CN116622369A - Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon dots, and preparation method and application thereof - Google Patents
Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon dots, and preparation method and application thereof Download PDFInfo
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- CN116622369A CN116622369A CN202310517808.6A CN202310517808A CN116622369A CN 116622369 A CN116622369 A CN 116622369A CN 202310517808 A CN202310517808 A CN 202310517808A CN 116622369 A CN116622369 A CN 116622369A
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- 238000002360 preparation method Methods 0.000 title claims abstract description 16
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- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/65—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing carbon
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
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- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
- G01N2021/6432—Quenching
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Abstract
The application provides a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots, and a preparation method and application thereof, wherein the preparation method comprises the following steps: placing the glutathione solution in a reaction kettle, and synthesizing the glutathione solution by a one-step hydrothermal method to obtain an N-CQDs solution; mixing the OPD solution, the N-CQDs solution and the buffer solution to obtain a first mixed solution, and constructing an N-CQDs-OPD sensing platform for detecting Ag (I) or Cr (VI) in a sample; and mixing the Cr solution, the OPD solution, the N-CQDs solution and the buffer solution to obtain a second mixed solution, and constructing an N-CQDs-OPD/Cr (VI) sensing platform for detecting formaldehyde in the sample. The optical sensor provides a double-signal detection method based on N-CQDs and OPD, which can efficiently detect Ag (I), cr (VI) and HCHO, and has the advantages that the N-CQDs with good optical and chemical stability are synthesized through a simple and environment-friendly process; the method has a dual mode of proportional fluorescence and colorimetric, so that the detection result is more reliable; the carbon dot-based dual read-out strategy has good Ag (I), cr (vi) and HCHO detection potential in the sample.
Description
Technical Field
The application relates to the technical field of fluorescent sensor preparation, in particular to a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon points, and a manufacturing method and application thereof.
Background
Currently, heavy metal pollution causes a lot of trouble to people's daily life, wherein silver ions and chromium ions are two typical heavy metal ions. Silver is an important noble metal, has great effect in catalysis, surface enhanced Raman scattering, biological application and the like, and simultaneously a large amount of silver ions are released into the environment to cause the increase of environmental pollution, and excessive contact of Ag (I) can cause various diseases such as heart enlargement, silver poisoning, slow growth, skin injury and the like. According to the world health organization report, the allowable Ag (I) concentration in drinking water should be lower than 0.5 mu M; chromium is also considered as a highly toxic heavy metal pollutant, and long-term contact with Cr (VI) can cause injury and even death of bronchitis, liver, kidney and nervous tissues, and along with the development of industry, a large amount of Cr (VI) is discharged into the environment through industrial wastewater and waste residues such as stainless steel manufacturing, dye production, tanning, chromium plating and the like, so that huge potential safety hazards are brought to people, and the world health organization prescribes 50 mug/L.
In addition, formaldehyde is a ubiquitous volatile organic compound, and is also a commonly used preservative for clothing, cosmetics and specimens. However, since formaldehyde can make foods bright in color, stronger in toughness and elasticity, longer in shelf life, and added to foods, once a large amount of foods containing excessive formaldehyde is ingested, chronic liver diseases, cardiovascular diseases, embryo malformations can be caused.
In summary, in order to ensure the health of human body, it is especially necessary to design a simple, sensitive and rapid detection method for detecting the contents of Ag (I), cr (VI) and formaldehyde in food in drinking water.
Currently, commonly used Ag (I) and Cr (VI) ion detection methods include Atomic Absorption Spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS) or inductively coupled plasma emission spectrometry (ICP-OES), electrochemistry (Electrochemical), high Performance Liquid Chromatography (HPLC) and the like; moreover, various strategies for monitoring formaldehyde in food samples have been proposed, including electrochemical, spectrophotometric, surface-enhanced raman spectroscopy, fluorescence, and the like. However, some methods have color development limited by time and temperature, and are difficult to meet the requirement of rapid detection after long time, and are unfavorable for field detection of samples. Based on the above, the application provides a novel, simple and rapid detection method for detecting Ag (I), cr (VI) and formaldehyde solution and a corresponding sensor.
Disclosure of Invention
Based on the expression, the application provides a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots, and a preparation method and application thereof, so as to solve the technical problems that in the prior art, the color rendering property of Ag (I), cr (VI) and formaldehyde is limited by time and temperature during the detection of the Ag (VI) and the Cr (VI), the time is long, the requirement of rapid detection is difficult to meet, and the on-site detection of a sample is not facilitated.
The technical scheme for solving the technical problems is as follows:
in a first aspect, the application provides a preparation method of a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots, which comprises the following steps:
s1, placing a glutathione solution in a reaction kettle, and synthesizing the glutathione solution by a one-step hydrothermal method to obtain an N-CQDs solution;
s2, mixing the OPD solution, the N-CQDs solution and the buffer solution to obtain a first mixed solution, and constructing an N-CQDs-OPD sensing platform, wherein the N-CQDs-OPD sensing platform is used for detecting Ag (I) or Cr (VI) in a sample;
s3, mixing the Cr solution, the OPD solution, the N-CQDs solution and the buffer solution to obtain a second mixed solution, and constructing an N-CQDs-OPD/Cr (VI) sensing platform which is used for detecting formaldehyde in the sample.
On the basis of the technical scheme, the application can be improved as follows.
Further, the step S1 specifically includes:
s101, weighing 0.25g of glutathione, adding the glutathione into a 25mL reaction kettle, adding 5mL of deionized water, and performing ultrasonic dissolution;
s102, reacting for 4 hours in a drying oven at 200 ℃, cooling the reaction kettle to room temperature, and filtering to obtain the N-CQDs solution.
