A pH-sensitive spectral response membrane online monitoring method based on chemical cross-linking

Abstract

The application discloses a kind of pH-sensitive spectrum response film online monitoring methods based on chemical crosslinking.It is technical solution: first polyvinyl alcohol is dissolved in water, then with cellulose solution, pH indicator is mixed according to certain proportion, prepare pH-sensitive original solution, then it is drop-coated to amino glass substrate and incubated, prepare pH-sensitive substrate.Using etching or molding method to make cover piece with microchannel, it is bonded after being treated with oxygen plasma with pH-sensitive substrate, obtain pH microfluidic chip.And it is used in combination with self-built integrated pH sensing system.Self-built integrated pH sensing system includes light source (1), pH sensing chip (2), spectrometer or colorimeter (3) and host computer (4).This pH microfluidic chip online monitoring system based on chemical crosslinking has long service life, wide pH response range, strong anti-interference ability, good stability and other advantages, and can realize online, real-time monitoring of pH.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pH-sensitive substrates, and relates to an on-line monitoring method for a pH-sensitive spectral response film based on chemical cross-linking. BACKGROUND

[0002] In recent years, optical pH sensors have attracted extensive attention of researchers due to their high sensitivity, strong anti-interference and low cost. An optical pH sensor mainly comprises a pH indicator and an organic carrier. The indicator reacts with hydrogen ions to change the molecular structure of the indicator, thereby changing the optical properties of the sensor. Generally, the pH indicator is fixed on the organic carrier by adsorption, chemical bonding and sol-gel, etc. Then, the carrier is directly fixed on a substrate to form an optical pH sensing substrate for sensing the pH change of a solution. Among them, the adsorption method is simple to operate, but the indicator is easy to leak; the sol-gel method has strong universality, but the prepared film has poor toughness; and the chemical bonding fixes the indicator through a covalent bond, and the prepared sensitive film has overwhelming advantages in service life and use performance.

[0003] Polyvinyl alcohol (PVA) is a water-soluble polymer with low price, good biocompatibility and biodegradability, and is widely used in biomedical materials, adhesives, surfactants and other fields. PVA has a large number of hydroxyl functional groups and high strength and toughness, so it is a good adhesive for porous hydrophilic surfaces such as wood and textiles. Because PVA has high transparency and high ductility, it has also attracted extensive attention in optical sensors. However, the adhesive strength of PVA on optical substrates with good light transmission (such as glass, quartz, etc.) is not high. The high adhesive strength on porous surfaces comes from the mechanical interlocking of two interfaces, but for smooth surfaces, this interlocking mechanism fails, so only dense intermolecular forces or chemical bonds can meet the requirements of high adhesive strength. However, most polymer adhesives generate residual stress when solidified, which will cause the adhesive strength of the interface to decrease, and in severe cases, the adhesive layer will automatically fall off. In this regard, the smooth substrate is chemically modified to modify the amino group, and the reaction product of PVA and nano-element fibers containing a large number of carboxyl and amino groups is coated, which can effectively reduce the falling off of the adhesive layer.

[0004] Existing photochemical pH sensors mostly measure solution pH by sampling. However, this method is relatively slow in detecting the ever-changing pH of industrial wastewater (it cannot respond to changes in the solution's acidity or alkalinity in real time). By the time a deviation from normal pH is detected, contamination has already occurred, preventing immediate control of the damage. Microfluidic chips are a chip-based technology platform that integrates multiple disciplines, including chemistry, physics, and biology. They can perform sample preparation, reaction, separation, and detection processes on a single chip. In pH measurement, microfluidic chips enable online, real-time monitoring, reducing reagent loss and improving efficiency and reproducibility. Specific channels can be designed based on specific experimental requirements and desired results, effectively controlling reaction conditions while maintaining liquid flow and driving efficient reactions. Furthermore, the chip's miniaturized integration and automation eliminate complex, step-by-step procedures, improving safety. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention proposes a method for online monitoring of a pH-sensitive spectrally responsive membrane based on chemical crosslinking. The method comprises: 1) chemically crosslinking the carboxyl groups in CNF with a pH indicator and amino groups on a substrate; and chemically crosslinking the hydroxyl groups in PVA with a pH indicator and amino groups in a glass sheet (or chemically crosslinking the amino groups on the substrate with CNF and carboxyl groups in a pH indicator; and chemically crosslinking the amino groups in CNF with carboxyl groups of a pH indicator and hydroxyl groups in PVA); preparing a long-life pH-sensitive substrate; 2) adopting a binary or ternary indicator method to broaden the pH detection range; and 3) constructing an integrated pH sensing system to achieve online and real-time pH monitoring.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] Step 1: Add a certain amount of polyvinyl alcohol (PVA) into water and stir at a certain temperature to completely dissolve it;

