CN114965413A

CN114965413A - Method for detecting ferulic acid by using nitrogen-doped carbon dots

Info

Publication number: CN114965413A
Application number: CN202210844593.4A
Authority: CN
Inventors: 颜范勇; 王秀乐; 易春辉; 徐茗
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2022-07-19
Filing date: 2022-07-19
Publication date: 2022-08-30

Abstract

Carbon dots are of great interest because of their low cost, environmental friendliness and good biocompatibility. Among them, heteroatom doping is an effective means for improving the fluorescence property of carbon dots. According to the invention, a one-step hydrothermal method is adopted, citric acid and L-histidine are used as raw materials, and the nitrogen-doped carbon dots with blue fluorescence are synthesized. The nitrogen-doped carbon dots have excellent fluorescence characteristics and good temperature and pH stability. It is worth noting that the nitrogen-doped carbon dots show specific selectivity and high sensitivity to ferulic acid, and the ferulic acid can effectively quench the fluorescence of the nitrogen-doped carbon dots within the concentration range of 0-200 mu mol/L, and the detection limit is as low as 0.192 mu mol/L. The sensing mechanism of the nitrogen-doped carbon dots and the ferulic acid is determined to be the inner filtering effect through the fluorescence spectrum, the ultraviolet absorption and the fluorescence lifetime. The invention not only develops a simple method for synthesizing the nitrogen-doped fluorescent carbon dots, but also provides a new idea for the rapid detection of ferulic acid.

Description

Method for detecting ferulic acid by using nitrogen-doped carbon dots

Technical Field

The invention belongs to the technical field of chemical detection, and particularly relates to a method for detecting ferulic acid by using nitrogen-doped carbon dots.

Background

Ferulic acid is an important medicinal compound, has wide source, mainly exists in Chinese herbal medicines such as rhizoma ligustici wallichii, angelica sinensis, rhizoma cimicifugae and the like, and can also be synthesized by chemical or biological means. Ferulic acid has high medicinal value, such as antioxidation, antithrombotic, blood lipid reducing, myocardial ischemia and oxygen consumption reducing, antibacterial, antivirus, anticancer, etc., and has been widely applied to the aspects of medicine, health care products, cosmetic raw materials, food additives, etc.

At present, ferulic acid detection technologies mainly comprise High Performance Liquid Chromatography (HPLC), thin layer scanning (TLCS), High Performance Capillary Electrophoresis (HPCE), liquid chromatography-mass spectrometry (HPLC-MS), fluorescence Spectrophotometry (SPF) and the like. These techniques, although highly sensitive and selective, generally require complex procedures and expensive equipment, and are difficult to achieve efficient, rapid and inexpensive detection of ferulic acid. Therefore, it is one of the focus problems of research to further develop a ferulic acid detection method with high sensitivity, good selectivity, simple operation and low cost.

The carbon dots refer to carbon nanoparticles with the particle size of less than 10nm, have excellent photoluminescence performance and light stability, adjustable luminous intensity, simple preparation, good water solubility and low toxicity. Scholars at home and abroad use carbon dots to carry out a great deal of work on the detection aspects of metal ions, organic small molecules, anions and the like, and the detection of medicines is rarely reported. At present, no technology for detecting ferulic acid by using a carbon dot is disclosed.

The Internal Filtering Effect (IFE) refers to a chemical sensor action mechanism in which the excitation or emission spectrum of a phosphor is overlapped with the absorption spectrum of an absorber to a considerable extent, resulting in quenching of the fluorescence of the phosphor by the absorber, and has advantages of high sensitivity and easy design compared with other action mechanisms such as Fluorescence Resonance Energy Transfer (FRET) or Photoinduced Electron Transfer (PET). Therefore, the development of the fluorescent probe based on the IFE action mechanism for detecting ferulic acid has important research and application significance.

Disclosure of Invention

The invention aims to change the light emitting characteristic of the carbon dots through the interaction between ferulic acid and nitrogen-doped carbon dots, thereby realizing the rapid detection of ferulic acid.

The method adopted for solving the problems comprises the following steps:

(1) dissolving citric acid and L-histidine in distilled water, transferring to a stainless steel autoclave after dissolving, heating at a constant temperature of 200 ℃ for 5h, cooling to room temperature, centrifuging, dialyzing, and evaporating the solvent under reduced pressure to obtain nitrogen-doped yellowish brown carbon dots.

