Controllable Fabrication,Luminescence Properties And Sensing Applications Of Thiolate-Protected Gold Nanoclusters

Luminogens with aggregation-induced emission(AIE)property have arouse wild attention in recent years.Except for the well-known organic AIEgens like hexaphenylsilole and tetraphenylethene,a novel kind of long-lived luminescent metal nanoclusters have been discovered to possess similar aggregation-induced emission behavior.These metal nanoclusters mainly consisting of gold,silver,and copper nanoclusters,and compared with those organic AIEgens,these metal nanoclusters have some merits such as facile preparation,good water-solubility,satisfied optical property,and make those specific metal nanoclusters widely used in bioimaging and biosensors.The poor stability of copper nanoclusters and disappointing low quantum yield of silver nanoclusters limit their applications to a great extent.Gold nanoclusters(AuNCs)exhibit its superiority such as excellent stability,highly luminescence efficiency,red emission.Thiolate-protected gold nanoclusters can be served as not only a stable luminogen but also show specific AIE property.Thiol-containing ligand was selected as both reductant and protecting ligand for the synthesis of AuNCs due to the intense Au-S bond between Au core and thiol-containing capping ligand.In addition,the synthesis process of AuNCs with AIE property is quite simple compared to those AuNCs protected by DNA oligonulceotides,proteins and peptides.The synthesis process need no expensive equipment and complicated operations,which further guarantees the real application of those metal materials.Now the study of AuNCs is mainly concentrated in macromolecular synthesis of gold nanoparticles cluster and its application in biological detection,imaging,but the luminescence performance research of AuNCs with AIE behavior and application of this nature is still in its early stages.In this dissertation,we proposed a facile synthesis to prepare stable luminescent AuNCs/Au complex,and lipoic acid,glutathione,dithiothreitol were selected as protecting ligand respectively.The prepared Au/Ag NCs was employed as a luminescent sensing platform for the real-time monitoring of tyrosinase activity;glutathione capped Au complex was used for sensitive measurement of aluminum species;and dithiothreitol protected AuNCs was devoted to the detection.of molecular oxygen.Besides,we developed a novel method for fabrication of AuNPs with highly quantum yield through rigidifying AuNCs.The main contents are as follows:(1)Brightly luminescent Au/Ag NCs were prepared via a facile one-step synthesis in aqueous solution,and dopamine-modified Au/Ag NCs were synthesized using dopamine and Au/Ag NCs through amide formation reaction.This sensor based on dopamine-modified Au/Ag NCs keep stable when there exists no oxidizing substances in the detection system.However,in the presence of molecular oxygen,dopamine moiety can be readily oxidized into o-dopaquinone derivative under the catalysis of tyrosinase.Due to the electron-deficiency property of o-dopaquinone,an efficient intraparticle photoinduced election transfer(PET)process could occur between Au/Ag NCs and o-dopaquinone moiety in the bioconjugate,which results in fluorescence quenching of the nanoprobe.The correlation between tyrosinase activity and fluorescence signal can be used for quantitative detection of tyrosinase activity.The detection limit for tyrosinase activity based on three standard deviations was calculated to be 13.5 U/L,and this study illustrates that gold/silver nanoclusters and o-dopaquninone can served as a good electron donor/acceptor pair.In addition,this Dopa-Au/Ag NCs-based assay provides another way to monitor tyrosinase level,and promise a great potential in medical diagnosis of tyrosinase-associated diseases.(2)Au-GSH-complex with.significant ATE property was prepared-using glutathione as reductant and capping ligand.The as-prepared Au complex(Au-GSH complex)exhibit good water-solubility and weak luminescence in neutral condition.In this work,its response to multiple external stimuli such as solvent polarity,pH,temperature,and cation coordination were first evaluated.Based on the coordinate bonding-induced emission property,Au-GSH complex was applied as chemical sensor for two aluminum species including aluminum cation and polyoxocation AlO4Al12(OH)24(H2O)127+(AL13).Under the introduction of a masking agent(mercaptoacetic acid),Au-GSH complex can selectively detect A13+ in alkaline condition.Au-GSH complex shows ultrahigh sensitivity toward AL13 at acidic condition.The detection limit for two aluminum species were 0.1 ?M and 13.2 nM,respectively.This work not only evaluates the multi-stimuli responsiveness of Au-GSH complex,but also establishes new detection methods for alumimum species based on gold complex with AIE characteristic,which makes progress in environmental monitoring.(3)Thiol-functionalized AuNCs was synthesis in a facile way.We report a novel luminescence turn-on detection strategy for molecular oxygen via the specific oxygen-triggered bonding-induced emission of thiol-functionalized AuNCs.In this work,The emission enhancement efficiencies induced by bonding-induced emission(BIE)and aggregation-induced emission(AIE)processes are compared and discussed.According to this experiment,it is evident that luminescence enhancement induced by the bonding-induced emission process is much more efficient than that caused by physical aggregation-induced emission process.This specific redox-triggered BIE is capable of quantitatively detecting dissolved oxygen in aqueous solution in a light-up manner,and trace amount of dissolved oxygen at ppb level is achieved based on this detection method.A facile and convenient test strip for oxygen detection was also developed to monitor molecular oxygen in a gas matrix.(4)A novel synthesis and functional method of luminescent AuNCs with highly quantum yield was established via hydrolyzing silyl-functionalized AuNCs.Silyl-functionalized AuNCs was synthesized in organic phase without water.Silica shell formed and encapsulated AuNCs by hydrolyzing silyl group and make them cross-linking just on the surface of AuNCs.Under similar hydrolyzing process,thiol-functionalized AuNCs can be obtained.As-prepared thiol-functionalized AuNCs exhibit highly luminescence,and the quantum yield of thiol-functionalized AuNCs is 19.78%.This highly luminescent AuNCs proved a basis for developing sensitive fluorescent probes of further use.To sum up,we first developed the bioenzyme probe using the stable optical properties of AuNCs,and successfully realized the real-time detection of tyrosinase activity.Second,the specific aggregation induced emission effect and its stimuli responsiveness of Au complex have been further studied.At the same time,Au complex was applied as chemical sensor for two aluminum species.Thirdly,a novel AuNCs probe was developed based on dynamic covalent disulfide bond to detect molecular oxygen.The formation of disulfide bonds enables the aggregation of AuNCs,then enhance the phosphorescence signal and a quantitative relationship can be established between luminescence signal and oxygen concentration.Meanwhile,oxygen test paper is developed for qualitative detection of gaseous oxygen.In the end,the rigidifying process of the surface ligand on AuNCs was used to improve the quantum yield of AuNCs,and the AuNCs with small particle size,good water solubility and high quantum yield were synthesized based on its bonding induced emission property.The AuNCs can not only be used as a stable fluorophore for biosensing,but also can be used to detect the chemical molecules by using the bonding induced emission mechanism.