Microfluidic Chip for In-situ Electrical Impedance Spectroscopy Detection of Nematodes

Abstract

The present invention discloses a microfluidic chip for in-situ impedance spectroscopy detection of nematodes. The chip has a three-layer structure, wherein: the lower layer is a glass substrate integrated with a microelectrode array, which is used for impedance spectroscopy measurement and nematode turning. The middle layer is a fluid channel layer, which is sequentially connected by a nematode injection channel, a storage chamber, a turning channel, an impedance spectroscopy measurement chamber, and a fluid output channel. The measurement medium injection channel is located between the nematode turning control channel and the impedance measurement chamber. The upper layer is a gas valve channel layer, wherein the storage chamber control valve is used to control the entry and exit of nematodes into and out of the storage chamber. The turning channel control valve is used to control the entry of nematodes into the measurement chamber. The nematode capture valve is used to control the capture and release of nematodes in the impedance spectroscopy measurement chamber. By adopting the above technical solutions, in-situ impedance spectroscopy measurement of nematodes can be realized based on microfluidic technology, which has the characteristics of being directional, positionable, and capable of high-speed measurement.

Description

Technical Field

[0001] The present invention belongs to the fields of microfluidic chips and micro-nano processing, and particularly relates to a microfluidic chip for in-situ impedance spectroscopy detection of nematodes. Background Art

[0002] Microfluidic technology is a technology for precisely manipulating microfluids, and the spatial characteristic scale range it studies is usually between 1 micrometer and 1 millimeter. Basic microfluidic technology has the characteristics of small capacity, small volume, low energy consumption, and high device integration. This technology is generally realized by micro-nano processing specific microfluidic chips, and it is a multi-cross field including disciplines such as engineering, fluid mechanics, electromagnetics, optics, chemistry, microfabrication, and bioengineering. At present, microfluidic chips integrated with microelectrode arrays have become an effective means for microbe-electronics research and have been applied in many fields such as DNA molecule detection, single-cell detection, microtissue sphere detection, and model organism detection. It has developed rapidly and has great scientific research potential.

[0003] Caenorhabditis elegans is a commonly used model animal in biological research and is widely used in research fields such as apoptosis, aging, nervous system, and meiosis. Research directly applying Caenorhabditis elegans has won the Nobel Prize three times and has great scientific research value. Compared with other model organisms, due to the following characteristics, Caenorhabditis elegans has become an ideal model for studying fields such as organism aging and sexual reproduction.

[0004] (1) Small body size, strong reproductive ability, and can be mass-produced under room temperature conditions.

[0005] (2) Short lifespan, it can develop into an adult in 3 - 4 days, and the average lifespan is about 2 - 3 weeks;

[0006] (3) The body of the worm is transparent, making it easy to microscopically observe its internal structure and fluorescence modification;

[0007] (4) The whole genome sequencing has been completed, making it easy to conduct gene analysis and gene modification, and about 40% of its genes are homologous to human genes;

[0008] (5) It has sex chromosomes and can be used for genetic research and research on sexual reproduction such as meiosis.

[0009] Electrical impedance spectroscopy (EIS) is a non-invasive, label-free, multi-parameter detection technique. By applying a swept-frequency alternating current excitation to the system under test and detecting the response signal, this method can accurately and quantitatively analyze the complex impedance of the system. Currently, electrical impedance spectroscopy is widely used in many fields such as electrochemical analysis, food safety detection, environmental monitoring, corrosion mechanism research, and biomedical research. In the field of biomedical research, it has applications at multiple levels such as biomacromolecules, cells, tissues, and model organisms.

