Patent ID: 12241851

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present disclosure is related to systems and methods for processing measurement signals obtained from analyte detection using magnetoresistive sensor technologies. For explanatory purposes, in accordance with embodiments, the devices, systems, and features are described with respect to utilizing GMR sensors.

As evident by the drawingsFIGS.1-4and the accompanying description, the signal processing technique in this disclosure may be used in a sample handling system (or “system” as noted throughout this disclosure) which may be used for detecting presence of an analyte (or analytes) such as metal, biomarkers, and the like, in a sample. In an embodiment, this system, depicted as system300inFIG.3, may include (1) a sample handling system or “cartridge assembly” that includes sample preparation microfluidic channel(s) and at least one sensing device (or sensor) for sensing biomarkers in a test sample, and (2) a data processing and display device or “cartridge reader unit” that includes a processor or controller for processing any sensed data of the sensing device of the cartridge assembly and a display for displaying a detection event. Together these two components make up the system. In an embodiment, these components may include variable features including, without limitation, one or more reagent cartridges, a cartridge for waste, and a flow control system which may be, for example, a pneumatic flow controller.

Generally, the process for preparing a sample in the cartridge assembly, in order for detection of analytes, biomarkers, etc. to happen by the assembly and output via the cartridge reader unit, is as-follows: A raw patient sample is loaded onto a card, optionally filtered via a filter membrane, after which a negative pressure generated by off-card pneumatics filters the sample into a separated test sample (e.g., plasma). This separated test sample is quantitated on-card through channel geometry. The sample is prepared on card by interaction with mixing materials (e.g., reagent(s) (which may be dry or wet), buffer and/or wash buffer, beads and/or beads solution, etc.) from a mixing material source (e.g., blister pack, storage chamber, cartridge, well, etc.) prior to flow over the sensor/sensing device. The sample preparation channels may be designed so that any number of channels may be stacked vertically in a card, allowing multiple patient samples to be used. The same goes for sensing microfluidic devices, which may also be stacked vertically. A sample preparation card, which is part of the cartridge assembly, includes one or more structures providing functionalities selected from filtering, heating, cooling, mixing, diluting, adding reagent, chromatographic separation and combinations thereof; and a means for moving a sample throughout the sample preparation card. Further description regarding these features is provided later below.

FIG.1shows an example of a cartridge reader unit100, used in system300(seeFIG.3) in accordance with an embodiment. The cartridge reader unit100may be configured to be compact and/or small enough to be a hand-held, mobile instrument, for example. The cartridge reader unit100includes a body or housing110that has a display120and a cartridge receiver130for receiving a cartridge assembly. The housing110may have an ergonomic design to allow greater comfort if the reader unit100is held in an operator's hand. The shape and design of the housing110is not intended to be limited, however.

The cartridge reader unit100may include an interface140and a display120for prompting a user to input and/or connect the cartridge assembly200with the unit and/or sample, for example. In accordance with an embodiment, in combination with the disclosed cartridge assembly200, the system300may process, detect, analyze, and generate a report of the results, e.g., regarding multiple detected biomarkers in a test sample, e.g., five cardiac biomarkers, using sensor (magnetoresistive) technology, and further display the biomarker results, as part of one process.

The display120may be configured to display information to an operator or a user, for example. The display120may be provided in the form of an integrated display screen or touch screen (e.g., with haptics or tactile feedback), e.g., an LCD screen or LED screen or any other flat panel display, provided on the housing110, and (optionally) provides an input surface that may be designed for acting as end user interface (UI)140that an operator may use to input commands and/or settings to the unit100, e.g., via touching a finger to the display120itself. The size of the display120may vary. More specifically, in one embodiment, the display120may be configured to display a control panel with keys, buttons, menus, and/or keyboard functions thereon for inputting commands and/or settings for the system300as part of the end user interface. In an embodiment, the control panel includes function keys, start and stop buttons, return or enter buttons, and settings buttons. Additionally and/or alternatively, although not shown inFIG.1, the cartridge reader100may include, in an embodiment, any number of physical input devices, including, but not limited to, buttons and a keyboard. In another embodiment, the cartridge reader100may be configured to receive input via another device, e.g., via a direct or wired connection (e.g., using a plug and cord to connect to a computer (PC or CPU) or a processor) or via wireless connection. In yet another embodiment, display120may be to an integrated screen, or may be to an external display system, or may be to both. Via the display control unit120, the test results (e.g., from a cartridge reader310, described with reference toFIG.3, for example) may be displayed on the integrated or external display. In still yet another embodiment, the user interface140may be provided separate from the display120. For example, if a touch screen UI is not used for display120, other input devices may be utilized as user interface140(e.g., remote, keyboard, mouse, buttons, joystick, etc.) and may be associated with the cartridge reader100and/or system300. Accordingly, it should be understood that the devices and/or methods used for input into the cartridge reader100are not intended to be limiting. All functions of the cartridge reader100and/or system300may, in one embodiment, be managed via the display120and/or input device(s), including, but not limited to: starting a method of processing (e.g., via a start button), selecting and/or altering settings for an assay and/or cartridge assembly200, selecting and/or settings related to pneumatics, confirming any prompts for input, viewing steps in a method of processing a test sample, and/or viewing (e.g., via display120and/or user interface140) test results and values calculated by the GMR sensor and control unit/cartridge reader. The display120may visually show information related to analyte detection in a sample. The display120may be configured to display generated test results from the control unit/cartridge reader. In an embodiment, real-time feedback regarding test results that have been determined/processed by the cartridge reader unit/controller (by receiving measurements from the sensing device, the measurements being determined as a result of the detected analytes or biomarkers), may be displayed on the display120.

Optionally, a speaker (not shown) may also be provided as part of the cartridge reader unit100for providing an audio output. Any number of sounds may be output, including, but not limited to speech and/or alarms. The cartridge reader unit100may also or alternatively optionally include any number of connectors, e.g., a LAN connector and USB connector, and/or other input/output devices associated therewith. The LAN connector and/or USB connector may be used to connect input devices and/or output devices to the cartridge reader unit100, including removable storage or a drive or another system.

In accordance with an embodiment, the cartridge receiver130may be an opening (such as shown inFIG.1) within the housing110in which a cartridge assembly (e.g., cartridge assembly200ofFIG.2) may be inserted. In another embodiment, the cartridge receiver130may include a tray that is configured to receive a cartridge assembly therein. Such a tray may move relative to the housing110, e.g., out of and into an opening therein, and to thereby receive the cartridge assembly200and move the cartridge assembly into (and out of) the housing110. In one embodiment, the tray may be a spring-loaded tray that is configured to releasably lock with respect to the housing110. Additional details associated with the cartridge reader unit100are described later with respect toFIG.3.

As previously noted, cartridge assembly200may be designed for insertion into the cartridge reader unit100, such that a sample (e.g., blood, urine) may be prepared, processed, and analyzed.FIGS.2A-2Cillustrate an exemplary embodiment of a cartridge assembly200in accordance with embodiments herein. Some general features associated with the disclosed cartridge assembly200are described with reference to these figures. However, as described in greater detail later, several different types of cartridge cards and thus cartridge assemblies may be utilized with the cartridge reader unit100and thus provided as part of system300. In embodiments, the sampling handling system or cartridge assembly200may take the form of disposable assemblies for conducting individual tests. That is, as will be further understood by the description herein, depending on a type of sample and/or analytes being tested, a different cartridge card configuration(s) and/or cartridge assembly(ies) may be utilized.FIG.2Ashows a top, angled view of a cartridge assembly200, in accordance with an embodiment herein. The cartridge assembly200includes a sample processing card210and a sensing and communication substrate202(see alsoFIG.2B). Generally, the sample processing card210is configured to receive the sample (e.g., via a sample port such as injection port, also described below) and, once inserted into the cartridge reader unit100, process the sample and direct flow of the sample to produce a prepared sample. Card210may also store waste from a sample and/or fluids used for preparing the test sample in an internal waste chamber(s) (not shown inFIG.2A, but further described below). Memory chip275may be read and/or written to and is used to store information relative to the cartridge application, sensor calibration, and sample processing required, for example. In an embodiment, the memory chip275is configured to store a pneumatic system protocol that includes steps and settings for selectively applying pressure to the card210of the cartridge assembly200, and thus implementing a method for preparation of sample for delivery to a magnetoresistive or magnetoresistance sensor (e.g., GMR sensor chip280). The memory chip may be used to mistake-proof each cartridge assembly200inserted into the unit100, as it includes the automation recipe for each assay. The memory chip275also contain traceability to the manufacturing of each card210and/or cartridge assembly200. The sensing and communication substrate202may be configured to establish and maintain communication with the cartridge reader unit100, as well as receive, process, and sense features of the prepared sample. The substrate202establishes communication with a controller in the cartridge reader unit100such that analyte(s) may be detected in a prepared sample. The sample processing card210and the sensing and communication substrate202(see, e.g.,FIG.2B) are assembled or combined together to form the cartridge assembly200. In an embodiment, adhesive material (see, e.g.,FIG.2D) may optionally be used to adhere the card210and substrate202to one another. In an embodiment, the substrate202may be a laminated layer applied to the sample processing card210. In one embodiment, the substrate202may be designed as a flexible circuit that is laminated to sample processing card210. In another embodiment, the sample processing card210may be fabricated from a ceramic material, with the circuit, sensor (sensor chip280) and fluid channels integrated thereon. Alternatively, the card210and substrate202may be mechanically aligned and connected together. In one embodiment, a portion of the substrate202may extend from an edge or an end of the card210, such as shown inFIG.2A. In another embodiment, such as shown inFIG.2B, the substrate202may be aligned and/or sized such that it has similar or smaller edges than the card210.

FIG.2Cschematically illustrates features of the cartridge assembly200, in accordance with an embodiment. As shown, some of the features may be provided on the sample processing card210, while other may be associated with the substrate202. Generally, to receive a test sample (e.g., blood, urine) (within a body of the card), the cartridge assembly200includes a sample injection port215, which may be provided on a top of the card210. Also optionally provided as part of the card210are filter220(also referred to herein as a filtration membrane), vent port225, valve array230(or valve array zone230), and pneumatic control ports235. Communication channels233are provided within the card210to fluidly connect such features of the card210. Pneumatic control ports235are part of a pneumatic interface on the cartridge assembly200for selectively applying pressurized fluid (air) to the communication channels233of the card, for directing flow of fluids (air, liquids, test sample, etc.) therein and/or valve array230. Optionally, the card210may include distinct valve control ports535connected to designated communication channels233for controlling the valves in the valve array230. The card210may also have one or more metering chambers240, gas permeable membranes245, and mixing channels250that are fluidly connected via communication channels233. Metering chamber(s) are designed to receive at least the test sample (either directly or filtered) therein via communication channels233. Generally, a sample may be injected into the cartridge assembly200through port215and processed by means of filtering with filter (e.g., filter220), metering in metering chamber(s)240, mixing in mixing channel(s)250, heating and/or cooling (optional), and directing and changing the flow rate via communication channels233, pneumatic control ports235, and valve array230. For example, flow of the fluid may be controlled using internal micro fluidic channels (also generally referred to as communication channels233throughout this disclosure) and valves via a connection of a pneumatic system (e.g., system330in the cartridge reader unit100, as shown inFIG.3) and a pneumatic interface e.g., on the card210that has pneumatic control ports235or a similar connection section. Optional heating of the test sample and/or mixing materials/fluids within the card210may be implemented, in accordance with an embodiment, via a heater259which may be in the form of a wire trace provided on a top side of a PCB/substrate202with a thermistor. Optional cooling of the test sample and/or mixing materials/fluids within the card210may be implemented, in accordance with an embodiment, via a TEC module integrated in the cartridge assembly200(e.g., on the substrate202), or, in another embodiment, via a module integrated inside of the cartridge reader unit100. For example, if the cooling module is provided in the unit100, it may be pressed against the cartridge assembly200should cooling be required. Processing may also optionally include introduction of reagents via optional reagent sections260(and/or blister packs) on the card210and/or via reagent cartridges in the housing110the cartridge reader unit100. Reagents may be released or mixed as required by the process for that sample and the cartridge assembly200being analyzed. Further, optional blister packs265may be provided on the card210to introduce materials such as reagents, eluants, wash buffers, magnetic nano particles, bead solution, or other buffers to the sample via communication channels233during processing. One or more internal waste chambers (also referred to herein as waste tanks for waste reservoirs)270may also be optionally provided on the card210to store waste from the sample and reagents. An output port255—also referred to as a sensor delivery port, or input port to the sensor—is provided to output a prepared sample from the card210to a GMR sensor chip280, as discussed below, for detecting analytes in the test sample. The output port255may be fluidly connected to a metering chamber for delivering the test sample and one or more mixing materials to the sensor. Accordingly, the sensor may be configured to receive the test sample and the one or more mixing materials via the at least one output port255. In embodiments, an input port257—also referred to as a waste delivery port, or output port from the sensor—is provided to output any fluid or sample from the GMR sensor chip280to a waste chamber270. Waste chamber(s)270may be fluidly connected to other features of the card210(including, for example, metering chamber(s)240, an input port257, or both) via communication channels233.