Further, the step S2 specifically includes:
s201, sequentially adding 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the first mixed solution; wherein, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s202, adding the filtered first sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s204, calculating F 560 /F 430 And determining the content of Ag (I) in the first sample according to the obtained working curve.
Further, before step S202, the method further includes:
the first sample was filtered using a 0.22 μm microfiltration membrane.
Further, the step S2 specifically includes:
s201, sequentially adding 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the first mixed solution; wherein, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s202, adding a filtered second sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s204, calculating F 560 /F 430 And determining the Cr (VI) content in the second sample according to the obtained working curve.
Further, before step S202, the method further includes:
using a centrifugal machine to carry out centrifugal treatment on the second sample at the rotating speed of 10000rpm for 10min;
the second sample after centrifugation was filtered using a 0.22 μm microfiltration membrane.
Further, the step S3 specifically includes:
s301, sequentially adding 300 mu LCr (VI) solution, 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the second mixed solution; wherein, the concentration of the Cr (VI) solution is 120 mug/mL, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s302, adding supernatant of a third sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s303, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s304, calculating F 560 /F 430 And determining the formaldehyde content in the third sample according to the obtained working curve.
Further, before step S302, the method further includes:
immersing 2g of the third sample in 4mL of ultrapure water; after soaking for 5 hours, centrifuging to remove residual sediment, and obtaining the supernatant.
In a second aspect, the present application also provides a carbon dot-based Ag (i), cr (vi) and formaldehyde ratio fluorescence sensor prepared by the preparation method described in the first aspect, including an N-CQDs-OPD sensing platform and an N-CQDs-OPD/Cr (vi) sensing platform; the N-CQDs-OPD sensing platform is used for detecting Ag (I) or Cr (VI) in a sample, and the N-CQDs-OPD/Cr (VI) sensing platform is used for detecting formaldehyde in the sample.
In a third aspect, the application also provides the use of the carbon dot based Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor according to the second aspect for detecting Ag (I), cr (VI) and formaldehyde.
Compared with the prior art, the technical scheme of the application has the following beneficial technical effects:
the preparation method of the Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on carbon points provided by the application is characterized in that an N-CQDs solution is firstly prepared by using a glutathione solution, an N-CQDs-OPD sensing platform and an N-CQDs-OPD/Cr (VI) sensing platform are further respectively constructed, and the N-CQDs-OPD sensing platform and the N-CQDs-OPD/Cr (VI) sensing platform are respectively used for detecting Ag (I) or Cr (VI) in a sample and formaldehyde in the sample, so that the detection of the double-signal sensing platform is realized. Cr (VI) has strong oxidizing capability in an acidic system, OPD can be oxidized into DAP, the OPD can generate DAP under the catalysis and oxidation of silver ions, the DAP can quench the fluorescence of N-CQDs based on the fluorescence resonance energy transfer effect, so that the fluorescence intensity of the DAP is increased, the fluorescence intensity of the N-CQDs is reduced, the oxidizing capability of Cr (VI) is inhibited after formaldehyde solution is added, the amount of generated DAP is reduced, the corresponding fluorescence intensity is reduced, and the fluorescence intensity of the N-CQDs is increased, so that the detection of Cr (VI), ag (I) and formaldehyde is realized.
Compared with the prior art, the Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon points provided by the application provides a double-signal (ratio fluorescence and colorimetric) detection method based on N-CQDs and OPDs, and can be used for efficiently detecting Ag (I), cr (VI) and HCHO, and the method has the following advantages:
(1) N-CQDs with good optical and chemical stability are synthesized through a simple and environment-friendly process;
(2) The sensing system has a proportion fluorescence mode and a colorimetric mode, and can display a plurality of output signals, so that the detection result is more reliable;
(3) The carbon dot-based dual read-out strategy has good Ag (I), cr (vi) and HCHO detection potential in practical samples.
Drawings
FIG. 1 is a schematic diagram of the synthesis of carbon dots and a mechanism of Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on the carbon quantum dots provided by the embodiment of the application;
FIG. 2 is a graph showing the effect of glutathione amount on fluorescence intensity of synthesized N-CQDs in example 3 of the present application;
FIG. 3 is a graph showing the characterization result of the fluorescent carbon quantum dots N-CQDs according to example 5 of the present application;
FIG. 4 is a graph showing the second characterization result of the N-CQDs of the fluorescent carbon quantum dots according to example 5 of the present application;
FIG. 5 is a third graph showing the characterization result of the N-CQDs of the fluorescent carbon quantum dots according to example 5 of the present application;
FIG. 6 is a graph showing the effect of pH on Ag (I), cr (VI) and formaldehyde ratio fluorescence sensors based on carbon quantum dots according to example 6 of the present application;
FIG. 7 is a graph showing the effect of OPD amount on Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on carbon dots according to example 7 of the application;
FIG. 8 is a graph showing the effect of the detection time provided in example 8 on Ag (I), cr (VI) and formaldehyde ratio fluorescence sensors based on carbon quantum dots;
FIG. 9 is a schematic diagram showing the results of a selective exploration of an N-CQDs-OPD sensing platform according to example 9 of the application;
FIG. 10 is a second schematic diagram of the result of the selective exploration of the N-CQDs-OPD sensor platform according to example 9 of the application;
FIG. 11 is a schematic diagram showing the results of time study on formaldehyde detection by the N-CQDs-OPD/Cr (VI) sensing platform provided in example 10 of the application;
FIG. 12 is a schematic diagram showing the results of a selective study of formaldehyde detection on an N-CQDs-OPD/Cr (VI) sensing platform according to example 11 of the application;
FIG. 13 is one of the schematic diagrams of the detection mechanism of Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on carbon quantum dots according to example 12 of the present application;
FIG. 14 is a second schematic spectrum of the detection mechanism of Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots according to example 12 of the present application;
FIG. 15 is a third spectral diagram of the detection mechanism of Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on carbon quantum dots according to example 12 of the present application.
