A pH optical fiber sensing system and method based on fluorescent carbon dots

Abstract

In view of the problems existing in the existing pH detection technology, the present invention provides a pH optical fiber sensing system and method based on fluorescent carbon dots. The sensing system is composed of a pH optical fiber sensor based on fluorescent carbon dots, an ultraviolet light source, a Y-type optical fiber coupler and a spectrometer to detect the pH of the water sample to be detected. The present invention adopts a pH optical fiber sensor based on fluorescent carbon dots. The sensing structure has a tiny volume, the diameter range of the sensing probe is 125 μm to 450 μm, and the response time is short, enabling real-time on-line detection of the pH of water samples in narrow environments; moreover, the carbon dot coating method proposed by the present invention requires no molds and can complete the assembly of the optical fiber sensing probe in just a few seconds.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensing, and particularly relates to a pH fiber optic sensing system and method based on fluorescent carbon dots. Background Art

[0002] As is well known, the pH value is an important parameter reflecting the acidity and alkalinity of a solution, which can represent the concentration of hydrogen ions in the solution. Many important processes in production and daily life, such as the growth of crops, chemical reactions, and the physiological activities of the human body, are closely related to the change of the pH value.

[0003] Currently reported pH detection methods still have some disadvantages. The traditional measurement of the pH value is achieved by the indicator method (phenolphthalein, methyl orange, litmus, etc.) and the electrochemical method. However, the former usually requires a complex detection process and a long reaction time. Although pH test papers are widely used for quickly estimating the pH value, the accuracy and reliability of the results are very poor, and only qualitative detection can be performed. Although the electrochemical pH meter has the widest range of use and is easy to operate, it requires frequent calibration, and the internal resistance and resistance temperature coefficient of the electrode are relatively high. At the same time, it is difficult to achieve remote and online measurement. The nuclear magnetic resonance method (NMR) requires relatively large-sized instruments, complex operations, and it is also difficult to perform real-time online detection. Summary of the Invention

[0004] In view of the above problems existing in the existing pH detection technology, the present invention provides a pH fiber optic sensing system and method based on fluorescent carbon dots. The sensing system is composed of a pH fiber optic sensing probe of fluorescent carbon dots, an ultraviolet light source, a Y-type fiber optic coupler, and a spectrometer to perform the pH detection of the water sample to be detected. The system has a short detection time, is easy to operate, and can realize the real-time online detection of the pH value in a narrow water sample environment.

[0005] One technical solution of the present invention is a pH fiber optic sensing probe based on fluorescent carbon dots, which is characterized by including a tapered fiber, pH-sensitive fluorescent carbon dots, a hydrogel formed by PEGDA and 2-hydroxy-2-methylpropiophenone; wherein the tapered fiber is made of a multimode fiber with a core / cladding diameter of 105μm / 125μm; the number average molecular weight of PEGDA is 700.

[0006] Among them, the preparation method of the pH-sensitive fluorescent carbon dots includes the following steps:

[0007] 1) Add 0.5 g of citric acid, 500 μL of diethylenetriamine, 0.2 g of reduced glutathione, and 0.1 g of urea to a 50 mL conical flask, and dissolve and disperse them in 40 mL of ultrapure water by ultrasonic treatment for 10 minutes;

[0008] 2) Pour the well - mixed solution into a 50 mL polytetrafluoroethylene - lined hydrothermal reactor; tighten the reactor and place it in a forced - air drying oven, and continuously heat it at 180 °C for 8 hours;

[0009] 3) After the heating is completed, wait for the reactor to cool to room temperature, and then open it to obtain a yellow transparent liquid; after the liquid is filtered through a 0.22 μm aqueous filter membrane, it is dialyzed and purified in ultrapure water using a dialysis membrane with a molecular cut - off of 500 for 48 hours to obtain a pH - sensitive fluorescent carbon dot solution;

[0010] 4) Dry the purified pH - sensitive fluorescent carbon dot solution in a vacuum dryer at 65 °C to obtain dry pH - sensitive fluorescent carbon dots.