The cartridge assembly200has the ability to store, read, and/or write data on a memory chip275, which may be associated with the card210or the substrate202. As noted previously, the memory chip275may be used to store information related and/or relative to the cartridge application, sensor calibration, and required sample processing (within the sample processing card), as well as receive additional information based on a prepared and processed sample. The memory chip275may be positioned on the sample processing card210or on the substrate200.

As previously noted, a magnetoresistive sensor may be utilized, in accordance with embodiments herein, to determine analytes (such as biomarkers) within a test sample using the herein disclosed system. While the description and Figures note use of a particular type of magnetoresistance sensor, i.e., a giant magnetoresistance (GMR) sensor, it should be understood that this disclosure is not limited to a GMR sensor platform. In accordance with some embodiments, the sensor may be an anisotropic magnetoresistive (AMR) sensor and/or magnetic tunnel junction (MTJ) sensors, for example. In embodiments, other types of magnetoresistive sensor technologies may be utilized. Nonetheless, for explanatory purposes only, the description and Figures reference use of a GMR sensor as a magnetoresistive sensor.

The substrate202of cartridge assembly200may be or include an electronic interface and/or a circuit interface such as a PCB (printed circuit board) that may have a giant magnetoresistance (GMR) sensor chip280and electrical contact pads290(or electrical contact portions) associated therewith. Other components may also be provided on the substrate202. The GMR sensor chip280is attached at least to the substrate202, in accordance with an embodiment. The GMR sensor chip280may be placed on and attached to the substrate202using adhesive, for example. In an embodiment, a liquid adhesive or a tape adhesive may be used between the GMR sensor280and the PCB substrate202. Such a design may require a bond to the PCB at the bottom and a bond to the processing card at the top, for example. Alternatively, other approaches for attaching the GMR sensor chip280to the substrate202include, but are not limited to: friction fitting the GMR sensor to the PCB, and connecting a top of the GMR sensor chip280directly to the sample processing card210(e.g., in particular when the substrate202is provided in the form of a flexible circuit that is laminated (to the back) of sample processing card210. The GMR sensor chip280may be designed to receive a prepared sample from the output port255of the sample processing card210. Accordingly, placement of the GMR sensor chip280on the substrate may be changed or altered based on a position of the output port255on card210(thus, the illustration shown inFIG.2Bis not intended to be limiting)—or vice versa. In an embodiment, the GMR sensor chip280is positioned on a first side of the substrate202(e.g., a top side that faces an underside of the card210, as shown inFIG.2B), e.g., so as to receive the prepared sample from an output port that outputs on an underside of the card210, and the contact pads290are positioned on an opposite, second side of the substrate (e.g., on a bottom side or underside of the substrate202, such that the contact pads290are exposed on a bottom side of the cartridge assembly200when fully assembled for insertion into the cartridge reader unit100). The GMR sensor chip280may include its own associated contact pads (e.g., metal strips or pins) that are electrically connected via electronic connections on the PCB/substrate202to the electrical contact pads290provided on the underside thereof. Accordingly, when the cartridge assembly200is inserted into the cartridge reader100, the electrical contact pads290are configured to act as an electronic interface and establish an electrical connection and thus electrically connect with electronics (e.g., cartridge reader310) in the cartridge reader unit100. Thus, any sensors in the sensor chip280are connected to the electronics in the cartridge reader unit100through the electrical contact pads290and contact pads of the GMR sensor chip280.

FIG.2Dshows a view of an exemplary cross section of a mating or connection interface of card210and substrate202. More specifically,FIG.2Dillustrates an interface, in accordance with one embodiment, between an output port255on the card210and GMR sensor chip280of the substrate202. For example, shown is a PCB substrate202positioned below and adjacent to a card210according to any of the herein disclosed embodiments. The substrate202may be attached to bottom surface of the card210. The card210has a channel feature, labeled here as microfluidic channel433(which is one of many communication channels within the card210), in at least one layer thereof, designed to direct a test sample that is processed within the card210to an output port255directed to GMR sensor280. Optionally, adhesive material may be provided between layers of the card210, e.g., adhesive434A may be provided between a layer in the card that has reagent ports434B and a layer with the channel433. The substrate202includes a GMR sensor chip280that is positioned adjacent to the channel433and output port255of the card210.

Magnetic field (from a magnetic field generator365that is different than magnetic field generator360, described below with reference toFIG.3) may be used to excite the nano magnetic particles located near sensors.

Referring now toFIG.3, additional features of the cartridge reader unit100are schematically shown to further describe how the cartridge reader unit100and cartridge assembly200are configured to work together to provide the system300for detecting analyte(s) in a sample. As depicted, the cartridge assembly200may be inserted into the housing110of the cartridge reader unit100. Generally, the housing110of the cartridge reader unit100may further include or contain a processor or control unit310, also called a “controller” and/or a “cartridge reader”310here throughout, a power source320, a pneumatic system330, a communications unit340, a (optional) diagnostic unit350, a magnetic field generator360, and a memory370(or data storage), along with its user interface140and/or display120. Optionally, a reagent opener (not shown inFIG.3), e.g., for opening a reagent source on an inserted cartridge assembly or for introducing reagent into the cartridge assembly (e.g., if the reagent is not contained in the assembly in a particular reagent section), may also be provided as part of the cartridge reader unit100. Once a cartridge assembly200is inserted into the housing110of the cartridge reader unit100, and the electrical and pneumatics system(s) are connected, and the cartridge memory chip275may be read from the cartridge assembly200(e.g., read by cartridge reader310/control unit, or PCB assembly, in the unit100) to determine the pneumatic system protocol that includes steps and settings for selectively applying pressure to the card210of the cartridge assembly200, and thus implementing a method for preparation of sample for delivery to a sensor (e.g., GMR sensor chip280), and thus the sample placed in the assembly200may be prepped, processed, and analyzed. The control unit or cartridge reader310may control inputs and outputs required for automation of the process for detecting the analyte(s) in a sample. The cartridge reader310may be a real-time controller that is configured to control, among other things, the giant magnetic resistance (GMR) sensor chip280and/or memory chip275associated with the cartridge assembly200and the pneumatic system330within the housing110, as well as the controls from user interface, driving the magnetic field generator360, and receiving and/or sending signals from/to sensor chip and/or memory associated with the cartridge assembly200, for example. In an embodiment, the cartridge reader310is provided in the form of a PCB (printed circuit board) which may include additional chips, memory, devices, therein. The cartridge reader310may be configured to communicate with and/or control an internal memory unit, a system operation initializer, a signal preparing unit, a signal preparing unit, a signal processing unit, and/or data storage (none of which are shown in the Figures), for example. The cartridge reader310may also be configured to send and receive signals with respect to the communications unit340such that network connectivity and telemetry (e.g., with a cloud server) may be established, and non-volatile recipes may be implemented, for example. Generally, the communications unit340allows the cartridge reader unit100to transmit and receive data using wireless or wired technology. Power can be supplied to the cartridge reader unit100via power source320in the form of an internal battery or in the form of a connector that receives power via an external source that is connected thereto (e.g., via a cord and a plug). Power source320is configured to supply power to parts of the cartridge reader unit100, when activated and/or when a cartridge assembly200is mated with the unit100. For example, power source320may supply power to the control unit and PCB assembly560of cartridge reader310, magnetic field generator360, display120and/or user interface140, and pneumatic system330(including, for example, any motors, valves, and/or pumps associated therewith). Power source320may be at least one internally mounted battery pack320, in accordance with an embodiment herein. The pneumatic system330is used to process and prepare a sample (e.g., blood, urine) placed into the cartridge assembly200by means of moving and directing fluids inside and along the sample processing card210(e.g., via pneumatic connection235, through its channels and connecting to direct elastomeric valves). The pneumatic system330may be a system and/or device for moving fluid, which could use, for example, plungers and/or pistons in contact with fluids. The magnetic field generator360may be an external magnetic coil or other field generating device that is mounted in the unit100or integrated in some fashion with one or more of the chips (e.g., sensor chip280) provided on the cartridge assembly200or provided on the circuit board of the cartridge reader unit100. The magnetic field generator360is used to stimulate magnetic nanoparticles near the GMR sensor chip280while reading the signal. In accordance with embodiments, a second magnetic field generator365, which may be a coil or other field generating device, may be provided as part of the cartridge reader unit100and in the housing110. For example, in accordance with an embodiment, the second magnetic field generator365may be separate and distinct from magnetic field generator360. This second magnetic field generator365may be configured to generate a non uniform magnetic field such that it may apply such a magnetic field to a part (e.g., top, bottom, sides) of the sample processing card210of an assembly200during preparation and processing of a sample, e.g., when moving mixing material(s), such as a buffer and/or magnetic beads from a mixing material source, and test sample within the card. In an embodiment, the second magnetic field generator365is provided on an opposite end or side of the cartridge reader unit (e.g., located in a top of the housing110of unit100), i.e. away from the magnetic field generator360, which is used for GMR sensing. In one embodiment, the second magnetic field generator365is provided on an opposite end of the cartridge reader unit as compared to the magnetic field generator360(e.g., second magnetic field generator is located in a top of the housing110of unit100and magnetic field generator360is provided at a bottom end of the unit100(e.g., near cartridge receiver130)). In an embodiment, the total magnetic field for sensing biomarkers includes an applied field from magnetic field generator360(either external or integrated with the sensor chip) along with any disturbance from magnetic nanoparticles near the GMR sensor chip280. The reagent opener is optionally used to introduce reagents during the sample processing and reading of the GMR sensor chip280(e.g., if the reagent is not contained in the card in a particular reagent section). As described previously, the user interface/display120allows an operator to input information, control the process, provide system feedback, and display (via an output display screen, which may be a touch screen) the test results.

FIG.4shows general steps of a method400for performing analyte detection in a sample using the herein disclosed system300. At step410, the system is initialized. For example, initialization of the system may include: applying power to the system300(including cartridge reader unit100), determining configuration information for the system, reading computations, determining that features (e.g., magnetic field generator and carrier signals) are online and ready, etc. At step415, a whole test sample is added or loaded into the cartridge assembly200(e.g., sample is injected into the injection port215, as shown inFIG.2C). The order of steps410and415may be changed; i.e., the addition of the whole test sample to the assembly200may be before or after the system is initialized. At step420, the cartridge assembly200is inserted into the cartridge reader unit100. Optionally, as part of method400, user instruction may be input to the cartridge reader unit100and/or system300via the user interface/display120. Then, at step425, the processing of sample is initiated via the control unit310. This initiation may include, for example, receiving input via an operator or user through the user interface/display120and/or a system that is connected to the reader unit100. In another embodiment, processing may be initiated automatically via insertion of the cartridge assembly200into the cartridge reader unit100and detecting presence of the cartridge assembly200therein (e.g., via electrical connection between electrical contact pads290on the assembly200with the control unit310, and automatically reading instructions from memory chip275). The sample is processed at step425using pneumatic control instructions (e.g., obtained from memory chip275) in order to produce a prepared sample. As generally described above (and further later below), the processing of the sample may be dependent upon the type of sample and/or the type of cartridge assembly200inserted into the reader unit100. In some cases, the processing may include a number of steps, including mixing, introduction of buffers or reagents, etc., before the sample is prepared. Once the sample is prepared, the prepared sample is sent (e.g., through channels in the card210and to output port255, via pneumatic control through pneumatic system330and control unit310) to the GMR sensor chip280. At step440, analytes in the prepared sample are detected at the GMR sensor chip280. Then, at step445, signals from the GMR sensor chip280are received and processed, e.g., via cartridge reader310(control unit; which may include one or more processors, for example). Once the signals are processed, test results may be displayed at450, e.g., via the display120/user interface. At455, test results are saved. For example, test results may be saved in a cloud server and/or memory chip275on board the cartridge assembly200. In embodiments, any fluids or sample may be directed from the GMR sensor chip280through an input port257to waste chamber270. Thereafter, once all tests are preformed and read by the sensing device/GMR sensor chip280, the cartridge assembly200may be ejected from the cartridge reader unit100. In accordance with an embodiment, this may be automatically performed, e.g., mechanics within the housing110of the cartridge reader unit100may push the assembly200out of the housing110, or performed manually (by way of a button or force) by the operator, for example.

