Construction And Application Of Fluorescent Sensor For Histidine And Glucose Based On Sulfur Quantum Dots

Sulfur quantum dots（SQDs）have shown great application potential in the fields of sensing analysis,bioimaging,photoelectrocatalysis,and light-emitting devices due to their excellent optical properties,good water solubility,low toxicity,and biocompatibility.Metal ions,biological small molecules and active oxygen participate in various physiological adjustments of the human body and are important substances in the human body.In this paper,two kinds of SQDs were synthesized with different modifiers,and proportional fluorescent probes were respectively constructed for the detection of Ni²⁺,histidine,H₂O₂and glucose.The specific research contents are as follows:1.Using sulfur powder as raw material,polyethylene glycol-400（PEG-400）as modifier,reacted in alkaline environment for 72 h,and further etched by H₂O₂,finally obtained blue fluorescent PEG-SQDs.Orange carbon dots（CDs）were synthesized by a simple solvothermal method using urea and citric acid as starting materials and N,N-dimethylformamide（DMF）as solvent.The morphology,optical properties,surface groups and elemental composition of PEG-SQDs and CDs were explored by transmission electron microscopy（TEM）,ultraviolet-visible（UV-Vis）spectroscopy,fluorescence spectroscopy,Fourier transform infrared（FT-IR）spectroscopy,X-ray photoelectron spectroscopy（XPS）.The SQDs and CDs solutions were mixed to construct a ratiometric fluorescent sensing system.After adding Ni²⁺,based on the combined mechanism of static and dynamic quenching,Ni²⁺combined with CDs rapidly.Under the excitation wavelength of 360 nm,the fluorescence of CDs at 620 nm was quenched,and the fluorescence of SQDs at 445 nm was almost unaffected.The fluorescence intensity ratio I₆₂₀/I₄₄₅ decreases with the increase of Ni²⁺,which can be used to detect Ni²⁺.In the range of 0.25-22.5μmol/L,I₆₂₀/I₄₄₅ showed a good linear relationship with Ni²⁺concentration,and the limit of detection（LOD）was0.17μmol/L.In the SQDs/CDs+Ni²⁺system,when histidine was added,Ni²⁺quickly combined with histidine,and the fluorescence of CDs recovered,which was used to detect histidine.The linear range is 1-50μmol/L,and the LOD is 0.77μmol/L.In addition,there is an obvious solution fluorescence color change in the system for visual detection of histidine.By exploring the influence of interfering substances,the ratiometric fluorescent probes showed high selectivity for the detection of His.The feasibility of this system in real samples of human urine and bovine serum was verified by the addition method.This method is expected to be used for the rapid and sensitive detection of histidine in clinic.2.Using sulfur powder as raw material and ethylenediamine as solvent,EDA-SQDs were synthesized by solvothermal method.The morphology,optical properties,surface groups,and elemental composition of EDA-SQDs were explored through a series of characterizations（TEM,UV-Vis,FL,FT-IR,and XPS）.Under the catalysis of I^-,H₂O₂promotes the oxidation of o-phenylenediamine（OPD）to produce yellow fluorescent 2,3-diaminophenazine（DAP）.Due to the inner filter effect（IFE）,DAP can reduce the intrinsic fluorescence intensity of SQDs（425 nm）.The ratio I₅₈₀/I₄₂₅ of the yellow fluorescence emission intensity of DAP to the blue fluorescence emission intensity of EDA-SQDs has a linear relationship with the concentration of H₂O₂.The linear range is 1-500μmol/L,and the LOD is 0.14μmol/L.The ratio of H₂O₂ is established Fluorometric method.The newly generated DAP has an obvious ultraviolet absorption peak at 420 nm,and the H₂O₂ level can be measured by colorimetry,with a linear range of 1-400μmol/L and an LOD of 0.56μmol/L.Under the catalysis of glucose oxidase（Gox）,glucose is oxidized to generate H₂O₂,so this sensing platform can be used for fluorescence/colorimetric dual-mode detection of glucose level.The linear range of the ratiometric fluorescence method is 1-1000μmol/L,and the LOD is 0.69μmol/L.The linear range of the colorimetric method is 5-1000μmol/L,and the LOD is 3.49μmol/L.In addition,the color of the system changes during the detection process,and this dual-modal approach（proportional fluorescence and colorimetry）can be combined with smartphone imaging to achieve visual detection of glucose content.