[0011] The manufacturing method of the pH optical fiber sensing probe based on fluorescent carbon dots includes the following steps:

[0012] 1) Dissolve a certain amount of pH - sensitive fluorescent carbon dots in a solution containing 38% (w / v) PEGDA and 1.8% (w / v) 2 - hydroxy - 2 - methylpropiophenone, so that the concentration of the pH - sensitive fluorescent carbon dots is 1.44×10⁻²%, to obtain a hydrogel solution containing pH - sensitive fluorescent carbon dots;

[0013] 2) Insert the tip of the tapered optical fiber into the prepared pH - sensitive fluorescent carbon dot hydrogel solution, and connect the other end of the optical fiber to an ultraviolet light source; the ultraviolet light is totally reflected and propagated in the fiber core, reaches the tapered tip and is transmitted to the external solution;

[0014] 3) After irradiating with ultraviolet light for several seconds, the hydrogel solution containing pH - sensitive fluorescent carbon dots can be coated on the surface of the fiber tip to form a pH optical fiber sensing probe based on fluorescent carbon dots.

[0015] The second technical solution of the present invention is a pH optical fiber sensing system based on fluorescent carbon dots, which is characterized by including a pH optical fiber sensing probe based on fluorescent carbon dots, an ultraviolet light source, a Y - type fiber coupler, and a spectrometer; wherein the ultraviolet light source uses a 375 nm laser light source; the splitting ratio of the Y - type fiber coupler is 50:50;

[0016] The ultraviolet light source is connected to one splitting end of the Y - type fiber coupler, the spectrometer is connected to the other splitting end of the Y - type fiber coupler, and the pH optical fiber sensing probe based on fluorescent carbon dots is connected to the coupling end of the Y - type fiber coupler.

[0017] The third technical solution of the present invention is

[0018] A pH optical fiber sensing method based on fluorescent carbon dots, which is characterized by using the pH optical fiber sensing system according to claim 5 and performing according to the following steps:

[0019] 1) Prepare acidic standard solutions with different pH values using HNO3 (1 mol / L) and NaOH (1 mol / L) and their gradually diluted solutions. The pH of the standard solutions ranges from 2.00 to 3.92.

[0020] 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable.

[0021] 3) Using water as the reference solution, insert the pH optical fiber sensing probe based on fluorescent carbon dots into acidic standard solutions with different pH values. After 10 s, measure the fluorescence intensity I of each standard solution at a wavelength of 493 nm. When the pH is 2.00, the fluorescence intensity measured at a wavelength of 493 nm is I01. Plot a standard curve with the pH value as the abscissa and (I - I01) / I01 as the ordinate, and form a standard curve equation y = ax + b, where y is (I - I01) / I01 and x is the pH value of the pH standard solution.

[0022] 4) Insert the pH optical fiber sensing probe based on fluorescent carbon dots into the water sample to be detected. After 10 s, measure the fluorescence intensity of the solution to be detected at a wavelength of 493 nm. Substitute the fluorescence intensity value into the standard curve equation to obtain the pH of the water sample to be detected. The fourth technical solution of the present invention is as follows.

[0023] A pH optical fiber sensing method based on fluorescent carbon dots, characterized in that the pH optical fiber sensing system based on fluorescent carbon dots described in claim 5 is adopted, and the following steps are carried out:

[0024] 1) Prepare alkaline standard solutions with different pH values using HNO3 (1 mol / L) and NaOH (1 mol / L) and their gradually diluted solutions. The pH of the standard solutions ranges from 8.00 to 13.02.

[0025] 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable.

