Micro-fluidic chip for trace detection of petroleum substances in water and application

Abstract

The invention discloses a micro-fluidic chip for trace detection of petroleum substances in water and application of the micro-fluidic chip in a detection device, trace enrichment is performed on the petroleum substances in the water by utilizing the super-hydrophobic and super-oleophylic characteristics of a processed PDMS substrate, and trace detection of the petroleum substances in the water is realized. Comprising the steps of preparation of a PDMS cylindrical array substrate, wettability modification of the PDMS cylindrical array substrate, preparation of an integrated micro-fluidic chip, design and manufacturing of a portable fluorescence detector, and on-chip enrichment fluorescence detection of the micro-fluidic chip. According to the microfluidic chip with the PDMS cylindrical array substrate, trace oil drops in water can be enriched without a large number of samples and complex operation steps, and compared with extraction, acidification, dehydration and professional infrared spectrum equipment required by the national standard (HJ 637-2018 water quality petroleum and animal and vegetable oil determination), the microfluidic chip with the PDMS cylindrical array substrate can realize on-site rapid detection, and has the advantages of high sensitivity, high sensitivity and the like. The method does not need professional operation, is low in detection content, and has great significance for preliminary detection of water quality.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano sensing and microfluidics. Specifically, the present invention relates to a microfluidics chip for detecting trace amounts of petroleum substances in water and its application in a detection device. Background Art

[0002] The invention of ultrafast femtosecond laser is an important milestone in the development of laser technology. Femtosecond laser refers to a laser with a pulse width of femtoseconds (10^-15 seconds), and its invention can be traced back to the 1980s. The principle of femtosecond laser is based on the coherence of light and ultrafast optical technology. When the laser passes through a nonlinear medium, the phase and frequency of the light will change, forming an extremely short pulse. In recent years, researchers have discovered that ultrafast femtosecond lasers have unique advantages in regulating the wettability of material surfaces. By applying femtosecond laser pulses to the surface of a material, its surface structure and chemical properties can be changed on a microscopic scale, thereby significantly affecting the wetting behavior of the liquid.

[0003] Fluorescence is a phenomenon in which a substance rapidly releases energy and emits fluorescence after absorbing light energy. When a fluorescent substance absorbs photons of a specific wavelength, the electrons are excited to a high-energy state, then return to the ground state in a short time and release light of a longer wavelength, forming fluorescence. In petroleum, the main fluorescent substances are hydrocarbon compounds, especially aromatic hydrocarbons and certain asphaltene and colloids. Petroleum fluorescence technology plays an important role in environmental monitoring. By detecting fluorescent signals in water and soil, oil leaks and pollution sources can be effectively identified, providing a scientific basis for environmental protection.

[0004] Microfluidics is a technology that uses micron-scale channels and structures to manipulate fluids. It is widely used in biomedicine, chemical analysis, environmental monitoring and other fields. The advantages of microfluidics are its high efficiency, reagent saving and rapid response. Due to the flow characteristics of fluids in microchannels, the reaction time is usually significantly shortened, and the amount of samples and reagents required is greatly reduced. In addition, microfluidics systems can realize parallel processing of multiple experiments, improving the throughput and efficiency of experiments. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the traditional detection method contains complicated operations and instruments and is difficult to achieve rapid on-site detection, and to provide an application of a microfluidic chip for trace detection of petroleum substances in water in a detection device.

[0006] To achieve the above purpose, the technical solution provided by the present invention is:

[0007] A microfluidic chip for detecting trace amounts of petroleum substances in water, wherein the preparation method of the microfluidic chip comprises the following steps:

[0008] Step S1, preparation of PDMS columnar array;

[0009] Fix the tungsten needle on the three-dimensional displacement platform, fix the cut PE board on the processing table, and pierce the tungsten needle into the PE board by controlling the movement of the three-dimensional displacement platform; due to the plasticity of polyethylene, the tungsten needle will leave a columnar pit inside the polyethylene board;

[0010] PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and the bubbles inside were removed and then poured into the PE plate with pits;

[0011] Dry at a constant temperature, wait for the PDMS to solidify and then peel it off to obtain the PDMS columnar array substrate;

[0012] Step S2, modifying the wettability of the PDMS columnar array substrate;

[0013] The PDMS columnar array substrate prepared in step S1 is fixed on the focal plane of the galvanometer of the ultrafast femtosecond laser system, and the femtosecond laser processing path is drawn using the host computer software, and the laser parameters are adjusted to process the PDMS columnar array substrate;

[0014] The PDMS columnar array substrate processed by femtosecond laser is cleaned and then surface treated using a plasma cleaning machine, and the treated PDMS columnar array substrate is immersed in a PVA aqueous solution for hydrophilic treatment;

[0015] Step S3, preparation of an integrated microfluidic chip;

[0016] The Su8-3035 photoresist is spread on the entire silicon wafer by a coating machine, and the pattern with the channel structure on the film plate is engraved on the silicon substrate under the light-induced cross-linking action of the ultraviolet photolithography machine;

[0017] Then, PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were heated and molded on a silicon substrate to form a microfluidic chip;

[0018] The PDMS columnar array substrate prepared in step S2 is embedded in the integrated microfluidic chip detection chamber prepared in step S3 and sealed, thereby completing the preparation of the microfluidic chip for trace detection of petroleum substances in water.

