Patent Publication Number: US-2018038820-A1

Title: Method and device for detection and quantification of analytes

Description:
TECHNICAL FIELD 
     The present disclosure relates to a microfluidic device for rapid, ultrasensitive and in situ detection and quantification of different target analytes such as clinically important biomarkers in food or agricultural samples, human or animal fluids, or any environmental complex matrices. The disclosure also relates to a method of using said device. 
     BACKGROUND 
     There are several approaches devised to separate and detect a biomolecule of interest from complex samples in a microfluidic environment, such a human fluids. 
     Patent application US 2006/0257958 A1 discloses a microfluidic chip for the detection of target analytes in environmental, food, animal or clinical body fluid samples. Detection using the microfluidic chip is based on a sandwich immunoassay according to which target analytes present in a complex sample are allowed to interact with capture reagent-magnetic beads in a first position. The resulting complexes are moved to a second position, by means of an external magnetic field, and along the way, the analytes are thus purified and concentrated. At the second position the captured target analytes on the surface of the magnetic beads interact with secondary or “reporter” reagent, such as fluorescent dye-, fluorophore-, fluorescent protein-, quantum dot (“QD”)-, nanoparticle-(“NP”), colloidal gold-, or enzyme-conjugated antibodies, nucleic acid aptamers or fluorescence resonance energy transfer (“FRET”) reagents such as FRET-aptamers or molecular beacons. In effect, a mobile or “rolling” sandwich assay is formed on the magnetic bead&#39;s surface. These reactants on the magnetic bead are further translated by the external magnetic field to a third position, which is a transparent miniature detection window for viewing of the resulting fluorescence or other visible reactions. 
     This microfluidic chip uses magnetic particles to trap the problem molecule and an external magnetic field to manipulate the sample along the chip allowing its manipulation, purification, and subsequent detection in different zones of the chip. 
     However, the sandwich immunoassay is done within the microfluidic chip increasing the need for more components and complicating its structure, like the microfluidic system which is complex. These aspects have a negative impact on the final cost of the microfluidic chip, the complexity of the method of using the chip and the cost of each measure. A further shortcoming of the assay can be seen in that the detection is based on optical measurements through a detection window, such as fluorescence, which needs a more complex and expensive detection hardware (light sources, filters, detection devices, . . . ) rising the global cost of the system and impeding its miniaturization and consequently its use as point-of-care (POC) device. 
     In view of the above there exists a need in the state of the art of providing an improved microfluidic device and method for the detection of a wide variety of analytes from complex fluid samples which overcomes at least part of these limitations. 
     SUMMARY 
     The present disclosure provides a device for detecting and quantifying an analyte in a complex sample which comprises: a disposable cartridge comprising: a microfluidic inlet for loading the sample to be tested, previously prepared, and therefore comprising the herein referred to as the reporter probe-analyte-capture probe-magnetic bead complexes, or for loading buffers, into the disposable cartridge; a purifying chamber for purifying the reporter probe-analyte-capture probe-magnetic bead complexes; a first microfluidic channel connecting the sample microfluidic inlet and the purifying chamber; a measure chamber comprising a chip comprising a working electrode, a reference electrode and a counter-electrode; a first waste microfluidic outlet for discharging residues derived from the purification of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the purifying chamber; a second waste microfluidic outlet for discharging waste products involved in the measuring process of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the measure chamber; a second microfluidic channel connecting purifying chamber and measure chamber; a first waste microfluidic channel connecting the second microfluidic channel to the first waste microfluidic outlet for discharging residues derived from the purification of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the purifying chamber; a second waste microfluidic channel connecting the measure chamber to the second waste fluid microfluidic outlet, for discharging residues involved in the measuring process of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the measure chamber; two external electromagnets situated one in front of the other, each on opposite sides of the purifying chamber which can be operated in a synchronized manner for retaining, or releasing or shaking the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber; a permanent magnet located under the working electrode of the measurement chamber, to attract and retain the reporter probe-analyte-capture probe-magnetic bead complexes on the surface of the working electrode of the chip; a potentiostat for carrying out the electrochemical detection and quantification of the analyte by electrochemical means; and an external microfluidic system. 
