Luminescent Property Improvement Of Metal Nanocluster And The Intrinsic Mechanism

Metal nanoclusters(NCs)have attracted great interests in past decades due to their excellent properties as ultra-small size,controllable emission range,high stability and water solubility,good biocompatibility and so on.They have been extensively used in small-molecules detection and fluorescence bio-imaging both in vitro and in vivo.Given that the quantum yields(QY)of them are still not competitive in comparison to those of quantum dots and/or organic chromophores,great efforts have been paid to improve their luminescence.On account of that,two supramolecular strategies,non-covalent interaction-based fluorescence resonance energy transfer(FRET)and ligand aggression induced emission enhancement(AIEE),are reported in the present study.Firstly,we have constructed a FRET assembly between the glutathione capped gold nanoclusters(AuNCs@GSH)and polyethyleneimine(PEI)based carbon dots(CDs),Which greatly enhance the emission of AuNCs@GSH.Given that charge of CDs is positive while charge of AuNCs@GSH is negative,they can assembly via electrostatic interactions.After assembly,energy of CDs can transfer to AuNCs@GSH by non-radiative pathway,where transfer efficiency is 65.7%.The quantum yields of AuNCs@GSH increase from 3.07% to 5.35%.The FRET assembly is further used to detect Cysteine(Cys).Due to the Quantum yields improvement,compared with existed methods,it exhibits advantages in detection limits(100 nM)and sensitivity.Secondly,an AIEE assembly is constructed between the adenosine monophosphate capped bimetallic nanoclusters(Au-AgNCs@AMP)and polyethylenimines(PEI).The QY of Au-AgNCs@AMP is largely improved from 8.64% to 25.02%via the assembly.This process contains two steps.In the first stage,they assembly together via electrostatic interactions,in which the radiative irradiation is greatly enhanced.In the second stage,they form micelle-like structures.During this process,the non-radiative transition of Au-AgNCs@AMPis suppressed.Finally,the fluorescence performance of Au-AgNCs@AMPis greatly enhanced.The QYs increase from 8.64% to 25.02%.