CN114814084A - Method for detecting pH by using microneedle - Google Patents

Abstract

The invention discloses a method for detecting pH by using a microneedle. The microneedle patch is prepared by a mold turning technology, is applied to the surface of food without wound, realizes real-time, quick and non-wound detection of the pH value, and can be used for quick food detection. The microneedle patch of the present invention contains two hydrogel components: one is CMC-pHEA nanometer hydrogel with pH response function, which will expand with different degrees along with the change of pH. The other is GelMA hydrogel which can be formed by ultraviolet curing, and can provide sufficient mechanical properties for the micro-needle by energy-conducting photocrosslinking and curing forming. The micro-needle can rapidly react to pH, the pH value can be analyzed and detected through the change of the size of the micro-needle, and the minimally invasive measurement result is highly related to the result of a pH meter. The micro-needle can pierce commercial food packages, then food containing certain moisture is sampled, and through proper calibration, the intelligent micro-needle can be suitable for food quality detection and has great significance for ensuring food safety.

Description

Method for detecting pH by using microneedle

Technical Field

The invention relates to the field of biomedicine, in particular to a preparation method and an application method of a microneedle patch for intelligent visual pH detection.

Background

The food safety is related to the health and life safety of people. The World Health Organization (WHO) estimates that food-borne pollution causes about 42 million deaths worldwide each year. Improving the efficiency of the food supply chain is also a priority measure to avoid current global loss of food production. Many consumers misunderstand the date label due to safety concerns and throw away food prematurely. The predetermined shelf life also increases public distrust of food safety and results in increased use of food preservatives by manufacturers to extend product shelf life.

Real-time monitoring of food quality has been of interest to researchers in order to ensure food safety and minimize food loss. Conventional monitoring techniques are generally based on Polymerase Chain Reaction (PCR) and cell culture techniques, involve complex laboratory equipment and professional operations, and have the disadvantages of being destructive, time consuming, and expensive, and thus are only suitable for use at the processing, storage, and transportation level of the food supply chain to meet quality control requirements. While currently available monitoring technologies applied downstream in the food supply chain, such as colorimetric sensors, are generally considered less sensitive, and securing the colorimetric sensor within the packaging material or in a sachet can limit detection of pathogenic microorganisms on and within the food.

In the process of processing and storing, the detection of the pH value of the food plays an important role in guaranteeing the quality of the food. The pH value represents the activity of hydrogen ions in food, which is a factor in maintaining biochemical reactions and affects the growth and viability of microorganisms during processing, storage and distribution, thus determining the quality of food. Traditionally, the pH of food is measured electrochemically using a pH sensitive glass electrode and a reference electrode, which is suitable for laboratory operations and tests, but not suitable for rapid tests of food by consumers. Therefore, there is a need to develop a new generation of rapid detection means for pH value of food, determine the acidity level in the food system, ensure the quality and safety of food, facilitate the use and reading by consumers, do not damage the food itself and have no harmful effect on human health.

Disclosure of Invention

In view of the above technical problems, it is an object of the present invention to develop a method for qualitatively or quantitatively detecting pH, which can rapidly detect pH by simply piercing the package directly into contact with the interior of the food (fig. 1). Therefore, the visual food quality and safety information is provided for consumers, the operation is simple, and the test is rapid.

The invention adopts biocompatible materials to prepare the micro-needle gel. The microneedle gel contains two hydrogel components: one is photosensitive hydrogel with photocuring forming characteristic; the other is pH-responsive hydrogel, which has pH-responsive deformation characteristics. The photosensitive hydrogel is methacrylic acid anhydridized gelatin (GelMA) and can also be other photosensitive hydrogels, and the main functions are favorable for photocuring crosslinking and provide sufficient puncture mechanical properties for the micro-needle; the pH response hydrogel is abbreviated as CMC-pHEA, and can also be other types of pH response hydrogels, and in order to accelerate the response of the CMC-pHEA hydrogel to pH, the CMC-pHEA hydrogel is subjected to ultrasonic crushing to form CMC-pHEA nano gel.