Detailed Description
The present application will be described in further detail with reference to specific examples so as to more clearly understand the present application by those skilled in the art.
The following examples are given for illustration of the application only and are not intended to limit the scope of the application. All other embodiments obtained by those skilled in the art without creative efforts are within the protection scope of the present application based on the specific embodiments of the present application.
In the examples of the present application, all raw material components are commercially available products well known to those skilled in the art unless specified otherwise; in the embodiments of the present application, unless specifically indicated, all technical means used are conventional means well known to those skilled in the art.
Currently, fluorescence analysis is favored by virtue of its simplicity, economy, and the like, wherein a ratio-type fluorescent probe with dual-signal response has low background signal and high precision, and is gradually applied to detection of environmental pollutants. Fluorescent sensing strategies have the significant advantage of simple operation, high sensitivity, and many organic fluorescent molecules have been designed to detect formaldehyde in food samples. Although they show a high selectivity towards formaldehyde, most reported probe syntheses are relatively complex.
Based on the above problems, the embodiment of the application provides a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots and a manufacturing method thereof, and the following is further described by combining specific examples:
example 1
The embodiment provides a preparation method of a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon quantum dots, which comprises the following steps:
step S1, preparing fluorescent carbon quantum dots (N-CQDs): and placing the glutathione solution in a reaction kettle, and synthesizing the glutathione solution by a one-step hydrothermal method to obtain the N-CQDs solution.
Specifically, it includes:
step S101, weighing 0.25g of Glutathione (GSH), adding the Glutathione (GSH) into a 25mL reaction kettle, adding 5mL of deionized water, and performing ultrasonic dissolution;
step S102, reacting for 4 hours in a drying box at 200 ℃, in a practical example, reacting for 4 hours in a forced air drying box at 200 ℃, and filtering by a filter head of 0.22 mu m after the reaction kettle is cooled to room temperature, thus obtaining the N-CQDs solution.
In addition, the resulting N-CQDs solution was placed in a refrigerator (4 ℃ C.) for later use.
S2, constructing an N-CQDs-OPD sensing platform: and mixing the OPD (o-phenylenediamine) solution, the N-CQDs solution and the buffer solution to obtain a first mixed solution, and constructing an N-CQDs-OPD sensing platform which is used for detecting Ag (I) or Cr (VI) in the sample.
The method comprises two detection modes:
first, the Ag (i) in the first sample is detected, specifically, the step 2 includes the steps of:
step S201, sequentially adding 30 mu L N-CQDs solution, 600 mu L of OPD solution and 625 mu L of citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain a first mixed solution; wherein the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M.
Step S202, filtering the first sample by using a 0.22 mu m microfiltration membrane; the filtered first sample was added to the first mixture and the volume was set to 4mL with deionized water.
And step S203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum.
Step S204, calculating F 560 /F 430 And determining the content of Ag (I) in the first sample according to the obtained working curve.
It should be noted that: the first sample is a lake water sample, and in practical detection, the lake water sample is taken from Qingshan lake, however, the first sample can also be other water samples, which are only convenient to understand and are not limiting on the protection scope of the application.
Second, the Cr (vi) in the second sample is detected, specifically, the step 2 includes the steps of:
step S201, sequentially adding 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into an EP tube with 5mL to obtain a first mixed solution; wherein, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
step S202, performing centrifugal treatment on the second sample by using a centrifugal machine, wherein the rotating speed of the second sample is 10000rpm, and the centrifugal time is 10min; filtering the centrifuged second sample with a 0.22 μm microfiltration membrane; adding the filtered second sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
step S203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
step S204, calculating F 560 /F 430 And determining the Cr (VI) content in the second sample according to the obtained working curve.
It should be noted that: the second sample is a sample such as red wine, and the second sample can also be other food samples, which are only convenient to understand and are not limiting on the protection scope of the present application.
And step S3, mixing the Cr solution, the OPD solution, the N-CQDs solution and the buffer solution to obtain a second mixed solution, and constructing an N-CQDs-OPD/Cr (VI) sensing platform which is used for detecting formaldehyde in the sample.
Specifically, it includes:
step S301, sequentially adding 300 mu LCr (VI) solution, 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain a second mixed solution; wherein, the concentration of the Cr (VI) solution is 120 mug/mL, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
step S302, taking 2g of a third sample, and soaking the third sample in 4mL of ultrapure water; after soaking for 5 hours, centrifuging to remove residual sediment, and obtaining supernatant; adding the supernatant of the third sample into the first mixed solution, and fixing the volume to 4mL by using deionized water;
step S303, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
step S304, calculating F 560 /F 430 And determining the formaldehyde content in the third sample according to the obtained working curve.
It should be noted that: the third sample is a frozen chicken, a frozen shrimp and other samples, and the third sample can also be other food samples, which are convenient to understand and are not limited by the protection scope of the application.
