Development And Analytical Application Of The Fluorescence Sensor Based On The N-doped Grapheme Quantum Dots

Graphene quantum dots(GQDs)are superior in terms of chemical inertness,resistance to photobleaching,low cytotoxicity,large surface area,fine surface grafting and excellent biocompatibility in comparison to conventional semiconductor QDs,thus making them promising in sensors,bioimaging,optoelectronic devices and so on.This paper introduced an easy,green,one-pot synthesis of nitrogen-doped graphene quantum dots(N-GQDs)was established by using citric acid and urea as carbon and nitrogen sources,respectively.The main contents are summarized as follows:1.The as-prepared N-GQDs are uniform with an average diameter of 4.7±0.60 nm.Because of the introduction of nitrogen atoms,N-GQDs exhibit excitation wavelength independent fluorescence with the maximum emission at 445 nm,and a high quantum yield is achieved at an excitation wavelength of 360 nm.Furthermore,a highly efficient fluorescence system based on the as-prepared N-GQDs was developed for the detection of Hg(?)because of the effective quenching effect of metal ions via nonradiative electron transfer.This system exhibits high sensitivity toward Hg(?)within a wide concentration range of 0.05–10 ?mol L-1,with a detection limit of 5.8 nmol L-1.The selectivity experiments reveal that the fluorescent sensor is specific for Hg(?).Most importantly,the practical use of the system based on N-GQDs for Hg(?)detection was successfully demonstrated in river-water samples with a recovery range of 96%–105%.2.A novel and highly sensitive fluorescence sensor,which was based on the recovered fluorescence of a N-GQDs–Hg(?)system,was developed for cysteine(Cys)detection.The fluorescence of N-GQDs was significantly quenched by Hg(?)because of the efficient electron transfer between N-GQDs and Hg(?).Subsequently,fluorescence was recovered gradually upon Cys addition to form a stable complex with Hg(?).The fluorescence sensor showed a response to Cys within a wide concentration range of 0.05–30 ?mol L-1,with a detection limit of 1.3 nmol L-1.The sensor was successfully applied to detect Cys in honey and beer samples,with a recovery range of 98%–105%.3.The dopamine-modulated N-GQDs system was explored to develop a fluorescent sensor based on chemical redox mechanism for the facile,sensitive and selective detection of glutathione(GSH)in biological samples.Dopamine could self-polymerize to poly dopamine-quinone and snap to the surface of N-GQDs to form a thin film in alkaline environment,leading to quenching of fluorescence due to fluorescence resonance energy transfer(FRET).Subsequently,GSH can reduce dopamine-quinone,and inhibit electron transfer process of N-GQDs and quinone,which result in the recovery of N-GQDs fluorescence.The fluorescence sensor showed a response to GSH within a wide concentration range of 0.20–85 ?mol L-1,with a detection limit of 43 nmol L-1.The sensor was successfully applied to detect GSH in human urine and serum samples with a recovery range of 96%–103%.