[0010] Although in-situ electrical impedance spectroscopy based on microfluidics has been widely applied to cell research at present, the electrical impedance spectroscopy detection for nematode research is still in its infancy. There are mainly the following problems. First, the movement of nematodes has a great impact on impedance measurement, and it is difficult to fix them, making it difficult to ensure the measurement accuracy. Second, nematodes are slender in shape, and a single pair of electrodes is difficult to accurately measure the impedance of various parts of nematodes. Moreover, the throughput of in-situ electrical impedance spectroscopy detection is low, and it is difficult to ensure the measurement efficiency. Therefore, in order to achieve high-efficiency, high-precision, and multi-site in-situ electrical impedance spectroscopy detection of nematodes, it is necessary to develop a microfluidic chip for in-situ electrical impedance spectroscopy detection of nematodes that integrates a microelectrode array, a measurement pipeline, and a nematode fixing valve. Summary of the Invention

[0011] The purpose of the present invention is to provide a microfluidic chip for in-situ electrical impedance spectroscopy detection of nematodes to solve the technical problems that the movement of nematodes has a great impact on impedance measurement, it is difficult to fix them, and it is difficult to ensure the measurement accuracy; second, nematodes are slender in shape, a single pair of electrodes is difficult to accurately measure the impedance of various parts of nematodes; and moreover, the throughput of in-situ electrical impedance spectroscopy detection is low, and it is difficult to ensure the measurement efficiency.

[0012] To solve the above technical problems, the specific technical solution of the present invention is as follows:

[0013] A microfluidic chip for in-situ electrical impedance spectroscopy detection of nematodes includes a glass substrate layer, a fluid channel layer, and a gas valve channel layer; among them, the glass substrate layer, the fluid channel layer, and the gas valve channel layer are connected by screws;

[0014] The glass substrate layer serves as the base of the entire chip to support the upper structure and integrates a microelectrode array above it;

[0015] The fluid channel layer includes a nematode injection channel, a storage chamber, a turning channel, an electrical impedance spectroscopy measurement chamber, and a fluid output channel; among them, the nematode injection channel, the storage chamber, the turning channel, the electrical impedance spectroscopy measurement chamber, and the fluid output channel are connected in sequence; a measurement medium injection channel is connected between the turning channel and the electrical impedance spectroscopy measurement chamber;

[0016] The storage chamber is used to store the nematode samples to be measured;

[0017] The turning channel is used for nematodes to freely turn inside the channel;

[0018] The impedance spectroscopy measurement chamber is used to form an indirect contact structure with the lower electrode;

[0019] The air valve channel layer includes a storage chamber control valve, a turning channel control valve, a nematode capture valve, and a nematode fixation valve, where:

[0020] There are 2 storage chamber control valves, respectively located above the slits on both sides of the storage chamber, used to control the entry and exit of nematodes into and out of the storage chamber;

[0021] The turning channel control valve is located above the slit between the turning channel and the impedance spectroscopy measurement chamber, used to control nematodes to enter the impedance spectroscopy measurement chamber;

[0022] The nematode capture valve is located above the slit between the impedance spectroscopy measurement chamber and the fluid output channel, used to control the capture and release of nematodes in the impedance spectroscopy measurement chamber;

[0023] The nematode fixation valve is located directly above the entire impedance spectroscopy measurement chamber, and the width of the air valve channel is wider than that of the impedance spectroscopy measurement chamber, used to fix the nematodes entering the measurement channel;

[0024] The microelectrode array includes square electrode pins located around the chip, used to connect the measurement circuit; and functional structures located around the impedance spectroscopy measurement chamber and the turning channel;

[0025] The functional structures are divided into two groups. The first group is the turning electrode pairs located on both sides of the turning channel, used to control nematode turning. The second group is the impedance spectroscopy measurement electrodes located around the impedance spectroscopy measurement chamber, used to measure the impedance spectroscopy of nematodes at different positions;

[0026] The storage chamber and the storage chamber control valves on both sides form a nematode storage area; the nematode storage area completes the one-time injection and storage of nematodes; when the storage chamber control valve on the inlet side is opened and the storage chamber control valve on the outlet side is closed, nematodes are injected; when the storage chamber control valve on the inlet side is closed and the storage chamber control valve on the outlet side is opened, nematodes enter the turning channel;

[0027] The turning channel, the turning electrode pairs, and the turning channel control valve form a nematode turning area; the nematode turning area quickly turns the nematodes about to enter the impedance spectroscopy measurement area;

[0028] The impedance spectroscopy measurement chamber, the measurement medium injection channel, the impedance spectroscopy measurement electrodes, the nematode capture valve, and the nematode fixation valve form an impedance spectroscopy measurement area; the impedance spectroscopy measurement area performs in-situ impedance spectroscopy measurement on multiple sites of nematodes;

[0029] The nematode storage area, the nematode turning area, and the impedance spectroscopy measurement area constitute a measurement pipeline.