In an embodiment, the system300described herein may utilize a pneumatic control system as disclosed in International Patent App. No. PCT/US2019/043720, entitled “SYSTEM AND METHOD FOR GMR-BASED DETECTION OF BIOMARKERS” filed Jul. 26, 2019, which is hereby incorporated by reference herein in its entirety.

In an embodiment, the system300described herein may utilize a cartridge assembly (e.g., for sample preparation and delivery to the sensor(s)) as disclosed in International Patent App. No. PCT/US2019/043753, entitled “SYSTEM AND METHOD FOR SAMPLE PREPARATION IN GMR-BASED DETECTION OF BIOMARKERS” filed Jul. 26, 2019, which is hereby incorporated by reference herein in its entirety.

In an embodiment, the system300described herein may sense analytes as disclosed in International Patent App. No. PCT/US2019/043766, entitled “SYSTEM AND METHOD FOR SENSING ANALYTES IN GMR-BASED DETECTION OF BIOMARKERS” filed Jul. 26, 2019, which is hereby incorporated by reference herein in its entirety. For example, in an embodiment, the sensing device, or GMR sensor chip280, may include one or more microfluidic channels and a plurality of sensor pads disposed within the one or more microfluidic channels as disclosed in the -0504848 application. In an embodiment, such a channel may optionally include a plurality of GMR sensors disposed within a channel. GMR sensors may be all identically configured to detect a single analyte, the redundancy allowing for enhanced detection. GMR sensors may also be all configured differently to detect a myriad of analytes or a combination of differently configured sensors with some redundancies. The configuration of the channel is not limiting. Collectively, the GMR sensors in the channel may be designed to provide the output (test results) from the GMR sensor chip280.

It should be understood that, with regards toFIGS.1and2A-2D, the features shown are representative schematics of a cartridge reader unit100and cartridge assembly200that are part of the herein disclosed system300for detecting the analyte(s) in a sample. Accordingly, the illustrations are explanatory only and not intended to be limiting.

Referring now toFIG.5Athere is shown an exemplary channel500in accordance with some embodiments. Channel500is shown as serpentine in structure, but it need not be so limited in geometry. Channel500comprises a plurality of GMR sensors510disposed within the channel body520. GMR sensors510may be all identically configured to detect a single analyte, the redundancy allowing for enhanced detection. GMR sensors510may also be all configured differently to detect a myriad of analytes or a combination of differently configured sensors with some redundancies. Channel500further comprises a channel entrance530where any samples, reagents, bead suspensions, or the like enter channel body520. Flow through channel body520may be mediated under positive pressure at channel entrance530or under vacuum applied at channel exit540.

FIG.5Bshows a plurality of channels500disposed within base550. Each channel500features channel expansions560which is an expanded area surrounding each GMR sensor510(FIG.5A; not shown inFIG.5Bfor clarity). Without being bound by theory, it is postulated that channel expansions560provide a means for better mixing of materials as they pass over the GMR sensors. At the periphery of base550are disposed a pair of contact pads570which serve as an electrical conduit between the GMR sensors located in channel expansions560and the rest of the circuitry. GMR sensors510are electronically linked via wiring (not shown) to contact pads570.

FIGS.6A,6B and6Cschematically illustrate the structure of a GMR sensor chip280which can be mounted on the cartridge assembly200according to an embodiment of the present disclosure. As shown inFIG.6A, the GMR sensor chip280includes: at least one channels610,620and630arranged approximately in the center of the chip; a plurality of GMR sensors680disposed within the channels; electric contact pads640A,640B arranged on two opposing ends of the GMR sensor chip; and metal wires650,660,670A,670B,670C,690A,690B,690C coupled to the electric contact pads640A,640B.

The channels610,620and630each can have a serpentine shape to allow for more sensors to be packed inside. A plurality of channel expansions685can be arranged along the channels to receive the plurality of GMR sensors. Fluid to be tested flows into and out of the channels610,620,630via channel entrances615A,625A,635A and channel exits615B,625B,635B, respectively. AlthoughFIG.6Ashows that the GMR sensors680are arranged in an 8×6 sensor array, with 16 sensors received in each of three channels610,620,630, other combinations can be used to satisfy the specific needs of the analyte to be sensed.

The electric contact pads640A,640B comprise a plurality of electric contact pins. The metal wires650,660,670A,670B,670C connect the GMR sensors to corresponding electric contact pins645A,645B,675. The electric contact pads640A,640B are in turn connected to the electrical contact pads290provided on the cartridge assembly200. When the cartridge assembly200is inserted to the cartridge reader310, electric connection is formed between the GMR sensor chip280and the cartridge reader310to enable sending of measurement signals from the GMR sensors to the cartridge reader310.

FIG.6Bshows more details of the GMR sensors. For example, each GMR sensor can be comprised of five GMR strips which are connected in parallel. At one end, each GMR sensor is connected by one of two main metal wires (i.e., either wire650or660) to one of two common pins (i.e., either pin645A or645B). The other ends of the GMR sensors are connected by separate metal wires670A,670B,670C to distinct pins675on the electric contact pads640A or640B.

FIG.6Aalso shows fluid detection metal wires690A,690B,690C which are arranged in the proximity of the channel entrances and/or exits, each corresponding to one of the channels. The fluid detection function is carried out by switches695A,695B,695C arranged in the respective fluid detection metal wires.FIG.6Cshows the structure of the switch695A in detail. In response to recognition that conductive fluid (for example, plasma) flows over it, the switch695A can couple the wire696A on one side to the wire696B on the other side, generating a fluid detection signal.

The structure and wiring of the GMR sensor chip shown inFIGS.6A-Care only exemplary in nature, it will be apparent to those skilled in the art that other structures and wirings are feasible to achieve the same or similar functions. Referring now toFIG.7, there is shown a cross-sectional view of channel700at a channel expansion730. Disposed within channel expansion730is GMR sensor710on which is immobilized one or more biomolecules725. Immobilization of biomolecule725to GMR sensor710is via conventional surface chemistry (shown in some further detail inFIG.8). Biomolecule725may be a peptide or protein, DNA, RNA, oligosaccharide, hormone, antibody, glycoprotein or the like, depending on the nature of the specific assay being conducted. Each GMR sensor710is connected by wire795to a contact pad770located outside of channel700. In some embodiments, wire795is connect to GMR sensor710at the bottom of the sensor.

Referring now toFIG.8A, there is shown a more detailed cross-sectional view of a channel800having a channel body830lacking a channel expansion at the location of a GMR sensor810. Biomolecule825is immobilized with respect to the sensor via attachment to a biosurface845. Such biosurface immobilization chemistry is known in the art. See, for example, Cha et al. “Immobilization of oriented protein molecules on poly(ethylene glycol)-coated Si(111),”Proteomics4:1965-1976, (2004); Zellander et al. “Characterization of Pore Structure in Biologically Functional Poly(2-hydroxyethyl methacrylate)-Poly(ethylene glycol) Diacrylate (PHEMA-PEGDA),”PLOS ONE9(5):e96709, (2014). In some embodiments, biosurface845comprises a PEG polymer crosslinked with PHEMA. In some embodiments, the crosslinking group is represented by Formula (I):
PA-LG-PA  (I)
wherein each PA is a photo- or metal-activated or activated group, and LG is a linking group. In some embodiments, each PA is the same and in other embodiments each PA is different. In some embodiments PA is photo- or metal-activated to form a nitrene intermediate capable of C—H and/or O—H insertion. See, for example, “Photogenerated reactive intermediates and their properties,” Chapter 2 inLaboratory Techniques in Biochemistry and Molecular Biology, Elsevier Press, 12:8-24 (1983). In some embodiments, PA is metal activated to form a carbene or carbenoid intermediate capable of C—H and/or O—H insertion. See, for example, Doyle et al. “Catalytic Carbene Insertion into C—H Bonds,”Chem. Rev.2:704-724 (2010).

In some embodiments, each PA is an azide (—N3) moiety and photoactivation generates nitrene intermediates capable of C—H and/or O—H insertion thereby mediating crosslinking of PEG and PHEMA polymers. In some embodiments, each PA is a diazo (—N2) and metal catalyzed decomposition reaction forms a carbene or carbenoid intermediate capable of C—H and/or O—H insertion thereby mediating crosslinking of PEG and PHEMA polymers. Both azide and diazo preparations are well known in the art, and in the case of azide are readily prepared by SN2displacement reaction of azide anion, N3−with an appropriate organic moiety possessing a leaving group.

LG in Formula (I) can be any organic fragment that will support the presence of each PA moiety. It can be a simple C2-C20hydrocarbon chain that is straight chained or branched. Such hydrocarbons can include fluorinated variants with any degree of fluorine substitution. In some embodiments, LG can include aromatic hydrocarbons including, without limitation, benzene, naphthalene, biphenyl, binaphthyl, or combinations of aromatic structures with C2-C20hydrocarbon chains. Thus, in some embodiments, LG can be alkyl, aryl, or aralkyl in structure. In some embodiments, alkyl linking groups may have one or more carbons in their chains substituted with oxygen (O), or an amine (NR), where R is H or C1-C6alkyl.

In accordance with the foregoing embodiments, a crosslinked PEG-PHEMA structure may be given by Formula (II):
PEG-A-LG-A-PHEMA
Wherein PEG is the polyethylene glycol moiety, each A is an attachment atom from the catalytic reaction of azide or diazo, i.e., CH2or NH, and LG is the linking group as described above.

InFIG.8A, a magnetic bead-bound entity815is configured to interact with biomolecule825or an analyte of interest, such as in a sandwich complex of antibody-analyte-magnetic bead-bound antibody. Below biosurface845is a further insulating layer855. Insulating layer855may be in direct contact with GMR sensors810and may comprise, for example, a metal oxide layer. Biosurface layer845is in direct contact with insulating layer845. A base865serves as the scaffold for each component above it, the GMR sensors810, insulating layer855, and biosurface layer845. In some embodiments, base865is made from silicon wafer.

FIG.8Bschematically illustrates the basic structure and principle of GMR sensors. A typical GMR sensor consists of a metallic multi-layered structure with a non-magnetic conductive interlayer890sandwiched between two magnetic layers880A and880B. The non-magnetic conductive interlayer890is often a thin copper film. The magnetic layers880A and880B can be made of ferromagnetic alloy material.

The electrical resistance of the metallic multi-layered structure changes depending on the relative magnetization direction of the magnetic layers880A and880B. Parallel magnetization (as shown in the right half ofFIG.8B) results in lower resistance, while anti-parallel magnetization (as shown in the left half ofFIG.8B) results in higher resistance. The magnetization direction can be controlled by a magnetic field applied externally. As a result, the metallic multi-layered structure displays a change in its electrical resistance as a function of the external magnetic field.

GMR sensors have sensitivities that exceed those of anisotropic magnetoresistance (AMR) or Hall sensors. This characteristic enables detection of stray fields from magnetic materials at nanometer scales. For example, stray fields from magnetic nanoparticles that bound on sensor surface will alter the magnetization in the magnetic layers, and thus change the resistance of the GMR sensor. Accordingly, changes in the number of magnetic nanoparticles bound to the GMR sensor per unit area can be reflected in changes of the resistance value of the GMR sensor.

Referring now toFIGS.9A and10A, there are shown two exemplary basic modes by which GMR sensors operate in accordance with various assay applications described herein. In the first mode, exemplified inFIG.9A, magnetic beads915are loaded proximal to a GMR sensor (seeFIG.8A,810) via biosurface965at the start of the assay. During the assay the presence of a query analyte results in magnetic beads915being displaced from biosurface965(and thus, displaced away from the GMR sensor); this mode is the so-called subtractive mode because magnetic beads are being taken away from the proximity of the sensor surface. The second main mode operation, typified inFIG.10A, is the additive mode. In such assays, there is a net addition of magnetic beads1015in the vicinity of the GMR sensor (seeFIG.8A,810) when a query analyte is present. Either mode, subtractive or additive, relies on the changed state in the number of beads (915,1015) proximal to the sensor surface thereby altering the resistance in the GMR sensor system. The change in resistance is measured and query analyte concentrations can be determined quantitatively.

Referring back toFIG.9A, there is shown a sensor structure diagram illustrating the sensor structures throughout an exemplary subtractive process. At the start of the process the system is in state900ain which the GMR sensor has disposed on its biosurface965a plurality of molecules (typically biomolecules)925with associated magnetic beads915. The volume above biosurface965may begin dry or with a solvent present. When dry, the detection process may include a solvent priming step with, for example, a buffer solution. After introduction of analyte, the system takes the form of state900bin which some of magnetic beads915have been removed from the molecules925in proportion to the concentration of analyte. The change in states900aand900bprovide a measurable change in resistance that allows quantitation of the analyte of interest. In some embodiments, the analyte may simply displace beads directly from molecules925. In other embodiments, the analyte may chemically react with molecules925to cleave a portion of the molecule attached to beads915, thereby releasing beads915along with the cleaved portion of molecule925.

