Synthesis Of Fluorescent Nanomaterials And Their Applications In The Detection Of Small Molecules

Owing to the advantages of such as stable optical properties,high quantum yield,and good biocompatibility,fluorescent nanomaterials have been widely used in environmental detection,food detection and disease diagnosis.So,in this thesis,we have mainly investigate the synthesis of fluorescent silicon quantum dots(Si NDs)and glutaraldehyde(GA)non-conjugated chitosan polymer fluorophores(GCPF)and their applications in analysis of picric acid(PA)and glutathione(GSH).1.Water-dispersible Si NDs were synthesized by one-pot hydrothermal method using tetraethyl orthosilicate(TEOS)as the silicon source and trisodium citrate as the reducing agent.The maximum excitation wavelength of the Si NDs is at 347 nm,the maximum emission wavelengthis at 440 nm,and the fluorescence quantum yield is 18%.It can be used as a fluorescent probe to detect PA.Based on this,we designed a fluorescence quenching method for PA detection.It has a linear response in the concentration range of PA from 8 n M to 50?M with a limit of detection(LOD)of 0.92n M.This method has a fast response and good selectivity in PA detection.In addition,the synthesized Si NDs can be combined with cotton swabs to visually detect PA.The average recovery of spiked lake water samples is between 98.4%and 100.8%.2.At room temperature,a water-dispersible GCPF with a quantum yield of 16%was synthesized by a Schiff base reaction of chitosan and glutaraldehyde.The synthesized GCPF can be stably stored at 4°C for two months.Owing to the spectral overlap of fluorescent spectrum of GCPF and absorption spectrum of PA,it satisfies the characteristics of the fluorescence resonance energy transfer(FRET).Herein a fluorescence quenching method based on FRET principle for detecting PA is designed.The R₀ between donor GCPF and acceptor PA is calculated to be 3.5 nm.This method has a linear response in the PA concentration range of 10 n M to 50?M,high sensitivity(LOD of 2.8 n M),and fast response in 2 minutes.In addition,GCPF can be combined with a cotton swab or used as a solid GCPF to visually detect PA,which paves the way for the application of fluorescent GCPF in our daily life.3.Based on the principle of FRET,a“turn on”fluorescent sensing platform was developed.GCPF was used as a fluorescent probe to selectively detect GSH.Since the absorption spectrum of Mn O₂ nanosheets overlaps with the fluorescence emission spectrum of fluorescent GCPF,Mn O₂ nanosheets can quench the fluorescence intensity of fluorescent GCPF by FRET.In the presence of GSH,due to the reducing nature of GSH,the Mn O₂ nanosheets are reduced and decomposed into Mn²⁺ions,so that the quenched fluorescence intensity is enhanced again.Therefore,this sensing platform based on fluorescent GCPF and Mn O₂ nanosheets can be used for“turn on”fluorescent determination of GSH with a detection range from 0.5?M to 50?M,with LOD of 84n M.Other ions and biomolecules(such as L-lysine,L-threonine,L-valine,L-glutamic acid and DL-aspartic acid)do not interfere with the detection of GSH.This method is also used to detect GSH in serum samples with a recovery rate of 101.48%-103.23%,which indicates that the“turn on”fluorescent method platform has good accuracy in biological analysis.