Optical sensing device with direct electrical signal readout and method of manufacturing thereof

Abstract

The application belongs to the field of electronic information, and relates to an optical sensing device for directly reading an electric signal and a preparation method thereof. An excitation light is irradiated to a periodic metal nanostructure array layer. A to-be-measured object is injected into a flow cell and immersed in a sensing chip. Then, the sensing chip has a reflection spectrum with a characteristic reflection valley. When the concentration or type of the to-be-measured object changes, the center position of the characteristic reflection valley of the reflection spectrum changes. Then, the characteristic peak position of the light response spectrum of the sensing device is displaced, and the photoelectric current between two leads directly changes. Through the change of the output photoelectric current of the device, the concentration or type of the to-be-measured object can be inversed. The device does not need an external semiconductor photoelectric detection unit, and can realize the working characteristic of directly reading an electric signal. In addition, the device can work in a self-driven working mode, and the light source used does not need to change the incident angle, power and wavelength in the sensing test process.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical sensing device for direct readout of electrical signals and a preparation method thereof, and relates to optoelectronics and micro-nano manufacturing, and belongs to the field of electronic information. BACKGROUND

[0002] In recent years, the sensing and detection of biological / chemical molecules play an increasingly important role and have an urgent demand in the fields of environmental monitoring, food safety, medical diagnosis, etc. High-performance, convenient operation, diversified functions, and intelligent biological / chemical sensing systems have attracted great attention and focused investment from the academic and industrial communities. According to the working principle, biological / chemical sensing devices mainly include electrochemical sensors, thermal sensors, acoustic sensors, and optical sensors, etc. Electrochemical sensors are a technology based on the electrochemical properties of the measured substance and convert the chemical quantity of the measured substance into an electrical quantity for sensing and detection. Although electrochemical sensors have the advantages of fast detection speed, high sensitivity, strong selectivity, and electrical signal readout, they still face great challenges in the real-time detection of living biological molecules and the label-free detection of biological / chemical substances due to the need to modify the sensing elements (such as enzymes) with specific recognition properties on the electrode. In contrast, optical sensors are based on the direct (or indirect through a medium) interaction between light waves and the measured substance. The change in optical properties (such as refractive index) causes a change in the characteristic spectrum, which is then used to infer the type or concentration of the measured substance. Common signal conversion techniques for optical sensing include fluorescence spectroscopy, Raman spectroscopy, reflection interference spectroscopy, extinction spectroscopy, and surface plasmon resonance (SPR), etc. Among them, SPR sensors can localize the incident light in the deep subwavelength region and can adjust the position and intensity of the resonance peak through parameters such as morphology and size, which shows significant technical advantages in real-time, label-free, and non-destructive detection.

[0003] Currently, there are two main types of commercialized SPR sensor architectures: one is the Kretschmann prism coupled metal thin film (such as the GE Biacore T200 system in the United States), and the other is the metal nanostructure array (Insplorion Xnano instrument in Sweden). The working principle of the former is that when the adsorbed substance on the surface of the metal thin film changes, the incident wavelength or angle of the surface plasmon polariton (SPP) excited will shift, and the adsorbed substance can be sensed and detected by monitoring the shift of these light information quantities. The working principle of the latter is that when the refractive index of the substance on or near the surface of the metal nanostructure changes, the reflection, transmission or absorption spectrum of the metal nanostructure array will have a characteristic peak or valley shift, and then the type or concentration of the background substance can be inferred. In the academic field, thanks to the rapid development of advanced micro-nano manufacturing technology, various morphologies or composite micro-nano structures of different materials have been proposed and prepared, and used to develop high-performance SPR sensing devices. For example, Ren et al. combined holographic lithography and electron beam evaporation technology to prepare a hexagonal array of gold nanohemisphere structures, and by precisely controlling the scattering body feature size, uniformity and surface roughness of the gold nanostructure, an SPR sensing detection with a half-height width as low as 3 nm and a figure of merit (FOM, defined as the ratio of optical sensitivity to resonance peak half-height width) of 730 was achieved [B. Liu et al. A plasmonic sensor array with ultrahigh figures of merit and resonance linewidths down to 3 nm, Advanced Materials, 2018, 30, 1706031]. Chinese patent (Patent No.: ZL 201711291796.0) proposes to use a self-assembled polystyrene microsphere array as a template to prepare a gold nanohole array film, and couple it with a gold film covered with a dielectric layer. Numerical calculation predicts that an ultra-low reflection peak with a half-height width of only 4 nm can be obtained, and the peak position appears a linear shift with the change of the background refractive index.

