Arrayed chemical molecular detection system based on organic electrochemical transistor

Abstract

The application discloses an arrayed chemical molecule detection system based on an organic electrochemical transistor, which comprises a multichannel OECT sensor array, a full-spectrum light source, a detector, a main control circuit and a motion module. The full-spectrum light source irradiates the sample in the multi-well plate, the detector detects the full-spectrum absorbance of the sample in the multi-well plate, the main control circuit controls the electrode voltage of the OECT in the multichannel OECT sensor array, and the electrode current of the OECT in the multichannel OECT sensor array is detected. The application can simultaneously measure the full-spectrum absorbance data of the sample and the current data of all channels of the multichannel OECT sensor array under different voltages, so that the biochemical molecule concentration and the optical characteristics are simultaneously detected, the incubation and other links are saved, the current signal generated by electrocatalysis can be detected, the current concentration is calculated according to the signal, and a curve diagram is displayed. The application is widely applied to the technical field of molecule detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular detection, and particularly relates to an arrayed chemical molecule detection system based on organic electrochemical transistors. BACKGROUND

[0002] Current biochemical molecule detection technologies are mainly optical detection. In the process of optical detection, a catalyst and a color developing agent are often added and placed in an incubator for incubation at a certain temperature for a certain time, such as 30 minutes. This greatly limits the detection environment and does not have the ability of rapid detection and on-site detection.

[0003] Term explanation:

[0004] OECT: Organic Electrochemical Transistors, organic electrochemical transistors. SUMMARY

[0005] In view of the technical problems of low detection efficiency and many detection environment restrictions of current biochemical molecule detection technologies based on optical detection, the present application aims to provide an arrayed chemical molecule detection system based on organic electrochemical transistors.

[0006] The embodiment of the present application comprises an arrayed chemical molecule detection system based on organic electrochemical transistors, comprising:

[0007] a multi-channel OECT sensor array; the multi-channel OECT sensor array is used for placing a multi-well plate, the multi-well plate is used for containing a sample, and the multi-channel OECT sensor array is used for electrocatalyzing the sample;

[0008] a full-spectrum light source; the full-spectrum light source is used for full-spectrum irradiation of the sample in the multi-well plate;

[0009] a detector; the detector is used for detecting the full-spectrum absorbance of the sample in the multi-well plate;

[0010] a main control circuit; the main control circuit comprises a voltage regulation module, a current detection module and a motion control module; the voltage regulation module is used for regulating the electrode voltage of an OECT in the multi-channel OECT sensor array; and the current detection module is used for detecting the electrode current of the OECT in the multi-channel OECT sensor array;

[0011] a motion module; the motion module is used for driving the multi-well plate to move relative to the full-spectrum light source under the control of the main control circuit.

[0012] Further, the motion module comprises a stepper motor, a power supply, a driver, a first guide rail, a second guide rail, a first sliding block, a second sliding block, a coupling, a host computer, a sensor, and a multi-well plate support for fixing the multi-well plate.

[0013] The first sliding block is defined to move in the first guide rail, and the second sliding block is defined to move in the second guide rail; the first guide rail and the first sliding block are arranged in an X direction, and the second guide rail and the second sliding block are arranged in a Y direction.

[0014] The multi-well plate support is fixed on the first sliding block, and the first sliding block and the bottom of the first guide rail are fixed on the second sliding block through the coupling.

[0015] The sensor is arranged at the origin position of the X and Y directions, and is used for origin positioning when the first guide rail and the second guide rail are reset.

[0016] Further, the multi-well plate support is a hollow structure in the middle, and the multi-well plate support is fixed in the middle with the edge of the multi-well plate, thereby bearing the multi-well plate.

[0017] Further, the host control circuit is used for acquiring a motion instruction and a voltage regulation parameter, sending the motion instruction to the driver, and driving the stepper motor to control the sliding block to move on the guide rail by the driver.

[0018] The host control circuit outputs a voltage to the sensor through a digital-to-analog conversion module.

[0019] The host computer sends a motion instruction according to the current position and the predetermined position of the guide rail and the sliding block.