[0019] Preferably,

[0020] The step S2 is specifically as follows:

[0021] Step S21, galvanometer and laser parameter setting;

[0022] The PDMS columnar array substrate prepared in step S1 is fixed to a glass slide and placed on an adjustable height platform, and the height of the platform is adjusted so that the processed sample is located on the focal plane of the galvanometer;

[0023] Open the galvanometer host computer control software, draw the femtosecond laser processing path, set the laser path to a row array, and set the row spacing to 20 μm;

[0024] Turn on the laser light source, select the laser wavelength as 1030nm, set the laser power to 30%, without frequency division, and enable laser output;

[0025] Return to the host computer control software and click the marking button to start processing the sample;

[0026] Wait for the sample to be removed after the processing is completed;

[0027] Step S22, PVA aqueous solution preparation and PDMS columnar array substrate modification treatment;

[0028] Prepare PVA aqueous solution at a concentration of 8 mg / ml, shake for 15 minutes after mixing, and observe that the PVA powder is completely dissolved;

[0029] The PDMS columnar array substrate processed in step S21 is placed in anhydrous ethanol and cleaned in an ultrasonic cleaner for 5 minutes;

[0030] After cleaning, the substrate was taken out and air-dried naturally. After air-drying, the PDMS columnar array substrate was placed in a plasma cleaning machine for surface treatment for 2 minutes. After the treatment, the substrate was immediately immersed in the above-configured PVA aqueous solution for 10 minutes. After 10 minutes, the substrate was taken out to complete the surface modification.

[0031] Preferably,

[0032] The step S3 is specifically as follows:

[0033] Step S31, preparing a silicon wafer template for a microfluidic chip;

[0034] Use alcohol and dust-free cloth to wipe the silicon wafer in the clean room. After wiping, pre-bake the silicon wafer and place it on a 95℃ heating table for 15 minutes.

[0035] Place the pre-baked silicon wafer into a coating machine, pour 3-5g of Su8-3035 photoresist into the center of the silicon wafer, set the coating machine speed and turn on the coating machine, and evenly spread the Su8-3035 photoresist on the entire silicon wafer with a thickness of 100μm;

[0036] In order to strengthen the adhesion between the photoresist and the silicon wafer, the silicon wafer needs to be post-baked. After the photoresist is applied, the silicon wafer is placed on a heating table at 105°C and heated for 20 minutes.

[0037] After the post-bake is completed, the silicon wafer is placed in the photolithography machine and placed close to the mask plate, and the ultraviolet light source is turned on to start photolithography;

[0038] Place the photolithographically completed silicon wafer on a heating table at 105°C for 5 minutes;

[0039] Finally, the silicon wafer was immersed in a developer (ethyl lactate), and the silicon wafer was shaken evenly to accelerate the development process. After about 5 minutes, the silicon wafer was taken out and its surface was cleaned with nitrogen to complete the preparation of the silicon wafer template for the microfluidic chip.

[0040] Step S32, PDMS mold is sealed with the chip;

[0041] PDM and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were poured onto the silicon substrate prepared in S31;

[0042] The whole was moved into an oven at 70°C and heated for 2 hours to accelerate the curing of poly-PDMS. After the curing was completed, a cutter was used to cut the microfluidic chip.

[0043] After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and the glass sheet are placed in a plasma cleaner, vacuumed for 90 seconds, and treated with oxygen plasma for 45 seconds. The PDMS columnar array substrate prepared in step S2 is embedded in the detection chamber for sealing.

[0044] The present invention also provides an application of a microfluidic chip for detecting trace amounts of petroleum substances in water in a detection device, that is, a detection device using the aforementioned microfluidic chip.

[0045] Preferably,

[0046] The detection device is provided with a matching portable fluorescence detector, and the specific steps of the method for making the portable fluorescence detector include:

[0047] The fluorescence detector adopts a confocal structure. The excitation light source is reflected by the dichroic mirror 2 to the second lens 3 and focused to the detection chamber of the integrated microfluidic chip. The petroleum pollutants in the chamber produce fluorescence under the excitation light. The fluorescence is collected by the second lens 3 and penetrates the dichroic mirror 2 and the second filter 4. Then, it is focused by the third lens 5 to the photosensitive surface of the photodiode. The photoelectric conversion module 10 measures the photocurrent of the photodiode; wherein,

[0048] The specific enrichment fluorescence detection on the microfluidic chip is as follows:

[0049] The diluted trace oil-water emulsion was passed into the microfluidic chip, and the fluorescence intensity of the substrate area was measured using the prepared fluorescence detector to calculate the concentration of the emulsion.

