Microfluidic chip for trace detection of petroleum substances in water and application thereof

Abstract

The application discloses a micro-fluidic chip for trace detection of oil substances in water, and application of the micro-fluidic chip in a detection device, and realizes trace detection of oil substances in water by using the super-hydrophobic and super-oleophilic characteristics of a processed PDMS base to enrich trace oil substances in water. The application comprises preparation of a PDMS column array base, modification of the wettability of the PDMS column array base, preparation of an integrated micro-fluidic chip, design and production of a portable fluorescence detection meter, and on-chip enrichment and fluorescence detection of the micro-fluidic chip. The micro-fluidic chip with the PDMS column array base can enrich trace oil droplets in water without a large amount of samples and complex operation steps, and compared with the national standard (HJ 637-2018 determination of oil and animal and plant oil in water), the micro-fluidic chip can realize on-site rapid detection without professional operation and has low detection content, and therefore has great significance for preliminary detection of water quality.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano sensing and microfluidics technology. Specifically, this invention relates to a microfluidic chip for trace detection of petroleum-based substances in water and its application in a detection device. Background Technology

[0002] The invention of ultrafast femtosecond lasers is a significant milestone in the development of laser technology. Femtosecond lasers refer to lasers with pulse widths on the order of femtoseconds (10^-15 seconds), and their invention can be traced back to the 1980s. The principle of femtosecond lasers is based on the coherence of light and ultrafast optics. When a laser beam passes through a nonlinear medium, the phase and frequency of the light change, forming extremely short pulses. In recent years, researchers have discovered that ultrafast femtosecond lasers have unique advantages in controlling the wettability of material surfaces. By applying femtosecond laser pulses to the surface of a material, its surface structure and chemical properties can be altered at the microscale, thereby significantly affecting the wetting behavior of liquids.

[0003] Fluorescence is a phenomenon where a substance absorbs light energy and rapidly releases it, emitting fluorescence. When a fluorescent substance absorbs photons of a specific wavelength, electrons are excited to a high-energy state, then quickly return to the ground state, releasing light of a longer wavelength, thus forming fluorescence. In petroleum, the main fluorescent substances are hydrocarbon compounds, especially aromatic hydrocarbons and certain asphaltenes and gums. Petroleum fluorescence technology plays an important role in environmental monitoring. By detecting fluorescence signals in water and soil, oil spills and pollution sources can be effectively identified, providing a scientific basis for environmental protection.

[0004] Microfluidics is a technology that uses micrometer-scale channels and structures to manipulate fluids, and it has wide applications in biomedicine, chemical analysis, and environmental monitoring. The advantages of microfluidics lie in its high efficiency, reagent savings, and rapid reaction characteristics. Due to the flow characteristics of fluids in microchannels, reaction times are typically significantly shortened, and the required sample and reagent volumes are greatly reduced. Furthermore, microfluidic systems enable parallel processing of multiple experiments, improving experimental throughput and efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that traditional detection methods involve complex operations and instruments, making it difficult to achieve rapid on-site detection. This invention provides a microfluidic chip for trace detection of petroleum substances in water, which is applied in a detection device.

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

[0007] A microfluidic chip for trace detection of petroleum-based substances in water, the fabrication method of the microfluidic chip comprising the following steps:

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

[0009] The tungsten needle is fixed on a three-dimensional displacement platform, and the cut PE board is fixed on the processing table. By controlling the movement of the three-dimensional displacement platform, the tungsten needle is inserted into the PE board. Due to the plasticity of polyethylene, the tungsten needle will leave a cylindrical pit inside the polyethylene board.

[0010] Mix PDMS and curing agent at a mass ratio of 10:1, remove internal air bubbles, and pour into a PE board with pits.

[0011] After constant temperature drying and waiting for PDMS to cure, the substrate is peeled off to obtain the PDMS columnar array substrate;

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

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

[0014] After cleaning the PDMS cylindrical array substrate processed by femtosecond laser, the surface of the substrate was treated with a plasma cleaner. The treated PDMS cylindrical array substrate was then immersed in a PVA aqueous solution for hydrophilic treatment.

[0015] Step S3, fabrication of integrated microfluidic chip;

[0016] Su8-3035 photoresist is spread all over the silicon wafer using a spin coater. Under the photo-initiated cross-linking effect of an ultraviolet lithography machine, the pattern with channel structure on the film is imprinted on the silicon substrate.