[0020] Further, the detector is used for generating optical waveform data and current waveform data according to the full-spectrum absorbance.

[0021] Further, the detector is used for sending the optical waveform data and the current waveform data to the host computer, and displaying the optical waveform data and the current waveform data.

[0022] Further, the arrayed chemical molecule detection system based on the organic electrochemical transistor further comprises a first collimating mirror, a second collimating mirror, and a fiber support.

[0023] The first collimating mirror and the second collimating mirror are oppositely arranged.

[0024] The fiber support is an E-shaped three-layer plate structure, the upper layer of the fiber support is used for fixing the first collimating mirror, and the lower layer of the fiber support is used for fixing the second collimating mirror.

[0025] The full spectrum light source is connected to the middle plate of the optical fiber support through an optical fiber and the first collimating mirror, and the first collimating mirror 5 is connected to the middle plate of the optical fiber support perpendicularly through a corresponding collimating mirror flange plate and a screw thread;

[0026] The detector is connected to the top plate of the optical fiber support through an optical fiber, the second collimating mirror and a corresponding flange plate; and the multi-channel OECT sensor array can be moved between the top plate and the middle plate of the optical fiber support.

[0027] Further, the OECT electrode surface or channel film surface in the multi-channel OECT sensor array is subjected to a molecular recognition agent surface modification treatment.

[0028] Further, the OECT in the multi-channel OECT sensor array contains an electrolyte solution, and the electrolyte solution contains an organic color developing agent.

[0029] Further, the electrolyte solution is a PBS solution or a hydrogel.

[0030] The arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment can simultaneously measure full spectrum absorbance data of a sample and current data at different voltages of all channels of the channel OECT sensor array, so as to realize simultaneous detection of biochemical molecule concentration and optical characteristics, accurately control the movement and positioning of the multi-well plate through the motion control module, ensure the accuracy of the test and realize high-throughput measurement, electrocatalyze the detected molecules to make them react quickly, save the incubation process, detect the current signal generated by electrocatalysis, measure the current concentration and display a curve according to the signal. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a physical structure diagram of the arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment.

[0032] Figure 2 It is a circuit structure diagram of the arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment.

[0033] Figure 3 It is a program flowchart of the main control circuit in the embodiment.

[0034] REFERENCE NUMERALS:

[0035] 1 - full spectrum light source, 2 - optical fiber, 3 - optical fiber support, 4 - collimator flange, 5 - first collimator, 6 - multi-channel OECT sensor array, 7 - multi-well plate support, 8 - housing, 9 - spectrometer in detector, 10 - ball screw, 11 - first guide rail, 12 - driver, 13 - stepper motor, 14 - coupling, 15 - sensor, 16 - workbench, 17 - main control circuit, 18 - power supply. DETAILED DESCRIPTION

[0036] In this embodiment, the physical structure of the arrayed chemical molecule detection system based on organic electrochemical transistor is shown in Figure 1 Referring to Figure 1 , the arrayed chemical molecule detection system based on organic electrochemical transistor includes a light-transmissive multi-channel OECT sensor array, a full spectrum light source, a detector, a main control circuit and a motion module.

[0037] Specifically, the arrayed chemical molecule detection system based on organic electrochemical transistor mainly includes a full spectrum light source, a detector (spectrometer), a high-precision ball screw two-dimensional slide and a light-transmissive multi-channel OECT sensor array, wherein the sensor array adopts a 24 or 96 well uniform arrangement. The high-precision ball screw two-dimensional slide specifically includes a stepper motor, a main control circuit, a power supply, a driver, two sets of guide rails and sliding blocks, a coupling, a multi-well plate support, an upper computer and a sensor. Among them, the two sets of guide rails and sliding blocks are arranged in X and Y directions respectively, the multi-well plate support 7 is fixed on the sliding block of one set of guide rails and sliding blocks, and the bottom of this set of guide rails and sliding blocks is fixed on the sliding block of the other set of guide rails and sliding blocks through the coupling. The proximity sensor is arranged on the side of the origin position of the guide rail, which is used for the origin positioning when the sliding block is reset.