[0050] More preferably,

[0051] In the fluorescence detector, the wavelength of the excitation light source is selected to be 310 nm.

[0052] The confocal structure of the fluorescence detector is specifically as follows:

[0053] According to the direction of the optical path, the light emitted by the excitation light source passes through the first lens 6 and the first filter 1, is refracted by the dichroic mirror 2, and then by the second lens 3, collects the fluorescent reflection excited by the sample, and passes through the dichroic mirror 2, the second filter 4, and the third lens 5, and then converges to the photosensitive surface of the photodiode of the photocurrent conversion module 10.

[0054] Preferably,

[0055] The optical lens and filter are selected as follows:

[0056] The selection of optical devices must be used in conjunction with the wavelength of the light source, and other optical devices must be adjusted according to the wavelength of the light source.

[0057] The function of the first filter 1 is to selectively filter light of a specific wavelength to ensure accurate detection of the fluorescence signal;

[0058] The first filter 1 is selected as a short-wave pass filter, and the cut-off wavelength can be selected to be 350-390nm.

[0059] The dichroic mirror 2 can effectively transmit the wavelength of the excitation light source, and at the same time effectively block the excitation light, ensuring that only the fluorescent signal is allowed to pass through. Therefore, the central wavelength of the dichroic mirror can be selected to be 320-370nm, the reflection band is 280-350nm, and the transmission band is 380-1200nm;

[0060] The second lens 3 effectively converges the excitation light to the focal point, and at the same time, the second lens 3 can collect the fluorescence excited by the sample, which can improve the sensitivity of the optical system; the material of the second lens 3 is selected to be ultraviolet fused quartz glass to ensure that the transmittance of the ultraviolet excitation light in the second lens 3 is greater than 90%;

[0061] The function of the second optical filter 4 is to filter out stray light in the excitation light to ensure that the wavelength of the excitation light is within a certain range. Therefore, the second optical filter 4 is selected as a long-wave pass filter with a cut-off wavelength of 350 nm.

[0062] The function of the third lens 5 is to converge the fluorescence onto the photosensitive surface of the photodiode. The third lens 5 needs to cooperate with the photodiode. Good cooperation can improve the sensitivity.

[0063] The function of the first lens 6 is to collimate the LED point light source 7. Since the LED point light source 7 is in the ultraviolet band, the ordinary optical glass K9 has insufficient light transmittance in the ultraviolet band, so ultraviolet fused quartz glass is required to ensure the light transmittance.

[0064] The preferred design and production of the photoelectric conversion module 10 are as follows:

[0065] The photoelectric conversion module 10 is based on a transimpedance amplifier circuit. The photodiode generates a weak pA-level photocurrent after being irradiated by light. The photocurrent is amplified by the feedback resistor and then output.

[0066] The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. The feedback resistor is selected to be 10G ohms. If the feedback resistor is too large, the output end will couple the power frequency interference.

[0067] The transimpedance amplifier circuit needs to be used in conjunction with a low-pass filter. The signal after passing through the low-pass filter is sampled by an ADC chip, and the photocurrent size is obtained after calculation by a single-chip microcomputer.

[0068] Preferably,

[0069] The low-pass filter adopts a second-order Sallen-Key low-pass filter with a cut-off frequency of 5 Hz and an amplification factor of less than -40 dB at 50 Hz.

[0070] Preferably, the on-chip enrichment fluorescence detection of the microfluidic chip is specifically:

[0071] Preparation of petroleum emulsions;

[0072] Oil-in-water emulsions were prepared by adding oil to water at a ratio of 500 mg / L and Tween 20 emulsifier at a ratio of 2 μl / ml;

[0073] After vigorous stirring at 500 rpm for 2 hours, the oil was placed in an ultrasonic cleaner to obtain a smaller oil droplet diameter through ultrasonic crushing. After ultrasonic treatment for 1 hour, a uniform emulsion was obtained, which could be stable for a week without obvious stratification. ;

[0074] Emulsified oil droplet enrichment experiment;

[0075] Dilute the prepared petroleum emulsion 200 times, mix well and draw 1 ml of the diluted emulsion into a syringe;

[0076] Use silicone tube to connect the needle of the syringe to the inlet of the integrated microfluidic chip prepared by S3;

[0077] Use a precision syringe pump to pass the diluted oil-water emulsion into the microfluidic chip;

[0078] After the introduction is completed, the fluorescence intensity of the substrate area is measured using a fluorescence detector and the concentration of the emulsion is calculated.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] 1. The integrated microfluidic chip of the present invention can detect petroleum pollutants in water with only a very small amount of sample;

[0081] 2. The fluorescence detection device of the present invention is simple to operate, convenient to carry, and has a high detection speed, and is suitable for preliminary detection of petroleum pollutants in water under field conditions.