In embodiments, biosurface965comprises a polymer. The specific polymer may be chosen to facilitate covalent attachment of molecules925to biosurface965. In other embodiments, molecules925may be associated with biosurface965via electrostatic interactions. Polymer coatings may be selected for or modified to use conventional linking chemistries for covalently anchoring biomolecules, for example. Linking chemistries include any chemical moieties comprising an organic functional group handle including, without limitation, amines, alcohols, carboxylic acids, and thiol groups. Covalent attachment chemistry includes, without limitation, the formation of esters, amides, thioesters, and imines (which can be subsequently subjected to reduction, i.e., reductive amination). Biosurface965may include surface modifiers, such as surfactants, including without limitation, anionic surfactants, cationic surfactants, and zwitterionic surfactants.

In embodiments, magnetic beads915may be nanoparticulate, including spheroidal nanoparticles. Such nanoparticles may have effective diameters in a range from about 2 to about 50 nanometers (nm), or about 5 to about 20 nm, or about 5 to about 10 nm. In embodiments, magnetic beads915may be coated to facilitate covalent attachment to molecules925. In other embodiments magnetic beads915may be coated to facilitate electrostatic association with molecules925. Magnetic beads915may be differentially tagged and/or coated to facilitate multiplex detection schemes. In such embodiments, the differential tagging and/or coating is configured such that the different beads interact with different molecules disposed on different GMR sensors or on a single sensor in which different molecules are spatially organized to create addressable signals.

FIG.9Bshows a process flow901associated with the sensor structure scheme ofFIG.9A. The process commences at920by injecting a sample into a cartridge assembly. The sample may then undergo processing at step930through any necessary steps such as filtration, dilution, and/or chemical modification. The sequencing of these pre-process steps will depend on the nature of the sample and query analyte to be detected. Movement through the system may be controlled pneumatically. Step940involves sending the processed sample to the GMR sensor at a target specified flow rate. Such flow rate may be selected to reflect the kinetics of the chemistry on the GMR sensor surface. Step950provides obtaining readings from the GMR sensors that reflect changes in the concentration of magnetic beads at the surface of the GMR sensor. These readings allow detecting changes in resistance at step960. Finally, step970provides computing the detect result based on the changes in resistance.

Referring now toFIG.10A, there is shown a sensor structure diagram illustrating the sensor structures throughout an exemplary additive process. At the start of the process the system is in state1000ain which the GMR sensor has disposed on its biosurface1065a plurality of molecules (typically biomolecules)1025. The plurality of molecules1025is selected to bind a query analyte1090, as indicated in second state1000b. Query analyte1095is configured to bind magnetic beads1015. In some embodiments, query analyte1095is associated with the bead prior to passing over biosurface1065. For example, this may take place during pre-processing of the sample being tested. (In other embodiments, query analyte1095may pass over the biosurface first, then query analyte1095may be modified with magnetic beads1015after the analyte is bound to biosurface1065, as described below with reference toFIG.17A). In some embodiments, a given query analyte1095may require chemical modification prior to binding magnetic particles1015. In some embodiments, magnetic beads1015may be modified to interact with query analyte1095. The ability to quantitate analyte is provided by changes in measured resistance from state1000a, where no magnetic beads1015are present, to state1000b, where magnetic beads1015are associated with biosurface1065.

FIG.10Bshows an exemplary process flow1001associated with the sensor structure scheme ofFIG.10A. The process commences at1020by injecting a sample into a cartridge assembly. The sample may then undergo processing at step1030through any necessary steps such as filtration, dilution, and/or chemical modification. The sequencing of these pre-process steps will depend on the nature of the sample and query analyte to be detected. Movement through the system may be controlled pneumatically. Step1040involves sending the processed sample to a reaction chamber and then at step1050beads are introduced into the reaction chamber to modify the query analyte. As described above, such modification may be performed directly on the sensor surface rather than in the reaction chamber. At step1060, the modified sample is sent to the GMR sensors at a target flow rate. Such flow rate may be selected to reflect the kinetics of the chemistry on the GMR sensor surface. Step1070provides obtaining readings from the GMR sensors that reflect changes in the concentration of magnetic beads at the surface of the GMR sensor. These readings allow detecting changes in resistance at step1080. Finally, step1090provides computing the detect result based on the changes in resistance.

Referring now toFIG.11A, there is shown a sensor structure diagram illustrating the sensor structure states1100a-dthroughout an exemplary additive process that employs a sandwich antibody strategy for detection of analyte1195(state1100b). At the start of the process the system is in state1100ain which the GMR sensor has disposed on its biosurface1165a plurality of antibodies1125. Analyte1195is then passed over biosurface1165, allowing binding of analyte1195to antibody1125, as indicated in state1100b. Analyte1195is then modified by binding to a second antibody1135to which a covalently linked biotin moiety (B) is provided, as indicated in state1100c. Magnetic beads1115modified with streptavidin (S) are then added, thereby allowing the strong biotin-streptavidin association to provide state1100d. In some embodiments, streptavidin is provided as a coating on magnetic beads1115.

FIG.11Bshows an exemplary process flow1101associated with the sensor structure scheme ofFIG.11A. The process commences at1110by injecting a sample into a cartridge assembly. The sample may then undergo processing at step1120through any necessary steps such as filtration, dilution, and/or the like. The sequencing of these pre-process steps will depend on the nature of the sample and query analyte to be detected. Movement through the system may be controlled pneumatically. At step1130, the processed sample is sent to GMR sensors at a specified flowrate. Such flow rate may be selected to reflect the kinetics of the chemistry on the GMR sensor surface between biosurface-bound antibody and the analyte. Next, step1140introduces biotinylated antibody (Ab) to the GMR sensors. This creates the “sandwich” structure of the analyte between two antibodies. At step1150streptavidin coated beads are introduced into the GMR sensors, which can now interact with the biotin-bound antibody. Step1160provides obtaining readings from the GMR sensors that reflect changes in the concentration of magnetic beads at the surface of the GMR sensor. These readings allow detecting changes in resistance at step1170. Finally, step1180provides computing the detect result based on the changes in resistance.

The schemes ofFIGS.11A and11Bwere put into practice with cardiac biomarkers and proof of concept results are shown inFIGS.12A-C.FIG.12Ashows a plot of GMR signal (in ppm) over time (in seconds) in a test run designed to detect cardiac biomarker D-dimer. To generate this data, a biosurface was prepared by printing a D-dimer capture antibody using 2 nL of a 1 mg/mL of D-dimer antibody in PBS buffer with 0.05% sodium azide. For testing potential cross reactivity, the biosurface was also functionalized with troponin I capture antibody by printing two combined capture antibodies using 2 nL of a solution of 1 mg/mL troponin I antibody in PBS buffer with 0.05% sodium azide. Additionally, two other controls were printed on the biosurface. The first is a negative control prepared by printing 2 nL of a solution of 0.5% BSA in PBS buffer with 0.05% sodium azide and the second is a positive control prepared by pringint 2 nL of 1 mg/mL of biotin conjugated to mouse IgG in PBS buffer with 0.05% sodium azide. The printed sensors were incorporated into a cardiac test cartridge and is configured to use the “sandwich” assay described above inFIGS.11A and11B.

In the sample test 120 microliters of plasma or whole blood was loaded into a sample well in the cartridge. A membrane filter serves to remove blood cells as the sample is pulled into the flow channel from the sample well. 40 microliters of plasma (or plasma portion of whole blood) is flowed into a metering channel and deposited powder including antibody/biotin conjugates, blockers, and mouse IgG in the channel dissolve into the sample solution. While flowing over the sensor area, the analytes, antibody/biotin conjugates and antibodies immobilized on the sensor surface form a sandwich of antibody-analyte-biotinylated antibody. Flow rates are modulated depending on the test. For troponin I, the sample is flowed over the sensor for 20 minutes at a flow rate of 1 microliter/minute. For D-dimer, the sample is flowed for 5 minutes at a flow rate of 4 microliters/minute. Following flow of the sample streptavidin-coated magnetic beads were introduced which allow binding to the sensor surface wherever there is a biotinylated antibody bound. The GMR sensor measure bound magnetic beads, which is proportional to the concentration of analytes with the sample. The bead solution is flowed over the sensor for 5 minutes at a flow rate of 4 to 10 microliters/minute. The signals were read from the peak value within 300 seconds after beads started to bind.

As indicated in the plot ofFIG.12A, a negative control with just printed BSA did not bind D-Dimer and thus, the signal remained near baseline as expected. The positive control with biotinylated mouse showed competent bead binding, as expected. A plot of the actual sample of 666.6 ng/mL of human D-dimer appears with a peak detection signal of about 750 ppm indicating successful detection of the D-dimer in an actual sample. There was no virtually no cross reactivity with the two bound troponin I capture antibodies (not shown for clarity because these lines were very close to the line with the negative control).

FIG.12Bshows a calibration curve (GMR signal in ppm vs. D-dimer concentration) for D-dimer by running samples with varied, fixed concentrations of D-dimer. The calibration curve allows concentrations to be computed for a future unknown sample containing the D-dimer as the query analyte. A similar plot inFIG.12Cis provided for the cardiac biomarker troponin I. Together, these results establish the viability of detecting D-dimer and troponin I in, blood or plasma samples of a subject.

FIG.13schematically shows functional blocks of the cartridge reader310in accordance with an embodiment of the present disclosure. As shown inFIG.13, the cartridge reader310can be divided roughly into a sample preparation control part and a signal processing part. A memory reading unit1310and a sample preparation control unit1320form the sample preparation control part. The memory reading unit1310is adapted to, upon receipt of a signal indicating that a cartridge assembly200has been inserted into the cartridge reader310, read information stored in the memory chip275on the cartridge assembly200. The sample preparation control unit1320is configured to, based on the information read from the memory chip275, generate pneumatic control signals and send them to the pneumatic system330. In some embodiments, when insertion of the cartridge assembly200into the cartridge reader310is recognized, an indication signal may be created by the cartridge assembly200and sent to the memory reading unit1310to inform of the insertion event. Alternatively, in other embodiments, such an indication signal may be created by other components at the cartridge reader310and sent to the memory reading unit1310.

The signal processing function of the cartridge reader310is mainly performed by a signal processor1330. The signal processor1330is adapted to control electrical elements, prepare and collect signals, and process, display, store, and/or relay detection results to external systems. For example, the signal processor1330operates to generate a control signal for controlling the magnetic field generator360, resulting in magnetic field excitation applied onto the GMR sensors in the cartridge assembly200. After receiving measurement signals from the GMR sensors in the cartridge assembly200and from at least one reference resistor disposed in the cartridge assembly200and/or the signal processor1330, the signal processor1330processes the measurements signals to obtain test results of the analyte detection. Via the display control unit120, the test results are displayed on an integrated or external display. Moreover, the signal processor1330is coupled to the user interface140for receiving instructions from the user. Additionally, in some embodiments, the signal processor1330is coupled to the communication unit340and/or with the diagnostic unit350, enabling evaluation and diagnosis from the test results alone or in combination with other externally available data.

FIG.14is a flowchart of the process of the cartridge reader310in accordance with an embodiment of the present disclosure. As shown inFIG.14, the cartridge reader310starts its operation at step1410by initializing the operation mode based on system configuration profile and/or instructions inputted by the user via the user interface140. Then, the process waits at step1420for a signal indicating that a cartridge assembly200has been inserted into the cartridge reader310. This signal can be created by either the cartridge assembly200or the cartridge reader310upon recognition of the insertion. In response to receiving such a signal, at step1430, the cartridge reader310reads the memory chip275on the cartridge assembly200. Then, at step1440, the cartridge reader310generates control signals based on the read information, and sending them to the pneumatic system330for pneumatic control used in preparation of the sample to be tested. At step1450, the cartridge reader310prepares measurement signals at the GMR sensors and at the at least one reference resistor and receives the signals. Then, at step1460, the cartridge reader310processes the received measurement signals to generate test results. Finally, at step1470, the cartridge reader310sends the generated test results to the display control unit120for display to the user.

FIG.15schematically shows the functional blocks of the signal processor1330in accordance with an embodiment of the present disclosure. As shown inFIG.15, the signal processor1330includes a system operation initializer1510, a configuration profile1520, a signal processing control unit1530, a signal preparing unit1540, a signal processing unit1550and an optional data storage1560. The system operation initializer1510is configured to, based on system configuration information read from the configuration profile1520and/or instructions received via the user interface140, set up a system operation environment and initialize the functions of the signal processor1330, in particular those of the signal processing control unit1530. The signal processing control unit1530operates to generate control signals for controlling the signal preparing unit1540and the signal processing unit1550. It also operates to control display of the detection results via the display control unit120on a display, and to control communication of data between the signal processing control unit1550and the communication unit340and/or the diagnostic unit350. The signal preparing unit1540is configured to, under the control of the signal processing control unit1530, prepare measurement circuits, excite an AC magnetic field applied to the GMR sensors and create carrier signal applied to the measurement circuits, collect measurement signals from the measurement circuits, and feed the measurement signals after amplification and analog-to-digital-conversion to the signal processing unit1550. The signal processing unit1550is configured to process the received measurement signals by analytically solving for detection results, and send the detection results to the signal processing control unit1530. Additionally, in some embodiments, the result data may be stored in the optional data storage1560.

