Surface Ligand-mediated Control Of Optical Properties Of Gold Nanoclusters And Sensor Construction

Gold nanoclusters(Au NCs)are widely used in analytical-related field due to their small size,tunable emission range,high stability,and excellent water solubility.At present,some researches on investigates the structural composition of Au NCs and the adjustment of its optical properties have been resported.However,rapidly regulation optical properties and sensing performance of Au NCs through changing the surface ligands is still rare.The purpose of this thesis is to study the effect of surface ligands on the optical properties and the sensing performance of Au NCs.The inevstigation is carried out through three different ways including:adding,replacing and removing surface ligands.The detialed contents are as follows:In this chapter,three different Au NCs with excitation and emission wavelength have been synthesized.By introducing β-CD ligand on the surface of three Au NCs,the purpose of identifying and capturing nitrophenol isomers were achieved.Three different ligands and a cocapping ligand β-cyclodextrin(β-CD)has been constructed for the facile discrimination of three nitrophenol isomers.Compare with no-functionalized Au NCs,nitrophenol isomers were accurately distinguish by co-functionalized Au NCs sensor array.The sensing principle is based on the different binding affinities between β-CD and each nitrophenol isomer,as well as the distinct quenching efficiencies of the isomers on the fluorescence of each Au NCs.Finally,we obtained satisfactory result by appling this senor array in mixture,unkown and real samples.In this part of work,we first purposed the host-guest interaction combine with inner filter effect to identify small molecules,which demonstrate the surface ligands being very important for distingulishing and sensing filed.In this chapter,we discovered unusual solvent-mediated aggregation-enhanced emission(AEE)character of MUA-Au NCs.Au NC has weaker fluorescence in alcohol solution because of good dispersion.However,the suppressed emission was selectively enhanced in the presence of H2S because H2S was absorbed onto Au NCs through the strong sulfur-gold bonding affinity.Meanwhile,we found that introduct hydrophilic thiol ligand(GSH)on the surface of Au NCs can expand the H2S-induce fluorescence enhancement.Basic on this principle,GSH and MUA co-functionalization Au NCs have been designed and synthesized,and applied in H2S molecule fluorescence enhance sensing,with a detection limit as low as 35 nM,and sucessully achieved the H2S in humun serum sensing.In this work,we not only showed that MUA ligand modified Au NCs has the character of aggregation enhance emission,but aslo achieved the high selectivity and sensitivity sensing of H2S using this feature.In this chapter,using MUA-Au NCs as the model,under alkaline condition,we successfully achieved MUA ligand removal via micellization of cationic surfactants.Such a ligand removal resulted in the complete disappearance of absorption and fluorescence of Au NCs.During the micellization strong electrostatic force between of cationic surfactants and MUA ligand can breakage of Au-S bond and lead to desorption of MUA.Then,cationic surfactants quickly absorbed onto the surface of Au NCs,and stablized it in solution.The ligand exchange effect can only be achieved in presence of cationic surfactants with long carbon chain(>11 carbon atom)through stding different surfactants.Based on this phemonemon,the introduction of cetyl trimethyl ammonium bromide(CTAB)can quickly change MUA-Au NCs into CTAB-Au NCs.CTAB-Au NCs exhibited excellent antibacterial activity to Gram-negative bacteria because it has ultrahigh local positive charge desnsity.This work shows a novel ligand exchange strategy for achieving surface ligand of nanomaterials.