Determination Of Baicalein,glutathione,Ag~+ And Ascorbic Acid Based On Fluorescent Nanomaterials As Probes

Fluorescent nanomaterials such as carbon dots（CDs）and gold nanoclusters（Au NCs）have emerged as new materials for constructing fluorescent probes due to their unique optical and chemical properties.They have the advantages of small size,high fluorescence intensity,good chemical and light stability,low toxicity and are widely used in fluorescence imaging,photocatalysis,ion determination,drug transportation and so on.In this paper,heteroatom-doped carbon dots and gold nanoclusters were prepared and characterized.Fluorescent probes for rapid and sensitive determination of baicalein,glutathione,Ag⁺and ascorbic acid were constructed based on carbon dots and gold nanoclusters.The main research content was as follows:1.N,S co-doped carbon dots as a dual-functional fluorescent probe for sensitive determination of baicalein and temperatureNitrogen and sulfur dual-doped CDs（N,S-CDs）were prepared via a facile one-pot hydrothermal method from citric acid and N-acetyl-L-cysteine with a high quantum yield（QY）.As-fabricated N,S-CDs had a size around 2.5 nm and exhibited excitation-independent emission and excellent luminescent properties.The excitation and emission wavelength of N,S-CDs were 350 nm and 420 nm,and the quantum yield was 49%.Baicalein could be effectively quenched the fluorescence of the N,S-CDs based on static quenching,and therefore the synthesized N,S-CDs could be used as a fluorescent probe for determination of baicalein.The fluorescent probe showed a highly sensitive determination of baicalein with a determination limit（LOD）of 0.21μmol?L^-1in the linear range from 0.69 to 70.0μmol?L^-1.In addition,the temperature sensor based on the synthesized N,S-CDs showed a good linear relationship between temperature and fluorescence（FL）intensity with a temperature range from 5°C to 75°C.Furthermore,the synthesized N,S-CDs were successfully applied to the measurement of baicalein in real samples.2.A novel“off-on-off”fluorescent-nanoprobe based on B,N co-doped carbon dots and Mn O₂ nanosheets for sensitive determination of GSH and Ag⁺B,N-CDs was fabricated by hydrothermal method using boric acid and ethylenediamine.Mn O₂ nanosheets were prepared by Mn SO₄ and BSA.The constructed nanoprobe was composed of B,N-CDs and Mn O₂ nanosheets.In the proposed system,Mn O₂ nanosheets could quench the fluorescence intensity of B,N-CDs through inner filter effect（IFE）.However,reductive GSH could reduce Mn（IV）of the Mn O₂nanosheets to Mn²⁺,accompanying the recovery of the fluorescence intensity of B,N-CDs.Moreover,when Ag⁺was added,the negatively charged sulfhydryl group of the GSH had a strong affinity with Ag⁺,inhibiting the reduction of Mn O₂nanosheets and the decrease in fluorescence of the probe.This strategy allowed the quantitative determination of GSH and Ag⁺with the linear range from 1.0–90.0μmol?L^-1and 0.91–70.0μmol?L^-1,and determination limit of 0.32μmol?L^-1and 0.24μmol?L^-1,respectively.The method was successfully used for the determination of GSH in serum and Ag⁺in tap water with satisfactory results.3.Ratiometric fluorescent probe for ascorbic acid determination based on Mn O₂nanosheets,gold nanoclusters and thiamineA ratiometric fluorescent probe was constructed by using Mn O₂ nanosheets,gold nanoclusters and thiamine.The fluorescence of Au NCs could efficiently be quenched by Mn O₂ nanosheets through fluorescence resonance energy transfer（FRET）,and Mn O₂nanosheets would oxidize non-fluorescent thiamine（vitamin B1,VB₁）to blue fluorescent thiochrome（ox VB₁）at the same time.While with the addition of ascorbic acid（AA）,Mn O₂ nanosheets were reduced to Mn²⁺and lose the oxidase-like property,accompanying with the increase fluorescence of the Au NCs and the decrease fluorescence of ox VB₁.Based on this phenomenon and the redox reaction between Mn O₂ nanosheets and AA,we have developed a sensitive ratiometric fluorescent method for AA determination.The proposed ratiometric fluorescent probe exhibited good linearity range of 1.5–100.0μmol?L^-1 and a low limit of determination of 0.45μmol?L^-1.