[0004] SPR sensors have been proven to have high optical sensitivity (defined as the shift of spectral characteristic peak or valley per refractive index change, unit: nm / RIU), label-free and real-time analysis in the field of biological / chemical molecule detection, but these sensing systems must be equipped with high-resolution spectrometers, external semiconductor photodetector modules or high-precision mechanical devices to realize the detection of spectral frequency domain information, light intensity change or precise control of incident angle. These requirements make the overall volume of the SPR sensor larger and the detection cost higher, which is not conducive to the development trend and requirement of integration, digitization and multifunctionalization of sensing devices. SUMMARY

[0005] The present application is to solve the technical problem that the existing optical sensing device needs to be configured with a spectrometer, a photoelectric detection module or a rotating motor and cannot directly read out an electrical signal, and proposes a technical solution that can directly read out an electrical signal, as follows.

[0006] An optical sensing device for directly reading out an electrical signal, comprising: an excitation light source, a sensing chip, a flow cell, and a counter electrode; the sensing chip is arranged in the flow cell, wherein the sensing chip comprises: a metal substrate layer, and a semiconductor thin film layer, a periodic metal nanostructure array layer arranged on the metal substrate layer in sequence; the flow cell is used for containing a to-be-measured substance, and the flow cell is provided with a to-be-measured substance input pipeline, a to-be-measured substance discharge pipeline, and a transparent window; a sensing chip lead end is arranged on the metal substrate layer; the counter electrode is arranged between the transparent window and the sensing chip, and a counter electrode lead end is arranged on the counter electrode; a digital source table or an ammeter is connected between the sensing chip lead end and the counter electrode lead end; and the light emitted by the excitation light source is incident on the transparent window.

[0007] The incident light emitted by the excitation light source is irradiated onto the periodic metal nanostructure array layer after passing through the transparent window, and the to-be-measured substance is injected through the input pipeline and fills the flow cell; when the to-be-measured substance immerses the sensing chip, the sensing chip will exhibit a reflection spectrum with a characteristic reflection valley; at the same time, when the concentration or type of the to-be-measured substance changes, the center position of the characteristic reflection valley of the reflection spectrum will change, thereby causing the characteristic peak position of the light response spectrum of the sensing device to shift, which directly manifests as a change in the photocurrent between the two leads; by monitoring the change in the photocurrent, the concentration or type of the to-be-measured substance is inverted.

[0008] The principle of generating an electrical signal by the optical sensing device is as follows: the incident photons of a specific wavelength generate surface plasmon resonance in the sensing chip, causing most of the energy of the incident light to be absorbed by the periodic metal nanostructure array layer; a pair of hot electrons and hot holes is generated in the periodic metal nanostructure array layer, and the hot holes diffuse to the surface of the periodic metal nanostructure to participate in the oxidation reaction of the to-be-measured substance; when the semiconductor thin film layer is an n-type semiconductor, the hot electrons are injected into the n-type semiconductor thin film layer and finally led out by the metal substrate layer, and the flowing electrons reach the counter electrode through the external lead wire to participate in the reduction reaction, thereby forming a closed-loop current. In addition, when the semiconductor thin film layer is a p-type semiconductor, and the to-be-measured substance is more easily reduced than oxidized, the hot electrons diffuse to the surface of the periodic metal nanostructure to participate in the reduction reaction, and the hot holes are injected into the p-type semiconductor thin film layer and finally led out by the metal substrate layer, and the flowing holes reach the counter electrode through the external lead wire to participate in the oxidation reaction, thereby forming a closed-loop current.

[0009] The technical scheme has the advantages that no external semiconductor photoelectric detection module is needed, and the heat holes generated in the sensing chip can be directly used to oxidize (or heat electrons to reduce) the measured object to form an electric signal; the sensing device does not need an external bias voltage and can work in a self-driven mode; a fixed-power light source can be used, and the wavelength and angle of the incident light do not need to be changed, and a spectrometer is not necessary; and the working wavelength (i.e., the wavelength of the light source) can be regulated by changing the period, width, shape of the periodic metal nanostructure and the thickness of the semiconductor thin film layer.