[0082] Explanation of terms

[0083] PDMS, polydimethylsiloxane;

[0084] PE board, polyethylene board;

[0085] PVA, polyvinyl alcohol aqueous solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 This is a schematic diagram of the principle of a device for detecting petroleum pollutants in water using the microfluidic chip of the present invention;

[0087] Figure 2 Scanning electron microscope image of polydimethylsiloxane (PDMS) pillar array substrate after femtosecond laser processing;

[0088] Figure 3 Comparative image of wettability of polydimethylsiloxane (PDMS) substrate processed by femtosecond laser;

[0089] Figure 4 This is a circuit rendering of the photoelectric conversion module;

[0090] Figure 5 This is a fluorescence experiment diagram of enriching emulsified oil droplets using an integrated microfluidic chip. DETAILED DESCRIPTION

[0091] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings.

[0092] Combined with Figure 1 As shown in the figure, a microfluidic chip for detecting trace amounts of petroleum substances in water according to the present invention, wherein the preparation method of the microfluidic chip comprises the following steps:

[0093] Step S1, preparation of PDMS columnar array;

[0094] Fix the tungsten needle on the three-dimensional displacement platform, fix the cut PE board on the processing table, and pierce the tungsten needle into the PE board by controlling the movement of the three-dimensional displacement platform; due to the plasticity of polyethylene, the tungsten needle will leave a columnar pit inside the polyethylene board;

[0095] PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and the bubbles inside were removed and then poured into the PE plate with pits;

[0096] The PDMS column array substrate is obtained by drying at a constant temperature and peeling after the PDMS is cured. Figure 2 shown.

[0097] Step S2, modifying the wettability of the PDMS columnar array substrate;

[0098] The PDMS columnar array substrate prepared in step S1 is fixed on the focal plane of the galvanometer of the ultrafast femtosecond laser system, and the femtosecond laser processing path is drawn using the host computer software, and the laser parameters are adjusted to process the PDMS columnar array substrate;

[0099] The PDMS columnar array substrate processed by femtosecond laser is cleaned and then surface treated using a plasma cleaning machine, and the treated PDMS columnar array substrate is immersed in a PVA aqueous solution for hydrophilic treatment;

[0100] The specific process of step S2 is as follows:

[0101] Step S21, galvanometer and laser parameter setting;

[0102] The PDMS columnar array substrate prepared in step S1 is fixed to a glass slide and placed on an adjustable height platform, and the height of the platform is adjusted so that the processed sample is located on the focal plane of the galvanometer;

[0103] Open the galvanometer host computer control software, draw the femtosecond laser processing path, set the laser path to a row array, and set the row spacing to 20 μm;

[0104] Turn on the laser light source, select the laser wavelength as 1030nm, set the laser power to 30%, without frequency division, and enable laser output;

[0105] Return to the host computer control software and click the marking button to start processing the sample;

[0106] Wait for the processing to be completed and then remove the sample;

[0107] Step S22, PVA aqueous solution preparation and PDMS columnar array substrate modification treatment;

[0108] Prepare PVA aqueous solution at a concentration of 8 mg / ml, shake for 15 minutes after mixing, and observe that the PVA powder is completely dissolved;

[0109] The PDMS columnar array substrate processed in step S21 is placed in anhydrous ethanol and cleaned in an ultrasonic cleaner for 5 minutes;

[0110] After cleaning, the substrate was taken out and air-dried naturally. After air-drying, the PDMS columnar array substrate was placed in a plasma cleaning machine for surface treatment for 2 minutes. After the treatment, the substrate was immediately immersed in the above-configured PVA aqueous solution for 10 minutes. After 10 minutes, the substrate was taken out to complete the surface modification. Figure 3 Comparative image of wettability of polydimethylsiloxane (PDMS) substrate processed by femtosecond laser. Figure 3 As shown, Figure 3 The right picture shows the contact angle image of a water droplet in the air on the original PDMS substrate without completing step S2. Figure 3 The left picture shows the contact angle image of a water droplet in the air on the PDMS substrate after completing step S2. The comparison shows that step S2 increases the contact angle of a water droplet in the air on the PDMS substrate, effectively improving the wetting properties of the PDMS.

[0111] Step S3, preparation of an integrated microfluidic chip;

[0112] The Su8-3035 photoresist is spread on the entire silicon wafer by a coating machine, and the pattern with the channel structure on the film plate is engraved on the silicon substrate under the light-induced cross-linking action of the ultraviolet photolithography machine;

[0113] Then, PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were heated and molded on a silicon substrate to form a microfluidic chip;

[0114] The PDMS columnar array substrate prepared in step S2 is embedded in the integrated microfluidic chip detection chamber prepared in step S3 and sealed, thereby completing the preparation of the microfluidic chip for trace detection of petroleum substances in water.