     The microfluidic device of the disclosure is a versatile tool that allows performing detection and quantification of a vast variety of analytes in complex samples such as environmental, food, animal or body fluid samples. The device of the disclosure has simplified microfluidics and structure with the subsequent fabrication cost reduction and assay performance enhancement. The reporter probe-analyte-capture probe-magnetic bead complexes preparation is advantageously carried out outside the disposable cartridge which allows a simpler cartridge design, with fewer chambers, fewer channels (and thus lower fabrication cost than other known cartridges of the art) and a reduced microfluidic actuation system (pump and valve system). Thus, just one prepared sample, containing the reporter probe-analyte-capture probe-magnetic bead complex, is introduced in the cartridge in the first place, and all the operations required are performed to the reporter probe-analyte-capture probe-magnetic bead complex contained therein, resulting in a sequential process, giving little room for errors and repetitiveness issues. 
     In a particular embodiment, the device of the disclosure further comprises a mechanical system to pick up the disposable cartridge, and place it in its proper position in the device, and make the microfluidic and electric connections. 
     In another particular embodiment, the device of the disclosure further comprises a control system for the automatization of all components of the device. 
     In another particular embodiment, the device of the disclosure further comprises a display. 
     In another particular embodiment, the device of the disclosure further comprises an outer casing. 
     The external microfluidic system comprises in a particular embodiment one or more microfluidic channels, one or more microfluidic connections, one or more pumps and one or more valves for manipulating the sample, buffers and residues. 
     The present disclosure also provides a method of using the device of the present disclosure for the detection and quantification of an analyte in a sample comprising the steps of: (a) loading the sample to be analyzed, magnetic beads coated with a capture probe and a reporter probe in a container to form a suspension comprising reporter probe-analyte-capture probe-magnetic bead complexes; (b) introducing the prepared sample (a resulting suspension) through the sample microfluidic inlet in the purifying chamber of the disposable cartridge; (c) purifying the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber by operating in a synchronized manner the two external electromagnets for retaining, releasing and shaking the reporter probe-analyte-capture probe-magnetic bead complexes present in the sample in the purifying chamber, (d) forwarding the purified reporter probe-analyte-capture probe-magnetic bead complexes resulting from previous step (c) through the second microfluidic channel to the measure chamber, (e) operating the permanent magnet to retain the reporter probe-analyte-capture probe-magnetic bead complexes on the working electrode surface of the chip, (f) detecting and quantifying the analyte (e.g. reporter probe-analyte-capture probe-magnetic bead complexes) by electrochemical means. 
     The method of the disclosure allows the detection and quantification of diverse analytes which can be present in complex samples with high efficacy and sensitivity. The method can be advantageously carried out in less steps than other known methods in the art, since the magnetic beads with the capture probes, the reporter probes and the samples eventually containing the analytes are put together in contact so that the reporter probe-analyte-capture probe-magnetic bead complexes are built in only one step. In addition detection and quantification is based on electrochemical means, a very accurate and sensitive detection technique, very cost effective and highly miniaturizable and portable, all of them essential characteristics in a POC device. 
     According to a particular embodiment, the purification of the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber comprises the steps of: (i) operating the two external electromagnets for retaining the reporter probe-analyte-capture probe-magnetic bead complexes on at least part of the inner surface of the purifying chamber, (ii) letting the rest of the sample present in the purifying chamber flow off, via the microfluidic channel and the first waste microfluidic outlet, (iii) loading buffer solution though the inlet into the purifying chamber, (iv) switching off the two external electromagnets for releasing the reporter probe-analyte-capture probe-magnetic bead complexes and re-suspending them in the buffer, (v) operating the two external electromagnets for shaking the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber, and (vi) optionally repeating steps (i) to (v) once or more times. 
     In a particular embodiment, the step of detecting and quantificating the analyte by electrochemical means is carried out by voltammetry, amperometry or impedance measurement techniques. 