FIG.16is a flowchart of the process for the signal processor1330in accordance with an embodiment of the present disclosure. As shown inFIG.16, the process starts at step1610by reading system configuration information from the configuration profile and/or receiving user instructions via the user interface140to initialize the system operation environment. Then, at step1620, a series of control signals are generated by the signal processing control unit1530for administrating the operations of the signal preparing unit1540and the signal processing unit1550. At step1630, measurement circuits are built up by the signal preparing unit1540based on the control signals from the signal processing control unit1530, so as to prepare measurement signals from the GMR sensors and the at least one reference resistor. Then, at step1640, the prepared measurement signals are processed by the signal processing unit1550to solve for test results of the analyte detection. Finally, at step1650, the generated test results are sent from the signal processing unit1550to the display control unit120for display to the user.

FIG.17schematically shows the functional blocks of the signal processing control unit1530in accordance with an embodiment of the present disclosure. As shown inFIG.17, the signal processing control unit1530includes a multiplexer control signal generator1710, a multiplexer control signal output unit1720, a D/A converter control signal generator1730, a D/A converter control signal output unit1740, and a solution and I/O control unit1750. Based on information related to system configuration and/or inputted via the user interface140, the multiplexer control signal generator1710generates control signals for one or more multiplexers in the signal preparing unit1540, and sends them to the multiplexers through the multiplexer control signal output unit1720. The D/A converter control signal generator1730and the D/A converter control signal output unit1740are responsible for the generation and sending of the control signal to one or more D/A converters in the signal preparing unit1540. The solution and I/O control unit1750administrates the processing of the measurement signals by the signal processing unit1550, receives the processing results, and sends them to the display control unit120. Optionally, the solution and I/O control unit1750also serves as an interface with the communication unit340and with the diagnostic unit350.

FIG.18is a flowchart of the process for the signal processing control unit1530in accordance with an embodiment of the present disclosure. The process starts at step1810by generating multiplexer control signals in the multiplexer control signal generator1710based on information read from configuration profile and/or user instructions received from the user interface140. At step1820, the generated control signals are sent to the at least one multiplexer in the signal preparing unit1540to configure the structure of measurement circuits. At step1830, D/A converter control signal is generated by the D/A converter control signal generator1730based on configuration information and or user instructions, and is sent at step1840to the at least one D/A converter in the signal preparing unit1540. Then, at step1850, based on the configuration information and/or user instruction, the solution and I/O control unit1750controls the signal processing of the measurement signals by the signal processing unit1550. After the signal processing is completed, at step1860, the solution and I/O control unit1750receives test results from the signal processing unit1550. Then, at step1870, the solution and I/O control unit1750sends the received test results to the display control unit120for display on an integrated or external display. The order of steps1810-1820and1830-1840may be changed; i.e., the control of the multiplexer(s) may be before or after the control of D/A converter(s); or they can be performed at the same time.

FIG.19schematically shows the functional blocks of the signal preparing unit1540in accordance with an embodiment of the present disclosure. As shown inFIG.19, the signal preparing unit1540comprises a carrier signal generation part, a magnetic field excitation part, a circuit configuration part, a signal pick up part, and a clock synchronization part. For ease of illustration,FIG.19also shows the magnetic field generator360and the GMR sensors in the cartridge assembly200, though they are not components of the signal preparing unit1540.

A D/A converter1910, a carrier signal generator1920and a carrier signal buffer1930form the carrier signal generation part. The D/A converter1910is configured to receive control signal from the D/A converter control signal output unit1740of the signal processing control unit1530, and generate carrier signal generation parameters based on the received control signal. The carrier signal generator1920is configured to, based on the carrier signal generation parameters from the D/A converter1910, generate AC carrier signal used in the measurement circuits. A carrier signal buffer1930is coupled between the carrier signal generator1920and the measurement circuits, making the carrier signal generator1920present a very low impedance output relative to the higher impedance of the measurement circuits. Optionally, filters can be disposed at the carrier signal input to the measurement circuits to remove potential harmonics.

Although an AC voltage signal is shown inFIG.19as the carrier signal applied to the measurement circuits, depending on the structure of the measurement circuits, the carrier signal can be an AC current signal, DC voltage signal, or DC current signal.

The D/A converter1910and a magnetic field drive1940form the magnetic field excitation part. Based on the control signal received from the D/A converter control signal output unit1740of the signal processing control unit1530, the D/A converter1910generates magnetic field generation parameters. The magnetic field drive1940is configured to drive the magnetic field generator360based on the magnetic field generation parameters, so as to apply AC magnetic field onto the GMR sensors. Though the carrier signal generation part and the magnetic field excitation part shown inFIG.19share a common D/A converter, they can use separate D/A converters to generate carrier signal control parameters and magnetic field excitation control parameters.

The circuit configuration part includes at least one multiplexer1950and at least one reference resistors1955. When the cartridge assembly200is inserted into the cartridge reader310, via the electrical contact pads290provided on the cartridge assembly200, electric connection is formed between the electric contact pads640A,640B of the GMR sensor chip280on the cartridge assembly200and the signal preparing unit1540of the cartridge reader310. Based on the multiplexer control signal received from the signal processing control unit1530, the at least one multiplexer1950routes one or more GMR sensors or one or more reference resistors in to configure appropriate measurement circuits.

In some embodiments, for the sake of cost advantages, multiplexer(s)1950and reference resistor(s)1955are disposed in the cartridge reader310. Alternatively, in other embodiments, they can be disposed in the cartridge assembly200to achieve many performance advantages like reduced trace length between the multiplexer(s) and the GMR sensors, reduced number of connections from the cartridge assembly200to the cartridge reader310, etc. Or, the multiplexer(s) and the reference resistor(s) can be placed on both the cartridge reader310and the cartridge assembly200.

A measurement signal buffer1960, a differential amplifier1970and an A/D converter form the signal pick up part (also called “differential voltage probe” or “voltage probe”). The measurement signal buffer1960is coupled between the multiplexer(s)1950and the differential amplifier1970and is used to make the measurement circuits present a relatively high impedance at the inputs of the differential amplifier1970. The differential amplifier1970operates to capture time series of the voltage observations from the measurement circuits, and send the amplified measurement signals to the A/D converter1980. The A/D converter1980is configured to send the analog-to-digital-converted measurement signals to the signal processing unit1550. Optionally, filters can be used at the differential amplifier1970and/or at the A/D converter1980to remove harmonics.

Preferably, in some embodiments, a clock synchronizer1990is used to provide synchronization between the carrier signal generation part, the magnetic field excitation part and the signal pick up part. More specifically, the generation of the carrier signal generation parameters and the magnetic field generation parameters by the D/A converter1910is clocked from the same source as the A/D converter1980, i.e. by the clock synchronizer1990.

FIG.20is a flowchart of the process for the signal preparing unit1540in accordance with an embodiment of the present disclosure. As shown inFIG.20, the process start at step2010by receiving multiplexer control signal from the signal processing control unit1530. Then, at step2015, the multiplexer1950in the signal preparing unit1540configures the measurement circuits based on the received multiplexer control signal by routing certain GMR sensors and/or reference resistor(s) in. At step2220, the signal preparing unit1540receives the D/A converter control signal from the signal processing control unit1530. Based on the D/A converter control signal, at step2025, the D/A converter1910in the signal preparing unit1540generates carrier signal generation parameters. Then, at step2230, the carrier signal is generated based on the generated carrier signal generation parameters, buffered and applied to the measurement circuits configured at step2015. At step2035, the D/A converter1910in the signal preparing unit1540generates magnetic field generation parameters based on the D/A converter control signal. Then, at step2040, magnetic field is excited by the magnetic field generator drive1940based on the magnetic field generation parameters, and applied to the GMR sensors via the magnetic field generator360. At step2045, the measurement signals collected at the configured measurement circuits are buffered, and then amplified by the differential amplifier1970in the signal preparing unit1540. At step2050, the amplified measurement signals are converted into digital signals by the A/D converter1980in the signal preparing unit1540. Finally, at step2055, the converted digital signals are sent to the signal processing unit1730for further processing. The order of steps2025-2030and2035-2040may be changed; i.e., generation of the magnetic field excitation may be before or after generation of the carrier signal; or they can be performed at the same time.

FIG.21schematically shows the functional blocks of the signal processing unit1550in accordance with an embodiment of the present disclosure. As shown inFIG.21, the signal processing unit1550comprises reference signal generators2110, a multiplier2120, an integrator2130, an integration timing controller2140, and a close-form solution unit2150.

The reference signal generators2110are configured to receive control signal from the solution and I/O control unit1750of the signal processing control unit1530, generate in-phase and quadrature (rotated 90 degrees) sinusoid reference signals at all frequencies of interest based on the received control signal, and send the generated reference signals to the multiplier2120. The multiplier2120is configured to receive the measurement signals from the A/D converter1980of the signal preparing unit1540, and multiply the measurement signals by the reference signals from the reference signal generators2110to produce an in-phase product and a quadrature product at each frequency of interest for each measurement signal. The in-phase products and quadrature products are sent to the integrator2130. The integrator2130is configured to accumulate these products under the control of the integration timing controller2140and send the accumulations to the close-form solution unit2150. The close-form solution unit2150is adapted to solve for, from the received accumulations, the phase-accurate GMR sensor resistance and magnetoresistance quantities that are not influenced by the frequency, amplitude or phase of the applied carrier signal, or by the amplitude or phase response of the circuits supplying this.

FIG.22is a flowchart of the process for the signal processing unit1550in accordance with an embodiment of the present disclosure. As shown inFIG.22, the process starts at step2210by receiving control signal from the solution and I/O control unit1750of the signal processing control unit1530. At step2215, in-phase and quadrature sinusoid reference signals at all frequencies of interest are generated in the signal processing unit1550based on the control signal. Then, at step2220, the reference resistor measurement signals are received from the signal preparing unit1540. At step2225, the reference resistor measurement signals are multiplied by the in-phase and quadrature sinusoid reference signals generated at step2215to generate in-phase and quadrature products at all frequencies of interest. At step2230, the in-phase and quadrature products obtained at step2225are accumulated under integration timing control. At steps2235-2250, similar processing is performed for the received measurement signals for the GMR sensors. At step2250, test results are solved for in a close-form way from the in-phase and quadrature products of both reference resistor measurement signals and GMR sensor measurement signals. Finally, at step2255, the solved test results are sent to the solution and I/O control unit1750of the signal processing control unit1530.

The order of steps2220-2230and2235-2245may be changed; i.e., accumulation for reference resistor measurement signals may be before or after accumulation for GMR sensor measurement signals.

As described above referring toFIG.8B, electrical resistance of a GMR sensor changes under the influence of a magnetic field. A GMR sensor can be monitored in real time while superparamagnetic nanoparticles bind through the assay to the GMR sensor. A local change in magnetic field is translated to a change in sensor resistance and observed as a change in voltage in a properly configured measurement circuit.

However, by use of traditional differential measurement circuits, for examples, a Wheatstone bridge circuit or an Anderson loop circuit, it is impossible to directly discern increasing magnetoresistance from decreasing magnetoresistance based on voltage at the voltage probe. An example of voltage measurements obtained with one available measurement circuit topology is plotted inFIG.23. As can be seen in the plot, in the lack of phase sensitivity, it's hard to derive the correct relationship between sensor impedance (Zs) and reference impedance (Zr). All one can tell from increasing voltage is that elements in the measurement circuit are changing with respect to each other. As a result, when using these traditional circuits with AC measurement, less optimal ways have to be taken to deal with this problem.

A common suboptimal option is to bias the measurement circuit away from balance such that the voltage signal at the voltage probe never crosses zero. This approach has negative impacts on signal-to-noise ratio of the measurement circuit. Further, even with a bias, increasing or decreasing magnetoresistance still must be deduced via inference or other indirect knowledge.

Otherwise, if a balanced measurement circuit is adopted to achieve a good signal-to-noise ratio level, large artifacts appear in telemetry: magnetoresistance appears to decrease to zero and then increase (a V shape as shown inFIG.23which always seems to be positive), while actually it may only be decreasing or be increasing.