In a first aspect, the present invention provides a method for microneedle pH detection, comprising the steps of:

(1) under the condition of keeping out of the sun, mixing a photosensitive hydrogel solution, a photoinitiator and a pH response functional hydrogel solution, pouring the mixture into a microneedle template, and performing high-speed centrifugation; then curing and forming the microneedle array under illumination; the sensitive hydrogel is methacrylic acid anhydrified gelatin hydrogel solution; the pH response function hydrogel solution is prepared from carboxymethyl cellulose and 2-hydroxyethyl acrylate under the combined action of potassium persulfate and polyethylene glycol diacrylate;

(2) coating transparent light-cured resin on the bottom surface of the microneedle array, and curing by ultraviolet light to form a substrate of the microneedle array;

(3) drying and demolding to form the hydrogel microneedle patch; the microneedle patch is a square matrix structure formed by a sharp conical microneedle hydrogel array on a substrate;

(4) pH test method:

(4.1) qualitative test: puncturing the microneedle patch obtained in the step (3) into a sample to be tested, and observing the change condition of the microneedle to determine the pH value;

(4.2) quantitative test: and (4) puncturing the microneedle patch obtained in the step (3) into a sample to be tested, and calculating the pH value by using a relation expansion curve of the microneedle expansion rate and the pH value.

As shown in fig. 3, since the prepared microneedle has a sharp inverted triangle shape, the microneedle has non-invasive or minimally invasive properties, and is beneficial to express puncture on food packaging bags, food surfaces and the like, sample liquid from the interior of food through capillary action, and rapidly respond to acidic substances in the liquid. After the microneedles were pulled out, the change in height and the change in swelling rate of the microneedles were observed to quantitatively detect the pH level in real time (fig. 1). When the environment of the microneedle is strong in acidity (low pH), the microneedle is small in swelling degree; microneedles swell to a greater extent when placed in a neutral environment (high pH) (figure 1). The swelling degree of the micro-needle and the pH value of the environment are in a linear positive correlation characteristic, and the pH value of the substance to be detected can be accurately analyzed through the size change of the micro-needle.

The intelligent microneedle patch disclosed by the invention has biocompatibility and sufficient mechanical properties, can be directly punctured and packaged to be in contact with the interior of food, including meat, vegetables and the like, samples liquid from the interior of food through capillary action, is sensitive to pH change response, and can obtain an accurate pH value through microneedle size analysis.

Further, the microneedle array at least comprises one microneedle, and can be in a single-row or array structure; the height of the conical microneedle is 100-800 μm; the pitch of the microneedles in a single row or array is 100-800 μm. Preferably, the height of the tapered microneedle is 600 μm; the distance between the microneedles in the microneedle array is 400 mu m; the dimensions of the matrix structure were 6.3 × 6.3mm, consisting of 11 × 11 needles.

Further, the photoinitiator is an I2959 ultraviolet photoinitiator or a LAP blue light initiator, and the mass percentage of the photoinitiator is 0.05-0.1% of the weight of the hydrogel.

Further, the transparent photosensitive resin was clear v4 resin manufactured by formlab corporation, usa.

Further, the methacrylic anhydrified gelatin hydrogel is prepared by dissolving methacrylic anhydrified gelatin in water according to the mass percent of 8-12% to obtain methacrylic anhydrified gelatin hydrogel solution.

Further, the preparation method of the pH response function hydrogel solution is as follows:

(a) dissolving carboxymethyl cellulose in water at 50-100 ℃ and at a stirring speed of 300-500 r/min:

(b) adding potassium persulfate into the solution obtained in the step (a) in the presence of inert gas, mixing and reacting:

(c) adding 2-hydroxyethyl acrylate to the solution of the step (b), and continuing the reaction until the solution is milky white:

(d) adding polyethylene glycol diacrylate into the solution in the step (c) and continuing the reaction until the reaction is finished:

(e) dialyzing the reaction product obtained in the step (d) to remove unreacted reactants to obtain the pH response hydrogel;

the carboxymethyl cellulose, the acrylic acid-2-hydroxyethyl ester, the initiator and the cross-linking agent have the following molar ratios: 1: ((5.48-8.62). times.10) ³ )：(2.65-3.60)：(28.77-86.33)。

Further, in the step (1), the illumination parameter is blue light, purple light or ultraviolet light, and the illumination time is 3-60 s; the ultraviolet curing time in the step (2) is 1-2 h. Preferably, in the step (1), the illumination parameter is 405nm blue-violet light, and the illumination time is 3 s; the ultraviolet curing time in the step (2) is 2 hours.

Further, the method for judging the acidity or basicity in the step (4.1) is as follows: if the shape change of the micro-needle is small and the needle gap is large, the acidity is strong; if the shape of the microneedle is obviously enlarged, the needle gap is reduced and a certain gap exists, the microneedle is weakly acidic; if the shape of the microneedle is significantly enlarged and the needles are closely adhered to each other, the microneedle is neutral or alkaline.

Further, the method for calculating the pH value in the step (4.2) is as follows:

puncturing a microneedle patch to a standard substance with standard gradient pH, measuring the expansion rate of the microneedle patch, and fitting a curve of the expansion rate changing along with the pH and a calculation formula;

the swelling rate of the puncture sample is measured, and the pH value is calculated according to a calculation formula.

Further, the change in the size of the microneedle patch is measured using a camera or a mobile phone having a macro function to calculate the expansion ratio.

The invention has the beneficial effects that:

the invention provides a novel, noninvasive and visual pH rapid detection method. The pH response characteristic and the photocuring characteristic of the intelligent hydrogel are utilized, and the micro-invasiveness of the micro-needle is combined to realize the rapid detection of the pH of the food quality. The micro-needle is small in size, simple and portable, high in sensitivity, simple to operate and suitable for quick detection of common consumers and relevant personnel for field detection and the like.

The testing method provided by the invention can be directly used for food, particularly solid or gelatinous food, is convenient and quick to sample, is simple and quick to test, and can carry out qualitative or quantitative test according to requirements.

Drawings

FIG. 1 is a schematic view of a microneedle patch for pH detection and its working principle;

fig. 2 is a process flow for preparing intelligent hydrogel double-layer microneedles;

fig. 3 is a microneedle appearance and microtopography in which (a) a picture of the overall microneedle; (b) scanning electron microscope pictures of the microneedles; (c) single row microneedle images;

FIG. 4 is a graph of the shape change of microneedles after exposure to solutions of different pH;

FIG. 5 is a graph of the pH responsiveness of microneedles in agarose gels; wherein, (a) the picture of the microneedle array after puncturing agarose gel with different pH values; (b) magnified pictures of individual microneedles; (c) the height of the micro-needle after puncturing agarose gel with different pH values; (d) the swelling ratio of the micro-needle after puncturing agarose gel with different pH values;

fig. 6 is the corresponding height of the microneedles after piercing different types of pork.

Detailed Description

The invention will be further illustrated with reference to specific examples, to which the present invention is not at all restricted.

Examples

Preparation of pH-responsive hydrogel CMC-pHEA

First, 50ml of distilled water and carboxymethylcellulose (CMC) (5.56X 10mo1) were placed in a 250m1 three neck round bottom flask and stirred in a water bath at 75 deg.C (50-100 deg.C, preferably 75 deg.C) and 400rpm (300-500rpm, preferably 400rpm) until the CMC was sufficiently dissolved. Then, nitrogen gas was injected into a pressure-dividing flask containing the CMC solution for 20 minutes to sufficiently lower the oxygen content of the solution, and then potassium perphobic (KPS, 1.85X 105mo1) was added as an initiator to the solution to mix and react for 20 minutes. Next, 3.92X 10mo1 of 2-hydroxyethyl Acrylate (2-HydroxyEthyl 1 Acrylate, 2-HEA) was added. When the reaction mixture became milky white, 0.32X 10mo1 crosslinker polyethylene glycol diacrylate PEGDA was added and the reaction was continued for 3 hours, after the reaction was completed, the mixture was fully cooled at room temperature. The stirring speed was adjusted during the synthesis to induce homogeneous synthesis. The compound was dialyzed with 5L of distilled water for 3 days or more to remove unreacted crosslinking agent and monomer to form a pH responsive hydrogel CMC-pHEA. And then crushing the hydrogel by using an ultrasonic crusher.