[0026] 3) Using water as the reference solution, insert the pH optical fiber sensing probe based on fluorescent carbon dots into alkaline standard solutions with different pH values. After 10 s, measure the fluorescence intensity I of each standard solution at a wavelength of 489 nm. When the pH is 8.00, the fluorescence intensity measured at a wavelength of 489 nm is I02. Plot a standard curve with the pH value as the abscissa and (I - I02) / I02 as the ordinate, and form a standard curve equation y = ax + b, where y is (I - I02) / I02 and x is the pH value of the pH standard solution.

[0027] 4) Insert the pH optical fiber sensing probe based on fluorescent carbon dots into the water sample to be detected. After 10 s, measure the fluorescence intensity of the solution to be detected at a wavelength of 489 nm. Substitute the fluorescence intensity value into the standard curve equation to obtain the pH of the water sample to be detected.

[0028] Compared with the prior art, the advantages of the present invention are as follows:

[0029] 1. The present invention adopts a pH optical fiber sensing probe based on fluorescent carbon dots. The sensing structure is tiny in volume, and the diameter range of the sensing probe is 125μm - 450μm, enabling the pH detection of water samples in narrow environments;

[0030] 2. The carbon dot coating method proposed by the present invention requires no molds and can complete the assembly of the optical fiber sensing probe in just a few seconds;

[0031] 3. The pH optical fiber sensing system based on fluorescent carbon dots proposed by the present invention has a short response time and can detect the pH change of environmental water samples in real-time online; BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the pH optical fiber sensing probe based on fluorescent carbon dots of the present invention;

[0033] Figure 2 Schematic diagram of the pH optical fiber sensing system based on fluorescent carbon dots of the present invention;

[0034] Figure 3 Process diagram of fabricating the pH optical fiber sensing probe based on fluorescent carbon dots of the present invention.

[0035] Among them, 1. pH optical fiber sensing probe based on fluorescent carbon dots, 2. Tapered optical fiber, 3. PEGDA hydrogel film containing pH-sensitive fluorescent carbon dots, 4. Y-shaped optical fiber coupler, 5. Coupling end of the Y-shaped optical fiber coupler, 6. Splitting end 1 of the Y-shaped optical fiber coupler, 7. Splitting end 2 of the Y-shaped optical fiber coupler, 8. Ultraviolet light source, 9. Spectrometer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The model of the Y-shaped optical fiber coupler is SUH105 / 125, purchased from Shenzhen Xinjin Optical Communication Co., Ltd.

[0037] The ultraviolet light source is a 375nm laser light source, purchased from Shanghai Fibonacci Optoelectronic Technology Co., Ltd.

[0038] The model of the spectrometer is QEPRO, purchased from OCEAN OPTICS.

[0039] Example 1

[0040] A pH optical fiber sensing probe based on fluorescent carbon dots, as Figure 1 shown, includes a tapered optical fiber 2 and a PEGDA hydrogel film 3 containing pH-sensitive fluorescent carbon dots; among them, the tapered optical fiber is made of a multimode optical fiber with a core / cladding diameter of 105μm / 125μm; the number average molecular weight of PEGDA is 700.

[0041] Among them, for the pH-sensitive fluorescent carbon dots, the manufacturing method thereof comprises the following steps:

[0042] 1) Add 0.5 g of citric acid, 500 μL of diethylenetriamine, 0.2 g of reduced glutathione, and 0.1 g of urea into a 50 mL conical flask, and dissolve and disperse them in 40 mL of ultrapure water by ultrasonic treatment for 10 minutes;

[0043] 2) Pour the uniformly mixed solution into a 50 mL polytetrafluoroethylene-lined hydrothermal reaction kettle; tighten the reaction kettle and place it in a forced air drying oven, and continuously heat it at 180 °C for 8 hours;

[0044] 3) After the heating is completed and the reaction kettle is cooled to room temperature, open it to obtain a yellow transparent liquid; after the liquid is filtered through a 0.22 μm aqueous filter membrane, dialyze and purify it in ultrapure water with a dialysis membrane having a molecular cut-off of 500 for 48 hours to obtain a pH-sensitive fluorescent carbon dot solution;

[0045] 4) Dry the purified pH-sensitive fluorescent carbon dot solution in a vacuum drying oven at 65 °C to obtain dry pH-sensitive fluorescent carbon dots.