(2) Preparing nitrogen-doped carbon dot mother liquor and 2mmol/L ferulic acid standard solution for later use.

(3) Equivalent nitrogen-doped carbon dots are respectively added with ferulic acid with different contents, and the fluorescence spectrum of 425nm is measured under the excitation wavelength of 300 nm. And drawing a standard fitting curve by taking the concentration of the ferulic acid as a horizontal coordinate and taking the ratio of the original fluorescence intensity of the nitrogen-doped carbon point to the fluorescence intensity after the ferulic acid is added as a vertical coordinate.

The final effects of the invention are as follows:

according to the invention, citric acid and histidine are used as precursors, and a one-step hydrothermal method is adopted to synthesize the nitrogen-doped carbon dots with high fluorescence. The prepared nitrogen-doped carbon dots have uniform particle size distribution and are rich in nitrogen-oxygen-containing functional groups such as carboxyl, amino and the like on the surface. Based on the phenomenon that the nitrogen-doped carbon dots can effectively quench the fluorescence of the ferulic acid, a method for efficiently and sensitively detecting the content of the ferulic acid in the solution is established. The fluorescence intensity of the carbon dots has a good linear response relation with ferulic acid in the concentration range of 0-200 mu M, and the detection limit is as low as 0.192 mu mol/L. The quenching mechanism is discussed and demonstrated as an internal filtration. The invention enriches the detection means of polyphenol compounds, and has wide application prospect in the fields of chemical sensing, environmental monitoring and the like.

Drawings

FIG. 1, TEM image of N-doped carbon dots

FIG. 2 is an X-ray photoelectron spectrum of a nitrogen-doped carbon dot

FIG. 3 is an infrared spectrum of a nitrogen-doped carbon dot

FIG. 4 shows fluorescence excitation and emission spectra of nitrogen-doped carbon dots

FIG. 5 is a graph showing the sensitivity of nitrogen-doped carbon dots to ferulic acid

FIG. 6, analysis chart of detection mechanism of ferulic acid by nitrogen-doped carbon dots

FIG. 7 is a graph showing the selectivity of ferulic acid by a nitrogen-doped carbon site

FIG. 8 shows fluorescence intensity changes of N-doped carbon dots at different pH values and at different temperatures

Detailed description of the preferred embodiments

The invention is further described below with reference to the accompanying drawings:

in order to clearly understand the morphology and size of the nitrogen-doped carbon dots, the nitrogen-doped carbon dots are characterized by TEM, as shown in fig. 1, it can be seen that the nitrogen-doped carbon dots are quasi-spherical particles, have uniform particle size, good dispersion, no aggregation, a size between 3.2 nm and 4.6nm, and narrow size distribution.

FIG. 2 is an X-ray photoelectron spectroscopy (XPS) chart of a nitrogen-doped carbon dot. The XPS total energy spectrum of the nitrogen-doped carbon dot in graph a shows three distinct characteristic peaks, which are respectively located at 284.8eV, 401.0eV and 530.1eV, and shows that the nitrogen-doped carbon dot is mainly composed of carbon, nitrogen and oxygen elements. In the spectrum of C1s in panel b, there are distinct absorption peaks, 284.9eV, 286.6eV and 288.2eV respectively correspond to C-C/C C, C-N/C-O, C ═ O. The presence of the N1s peak in graph c indicates that the N element has been driven into the nitrogen-doped carbon dots by autodoping. The different compositions of the N element show obvious absorption peaks at 399.7eV and 401.2 eV. In the O1s spectrum of dot plot d, the peaks at 531.2eV and 532.7eV are clearly corresponding to C ═ O and C — OH groups.

The surface functional groups of N-CDs were analyzed by FT-IR, and FIG. 3 shows that the nitrogen-doped carbon dots are 4000-500cm ^-1 FT-IR plot over the range. Wherein 3722-2371cm ^-1 Expansion and contraction vibration peak of 1695cm and belonging to O-H ^-1 The central strong absorption peak should be C ═ O stretching vibration peak in-COOH, 1426cm ^-1 The in-plane bending vibration peak corresponding to O-H. 1227cm ^-1 The smaller absorption peak is the C-O-C/C-N stretching vibration peak. 1035cm ^-1 Should be the stretching vibration peak of O-H and N-H. FT-IR results indicate. The above analysis shows that the surface of the nitrogen-doped carbon dot has a large number of polar groups including carboxyl, amino, etc., which also imparts good water solubility to the nitrogen-doped carbon dot.