The present disclosure introduces phase sensitivity into the context of GMR-based detection to derive correct measurements. The signal processing technique disclosed here has an ability to measure across a perfectly balanced GMR measurement circuit (for example, a balanced Wheatstone bridge) without the issues encountered by the prior art. Moreover, the technique is sufficiently general to apply to any of the available circuit topologies to achieve phase-sensitive measurements and calculation of magneto resistance in GMR sensors. The generality of the approach disclosed here provides an additional competitive advantage because it enables a direct comparison of different circuit topologies while continuing to deliver the same output signal to the end user.

FIG.24Ashows a simple circuit topology for embodying this technique.FIGS.24B-Cshow several other available circuit topologies. For example, a circuit topology based on the Anderson loop and an AC current source is exemplarily illustrated inFIG.24B, while a circuit topology based on the Wheatstone bridge and an AC voltage source is shown inFIG.24C. The circuit topologies include a carrier source2410or2415, a first control circuit Ckt12420, a second control circuit Ckt22430, a voltage probe2440, at least one GMR sensor2450, at least one high-precision reference resistor2460, and a magnetic field generator2470.

As shown inFIG.24A, the carrier source2410is configured to provide a buffered current source for applying an AC carrier signal at frequency ω1(for different measurement circuit configurations, a carrier source2415may operate to provide a buffered voltage source). InFIG.24A, the first control circuit Ckt12420allows switching between the GMR sensor2450and the similarly arranged high-precision reference resistor2460with known characteristics in order to apply the AC carrier signal from the carrier source2410to the GMR sensor2450or to the high-precision reference resistor2460. By constructing a sensing path and replicating a reference path in Ckt1, the present technique achieves balanced parasitic elements. In these structures, parasitic elements appear in equivalent locations. Thus, the differential voltage at the voltage probe primarily arises from the differences in the GMR sensor and reference resistor being measured due to common mode rejection in the differential voltage probe. In other embodiments, additionally or alternatively, the parasitic elements are explicitly modeled for decomposition from measurement signals so as to cancel the effects of the parasitic elements.

The second control circuit Ckt22430and the magnetic field generator2470are used to apply a sinusoidal magnetic field at frequency ω2to the GMR sensor2450. The applied magnetic field will modulate the GMR sensor's resistance, but will not affect the high-precision reference resistor2460.

The differential voltage probe2440is connected to detect the impedance of the GMR sensor2450or of the high-precision reference resistor2460. The voltage probe2440is designed as having sufficiently high impedance, and thus measurements of the GMR sensor and the reference resistor are not perturbed.

As the applied sinusoidal magnetic field modulates the GMR sensor's resistance, application of this sinusoidal magnetic field at frequency ω2while also applying the carrier signal at frequency ω1will modulate the amplitude of the voltages associated with the GMR sensor2450, giving rise to sideband voltages. The first set of sideband voltages occur at frequencies ω1−ω2and ω1+ω2.

However, these sideband voltages will not be induced across the high-precision reference resistor2460by application of the sinusoidal magnetic field. Thus, it is necessary to manually induce these sideband voltages across the reference resistor2460when the high-precision reference resistor2460is switched into the measurement circuit for observation. It can be carried out by mixing the sideband signals into the carrier with amplitudes equal to the amplitude of the carrier. In other words, the sideband signals can be induced by addition to the carrier signal upstream of the buffer for the buffered voltage or current source. More especially, the sideband signals may be added to the carrier signal with equal amplitude to the carrier.

The measurement process for the topology shown inFIG.24Ais as follows. Via the first control circuit Ckt12420, the GMR sensor2450is switched into the measurement circuit while both the carrier signal and the sinusoidal magnetic field are applied. Using the voltage probe2440, a time series of voltages are captured for a duration t1which is chosen based upon noise requirements.

Similarly, the high-precision reference resistor2460is switched into the measurement circuit. This time, the carrier signal at frequency φ1and mixed signals at frequencies ω1−ω2and ω1+ω2with amplitudes equal to the carrier are applied. Using the voltage probe2440, again, a time series of voltages are captured for a duration t2which is also chosen based upon noise requirements.

Then, each sample of the respective time series is multiplied by samples from in-phase sine wave time series at frequencies ω1, ω1−ω2and ω1+ω2and quadrature sine waves at frequencies ω1, ω1−ω2and ω1+ω2offset 90 degrees, respectively. By accumulating at an integrator the in-phase and quadrature products at each frequency for the GMR sensor2450and the high-precision reference resistor2460, six complex quantities are generated which are proportional to the probed voltages at frequencies ω1, ω1−ω2and ω1+ω2during observation of the GMR sensor2450and the high-precision reference resistor2460.

Then, the GMR sensor accumulations are divided by t1, and the reference resistor accumulations by t2. By designating the in-phase accumulations as real components and the quadrature accumulations as imaginary components, complex voltage-proportional terms vs associated with the GMR sensor2450are constructed, obtaining vs(ω1), vs(ω1−ω2), and vs(ω1+ω2). Similarly, complex voltage-proportional terms vtxassociated with the high-precision reference resistor2460are obtained, i.e., vtx(ω1), vtx(ω1−ω2), and vtx(ω1+ω2). Then, from the six complex terms vs(ω1), vs(ω1−ω2), vs(ω1+ω2), vtx(ω1), vtx(ω1−ω2), and vtx(ω1+ω2), analytically solve for zero-field resistance (R0) of GMR sensor, and solve for dR from the Taylor Series expansion at the side tones. From dR/R0, obtain magneto resistance ratio MR, which is GMR sensor's change in resistance with a sinusoidal magnetic field applied divided by the sensor's resistance with zero magnetic field applied.

In the above, both duration t1and duration t2are chosen to meet noise requirements. Noise introduced by the time-variance of the system that results from a finite t1can be minimized by choosing a t1such that the proportion of accumulation time that is not modulo 2π radians for the signals at ω1, ω1, ω1−ω2and ω1+ω2is small compared to the total accumulation time. Random noise can be reduced by increasing t1. In a similar way to t1, duration t2is chosen.

With the disclosed technique, there is no need to bias away from balance, allowing for optimal gain staging and improved signal-to-noise ratio level. Resistive and reactive components can be decomposed, and parasitic elements can be measured and removed. Moreover, some difficult-to-deal-with artifacts can be cancelled, such as converter group delays which otherwise appear as large phase offsets without special handling. Further, cancellation of transfer functions upstream and downstream of the GMR sensor which is under test provides an obvious research and development advantage because of high hardware independence on tolerance of components. As the measurement will not be perturbed by elements outside of Ckt1and Ckt2, there are three distinct benefits: (1) Designers are afforded great freedom to modify circuit elements external to Ckt1and Ckt2without changing output telemetry; (2) A high precision measurement can be obtained even without tight tolerances for elements external to Ckt1and Ckt2; (3) High precision measurement requires no explicit modeling for elements outside of Ckt1.

One skilled in the art will understand thatFIGS.24A-Care only a few limited examples of the applicable circuit topologies. The GMR-based analyte detection system can be built around any of these and other available circuit topologies. Output of R0, dR and MR telemetry may be directly compared in any of these circuits. The performance of these circuits can be evaluated in terms of system specifications. These evaluations during system development will likely lead to changes to the circuit topology. By outputting signals in terms of magnetoresistance instead of voltage, circuit topologies can be changed without disruption of workflow of the end user.

An exemplary GMR-based analyte detection system is given hereafter to illustrate in detail the performance and structure of such systems. This exemplary system describes a phase-sensitive AC measurement of an amplitude-modulated magnetoresistance signal in a reconfigurable on-chip Wheatstone Bridge topology shown inFIG.24C. The Wheatstone Bridge shown inFIG.24Cincludes GMR sensor pairs in the GMR sensor chip280and reference resistor pairs RTX1a-RTX2bdisposed on the cartridge assembly200or the cartridge reader310or both. The GMR sensors marked in black color GMR1a, GMR2bare functionalized for the assay and the GMR sensors marked in white color GMR1b, GMR2aare blocked.

As mentioned above, a GMR sensor itself is an electrically resistive element with resistance that depends on the size and direction of total magnetic field. The total magnetic field includes the field applied from a magnetic field generator (which can be either external or integrated with the GMR sensor chip) along with any disturbance from magnetic nanoparticles near the sensor.

Thus, the basic principle of the system is to monitor the resistance and magnetoresistance of GMR sensing elements before, during, and after application of functionalized magnetic nanoparticles. Components of the assay may either cause an increase or decrease in the number of magnetic nanoparticles bound to the sensor surface. This increase or decrease can be observed relative to reference elements. The reference elements can be reference sensors with negative control or reference resistors. This group of reference elements may serve as a baseline to observe a change in the active sensors.

The exemplary system uses electrical subtraction to observe the change in resistance and magnetoresistance of active GMR sensors as compared to reference sensors with negative control (or reference resistors) after the application of functionalized magnetic nanoparticles by applying a sinusoidal voltage and simultaneously observing the sensor behavior as compared to the reference elements in the presence of this sinusoidal voltage or current. In this example, because the applied signal is voltage, the currents through the sensor and reference elements may be subtracted directly. The electrical subtraction in the presence of an applied sinusoidal voltage may be accomplished by placing the active GMR sensor and reference elements into voltage dividers and subtracting the voltages at the midpoints. In other examples, if the applied sinusoid is current, the electrical subtraction may be accomplished by subtracting the voltage drops across the active GMR sensor and reference elements.

Between each observation of the active-sensor-and-reference-element subtraction, the system observes a signal subtraction across high-precision reference resistors with values known to the code in the signal processor1330. The signal processor1330uses arithmetic division of each sensor, reference element observation by its preceding (or following) reference resistor, reference resistor observation to cancel the transfer functions of all circuitry supplying the sinusoidal voltage or current signal upstream from the sensor and to cancel the transfer functions of all circuitry being used to observe the signals downstream from the sensor. This provides a phase-sensitive measurement that is also immune to variations in the circuitry for which the transfer functions have been cancelled. This immunity to variation is effective within a single unit over time, from one unit to the next, and from one system design revision to the next.

The amplitude-response of the circuitry supplying the applied field is dealt with separately from the signal processor1330's division-based transfer function cancellation with a per-unit calibration to ensure the strength of the applied magnetic field is as intended. In the case the applied field is sinusoidal and not DC, this creates an amplitude modulation of the applied sinusoidal current or voltage carrier. In the presence of this amplitude modulation, the magnetoresistance appears in upper and lower sidebands. The phase response of the circuitry supplying the applied field appears in the sidebands, where the lower sideband is rotated by the negative of the phase of the applied field and the upper sideband is rotated by the positive of the phase of the applied field. This rotation from the field is cancelled by the code of the signal processor system1330by rotating the phases of the sidebands to their mean. Thus, the transfer function of the circuitry applying the field is fully accounted for, enabling a phase-sensitive and phase-accurate magnetoresistance measurement even when the applied field is AC. Importantly, the phase-sensitive and phase-accurate measurement allows for distinction between scenarios where magnetoresistance is decreasing from those where it is increasing. Without a phase-sensitive measurement, this can otherwise be difficult to discern.

The high precision reference resistors2460can be placed on either the cartridge reader310or the cartridge assembly200. In either location, their logical function and connection is the same, but there is a cost-performance trade off to their physical placement. Placing the high precision reference resistors2460in proximity to the GMR sensors on the cartridge assembly200can theoretically improve performance through further cancellation of common artifacts. This can also allow matching of the reference resistors to their mating GMR sensors on a cartridge-by-cartridge basis. However, if the cartridge assembly200is very cost-sensitive and the cartridge assembly200is a higher-volume-production-item than the signal preparing unit1540of the cartridge reader310, there is a cost advantage to placing the high precision reference resistors2460on the cartridge reader310.

Similarly, the multiplexer(s) can be placed on the cartridge assembly200, the cartridge reader310, or both. The placement of the multiplexer(s) should be chosen to optimize system cost and performance, while constraining the design to a manageable number of connections between the cartridge assembly200and the cartridge reader310and yet supporting the desired number of addressable sensors in the system. In the design where multiplexers are placed on both the cartridge assembly200and the cartridge reader310and are all used together to address GMR sensors, many signals are run from the cartridge assembly200to on-reader multiplexers. A second layer of multiplexers on the cartridge assembly allow for bank switching. With this, the number of sensors that can be addressed is multiplied.

Observations of the GMR sensors and reference resistors are made by measuring currents through them or voltages across them in discrete time with the analog-to-digital converter1910. The digital-to-analog converter1910generating the applied sinusoidal voltage or current and generating the applied field are clocked from the same source as the analog-to-digital converter1980. The signal processor1330implements a lock-in amplifier in code that measures the correlation between the signals observed at the analog-to-digital converter1980and in-phase and quadrature (rotated 90 degrees) sinusoids generated internally at all frequencies of interest. The signals from the analog-to-digital converter1980are multiplied by the internal in-phase and quadrature sinusoids producing an in-phase product and a quadrature product for each sample at each frequency of interest. These products are accumulated through the duration of each observation.