[0030] Further, the air valve channel layer is prepared from polydimethylsiloxane (PDMS) by soft lithography.

[0031] Further, the microelectrode array is made of one of Cr-Au (chromium-copper) or TiW-Pt (tungsten titanium-platinum).

[0032] Further, the storage chamber is circular; the steering channel is bar-shaped with a width twice that of an adult nematode body; the impedance spectroscopy measurement chamber is bar-shaped with a width wider than that of an adult nematode body, and multiple pairs of slits are evenly distributed on both sides of this chamber.

[0033] Further, the connections between the nematode injection channel, the storage chamber, the steering channel, the impedance spectroscopy measurement chamber, and the fluid output channel are all in an inverted triangle shape, which is used to cooperate with the control valve to open and close the flow channel; the inverted triangle slits limit the nematodes to pass through the slits one by one.

[0034] Further, the glass substrate layer, the fluid channel layer, and the air valve channel layer are fixedly connected by a multi-layer bonding method, where the glass substrate layer is located at the bottom layer, the fluid channel layer is located in the middle layer, and the air valve channel layer is located at the upper layer.

[0035] Further, the glass substrate layer integrated with the micro-motor array is isolated from the fluid channel layer by a silicon nitride passivation layer, and the fluid channel layer is isolated from the air valve channel layer by a polydimethylsiloxane (PDMS) thin film.

[0036] Further, for the microelectrode array, the lateral electrodes in the impedance spectroscopy measurement electrodes adopt a liquid electrode method, that is, the electrodes do not directly contact the measurement chamber, but indirectly contact through the slits of the fluid channel;

[0037] The microfluidic chip for in-situ impedance spectroscopy detection of nematodes of the present invention has the following advantages: The present invention designs and processes the chip through micro-nano processing technology, and combines microfluidic technology with impedance spectroscopy technology. A multi-layer design is adopted in the design structure, and the idea of an assembly line is introduced. The in-situ impedance spectroscopy detection of nematodes with high efficiency, high precision, and multiple sites is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic structural diagram of the microfluidic chip for in-situ impedance detection of nematodes provided by the present invention;

[0039] Figure 2 It is a two-dimensional structure diagram of the glass substrate and electrodes of the present invention;

[0040] Figure 3 It is a two-dimensional structure diagram of the fluid channel of the present invention;

[0041] Figure 4This is the two-dimensional structure diagram of the pneumatic diaphragm valve channel of the present invention;

[0042] Figure 5 This is the three-dimensional structure diagram of the impedance measurement area of the present invention;

[0043] Figure 6 This is the sectional view taken along the A-A direction of the three-dimensional structure of the impedance measurement area of the present invention;

[0044] Explanation of the markings in the figure: 1. Glass substrate layer; 2. Nematode injection channel; 3. Nematode storage area; 4. Storage chamber; 5. Nematode turning area; 6. Turning channel; 7. Measurement medium injection channel; 8. Turning electrode pair; 9. Impedance spectroscopy measurement chamber; 10. Impedance spectroscopy measurement area; 11. Fluid output channel; 12. Impedance spectroscopy measurement electrode; 13. Nematode capture valve; 14. Nematode fixation valve; 15. Turning channel control valve; 16. Storage chamber control valve; 601. Pneumatic valve channel layer; 602. Fluid channel layer. Detailed implementation mode

[0045] In order to better understand the purpose, structure and function of the present invention, the following further describes in detail a microfluidic chip for in-situ impedance spectroscopy detection of nematodes of the present invention with reference to the accompanying drawings.

[0046] Refer to Figure 1 , which is a schematic structural diagram of a microfluidic chip for in-situ impedance detection of nematodes provided in the implementation of the present invention.

[0047] In terms of structure, it includes a glass substrate layer 1, a fluid channel layer 602, and a pneumatic valve channel layer 601. Among them:

[0048] The glass substrate layer 1 serves as the base of the entire chip to support the upper structure and integrates a microelectrode array on the upper side.