[0017] Then, PDMS and curing agent are mixed and stirred at a mass ratio of 10:1. After removing the internal air bubbles, the mixture is heated and molded on a silicon substrate to form a microfluidic chip.

[0018] The PDMS cylindrical array substrate prepared in step S2 is embedded into the integrated microfluidic chip detection chamber prepared in step S3 and sealed to complete the preparation of a microfluidic chip for trace detection of petroleum substances in water.

[0019] Preferred,

[0020] The specific steps of step S2 are as follows:

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

[0022] The PDMS cylindrical array substrate prepared in step S1 is fixed onto a glass slide and placed on an adjustable height platform. The height platform is adjusted so that the sample to be processed 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. ;

[0024] Turn on the laser source, select the laser wavelength as 1030nm, set the laser power to 30%, do not divide the frequency, 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 processing to complete before removing the sample;

[0027] Step S22: Preparation of PVA aqueous solution and modification treatment of PDMS columnar array substrate;

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

[0029] The PDMS cylindrical array substrate processed in step S21 was placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 5 minutes.

[0030] After cleaning, the substrate is removed and air-dried naturally. After air-drying, the PDMS cylindrical array substrate is placed in a plasma cleaner for surface treatment for 2 minutes. After treatment, the substrate is immediately immersed in the PVA aqueous solution prepared above for 10 minutes. After 10 minutes, the substrate is removed to complete the surface modification.

[0031] Preferred,

[0032] The specific steps of step S3 are as follows:

[0033] Step S31: Fabrication of a silicon wafer template for a microfluidic chip;

[0034] Wipe the silicon wafer with alcohol and a lint-free cloth in a clean room. After wiping, pre-bake the silicon wafer by placing it on a 95°C heating table and heating it for 15 minutes.

[0035] Place the pre-baked silicon wafer into a spin coater, pour 3-5g of Su8-3035 photoresist onto the center of the wafer, set the spin coater speed, and turn it on. The Su8-3035 photoresist will evenly spread across the entire wafer, with a thickness of 100 mm. ;

[0036] To enhance the adhesion between the photoresist and the silicon wafer, the silicon wafer needs to be baked afterward. After the photoresist is homogenized, the silicon wafer is placed on a 105°C heating stage and heated for 20 minutes.

[0037] After post-baking, the silicon wafer is placed in the lithography machine and placed close to the photomask. The ultraviolet light source is then turned on to begin lithography.

[0038] Place the silicon wafer after photolithography on a heating stage at 105°C for 5 minutes;

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

[0040] Step S32: PDMS molding and chip sealing;

[0041] PDM and curing agent were mixed and stirred at a mass ratio of 10:1. After removing the internal air bubbles, the mixture was poured onto the silicon substrate prepared by S31.

[0042] The entire assembly was placed in a 70°C oven and heated for 2 hours to accelerate the curing of polyPDMS. After curing, the microfluidic chip was obtained by cutting with a tool.

[0043] After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and glass slide are placed in a plasma cleaner, vacuumed for 90 seconds, treated with oxygen plasma for 45 seconds, and the PDMS cylindrical 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 trace detection of petroleum substances in water in a detection device, namely a detection device using the aforementioned microfluidic chip.

[0045] Preferred,

[0046] The detection device includes a portable fluorescence detector, and the specific steps for manufacturing the portable fluorescence detector include:

[0047] The fluorescence detector employs a confocal structure. The excitation light source is reflected by a dichroic mirror 2 to a second lens 3 and focused onto the detection chamber of the integrated microfluidic chip. Petroleum-based contaminants within the chamber fluoresce under the excitation light. The fluorescence is collected by the second lens 3 and, after passing through the dichroic mirror 2 and the second filter 4, is converged by a third lens 5 onto the photosensitive surface of the photodiode. The photocurrent of the photodiode is measured by the photoelectric conversion module 10.

[0048] On-chip enrichment of fluorescence detection in microfluidic chips specifically involves:

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

[0050] More preferably,

[0051] In the fluorescence detector described above, the excitation light source wavelength is selected as 310nm.

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

[0053] Following the direction of the light path, the light emitted from the excitation source passes through the first lens 6 and the first filter 1, and is refracted by the second lens 3 through the dichroic mirror 2. The fluorescence reflection excited by the sample is collected, and after passing through the dichroic mirror 2, the second filter 4, and the third lens 5, it converges to the photosensitive surface of the photodiode in the photoelectric conversion module 10.