[0038] It should be pointed out that the detector for measuring the full spectrum absorbance of the sample in the OECT sensor array irradiated by the full spectrum is any detector containing CCD, which can measure the full spectrum, such as spectrometer, etc.; the control device can be belt drive, slide, etc.

[0039] In this embodiment, the circuit structure of the arrayed chemical molecule detection system based on organic electrochemical transistor is shown in Figure 2

[0040] ​In the embodiment, the multi-channel OECT sensor array is used to place the multi-well plate. When the detection system is used, the sample (for example, the solution to be detected) is added to the multi-well plate, and the sample is subjected to electrocatalysis by the multi-channel OECT sensor array. The multi-channel OECT sensor array includes a plurality of electrochemical organic transistors (OECTs). The OECT electrode surface or the channel film surface is subjected to surface modification treatment by a molecular recognition agent, and the OECT contains an electrolyte solution or has the electrolyte solution inside, and the electrolyte solution contains an organic color developing agent. Specifically, a PBS solution or a hydrogel can be used as the electrolyte solution.

[0041] In the embodiment, the multi-channel OECT sensor array uses OECT as a sensing element, and the voltage regulation module in the main control circuit is used to apply voltage to two of the source, drain and gate of the OECT (the voltage can be adjusted in real time by software), so as to electrocatalyze the sample added with the color developing agent and cause the solution to change color. The sample in the multi-well plate is subjected to full-spectrum illumination (the illumination wavelength band can be between 360 nm and 2000 nm) by a full-spectrum light source.

[0042] The motion module is used to drive the multi-well plate to move relative to the full-spectrum light source under the control of the main control circuit.

[0043] In the embodiment, the motion module includes a stepper motor, a power supply, a driver, a first guide rail, a second guide rail, a first sliding block, a second sliding block, a coupling, an upper computer, a sensor and a multi-well plate support for fixing the multi-well plate. The first sliding block is limited to move in the first guide rail to form an assembly, and the second sliding block is limited to move in the second guide rail to form another assembly. The first guide rail and the first sliding block are arranged in the X direction, and the second guide rail and the second sliding block are arranged in the Y direction, wherein the X direction and the Y direction are perpendicular to each other. The sensor is arranged at the origin position of the X and Y directions, and the sensor is positioned at the origin when the first guide rail and the second guide rail are reset.

[0044] In the embodiment, the multi-well plate support has a hollow structure in the middle, and the middle of the multi-well plate support is fixed to the edge of the multi-well plate to support the multi-well plate, facilitate light path measurement, and take and place the multi-well plate. The multi-well plate support is fixed to the first sliding block, and the first sliding block and the bottom of the first guide rail are fixed to the second sliding block through the coupling.

[0045] In the embodiment, the main control circuit is integrated with a control chip, a serial chip and a signal output circuit, and the signal output circuit is connected with the driver, wherein the control chip uses STM32F103RCT6, and the serial chip uses CH340. Through the serial chip, the main control circuit can communicate with the upper computer (which can be a personal computer or the like). The main control circuit also has a power supply module, which can convert 12V DC input into 5V, -5V and 3.3V voltages to supply power to each component in the detection system.

[0046] The main control circuit 17 is mainly used for receiving the motion instruction and the sensor voltage regulation parameter sent by the upper computer, and sending the signal for controlling the motor to the driver 12. The power supply 18 is connected with the driver 12, the driver 12 drives the stepping motor 13 to operate, and outputs different voltages to the OECT sensor array 6. The main control circuit 17 is integrated with a control chip, a serial chip, a key, a motor signal output circuit, a multi-channel digital-to-analog conversion voltage output circuit and a current detection circuit. Preferably, the control chip adopts STM32, the serial chip adopts CH340, and the digital-to-analog conversion chip adopts DAC81416. The motor signal output circuit is directly connected with the signal input port of the driver.