[0049] The microelectrode array includes square electrode pins located around the chip for connecting the measurement circuit; and functional structures located around the impedance spectroscopy measurement chamber 9 and the turning channel 6;

[0050] The functional structures are divided into two groups. The first group is the turning electrode pair 8 located on both sides of the turning channel 6 for controlling nematode turning, and the second group is the impedance spectroscopy measurement electrode 12 located around the impedance spectroscopy measurement chamber 9 for measuring the impedance spectra of nematodes at different positions;

[0051] The microelectrode array, its material is Cr-Au, where Cr is the seed layer with a thickness of 50 nm and Au is the electrode layer with a thickness of 150 nm;

[0052] For the microelectrode array, a 500-nm-thick silicon nitride film is deposited on the upper side as a passivation layer.

[0053] Microelectrode array, in which the lateral electrodes in the electrical impedance spectroscopy measurement electrode 12 adopt a liquid electrode method, that is, the electrode does not directly contact the measurement chamber, but indirectly contacts through the slit of the fluid channel.

[0054] The fluid channel layer 602 includes: a nematode injection channel 2, a storage chamber 4, a turning channel 6, an electrical impedance spectroscopy measurement chamber 9, and a fluid output channel 11 connected in sequence. The measurement medium injection channel 7 is connected between the turning channel 6 and the electrical impedance spectroscopy measurement chamber 9. Among them:

[0055] The storage chamber 4 is circular and is used to store nematode samples to be measured;

[0056] The turning channel 6 is a strip structure with a width approximately twice the width of an adult nematode body, facilitating the free turning of nematodes in the channel;

[0057] The electrical impedance spectroscopy measurement chamber 9 is a strip structure with a width slightly wider than the width of an adult nematode body. There are 8 pairs of slits evenly distributed on both sides of the channel, which are used to form an indirect contact structure with the lower electrode.

[0058] The connections between the nematode injection channel 2, the storage chamber 4, the turning channel 6, the electrical impedance spectroscopy measurement chamber 9, and the fluid output channel 11 are all in an inverted triangle shape, which is used to cooperate with the control valve to open and close the flow channel. The inverted triangle slit is beneficial to restricting nematodes to pass through the slit only one by one.

[0059] The air valve channel layer 601 includes: a storage chamber control valve 16, a turning channel control valve 15, a nematode capture valve 13, and a nematode fixation valve 14, among which:

[0060] There are 2 pairs of storage chamber control valves 16, which are respectively located above the inverted triangle slits on both sides of the storage chamber 4 and are used to control the entry and exit of nematodes from the storage chamber.

[0061] The turning channel control valve 15 is located above the slit between the turning channel 6 and the electrical impedance spectroscopy measurement chamber 9 and is used to control the entry of nematodes into the electrical impedance spectroscopy measurement chamber 9.

[0062] The nematode capture valve 13 is located above the slit between the electrical impedance spectroscopy measurement chamber 9 and the fluid output channel 11 and is used to control the capture and release of nematodes in the electrical impedance spectroscopy measurement chamber 9.

[0063] The nematode fixation valve 14 is located directly above the entire electrical impedance spectroscopy measurement chamber 9, and the width of the air valve channel is slightly wider than that of the electrical impedance spectroscopy measurement chamber 9, which is used to fix the nematodes entering the measurement channel.

[0064] A microfluidic chip for in-situ impedance spectroscopy detection of nematodes. In the manufacturing process, a multi-layer bonding method is adopted. Among them, a silicon nitride passivation layer is used to isolate the glass substrate layer 1 integrated with the micro-motor array from the fluid channel layer 602, and a PDMS film is used to isolate the fluid channel layer 602 from the air valve channel layer 601.

[0065] The microelectrode array of the glass substrate layer 1 is obtained by lithography and development of AZ5214 photoresist, and then by Au electron beam evaporation. Finally, a passivation layer is obtained through silicon nitride deposition and ion reaction etching.