The fluorescence spectrum can be used for preliminary characterization of the optical properties of the nitrogen-doped carbon dots. FIG. 4 is a fluorescence spectrum of nitrogen-doped carbon dots. The graphs a and b show the fluorescence spectra of the N-doped carbon dots at different emission wavelengths (440-510nm) and different excitation wavelengths (260-360nm), respectively. It can be observed that the fluorescence intensity of the nitrogen-doped carbon dots increases and then decreases as the excitation wavelength increases from 260nm to 360nm, and exhibits typical excitation-dependent emission characteristics. The optimum emission peak of the nitrogen-doped carbon spot was located at 425nm when the excitation wavelength was 300 nm.

The sensing performance of the solution is evaluated by adding ferulic acid with different concentrations into the solution of the carbon dots, and the linear range and the lowest detection limit of detecting the ferulic acid by the nitrogen-doped carbon dots are investigated. As shown in FIG. 5a, the fluorescence intensity of the nitrogen-doped carbon spot gradually decreased as the ferulic acid concentration increased in the range of 0 to 200. mu. mol/L. Subsequently, a standard curve was plotted based on the study results, as shown in fig. 5 b. Establishing a linear regression equation Y-0.01293X +0.98101 and a linear correlation coefficient R by taking the concentration of ferulic acid as X and the relative fluorescence intensity F/F0 of the nitrogen-doped carbon point as Y ² Is 0.998. Wherein, F ₀ And F respectively represent the fluorescence intensity of the nitrogen-doped carbon spot before and after the addition of ferulic acid. As can be seen, the relative fluorescence intensity F/F of the nitrogen-doped carbon dots ₀ Shows a good linear relationship with the ferulic acid concentration in the range of 0-200 mu mol/L. The lowest detection limit was calculated to be 0.192 μmol/L based on LOD 3 σ/K.

Further researches the induction mechanism of ferulic acid on nitrogen-doped carbon dots. Fig. 6a shows a change in the uv-vis absorption spectrum, the nitrogen-doped carbon dot and ferulic acid did not produce a new uv absorption peak compared to the uv-vis absorption spectrum of the nitrogen-doped carbon dot and ferulic acid, indicating that no new non-luminescent ground-state complex was formed between the nitrogen-doped carbon dot and ferulic acid, thus excluding the possibility of static quenching thereof. As can be seen from fig. 6b, the optimum excitation spectrum of the nitrogen-doped carbon spot overlaps with the uv-vis absorption spectrum of ferulic acid. Therefore, it is presumed that the fluorescence quenching of the nitrogen-doped carbon spot may be caused by fluorescence resonance energy transfer or an internal filtering effect between the two. The fluorescence decay curves before and after addition of ferulic acid were measured, and it is evident from FIG. 6c that the fluorescence lifetimes of both were almost unchanged. The above results indicate that ferulic acid has little effect on the fluorescence lifetime of nitrogen-doped carbon dots. Thus, the possibility of fluorescence quenching due to kinetic quenching and fluorescence resonance energy transfer is excluded. In conclusion, it is determined that the sensing mechanism of the nitrogen-doped carbon dot on ferulic acid is an inner filtering effect.

