reused. By depositing the capture agents  32  on the extension member  41 , the analytes  34  do not bind to the surface of the biosensor  30 . Consequently, the biosensor  30  may be reused and the extension member  41  may be replaced after the analysis is complete. 
         [0030]    It is also envisioned that the biosensor  30  may be disposed within the venous system using a variety of other types of medical devices adapted for insertion into blood vessels which provide for blood flow therethrough. Contemplated devices include but are not limited to shunts and stents. 
         [0031]    A method for performing a blood assay is illustrated in  FIG. 4 . In step  100 , the biosensor  30  is positioned in fluid communication with the blood vessel “V.” This is accomplished by positioning the biosensor  30  within an access member (e.g., probe  12 ) which is then inserted into the blood vessel. As discussed above, when the probe  12  is inserted into the blood vessel, the blood flows into the lumen  22  thereby positioning the biosensor  30  in fluid communication with the blood. 
         [0032]    In step  102 , the biosensor  30  is excited by the oscillator, which generates a mechanical wave form in the biosensor  30  at the resonant frequency thereof. The resonant frequency of the biosensor  30  is monitored by the detector which detects changes in resonant frequency as a result of the increase in effective mass of the biosensor  30 . The increase in effective mass is attributed to the binding of the analyte  34  to the capture agent  32  disposed on the surface of the biosensor  30 . 
         [0033]    In step  104 , the concentration and change in concentration of the analyte  34  is determined by the detector. The detector calculates the concentration by measuring the change in the resonant frequency. The change in concentration of the analyte  34  is determined by calculating the rate of increase of the effective mass of the biosensor  30 . The rate of change of concentration of the analyte  34  is calculated by taking a second time derivative of the effective mass of the biosensor  30 . 
         [0034]    In step  106 , the detector transmits the signal relating to the mass change (e.g., change in resonant frequency) to the display of the monitor  20  to provide a clinician with real time analysis of the level of the analyte  34 . The signal may include, but is not limited to, an indicator that analyte  34  is present, an indicator of the concentration of the analyte  34 , and an indicator of the change in concentration of the analyte  34 . The clinician then compares the concentration of the analyte to a first predetermined clinical threshold to determine if a particular treatment is warranted. 
         [0035]    Further, the monitor  20  is also adapted to display the rate of change in the analyte concentration. The clinician compares the rate of change in analyte concentration to a second predetermined clinical threshold to determine if a particular treatment is warranted. The monitor  20  may optionally include automatic alarms to alert the clinician that the analyte concentration has exceeded one or more threshold values. 
         [0036]    While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. For example, it is envisioned that the biosensor and/or monitor could evaluate or perform an assay on other body fluid, tissues, enzymes etc. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.