[0008] Step 2: PVA aqueous solution, cellulose (CNF) solution prepared by TEMPO oxidation method and pH indicator are mixed and stirred in a certain proportion to prepare pH sensitive membrane stock solution;

[0009] Step 3: Amination treatment is performed on the glass substrate using (3-aminopropyl)triethoxysilane (APTES), and the pH sensitive membrane solution prepared in step 2 is drop-coated on the amination-treated glass substrate, incubated at room temperature, and then dried to form a film to obtain a pH sensitive substrate;

[0010] The PVA has an alcoholysis degree of 99% and a polymerization degree of 1799-2499.

[0011] The pH indicator can be neutral red, methyl red, Congo red, etc.

[0012] The pH-sensitive film can contain two or three different pH indicators, which can expand the pH response range of the sensitive film.

[0013] The pH-sensitive substrate is bonded with a cover sheet (material can be glass, polydimethylsiloxane (PDMS), polymethyl methacrylate, etc.) with microchannels made by etching or molding method after oxygen plasma treatment, to obtain a pH microfluidic chip.

[0014] The pH-sensitive substrate can be placed in a self-built integrated pH sensing system for testing. The system includes a light source (1), a pH sensing chip (2), a spectrometer or colorimeter (3), and a host computer (4). The device uses LabVIEW and WaveForms to write a voltage reading program, reads the pH electrical signal, and substitutes it into the corresponding electrical signal-pH model trained in Matlab to realize automatic pH output.

[0015] The online monitoring method of the pH-sensitive spectral response film based on chemical crosslinking of the present application 1) solves the problems of indicator leakage and easy peeling of the pH-sensitive film of the current photochemical pH sensor; 2) breaks the barrier of narrow detection range of the current pH sensor based on indicator; 3) through the microfluidic device, continuous pH monitoring with ultra-low reagent consumption can be realized.

[0016] The integrated pH sensing system built by the present application realizes the integration of incident light path, detection circuit and signal output, can overcome the disadvantages of traditional pH detection devices, and realizes wide dynamic range pH automatic online monitoring under complex conditions. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The absorption spectrum of the pH-sensitive substrate based on neutral red under different pH conditions.

[0018] Figure 2 The absorption peak position of the pH-sensitive substrate based on neutral red under different pH conditions.

[0019] Figure 3 The 3D printed positive film.

[0020] Figure 4 The pH microfluidic chip.

[0021] Figure 5 The 3D drawing of the packaging system (parameter unit: mm).

[0022] Figure 6 The framework of the online pH detection system. EMBODIMENT

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the coverage of the present application.

[0024] The present application proposes a chemical cross-linking based pH sensitive substrate for neutral range.

[0025] Step one, preparation of PVA aqueous solution

[0026] First, 2 mg of PVA (99%, 1799) is added to 20 mL of water and stirred at 95°C for 30 minutes until the solution appears clear and transparent;

[0027] Step two, preparation of pH sensitive film solution

[0028] 5 mg of neutral red is added to the mixed solution containing 18 mL of PVA aqueous solution and 2 mL of CNF solution, and stirred at room temperature for 1 h to prepare a neutral red pH sensitive film solution;

[0029] Step three, amino treatment of the substrate

[0030] The cleaned glass substrate is placed in a petri dish containing ethanol, then (3-aminopropyl) triethoxysilane (APTES) is added to the petri dish, and then heated at 60°C for 2 h. After cooling to room temperature, rinse with ethanol and water.

[0031] Step four, preparation of pH sensitive substrate

[0032] The pH sensitive film solution prepared in step two is drop-coated on the amino-functionalized glass substrate, incubated at room temperature for 1 h, and then dried into a film at 65°C to obtain a pH sensitive substrate.

