Monochromatic,Low-Potential,and Coreactant-Free Electrochemiluminescence With Nanoparticles As Emitters

Electrochemiluminescence(ECL)is the light emission triggered by electrochemical redox reactions.The molecular ECL system with tris(bipyridyl)ruthenium(Ru(bpy)32+)as luminophore and tripropylamine(TPrA)as coreactant,i.e.,Ru(bpy)32+/TPrA,has been extensively utilized in commercially available ECL bioassays.Developing novel ECL luminophores and systems,which are potentially superior to Ru(bpy)32+/TPrA system,is strongly anticipated for ECL evolution.As the performance of Ru(bpy)32+/TPrA system is limited by its high triggering potential(～1,20 V vs.Ag/AgCl),confined waveband of red region(-620 nm),as well as the toxic and exogenous effects of coreactant,herein,nanoparticles are successfully utilized as ECL luminophores to achieve ECL with a changed waveband to near infrared region Ⅱ(NIR-Ⅱ),a lower triggering potential to 0.55 V vs.Ag/AgCl,as well as a coreactant-free route for simplified operating procedure and setups.1.Developing monochromatic ECL of longer wavelengths,especially monochromatic NIR-II ECL with wavelengths beyond 900 nm,is highly demanded for ECL evolution.By extensively exploiting the red-shifting nature of surface-defect-induced ECL to bandgapengineered ECL of nanoparticles,surface-defect-induced NIR-Ⅱ ECL with a single emission peak around 915 nm is achieved by employing methionine capped Au-Ag(Met@Au-Ag)bimetallic nanoclusters(BNCs)as luminophores and triethanolamine as a coreactant.Not only effect of synthesizing conditions,such as Au/Ag element ratio and pH of precursors,on the ECL wavelengths of Met@Au-Ag BNCs are extensively explored,but also charge transfer mechanism of the monochromatic NIR ECL from Met@Au-Ag BNCs is discussed.A spectrum-resolved monochromatic NIR-Ⅱ ECL immunosensor is developed by employing Met@Au-Ag BNCs as ECL tags,which could sensitivity and selectively determine carcinoma antigen 125.2.Coreactants of a low oxidative potential play an important role in developing oxidative-reduction ECL systems with low-triggering-potential for less electrochemical interference.By effectively exploring the reductive and low oxidative potential nature of N2H4·H2O,an efficient ECL system of low triggering potential with nanoparticle as emitters is developed by employing CuInS2/ZnS(CIS/ZnS)nanocrystals(NCs)as luminophore and N2H4·H2O as coreactant.Glutathione and citrate capped CIS/ZnS NCs can be electrochemically injected with valence band hole at around 0.46 and 0.87 V,and then couple with the electrons injected from the N2H4·H2O around 0.10 V,which eventually enabled two efficient near-infrared ECL processes at 0.55 and 0.87 V.All the holes injected at different electrochemical oxidative potentials can be involved in the same internal Cu(Ⅰ)/Cu(Ⅱ)couple cycling within CIS/ZnS NCs,and enable surface-defects-invovled ECL of the same excited states.The low-potential ECL process around 0.55 V from CIS/ZnS NCs/N2H4 system is around 731 nm,and can be utilized to sensitivity determine Cu2+ ion.3.Screening universal low-triggering-potential ECL system is anticipated for ECL evolution towards high electrode compatibility as well as less electrochemical interference.A low-potential strategy is developed by employing the environmental-friendly carbohydrazideas a coreactant,which can enable serial luminophores with oxidative-reduction ECL at one similar low-triggering potential around 0.55 V,including Ru(bpy)32+as well as CdTe,CdSe,CIS/ZnS NCs,and Au nanoclusters.Because the eight-electron releasing process of carbohydrazide can be electrochemically triggered at～0.25 V versus Ag/AgCl,the radicals generated via electrochemical oxidation of carbohydrazide could reduce the luminophores at a much lower potential than those of traditional coreactants.The maximum emission wavelength of these low-triggering-potential ECL is ranged from green light region(540 nm)to near infrared I region(783 nm)via the selection of luminophores.4.The coreacant-free ECL generated via merely oxidizing the luminophores would break through the ceiling of coreactant ECL via excluding the detrimental effects of potential toxic and exogenous coreactant.By exploiting the rich-electron nature of n-type nanoparticles,coreacant-free ECL is achieved via merely oxidizing 3-mercaptopropionic acid(MPA)and mercaptosuccinic acid(MSA)capped InP/ZnS NCs,i.e.,InP/ZnSMPA-MSA,The influencing factors on the coreactant-free ECL are discussed,and the mechanism of the coreactant-free ECL is explored.The coreactant-free ECL can be utilized for coreactant-free ECL immunoassay with prostate-specific antigen as analyte and InP/ZnSMPA-MSA as tags.The coreactant-free ECL route would avoid the toxicity and exogenous interference of coreactants,simplify the ECL assay procedure,and improve analysis efficiency.