As shown in FIG. 1, based on a detection mechanism, the preparation method of the Ag (I), cr (VI) and formaldehyde ratio fluorescence sensor based on carbon dots provided by the application is characterized in that an N-CQDs solution is firstly prepared by using a glutathione solution, and an N-CQDs-OPD sensing platform and an N-CQDs-OPD/Cr (VI) sensing platform are further respectively constructed and are respectively used for detecting Ag (I) or Cr (VI) in a sample and detecting formaldehyde in the sample, so that the detection of the double-signal sensing platform is realized. Cr (VI) has strong oxidizing capability in an acidic system, OPD can be oxidized into DAP, the OPD can generate DAP under the catalysis and oxidation of silver ions, the DAP can quench the fluorescence of N-CQDs based on the fluorescence resonance energy transfer effect, so that the fluorescence intensity of the DAP is increased, the fluorescence intensity of the N-CQDs is reduced, the oxidizing capability of Cr (VI) is inhibited after formaldehyde solution is added, the amount of generated DAP is reduced, the corresponding fluorescence intensity is reduced, and the fluorescence intensity of the N-CQDs is increased, so that the detection of Cr (VI), ag (I) and formaldehyde is realized.
Compared with the prior art, the method has the following advantages:
(1) N-CQDs with good optical and chemical stability are synthesized through a simple and environment-friendly process;
(2) The sensing system has a proportion fluorescence mode and a colorimetric mode, and can display a plurality of output signals, so that the detection result is more reliable;
(3) The carbon dot-based dual read-out strategy has good Ag (I), cr (vi) and HCHO detection potential in practical samples.
In addition, under the experimental conditions, the constructed N-CQDs-OPD sensing platform is applied to analysis of Ag (I) and Cr (VI) in water and red wine, and the N-CQDs-OPD/Cr (VI) sensing platform is applied to formaldehyde analysis in frozen aquatic products, so that the practical application value of the method is further explored.
In the case that no corresponding target object is detected in the actual sample, a labeling recovery experiment can be further carried out, and the results are shown in the table 1, and the labeling recovery rate is 93% -105% and the RSD is lower than 2.91% as shown in the table, so that the method provided by the embodiment has the capability of detecting Ag (I), cr (VI) and formaldehyde in different matrix samples.
TABLE 1 detection of Ag (I), cr (VI) and Formaldehyde in actual samples
Colorimetric determination of silver (I) in actual samples
Example 2
This example provides a carbon quantum dot based Ag (i), cr (vi) and formaldehyde ratio fluorescence sensor prepared by the preparation method described in example 1.
The device comprises an N-CQDs-OPD sensing platform and an N-CQDs-OPD/Cr (VI) sensing platform; the N-CQDs-OPD sensing platform is used for detecting Ag (I) or Cr (VI) in a sample, and the N-CQDs-OPD/Cr (VI) sensing platform is used for detecting formaldehyde in the sample.
Since it is obtained by the preparation method of example 1, example 1 has the advantages that it also has, and will not be described here.
Example 3
This example provides a study of the effect of glutathione amount on the fluorescence intensity of synthetic N-CQDs, and the effect of glutathione amount on the fluorescence intensity of synthetic N-CQDs was examined by setting different glutathione amounts of 0.25g, 1g, 0.75g, 0.5g, 0.25g, respectively, as the main substance of synthetic carbon dots, and the results are shown in FIG. 2.
As can be seen from FIG. 2, the fluorescence intensity of the N-CQDs does not significantly change with the increase of the amount of glutathione, and neither the excitation wavelength nor the emission wavelength of the N-CQDs has a large blue shift or red shift, indicating that the effect of the amount of glutathione on the N-CQDs is not large, so that the amount of glutathione falls within the scope of the present application regardless, but the present embodiment preferably uses 0.25g of glutathione as the optimal amount in view of cost.
Example 4
The present example provides a study of the effect of synthesis temperature and time on fluorescence intensity of synthetic N-CQDs, and the synthesis temperature and time in a one-step hydrothermal method are also an important factor affecting quantum dot performance, and the synthesis temperature and time are optimized by quantum yield under different conditions.
TABLE 2 influence of different reaction temperatures and time on fluorescence quantum yield of synthetic N-CQDs
Table 2 shows the effect of different reaction times (2 h, 4h, 6h, 8 h) and different reaction temperatures (160 ℃, 180 ℃,200 ℃) on the quantum yields of N-CQDs. The results show that the higher the reaction temperature, the higher the quantum yield at the same reaction time, within 8h, whereas the quantum yields at 200 ℃ for reaction for 4h and 6h are not much different. Therefore, in order to consider the timeliness of the experiment, 4h was chosen as the reaction time and 200℃as the reaction temperature.
In combination with example 3,0.25g of glutathione, 200℃and 4h of hydrothermal reaction are the optimal reaction conditions for the synthesis of N-CQDs.
Example 5
The fluorescent carbon quantum dots (N-CQDs) obtained in example 1 were characterized to verify the success of the one-step process for preparing fluorescent carbon dots (N-CQDs) as follows:
first, observing the morphology of N-CQDs using TEM, as shown in fig. 3, fig. 3 (a) shows that the carbon dots are distributed in the form of uniform spherical particles throughout the image, and that most of the particles are amorphous carbon particles without crystal lattice, with a particle size range of 1.25 to 4.25nm and an average particle size of 2.5±0.5nm, as observed from a high resolution transmission electron microscope (fig. 3 (a) inset);
FIG. 3 (b) is an XRD diffraction pattern for CDs showing two broad peaks at 20.6 and 22.3, again due to the highly disordered graphite structure of the carbon atoms;
FIG. 3 (c) shows that the zeta potential of N-CQDs is 8.01mV, indicating that the surface of the carbon quantum dot is positively charged.