[0066] Both the fluid channel layer 602 and the air valve channel layer 601 are prepared by soft lithography using PMDS (polydimethylsiloxane), specifically including the preparation of a silanized mold, the ratio and mixing of PDMS and a curing agent, degassing to remove bubbles, pouring PDMS on the mold, baking PDMS, peeling the PDMS from the mold, cutting and punching the PDMS. Among them, the mold uses an SU-8 male mold.

[0067] When pouring PDMS for the fluid channel layer 602, the thickness needs to be controlled by a spin coater, and the peeling of this layer needs to be carried out after the bonding of the fluid channel layer 602 and the air valve channel layer 601.

[0068] For the bonding process of the glass substrate layer 1, the fluid channel layer 602 and the air valve channel layer 601, plasma activation is required, and then bonding is carried out by a bonder using the alignment marks on each layer, and then heated at 90 °C for 30 minutes.

[0069] The present invention functionally includes a nematode storage area 3, a nematode turning area 5, and an impedance spectroscopy measurement area 10. The three form a measurement pipeline, which can complete the turning of the next nematode while measuring the impedance of the previous one. When the previous nematode finishes measurement and is discharged, the next nematode can enter the measurement channel, and so on in a cycle.

[0070] The nematode storage area 3 includes a storage chamber 4 and storage chamber control valves 16 on both sides. The main function of this area is to complete the one-time injection and storage of a large number of nematodes. When the control valve on the inlet side is opened and the control valve on the outlet side is closed, nematodes are injected. When the control valve on the inlet side is closed and the control valve on the outlet side is opened, nematodes enter the turning channel.

[0071] The nematode turning area 5 includes: a turning channel 6, turning electrode pairs 8, and a turning channel control valve 15. The main function of this area is to quickly turn the nematodes about to enter the impedance spectroscopy measurement area 10. This scheme utilizes the nematode's electrotaxis, that is, nematodes will tend to move towards the direction of lower electric potential. By applying an electric field from left to right in the measurement area, nematodes can be quickly guided to move to the right. And through the turning control valve, it is ensured that nematodes enter the impedance spectroscopy measurement area 10 after completing the turn.

[0072] The impedance spectroscopy measurement area 10 includes: an impedance spectroscopy measurement chamber 9, a measurement medium injection channel 7, impedance spectroscopy measurement electrodes 12, a nematode capture valve 13, and a nematode fixation valve 14. The main function of this area is to perform in-situ impedance spectroscopy measurements on multiple sites of nematodes. Among them, the nematode capture valve 13 and the nematode fixation valve 14 are used in cooperation to capture nematodes and ensure the stability of nematodes during the measurement. The measurement medium injection channel 7 injects the measurement medium and other solutions required for experiments. The impedance spectroscopy measurement electrodes 12 cyclically scan the impedance spectra of different sites of nematodes. After the measurement is completed, the nematode capture valve and the nematode fixation valve are opened to release the nematodes. By turning to the measurement process in a cycle, rapid in-situ impedance spectroscopy measurements of a large number of nematodes can be completed.