[0047] Specifically, the program flow of the main control circuit is as shown in Figure 3 The current position is automatically zeroed after the system is powered on, that is, the main control circuit starts the timer, judges whether the proximity sensor signal reaches the threshold value, if yes, the current position is the original position, the control signal is stopped from being sent to the driver, the current position is sent to the upper computer as zero, and the timer is interrupted, if not, the control signal is sent to the driver, the sensor signal is judged again until the threshold value is reached. Then the main control circuit receives the instruction of the upper computer, judges whether the correct instruction is received, if yes, the control signal is sent to the driver, the driver controls the stepping motor to move, the current position after moving is calculated according to the pulse, and the current position is sent to the upper computer, otherwise, the instruction of the upper computer is accepted again until the predetermined position is reached.

[0048] In the embodiment, the main control circuit obtains the motion instruction and the voltage regulation parameter, sends the motion instruction to the driver, and drives the stepping motor to control the slider to move on the guide rail under the control of the driver. The main control circuit outputs the voltage to the sensor through the digital-to-analog conversion module; the upper computer sends the motion instruction according to the current position and the predetermined position of the guide rail and the slider.

[0049] In the embodiment, under the control of the main control circuit, the first slider can drive the multi-well plate along the first guide rail in the X direction and along the second guide rail in the Y direction through the multi-well plate support, so that the sample in the multi-well plate can reach different positions of the multi-channel OECT sensor array, and different OECTs in the multi-channel OECT sensor array can catalyze the sample.

[0050] In the embodiment, the detector includes a micro spectrometer, the spectrum or absorbance information of the sample can be detected through the spectrometer, so as to generate optical waveform data. The electrode current generated by catalysis on the OECT is accurately detected through the current detection module in the main control circuit, so as to generate current waveform data.

[0051] The detector can store the optical waveform data and the current waveform data locally, and in the case that the detection system is provided with a display, the detector can send the optical waveform data and the current waveform data to the display, and display the optical waveform data and the current waveform data through the display.

[0052] The detector can also send the optical waveform data and the current waveform data to a host computer, and the host computer can store and display the optical waveform data and the current waveform data. The host computer is used to select a channel to be optically measured, set a predetermined position, and set the output voltage of each channel sensor, and send a motion instruction according to the current position and the predetermined position of the two guide rails and the slider. The current waveform data is displayed at the same time, and the current data is saved. The waveform data includes voltage, current data and absorbance data. The data can be saved in an array form locally.

[0053] By displaying the optical waveform data and the current waveform data, the photoelectric hybrid detection of the sample is realized.

[0054] In the embodiment, the arrayed chemical molecule detection system based on organic electrochemical transistors further comprises a first collimating mirror, a second collimating mirror and a fiber support. The first collimating mirror and the second collimating mirror are oppositely arranged, i.e. the first collimating mirror and the second collimating mirror are located in the visual field range of each other.

[0055] In the embodiment, the fiber support is an E-shaped three-layer plate structure, the upper layer of the fiber support is used to fix the first collimating mirror, and the lower layer of the fiber support is used to fix the second collimating mirror. The full-spectrum light source is connected with the first collimating mirror through the fiber of the SMA905 joint and a thread, the first collimating mirror is connected with the corresponding collimating mirror flange plate through a thread, and is vertically connected to the middle plate of the fiber support.

[0056] In the embodiment, the spectrometer in the detector is connected to the top plate of the fiber support through the fiber, the second collimating mirror and the corresponding flange plate; and the multi-channel OECT sensor array can move between the top plate and the middle plate of the fiber support, align the sample solution of a specified channel to the measurement light path, and perform measurement.

[0057] In the embodiment, the working principle of the arrayed chemical molecule detection system based on organic electrochemical transistors is that the absorbance data of the full spectrum (200nm-850nm) of the sample and the current data of all channels of the channel OECT sensor array under different voltages are measured at the same time, so as to realize the simultaneous detection of the biochemical molecule concentration and the optical characteristics. The motion control module can accurately control the motion and positioning of the multi-well plate, ensure the accuracy of the test, and realize high-throughput measurement. Through the above working principle, the arrayed chemical molecule detection system based on organic electrochemical transistors has the following advantages:

[0058] (1) can electrocatalyze the detected molecules to make them react quickly, saving the incubation process, can detect the current signal generated by electrocatalysis, and measure the current concentration and display the curve according to the signal;

[0059] (2) After adding a color developing agent to the detection solution, the spectral information can be detected;

[0060] (3) The concentration information, electrocatalytic pressure voltage, and optical waveform data and current waveform data can be displayed on the computer operation interface of the host computer and saved locally in real time, wherein the optical waveform data can be displayed in the form of a spectral graph, and the current waveform data can be displayed in the form of an I-V curve.