Preparation of GelMA photoresponsive hydrogel

GelMA raw material is dissolved in deionized water in a mass percent of 10% (8% -12%, preferably 10%). The LAP blue light initiator is dissolved in 10 percent GelMA solution according to the mass percent of 0.05 percent to 0.1 percent. The operation is carried out under the condition of avoiding light, and GelMA is prevented from being crosslinked under natural light. And sonicated at 37 ℃ (28-45 ℃, preferably 37 ℃) for 5 minutes in the dark to mix thoroughly: then soaking in hot water at 37 deg.C for half an hour to dissolve completely. Irradiating the mixed solution under a light source of 405m, and instantly (about 1-2s) curing to obtain the photocured GelMA photosensitive hydrogel.

3. Preparation of a two-network hydrogel System

Mixing the two hydrogels prepared in the steps 1 and 2 according to the volume ratio of 1:3, and placing the two hydrogels in an oven at 50 ℃ for heat preservation until bubbles disappear and the hydrogels become clear. And (2) performing photocuring by using the pH response characteristic of the CMC-pHEA nano gel and the photocuring forming characteristic of the GelMA hydrogel and adopting 405nm ultraviolet irradiation to obtain the pH response double-network hydrogel.

4. Preparation of hydrogel microneedle arrays

As shown in fig. 2, the hydrogel prepolymer incubated at 50 ℃ was dropped on the surface of the microneedle mold, and centrifuged three times by a high speed centrifuge (40 ℃, 3800rpm, 10min) to fill the hydrogel into the mold cavity. Scraping off excessive hydrogel on the surface with a knife, and curing with blue-violet light with wavelength of 405nm, wherein the light intensity is 20%, and the irradiation time is about 3 s. And dropwise adding a certain amount of light-cured resin on the surface of the mold, and after the surface of the resin is flat, irradiating ultraviolet light again for curing, wherein the light intensity is 20 percent, and the irradiation time is about 2 hours. And drying and demolding to obtain the hydrogel microneedle array with the substrate of hard transparent resin and the tip of the hydrogel microneedle array with pH responsiveness.

As shown in fig. 3, the prepared microneedle patch was intact in appearance, and contained 11 × 11 microneedles each exhibiting a sharp conical structure.

The contact angle tester and the CCD camera thereof are used for recording and analyzing the size and volume change of the single microneedle under different conditions.

5. pH responsiveness test of microneedle arrays

Pure water was adjusted to pH 3, 5, 7, respectively, by phosphoric acid (20%).

And (3) placing the microneedle on an objective table of a contact angle instrument, and dropwise adding aqueous solutions with different pH values after fixing the microneedle. After completely soaking the microneedles for 3s, the moisture on the surface of the sample is sucked dry by using dust-free paper, and the morphological change of the microneedles is observed.

The results are shown in FIG. 4: the shape of the microneedle changes little under the action of a low-pH (pH 3) aqueous solution, and the original conical shape of the microneedle is almost maintained; under the action of an aqueous solution with the pH value of 5, the microneedle is obviously enlarged, and the gap between the microneedles is reduced; under the action of an aqueous solution with a high pH (pH 7), the microneedle became significantly large, the needle was closely attached to the needle, and even slightly toppled in shape due to excessive swelling. Indicating that the microneedle has a rapid and sensitive pH response capability. The acidity or basicity of the unknown solution can be inferred from the swelling ratio of the microneedles.