Selectivity is an important parameter for studying the performance of the fluorescence sensing platform. By adding common ions (Na) ⁺ ，K ⁺ ，Ca ²⁺ ，Ag ⁺ ，Mg ²⁺ ，Fe ³⁺ ，NH ₄ ⁺ ，NO ^3- ，8O ₄ ^2- ，Cl ^- ) And possible organic co-occurrences (GSH, Cys, His, (C) ₆ H ₁₀ O ₅ ) _n ，C ₆ H ₁₂ O ₆ ，C ₁₂ H ₂₂ O ₁₁ ) And evaluating the specific recognition of the nitrogen-doped carbon point to the ferulic acid. As shown in fig. 7a, only ferulic acid clearly interacts with the nitrogen-doped carbon spot, and the fluorescence intensity of the nitrogen-doped carbon spot is significantly reduced. The remaining ions and possible organic coexisting species have little effect on the fluorescence intensity of the nitrogen-doped carbon dots. This indicates that the nitrogen-doped carbon dots have significant selectivity for ferulic acid detection. In a real sample, interference of other coexisting ions is inevitably present. The anti-interference capability of the nitrogen-doped carbon dots is investigated by observing the change condition of the fluorescence intensity of the nitrogen-doped carbon dots before and after the ferulic acid is added. As a result, as shown in FIG. 7b, in the absence of ferulic acid, the fluorescence intensity of the nitrogen-doped carbon spot hardly changed after the addition of the above substance. After the ferulic acid with the same concentration is added, the fluorescence intensity is obviously reduced. Therefore, even if the interference substances exist, the ferulic acid can still quench the fluorescence of the nitrogen-doped carbon dots, and the detection of the ferulic acid by the nitrogen-doped carbon dots has strong anti-interference capability.

The optical stability of CDs is one of the important factors influencing the construction of fluorescent sensors and optical devices and the practical detection of applications. And respectively adding the nitrogen-doped carbon dots into the aqueous solution with the pH value of 3-13 to characterize the fluorescence property of the sample. As a result, as shown in fig. 8a, the fluorescence intensity of the nitrogen-doped carbon dot was substantially unchanged, indicating that the synthesized nitrogen-doped carbon dot has stable optical properties and is resistant to acids and bases. The fluorescence intensity of the nitrogen-doped carbon dots was recorded at intervals of 5 ℃ in the range of 15-55 ℃. The fluorescence intensity of the nitrogen-doped carbon dots in FIG. 8b remained constant throughout, indicating that the temperature had little effect on the nitrogen-doped carbon dots. The result shows that the prepared nitrogen-doped carbon dot has good pH and temperature stability, is an excellent fluorescent sensor and is beneficial to the application of the fluorescent sensor in practice.

Claims

1. A method for detecting ferulic acid is characterized in that a nitrogen-doped carbon dot is adopted to detect ferulic acid.

2. The detection method according to claim 1, wherein the nitrogen-doped carbon dots are synthesized by a method comprising:

(1) dissolving citric acid and L-histidine in distilled water, transferring to a stainless steel autoclave after dissolving, heating for 5 hours at the constant temperature of 200 ℃, cooling to room temperature, centrifuging, dialyzing, and evaporating the solvent under reduced pressure to obtain nitrogen-doped blue fluorescent carbon dots;

(2) preparing nitrogen-doped carbon dot mother liquor and 2mmol/L ferulic acid standard solution for later use;

(3) respectively adding equivalent nitrogen-doped carbon points into ferulic acid standard solutions with different concentrations, carrying out volume metering by using distilled water, standing for 10 minutes, and measuring fluorescence spectrum data under the excitation wavelength of 340 nm; and drawing a standard fitting curve by taking the concentration of the ferulic acid as a horizontal coordinate and taking the ratio of the original fluorescence intensity of the nitrogen-doped carbon point to the fluorescence intensity after the ferulic acid is added as a vertical coordinate.

(4) And (3) measuring fluorescence spectrum data of the actual sample to be detected in the solution of the nitrogen-doped carbon dots under the excitation wavelength of 340nm, and calculating the content of ferulic acid in the actual sample according to the fitted curve obtained in the step (3).

3. The detection method according to claim 1, characterized in that: preparing nitrogen-doped carbon dot mother liquor; preparing a ferulic acid standard solution; taking the nitrogen-doped carbon dot mother liquor, adding a ferulic acid standard solution, fixing the volume with distilled water, shaking up, standing, and measuring the fluorescence intensity of the mixed solution by using a fluorescence spectrophotometer.

4. The assay of claim 2 which uses spectrofluorometer parameters which are: excitation wavelength was 340nm, emission start wavelength was 360nm, emission stop wavelength was 650nm, excitation slit 5nm, and emission slit 5 nm.

5. The detection method according to claims 1 to 4, wherein the nitrogen-doped carbon dots are prepared using citric acid and histidine.

6. The assay of claims 1-4 for use in drug testing.

7. Nitrogen doped carbon spot detection of ferulic acid, characterised in that a method according to any one of claims 1 to 4 is used.