| Electrochemiluminescence(ECL)is a phenomenon,in which luminophores reach excited states via electrochemical redox reaction on the electrode surface and then return to the ground state via light emission.Benefiting from the advantages of low background,high sensitivity,wide sensing dynamic range and simple equipment requirements,ECL technology has been widely used in biosensing,environmental monitoring,food safety and disease diagnosis.All the commercialized ECL bioassays are performed at a high triggering potential of+1.4 V(vs.Ag/AgCl)to trigger the emission from tris(bipyridyl)rutheni1m(Ru(bpy)32+)/tri-n-propylamine(TPrA),which is limited by high triggering potential as well as the toxic and exogenous effects of coreactant.To overcome the limitation of high ECL-potential as well as the toxic and exogenous effects of coreactant from nanoparticles(NPs),herein,the ECL nature of metal nanoclusters(NCs)are systematically explored to achieve efficient low-potential and coreactant-free ECL of NCs for bioassays.Specific work is as follows:1.A valence-state engineering strategy is developed to adjust NCs ECL with bovine serum albumin(BSA)-capped AuNCs as model,in which engineering the valence-state of Au body element,i.e.Au(0)and Au(Ⅰ),is performed via successively reducing the Au(Ⅲ)of precursor AuCl4-to Au(Ⅰ)and Au(0)with BSA.Using hydrazine hydrate(N2H4)as a coreactant,BSAAuNCs can give off three anodic ECL processes around 0.37(ECL-1),0.85(ECL-2),and 1.45 V(ECL-3)respectively.Valence state involved particle growth,internal electronic structure and ECL from AuNCs are investigated,and the mechanism of the low-potential ECL from AuNCs is explored.Upon successively engineering the valence-state of body element Au,BSA-AuNCs exhibit successively changed and four different internal structure,which can be employed to selectively generated and/or quench three different anodic ECL processes,and turn the generation of ECL emission from high-triggering-potential to low-triggering-potential as well as from bandgap engineered route to surface-defect-involved route.This strategy not only can be exploited to engineer both the body element valence and internal structure of AuNCs for tunable ECL emission,but also provided that Au(0)is crucial to achieve efficient and lowtriggering-potential ECL from AuNCs.2.A low-potential ECL system(740 nm)with onset potentials of 0.0 V as well as the maximum emission potential of around 0.37 V is constructed using BSA-AuNCs as ECL reagent and N2H4 as coreactant,and the feasibility of using BSA-AuNCs as ECL tags for constructing low-potential ECL immunosensor is verified.The influence of the synthesis condition and dispersion state of BSA-AuNCs as well as coreactants on the low-potential ECL of BSA-AuNCs/coreactants system are systematically explored,and the mechanism of lowpotential ECL emission is proposed.BSA-AuNCs can be utilized as ECL tags to perform sandwich-typed immunoassay with acceptable sensitivity and selectivity,which exhibits a wide linear response for determining carbohydrate antigen 125 from 0.5 mU/mL to 1000 mU/mL and the limit of detection(LOD)of 0.05 mU/mL(S/N=3).The low-potential ECL of BSAAuNCs/N2H4 system can effectively reduce electrochemical interference in ECL assays and improve the performance of ECL analysis.3.A series of carboxylated CuNCs are prepared using thiol compounds as surface ligands,the effects of thiol-capping-agents on ECL of thiol-CuNCs/TPrA system is systematically explored,and a promising strategy to achieve low-potential coreactant ECL is proposed around 0.95 V using cysteine(Cys)-capped CuNCs as ECL reagent.Cys-CuNCs can be inject valence band(VB)hole through the electrochemical oxidative processes around 0.55 and 0.85 V,and then couple with the electrons injected from TPrA around 0.60 V(vs.SCE),which eventually enabled two synchronous ECL processes around 0.95(ECL-1)and 1.15 V(ECL-2).A lowpotential ECL immunosensor is developed by employing CuNCs as ECL tags,both ECL-1 and ECL-2 of the Cys-CuNCs/TPrA system can be used for selective and sensitive detection of carcinoembryonic antigen with a linear range of 0.05 pg/mL to 500 pg/mL and LOD of 0.01 pg/mL(S/N=3).The prepared ECL immunosensor has excellent selectivity and stability,and can achieve detection of actual samples.4.An n-type AuAg bimetallic nanocluster(AuAgBNCs)is prepared with 4-amino-2(methylthio)pyrimidine-5-carboxylic acid as the surface ligand using an element doping strategy,and a low-potential coreactant-free ECL of water-soluble AuAgBNCs is achieved around 0.8 V.Based on the rich-electron nature of n-type NPs,AuAgBNCs can inject holes through an electrochemical oxidation process around 0.8 V,and the exogenous hole can directly combine the conduction band(CB)electron of AuAgBNCs,resulting in coreactant-free ECL around 0.8 V without employing any exogenous coreactant.The influence of experimental conditions such as Au/Ag element ratio on the low-potential coreactant-free ECL of AuAgBNCs is systematically investigated,and the mechanism of low-potential coreactant-free ECL mechanism is proposed.A low-potential coreactant-free ECL immunosensor is developed by employing AuAgBNCs as ECL tags,which can be utilized to sensitively detect prostatespecific antigen with a linear range of 0.5 pg/mL to 1000 pg/mL and LOD of 0.1 pg/mL(S/N=3).The prepared low-potential coreactant-free ECL immunosensor has excellent selectivity and anti-interference.The low-potential coreactant-free ECL route avoids the toxicity and exogenous interference of coreactants,reduces electrochemical interference,simplify the ECL experimental process,and improves ECL analysis performance.5.A kind of water-soluble AgNCs coated with multiple ligands is prepared by ligand exchange strategy,which exhibit the nature of n-p type NPs rich CB electrons and VB holes.AgNCs can be inject holes via electrochemical oxidative process,and the exogenous hole can directly combine the CB electron of AgNCs,resulting in anodic coreactant-free ECL at around 0.75 V without the participation of any coreactant,and AgNCs can also inject electrons via electrochemical reduction process,and exogenous electron can directly combine VB hole of AgNCs to produce a cathodic coreactant-free ECL at around-1.35 V.The influence factors of the low-potential coreactant-free ECL form AgNCs is systematically investigated,and a new mechanism for achieving low-potential coreactant-free form ECL emission is proposed.Because the emission intensity of anodic coreactant-free ECL is about 12 times that of cathodic coreactant-free ECL,a low-potential coreactant-free ECL immunosensor is developed by employing AgNCs as ECL tags,which can be utilized to sensitively detect alpha-fetoprotein antigen with a linear range of 0.5 pg/mL to 100 pg/mL and LOD of 0.05 pg/mL(S/N=3).The low-potential coreactant-free ECL system not only effectively avoid electrochemical interference as well as avoid the toxicity and exogenous interference of coreactants,but also opens promising avenues to develop new ECL systems. |