[0115] The step S3 is specifically as follows:

[0116] Step S31, preparing a silicon wafer template for a microfluidic chip;

[0117] Use alcohol and dust-free cloth to wipe the silicon wafer in the clean room. After wiping, pre-bake the silicon wafer and place it on a 95℃ heating table for 15 minutes.

[0118] Place the pre-baked silicon wafer into a coating machine, pour 3-5g of Su8-3035 photoresist into the center of the silicon wafer, set the coating machine speed and turn on the coating machine, and evenly spread the Su8-3035 photoresist on the entire silicon wafer with a thickness of 100μm;

[0119] In order to strengthen the adhesion between the photoresist and the silicon wafer, the silicon wafer needs to be post-baked. After the photoresist is applied, the silicon wafer is placed on a heating table at 105°C and heated for 20 minutes.

[0120] After the post-bake is completed, the silicon wafer is placed in the photolithography machine and placed close to the mask plate, and the ultraviolet light source is turned on to start photolithography;

[0121] Place the photolithographically completed silicon wafer on a heating table at 105°C for 5 minutes;

[0122] Finally, the silicon wafer was immersed in the developer and shaken evenly to accelerate the development process. After 5 minutes, the silicon wafer was taken out and its surface was cleaned with nitrogen to complete the preparation of the silicon wafer template for the microfluidic chip.

[0123] Step S32, PDMS mold is sealed with the chip;

[0124] PDM and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were poured onto the silicon substrate prepared in S31;

[0125] The whole was moved into an oven at 70°C and heated for 2 hours to accelerate the curing of poly-PDMS. After the curing was completed, a cutter was used to cut the microfluidic chip.

[0126] After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and the glass sheet are placed in a plasma cleaner, vacuumed for 90 seconds, and treated with oxygen plasma for 45 seconds. The PDMS columnar array substrate prepared in step S2 is embedded in the detection chamber for sealing.

[0127] The present invention also provides an application of a microfluidic chip for detecting trace amounts of petroleum substances in water in a detection device.

[0128] The detection device is provided with a matching portable fluorescence detector, and the specific steps of the method for making the portable fluorescence detector include:

[0129] The fluorescence detector adopts a confocal structure. The excitation light source is reflected by the dichroic mirror 2 to the second lens 3 and focused to the detection chamber of the integrated microfluidic chip. The petroleum pollutants in the chamber produce fluorescence under the excitation light. The fluorescence is collected by the second lens 3 and penetrates the dichroic mirror 2 and the second filter 4. Then, it is focused by the third lens 5 to the photosensitive surface of the photodiode. The photoelectric conversion module 10 measures the photocurrent of the photodiode; wherein,

[0130] On-chip enrichment fluorescence detection on microfluidic chip;

[0131] The diluted trace oil-water emulsion was passed into the microfluidic chip, and the fluorescence intensity of the substrate area was measured using the prepared fluorescence detector to calculate the concentration of the emulsion.

[0132] The on-chip enrichment fluorescence detection of the microfluidic chip is specifically as follows:

[0133] Preparation of petroleum emulsions;

[0134] Oil-in-water emulsions were prepared by adding oil to water at a ratio of 500 mg / L and Tween 20 emulsifier at a ratio of 2 μl / ml;

[0135] After vigorous stirring at 500 rpm for 2 h, the mixture was placed in an ultrasonic cleaner to obtain a smaller oil droplet diameter through ultrasonic crushing, and a uniform emulsion was obtained after ultrasonic treatment for 1 h.

[0136] Emulsified oil droplet enrichment experiment;

[0137] The emulsified oil droplets aggregate under the capture effect of polydimethylsiloxane (PDMS) columnar substrate, such as Figure 5 After the injection is completed, the fluorescence intensity of the substrate area is measured using a fluorescence detector and the concentration of the emulsion is calculated. The specific process is:

[0138] Dilute the prepared petroleum emulsion 200 times, mix well and draw 1 ml of the diluted emulsion into a syringe;

[0139] Use silicone tube to connect the needle of the syringe to the inlet of the integrated microfluidic chip prepared by S3;

[0140] Use a precision syringe pump to pass the diluted oil-water emulsion into the microfluidic chip;

[0141] After the introduction is completed, the fluorescence intensity of the substrate area is measured using a fluorescence detector and the concentration of the emulsion is calculated.

[0142] In the fluorescence detector,

[0143] The wavelength of the excitation light source should be near the excitation peak of the dye to ensure maximum excitation of fluorescence. The fluorescence properties of petroleum substances are usually closely related to their chemical composition and molecular structure. Different types of petroleum substances (such as crude oil, diesel, gasoline, etc.) may have different fluorescence properties, so the excitation wavelengths will also be different. Generally speaking, the fluorescence excitation wavelength of petroleum substances is usually in the ultraviolet light region, and the specific range is roughly between 250nm and 350nm. After comprehensive consideration, 310nm was selected as the excitation light wavelength of the portable fluorescence detector.