[0033] Step five, performance test of pH sensitive substrate

[0034] The pH sensitive substrate obtained in step four is tested for absorption, transmission or reflection spectra in different pH buffer solutions using a spectrometer, wherein the absorption spectrum is as shown in Figure 1 , and the absorption peak position is used to plot different pH values Figure 2 .

[0035] The present application proposes a chemical cross-linking based pH sensitive substrate for acidic and neutral range.

[0036] Neutral red and Congo red are selected as pH indicators to prepare the sensitive substrate, and the remaining operation steps are the same as in Example 1.

[0037] First, 3D printed positive film (PAN) is prepared by mixing 3D printing resin with 3D printing initiator and then irradiating with UV light for 30 minutes. Figure 3)Use double-sided tape to fix on a plastic culture dish, then weigh the PDMS prepolymer and the curing material, the mass ratio is 10:1, mix evenly, then pour the mixed PDMS into the culture dish to completely cover the positive film, put it into a vacuum drying oven, bake at 80 degrees Celsius for 2 hours. The cured PDMS and the pH-sensitive substrate obtained in Example 1 or 2 are subjected to plasma treatment for chemical bonding to prepare a pH microfluidic chip preparation Figure 4 )。

[0038] The application proposes an on-line monitoring method of pH-sensitive spectral response film based on chemical cross-linking. In order to realize on-line real-time monitoring of pH, an integrated pH monitoring system is built.

[0039] Step one: first, use 3ds MAX to draw the packaging system, which has three layers of partitions, respectively for placing LED modules, microfluidic chips and photoelectric conversion circuits, the left strip-shaped vacancy is used for leading out power lines, signal lines and microfluidic tubes Figure 5 )。

[0040] Step two: the LED module (1) is placed above the first layer of partition, the pH microfluidic chip (2) is placed above the second layer of partition, and the spectrometer or colorimeter (3) is placed above the third layer of partition and connected with the upper machine position (4). The device uses LabVIEW and WaveForms to write voltage reading program, reads pH electric signal, and substitutes it into the corresponding electric signal-pH model trained by Matlab to realize automatic output of pH Figure 6 )。

[0041] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present application.

[0042] The above-described embodiments only express several implementation manners of the present application, the description is more specific and detailed, but it should not be understood as the limitation of the scope of the present application. It should be pointed out that, for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A pH-sensitive spectral response membrane online monitoring method based on chemical cross-linking, characterized in that The preparation method is: Step 1: First, add a certain amount of polyvinyl alcohol into water and stir at a certain temperature to completely dissolve it; Step 2: Mixing a polyvinyl alcohol aqueous solution, a cellulose solution prepared by a tetramethylpiperidinium oxide oxidation method, and a pH indicator in a certain proportion to prepare a pH sensitive membrane stock solution; Step 3: Amination treatment is performed on the glass substrate using (3-aminopropyl)triethoxysilane. The pH-sensitive membrane solution prepared in step 2 is drop-coated on the amination-treated glass substrate, incubated at room temperature, and then dried to form a film to obtain a pH-sensitive substrate whose absorption, transmission, or reflection spectral response changes with different pH values.

2. The preparation method according to claim 1, wherein Polyvinyl alcohol with an alcoholysis degree of 99% and a polymerization degree of 1799-2499 is selected.

3. The preparation method according to claim 1, wherein The pH indicator is selected from neutral red, methyl red, and Congo red.

4. The preparation method according to claim 1, wherein a sensitive membrane containing two or three different pH indicators is prepared to broaden the pH response range of the sensitive membrane.

5. The preparation method according to claim 1, wherein the pH sensitive substrate is bonded to a cover sheet with microchannels formed by etching or molding after oxygen plasma treatment, wherein the material of the cover sheet is selected from glass, polydimethylsiloxane or polymethyl methacrylate, thereby obtaining a pH microfluidic chip.

6. The preparation method according to claim 1, wherein the pH sensitive substrate is placed in an independently constructed integrated pH sensing system for testing, the system comprising a light source (1), a pH sensor chip (2), a spectrometer or a colorimeter (3) and a host computer (4), and a voltage reading program is written using LabVIEW and WaveForms to read the pH electrical signal, and the voltage is substituted into the corresponding electrical signal-pH model trained by Matlab to achieve automatic pH output.

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