[0054] Preferred,

[0055] The optical lenses and filters are selected as follows:

[0056] The selection of optical components must be coordinated, with priority given to the wavelength of the light source. Other optical components need to 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] Select the first filter 1 as a short-pass filter, with a cutoff wavelength of 350-390nm.

[0059] Dichroic mirror 2 can effectively transmit the wavelength of the excitation light source while effectively blocking the excitation light, ensuring that only the fluorescence signal is allowed to pass through. Therefore, the center wavelength of the dichroic mirror can be selected as 320-370nm, its reflection band is 280-350nm, and its transmission band is 380-1200nm.

[0060] The second lens 3 effectively focuses the excitation light to the 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 material of the second lens 3 is ultraviolet fused silica glass, which ensures that the transmittance of ultraviolet excitation light in the second lens 3 is greater than 90%.

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

[0062] The function of the third lens 5 is to focus the fluorescence onto the photosensitive surface of the photodiode, and to work in conjunction with the photodiode. Good coordination can improve 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. Therefore, ultraviolet fused silica glass is required to ensure light transmittance.

[0064] Preferred

[0065] The design and fabrication of the photoelectric conversion module 10 are as follows:

[0066] The photoelectric conversion module 10 uses a transimpedance amplifier circuit as its core. The photodiode generates a weak pA-level photocurrent after being illuminated by light, and this photocurrent is amplified by a feedback resistor before being output.

[0067] The value of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. A 10 GΩ feedback resistor is chosen. An excessively large feedback resistor would cause power frequency interference to couple out at the output.

[0068] The transimpedance amplifier circuit mentioned above needs to be used in conjunction with a low-pass filter. The signal after passing through the low-pass filter is sampled by the ADC chip, and the microcontroller calculates the photocurrent magnitude.

[0069] Preferred,

[0070] The low-pass filter described is a second-order Sallen-Key low-pass filter with a cutoff frequency of 5Hz and an amplification factor of less than -40dB at 50Hz.

[0071] Preferably, the on-chip enrichment of fluorescence detection in the microfluidic chip specifically includes:

[0072] Preparation of petroleum emulsions;

[0073] By adding oil and water at a ratio of 500 mg / L, according to 2 To prepare an oil-in-water emulsion, Tween 20 emulsifier was added in a certain proportion.

[0074] After vigorous stirring at 500 rpm for 2 hours, the mixture was placed in an ultrasonic cleaner for ultrasonic breakup to obtain smaller oil droplet diameters. After 1 hour of sonication, a homogeneous emulsion was obtained, which remained stable for one week without significant stratification.

[0075] Emulsified oil droplet enrichment experiment;

[0076] The prepared petroleum emulsion was diluted 200 times, mixed evenly, and 1 ml of the diluted emulsion was drawn into a syringe.

[0077] A silicone tube is used to connect the needle tip of the syringe to the inlet of the integrated microfluidic chip prepared by S3.

[0078] A precision syringe pump is used to pass the diluted oil-water emulsion into the microfluidic chip.

[0079] After the injection is completed, a fluorescence detector is used to measure the fluorescence intensity of the substrate area and calculate the concentration of the emulsion.

[0080] Compared with the prior art, the beneficial effects of the present invention are:

[0081] 1. The integrated microfluidic chip of the present invention can detect petroleum pollutants in water with only a very small sample volume;

[0082] 2. The fluorescence detection device of the present invention is simple to operate, easy to carry, and has a fast detection speed, making it suitable for preliminary detection of petroleum pollutants in water under field conditions.

[0083] Terminology Explanation

[0084] PDMS, polydimethylsiloxane;

[0085] PE board, polyethylene board;

[0086] PVA, an aqueous solution of polyvinyl alcohol. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the principle of a water petroleum pollutant detection device using the microfluidic chip of the present invention;

[0088] Figure 2 Scanning electron microscope image of a polydimethylsiloxane (PDMS) cylindrical array substrate after femtosecond laser processing;

[0089] Figure 3 Comparative images of the wettability of polydimethylsiloxane (PDMS) substrates processed by femtosecond laser;

[0090] Figure 4 A circuit rendering of the photoelectric conversion module;

[0091] Figure 5 Fluorescence experimental image of enriching emulsified oil droplets on an integrated microfluidic chip. Detailed Implementation

[0092] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0093] Combination such as Figure 1 As shown, the present invention provides a microfluidic chip for trace detection of petroleum-based substances in water. The fabrication method of the microfluidic chip includes the following steps:

[0094] Step S1, Fabrication of PDMS columnar array;

[0095] The tungsten needle is fixed on a three-dimensional displacement platform, and the cut PE board is fixed on the processing table. By controlling the movement of the three-dimensional displacement platform, the tungsten needle is inserted into the PE board. Due to the plasticity of polyethylene, the tungsten needle will leave a cylindrical pit inside the polyethylene board.

