A green fluorescent carbon dot-based wedge microstructure pH optical fiber sensor and a sensing method

Abstract

The present application provides a kind of sensor and sensing method based on green fluorescent carbon dot microfabrication technology etching structure to solve the problems of pH detection in prior art, belongs to the field of optical fiber sensor.The sensor mainly includes: microstructure optical fiber sensing probe, central emission wavelength is 415nm laser light source, Y type optical fiber coupler and optical fiber spectrometer.The present application coats the hydrogel film containing green fluorescent carbon dots on the tip of optical fiber, produces different fluorescence intensity signals at different pH, realizes sensitive detection of pH value;The sensor probe is made of microstructure optical fiber tip etched by microfabrication system, and the diameter is small, which can realize real-time online detection of pH of water sample in narrow environment;The sensor does not need frequent calibration, has short response time and is easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, and specifically relates to a pH fiber optic sensor and sensing method based on a wedge-shaped microstructure of green fluorescent carbon dots. Background Technology

[0002] pH is a measure of the acidity or alkalinity of a solution, indicating the concentration of hydrogen ions in the solution. pH measurement plays a crucial role in various fields, including drinking water safety, industrial wastewater treatment, health monitoring, and agricultural production. pH serves as an important indicator in many studies. For example, in oil and mineral exploration, pH reflects the acidity or alkalinity of soil and rock formations; the pH of drilling fluids directly affects drill bit life and borehole stability; changes in pH can reflect changes in mineral dissolution, ion migration, and soil and rock mechanical properties. In agriculture, different crops exhibit significant differences in their adaptability to soil pH, and pH influences soil ecosystems and nutrient release processes. In medicine, pH is used as an important indicator in the diagnosis and treatment of some diseases (such as gout and gastroesophageal reflux disease). In the food industry, acidity control directly affects the texture and taste of food; during fermentation, pH is an important indicator for assessing microbial activity. In environmental protection, pH is also used to identify sources of air and water pollution and evaluate the effectiveness of environmental protection measures. Therefore, accurate pH measurement is crucial.

[0003] Traditional pH detection methods are mostly based on test strips or chemical and electrochemical methods, which have the disadvantages of low detection accuracy, long response time, and complicated operation. In recent years, some new detection methods have emerged, such as optical chemical pH sensors based on perylene diimide (PDI), pH color-changing nanoprobes, and hydrogel piezoresistive pH sensors. These emerging sensing methods often have disadvantages such as low reliability of continuous detection, biotoxicity, and poor sensor reusability. Summary of the Invention

[0004] This invention addresses existing pH detection technologies by proposing a fiber optic sensor and method based on green fluorescent carbon dots for real-time online pH detection. The sensor comprises a wedge-shaped fiber optic probe coated with fluorescent carbon dots, a centrally emitting 415nm laser light source, a Y-type fiber optic coupler, and a miniaturized fiber optic spectrometer, enabling accurate, rapid, and highly sensitive online pH detection.

[0005] One of the technical solutions of the present invention is a pH fiber sensor based on a wedge-shaped microstructure with fluorescent carbon dots, characterized in that it includes a wedge-shaped microstructure fiber tip made by microfabrication technology, pH-sensitive green fluorescent carbon dots, a hydrogel film formed by polyethylene glycol diacrylate (PEGDA) and 2-hydroxy-2-methylphenylacetone; wherein the fiber tip of the wedge-shaped microstructure is made using a multimode fiber with a core / cladding diameter of 105μm / 125μm.

[0006] The method and steps for fabricating the fiber tip of the wedge-shaped microstructure are as follows:

[0007] 1) Use fiber optic strippers to remove the coating from the fiber tip, and wipe the exposed fiber surface with anhydrous ethanol. Use a fiber optic cleaver to cut the fiber tip flat, obtaining a smooth fiber end face, and transfer the fiber to the processing platform of the femtosecond laser processing system;

[0008] 2) Turn on the femtosecond laser and its associated processing platform. Position the sample platform within the field of view of the operating interface, adjust the objective lens height, and focus the LED illumination light onto the sample surface to obtain a clear image. Input the designed processing pattern into the micromachining system: isosceles triangles with lengths of 36μm, 36μm, and 51μm, and a processing depth of 80μm.

[0009] 3) Position the laser and begin etching; after completing the processing steps described in 2), move the starting point of the processing down 200μm along the Y-axis and etch the second wedge-shaped microstructure. Process isosceles triangles with lengths of 36μm, 36μm, and 51μm and a processing depth of 80μm. Repeat this process multiple times until 3-8 wedge-shaped structures are etched.