[0046] For the pH optical fiber sensing probe based on fluorescent carbon dots, the manufacturing method thereof comprises the following steps:

[0047] 1) Dissolve a certain amount of pH-sensitive fluorescent carbon dots in a solution containing 38% (w / v) PEGDA and 1.8% (w / v) 2-hydroxy-2-methylpropiophenone, so that the concentration of the pH-sensitive fluorescent carbon dots is 1.44×10-2%, to obtain a hydrogel solution containing pH-sensitive fluorescent carbon dots;

[0048] 2) Insert the end of the tapered optical fiber into the prepared pH-sensitive fluorescent carbon dot hydrogel solution, and connect the other end of the optical fiber to a 365 nm LED ultraviolet light source with a working current of 0.15 A; the ultraviolet light is totally reflected and propagated in the fiber core, reaches the tapered end and is transmitted to the external solution;

[0049] 3) After irradiating with ultraviolet light for 10 s, the hydrogel solution containing pH-sensitive fluorescent carbon dots can be coated on the surface of the fiber tip to form a pH optical fiber sensing probe based on fluorescent carbon dots.

[0050] After inserting the pH optical fiber sensing probe based on fluorescent carbon dots into the water sample to be detected, the pH-sensitive fluorescent carbon dots will change the measured fluorescence intensity according to the change of the pH of the water sample; therefore, the pH optical fiber sensing probe based on fluorescent carbon dots can be used to detect the pH of the water sample to be detected.

[0051] Example 2

[0052] A pH optical fiber sensing system based on fluorescent carbon dots, such asFigure 2 As shown in the figure, it includes a pH optical fiber sensing probe 1 based on fluorescent carbon dots, an ultraviolet light source 8, a Y-shaped optical fiber coupler 4, and a spectrometer 9. Among them, the ultraviolet light source uses a 375nm laser light source; the spectrometer uses an Ocean Optics spectrometer; the splitting ratio of the Y-shaped optical fiber coupler is 50:50;

[0053] The ultraviolet light source 8 is connected to one splitting end 6 of the Y-shaped optical fiber coupler 4, the spectrometer is connected to the other splitting end 7 of the Y-shaped optical fiber coupler, and the pH optical fiber sensing probe 1 based on fluorescent carbon dots is connected to the coupling end 5 of the Y-shaped optical fiber coupler.

[0054] Example 3

[0055] Using the pH optical fiber sensing method based on fluorescent carbon dots in Example 2, it is carried out according to the following steps:

[0056] 1) Use HNO3 (1mol / L) and NaOH (1mol / L) and their gradually diluted solutions to prepare acidic standard solutions with different pH values. The pH of the standard solutions is between 2.00 and 3.92, which are 2.00, 2.36, 2.66, 3.20, 3.37, and 3.92 respectively;

[0057] 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable;

[0058] 3) Using water as a reference solution, insert the pH optical fiber sensing probe based on fluorescent carbon dots into standard solutions with different pH values. After 10s, measure the fluorescence intensity I of each standard solution. When the pH is 2.00, the measured fluorescence intensity is I01. Taking the pH value as the abscissa and (I - I01) / I01 as the ordinate, plot the standard curve, and form the standard curve equation y = ax + b, where y is (I - I01) / I01 and x is the pH value of the pH standard solution.

[0059] 4) Use HNO3 (1mol / L) and NaOH (1mol / L) and their gradually diluted solutions to prepare the water sample solutions to be detected with pH values of 2.96 and 3.22 respectively. Repeatedly insert the pH optical fiber sensing based on fluorescent carbon dots into the solutions with pH = 2.96 and pH = 3.22, and the fluorescence intensity will change significantly accordingly; substituting the fluorescence intensity into the standard curve equation, the pH values of the water sample solutions to be detected can be obtained as 2.96 and 3.22 respectively; use a pH meter to detect the water sample to be detected, and the obtained results are consistent with the above method.