     More particularly, step (f) of the method of using the device of the present disclosure comprises the following steps: connecting the chip to the potentiostat by electrical contacts; filling the measure chamber with buffer containing an electron transfer mediator substance; monitoring the initial electrochemical signal, launching the electrochemical detection procedure using the potentiostat; adding the substrate to trigger a redox reaction; recording electrochemical signal shift produced by a redox reaction; and translating resulting electrochemical signal shift in a numeric value on the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 : shows a schematic representation of a device of the present disclosure with a perspective view of the disposable cartridge and some of its components; and 
         FIG. 2 : shows a perspective view of the separated two halves of the disposable cartridge of the present disclosure before they build together the cartridge. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic representation of a device for detecting and quantifying an analyte in a sample according to a particular embodiment of the present disclosure. The device comprises a disposable cartridge  8 , two external (and opposed) electromagnets  13  and  13 ′, a permanent magnet  14 , a potentiostat  15 , and an external microfluidic system  18 . 
     The external microfluidic system  18  comprises one or more microfluidic channels, one or more microfluidic connections, one or more pumps and one or more valves for manipulating the sample, buffers, and fluid residues. In a particular embodiment the external microfluidic system  18  comprises two pumps. In another particular embodiment the extern microfluidic system  18  comprises a selection valve and an injection valve. 
     The disposable cartridge  8  comprises a microfluidic inlet  1 , a first microfluidic channel  9 , a purifying chamber  4 , a measure chamber  5  comprising a chip  6 , a second microfluidic channel  11 , a first waste microfluidic channel  10 , a first waste microfluidic outlet  2 , a second waste microfluidic channel  12 , and a second waste microfluidic outlet  3 . 
     Both waste microfluidic outlets  2  and  3  are connected to a waste container not shown in  FIG. 1 . 
     In the aforementioned cartridge  8  the microfluidic inlet is for loading the sample to be analyzed. The sample is prepared outside the device in a suitable container, such as a vial, and comprises after its preparation, provided that the analyte to be detected is present, the herein referred to as reporter probe-analyte-capture probe-magnetic bead complexes. The microfluidic inlet  1  is also for loading buffer into the cartridge. The sample comprising the reporter probe-analyte-capture probe-magnetic bead complexes is prepared by putting into contact a sample containing an analyte to be detected and quantified, magnetic beads coated with a capture probe which binds the analyte of interest through affinity mechanisms and a reporter probe which also binds said analyte of interest through affinity mechanisms. The sample comprising the reporter probe-analyte-capture probe-magnetic bead complexes flows from the inlet  1  through the first microfluidic channel  9  until the purifying chamber  4 . 
     In the aforementioned cartridge  8  the purifying chamber  4  is for purifying the reporter probe-analyte-capture probe-magnetic bead complexes from the rest of the components of the sample. This is achieved with the help of the two external electromagnets  13  and  13 ′ which can be operated in a synchronized manner for retaining, or releasing or shaking the reporter probe-analyte-capture probe-magnetic bead complexes present in the purifying chamber  4 . First the magnets are operated to retain the complexes at least on part of the inner surface of the purifying chamber  4 . Subsequently, the rest of the sample which is not retained flows through the microfluidic channels  11 ,  10 , and finally outside the cartridge  8  through the first waste microfluidic outlet  2 . This first waste microfluidic outlet  2  is for discharging residues derived from the purification of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the purifying chamber  4 . Fresh buffer solution may be again loaded though inlet  1  into the purifying chamber  4 . The two external electromagnets  13  and  13 ′ are then switched off for releasing the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber  4  rendering a suspension of the complexes in the fresh buffer. The two external electromagnets  13  and  13 ′ are then operated in a synchronized manner for shaking the suspension. Again the two external electromagnets  13  and  13 ′ can be operated to retain the complexes at least on part of the inner surface of the purifying chamber  4 . Subsequently, the rest of the buffer which is not retained flows through the microfluidic channels  11  and  10  and finally outside the cartridge  8  through the first waste microfluidic outlet  2 . Fresh buffer solution is loaded then though inlet  1  into the purifying chamber  4 . The two external electromagnets  13  and  13 ′ are then switched off for releasing the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber  4  rendering a suspension of the complexes in the fresh buffer. The two external electromagnets  13  and  13 ′ are then operated in a synchronized manner for shaking the suspension. 
     This combination of steps for the purification of the complexes can be repeated once or more times until the desired degree of purity is achieved. 
     In the aforementioned cartridge  8  the microfluidic channel  11  is for conducting the purified reporter probe-analyte-capture probe-magnetic bead complexes to the a measure chamber  5 . The measure chamber  5  is for measuring the analyte and comprises a chip  6  comprising a working electrode, a reference electrode and a counter-electrode. The electrodes may be made according to a particular embodiment of gold. 