In a time invariant system with an infinite duration of observation, for given circuit and sensor conditions, the ratio of the in-phase and quadrature accumulations will be fixed. The signal processor1330automatically selects generator frequencies and observation duration such that all signals of interest are at the same phase angle at the beginning and end of each observation. This allows the system to mimic the operation of a time invariant system, even with very short observation periods. The signal processor1330also starts sensor observations with all generator phase angles consistent from one observation to the next. This removes variability that could otherwise be introduced by differences in phase response and group delay of the circuits generating the applied sinusoidal current or voltage and the circuitry generating an applied field.

The GMR sensor measurement proceeds as follows. The signal processor1330configures the circuit for observation of the reference resistor structure by sending appropriate commands to the multiplexer1950which can be on the cartridge assembly200or on the cartridge reader310or both. The digital-to-analog converter1910is used to generate the applied sinusoidal voltage or current and the applied field. A minimum wait time is observed in order to allow transients from multiplexer switching to settle. After this minimum wait time, the signal processor1330begins accumulating the in-phase and quadrature products derived from the reference resistor signals observed at the analog-to-digital converter1980. After an integer number of cycles have elapsed for all internal (and external) sine wave generators2110, the integrator2130is frozen and captured. The numbers of elapsed cycles will be different at the various observation frequencies, but must all be integers. After initial capture of the integrator2130, signal generation from the digital-to-analog generator1910continues while the signal processor1330commands the multiplexer1950to configure the circuit for observation of GMR sensor(s). A minimum wait time is observed in order to allow transients from multiplexer switching to settle. After this minimum wait time, the signal processor1330waits for all signal generators to arrive at a predefined phase angle. After arrival at the predefined phase angle, the signal processor1330begins accumulating the in-phase and quadrature products derived from the sensor signals observed at the analog-to-digital converter1980. After integer numbers of cycles have elapsed for all internal (and external) sine wave generators2110, the integrator2130is again frozen and captured. The signal processor1330divides the captured sensor accumulations by the captured reference accumulations and, with prior knowledge of the reference resistance values, uses the quotients to compute phase-accurate sensor resistance and magnetoresistance quantities that are not influenced by the frequency, amplitude or phase of the applied sinusoidal current or voltage, or by the amplitude or phase response of the circuits supplying this. The sensor resistance and magnetoresistance quantities are also not influenced by the frequency or phase angle of the applied field, and are not influenced by the phase response of the circuits supplying this. Thus, any of these elements can be freely modified, for instance to achieve optimal signal-to-noise ratio, without perturbation of the resistance and magnetoresistance telemetry.

As mentioned above, a GMR sensor is modeled as a resistance that changes in proportion to the total magnetic field. This resistance value may be expressed as
R=Rn(1+kH),
where Rn is the nominal resistance of the GMR sensor with zero magnetic field applied to it, H is the total magnetic field, k is a property of the GMR sensor that relates the change in resistance to the total magnetic field, and R is the total resistance with inclusion of the change in resistance induced by the magnetic field.

A dimensionless quantity, magneto resistance (MR), is defined as a measure of the change in resistance of the GMR sensor. It is expressed as the total resistance in the presence of the magnetic field divided by the nominal resistance with zero field. Thus:
MR=Rn(1+kH)/Rn=1+kH.

For those GMR sensors functionalized for the assay, magnetic nanoparticles become bound to the sensor surface, thus changing the total field, which will in turn change the magneto resistance. This change in MR, delta(MR), is what is ultimately observed, as this is a quantity directly related to the concentration of magnetic nanoparticles in close proximity to the functionalized sensor and can therefore be used to infer their presence and measure their concentration.

As shown inFIG.24C, voltage divider sensor pairs are provided for the full bridge topology, where each pair comprises one sensor functionalized for the assay and one blocked sensor. Applying voltage across any of these voltage dividers, and assuming behavior of the functionalized and blocked sensors are otherwise identical, one can observe a voltage at the midpoint of each divider that changes solely due to the delta(MR) imparted by attachment of magnetic nanoparticles to the functionalized sensor. To the extent the other aspects of the sensors' behavior may be unstable over time, the arrangement of the otherwise identical sensors into voltage divider pairs also provides a mechanism for cancellation of the artifacts introduced by these changes over time (for instance, thermal changes).

As can be seen inFIG.24C, the voltage divider sensor pairs may have one of two arrangements. The functionalized sensors (the black GMR1a, GMR2binFIG.24C) may either be connected to the voltage source or to ground; the blocked sensors (the white GMR1b, GMR2ainFIG.24C) are adjacent. Although at least one multiplexer is shown in the topologies, actually, banks of freely configurable switches can be used such that multiple nodes can be routed in at the same time. By use of a freely configurable, multi-channel switch with drains (for example, drains A and B), one can connect the midpoint of any voltage divider to either the inverting or non-inverting input of an instrumentation amplifier.

For example, a meaningful delta(MR) measurement may be performed by connecting one or more dividers of one arrangement to drain A and one or more dividers of the other arrangement to drain B. Alternatively, the midpoints of dividers of like arrangement may be connected to drain A or B and the midpoint of a high-precision reference resistor divider pair (where reference resistors are designated RTX1a, RTX1b, RTX2aand RTX2binFIG.24C) may be connected to the other drain. Yet a third arrangement is to connect the midpoints of two high-precision reference resistor divider pairs, one to each drain. This third arrangement provides a means to measure characteristics of the circuitry external to the bridge.

As an example, the measurement of the topology shown inFIG.24Cmay proceed as follows: prior to introduction of magnetic nanoparticles, all sensor dividers may be measured separately in bridges configured with a sensor divider's midpoint connected to one drain and a high-precision resistor divider's midpoint connected to the other. One can confirm resistive balance and magneto-resistive balance for each sensor divider individually. For dividers that are out of specification, one can quarantine individual dividers rather than entire bridges as would be necessary in designs where bridges are statically configured.

For the assay measurement itself, in some embodiments, any number of divider pair' midpoints may be connected to the drains simultaneously, so long as divider pairs' functionalized sensors are functionalized for the same target and the midpoints of dividers of like arrangement are connected to the same drain, with the midpoints of dividers of the other arrangement connected to the other drain. In other embodiments, since the differential voltage probe does not need to be biased away from 0 volts, midpoint(s) of one or more divider sensor pairs in Arrangement 1 (or 2) may be connected to one input, and midpoint(s) of one or more divider sensor pairs also in Arrangement 1 (or 2) to the other input of the voltage probe. The advantages are then two-fold: first, effective sensor area can be increased by routing in many dividers, and second, the voltage that appears at the differential probe is 0 until functionalized sensors change with respect to non-functionalized sensors. In other words, voltage only arises due to this difference, which means optimal gain staging and improved SNR.

It is advantageous to connect many voltage dividers simultaneously, as this can reduce noise and the coefficient of variation: for dividers connected simultaneously, their sensors then act as a single unit and combine the free layer volume, and magneto-resistive sensor noise drops off as one over the square root of the free layer volume. The coefficient of variation is reduced because the random distribution of magnetic nanoparticles will be better measured by a larger sensing area (and it is well known in the literature that magneto-resistive sensors detect nanoparticles differently based on the position of nanoparticles relative to the free layer).

In an example, a further refinement is carried out to ensure that the same number of divider pairs are connected to drain A as are connected to drain B. Connecting an equal number of dividers presents balanced impedances to the instrumentation amplifier's inverting and non-inverting inputs, and thus maximizes the instrumentation amplifier's common mode rejection ratio. However, the procedures and algorithms described in this example are equally valid for other examples wherein a mismatched number of dividers are connected to the two drains.

For the observation of sensor magnetoresistance, an AC voltage is connected to the configured bridge while an AC magnetic field is applied. Application of the AC field modulates the sensors' resistances via the magneto-resistive effect. With attachment of magnetic nanoparticles to sensors functionalized for the assay, the sensor voltage dividers become unbalanced in a way that's predictably related to delta(MR). This in turn presents an amplitude-modulated voltage across the instrumentation amplifier with upper and lower sideband components related to delta(MR).

The analog-to-digital converter1980is connected to the output of the instrumentation amplifier1970. The analog-to-digital converter1980's output is collected by the signal processing unit1550. Internal to the signal processing unit1550, in-phase and quadrature (rotated 90 degrees) sinusoids are generated at the frequency of the carrier voltage applied to the bridge and at the frequencies of the sideband voltages arising from the amplitude modulation of the carrier. Correlations between the internal in-phase and quadrature signals and the signals observed at the analog-to-digital converter1980are measured by evaluating the accumulated means of the products of the internally-generated signals and the samples observed at the output of the analog-to-digital converter1980over a course of time during which an integer number of cycles have elapsed at all three frequencies. The in-phase and quadrature correlations at each frequency are equivalent to the complex voltages observed at each frequency, normalized by multiplication with the transfer functions of the circuitry and logic external to the bridge.

Immediately before or after each sensor bridge observation, an observation of the high-precision reference resistor bridge is performed. In order to create a non-zero voltage across the reference resistor bridge, one or more reference resistors1955must be mismatched from the others. In the arithmetic presented here, one resistor may be mismatched from the others, and the other three may be of equal value.

Because the reference resistor bridge is insensitive to the field, no amplitude-modulated sidebands voltages will appear across it. Instead, voltages at the carrier and two sideband frequencies generated, added and applied together directly to the reference resistor bridge. As with the sensor bridge observation, the complex voltages at the three frequencies are measured by multiplication by internally generated in-phase and quadrature sinusoids. The mean correlations are here also accumulated over a period of time during which an integer number of cycles have elapsed at all three frequencies. The observed complex voltages across the reference resistor bridge at the three frequencies of interest are normalized by multiplication with the same transfer functions as appear in the sensor voltages.

For a solution to delta(MR) from these six voltages, three observed across the sensor bridge and three observed at the same frequencies across the reference resistor bridge, the model of magnetoresistance, R=Rn(1+kH), is decomposed into a first-order Taylor approximation where the constant term describes the relation between the observed sensor bridge voltage at the carrier frequency and the second term, proportional to H, describes the relation between the sensor bridge voltage observed at the two sidebands and all of Rn, k and H.

A division by the voltages observed across the reference resistor bridge can lead to direct, phase-sensitive solutions for the components of delta(MR) appearing at the lower and upper sidebands as follows:
delta(MR,lower)=(4*(RTX′−RTX)*(RTX+RTX′)*vs(lower)*vtx(carrier)*vtx(carrier))/((RTX′−RTX)*(RTX′−RTX)*vs(carrier)*vs(carrier)*vtx(lower)−4*(RTX+RTX′)*(RTX+RTX′)*vtx(lower)*vtx(carrier)*vtx(carrier))
delta(MR,upper)=(4*(RTX′−RTX)*(RTX+RTX′)*vs(upper)*vtx(carrier)*vtx(carrier))/((RTX′−RTX)*(RTX′−RTX)*vs(carrier)*vs(carrier)*vtx(upper)−4*(RTX+RTX′)*(RTX+RTX′)*vtx(upper)*vtx(carrier)*vtx(carrier))
In the above equations, variables are defined as:delta(MR, lower): a complex quantity; the component of delta-MR observed from the lower sideband voltagedelta(MR, upper): a complex quantity; the component of delta-MR observed from the upper sideband voltageRTX: the value of the three matched resistors in the reference resistor bridgeRTX′: the value of a fourth, mis-matched resistor in the reference resistor bridgevs(carrier): the complex voltage at the carrier frequency observed across the sensor bridgevs(lower): the complex voltage at the lower sideband frequency observed across the sensor bridgevs(upper): the complex voltage at the upper sideband frequency observed across the sensor bridgevtx(carrier): the complex voltage at the carrier frequency observed across the reference resistor bridgevtx(lower): the complex voltage at the lower sideband frequency observed across the reference resistor bridgevtx(upper): the complex voltage at the upper sideband frequency observed across the reference resistor bridge

By virtue of the reference resistor voltage division, transfer functions of the circuitry external to the sensor bridge are largely canceled. The only remaining step to obtaining a phase-sensitive and phase-accurate measurement of delta(MR) is to cancel the phase angle of the applied AC magnetic field, by which both delta(MR, lower) and delta(MR, upper) are rotated, one negatively and one positively. It is known that MR is purely resistive, and so the components of delta(MR) appearing at the various frequencies should all be the same and should all be strictly real. Therefore, the rotation of delta(MR) by the phase offset of the applied field can be canceled by computing the mean of the apparent phase angles of delta(MR, lower) and delta(MR, upper). This will be approximately 0 for positive delta(MR) and approximately 180 degrees for negative delta(MR). That is, delta(MR) appears on the real axis. The apparent deviation of delta(MR) from the real axis can be minimized by balanced placement of parasitic elements on each side of the bridge. With such balanced placement (for instance, by use of a single multi-channel switch for configuration of both sides of the bridge), the apparent deviation of delta(MR) from the real axis can be minimized, often to the system's noise floor.