FIG. 3 (d) shows the result of the infrared spectrum, 3400cm from the drawing -1 There is a telescopic vibration peak with wide peaks of N-H and O-H nearby, and the peaks at 1733 and 1641cm-1 are respectively attributed to the telescopic vibration peak and N-H bending vibration peak of C=O in-CO-NH-, 1391cm -1 The peak of (C) is derived from C-N bending vibration at 1227cm -1 The peak at which is considered to be the C-O-C telescopic shock absorption band, whereas the original glutathione is 2050cm -1 The characteristic peak of the nearby-SH does not appear significantly in the N-CDs infrared spectrum because the mercapto group has been decomposed under the conditions of high pressure and high temperature.
Further, fig. 4 is an X-ray diffraction diagram (XPS) of carbon points, which are apparent from XPS full spectrum (fig. 4 (a)), having 3 strong peaks at 531.36, 285.3, 400.05eV, respectively, signal peaks of O1s, graphite C1s, N1 s. The C1s spectrum shows four peaks, C-C/c=c at 284.8eV, C-N at 286.05eV, C-O at 287.8eV and-COOH at 288.65 eV; the O1s spectrum shows two peaks at 532.7eV and 531.3eV, representing C-O-C/C-OH and C=O, respectively; the N1 s spectra have two peaks, C-N and N-H, at 399.5eV and 401.5eV, respectively, and in combination with XPS spectra and FT-IR, the carbon dot surface is rich in hydrophilic group functionalities of amino, carboxyl and hydroxyl groups, and c=o groups that provide luminescence properties.
In order to further understand the optical properties of N-CQDs, the UV-visible absorption spectrum and fluorescence spectrum of the aqueous N-CQDs solution were also tested as shown in FIG. 5, and the fluorescence spectrum of FIG. 5 (a) shows that the optimal excitation wavelength of N-CQDs is 360nm and the optimal emission wavelength is 430nm. The uv absorbance spectrum is shown in fig. 5 (b), with a sharp peak at 294nm and also absorbance between 300-400nm, mainly due to the pi-pi transition of c=c and the N-pi transition of c=o/C-N bonds in the sp2 domain of the CDs core. Subsequently, the fluorescence behavior of N-CQDs was also studied by increasing the excitation wavelength from 350nm to 380nm in a step of 10nm, and it can be seen from FIG. 5 (c) that the position of the emission peak does not change with the change in the excitation wavelength. This behavior is due to the variety of oxygen-containing functional groups in N-CQDs, which contain many localized energy levels, which can be achieved.
The mechanisms that cause carbon dots to fluoresce are mainly size effect luminescence, surface state luminescence, molecular state luminescence and defect state luminescence mechanisms, wherein surface state luminescence is a main mechanism for explaining the origin of carbon dot luminescence, and generally refers to that the fluorescence property of carbon dots is influenced by functional groups on the surface or certain surface luminescence centers, and the fluorescent properties of N-CQDs synthesized by GSH as a single precursor are realized based on the modified reasons.
Example 6
The pH optimization analysis was performed for the detection platform in example 1:
as shown in FIG. 6, the change in fluorescence intensity of different systems at different pH (0.1M citrate-sodium citrate buffer) was studied.
FIG. 6 (a) shows the change of fluorescence intensity of carbon quantum dots at different pH values, and it can be seen that pH has little effect on the fluorescence intensity of carbon dots;
FIG. 6 (b) shows that the fluorescence intensity of N-CQDs+OPD+Ag (I) at 430nm and 560nm is very weak at 560nm in the range of 3.0 to 4.6, because the amino group of OPD is protonated in a strongly acidic medium, suppressing oxidation of Ag (I), and the peak between 5.0 and 5.8 increases gradually with increasing pH 560nm, so that only pH greater than 5.0 is considered according to CDs+OPD+Ag (I) system;
FIG. 6 (c) shows the difference between 430nm and 560nm in two fluorescence maps of N-CQDs+OPD+Ag (I) and N-CQDs+HCHO+OPD+Ag (I) at different pH values, we selected ΔF for more sensitivity in subsequent formaldehyde detection 430 And DeltaF 560 Less different pH (pH=5.4) was optimal, and we finally selected a citric acid-sodium citrate buffer (0.1M) with ph=5.4 as the experimental condition of the present application, in view of the subsequent experiments.
Example 7
The amount of OPD used for the detection platform in example 1 was studied and analyzed:
from the mechanistic analysis of fig. 1, OPD concentration affects the total DAP, which is directly related to the sensitivity of ion detection. Thus, when the amount of OPD was examined, the data shown in FIG. 7 shows that the concentration of OPD was evaluated, and it can be seen that F was increased with the increase in the concentration of OPD 560 /F 430 The fluorescence intensity ratio of (2) was significantly increased and then gradually smoothed after reaching a concentration of 8mM, so that the experiment of the example of the present application selected an OPD of 10 mM.
Example 8
The investigation analysis was performed on the detection time of the detection platform in example 1:
in order to investigate the analysis speed of the sensing platform on Ag (I) and Cr (VI), the reaction time of the N-CQDs/OPD sensing platform for detecting Ag (I) and Cr (VI) was detected under the optimal condition, and the result is shown in FIG. 8.