[0096] Mix PDMS and curing agent at a mass ratio of 10:1, remove internal air bubbles, and pour into a PE board with pits.

[0097] After constant temperature drying and curing of PDMS, the substrate is peeled off to obtain the PDMS columnar array. The prepared polydimethylsiloxane (PDMS) columnar array is shown below. Figure 2 As shown.

[0098] Step S2, wettability modification of PDMS columnar array substrate;

[0099] The PDMS cylindrical array substrate prepared in step S1 is fixed on the focal plane of the galvanometer of the ultrafast femtosecond laser system. The femtosecond laser processing path is drawn using the host computer software, the laser parameters are adjusted, and the PDMS cylindrical array substrate is processed.

[0100] After cleaning the PDMS cylindrical array substrate processed by femtosecond laser, the surface of the substrate was treated with a plasma cleaner. The treated PDMS cylindrical array substrate was then immersed in a PVA aqueous solution for hydrophilic treatment.

[0101] The specific process of step S2 is as follows:

[0102] Step S21, setting galvanometer and laser parameters;

[0103] The PDMS cylindrical array substrate prepared in step S1 is fixed onto a glass slide and placed on an adjustable height platform. The height platform is adjusted so that the sample to be processed is located on the focal plane of the galvanometer.

[0104] 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. ;

[0105] Turn on the laser source, select the laser wavelength as 1030nm, set the laser power to 30%, do not divide the frequency, and enable laser output;

[0106] Return to the host computer control software and click the marking button to start processing the sample;

[0107] Wait for the processing to complete before removing the sample;

[0108] Step S22: Preparation of PVA aqueous solution and modification treatment of PDMS columnar array substrate;

[0109] Prepare a PVA aqueous solution at a concentration of 8 mg / ml. After mixing, shake for 15 minutes and observe that the PVA powder is completely dissolved.

[0110] The PDMS cylindrical array substrate processed in step S21 was placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 5 minutes.

[0111] After cleaning, the substrate is removed and air-dried naturally. After air-drying, the PDMS cylindrical array substrate is placed in a plasma cleaner for surface treatment for 2 minutes. After treatment, the substrate is immediately immersed in the PVA aqueous solution prepared above for 10 minutes. After 10 minutes, the substrate is removed to complete the surface modification. Figure 3 Comparative images of the wettability of femtosecond laser-processed polydimethylsiloxane (PDMS) substrates, such as... Figure 3 As shown, Figure 3 The right image shows the contact angle of a water droplet in air on the original PDMS substrate before step S2 was completed. Figure 3 The left image shows the contact angle of water droplets in the air on the PDMS substrate after step S2. The comparison shows that step S2 increases the contact angle of water droplets in the air on the PDMS, effectively improving the wetting performance of the PDMS.

[0112] Step S3, fabrication of integrated microfluidic chip;

[0113] Su8-3035 photoresist is spread all over the silicon wafer using a spin coater. Under the photo-initiated cross-linking effect of an ultraviolet lithography machine, the pattern with channel structure on the film is imprinted on the silicon substrate.

[0114] Then, PDMS and curing agent are mixed and stirred at a mass ratio of 10:1. After removing the internal air bubbles, the mixture is heated and molded on a silicon substrate to form a microfluidic chip.

[0115] The PDMS cylindrical array substrate prepared in step S2 is embedded into the integrated microfluidic chip detection chamber prepared in step S3 and sealed to complete the preparation of a microfluidic chip for trace detection of petroleum substances in water.

[0116] The specific steps of step S3 are as follows:

[0117] Step S31: Fabrication of a silicon wafer template for a microfluidic chip;

[0118] Wipe the silicon wafer with alcohol and a lint-free cloth in a clean room. After wiping, pre-bake the silicon wafer by placing it on a 95°C heating table and heating it for 15 minutes.

[0119] Place the pre-baked silicon wafer into a spin coater, pour 3-5g of Su8-3035 photoresist onto the center of the wafer, set the spin coater speed, and turn it on. The Su8-3035 photoresist will evenly spread across the entire wafer, with a thickness of 100 mm. ;

[0120] To enhance the adhesion between the photoresist and the silicon wafer, the silicon wafer needs to be baked afterward. After the photoresist is homogenized, the silicon wafer is placed on a 105°C heating stage and heated for 20 minutes.