[0010] Preferably, the periodic metal nanostructure array layer and the semiconductor thin film layer form a Schottky contact, and the corresponding barrier height is less than the photon energy corresponding to the plasmon resonance wavelength.

[0011] Preferably, the period of the periodic metal nanostructure array layer is 300-2000 nm, and the width is 20%-90% of the period.

[0012] Preferably, the material of the periodic metal nanostructure array layer is one of gold, silver, palladium and transition metal nitride.

[0013] Preferably, the semiconductor thin film layer is an n-type semiconductor, and the material is one of titanium oxide, zinc oxide, tin oxide, magnesium oxide and lithium fluoride.

[0014] Preferably, the semiconductor thin film layer is a p-type semiconductor, and the material is one of nickel oxide, molybdenum oxide and vanadium oxide.

[0015] Preferably, the metal substrate layer comprises a polished metal substrate and a deposited metal thin film.

[0016] Preferably, the material of the metal substrate layer is determined according to the material of the semiconductor thin film layer, so that the contact barrier formed by the metal substrate layer and the semiconductor thin film layer is as small as possible.

[0017] Preferably, the counter electrode is a platinum wire electrode.

[0018] The preparation method of the optical sensing device for directly reading an electric signal in the above scheme is as follows:

[0019] 1) Depositing a semiconductor thin film layer on a metal substrate layer;

[0020] 2) Obtaining a photoresist with a periodic nanostructure pattern on the semiconductor thin film layer through a photoetching process;

[0021] 3) Depositing a metal thin film on the patterned photoresist, and obtaining a reverse structure of the photoresist pattern, i.e., a periodic metal nanostructure array layer, through a stripping process;

[0022] 4) welding the sensing chip lead on the metal substrate layer, obtaining a sensing chip composed of a periodic metal nanostructure array layer, a semiconductor thin film layer and a metal substrate layer;

[0023] 5) making a flow cell and setting a transparent window in the center of the front face, so that the window area is larger than the spot area of the excitation light source used;

[0024] 6) placing the sensing chip into the flow cell and making the periodic metal nanostructure array layer directly below the transparent window;

[0025] 7) placing a counter electrode above the sensing chip inside the flow cell and setting a counter electrode lead on the counter electrode;

[0026] 8) setting two opposite round holes at the edge of the transparent window of the flow cell and welding a thin tube on each hole for serving as a substance input pipe and a substance discharge pipe;

[0027] 9) connecting a digital source meter or a current meter between the sensing chip lead and the counter electrode lead;

[0028] 10) setting an excitation light source and coupling or directly irradiating the spot to the transparent window of the flow cell. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 : a structural schematic diagram of an optical sensing device with direct reading of electrical signals;

[0030] wherein: 10 - sensing chip, 11 - sensing chip lead, 12 - counter electrode lead, 13 - substance input pipe, 14 - substance discharge pipe, 15 - transparent window, 16 - excitation light source, 17 - flow cell.

[0031] Figure 2 : a structural schematic diagram of a sensing chip;

[0032] wherein: 21 - metal substrate layer, 22 - semiconductor thin film layer, 23 - periodic metal nanostructure array layer.

[0033] Figure 3 : a typical optical absorption spectrum of an optical sensing device with direct reading of electrical signals;

[0034] wherein: 31 - background substance is air, 32 - background substance is deionized water, 33 - background substance is glucose solution.

[0035] Figure 4 : a working principle diagram of an optical sensing device with direct reading of electrical signals;

[0036] wherein: 44 - counter electrode, 45 - digital source meter, 46 - surface plasmon resonance.

[0037] Figure 5 : Typical photoresponsivity spectrum of an optical sensing device with direct readout of electrical signals. DETAILED DESCRIPTION

[0038] In order to more clearly illustrate the present invention, further description is given below with reference to the accompanying drawings and embodiments.