As can be seen from FIG. 8 (a), after addition of Ag (I), the fluorescence intensity ratio (F) 560 /F 430 ) Rapidly increases within 0-5min and remains substantially unchanged after 5min, so that 10min is preferred as the optimal reaction time for detecting Ag (I);
as can be seen from FIG. 8 (b), the fluorescence intensity ratio (F) of the sensor platform after Cr (VI) is added 560 /F 430 ) The increase is sharp within 0-6min and remains substantially unchanged after 6min, preferably 10min being the optimal reaction time for detecting Cr (VI).
Example 9
Investigation analysis was performed on the selectivity of the N-CQDs-OPD sensing platform in example 1:
the influence of K (I), ca (II), mg (II), co (II), cr (III), mn (II), ba (II), zr (IV), cd (II), cu (II), ag (I), fe (II) and Fe (III) on the fluorescence intensity of a CDs/OPD system is explored, and the result is shown in a graph 9, and the influence of other ions on the fluorescence intensity of a sensing platform is not great except Cr (VI) and Ag (I), so that the sensing platform has better selectivity on the detection of Cr (VI) and Ag (I), and meanwhile, the ratio type fluorescent probe can effectively reduce some interference.
Further, in order to be able to detect Cr (VI) and Ag (I) separately, one needs to select a suitable masking agent to eliminate the interference of another ion on the test when detecting one of the ions.
As shown in FIG. 10 (a), H can be used in the detection of Ag (I) 2 O 2 To mask the interference of Cr (VI) because of H in an acidic solution 2 O 2 Will react with Cr (VI) to generate Cr (III) and O 2 And H 2 O can not affect the system, while silver nitrate can not react with H under the acidic condition 2 O 2 And (3) reacting.
In the detection of Cr (VI), KCl can be used to eliminate the interference of Ag (I), and as shown in FIG. 10 (b), in an acidic solution, KCl reacts with silver nitrate to form AgCl precipitate, thereby masking Ag (I).
From the experimental results, it is shown that accurate detection of a single ion can be achieved.
Example 10
Investigation was made on the time for formaldehyde detection by the N-CQDs-OPD/Cr (VI) sensing platform in example 1:
in order to obtain the best sensitivity of formaldehyde detection, the effect of reaction time and Cr (VI) concentration on formaldehyde detection was studied and the results are shown in FIG. 11.
As seen from FIG. 11 (a), the ratio of fluorescence intensity gradually increases with the increase of the reaction time within 6 minutes, while the fluorescence intensity is substantially unchanged after 6 minutes, so 10 minutes was selected as the optimal time for detecting formaldehyde.
The concentration of Cr (VI) determines the detection range of formaldehyde, since Cr (VI) acts as an oxidizing agent in the system, and as can be seen from FIG. 11 (b), deltaF is found at a concentration of 7. Mu.g/mL 430 /△F 560 Maximum. When the concentration is less than 7. Mu.g/mL, the redox reaction is insufficient, whereas when Cr (VI) is present in excess, the redox reaction is hardly affected by a certain concentrationThe confinement of formaldehyde results in a signal insensitive change.
Thus, 7. Mu.g/mL was chosen for formaldehyde analysis performance experiments.
Example 11
The selectivity of the N-CQDs-OPD/Cr (VI) sensing platform in example 1 for formaldehyde detection was investigated:
in order to evaluate the detection specificity of the N-CQDs-OPD/Cr (VI) sensor platform, the effect of some common aldehyde compounds and compounds possibly present in actual samples on the fluorescence intensity of N-CQDs-OPD/Cr (VI) was tested under the same conditions, and the results are shown in FIG. 12.
These compounds mainly comprise formaldehyde, glutathione (GSH), H 2 S、H 2 O 2 、Na 2 SO 3 、Na 2 SO 4 Phenol, glucose, fe 3+ Glutaraldehyde, benzaldehyde, acetaldehyde.
The concentration of all compounds was fixed at 200. Mu.M, and it can be seen from the graph that the ratio of fluorescence intensities of the N-CQDs-OPD/Cr (VI) sensor platform after addition of formaldehyde solution (F 430 /F 560 ) The fluorescent intensity of other compounds is obviously improved, the influence of other compounds on the fluorescent intensity is weak, and the mixed solution added with the formaldehyde solution is blue fluorescent under the irradiation of a 365nm ultraviolet lamp, so that the N-CQDs-OPD/Cr (VI) sensing system shows excellent selectivity on formaldehyde due to the strong reducibility of formaldehyde, and the fluorescent probe can be used for detecting formaldehyde in complex samples.
Example 12
The detection mechanism of the Ag (i), cr (vi) and formaldehyde ratio fluorescence sensor based on carbon quantum dots provided in example 2 was examined and analyzed:
FIG. 13 shows the fluorescence emission spectrum and the ultraviolet absorption spectrum under different conditions, and it can be seen from the graph that the influence of Cr (VI), formaldehyde (FA) and OPD alone on N-CQDs is not very sensitive. The mixed solution of OPD and Cr (VI) shows a new peak at 560 nm; then after adding N-CQDs on the basis, the fluorescence intensity at 430nm is reduced, a new peak appears at 560nm, and the ultraviolet absorption of the mixed solution also appears at 432nm, mainly because Cr (VI) oxidizes OPD to generate oxoPD (DAP), the emission wavelength of DAP is 560nm, the ultraviolet absorption peak is 432nm, and the DAP quenches the fluorescence of the N-CQDs, so that a ratio fluorescent platform and colorimetric platform can be constructed for detecting Cr (VI).