The magnitude of delta(MR) may be computed simply as the sum of the magnitudes of delta(MR, lower) and delta(MR, upper). Taking then the real component of this computed delta(MR), a phase-sensitive and phase-accurate (i.e. real) notion of magnetoresistance is realized in a single, dimensionless quantity which may be negative or positive, and may cross zero freely without perturbation. This delta(MR) is also immune to a large collection of possible variations in external circuitry, as well as non-MR variations in the sensors themselves.

In GMR detection systems according to prior art, the GMR-depended voltage magnitudes were used directly without calculating the phase. This works to some degree, but has disadvantages relative to the design described above. In contrast, the present disclosure has the following advantages:constant runtime calibration of circuitry for which there is transfer function cancellation;immunity to variation over time in these circuits with respect to things like temperature;very good unit-to-unit consistency for aspects of system operation related to these circuits without any particular additional effort on our part;ability to freely optimize design for performance without disturbance of output telemetry, which streamlines R&D;phase sensitivity, which means one always retains the ability to discern cases where magnetoresistance is increasing from case where magnetoresistance is decreasing.

In accordance with embodiments herein, there is provided a signal processing system used for GMR-based detection of a target analyte in a sample under test. The system comprises: a measurement circuit configuration unit configured to build a GMR sensor measurement circuit by routing in at least one GMR sensor, and to build a reference resistor measurement circuit by routing in at least one reference resistor; a magnetic field excitation unit configured to apply an AC magnetic field of frequency ω2 to the at least one GMR sensor; a carrier signal applying unit configured to apply a carrier signal of frequency ω1 to the GMR sensor measurement circuit, and apply carrier signals of frequency ω1, ω1+ω2, and ω1−ω2 to the reference resistor measurement circuit; a measurement signal pick-up unit coupled to the measurement circuits, configured to collect reference resistor measurement signals from the reference resistor measurement circuit and GMR sensor measurement signals from the GMR sensor measurement circuit; and a phase sensitive solution unit coupled to the measurement signal pick-up unit, configured to analytically solve for resistance change of the at least one GMR sensor based on both the reference resistor measurement signals from the reference resistor measurement circuit and the GMR sensor measurement signals from the GMR sensor measurement circuit.

In some embodiments, the phase sensitive solution unit comprises: reference signal generators, configured to generate in-phase and quadrature sinusoid reference signals at all frequencies of interest; a multiplier, configured to multiply the measurement signals by the reference signals to produce in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals; an integrator, configured to accumulate the in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals; and a close-form solver, configured to solve for the resistance change of the GMR sensor from the accumulations of the in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals. In some embodiments, the frequencies of interest are ω1, ω1+ω2, and ω1−ω2.

In some embodiments, the phase sensitive solution unit is further configured to solve for magnetoresistance change of the at least one GMR sensor. In some embodiments, the signal processing system comprises a detection result determination unit which is configured to determine, from the solved magnetoresistance change of the at least one GMR sensor, presence or not of the target analyte in the sample under test. In some embodiments, the signal processing system further comprises a detection result determination unit which is configured to determine, from the solved magnetoresistance change of the at least one GMR sensor, concentration of the target analyte in the sample under test.

In some embodiments, the carrier signal applying unit is a carrier current source which is configured to apply a carrier current to the measurement circuits, wherein the reference resistor measurement circuit is formed by a reference resistor connected in series between the carrier current source and ground, wherein the GMR sensor measurement circuit is formed by a GMR sensor connected in series between the carrier current source and ground, or by a parallel combination of more than one GMR sensor which is connected in series between the carrier current source and ground, and wherein the GMR sensor is functionalized for the target analyte.

In some embodiments, the carrier signal applying unit is a carrier voltage source which is configured to apply a carrier voltage to the measurement circuits, wherein the GMR sensor measurement circuit is a Wheatstone full bridge circuit formed by a first bridge arm and a second bridge arm, wherein the first bridge arm comprises one first voltage divider or a parallel combination of more than one first voltage divider, wherein the first voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the second bridge arm comprises one second voltage divider or a parallel combination of more than one second voltage divider, wherein the second voltage divider formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the functionalized GMR sensor in the first voltage divider is connected to the carrier voltage source while the reference element in the first voltage divider is connected to ground, and wherein the functionalized GMR sensor in the second voltage divider is connected to ground while the reference element in the second voltage divider is connected to the carrier voltage source.

In some embodiments, the carrier signal applying unit is a carrier voltage source which is configured to apply a carrier voltage to the measurement circuits, wherein the GMR sensor measurement circuit is a Wheatstone full bridge circuit formed by a first bridge arm and a second bridge arm, wherein the first bridge arm comprises one first voltage divider or a parallel combination of more than one first voltage divider, wherein the first voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the second bridge arm comprises one second voltage divider or a parallel combination of more than one second voltage divider, wherein the second voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the functionalized GMR sensor in the first voltage divider is connected to the carrier voltage source while the reference element in the first voltage divider is connected to ground, and wherein the functionalized GMR sensor in the second voltage divider is connected to the carrier voltage source while the reference element in the second voltage divider is connected to ground.

In some embodiments, the reference resistor measurement circuit is a Wheatstone full bridge circuit formed by four reference resistors, wherein three of the four reference resistors have matched resistance value, and wherein the fourth reference resistor has a mis-matched resistance value.

In some embodiments, the carrier signal applying unit is a carrier current source which is configured to apply a carrier current to the measurement circuits, wherein the reference resistor measurement circuit are an Anderson loop circuit comprised of a reference resistor voltage divider formed of two reference resistors, wherein the GMR sensor measurement circuit are an Anderson loop circuit comprised of one GMR sensor voltage divider or a parallel combination of more than one GMR sensor voltage divider, and wherein the GMR sensor voltage divider is formed of a GMR sensor functionalized for the target analyte and a reference element.

In some embodiments, the reference element is a GMR sensor un-functionalized to the analyte to be detected.

In some embodiments, the reference element is a reference resistor.

In some embodiments, the measurement circuit configuration unit comprises at least one multiplexer.

In some embodiments, the measurement circuit configuration unit comprises a bank of freely configurable switches.

In some embodiments, a buffer is coupled between the carrier signal applying unit and the measurement circuits, making the carrier signal applying unit present a low impedance output relative to the measurement circuits.

In some embodiments, the measurement signal pick-up unit comprises a differential amplifier and an A/D converter, wherein the differential amplifier is coupled to the measurement circuits, and is configured to differentially amplify the measurement signals from the measurement circuits, and wherein the A/D converter is coupled to the differential amplifier and is configured to convert the amplified measurement signals from analog signals to digital signals.

In some embodiments, a buffer is coupled between the measurement circuits and the differential amplifier, making the measurement circuits present a high impedance output relative to the differential amplifier.

In accordance with embodiments, a signal processing method is used for GMR-based detection of a target analyte in a sample under test, comprising: obtaining GMR sensor measurement signals, which comprises: building a GMR sensor measurement circuit by routing in at least one GMR sensor, applying a carrier signal of frequency ω1 to the GMR sensor measurement circuit, applying an AC magnetic field of frequency ω2 to the at least one GMR sensor, and collecting the GMR sensor measurement signals from the GMR sensor measurement circuit; obtaining reference resistor measurement signals, which comprises: building a reference resistor measurement circuit by routing in at least one reference resistor, applying carrier signals of frequency ω1, ω1+ω2, and ω1−ω2 to the reference resistor measurement circuit, and collecting the reference resistor measurement signals from the reference resistor measurement circuit; and analytically solving for resistance change of the at least one GMR sensor based on both the reference resistor measurement signals from the reference resistor measurement circuit and the GMR sensor measurement signals from the GMR sensor measurement circuit.

In some embodiments, the method comprises obtaining the reference resistor measurement signals precedes to obtaining the GMR sensor measurement signals.

In some embodiments, analytically solving for resistance change of the at least one GMR sensor comprises: generating in-phase and quadrature sinusoid reference signals at all frequencies of interest; multiplying the measurement signals by the reference signals to produce in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals; accumulating the in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals; and solving for the resistance change of the GMR sensor from the accumulations of the in-phase products and quadrature products at all frequencies of interest for each of the reference resistor measurement signals and the GMR sensor measurement signals. In some embodiments, the frequencies of interest are ω1, ω1+ω2, and ω1−ω2.

In some embodiments, analytically solving for resistance change of the at least one GMR sensor further comprises solving for magnetoresistance change of the at least one GMR sensor. In some embodiments, the method comprises: determining, from the solved magnetoresistance change of the at least one GMR sensor, presence or not of the target analyte in the sample under test.

In some embodiments, the method comprises determining, from the solved magnetoresistance change of the at least one GMR sensor, concentration of the target analyte in the sample under test.

In some embodiments, applying the carrier signal to the measurement circuits comprises applying a carrier current to the measurement circuits using a carrier current source, wherein building the reference resistor measurement circuit comprising connecting a reference resistor in series between the carrier current source and ground, wherein building the GMR sensor measurement circuit comprising connecting a GMR sensor in series between the carrier current source and ground, or connecting a parallel combination of more than one GMR sensor in series between the carrier current source and ground, and wherein the GMR sensor is functionalized for the target analyte.

In some embodiments, applying the carrier signal to the measurement circuits comprises applying a carrier voltage to the measurement circuits using a carrier voltage source, wherein building the GMR sensor measurement circuit comprises building a Wheatstone full bridge circuit formed by a first bridge arm and a second bridge arm, wherein the first bridge arm comprises one first voltage divider or a parallel combination of more than one first voltage divider, wherein the first voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the second bridge arm comprises one second voltage divider or a parallel combination of more than one second voltage divider, wherein the second voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the functionalized GMR sensor in the first voltage divider is connected to the carrier voltage source while the reference element in the first voltage divider is connected to ground, and wherein the functionalized GMR sensor in the second voltage divider is connected to ground while the reference element in the second voltage divider is connected to the carrier voltage source.

In some embodiments, applying the carrier signal to the measurement circuits comprises applying a carrier voltage to the measurement circuits using a carrier voltage source, wherein building the GMR sensor measurement circuit comprises building a Wheatstone full bridge circuit formed by a first bridge arm and a second bridge arm, wherein the first bridge arm comprises one first voltage divider or a parallel combination of more than one first voltage divider, wherein the first voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the second bridge arm comprises one second voltage divider or a parallel combination of more than one second voltage divider, wherein the second voltage divider is formed by a GMR sensor functionalized for the target analyte and a reference element, wherein the functionalized GMR sensor in the first voltage divider is connected to the carrier voltage source while the reference element in the first voltage divider is connected to ground, and wherein the functionalized GMR sensor in the second voltage divider is connected to the carrier voltage source while the reference element in the second voltage divider is connected to ground.

In some embodiments, building the reference resistor measurement circuit comprises building a Wheatstone full bridge circuit formed by four reference resistors, wherein three of the four reference resistors have matched resistance value, and wherein the fourth reference resistor has a mis-matched resistance value.

In some embodiments, applying the carrier signal to the measurement circuits comprises applying a carrier voltage to the measurement circuits using a carrier voltage source, wherein building the reference resistor measurement circuit comprises building an Anderson loop circuit comprised of a reference resistor voltage divider formed of two reference resistors, wherein building the GMR sensor measurement circuit comprises building an Anderson loop circuit comprised of one GMR sensor voltage divider or a parallel combination of more than one GMR sensor voltage divider, and wherein the GMR sensor voltage divider is formed of a GMR sensor functionalized for the target analyte and a reference element.

In some embodiments, the reference element in the method is a GMR sensor un-functionalized to the analyte to be detected.

In some embodiments, the reference element in the method is a reference resistor.

In some embodiments, building the measurement circuits comprises configuring at least one multiplexer.

In some embodiments, building the measurement circuits comprises configuring a bank of freely configurable switches.

In some embodiments, collecting measurement signals at the measurement circuits comprises: differentially amplifying the measurement signals at the measurement circuits, and converting the amplified measurement signals from analog signals to digital signals.

While the principles of the disclosure have been made clear in the illustrative embodiments set forth above, it will be apparent to those skilled in the art that various modifications may be made to the structure, arrangement, proportion, elements, materials, and components used in the practice of the disclosure.

It will thus be seen that the features of this disclosure have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of illustrating the functional and structural principles of this disclosure and are subject to change without departure from such principles. Therefore, this disclosure includes all modifications encompassed within the spirit and scope of the following claims.