A Study On The Synthesis And Application Of Polyethyleneimine-Templated Metal Nanoclusters

The synthesis and application of metal nanoclusters (such as gold, silver, and copper) have been stimulated extensive theoretical and experimental researches due to their remarkable optical and electronic properties different from those of the bulk materials and nanoparticles. Metal nanoclusters cover a wide range of properties like small size, photostability, biocompatibility, water solubility, high emission rates, and large Stokes shift. These merits make metal nanoclusters a good candidate for the application in biosensors, nanoelectronics, and novel catalysts. In this paper, two optical sensors for the detection of biothiols and copper (Ⅱ) based on silver nanoclusters have been designed, respectively. And one synthesis of copper nanoclusters capped with polyethyleneimine has been studied. The main contains are listed as follows:1. Sensitive and selective detection, of biothiols based on target-induced agglomeration of silver nanoclusters. In this work, a label-free biosensor for the sensing of biothiols such as cysteine, homocysteine, and glutathione based on the fluorescent probe, polyethyleneimine-capped silver nanoclusters, was presented. The selective binding of silver nanoclusters to biothiols promotes the silver nanoclusters agglomeration to yield larger non-fluorescent silver nanoparticles. And the fluorescence intensity of silver nanoclusters was quenched efficiently with increasing concentration of biothiols. The other amino acids introduced to the silver nanoclusters probe solution did not quench the fluorescence of the probe as they do not have thiol group which has strong affinity to the silver nanoclusters. A label-free, sample, and cost-effective biosensor for biothiols was developed. 2. Sensitive signal-on fluorescent sensing for copper ions based on the polyethyleneimine-capped silver nanoclusters-cysteine system. In this work, a label-free sensor for copper ions was presented. This sensor was composed of silver nanoclusters and cysteine. The fluorescence of the silver nanoclusters was quenched by cysteine, which was recovered in the presence of copper ions. This binding of silver nanoclusters with cysteine promotes the silver nanoclusters agglomeration to yield larger non-fluorescent silver nanoparticles. The presence of copper ions resulted in the oxidation of cysteine to form a disulfide compound, leading to recovery of fluorescence of the silver nanoclusters. The fluorescence intensity of the silver nanoclusters in the presence of cysteine increased with increasing concentration of copper ions over the range from10to200nM. And the detection limit of this sensor for copper ions was2.3nM. The silver nanoclusters-cysteine sensor provides a simple, cost-effective, and sensitive platform for the detection of copper ions.3. Synthesis of polyethyleneimine-templated fluorescent copper nanoclusters. A one-pot synthesis based on chemical reduction to obtain subnanometer-sized, extremely stable, and water soluble copper nanoclusters capped with polyethyleneimine was reported. The synthesis was performed by the reduction of copper ions with hydrazine in the presence of polyethyleneimine capping agent under atmosphere air. The synthesized copper nanoclusters were water soluble and very stable for at least one month without any obvious colloidal aggregation. The results demonstrated that the concentration of polyethyleneimine, the amount of reduce agent, reaction temperature, and reaction time played key roles for the formation of the copper nanoclusters. The prepared copper nanoclusters showed luminescence properties with a quantum yield of1.05%. And the excitation and emission maxima of the copper nanoclusters were at355and480nm, respectively.