[0073] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A microfluidic chip for in-situ impedance spectroscopy detection of nematodes, characterized in that, It includes a glass substrate layer (1), a fluid channel layer (602), and a gas valve channel layer (601); among them, the glass substrate layer (1), the fluid channel layer (602), and the gas valve channel layer (601) are connected by screws. The glass substrate layer (1) serves as the base of the entire chip to support the upper structure and integrates a microelectrode array above it. The fluid channel layer (602) includes a nematode injection channel (2), a storage chamber (4), a turning channel (6), an impedance spectroscopy measurement chamber (9), and a fluid output channel (11); among them, the nematode injection channel (2), the storage chamber (4), the turning channel (6), the impedance spectroscopy measurement chamber (9), and the fluid output channel (11) are connected in sequence; a measurement medium injection channel (7) is connected between the turning channel (6) and the impedance spectroscopy measurement chamber (9). The storage chamber (4) is used to store nematode samples to be measured. The turning channel (6) is used for nematodes to freely turn in the channel. The impedance spectroscopy measurement chamber (9) is used to form an indirect contact structure with the lower electrode. The gas valve channel layer (601) includes a storage chamber control valve (16), a turning channel control valve (15), a nematode capture valve (13), and a nematode fixation valve (14), where: There are 2 storage chamber control valves (16), which are respectively located above the slits on both sides of the storage chamber (4) and are used to control the entry and exit of nematodes into and out of the storage chamber (4). The turning channel control valve (15) is located above the slit between the turning channel (6) and the impedance spectroscopy measurement chamber (9) and is used to control the entry of nematodes into the impedance spectroscopy measurement chamber (9). The nematode capture valve (13) is located above the slit between the impedance spectroscopy measurement chamber (9) and the fluid output channel (11) and is used to control the capture and release of nematodes in the impedance spectroscopy measurement chamber (9). The nematode fixation valve (14) is located directly above the entire impedance spectroscopy measurement chamber (9), and the width of the gas valve channel is wider than that of the impedance spectroscopy measurement chamber (9) and is used to fix the nematodes entering the measurement channel. The microelectrode array includes square electrode pins located around the chip for connecting the measurement circuit; and functional structures located around the impedance spectroscopy measurement chamber (9) and the turning channel (6). The functional structures are divided into two groups. The first group is the turning electrode pairs (8) located on both sides of the turning channel (6) and are used to control nematode turning. The second group is the impedance spectroscopy measurement electrodes (12) located around the impedance spectroscopy measurement chamber (9) and are used to measure the impedance spectra of nematodes at different positions. The storage chamber (4) and the storage chamber control valves (16) on both sides form a nematode storage area (3); the nematode storage area (3) completes the one-time injection and storage of nematodes; when the storage chamber control valve (16) on the inlet side is opened and the storage chamber control valve (16) on the outlet side is closed, nematodes are injected; when the storage chamber control valve (16) on the inlet side is closed and the storage chamber control valve (16) on the outlet side is opened, nematodes enter the turning channel (6). The impedance spectroscopy measurement chamber (9), the measurement medium injection channel (7), the impedance spectroscopy measurement electrode (12), the nematode capture valve (13), and the nematode fixation valve (14) constitute the impedance spectroscopy measurement area (10); the impedance spectroscopy measurement area (10) performs in-situ impedance spectroscopy measurement on multiple sites of nematodes. The steering channel (6), the steering electrode pair (8), and the steering channel control valve (15) constitute the nematode steering area (5); the nematode steering area (5) quickly steers the nematodes about to enter the impedance spectroscopy measurement area (10). The nematode storage area (3), the nematode steering area (5), and the impedance spectroscopy measurement area (10) constitute a measurement pipeline.

2. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, characterized in that The air valve channel layer (601) is prepared by a soft lithography process using polydimethylsiloxane PDMS.

3. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, characterized in that, The microelectrode array is made of one of Cr-Au or TiW-Pt.

4. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, wherein The storage chamber (4) is circular; the steering channel (6) is a strip structure with a width twice that of the body width of adult nematodes; the impedance spectroscopy measurement chamber (9) is a strip structure with a width wider than the body width of adult nematodes, and multiple pairs of slits are evenly distributed on both sides of the chamber.

5. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, wherein, The connections between the nematode injection channel (2), the storage chamber (4), the steering channel (6), the impedance spectroscopy measurement chamber (9), and the fluid output channel (11) are all in an inverted triangle shape, which is used to cooperate with the control valve to open and close the flow channel; the inverted triangle slits limit the nematodes to pass through the slits only one by one.

6. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, characterized in that, The glass substrate layer (1), the fluid channel layer (602), and the air valve channel layer (601) are fixedly connected by a multi-layer bonding method.

7. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, characterized in that The glass substrate layer (1) integrated with the micro-motor array is isolated from the fluid channel layer (602) by a silicon nitride passivation layer, and the fluid channel layer (602) is isolated from the air valve channel layer (601) by a polydimethylsiloxane PDMS film.

8. The microfluidic chip for in-situ impedance spectroscopy detection of nematodes according to claim 1, characterized in that, For the microelectrode array, the lateral electrodes in the impedance spectroscopy measurement electrode (12) adopt a liquid electrode method, that is, the electrode does not directly contact the measurement chamber, but indirectly contacts through the slits of the fluid channel.

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