[0144] Combination Figure 1 As shown in , the confocal structure of the fluorescence detector is specifically as follows:

[0145] According to the direction of the optical path, the light emitted by the excitation light source passes through the first lens 6 and the first filter 1, is refracted by the dichroic mirror 2, and then by the second lens 3, collects the fluorescent reflection excited by the sample, and passes through the dichroic mirror 2, the second filter 4, and the third lens 5, and then converges to the photosensitive surface of the photodiode of the photocurrent conversion module 10.

[0146] The optical lens and filter are selected as follows:

[0147] The selection of optical devices must be used in conjunction with the wavelength of the light source, and other optical devices must be adjusted according to the wavelength of the light source.

[0148] The function of the first filter 1 is to selectively filter light of a specific wavelength to ensure accurate detection of the fluorescence signal;

[0149] The first filter 1 is selected as a short-wave pass filter, and the cut-off wavelength can be selected to be 350-390nm.

[0150] The dichroic mirror 2 can effectively transmit the wavelength of the excitation light source, and at the same time effectively block the excitation light, ensuring that only the fluorescent signal is allowed to pass through. Therefore, the central wavelength of the dichroic mirror can be selected to be 320-370nm, the reflection band is 280-350nm, and the transmission band is 380-1200nm;

[0151] The second lens 3 effectively converges the excitation light to the focal point, and at the same time, the second lens 3 can collect the fluorescence excited by the sample, which can improve the sensitivity of the optical system; the material of the second lens 3 is selected to be ultraviolet fused quartz glass to ensure that the transmittance of the ultraviolet excitation light in the second lens 3 is greater than 90%;

[0152] The function of the second optical filter 4 is to filter out stray light in the excitation light to ensure that the wavelength of the excitation light is within a certain range. Therefore, the second optical filter 4 is selected as a long-wave pass filter with a cut-off wavelength of 350 nm.

[0153] The function of the third lens 5 is to converge the fluorescence onto the photosensitive surface of the photodiode. The third lens 5 needs to cooperate with the photodiode. Good cooperation can improve the sensitivity.

[0154] The function of the first lens 6 is to collimate the LED point light source 7. Since the LED point light source 7 is in the ultraviolet band, the ordinary optical glass K9 has insufficient light transmittance in the ultraviolet band, so ultraviolet fused quartz glass is required to ensure the light transmittance.

[0155] Figure 4 is a circuit rendering of the photoelectric conversion module 10, such as Figure 4 As shown in , the photoelectric conversion module 10 of the present invention is based on a transimpedance amplifier circuit. The photodiode generates a weak pA-level photocurrent after being irradiated by light, and the photocurrent is output after being amplified by a feedback resistor;

[0156] The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. The feedback resistor is selected to be 10G ohms. If the feedback resistor is too large, it will cause the output end to couple the power frequency interference. Therefore, the transimpedance amplifier circuit needs to be used in conjunction with a low-pass filter. The signal after the low-pass filter is sampled by the ADC chip, and the microcontroller calculates the photocurrent size.

[0157] The low-pass filter adopts a second-order Sallen-Key low-pass filter with a cut-off frequency of 5 Hz and an amplification factor of less than -40 dB at 50 Hz.

[0158] Step S43, designing and manufacturing a photoelectric conversion module;

[0159] The photoelectric conversion module 10 is based on a transimpedance amplifier circuit. The photodiode generates a weak photocurrent after being irradiated by light, and the photocurrent is output after passing through the feedback resistor for amplification. The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. The feedback resistor is selected to be 10G ohms. If the feedback resistor is too large, the output end will couple the power frequency interference. Therefore, the transimpedance amplifier circuit needs to be used in conjunction with a low-pass filter. The cutoff frequency of the second-order Sallen-Key low-pass filter is designed to be 5Hz, and the amplification factor at 50Hz is less than -40dB. The signal after the low-pass filter is sampled by the ADC chip, and the photocurrent size is obtained after calculation by the single-chip microcomputer.

[0160] Step S5, on-chip enrichment fluorescence detection on the microfluidic chip;

[0161] Step S51, preparing petroleum emulsion;

[0162] The oil-in-water emulsion was prepared by adding oil to water at a ratio of 500 mg / L and adding Tween 20 emulsifier at a ratio of 2 μl / ml. After vigorous stirring at 500 rpm for 2 h, the oil droplet diameter was obtained by ultrasonication in an ultrasonic cleaner. After ultrasonication for 1 h, a uniform emulsion was obtained, which was stable for one week without obvious stratification.

[0163] Step S52, emulsified oil droplet enrichment experiment;

[0164] Dilute the petroleum emulsion prepared in step S51 200 times, mix well and draw 1 ml of the diluted emulsion into the syringe. Use a silicone tube to connect the syringe needle to the inlet of the integrated microfluidic chip prepared in step S3. Use a precision syringe pump to pass the diluted oil-water emulsion into the microfluidic chip.