[0061] The computer program for executing the arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment can be written into a storage medium or a computer device, and when the computer program is read out and run, the arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment is executed, so as to realize the same technical effect as the arrayed chemical molecule detection system based on the organic electrochemical transistor in the embodiment.

[0062] It should be noted that, unless otherwise specified, when a certain feature is referred to as being "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. In addition, the up, down, left, right and the like used in the disclosure are only relative to the relative position relationship of the components of the disclosure in the drawings. In the disclosure, the singular forms "a", "an" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. In addition, unless otherwise defined, all technical and scientific terms used in the embodiments have the same meanings as those commonly understood by those skilled in the art. The terms used in the embodiments are only used to describe the specific embodiments, and are not intended to limit the present application. The term "and / or" used in the embodiments includes any combination of one or more related listed items.

[0063] It should be understood that although the terms first, second, third, etc. can be used in the disclosure to describe various elements, these elements should not be limited to these terms. These terms are only used to distinguish elements of the same type from each other. For example, without departing from the scope of the disclosure, the first element can also be referred to as the second element, and similarly, the second element can also be referred to as the first element. The use of any and all examples or exemplary language (for example, "for example", "for example", etc.) provided in the embodiments is only intended to better illustrate the embodiments of the present application, and unless otherwise required, does not impose any limitation on the scope of the present application.

[0064] It should be recognized that embodiments of the present invention can be implemented or carried out by computer hardware, a combination of hardware and software, or by computer instructions stored in a non-transitory computer-readable storage medium. The method can be implemented using standard programming techniques—including a non-transitory computer-readable storage medium configured with a computer program, wherein such a storage medium causes the computer to operate in a specific and predefined manner—according to the methods and drawings described in the specific embodiments. Each program can be implemented in a high-level procedural or object-oriented programming language to communicate with the computer system. However, if desired, the program can be implemented in assembly or machine language. In any case, the language can be a compiled or interpreted language. Furthermore, for this purpose, the program can run on a programmed application-specific integrated circuit (ASIC).

[0065] Furthermore, the procedures described in this embodiment can be performed in any suitable order unless otherwise indicated by this embodiment or clearly contradicted by the context. The procedures (or variations and / or combinations thereof) described in this embodiment can be executed under the control of one or more computer systems configured with executable instructions, and can be implemented by hardware or a combination thereof as code (e.g., executable instructions, one or more computer programs, or one or more applications) that commonly executes on one or more processors. The computer program includes a plurality of instructions executable by one or more processors.

[0066] Furthermore, the method can be implemented in any suitable type of computing platform, including but not limited to personal computers, minicomputers, mainframes, workstations, networked or distributed computing environments, standalone or integrated computer platforms, or in communication with charged particle tools or other imaging devices. Aspects of the invention can be implemented as machine-readable code stored on a non-transitory storage medium or device, whether removable or integrated into a computing platform, such as a hard disk, optical read and / or write storage medium, RAM, ROM, etc., such that it is readable by a programmable computer, and when the storage medium or device is read by the computer, it can be used to configure and operate the computer to perform the processes described herein. Furthermore, the machine-readable code, or portions thereof, can be transmitted via wired or wireless networks. The invention described in this embodiment includes these and other different types of non-transitory computer-readable storage media when such media comprises instructions or programs that implement the steps described above in conjunction with a microprocessor or other data processor. When programmed according to the methods and techniques described in the invention, the invention also includes the computer itself.

[0067] A computer program can be applied to input data to perform the functions described in this embodiment, thereby transforming the input data to generate output data that is stored to non-volatile memory. The output information can also be applied to one or more output devices such as a display. In a preferred embodiment of the application, the transformed data represents a physical and tangible object, including a particular visual depiction of a physical and tangible object produced on a display.