[0060] In summary, it shows that this system and method can realize the pH of the water sample to be detected in real-time online.

[0061] Example 4

[0062] The pH optical fiber sensing method based on fluorescent carbon dots of Example 2 is carried out according to the following steps:

[0063] 1) Alkaline standard solutions with different pH values are prepared using HNO3 (1 mol / L) and NaOH (1 mol / L) and their gradually diluted solutions respectively. The pH of the standard solutions is between 8.00 and 13.02, which are 8.00, 9.12, 9.87, 11.14, 12.15, and 13.02 respectively.

[0064] 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable.

[0065] 3) Using water as the reference solution, insert the pH optical fiber sensor probe based on fluorescent carbon dots into standard solutions with different pH values. After 10 s, measure the fluorescence intensity I of each standard solution. The fluorescence intensity measured at pH = 8.00 is I02. Taking the pH value as the abscissa and (I - I02) / I02 as the ordinate, plot the standard curve, and the standard curve equation is y = ax + b, where y is (I - I02) / I02 and x is the pH value of the pH standard solution.

[0066] 4) Prepare the water sample solutions to be detected with pH values of 8.00 and 13.00 using HNO3 (1 mol / L) and NaOH (1 mol / L) and their gradually diluted solutions respectively. Repeatedly insert the pH optical fiber sensor based on fluorescent carbon dots into the solutions with pH = 8.00 and pH = 13.00, and the fluorescence intensity will change significantly accordingly. Substitute the fluorescence intensity into the standard curve equation, and the pH values of the water sample solutions to be detected can be obtained as 8.00 and 13.00 respectively. Use a pH meter to detect the water sample to be detected, and the results are consistent with the above method.

Claims

1. A pH optical fiber sensing probe based on fluorescent carbon dots, characterized in that it includes a tapered optical fiber, pH-sensitive fluorescent carbon dots, and a hydrogel formed by PEGDA and 2-hydroxy-2-methylpropiophenone; wherein the tapered optical fiber is made of a multimode optical fiber with a core / cladding diameter of 105μm / 125μm; the number-average molecular weight of PEGDA is 700; the manufacturing method of the pH-sensitive fluorescent carbon dots includes the following steps: 1) Add 0.5 g of citric acid, 500 μL of diethylenetriamine, 0.2 g of reduced glutathione, and 0.1 g of urea to a 50 mL conical flask, and dissolve and disperse them in 40 mL of ultrapure water by ultrasonic treatment for 10 minutes; 2) Pour the well-mixed solution into a 50 mL polytetrafluoroethylene-lined hydrothermal reaction kettle; tighten the reaction kettle and place it in a forced-air drying oven, and continuously heat it at 180 °C for 8 hours; 3) After heating is completed and the reaction kettle is cooled to room temperature, open it to obtain a yellow transparent liquid: after the liquid is filtered through a 0.22 μm aqueous filter membrane, it is dialyzed and purified in ultrapure water with a dialysis membrane with a molecular cut-off of 500 for 48 hours to obtain a pH-sensitive fluorescent carbon dot solution; 4) Dry the purified pH-sensitive fluorescent carbon dot solution in a vacuum drying oven at 65 °C to obtain dry pH-sensitive fluorescent carbon dots.