6. Preparation of agarose gels at different pH levels

In order to simulate the puncture application of the microneedle on a real object and accurately measure the size change of the microneedle under different pH values, agarose gel is prepared to simulate food.

0.5g of agarose was dissolved in 10ml of water, and the pH was adjusted to 1.7, 2.5, 3.5, 4.5, 5.0, and 7.0, to prepare 6 groups of samples, respectively. The mixture was heated to 70 ℃ with constant stirring until the agarose was completely dissolved. The agarose solution was poured into a small cell culture dish, cooled to room temperature, and covered for 30min to obtain agarose gels with different pH values, 3mm in height, for the next microneedle puncture experiment.

7. Detection of pH value in agarose gel

Similarly, the change in height of the microneedles was measured using a contact angle tester and its own CCD camera.

Fixing the microneedle patch on a contact angle sample platform, adjusting the position of a contact angle needle to enable the needle point to be close to the microneedle needle point, enabling the microneedle patch and the microneedle arranged at the forefront of the microneedle array to be positioned on a horizontal plane, and focusing to enable the two needle points to be clear at the same time. The diameter of the contact angle needle and the height of the individual needles of the microneedle array at this time were recorded using the CCD camera of the contact angle tester (fig. 5 a).

The microneedle patch was removed, the microneedle array was pressed into agarose gel with a finger, held for 5 seconds and pulled out, and the height of the microneedle was measured again using a contact angle meter (fig. 5 a). And (4) replacing the micro-needle and the gel, repeating the test, and recording the height change condition of the micro-needle after the micro-needle penetrates into the agarose gel with different pH values.

Results and analysis:

after puncturing agarose gels of different pH values, the microneedle size showed a positive linear correlation change with pH change (fig. 5 b-d). When the pH is 1.7, the height change of the microneedle is small, and the expansion rate is only 0.92%; the microneedles became higher in height and larger in swelling with increasing pH, and the swelling rate of the affected microneedles reached 28.8% at pH7.0 (fig. 5 c-d).

Based on the results in vitro agarose gels, the pH in unknown moisture-laden foods can be calculated by fitting a transformation curve of the expansion ratio with the pH and a calculation formula.

8. pH detection of different meats

Meat is easily deteriorated due to microbial contamination. Microbial spoilage can produce high levels of volatile basic nitrogen (TVB-N) and alter the pH of meat.

The pH sensitivity and the responsiveness of the intelligent microneedle are combined, so that the pH responsive microneedle can be widely applied to pH value detection and evaluation of different food systems. For example, the size deformation of the microneedles is used to monitor the pH of different meats, reflecting their different freshness/spoilage levels, and to verify the compatibility of the microneedles in food system testing.

The intelligent microneedles were used to puncture pork of different freshness/decay levels at different time points. After the microneedle punctured the pork sample, the microneedle was held for 5 seconds, pulled out, and the dimensional change of the microneedle was observed (fig. 6).

The experimental results are as follows:

storing fresh pork at 25 deg.C for 48 hr, and measuring pH to 7.4 with pH paper; after the fresh pork was punctured by the microneedles, the height of the microneedles was 636 microns.

Placing pork in natural environment in summer for 48 hours, simulating deteriorated pork, and measuring the pH value of the deteriorated pork to be 6.0 by using pH test paper; after the modified pork is punctured by the micro-needle, the height of the micro-needle is lower and is 628 microns.

Similar to the results in the agarose hydrogel described above, pH acidity in pork of different freshness/rotting degrees has a positive linear correlation with the height of the microneedles after puncture.

Through the evaluation of the pH value of meat, the method provided by the invention is found to have very good sensitivity on monitoring the freshness of the meat, and the pH value of the food can be reversely deduced through the size of the microneedle, so that the method can be used as a pH detection method with low cost and simple and convenient operation.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope of the present invention should be included in the scope of the present invention.