     A second waste microfluidic channel  12  is for connecting the measure chamber  5  to a second waste microfluidic outlet  3 , for discharging residues involved in the measuring and sensing process of the reporter probe-analyte-capture probe-magnetic bead complexes carried out in the measure chamber  5 . 
     As schematically shown in  FIG. 2 , the disposable cartridge  8  is fabricated from two halves  16  and  17  typically composed of disposable plastic. The two halves  16  and  17  can be joined by way of heat (such as fusion, laser, welding, ultrasound, microwaves, solvents or other means of melting the halves together), or adhesives (such as pressure sensitive adhesives). In  FIG. 2 , the chip  6  comprising a working electrode, a reference electrode and a counter-electrode and the electrical contacts  7  can be seen. The chip is imprinted on the lower half of the cartridge by means of screen printing of thin film deposition or any other metal imprinting technique. The microfluidic channels are carved in the top half of the cartridge by any polymer fabrication techniques (mechanization, injection, hot embossing, laser, etc.). 
     The electrical contacts  7  are for connecting the chip  6  and the potentiostat  15  (not shown in  FIG. 2 ), which is the equipment for carrying out the electrochemical detection and quantification of the analyte by electrochemical means. 
     The permanent magnet  14  is for retaining the reporter probe-analyte-capture probe-magnetic bead complexes to allow its detection. According to a particular embodiment, as shown in  FIG. 1 , the permanent magnet  14  is situated under the working electrode and thus when the reporter probe-analyte-capture probe-magnetic bead complexes reach the measure chamber  5 , they are retained by the influence of permanent magnet  14  covering thus only the working electrode. 
     The potentiostat  15 , also shown in  FIG. 1 , is for carrying out the electrochemical detection and quantification of the analyte by electrochemical means. 
     The device of the disclosure comprises further components which are not shown in  FIG. 1 : like a mechanical system to pick up the disposable cartridge  8  and place it in its proper position in the device, and make the microfluidic and electric connections; a control system for the automatization of all components of the device; a display for showing the instructions of use to the operator, the assay steps or the results of the analysis; or an outer casing for integrating all components. 
     A method of using the device of the disclosure allows for the detection and quantification of an analyte in a sample. The method only requires a short assay time, very small target substance amounts, even trace quantities, and exhibits high sensitivity. This method, hereinafter also referred to as the method of the disclosure comprises the following steps: 
     (a) loading the sample to be analyzed, magnetic beads coated with a capture probe and a reporter probe in a container to form a suspension comprising the reporter probe-analyte-capture probe-magnetic bead complexes, 
     (b) introducing the resulting suspension through a sample microfluidic inlet  1  in the purifying chamber  4  of a disposable cartridge  8 ; 
     (c) purifying the reporter probe-analyte-capture probe-magnetic bead complexes in the purifying chamber  4  by operating in a synchronized manner the two external electromagnets  13  and  13 ′ for retaining, releasing and shaking the reporter probe-analyte-capture probe-magnetic bead complexes present in the sample in the purifying chamber  4 , 
     (d) forwarding the purified reporter probe-analyte-capture probe-magnetic bead complexes resulting from previous step (c) through the second microfluidic channel  11  to the measure chamber  5 , 
     (e) operating the permanent magnet  14  to retain the reporter probe-analyte-capture probe-magnetic bead complexes on the working electrode surface of the chip  6 , and 
     (f) detection and quantification of the analyte (e.g. reporter probe-analyte-capture probe-magnetic bead complexes) by electrochemical means. 
     Further advantages of the method of the disclosure are its high accuracy and reliability. 
     The samples that can be analyzed in accordance with embodiments of the disclosure include, without limitation, plasma, serum, urine, saliva, tear, whole blood, blood analogs, and liquid solution from dilution of solid biological matter or other biological fluids, such as milk, meat, fruit, vegetable, or any environmental sample potentially containing the analyte to be tested such as soil or water. 
     Analytes, without limitation, that can be detected and quantified in accordance with embodiments of the disclosure include, without limitation, proteins, protein fragments, antigens, antibodies, antibody fragments, peptides, DNA, RNA, DNA fragments, RNA fragments, or any other molecular target of interest from complex samples. 