[0068] The above description is only preferred embodiments of the present application, the present application is not limited to the above-described embodiments, as long as the same means to achieve the technical effects of the present application, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the scope of protection of the present application. The technical solutions and / or embodiments within the scope of protection of the present application can have various modifications and changes.

Claims

1. An arrayed chemical molecule detection system based on organic electrochemical transistors, characterized in that, The arrayed chemical molecule detection system based on organic electrochemical transistors includes: A multi-channel OECT sensor array; the multi-channel OECT sensor array is used to house a multi-well plate, the multi-well plate is used to contain a sample, the surface of the OECT electrode or the surface of the channel film in the multi-channel OECT sensor array is modified with a molecular recognition agent, the multi-channel OECT sensor array is used to electrocatalyze the sample to change the color of the solution; the OECT in the multi-channel OECT sensor array contains an electrolyte solution, the electrolyte solution contains an organic colorimetric agent. A full-spectrum light source; the full-spectrum light source is used to irradiate the sample in the porous plate with the full spectrum; Detector; the detector is used to detect the full-spectrum absorbance of the sample in the porous plate; The main control circuit includes a voltage regulation module, a current detection module, and a motion control module. The voltage regulation module is used to regulate the electrode voltage of the OECT in the multi-channel OECT sensor array, wherein the electrode voltage is the voltage between two of the source, drain, and gate electrodes of the OECT. The current detection module is used to detect the electrode current generated by catalysis on the OECT in the multi-channel OECT sensor array. Motion module; the motion module is used to drive the porous plate to move relative to the full-spectrum light source under the control of the main control circuit.

2. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 1, characterized in that, The motion module includes a stepper motor, a power supply, a driver, a first guide rail, a second guide rail, a first slider, a second slider, a coupling, a host computer, a sensor, and a perforated plate bracket for fixing the perforated plate. The first slider is confined to move within the first guide rail, and the second slider is confined to move within the second guide rail; the first guide rail and the first slider are arranged in the X direction, and the second guide rail and the second slider are arranged in the Y direction; The perforated plate bracket is fixed to the first slider, and the bottom of the first slider and the first guide rail are fixed to the second slider by the coupling; The sensor is positioned at the origin in the X and Y directions to perform origin positioning when the first and second guide rails move and reset.

3. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 2, characterized in that, The perforated plate support has a hollow structure in the middle, and the middle of the perforated plate support is fixed to the edge of the perforated plate, thereby supporting the perforated plate.

4. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 2, characterized in that: The main control circuit is used to acquire motion commands and voltage regulation parameters, and send the motion commands to the driver, which drives the stepper motor to control the slider to move on the guide rail. The main control circuit outputs voltage to the sensor via a digital-to-analog converter module; The host computer issues motion commands based on the current and predetermined positions of the guide rail and slider.

5. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 1, characterized in that, The detector is used to generate optical waveform data and current waveform data based on the full-spectrum absorbance.

6. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 5, characterized in that, The detector is used to send the optical waveform data and the current waveform data to the host computer and display the optical waveform data and the current waveform data.

7. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 1, characterized in that, The arrayed chemical molecule detection system based on organic electrochemical transistors also includes a first collimating mirror, a second collimating mirror, and an optical fiber support. The first collimating lens and the second collimating lens are arranged opposite to each other; The fiber optic bracket has an E-shaped three-layer structure. The upper layer of the fiber optic bracket is used to fix the first collimating lens, and the lower layer of the fiber optic bracket is used to fix the second collimating lens. The full-spectrum light source is connected to the first collimating lens via optical fiber and threads, and the first collimating lens is vertically connected to the middle plate of the optical fiber support via threads and a corresponding collimating lens flange. The detector is connected to the top plate of the fiber optic bracket via an optical fiber, the second collimating lens, and a corresponding flange; the multi-channel OECT sensor array is movable between the top plate and the middle plate of the fiber optic bracket.

8. The arrayed chemical molecule detection system based on organic electrochemical transistors according to claim 1, characterized in that, The electrolyte solution is a PBS solution or a hydrogel.

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