[0010] The pH-sensitive green fluorescent carbon dots used are prepared using the following methods and steps:

[0011] 1) Weigh L-glutamic acid and ethylenediamine in a molar ratio of 60:485 using an electronic balance, and dissolve them in a beaker containing 30 ml of ultrapure water.

[0012] 2) Place the mixed solution into a 50ml polytetrafluoroethylene-lined reactor and heat it continuously in a constant temperature drying oven for 6 hours at a temperature of 180℃.

[0013] 3) After heating is complete, allow the reactor to cool naturally to room temperature. Open the reactor to obtain an orange transparent solution. Purify the carbon dots in the solution to remove large-particle polymers and unreacted small molecules such as L-glutamic acid and ethylenediamine.

[0014] 4) Transfer the purified liquid to a clean beaker and dry it in an oven at 70°C to obtain a brownish-black pH-sensitive carbon dot material powder. Dissolve the powder again in water at a ratio of 1:444446, and under ultraviolet light irradiation, green fluorescent carbon dots can be obtained.

[0015] The optical fiber tip is coated with a hydrogel film containing pH-sensitive fluorescent carbon dots, and the fabrication method and steps are as follows:

[0016] 1) Solid PEGDA and 2-hydroxy-2-methylphenylacetone were mixed at a mass ratio of 20:1 and dissolved in ultrapure water to obtain concentrations of 40% (w / v) and 2.1% (w / v), respectively. A certain amount of pH-sensitive green fluorescent carbon dot powder was then added to bring the carbon dot concentration to 3 × 10⁻⁶. -3 % (w / v).

[0017] 2) Insert the tip of an optical fiber with a wedge-shaped microstructure into the solution described in 1). The other end of the optical fiber is connected to a 360nm ultraviolet laser source. The ultraviolet light is propagated by total internal reflection in the optical fiber and reaches the tip of the etched microstructure, where it comes into contact with the external solution.

[0018] 3) After irradiation with a 360nm ultraviolet laser for 8 seconds, pH-sensitive fluorescent carbon dots are solidified on the surface of the microstructured optical fiber, forming a hydrogel film at the tip of the wedge-shaped microstructured optical fiber. The wedge-shaped microstructured optical fiber tip and the hydrogel film covering it form a sensor probe.

[0019] The second technical solution of the present invention is a wedge-shaped microstructure pH fiber optic sensor based on fluorescent carbon dots, characterized in that it includes a wedge-shaped microstructure pH fiber optic sensor probe based on fluorescent carbon dots, an excitation source, a Y-type fiber optic coupler, and a spectrometer; wherein the excitation source is a laser source with a center emission wavelength of 415 nm; the spectrometer is a miniature fiber optic spectrometer; the splitting ratio of the Y-type fiber optic coupler is 50:50; the laser source and the spectrometer are respectively connected to the two splitting ends of the Y-type fiber optic coupler, and the wedge-shaped microstructure pH fiber optic sensor probe is connected to the coupling end of the Y-type fiber optic coupler.

[0020] The third technical solution of the present invention is a pH fiber optic sensing method based on fluorescent carbon dot wedge microstructures, characterized in that it uses the above-mentioned pH fiber optic sensor based on fluorescent carbon dot wedge microstructures, and is carried out according to the following steps:

[0021] 1) Prepare buffer solutions with different pH values, ranging from 3.00 to 12.04, with a pH interval of approximately 1.

[0022] 2) Detection was initiated using a wedge-shaped microstructure pH fiber sensor based on fluorescent carbon dots. A laser source with a central emission wavelength of 415 nm was turned on, and the light intensity was allowed to stabilize.

[0023] 3) Insert the sensor probe into buffer solutions with different pH values; measure the fluorescence intensity of each pH buffer solution at a wavelength of 518 nm and record it as I1, and use the fluorescence intensity at 850 nm as the blank background light and record it as I0. Plot the pH value of the buffer solution on the x-axis and (I1-I0) on the y-axis to form a fitting curve. The standard curve equation is y=ax+b, where y is (I1-I0) and x is the pH value.

[0024] 4) Insert the sensor probe into the actual water sample solution and measure the fluorescence intensity of the solution at a wavelength of 518 nm. Substitute the fluorescence intensity value into the standard curve equation to calculate the pH value of the actual water sample.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] 1. The pH fiber optic sensor based on a wedge-shaped microstructure with fluorescent green carbon dots proposed in this invention has a small sensing structure and can realize pH detection of water samples in narrow environments.