Claims (10)

1. A microneedle pH detection method is characterized by comprising the following steps:

(1) under the condition of keeping out of the sun, mixing a photosensitive hydrogel solution, a photoinitiator and a pH response functional hydrogel solution, pouring the mixture into a microneedle template, and performing high-speed centrifugation; then curing and forming the microneedle array under illumination; the sensitive hydrogel is methacrylic acid anhydrified gelatin hydrogel solution; the pH response function hydrogel solution is prepared from carboxymethyl cellulose and 2-hydroxyethyl acrylate under the combined action of potassium persulfate and polyethylene glycol diacrylate;

(2) coating transparent photosensitive resin on the bottom surface of the microneedle array, and curing by ultraviolet light to form a substrate of the microneedle array;

(3) drying and demolding to form the hydrogel microneedle patch; the microneedle patch is a square matrix structure formed by a sharp conical microneedle hydrogel array on a substrate;

(4) pH test method:

(4.1) qualitative test: puncturing the microneedle patch obtained in the step (3) into a sample to be tested, and observing the change condition of the microneedle to determine the pH value;

(4.2) quantitative test: and (4) puncturing the microneedle patch in the step (3) into a sample to be tested, and calculating the pH value by using a relation expansion curve of the microneedle expansion rate and the pH value.

2. The method of claim 1, wherein: the microneedle array at least comprises one microneedle, and can be in a single-row or array structure; the height of the conical microneedle is 100-800 μm; the pitch of the microneedles in a single row or array is 100-800 μm.

3. The method of claim 1, wherein: the photoinitiator is I2959 ultraviolet initiator or LAP blue light initiator, and the mass percentage of the photoinitiator is 0.05-0.1% of the weight of the hydrogel.

4. The method of claim 1, wherein: the transparent photosensitive resin is clear v4 resin manufactured by formlab corporation in the U.S.A.

5. The method according to claim 1, wherein the methacrylic anhydrified gelatin hydrogel is obtained by dissolving methacrylic anhydrified gelatin in water in an amount of 8 to 12 mass% to obtain a methacrylic anhydrified gelatin hydrogel solution.

6. The method according to claim 1, wherein the pH-responsive functional hydrogel solution is prepared by:

(a) dissolving carboxymethyl cellulose in water at 50-100 ℃ and at a stirring speed of 300-500 r/min:

(b) adding potassium persulfate into the solution obtained in the step (a) in the presence of inert gas, mixing and reacting:

(c) adding 2-hydroxyethyl acrylate to the solution of the step (b), and continuing the reaction until the solution is milky white:

(d) adding polyethylene glycol diacrylate into the solution in the step (c) and continuing the reaction until the reaction is finished:

(e) dialyzing the reaction product obtained in the step (d) to remove unreacted reactants to obtain the pH response hydrogel;

the carboxymethyl cellulose, the acrylic acid-2-hydroxyethyl ester, the initiator and the cross-linking agent have the following molar ratios: 1: ((5.48-8.62). times.10) ³ )：(2.65-3.60)：(28.77-86.33)。

7. The method of claim 1, wherein: in the step (1), the illumination parameter is blue light, purple light or ultraviolet light, and the illumination time is 3-60 s; the ultraviolet curing time in the step (2) is 1-2 h.

8. The method according to claim 1, wherein the method for determining the acidity or basicity in step (4.1) is as follows: if the shape change of the micro-needle is small and the needle gap is large, the acidity is strong; if the shape of the microneedle is obviously enlarged, the needle gap is reduced and a certain gap exists, the microneedle is weakly acidic; if the shape of the microneedle is significantly enlarged and the needles are closely adhered to each other, the microneedle is neutral or alkaline.

9. The method according to claim 1, wherein the calculation of the pH value in step (4.2) is carried out as follows:

puncturing a microneedle patch with a standard substance with standard gradient pH, measuring the expansion rate of the microneedle patch, and fitting a curve of the expansion rate changing along with the pH and a calculation formula;

the swelling rate of the puncture sample is measured, and the pH value is calculated according to a calculation formula.

10. The method of claim 9, wherein: and measuring the size change of the microneedle patch by using a camera or a mobile phone with a microspur function to calculate the expansion rate.

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