[0039] Example 1

[0040] An optical sensing device that directly reads out electrical signals, such as Figure 1 As shown, it includes: an excitation light source 16, a sensor chip 10, a flow cell 17, and a counter electrode; the sensor chip is arranged in the flow cell, wherein the sensor chip structure is a layer structure, such as Figure 2 As shown, it includes: a metal base layer 21, and a semiconductor thin film layer 22 and a periodic metal nanostructure array layer 23 sequentially arranged on the metal base layer 21; a circulation pool 17 is used to hold the object to be tested, and the circulation pool is provided with an object to be tested input pipe 13, an object to be tested discharge pipe 14, and a transparent window 15; the sensor chip lead terminal 11 is provided on the metal base layer; the counter electrode is provided between the transparent window and the sensor chip, and the counter electrode lead terminal 12 is provided on the counter electrode; the light emitted by the excitation light source 16 is incident on the transparent window 15; a digital source meter or an ammeter is connected between the sensor chip lead terminal and the counter electrode lead terminal.

[0041] The preparation process of an optical sensing device for direct readout of electrical signals is as follows:

[0042] 1) Using a polished aluminum substrate as the base;

[0043] 2) depositing a 100 nm thick titanium oxide film on a cleaned and polished aluminum substrate;

[0044] 3) A nanodisk patterned photoresist with a period of 1000 nm and a diameter of 750 nm was obtained on the titanium oxide film by a micro-nanosphere photolithography process;

[0045] 4) electron beam evaporating a gold film on the patterned photoresist, and obtaining the inverse structure of the photoresist nanodisk (i.e., gold nanohole array) through a lift-off process;

[0046] 5) welding wires to the back of the polished aluminum substrate to obtain a sensor chip consisting of the gold nanopore array, titanium oxide film, and aluminum substrate;

[0047] 6) Make a flow cell, set a transparent window in the center of its front, and make the window area larger than the spot area of ​​the light source used;

[0048] 7) placing the sensor chip into the flow cell so that the periodic metal nanostructure array layer is directly below the transparent window;

[0049] 8) Put platinum wire electrode above the sensing chip, below the transparent window, and lead out the wire end;

[0050] 9) Set two opposite round holes at the edge of the transparent window, and connect the thin tubes respectively as the injection and discharge channels of the measured substance;

[0051] 10) Connect the digital source meter or ammeter between the wire end of the sensing chip and the wire end of the counter electrode;

[0052] 11) Couple or directly irradiate the incident light to the transparent window.

[0053] Test the reflection and transmission spectra of the sensing chip prepared by the above steps, and calculate the absorption efficiency spectrum by 100%-(reflectivity+transmissivity). As shown in the figure, Figure 3 when the background substance of the sensing chip changes (i.e. from air 31 to deionized water 32, and then to glucose solution 33), the light absorption peak formed due to surface plasmon resonance will move obviously (i.e. red shift significantly with the increase of the refractive index of the background substance).

[0054] Take the detection of hydrogen peroxide (H2O2) concentration as an example to introduce the testing process and working principle of the optical sensing device. First, test the reflection spectrum and light absorption spectrum of the sensing chip in the background of dilute hydrochloric acid (such as 0.2 mol / L), and obtain the characteristic peak of the light absorption spectrum as λ SPR . Then inject the dilute hydrochloric acid and H2O2 with different concentrations through the measured liquid input channel into the flow cell, and irradiate the transparent window with monochromatic light with a wavelength of λ SPR . Figure 4 The working principle of an optical sensing device for direct reading of electrical signals is shown. The sensing chip composed of a periodic nanostructure array layer 23, an n-type semiconductor thin film layer 22, and a metal substrate layer 21 can excite surface plasmon resonance 46 near the wavelength λ SPR , and form hot electrons e and hot holes h in the periodic metal nanostructure array layer. The hot electrons cross the Schottky barrier F B , inject into the conduction band E C of the n-type semiconductor thin film layer 22, and are finally collected by the metal substrate layer 21. The hot holes h of the periodic nanostructure array layer 23 diffuse to the metal-solution interface and participate in the oxidation reaction of H2O2, and the hot electrons e flow to the counter electrode 44 through the external lead to participate in the reduction reaction of H + . Since a closed loop of electron flow is formed at the two wire ends, a certain size of photocurrent can be measured by the digital source meter 45. When the concentration of H2O2 increases, the light absorption spectrum of the sensing chip red shifts, and the characteristic peak of the light responsivity spectrum (defined as: photocurrent density / incident light power density) red shifts (from λ1 to λ2) and the peak height decreases, asFigure 5 As shown in the figure. When the incident light conditions (wavelength and power density) remain unchanged, the sensor chip's light absorption efficiency and photoresponsivity at the original incident light wavelength change (i.e., the photoresponsivity at wavelength λ1 decreases by D), and this change is closely related to the H2O2 concentration. Preliminary systematic testing of H2O2 concentrations reveals the relationship between photocurrent and H2O2 concentration. Ultimately, the unknown H2O2 concentration can be inferred by detecting changes in photocurrent.