[0121] After post-baking, the silicon wafer is placed in the lithography machine and placed close to the photomask. The ultraviolet light source is then turned on to begin lithography.

[0122] Place the silicon wafer after photolithography on a heating stage at 105°C for 5 minutes;

[0123] Finally, the silicon wafer is immersed in the developing solution and shaken evenly to accelerate the developing process. After 5 minutes, the silicon wafer is taken out and its surface is cleaned with nitrogen to complete the preparation of the microfluidic chip silicon wafer template.

[0124] Step S32: PDMS molding and chip sealing;

[0125] PDM and curing agent were mixed and stirred at a mass ratio of 10:1. After removing the internal air bubbles, the mixture was poured onto the silicon substrate prepared by S31.

[0126] The entire assembly was placed in a 70°C oven and heated for 2 hours to accelerate the curing of polyPDMS. After curing, the microfluidic chip was obtained by cutting with a tool.

[0127] After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and glass slide are placed in a plasma cleaner, vacuumed for 90 seconds, treated with oxygen plasma for 45 seconds, and the PDMS cylindrical array substrate prepared in step S2 is embedded in the detection chamber for sealing.

[0128] The present invention also provides an application of a microfluidic chip for trace detection of petroleum-based substances in water in a detection device.

[0129] The detection device includes a portable fluorescence detector, and the specific steps for manufacturing the portable fluorescence detector include:

[0130] The fluorescence detector employs a confocal structure. The excitation light source is reflected by a dichroic mirror 2 to a second lens 3 and focused onto the detection chamber of the integrated microfluidic chip. Petroleum-based contaminants within the chamber fluoresce under the excitation light. The fluorescence is collected by the second lens 3 and, after passing through the dichroic mirror 2 and the second filter 4, is converged by a third lens 5 onto the photosensitive surface of the photodiode. The photocurrent of the photodiode is measured by the photoelectric conversion module 10.

[0131] On-chip fluorescence enrichment detection in microfluidic chips;

[0132] The diluted trace amount of oil-water emulsion was passed into a microfluidic chip, and the fluorescence intensity of the substrate region was measured using a fabricated fluorescence detector to calculate the concentration of the emulsion.

[0133] The on-chip enrichment of fluorescence detection in the microfluidic chip specifically includes:

[0134] Preparation of petroleum emulsions;

[0135] By adding oil and water at a ratio of 500 mg / L, according to 2 To prepare an oil-in-water emulsion, Tween 20 emulsifier was added in a certain proportion.

[0136] After vigorous stirring at 500 rpm for 2 hours, the mixture was placed in an ultrasonic cleaner to break up the oil droplets with ultrasound, resulting in smaller droplet diameters. After 1 hour of ultrasonication, a uniform emulsion was obtained.

[0137] Emulsified oil droplet enrichment experiment;

[0138] Emulsified oil droplets aggregate under the trapping effect of a polydimethylsiloxane (PDMS) columnar substrate, such as... Figure 5 As shown. After the injection is complete, a fluorescence detector is used to measure the fluorescence intensity of the substrate area and calculate the concentration of the emulsion. The specific process is as follows:

[0139] The prepared petroleum emulsion was diluted 200 times, mixed evenly, and 1 ml of the diluted emulsion was drawn into a syringe.

[0140] A silicone tube is used to connect the needle tip of the syringe to the inlet of the integrated microfluidic chip prepared by S3.

[0141] A precision syringe pump is used to pass the diluted oil-water emulsion into the microfluidic chip.

[0142] After the injection is completed, a fluorescence detector is used to measure the fluorescence intensity of the substrate area and calculate the concentration of the emulsion.

[0143] In the aforementioned fluorescence detector,

[0144] The excitation wavelength should be near the excitation peak of the dye to ensure maximum fluorescence excitation. The fluorescence properties of petroleum-based substances are usually closely related to their chemical composition and molecular structure. Different types of petroleum-based substances (such as crude oil, diesel, and gasoline) may have different fluorescence properties, and therefore different excitation wavelengths. Generally, the fluorescence excitation wavelength of petroleum-based substances is usually in the ultraviolet region, specifically between 250 nm and 350 nm. Considering all factors, 310 nm was chosen as the excitation wavelength for the portable fluorescence detector.