2. A pH optical fiber sensing probe based on fluorescent carbon dots according to claim 1, characterized in that, its manufacturing method includes the following steps: 1) Dissolve a certain amount of pH-sensitive fluorescent carbon dots in a solution containing 38% (w / v) PEGDA and 1.8% (w / v) 2-hydroxy-2-methylpropiophenone, such that the concentration of the pH-sensitive fluorescent carbon dots is 1.44×10 -2 %, to obtain a hydrogel solution containing pH-sensitive fluorescent carbon dots; 2) Insert the end of the tapered optical fiber into the prepared pH-sensitive fluorescent carbon dot hydrogel solution, and connect the other end of the optical fiber to a 365 nm LED ultraviolet light source; ultraviolet light is totally reflected and propagated in the core, reaches the tapered end and is transmitted to the external solution; 3) After irradiating with ultraviolet light for 10 s, the hydrogel solution containing pH-sensitive fluorescent carbon dots is coated on the surface of the fiber tip to form a pH optical fiber sensing probe based on fluorescent carbon dots.

3. A pH optical fiber sensing system based on fluorescent carbon dots, characterized in that it includes the pH optical fiber sensing probe based on fluorescent carbon dots described in claim 1, an ultraviolet light source, a Y-type fiber coupler, and a spectrometer; wherein the ultraviolet light source uses a 375 nm laser light source; the spectrometer uses an Ocean Optics spectrometer; the splitting ratio of the Y-type fiber coupler is 50:50; the ultraviolet light source is connected to one splitting end of the Y-type fiber coupler, the spectrometer is connected to the other splitting end of the Y-type fiber coupler, and the pH optical fiber sensing probe based on fluorescent carbon dots is connected to the coupling end of the Y-type fiber coupler.

4. A pH optical fiber sensing method based on fluorescent carbon dots, characterized in that, using the pH optical fiber sensing system based on fluorescent carbon dots described in claim 3, the following steps are carried out: 1) Use 1 mol / L HNO 3 and 1 mol / L NaOH and their gradually diluted solutions to prepare acidic standard solutions with different pH values. The pH of the standard solutions ranges from 2.00 to 3.92; 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable; 3) Using water as a reference solution, insert the pH optical fiber sensing probe based on fluorescent carbon dots into acidic standard solutions with different pH values. After 10 s, measure the fluorescence intensity I of each standard solution at a wavelength of 493 nm; When the pH is 2.00, the fluorescence intensity measured at a wavelength of 493 nm is I 01 , with the pH value as the abscissa and (I - I 01 ) / I 01 as the ordinate to plot the standard curve, and the standard curve equation is y = ax + b, where y is (I - I 01 ) / I 01 , and x is the pH value of the pH standard solution; 4) Insert the pH optical fiber sensing probe based on fluorescent carbon dots into the water sample to be detected. After 10 s, measure the fluorescence intensity of the solution to be detected at a wavelength of 493 nm, and substitute the fluorescence intensity value into the standard curve equation to obtain the pH of the water sample to be detected.

5. A pH optical fiber sensing method based on fluorescent carbon dots Characterized in that Adopt the pH optical fiber sensing system based on fluorescent carbon dots described in claim 3 and proceed according to the following steps; 1) Use 1 mol / L HNO 3 and 1 mol / L NaOH and their stepwise diluted solutions to prepare alkaline standard solutions with different pH values. The pH of the standard solutions is between 8.00 and 13.02; 2) Turn on the ultraviolet light source and the spectrometer until the light intensity is stable; 3) Using water as the reference solution, insert the pH optical fiber sensing probe based on fluorescent carbon dots into alkaline standard solutions with different pH values. After 10 s, measure the fluorescence intensity I of each standard solution at a wavelength of 489 nm; When the pH is 8.00, the fluorescence intensity measured at a wavelength of 489 nm is I 02 , with the pH value as the abscissa and (I - I 02 ) / I 02 as the ordinate, a standard curve is plotted, and the standard curve equation is y = ax + b, where y is (I - I 02 ) / I 02 , and x is the pH value of the pH standard solution; 4) Insert the pH optical fiber sensing probe based on fluorescent carbon dots into the water sample to be detected. After 10 s, measure the fluorescence intensity of the solution to be detected at a wavelength of 489 nm, and substitute the fluorescence intensity value into the standard curve equation to obtain the pH of the water sample to be detected.

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