[0055] Example 2

[0056] Compared to Example 1, the sensor chip changes from a photoanode to a photocathode (i.e., the object to be measured undergoes an "oxidation reaction" on the surface of the periodic metal nanostructure array layer and then a "reduction reaction," thereby generating an electrical signal). At this point, the semiconductor thin film layer in the corresponding optical sensor device changes from "n-type" to "p-type."

[0057] The preparation process of an optical sensing device for direct readout of electrical signals is as follows:

[0058] 1) Quartz glass is used as substrate;

[0059] 2) depositing a 200 nm thick palladium film on a cleaned quartz glass substrate;

[0060] 3) depositing an 80 nm thick nickel oxide film on the palladium film;

[0061] 3) forming a nanopore patterned photoresist with a period of 1000 nm and a diameter of 750 nm on the nickel oxide film by photolithography;

[0062] 4) Electron beam evaporation of a silver film on the patterned photoresist, and a silver nanodisk array formed by a lift-off process;

[0063] 5) Leading out external wires from the palladium film to obtain a sensor chip composed of a silver nanodisk array, a nickel oxide film, and a palladium film;

[0064] 6) Make a flow cell, set a transparent window in the center of its front, and make the window area larger than the spot area of ​​the light source used;

[0065] 7) Place the sensor chip into the flow cell, with the silver nanodisk array directly below the transparent window;

[0066] 8) Place a platinum wire electrode above the sensor chip and below the transparent window, and lead out the terminal;

[0067] 9) Two opposing circular holes are provided on the edge of the transparent window and connected to thin tubes, respectively, to serve as injection and discharge channels for the substance to be tested;

[0068] 10) The two leads of the palladium thin film and platinum wire electrode are connected to a digital source meter;

[0069] 11) The incident light spot is coupled or directly irradiated onto the transparent window.

[0070] The optical sensing device for reading out electrical signal can be used to detect heavy metal ions (such as Hg 2+ , Cu 2+ , Cd 2+ and Pb 2+ ) and easily reduced liquid substances (such as p-nitrophenol, bromine and iodine). When used for detecting heavy metal ions, as the concentration of the detected ions increases, the surface plasmon resonance peak of the sensing chip red shifts, the generation rate of hot electrons and hot holes will decrease under the irradiation of the light source with fixed wavelength and power, and since the reduced metal ions are deposited on the surface of the periodic metal nano structure, it becomes more and more difficult to extract the hot electrons inside the photocathode to the electrode surface, and finally the photocurrent decreases with the increase of the concentration of the heavy metal ions to be detected.

[0071] The optical sensing device for reading out electrical signal directly is proposed, the charge transfer between the metal nano structure and the liquid to be detected is realized through the oxidation or reduction reaction of the target molecules to be detected and the sensing chip, and then the photocurrent is formed. In addition, the size of the photocurrent is closely related to the type and concentration of the target molecules to be detected. The optical sensing device prepared by the scheme has the working characteristics of realizing the reading out of electrical signal without external semiconductor photodetector unit, can work in a self-driven working mode, the light source used does not need to change the incident angle, power and wavelength, and can also work in a light signal reading out working mode (that is, the characteristic peak of the spectrum of the sensing chip is detected by an external detector to inverse the substance to be detected).