     Any magnetic beads that respond to a magnetic field may be employed in the devices and methods of the disclosure. Desirable beads are those that have surface chemistry that can be chemically or physically modified, e.g., by chemical reaction, physical adsorption, entanglement, or electrostatic interaction. 
     Capture probes can be bound to magnetic beads coating them by any means known in the art. Examples include chemical reaction, physical adsorption, entanglement, or electrostatic interaction. How the capture probe binds to the magnetic bead will depend on the nature of the analyte targeted. Examples of capture probes in accordance with embodiments of the disclosure include, without limitation, proteins (such as antibodies), DNA, RNA, PNA or similar nucleic acid based probes for DNA or RNA, aptamers, molecularly imprinted polymers or any other molecule capable of binding efficiently and specifically to the analyte of interest. 
     Reporter probes are in principle any chemical species capable of binding efficiently and specifically to the analyte of interest and are labeled with a molecule capable of producing a redox reaction, usually a redox enzyme such as horseradish peroxidase or alkaline phosphatase. Examples in accordance with embodiments of the disclosure include, without limitation, proteins (such as antibodies), DNA, RNA, PNA or similar nucleic acid based probes for DNA or RNA, aptamers, molecularly imprinted polymers or any other molecule capable of binding efficiently and specifically to the analyte of interest. 
     By “specifically binding” to the analyte is meant binding analytes by a specified mechanism, e. g., antibody-antigen interaction, ligand-receptor interaction, nucleic acid complementarity, protein-protein interaction, charge-charge interaction, and hydrophobic-hydrophobic or hydrophilic-hydrophilic interactions. “Efficiently” means that the strength of the bond is enough to prevent detachment by the flow of fluid present when analytes are bound, although individual analytes may occasionally detach under normal operating conditions. 
     One remarkable advantage of the method of the disclosure can be seen in that the samples to be tested containing the analyte are prepared in one single, simple step, outside the disposable cartridge of the device used for carrying out the method of the present disclosure. Accordingly, the reporter probe and magnetic beads coated with capture probes are provided together in an adequate container such as a vial. As long as no target molecule is present, these two components remain separated. At the beginning of the assay, the sample is added to this vial, and if the analyte is present in the sample, the reporter probe-analyte-capture probe-magnetic bead complex is thus obtained. The reporter probe and the capture probe can be readily selected by the skilled person in the art depending on the analyte to be detected in each case. The molecule capable of producing a redox reaction for labeling the reporter probe and the magnetic bead can also be selected by the skilled person in each case without the need of any inventive step. 
     According to a particular embodiment, the analyte to be detected is an antigen. Magnetic beads are coated with a capture probe which is a first antigen specific monoclonal antibody (Ab1) binding to a first region (first epitope) of the antigen; the reporter probe is a second antigen specific polyclonal antibody (Ab2) binding to a second region of the antigen and labeled with a redox enzyme. 
     The suspension of complexes is introduced through the sample microfluidic inlet  1  in the purifying chamber  4  of the disposable cartridge  8 . In the purifying chamber  4  the reporter probe-analyte-capture probe-magnetic bead complexes are purified, thus separated from the rest of the sample. In accordance with embodiments of the disclosure the purification is done as follows with the help of the two external electromagnets  13  and  13 ′. The two external electromagnets  13  and  13 ′ are operated for retaining the reporter probe-analyte-capture probe-magnetic bead complexes on at least part of the inner surface of the purifying chamber  4 . While the complexes are retained, the rest of the sample of no interest flows off via the microfluidic channel  10  and through the first waste microfluidic outlet  2  outside the cartridge for example into a waste container. A buffer solution is loaded though the inlet  1  into the purifying chamber  4 , and then the two external electromagnets  13  and  13 ′ are switched off for releasing the reporter probe-analyte-capture probe-magnetic bead complexes from the inner wall, resulting in a suspension of the complexes in the fresh buffer. The two external electromagnets are operated for shaking the reporter probe-analyte-capture probe-magnetic bead complexes in suspension present in the purifying chamber  4 , which helps dispersing the complexes in the buffer and favors its cleaning process. The previous steps may then be repeated to further increase the purification degree of the complexes. 