After addition of formaldehyde solution, the absorption band of DAP at 432nm was significantly limited (FIG. 13 (b)) and fluorescence emission of N-CQDs at 430nm was enhanced and fluorescence at 560nm was reduced (FIG. 13 (a)) due to the oxidation of OPD suppressed by the redox reaction with Cr (VI). Based on this, the ratio of fluorescence emission intensity at 430nm to that at 560nm (F 430 /F 560 ) And absorbance at 420nm (a 420) to indicate the amount of formaldehyde in the test system.
To further understand the interaction mechanism of N-CQDs with DAP, fluorescence excitation, emission spectra of N-CQDs and ultraviolet-visible absorption spectra of DAP were measured as shown in FIG. 14, and as can be seen from FIG. 14 (a), the excitation wavelength of N-CQDs was 360nm and the emission wavelength was 430nm. The absorption spectrum of DAP overlaps with the excitation spectrum and the emission spectrum of N-CQDs, and the presence of an in-filter effect (IFE) or Fluorescence Resonance Energy Transfer (FRET) is judged.
Fluorescence lifetime is considered to be one of the effective methods of distinguishing IFE from FRET. FIG. 14 (b) shows that DAP is absent (τ 0 ) And fluorescence decay curves of N-CQDs in the presence of (τ). The fluorescence lifetimes of N-CQDs and N-CQDs/DAP were 7.43ns and 6.01ns, respectively. The results indicate that the fluorescence lifetime of N-CQDs decays over time, so the fluorescence quenching mechanism of DAP to N-CQDs is mainly due to FRET rather than IFE.
Further, the reason why the signal at 560nm is weakened after formaldehyde is added is explored, formaldehyde cannot react with DAP directly, cr (VI) can react with formaldehyde in oxidation-reduction reaction, OPD can react with formaldehyde in Schiff base reaction, so that in order to investigate which plays a leading role, the concentration of one of OPD or Cr (VI) is fixed, the concentration of the other one of the OPD and Cr (VI) is changed or not, the corresponding fluorescence intensity is measured, and then a curve of the change of the fluorescence intensity with the concentration is drawn, and the result is shown in FIG. 15.
As can be seen from FIG. 15 (a), no significant fluorescence was detected in the presence of 100. Mu.M formaldehyde and 10mM OPD until the Cr (VI) concentration reached 5. Mu.g/mL. The fluorescence intensity then starts to increase at a comparable rate to that in the absence of formaldehyde, indicating that the inhibition of the Cr (vi) -OPD interaction by formaldehyde can be substantially saturated by the equivalent Cr (vi). In contrast, when 100. Mu.M formaldehyde and 9. Mu.g/mL Cr (VI) were present, the increase in fluorescence intensity was much slower with increasing OPD concentration than in the absence of formaldehyde (FIG. 15 (b)).
The influence of the sample adding sequence is also considered, and the experimental results are the same whether formaldehyde is added firstly or added later. The above results indicate that formaldehyde interactions with Cr (VI) under experimental conditions may be a major factor affecting signal attenuation at 560 nm. This is probably because Cr (vi) has a strong oxidizing property under acidic conditions, can undergo oxidation-reduction reaction with formaldehyde and has a larger reactivity than the capability of schiff base reaction of aldehyde groups on formaldehyde and amino groups on OPD, resulting in interaction of HCHO with Cr (vi) being a dominant factor.
Example 13
This example provides analytical performance for detecting Ag (I), cr (VI) based on N-CQDs-OPD dual-mode sensing system:
analytical performance of Ag (I) detection
Under the best conditions explored in the above examples, analytical performance of detecting Ag (I) by fluorescence and colorimetry based on N-CQDs/OPD system was studied by adding different concentrations of Ag (I).
In the range of 1.0 mu M-180 mu M, the specific fluorescence intensity and the Ag (I) concentration are in linear relation, and the fitting equation is F 560 /F 430 ＝0.0035C+0.0828，R 2 =0.9981, lod is 0.416 μm.
Meanwhile, under the optimal condition, the ultraviolet absorption spectrum of the system is measured by adding Ag (I) with different concentrations, the ultraviolet absorption intensity and the concentration of Ag (I) are in a linear relation within the range of 1.0 mu M-200 mu M, the linear equation is A=0.0045C+0.0342, R 2 =0.9973, lod of 0.583 μm (R 2 ＝0.9973)。
Analytical performance of Cr (VI) detection
Under the optimal conditions as studied in the above examples, the linear equation of the ratio fluorescence intensity to Cr (VI) concentration in the range of 0.15-15. Mu.g/mL was F 560 /F 430 ＝0.2449C-0.1201(R 2 = 0.9901), LOD is 0.028 μg/mL.
The result of the ultraviolet absorption spectrum shows that the ultraviolet absorption intensity (A 432 ) Is in linear relation with Cr (VI) concentration in the range of 0.05-21 mug/mL, and the linear equation is A= 0.1636C-0.0268 (R 2 =0.9980), LOD is 0.030 μg/mL.
Example 14
This example provides analytical performance for formaldehyde detection based on N-CQDs-OPD/Cr (VI) dual signal ratio probes:
based on the above examples, the ability of the proportional fluorescent probe for quantitative detection of Formaldehyde (FA) was further investigated. The fluorescence and ultraviolet absorption spectra of the proportional fluorescence probes after adding formaldehyde solutions of different concentrations to N-CQDs-OPD/Cr (VI) were tested.
In the range of 0.5 to 120. Mu.M, the specific fluorescence intensity (F 560 /F 430 ) The linear equation with FA concentration is F 560 /F 430 ＝0.01118C+0.4525，R 2 Detection limit LOD of fa is 0.294 μm=0.9933.
