Study On Synthesis And Application Of Silver Nanoclusters And Maillard Reaction Fluorescent Products Based On Glutathione

Glutathione?GSH?is one of small molecular peptides with sulfhydryl group and g-amide bond,and it exists extensively in organisms and is involved in lots of physiological actions.Because GSH possesses reducibility and antioxidant effect,it in organisms can protect cell and nerve from injury of oxygen-free radicals.Moreover,GSH contains various functional groups,such as amino,carboxy,sulfhydryl and acylamino groups,which makes it a chelating agent of many metal ions.The sulfhydryl group of GSH can interact with heavy metal ions,especially for the Au and Ag,therefore,GSH can be used as a template for synthesis of Au or Ag nanoclusters.Accordingly,we first use GSH as an etching agent to synthesiz blueemitting Ag nanoclusters from the citrate-coated Ag nanoparticles.In addition,GSH is a typical amino compound,and can react with carbonyl compounds to perform Maillard reaction,so in this paper,we further prepare the Maillard reaction fluorescent products based on the Maillard reaction of GSH and ascorbic acid.At the same time,combining with the fluorescence and UV-vis spectra analysis technique,we study the optical property and application of the Ag nanoclusters and Maillard reaction fluorescent products in aqueous solutions,and establish the optical sensors to detect the biomolecules and environmental pollutants.1.Synthesis of Ag nanoclusters based on glutathione as an etching agentStable and blue-emitting Ag nanoclusters have been successfully prepared,and the citrate-coated Ag nanoparticles and GSH are used as precursor and etching agent,respectively.The average diameter of as-prepared Ag nanoclusters is about 1.93 nm,and the fluorescence quantum yield of the Ag nanoclusters is about 1.8% in aqueous sulutions.In the experiments,the best proper amounts of Na BH4,citrate,and GSH have been investigated by fixing the addition amount of Ag NO3 in the synthesis process?Moreover,the entire etching process from large Ag nanoparticles to small Ag nanoclusters has been monitored with fluorescence spectra,UV-vis absorption spectra,and high resolution transmission electron microscopy.The as-prepared Ag nanoclusters have been characterized by the Fourier transform infrared spectra,the energy dispersive X-ray spectrum and element analysis technique.2.Establishment of the optical urea and glucose sensors based the p Hswitchable Ag nanolcustersIn this paper,increased and decreased p H can cause the Ag nanolcusters to switch between agglomeration and dispersion,accompanied by decreases in and recoveries of fluorescence intensity and absorbance.The p H switchable behavior of the Ag nanolcusters is attributed to carboxyl groups on the nanocluster surface that are rich in the citrate and amido functional groups of ligands?glutathione?,creating an easily formed,weak molecular interaction among Ag nanolcusters?for example,hydrogen bonding?,and maintaining a balance in the colloidal solution,whereas a change in p H will disrupt the balance,leading to the reversible agglomeration of Ag nanolcusters and the switchable spectral signal response.In addition,because urea and glucose can change the p H of a solution by producing NH3 and gluconic acid in enzyme-catalyzed reactions,the p H-switchable behavior of the Ag NCs is used for developing them as an optical probe to establish a regenerated biosensing platform for the sensitive and selective detection of urea and glucose,and the test results are satisfactory.3.Establishment of the selective and sensitive dissolved ammonia sensor based on the Ag nanoclusters and headspace-single drop microextraction techniqueIn this paper,a simple sensor platform is presented for highly selective and sensitive detection of dissolved ammonia in aqueous solutions based on fluorescence and UV-vis spectrophotometry,and headspace-single drop microextraction technique with the Ag nanoclusters from etching method as the probe.The sensing mechanism is based on the volatility of ammonia gas and the active response of Ag NCs to p H change caused by the introduction of ammonia.High p H can make the Ag NCs agglomerate and lead to the obvious decrease of fluorescence intensity and absorbance of Ag NCs solution.Moreover,the presented method exhibits a remarkably high selectivity toward dissolved ammonia over most of inorganic ions and amino acid,and shows a good linear range of 10 – 350 ?M with a low detection limit of 336 n M at a signal-to-noise ratio of 3.In addition,the practical applications of the sensor have been successfully demonstrated by detecting dissolved ammonia in real samples.4.Preparation of the Maillard reaction fluorescent product from glutathione and ascorbic acid for rapid and label-free dual detection of Hg²⁺ and biothiolsMaillard reactions and their fluorescent products have drawn much attention in the fields of food and life science,however,the application of fluorescent products separated from the reaction as an indicator for detection of certain substances in sensor field has not been mentioned.In this article,we report on an easy-tosynthesize and water-soluble fluorescent probe separated from the typical Maillard reaction products of glutathione and ascorbic acid,with excellent stability and high quantum yield?18.2%?.The further application of the probe has been explored for dual detection of Hg²⁺ and biothiols including cysteine,homocysteine,and glutathione,which is based on Hg²⁺-induced fluorescence quenching of the Maillard reaction fluorescent products and the fluorescence recovery as the introduction of biothiols.This sensing system exhibits a good selectivity and sensitivity,and the linear ranges for Hg²⁺,cysteine,homocysteine,and glutathione are 0.05 – 12,0.5 – 10,0.3 – 20,and 0.3 – 20 ?M,respectively.The detection limits for Hg²⁺,cysteine,homocysteine,and glutathione are 22,47,96,and 30 n M at a signal-to-noise ratio of 3,respectively.Furthermore,the practical applications of this sensor for Hg²⁺ and biothiols determination in water samples and human plasma sample have been demonstrated with satisfactory results.5.Bio-friendly Maillard reaction fluorescent products from glutathione and ascorbic acid for the selective detection of Fe³⁺ in living cellsDeveloping probes with good biocompatibility and realizing intracellular detection in living cells are of great significance for biomedicine and life sciences,but remain a challenge presently.In this paper,we describe a rapid and highly selective biosensor for Fe³⁺ detection in living cells based on the Maillard reaction fluorescent products?MRFPs?of glutathione and ascorbic acid as a probe. Experiments show that the MRFPs are non-cytotoxic and possess excellent biocompatibility.Moreover,the MRFPs show a rapid response and good selectivity towards Fe³⁺ over other metal ions under physiological p H conditions in vitro.The introduction of Fe³⁺ can quench the fluorescence of MRFPs,and the fluorescence intensity of system decreases linearly with the increasing concentration of Fe³⁺ in the range of 0.05 – 50 m M with the detection limit of 4.6 n M at a signal-to-noise ratio of 3.Moreover,the recognition mechanism has been discussed,which is attributed to the charge transfer from excited-state MRFPs molecules to metal ions.In addition,the MRFPs have been successfully demonstrated to be a good imaging probe for Fe³⁺ sensing in living cells.