     Thus, the two external electromagnets  13  and  13 ′ may again be operated for retaining the reporter probe-analyte-capture probe-magnetic bead complexes on at least part of the inner surface of the purifying chamber  4 . While the complexes are retained, the rest of the buffer flows off via the microfluidic channel  10  and through the first waste microfluidic outlet  2  outside the cartridge for example into a waste container. Fresh buffer solution is loaded though the inlet  1  into the purifying chamber  4 , and then the two external electromagnets  13  and  13 ′ are switched off for releasing the reporter probe-analyte-capture probe-magnetic bead complexes from the inner wall, resulting in a suspension of the complexes in the fresh buffer. The two external electromagnets are operated for shaking the reporter probe-analyte-capture probe-magnetic bead complexes in suspension present in the purifying chamber  4 . 
     When the complexes are considered to be pure enough a suspension comprising them is forwarded to measure chamber  5  though microfluidic channel  11 . 
     Detection and quantification of the analyte (e.g. reporter probe-analyte-capture probe-magnetic bead complexes) is carried out by electrochemical means with a potentiostat  15 . Voltammetry, amperometry or impedance measurement techniques can be used. These techniques are based on the application of an electrical potential and the measurement of the produced electrical current, such as voltammetries (cyclic voltammetry, linear sweep voltammetry, differential pulse voltammetry, or square wave voltammetry), amperometries (chrono amperometry) or impedance measurements. 
     Despite the fact that a great variety of different electrochemical measurement techniques fit the needs of the detection procedure, according to a particular embodiment, amperometric measurement is used. 
     In accordance with the embodiments disclosed herein, the method includes the following steps:
         Connecting the chip  6  to the potentiostat  15  by electrical contacts  7 ;   Filling the measure chamber  5  with buffer containing an electron transfer mediator substance,   Monitoring the initial electrochemical signal, launching the electrochemical detection procedure using the potentiostat,   Adding the substrate to trigger a redox reaction,   Recording electrochemical signal shift produced by a redox reaction, and   Translating resulting electrochemical signal shift in a numeric value on the display.       

     When complexes reach the measure chamber  5  the permanent magnet  14  retains the reporter probe-analyte-capture probe-magnetic bead complexes to allow its detection. According to a particular embodiment, the permanent magnet  14  is situated under the working electrode and thus when the reporter probe-analyte-capture probe-magnetic bead complexes reach the measure chamber they are retained by magnet  14  on the working electrode. The buffer is consequently eliminated via microfluidic channel  12  and through waste microfluidic outlet  3 , for example, to a waste container. Then, the measure chamber  5  is filled with buffer comprising an electron transfer mediator substance, which is introduced though the microfluidic inlet  1 . 
     The electron transfer mediator substances that can be used are active charge-carrier substances that act as intermediates, enabling electrical contacting between the electrode surface and the active center of redox enzymes, such as ferrocene or hydroquinone. 
     The substrate that can be used to trigger the redox reaction is any chemical species upon which the enzyme acts, catalyzing chemical reactions involving the substrate. The substrate is specific to the enzyme used to label the reporter probe, for example hydrogen peroxide for the horseradish peroxidase. 
     To perform an amperometric measurement according to a particular embodiment of the disclosure, the reporter probe-analyte-capture probe-magnetic bead complex is captured onto the measurement chip working electrode by means of the permanent magnet situated exactly under. The measurement chamber is then filled with a buffer solution (like phosphate solution), containing the electrochemical mediator substance (hydroquinone, for example), but not the enzymatic substrate. The potentiostat, connected to the chip, is switched on and the amperometric signal (electrical current) is monitored while applying an electrical potential (vs. the reference electrode). After obtaining a stable signal (baseline), a buffer change is performed. This new buffer is the same used in the recording of a baseline, but with the addition of a given concentration the enzymatic substrate. When this new buffer containing the enzymatic substrate fills the measurement chamber, the enzymatic redox reaction is triggered and a current change induced. This current change is proportional to the amount of enzyme captured on the magnetic beads which at the same time is proportional to the analyte concentration present in the sample. Thus, the monitored current change is used to calculate the analyte concentration present in the sample. This electrical signal is translated to a numerical value and presented to the user via the display situated in the outer casing of the device.