[0027] 2. The wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots proposed in this invention has a short response time and can obtain detection results within 4-8 seconds, enabling rapid online detection;

[0028] 3. The pH fiber sensing method based on the wedge-shaped microstructure of fluorescent carbon dots proposed in this invention does not require frequent calibration and is easy to operate. Attached Figure Description

[0029] Figure 1 Schematic diagram of a wedge-shaped microstructure pH fiber optic sensing probe;

[0030] Figure 2 A schematic diagram of a wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots;

[0031] Figure 3 Image of a wedge-shaped microstructure pH fiber optic sensing probe;

[0032] The components include: 1. pH fiber optic sensing probe based on a wedge-shaped microstructure of fluorescent carbon dots; 2. Fiber optic tip with wedge-shaped microstructure; 3. Hydrogel film containing pH-sensitive fluorescent carbon dots; 4. Y-type fiber optic coupler; 5. Coupler end of Y-type fiber optic coupler; 6. Splitting end 1 of Y-type fiber optic coupler; 7. Splitting end 2 of Y-type fiber optic coupler; 8. Laser source with a center emission wavelength of 415nm; and 9. Miniature fiber optic spectrometer. Detailed Implementation

[0033] The Y-type fiber coupler, model SUH105 / 125, was purchased from Shenzhen Xinjin Optical Communication Co., Ltd.; the central emission wavelength laser source, model 415nm, was purchased from Shanghai Fibo Optoelectronics Technology Co., Ltd.; and the fiber optic spectrometer, model QEPRO, was purchased from Weihai Optical Instruments (Shanghai) Co., Ltd.

[0034] Example 1

[0035] A pH fiber optic sensing probe 1 based on a wedge-shaped microstructure with fluorescent carbon dots, characterized in that it includes an optical fiber 2 with a wedge-shaped microstructure and a hydrogel film 3 containing pH-sensitive green fluorescent carbon dots.

[0036] The fiber tip 2 with wedge-shaped microstructures is fabricated by processing 3 to 8 wedge-shaped microstructures on the fiber tip after the coating layer is removed, as described in technical solution one for fabricating fiber tips; the pH-sensitive green fluorescent carbon dots are fabricated as described in technical solution one; and the hydrogel containing pH-sensitive fluorescent carbon dots is fabricated as described in technical solution one.

[0037] A method for fabricating a pH fiber optic sensing probe based on a wedge-shaped microstructure with fluorescent carbon dots is as follows: Figure 1 , Figure 2 and Figure 3 As shown, firstly, a laser source with a central emission wavelength of 360nm is connected to one beam splitter 6 of the fiber coupler 4. The 360nm laser source is then turned on. The fiber tip 2, with its wedge-shaped microstructure, is inserted below the surface of a hydrogel solution containing pH-sensitive fluorescent carbon dots. After waiting 6–12 seconds, it is removed, resulting in the following... Figure 1 The pH fiber optic sensing probe 1, which is based on a wedge-shaped microstructure of fluorescent carbon dots, is shown in the figure. 3 is a pH-sensitive green fluorescent carbon dot hydrogel film.

[0038] A pH fiber optic sensor based on a wedge-shaped microstructure with fluorescent carbon dots, characterized in that: Figure 2 As shown, the device includes a pH fiber optic sensor 1 based on a wedge-shaped microstructure with fluorescent carbon dots, a laser source 8 with a central emission wavelength of 415 nm, a Y-type fiber optic coupler 4, and a spectrometer 9; the splitting ratio of the Y-type fiber optic coupler is 50:50; the 415 nm laser source 8 is connected to one splitting end 6 of the Y-type fiber optic coupler 4, the spectrometer is connected to the other splitting end 7 of the Y-type fiber optic coupler, and the pH fiber optic sensor 1 based on the wedge-shaped microstructure with fluorescent carbon dots is connected to the coupling end 5 of the Y-type fiber optic coupler.

[0039] When the central 415nm laser light source is turned on, the fiber optic sensing probe 1 is lit, and the emitted fluorescence is transmitted along the Y-type fiber optic coupler coupling end 5, fiber optic coupler 4, and beam splitter 7 to be received by the spectrometer. During detection, the fiber optic probe 1 connected to the Y-type fiber optic coupler coupling end 5 is inserted below the surface of the water sample to be tested. After holding it for 4 to 8 seconds, the fluorescence intensity change of the fiber optic sensing probe is obtained by the spectrometer.

