The Study On Electrochemiluminescence Mechanism And Applications Of Gold-Silver Bimetallic Nanoclusters

Electrochemiluminescence（ECL）is electrochemical redox induced radiative-charge-transfer at the electrode surface,in which luminophores can reach excited states via electrochemical redox induced charge transfer and then return to the ground state via light emission.ECL analysis is the combination of electrochemical and chemiluminescence methods.Therefore,ECL has been widely applied in biosensing applications,which has the advantages of the low background interference signal,wide detection linear range,high sensitivity,good selectivity,and controllable experimental process.Benefiting from their low toxicities and unique physicochemical properties,nanoclusters（NCs）are promising ECL luminophores.Although NCs are biocompatible for ECL bioassays,their low ECL efficiencies have hindered their possible application.Consequently,the development of electrochemiluminophores with high ECL efficiencies plays an important role in the research of ECL.In this paper,water-soluble Au-Ag bimetallic NCs（Au-Ag BNCs）with synergetic effects were synthesized via introducing Ag NO₃ into Au NCs and Au NCs-FW with aggregation-induced emission（AIE）was synthesized by introducing zinc acetate to Au₄（MHA）₄.As a new type of electrochemiluminophores,their ECL mechanisms were studied by electrochemical methods and ECL spectra.The main research contents are as follows:（1）For the first time,6-aza-2-thiothymidine（ATT）stabilized Au-Ag BNCs was synthesized as luminophore.By changing the molar amount of Ag NO₃,the Au-Ag BNCs with different Au/Ag molar ratios were explored in the PL and ECL properties.Experimental results showed that the Au-Ag BNCs at the optimal molar ratio exhibited a 54-fold enhancement in ECL and a 3-fold enhancement in photoluminescence（PL）compared to Au NCs.Moreover,the ECL spectra and spooling ECL spectra indicated that Au-Ag BNCs not only had the ECL process of bandgap-engineered at 520nm,but also produced a new radiative-charge-transfer route,i.e.surface-defect related ECL at710nm.The combined effects of the two ECL modes increase the total ECL intensity.This provides a strategy for screening new electrochemiluminophores.（2）Low-toxic,water-soluble and biocompatible Au-Ag BNCs were synthesized using methionine（Met）as a reducing agent.Compared with Au NCs,Au-Ag BNCs had a red-shifted PL emission and low PL intensity,and ECL intensity was improved by 5.8 times.Therefore,the synergetic effects between Au and Ag elements of Au-Ag BNCs were more favourable for promoting electrochemical redox induced ECL rather than photoexcitation induced PL.The ECL spectra collected by the ECL spectrometer with thermoelectric cooling showed that the ECL emission wavelength of Au-Ag BNCs was red-shifted to 900nm for the first time due to the synergistic effect and the surface-defect-related.Besides,the ECL was collected on a self-built electrochemical workstation,which applied to the detection of Hg²⁺ions.The ECL spectra of NCs in most aqueous media are located in the visible region,and Au-Ag BNCs with NIR ECL are of great significance for the realization of spectrum-resolved multiplexing ECL assay and biological imaging.（3）The co-reactants,buffer solutions,and working electrodes were optimized using Au NCs-FW with aggregation-induced emission（AIE）as luminophore.When Au electrode was used as the working electrode,the Au NCs-FW exhibited an ECL efficiency of about 10 times that of GCE.With N₂H₄·H₂O as the co-reactant,the Au NCs-FW not only exhibited the ECL process of bandgap-engineered at 483nm,but also induced a new ECL process by surface-defect related at 683nm;while triethylamine（TEA）was used as the co-reaction,the Au NCs-FW only had the ECL process of surface-defect related at 683nm.And the spooling ECL spectra further confirmed that the ECL process of the Au NCs-FW was controlled by co-reactants.As far as we know,this is the first time that co-reactant has been used to adjust the ECL process of water-soluble electrochemiluminophores,which is of great significance for the study of the ECL mechanism and the screening of luminophores.