[0165] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A microfluidic chip for detecting trace amounts of petroleum substances in water, characterized in that: The method for preparing the microfluidic chip comprises the following steps: Step S1, preparation of PDMS columnar array; Fix the tungsten needle on the three-dimensional displacement platform, fix the cut PE board on the processing table, and pierce the tungsten needle into the PE board by controlling the movement of the three-dimensional displacement platform; due to the plasticity of polyethylene, the tungsten needle will leave a columnar pit inside the polyethylene board; PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and the bubbles inside were removed and then poured into the PE plate with pits; Dry at a constant temperature, wait for the PDMS to solidify and then peel it off to obtain the PDMS columnar array substrate; Step S2, modifying the wettability of the PDMS columnar array substrate; The PDMS columnar array substrate prepared in step S1 is fixed on the focal plane of the galvanometer of the ultrafast femtosecond laser system, and the femtosecond laser processing path is drawn using the host computer software, and the laser parameters are adjusted to process the PDMS columnar array substrate; The PDMS columnar array substrate processed by femtosecond laser is cleaned and then surface treated using a plasma cleaning machine, and the treated PDMS columnar array substrate is immersed in a PVA aqueous solution for hydrophilic treatment; Step S3, preparation of an integrated microfluidic chip; The Su8-3035 photoresist is spread on the entire silicon wafer by a coating machine, and the pattern with the channel structure on the film plate is engraved on the silicon substrate under the light-induced cross-linking action of the ultraviolet photolithography machine; PDMS and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were heated and molded on a silicon substrate to form a microfluidic chip; The PDMS columnar array substrate prepared in step S2 is embedded in the integrated microfluidic chip detection chamber prepared in step S3 and sealed, thereby completing the preparation of the microfluidic chip for trace detection of petroleum substances in water.

2. A microfluidic chip for detecting trace amounts of petroleum substances in water according to claim 1, characterized in that: The step S2 is specifically as follows: Step S21, galvanometer and laser parameter setting; The PDMS columnar array substrate prepared in step S1 is fixed to a glass slide and placed on an adjustable height platform, and the height of the platform is adjusted so that the processed sample is located on the focal plane of the galvanometer; Open the galvanometer host computer control software, draw the femtosecond laser processing path, set the laser path to a row array, and set the row spacing to 20 μm; Turn on the laser light source, select the laser wavelength as 1030nm, set the laser power to 30%, without frequency division, and enable laser output; Return to the host computer control software and click the marking button to start processing the sample; Wait for the processing to be completed and then remove the sample; Step S22, PVA aqueous solution preparation and PDMS columnar array substrate modification treatment; Prepare PVA aqueous solution at a concentration of 8 mg / ml, shake for 15 minutes after mixing, and observe that the PVA powder is completely dissolved; The PDMS columnar array substrate processed in step S21 is placed in anhydrous ethanol and cleaned in an ultrasonic cleaner for 5 minutes; After cleaning, the substrate was taken out and air-dried naturally. After air-drying, the PDMS columnar array substrate was placed in a plasma cleaning machine for surface treatment for 2 minutes. After the treatment, the substrate was immediately immersed in the above-configured PVA aqueous solution for 10 minutes. After 10 minutes, the substrate was taken out to complete the surface modification.

3. A microfluidic chip for trace detection of petroleum substances in water according to claim 1, characterized in that: The step S3 is specifically as follows: Step S31, preparing a silicon wafer template for a microfluidic chip; Use alcohol and dust-free cloth to wipe the silicon wafer in the clean room. After wiping, pre-bake the silicon wafer and place it on a 95℃ heating table for 15 minutes. Place the pre-baked silicon wafer into a coating machine, pour 3-5g of Su8-3035 photoresist into the center of the silicon wafer, set the coating machine speed and turn on the coating machine, and evenly spread the Su8-3035 photoresist on the entire silicon wafer with a thickness of 100μm; After the coating is completed, place the silicon wafer on a heating table at 105°C and heat for 20 minutes; After the post-bake is completed, the silicon wafer is placed in the photolithography machine and placed close to the mask plate, and the ultraviolet light source is turned on to start photolithography; Place the photolithographically completed silicon wafer on a heating table at 105°C for 5 minutes; Finally, the silicon wafer was immersed in the developer and shaken evenly to accelerate the development process. After 5 minutes, the silicon wafer was taken out and its surface was cleaned with nitrogen gas to complete the preparation of the silicon wafer template for the microfluidic chip. Step S32, PDMS mold is sealed with the chip; PDM and curing agent were mixed and stirred at a mass ratio of 10:1, and after removing the bubbles inside, they were poured onto the silicon substrate prepared in S31; The whole was moved into an oven at 70°C and heated for 2 hours to accelerate the curing of poly-PDMS. After the curing was completed, a cutter was used to cut the microfluidic chip. After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and the glass sheet are placed in a plasma cleaner, vacuumed for 90 seconds, and treated with oxygen plasma for 45 seconds. The PDMS columnar array substrate prepared in step S2 is embedded in the detection chamber for sealing.