[0040] Example 2

[0041] The pH fiber optic sensing method based on the wedge-shaped microstructure of fluorescent carbon dots described in Example 1 is performed according to the following steps:

[0042] 1) Prepare buffer solutions with different pH values: 3.08, 4.00, 4.98, 5.97, 7.04, 8.03, 9.08, 11.07, and 12.04.

[0043] 2) Turn on the laser source with a central emission wavelength of 415nm and the spectrometer until the light intensity stabilizes;

[0044] 3) Insert the sensor probe into buffer solutions with different pH values; measure the fluorescence intensity of each pH buffer solution at a wavelength of 518 nm and record it as I1, and use the fluorescence intensity at 850 nm as the blank background light and record it as I0. Plot the pH value of the buffer solution on the x-axis and (I1-I0) on the y-axis to form a fitting curve. The standard curve equation is y=ax+b, where y is (I1-I0) and x is the pH value.

[0045] 4) Insert the sensor probe into the actual water sample solution and measure the fluorescence intensity of the solution at a wavelength of 518 nm. Substitute the fluorescence intensity value into the standard curve equation to calculate the pH value of the actual water sample.

[0046] 5) After the measurement is completed, the probe can be removed to measure other samples.

[0047] Example 3

[0048] The pH fiber optic sensor based on a fluorescent carbon dot-shaped microstructure fabricated in Example 1 exhibits certain anti-interference capabilities. Its verification method is carried out according to the following steps.

[0049] 1) Prepare a PBS buffer with a pH of 7.04, and then prepare a 10 mmol / L Li solution in the PBS buffer with a pH of 7.04. + Zn 2+ Mg 2+ Ca 2+ N + K + Cu 2+ Cr 3+Cl - NO3 - SO4 2- Ion standard solutions;

[0050] 2) Turn on the central emission wavelength 415nm laser source and spectrometer until the light intensity stabilizes;

[0051] 3) Using a buffer solution with a pH of 7.04 as a reference solution, a wedge-shaped microstructure pH fiber optic sensor based on green fluorescent carbon dots was sequentially inserted into standard solutions of different ions. The fluorescence intensity I of each ion standard solution was recorded and compared with the results of the pH 7.04 reference solution. The results showed that the fluorescence changes caused by the other ion solutions were all less than 5%.

[0052] Therefore, it is believed that the presence of common metal ions does not affect the pH detection of the wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots.

[0053] Example 4

[0054] The pH fiber optic sensor based on a fluorescent carbon dot-shaped microstructure fabricated in Example 1 can be used for pH detection of actual samples. The detection method is performed according to the following steps:

[0055] 1) Purchased some beverage samples from the market, namely Sample 1: Beer A, Sample 2: Soda A, and Sample 3: Soda B, and divided them into two portions;

[0056] 2) Using the detection platform built in Example 2, samples 1, 2 and 3 were detected respectively. The light intensity change at the peak at 518nm was measured and recorded using a spectrometer. The obtained values ​​were substituted into the fitting curve obtained in Example 2 to calculate the pH value of the samples.

[0057] 3) The pH value of a second sample of each sample was measured using a Leici pH meter, and the results were compared with those of each test.

Claims

1. A wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots, characterized in that... The fiber tip with a wedge-shaped microstructure etched by a femtosecond laser micromachining system, pH-sensitive green fluorescent carbon dots, and a hydrogel film composed of polyethylene glycol diacrylate (PEGDA) and 2-hydroxy-2-methylphenylacetone (photoinitiator) are included. The wedge-shaped microstructure is etched on a multimode fiber with a core / cladding diameter of 105 μm / 125 μm (inner diameter / outer diameter).

2. A wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots as described in claim 1, characterized by its wedge-shaped microstructure, is fabricated as follows: 1) Use fiber optic strippers to remove the coating from the fiber tip, and wipe the exposed fiber surface with anhydrous ethanol. Use a fiber optic cleaver to cut the fiber tip flat, obtaining a smooth fiber end face, and transfer the fiber to the processing platform of the femtosecond laser processing system; 2) Turn on the femtosecond laser and its associated processing platform. Position the sample platform within the field of view of the operating interface, adjust the objective lens height, and focus the LED illumination light onto the sample surface to obtain a clear image. Input the designed processing pattern into the micromachining system: isosceles triangles with lengths of 36μm, 36μm, and 51μm, and a processing depth of 80μm. 3) Position the laser and begin etching; after completing the processing steps described in 2), move the starting point of the processing down 200μm along the Y-axis and etch the second wedge-shaped microstructure. Process isosceles triangles with lengths of 36μm, 36μm, and 51μm and a processing depth of 80μm. Repeat this process multiple times until 3-8 wedge-shaped structures are etched.