Claims

1. An optical sensing device for direct readout of an electrical signal, characterized in that Comprise: excitation light source, sensing chip, flow cell, counter electrode; sensing chip is arranged in the flow cell, wherein the sensing chip comprises: metal substrate layer, and semiconductor thin film layer, periodic metal nanostructure array layer arranged on the metal substrate layer in sequence; the flow cell is used for containing the measured substance, and the flow cell is provided with measured substance input pipeline, measured substance discharge pipeline and transparent window; the sensing chip lead end is arranged on the metal substrate layer; the counter electrode is arranged between the transparent window and the sensing chip, and the counter electrode lead end is arranged on the counter electrode; the digital source table or ammeter is connected between the sensing chip lead end and the counter electrode lead end; the light emitted by the excitation light source is incident on the transparent window; the incident light emitted by the excitation light source is irradiated on the periodic metal nanostructure array layer after passing through the transparent window, and the incident photons generate surface plasmon resonance in the sensing chip, so that most of the energy of the incident light is absorbed by the periodic metal nanostructure array layer; the hot electron and hot hole pairs are generated in the periodic metal nanostructure array layer, when the semiconductor thin film layer is n-type semiconductor, the hot electron is injected into the n-type semiconductor thin film layer and is finally led out by the metal substrate layer, the flowing electron reaches the counter electrode through the external lead wire to participate in the reduction reaction, and the hot hole diffuses to the surface of the periodic metal nanostructure array layer to participate in the oxidation reaction of the measured substance, so that the closed loop current is formed; when the semiconductor thin film layer is p-type semiconductor, the hot electron diffuses to the surface of the periodic metal nanostructure array layer to participate in the reduction reaction of the measured substance, and the hot hole is injected into the p-type semiconductor thin film layer and is finally led out by the metal substrate layer, the flowing hole reaches the counter electrode through the external lead wire to participate in the oxidation reaction, so that the closed loop current is formed; the measured substance is injected through the input pipeline and fills the flow cell; when the concentration or type of the measured substance changes, the photoelectric current between the two lead wires changes after the measured substance immerses the sensing chip; the concentration or type of the measured substance is inversed by monitoring the change of the photoelectric current.

2. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The periodic metal nanostructure array layer and the semiconductor thin film layer form Schottky contact, and the corresponding barrier height is less than the photon energy corresponding to the plasmon resonance wavelength.

3. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The period of the periodic metal nanostructure array layer is 300-2000 nm, and the width is 20%-90% of the period.

4. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The material of the periodic metal nanostructure array layer is one of gold, silver, palladium and transition metal nitride.

5. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The semiconductor thin film layer is n-type semiconductor, and the material is one of titanium oxide, zinc oxide, magnesium oxide and lithium fluoride.

6. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The semiconductor thin film layer is p-type semiconductor, and the material is one of nickel oxide, molybdenum oxide and vanadium oxide.

7. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that: The metal substrate layer comprises: polished metal substrate and deposited metal thin film.

8. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that The material of the metal substrate layer is selected according to: the contact barrier formed by the metal substrate layer and the semiconductor thin film layer is minimum.

9. An optical sensing device for direct readout of an electrical signal according to claim 1, characterized in that The counter electrode is platinum wire electrode.

10. A method of fabricating an optical sensing device for direct readout of an electrical signal, characterized by The method for preparing the optical sensing device for directly reading out electrical signal according to claim 1 comprises the following steps: 1) depositing the semiconductor thin film layer on the metal substrate layer; 2) obtaining periodic nanostructure patterned photoresist on the semiconductor thin film layer through photolithography process; 3) depositing a metal thin film on the patterned photoresist, and obtaining the inverse structure of the photoresist pattern, i.e. a periodic metal nanostructure array layer, by a stripping process; 4) soldering the sensing chip lead terminals on the metal substrate layer, to obtain a sensing chip composed of a periodic metal nanostructure array layer, a semiconductor thin film layer and a metal substrate layer; 5) fabricating a flow cell, and setting a transparent window in the center of the front face of the flow cell, so that the window area is larger than the light spot area of the excitation light source used; 6) placing the sensing chip into the flow cell, and making the periodic metal nanostructure array layer directly below the transparent window; 7) placing a counter electrode above the sensing chip inside the flow cell, and setting counter electrode lead terminals on the counter electrode; 8) setting two opposite round holes on the edge of the transparent window of the flow cell, and soldering a thin tube on each hole, for serving as the input channel of the substance to be measured and the output channel of the measured substance; 9) connecting a digital source meter or ammeter between the sensing chip lead terminals and the counter electrode lead terminals; 10) setting an excitation light source, and coupling or irradiating the light spot to the transparent window of the flow cell.

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