[0145] Combination Figure 1 The confocal structure of the fluorescence detector shown in the figure is specifically as follows:

[0146] Following the direction of the light path, the light emitted from the excitation source passes through the first lens 6 and the first filter 1, and is refracted by the second lens 3 through the dichroic mirror 2. The fluorescence reflection excited by the sample is collected, and after passing through the dichroic mirror 2, the second filter 4, and the third lens 5, it converges to the photosensitive surface of the photodiode in the photoelectric conversion module 10.

[0147] The optical lenses and filters are selected as follows:

[0148] The selection of optical components must be coordinated, with priority given to the wavelength of the light source. Other optical components need to be adjusted according to the wavelength of the light source.

[0149] The function of the first filter 1 is to selectively filter light of a specific wavelength to ensure accurate detection of the fluorescence signal;

[0150] Select the first filter 1 as a short-pass filter, with a cutoff wavelength of 350-390nm.

[0151] Dichroic mirror 2 can effectively transmit the wavelength of the excitation light source while effectively blocking the excitation light, ensuring that only the fluorescence signal is allowed to pass through. Therefore, the center wavelength of the dichroic mirror can be selected as 320-370nm, its reflection band is 280-350nm, and its transmission band is 380-1200nm.

[0152] The second lens 3 effectively focuses 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 ultraviolet fused silica glass, to ensure that the transmittance of ultraviolet excitation light in the second lens 3 is greater than 90%.

[0153] The function of the second filter 4 is to filter out stray light in the excitation light and ensure that the wavelength of the excitation light is within a certain range. Therefore, the second filter 4 is selected as a long-pass filter with a cutoff wavelength of 350nm.

[0154] The function of the third lens 5 is to focus the fluorescence onto the photosensitive surface of the photodiode. It needs to work in conjunction with the photodiode, and good coordination can improve sensitivity.

[0155] 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. Therefore, ultraviolet fused silica glass is required to ensure light transmittance.

[0156] Figure 4 A circuit rendering of the photoelectric conversion module 10, such as... Figure 4 As shown, the photoelectric conversion module 10 of the present invention uses a transimpedance amplifier circuit as its core. The photodiode generates a weak pA-level photocurrent after being illuminated by light, and the photocurrent is amplified by a feedback resistor before being output.

[0157] The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. A 10 GΩ feedback resistor is selected. If the feedback resistor is too large, it will cause power frequency interference to be coupled out of the output terminal. Therefore, 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 the ADC chip, and the photocurrent is obtained by the microcontroller calculation.

[0158] The low-pass filter described is a second-order Sallen-Key low-pass filter with a cutoff frequency of 5Hz and an amplification factor of less than -40dB at 50Hz.

[0159] Step S43, design and fabrication of photoelectric conversion module;

[0160] The photoelectric conversion module 10 uses a transimpedance amplifier circuit as its core. The photodiode generates a weak photocurrent after being illuminated, and this photocurrent is amplified by a feedback resistor before being output. The size of the feedback resistor directly determines the sensitivity of the photoelectric conversion module 10. A 10GΩ feedback resistor is chosen. An excessively large feedback resistor would cause power frequency interference to couple out at the output. Therefore, the transimpedance amplifier circuit needs to be used in conjunction with a low-pass filter. The second-order Sallen-Key low-pass filter is designed with a cutoff frequency of 5Hz, and the amplification factor at 50Hz is less than -40dB. The signal after the low-pass filter is sampled by an ADC chip, and the microcontroller calculates the photocurrent magnitude.

[0161] Step S5: On-chip enrichment and detection of fluorescence in the microfluidic chip;

[0162] Step S51, preparation of petroleum emulsion;

[0163] By adding oil and water at a ratio of 500 mg / L, according to 2 An oil-in-water emulsion was prepared by adding Tween 20 emulsifier in a certain proportion. After vigorous stirring at 500 rpm for 2 hours, the emulsion was placed in an ultrasonic cleaner to break up the oil droplets with ultrasound, resulting in smaller droplet diameters. After sonication for 1 hour, a homogeneous emulsion was obtained, which remained stable for one week without significant stratification.

[0164] Step S52, emulsified oil droplet enrichment experiment;

[0165] The petroleum emulsion prepared in step S51 was diluted 200 times and mixed thoroughly. 1 ml of the diluted emulsion was then drawn into a syringe. A silicone tube was used to connect the syringe needle to the inlet of the integrated microfluidic chip prepared in step S3. A precision syringe pump was then used to flow the diluted oil-water emulsion into the microfluidic chip.