3. A wedge-shaped microstructure pH fiber optic sensor based on green fluorescent carbon dots as described in claim 1, characterized by pH-sensitive green fluorescent carbon dots, wherein the carbon dots are fabricated as follows: 1) Weigh L-glutamic acid and ethylenediamine in a molar ratio of 60:485 using an electronic balance, and dissolve them in a beaker containing 30 ml of ultrapure water. 2) Place the mixed solution into a 50ml polytetrafluoroethylene-lined reactor and heat it continuously in a constant temperature drying oven for 6 hours at a temperature of 180℃. 3) After heating is complete, allow the reactor to cool naturally to room temperature. Open the reactor to obtain an orange transparent solution. Purify the carbon dots in the solution to remove large-particle polymers and unreacted small molecules such as L-glutamic acid and ethylenediamine. 4) Transfer the purified liquid to a clean beaker and dry it in an oven at 70°C to obtain a brownish-black pH-sensitive carbon dot material powder. Dissolve the powder again in water at a ratio of 1:444446, and under ultraviolet light irradiation, green fluorescent carbon dots can be obtained.

4. The wedge-shaped microstructure pH fiber sensor based on green fluorescent carbon dots as mentioned in claim 1, characterized in that... A hydrogel film with pH-sensitive fluorescent carbon dots coated on the tip of an optical fiber is fabricated by the following steps: 1) Solid PEGDA and 2-hydroxy-2-methylphenylacetone were mixed at a mass ratio of 20:1 and dissolved in ultrapure water to obtain concentrations of 40% (w / v) and 2.1% (w / v), respectively. A certain amount of pH-sensitive green fluorescent carbon dot powder was then added to bring the carbon dot concentration to 3 × 10⁻⁶. -3 % (w / v). 2) Insert the tip of an optical fiber with a wedge-shaped microstructure into the solution described in 1). The other end of the optical fiber is connected to a 360nm ultraviolet laser source. The ultraviolet light is propagated by total internal reflection in the optical fiber and reaches the tip of the etched microstructure, where it comes into contact with the external solution. 3) After irradiation with a 360nm ultraviolet laser for 8 seconds, pH-sensitive fluorescent carbon dots are solidified on the surface of the microstructured optical fiber, forming a hydrogel film at the tip of the wedge-shaped microstructured optical fiber. The wedge-shaped microstructured optical fiber tip and the hydrogel film covering it form a sensor probe.

5. A wedge-shaped microstructure pH fiber optic device based on fluorescent carbon dots, characterized in that... The device includes a wedge-shaped microstructure pH fiber optic sensor probe based on fluorescent carbon dots, an excitation source, a Y-type fiber optic coupler, and a spectrometer. The excitation source is a laser source with a center emission wavelength of 415 nm. The spectrometer is a miniature fiber optic spectrometer. The splitting ratio of the Y-type fiber optic coupler is 50:

50. The laser source and the spectrometer are respectively connected to the two splitting ends of the Y-type fiber optic coupler, and the wedge-shaped microstructure pH fiber optic sensor probe is connected to the coupling end of the Y-type fiber optic coupler.

6. A pH fiber optic sensing method based on a wedge-shaped microstructure with fluorescent carbon dots, characterized in that: The pH fiber optic sensor with fluorescent carbon dot wedge-shaped microstructure as described in claim 5 is operated according to the following steps: 1) Prepare buffer solutions with different pH values, ranging from 3.00 to 12.04, with a pH interval of approximately 1. 2) Detection was initiated using a wedge-shaped microstructure pH fiber sensor based on fluorescent carbon dots. A laser source with a central emission wavelength of 415 nm was turned on, and the light intensity was allowed to stabilize. 3) Insert the sensor probe into buffer solutions with different pH values; measure the fluorescence intensity of each pH buffer solution at a wavelength of 518 nm and record it as I1, and use the fluorescence intensity at 850 nm as the blank background light and record it as I0. Plot the pH value of the buffer solution on the x-axis and (I1-I0) on the y-axis to form a fitting curve. The standard curve equation is y=ax+b, where y is (I1-I0) and x is the pH value. 4) Insert the sensor probe into the actual water sample solution and measure the fluorescence intensity of the solution at a wavelength of 518 nm. Substitute the fluorescence intensity value into the standard curve equation to calculate the pH value of the actual water sample.

Images