The ultraviolet absorption spectrum results show that the ultraviolet absorption intensity (A 432 ) Is in linear relation with formaldehyde concentration in the range of 1-200 mu M, and the linear equation is A= -0.0060C+1.3279 (R 2 =0.9961), the limit of detection (LOD) was 0.342 μm. The analytical properties of the three substances are summarized in Table 3.
TABLE 3 analytical properties of Ag (I), cr (VI) and formaldehyde
In summary, the Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on the carbon quantum dots and the preparation method thereof provided by the embodiment of the application are based on the double-signal (ratio fluorescence and colorimetric) detection method of N-CQDs and OPD, and can be used for efficiently detecting Ag (I), cr (VI) and HCHO. The method has the advantages that N-CQDs with good optical and chemical stability are synthesized through a simple and environment-friendly process; the sensing system has a proportion fluorescence mode and a colorimetric mode, and can display a plurality of output signals, so that the detection result is more reliable; the carbon-dot-based dual-readout strategy has good Ag (I), cr (VI) and HCHO detection potential in practical samples
In the description of the present specification, the description with reference to the term "particular example" or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the embodiments of the application. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims (10)
1. A preparation method of a Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor based on carbon dots is characterized by comprising the following steps:
s1, placing a glutathione solution in a reaction kettle, and synthesizing the glutathione solution by a one-step hydrothermal method to obtain an N-CQDs solution;
s2, mixing the OPD solution, the N-CQDs solution and the buffer solution to obtain a first mixed solution, and constructing an N-CQDs-OPD sensing platform, wherein the N-CQDs-OPD sensing platform is used for detecting Ag (I) or Cr (VI) in a sample;
s3, mixing the Cr solution, the OPD solution, the N-CQDs solution and the buffer solution to obtain a second mixed solution, and constructing an N-CQDs-OPD/Cr (VI) sensing platform which is used for detecting formaldehyde in the sample.
2. The method for preparing the carbon dot-based Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor according to claim 1, wherein the step S1 specifically comprises:
s101, weighing 0.25g of glutathione, adding the glutathione into a 25mL reaction kettle, adding 5mL of deionized water, and performing ultrasonic dissolution;
s102, reacting for 4 hours in a drying oven at 200 ℃, cooling the reaction kettle to room temperature, and filtering to obtain the CDs solution.
3. The method for preparing the carbon dot-based Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor according to claim 1, wherein the step S2 specifically comprises:
s201, sequentially adding 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the first mixed solution; wherein, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s202, adding the filtered first sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s204, calculating F 560 /F 430 And determining the content of Ag (I) in the first sample according to the obtained working curve.
4. The method for preparing a carbon dot based Ag (i), cr (vi) and formaldehyde ratio fluorescent sensor according to claim 3, further comprising, before step S202:
the first sample was filtered using a 0.22 μm microfiltration membrane.
5. The method for preparing the carbon dot-based Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor according to claim 1, wherein the step S2 specifically comprises:
s201, sequentially adding 30 mu L N-CQDs solution, 600 mu L of OPD solution and 625 mu L of citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the first mixed solution; wherein, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s202, adding a filtered second sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s203, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s204, calculating F 560 /F 430 And determining the Cr (VI) content in the second sample according to the obtained working curve.
6. The method for preparing a carbon dot based Ag (i), cr (vi) and formaldehyde ratio fluorescent sensor according to claim 5, further comprising, before step S202:
using a centrifugal machine to carry out centrifugal treatment on the second sample at the rotating speed of 10000rpm for 10min;
the second sample after centrifugation was filtered using a 0.22 μm microfiltration membrane.
7. The method for preparing the carbon dot-based Ag (I), cr (VI) and formaldehyde ratio fluorescent sensor according to claim 1, wherein the step S3 specifically comprises:
s301, sequentially adding 300 mu LCr (VI) solution, 30 mu LN-CQDs solution, 600 mu L OPD solution and 625 mu L citric acid-sodium citrate buffer solution into a 5mL EP tube to obtain the second mixed solution; wherein, the concentration of the Cr (VI) solution is 120 mug/mL, the concentration of the OPD solution is 10 mM-50 mM, the pH of the citric acid-sodium citrate buffer solution is 5.4, and the concentration is 0.1M;
s302, adding supernatant of a third sample into the first mixed solution, and fixing the volume to 4mL by deionized water;
s303, placing the solution with the fixed volume for 15min, and collecting a fluorescence spectrum and an ultraviolet absorption spectrum;
s304, calculating F 560 /F 430 Determining the formaldehyde content of the third sample according to the obtained working curveAmount of the components.
8. The method for preparing a carbon dot based Ag (i), cr (vi) and formaldehyde ratio fluorescent sensor according to claim 7, further comprising, before step S302:
immersing 2g of the third sample in 4mL of ultrapure water; after soaking for 5 hours, centrifuging to remove residual sediment, and obtaining the supernatant.
9. A carbon dot based Ag (i), cr (vi) and formaldehyde ratio fluorescence sensor prepared by the preparation method of any one of claims 1 to 8, characterized by comprising a CDs-OPD sensing platform and an N-CQDs-OPD/Cr (vi) sensing platform; the N-CQDs-OPD sensing platform is used for detecting Ag (I) or Cr (VI) in a sample, and the N-CQDs-OPD/Cr (VI) sensing platform is used for detecting formaldehyde in the sample.
10. Use of a carbon dot based Ag (i), cr (vi) and formaldehyde ratio fluorescence sensor according to claim 9 for the detection of Ag (i), cr (vi) and formaldehyde.
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