[0166] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microfluidic chip for trace detection of petroleum-based substances in water, characterized in that, The method for fabricating the microfluidic chip includes the following steps: Step S1, Fabrication of PDMS columnar array; The tungsten needle is fixed on a three-dimensional displacement platform, and the cut PE board is fixed on the processing table. By controlling the movement of the three-dimensional displacement platform, the tungsten needle is inserted into the PE board. Due to the plasticity of polyethylene, the tungsten needle will leave a cylindrical pit inside the polyethylene board. Mix PDMS and curing agent at a mass ratio of 10:1, remove internal air bubbles, and pour into a PE board with pits. After constant temperature drying and waiting for PDMS to cure, the substrate is peeled off to obtain the PDMS columnar array substrate; Step S2, wettability modification of PDMS columnar array substrate; The PDMS cylindrical array substrate prepared in step S1 is fixed on the focal plane of the galvanometer of the ultrafast femtosecond laser system. The femtosecond laser processing path is drawn using the host computer software, the laser parameters are adjusted, and the PDMS cylindrical array substrate is processed. After cleaning the PDMS cylindrical array substrate processed by femtosecond laser, the surface of the substrate was treated with a plasma cleaner. The treated PDMS cylindrical array substrate was then immersed in a PVA aqueous solution for hydrophilic treatment. The specific steps of step S2 are as follows: Step S21, setting galvanometer and laser parameters; The PDMS cylindrical array substrate prepared in step S1 is fixed onto a glass slide and placed on an adjustable height platform. The height platform is adjusted so that the sample to be processed 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 row array, and set the row spacing to [value missing]. ; Turn on the laser source, select a laser wavelength of 1030nm, set the laser power to 30%, do not divide the frequency, and output the laser. Return to the host computer control software and click the marking button to start processing the sample; Wait for the processing to complete before removing the sample; Step S22: Preparation of PVA aqueous solution and modification treatment of PDMS columnar array substrate; Prepare a PVA aqueous solution at a concentration of 8 mg / ml. After mixing, shake for 15 minutes and observe that the PVA powder is completely dissolved. The PDMS cylindrical array substrate processed in step S21 was placed in anhydrous ethanol and cleaned with an ultrasonic cleaner for 5 minutes. After cleaning, the substrate is removed and air-dried naturally. After air-drying, the PDMS cylindrical array substrate is placed in a plasma cleaner for surface treatment for 2 minutes. After treatment, the substrate is immediately immersed in the PVA aqueous solution prepared above for 10 minutes. After 10 minutes, the substrate is removed to complete the surface modification. Step S3, fabrication of integrated microfluidic chip; Su8-3035 photoresist is spread all over the silicon wafer using a spin coater. Under the photo-initiated cross-linking effect of an ultraviolet lithography machine, the pattern with channel structure on the film is imprinted on the silicon substrate. PDMS and curing agent are mixed and stirred at a mass ratio of 10:

1. After removing internal air bubbles, the mixture is heated and molded on a silicon substrate to form a microfluidic chip. The PDMS cylindrical array substrate prepared in step S2 is embedded into the integrated microfluidic chip detection chamber prepared in step S3 and sealed to complete the preparation of a microfluidic chip for trace detection of petroleum substances in water.

2. The microfluidic chip for trace detection of petroleum-based substances in water according to claim 1, characterized in that, The specific steps of step S3 are as follows: Step S31: Fabrication of a silicon wafer template for a microfluidic chip; Wipe the silicon wafer with alcohol and a lint-free cloth in a clean room. After wiping, pre-bake the silicon wafer by placing it on a 95°C heating table and heating it for 15 minutes. Place the pre-baked silicon wafer into a spin coater, pour 3-5g of Su8-3035 photoresist onto the center of the wafer, set the spin coater speed, and turn it on. The Su8-3035 photoresist will evenly spread across the entire wafer, with a thickness of 100 mm. ; After homogenization, the silicon wafer is baked by placing it on a 105℃ heating table for 20 minutes. After post-baking, the silicon wafer is placed in the lithography machine and placed close to the photomask. The ultraviolet light source is then turned on to begin lithography. Place the silicon wafer after photolithography on a heating stage at 105°C for 5 minutes; Finally, the silicon wafer is immersed in the developing solution and shaken evenly to accelerate the developing process. After 5 minutes, the silicon wafer is taken out and its surface is cleaned with nitrogen gas to complete the preparation of the microfluidic chip silicon wafer template. Step S32: PDMS molding and chip sealing; PDMS and curing agent were mixed and stirred at a mass ratio of 10:

1. After removing the internal air bubbles, the mixture was poured onto the silicon substrate prepared by S31. The entire assembly was placed in a 70°C oven and heated for 2 hours to accelerate PDMS curing. After curing, the microfluidic chip was obtained by cutting with a tool. After the prepared chip is ultrasonically cleaned and dried, it can be sealed. The chip and glass slide are placed in a plasma cleaner, vacuumed for 90 seconds, treated with oxygen plasma for 45 seconds, and the PDMS cylindrical array substrate prepared in step S2 is embedded in the detection chamber for sealing.