4. Use of the microfluidic chip for trace detection of petroleum substances in water as claimed in any one of claims 1 to 3 in a detection device.

5. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 4, characterized in that: The detection device is provided with a matching portable fluorescence detector, and the specific steps of the method for making the portable fluorescence detector include: The fluorescence detector adopts a confocal structure. The excitation light source is reflected by a dichroic mirror (2) to a second lens (3) and focused to a detection chamber of an integrated microfluidic chip. The petroleum pollutants in the chamber generate fluorescence under the excitation light. The fluorescence is collected by the second lens (3) and penetrates the dichroic mirror (2) and a second filter (4). The fluorescence is then focused by a third lens (5) to a photosensitive surface of a photodiode. The photoelectric conversion module (10) measures the photocurrent of the photodiode. The specific enrichment fluorescence detection on the microfluidic chip is as follows: The diluted trace oil-water emulsion was passed into the microfluidic chip, and the fluorescence intensity of the substrate area was measured using the prepared fluorescence detector to calculate the concentration of the emulsion.

6. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 5, characterized in that: In the fluorescence detector, the wavelength of the excitation light source is selected to be 310 nm; The confocal structure of the fluorescence detector is specifically as follows: According to the direction of the optical path, the light emitted from the excitation light source passes through the first lens (6) and the first filter (1), is refracted by the dichroic mirror (2) and the second lens (3), collects the fluorescent reflection excited by the sample, passes through the dichroic mirror (2), the second filter (4) and the third lens (5), and converges to the photosensitive surface of the photodiode of the photocurrent conversion module (10).

7. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 6, characterized in that: The optical lens and filter are selected as follows: The function of the first filter (1) is to selectively filter light of a specific wavelength to ensure accurate detection of the fluorescent signal; The first filter (1) is selected as a short-wave pass filter, and the cut-off wavelength can be selected to be 350-390nm; The dichroic mirror (2) can effectively transmit the wavelength of the excitation light source and effectively block the excitation light to ensure that only the fluorescent signal is allowed to pass through. The central wavelength of the dichroic mirror is selected to be 320-370nm, the reflection band is 280-350nm, and the transmission band is 380-1200nm. The second lens (3) effectively converges the excitation light to a focal point, and at the same time, the second lens (3) can collect the fluorescence excited by the sample, thereby improving the sensitivity of the optical system; the second lens (3) is made of ultraviolet fused quartz glass to ensure that the transmittance of the ultraviolet excitation light in the second lens (3) is greater than 90 percent; The function of the second filter (4) is to filter out stray light in the excitation light. The second filter (4) is selected to be a long-wave pass filter with a cut-off wavelength of 350 nm. The function of the third lens (5) is to focus the fluorescence onto the photosensitive surface of the photodiode, and needs to cooperate with the photodiode to improve the sensitivity; The function of the first lens (6) is to collimate the LED point light source (7). The LED point light source (7) uses ultraviolet fused quartz glass to ensure light transmittance in the ultraviolet band.

8. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 5, characterized in that: The photoelectric conversion module (10) is based on a transimpedance amplifier circuit. The photodiode generates a weak pA-level photocurrent after being irradiated by light. The photocurrent is amplified by a feedback resistor and then output. The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module (10). The size of the feedback resistor is selected to be 10G ohms. The transimpedance amplifier circuit is used in conjunction with a low-pass filter. The signal after passing through the low-pass filter is sampled by an ADC chip, and the photocurrent size is obtained after calculation by a single-chip microcomputer.

9. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 8, characterized in that: The low-pass filter adopts a second-order Sallen-Key low-pass filter with a cut-off frequency of 5 Hz and an amplification factor of less than -40 dB at 50 Hz.

10. The use of the microfluidic chip for trace detection of petroleum substances in water in a detection device according to claim 5, characterized in that: The on-chip enrichment fluorescence detection of the microfluidic chip is specifically as follows: Preparation of petroleum emulsions; Oil-in-water emulsions were prepared by adding oil to water at a ratio of 500 mg / L and Tween 20 emulsifier at a ratio of 2 μl / ml; After vigorous stirring at 500 rpm for 2 h, the mixture was placed in an ultrasonic cleaner to obtain a smaller oil droplet diameter through ultrasonic crushing, and a uniform emulsion was obtained after ultrasonic treatment for 1 h. Emulsified oil droplet enrichment experiment; Dilute the prepared petroleum emulsion 200 times, mix well and draw 1 ml of the diluted emulsion into a syringe; Use silicone tube to connect the needle of the syringe to the inlet of the integrated microfluidic chip prepared by S3; Use a precision syringe pump to pass the diluted oil-water emulsion into the microfluidic chip; After the introduction is completed, the fluorescence intensity of the substrate area is measured using a fluorescence detector and the concentration of the emulsion is calculated.

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