3. The application of the microfluidic chip for trace detection of petroleum substances in water as described in any one of claims 1-2 in a detection device.

4. The application of the microfluidic chip for trace detection of petroleum substances in water according to claim 3 in a detection device, characterized in that, The detection device includes a portable fluorescence detector, and the specific steps for manufacturing 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 onto the detection chamber of the integrated microfluidic chip. Petroleum pollutants in the chamber generate fluorescence under excitation light. The fluorescence is collected by the second lens (3) and passes through the dichroic mirror (2) and the second filter (4) before being focused by the third lens (5) onto the photosensitive surface of the photodiode. The photoelectric conversion module (10) measures the photocurrent of the photodiode. The specific process of fluorescence enrichment detection on microfluidic chips is as follows: The diluted trace amount of oil-water emulsion was passed into a microfluidic chip, and the fluorescence intensity of the substrate region was measured using a fabricated fluorescence detector to calculate the concentration of the emulsion.

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

6. The application of the microfluidic chip for trace detection of petroleum substances in water according to claim 5 in a detection device, characterized in that, The function of the first filter (1) is to selectively filter light of a specific wavelength to ensure accurate detection of the fluorescence signal; Select the first filter (1) as a short-pass filter with a cutoff wavelength of 350-390nm; The dichroic mirror (2) can effectively transmit the wavelength of the excitation source and effectively block the excitation light, ensuring that only the fluorescence signal is allowed to pass through. The center wavelength of the dichroic mirror is selected as 320-370nm, its reflection band is 280-350nm, and its transmission band is 380-1200nm. The second lens (3) effectively focuses the excitation light to the 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 material of the second lens (3) is ultraviolet fused silica glass, which ensures that the transmittance of ultraviolet excitation light in the second lens (3) is greater than 90%. The function of the second filter (4) is to filter out stray light in the excitation light. The second filter (4) is selected as a long-pass filter with a cutoff wavelength of 350nm. The function of the third lens (5) is to focus the fluorescence onto the photosensitive surface of the photodiode and work with the photodiode to improve sensitivity; The function of the first lens (6) is to collimate the LED point light source (7). Since the LED point light source (7) uses ultraviolet fused silica glass in the ultraviolet band to ensure light transmittance.

7. The application of the microfluidic chip for trace detection of petroleum substances in water according to claim 5 in a detection device, 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 illuminated by light. This 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 as 10 G 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 the ADC chip, and the photocurrent is obtained by the microcontroller calculation.

8. The application of the microfluidic chip for trace detection of petroleum substances in water according to claim 7 in a detection device, characterized in that, The low-pass filter described is a second-order Sallen-Key low-pass filter with a cutoff frequency of 5Hz and an amplification factor of less than -40dB at 50Hz.

9. The application of the microfluidic chip for trace detection of petroleum substances in water according to claim 5 in a detection device, characterized in that, The aforementioned fluorescence enrichment detection on the microfluidic chip specifically includes: Preparation of petroleum emulsions; By adding oil and water at a ratio of 500 mg / L, according to 2 To prepare an oil-in-water emulsion, Tween 20 emulsifier was added in a certain proportion. After vigorous stirring at 500 rpm for 2 hours, the mixture was placed in an ultrasonic cleaner to break up the oil droplets with ultrasound, resulting in smaller droplet diameters. After 1 hour of ultrasonication, a uniform emulsion was obtained. Emulsified oil droplet enrichment experiment; The prepared petroleum emulsion was diluted 200 times, mixed evenly, and 1 ml of the diluted emulsion was drawn into a syringe. A silicone tube is used to connect the needle tip of the syringe to the inlet of the integrated microfluidic chip prepared by S3. A precision syringe pump is used to pass the diluted oil-water emulsion into the microfluidic chip. After the injection is completed, a fluorescence detector is used to measure the fluorescence intensity of the substrate area and calculate the concentration of the emulsion.

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