Electrochemiluminescence Of Copper Indium Sulfide Nanocrystals And Its Biosensing Application

Electrochemiluminescence(ECL)is a radiative charge transfer process from the excited states,which is generated via electrochemical redox reaction:ECL is superior to fluorescence in terms of sensitivity and signal-to-noise ratio due to absence of background from unselective photoexcitation.III-V and II-VI NCs contain either class A element(Cd,Pb,and Hg)or class B element(Se and As),their potential toxicity is a subject of serious concerns.Copper indium sulfide(CIS)nanocrystals(NCs)are a promising solution to the toxicity issue of Cd-and Pb-based NCs.This dissertation includes the following three parts:1.Electrochemical redox-induced radiative charge transfer in p-type CIS NCs was explored for the first time by electrochemiluminescence(ECL).The CIS NCs displayed a weak reductive process for injecting electrons into the conduction band(CB)and four strong oxidative processes for injecting holes into the valence band(VB).Potential-resolved ECL demonstrated that the electrochemically injected CB electrons were stable in the CIS NCs and could recombine with Cu2+ defects(preexisting in the CIS NCs and/or generated via electrochemically oxidizing the CIS NCs)for radiative charge transfer in the CIS NCs.Annihilation ECL confirmed that all the highly mobile VB holes generated via electrochemical oxidation at different potentials could be rapidly re-localized by Cu+ to form Cu2+ defects and then couple with electrochemically injected CB electrons for near-infrared ECL of the same excited states.Coreactant ECL demonstrated that simultaneously injecting VB holes and CB electrons into CIS NCs could improve their radiative charge transfer efficiency for efficient ECL.The CIS NCs are promising electrochemiluminophores;ECL provides an effective alternative for investigating radiative charge transfer in CIS NCs upon photoexcitation.2.Copper indium sulfide(CuInS2,CIS)nanocrystals(NCs)are a promising solution to the toxic issue of Cd-and Pb-based NCs.Herein,electrochemiluminescence(ECL)of CIS NCs in aqueous medium is investigated for the first time with L-glutathione and sodium citrate-stabilized water-soluble CIS/ZnS NCs as model.The CIS/ZnS NCs can be oxidized to hole-injected states via electrochemically injecting holes into valence band at 0.55 and 0.94 V(vs Ag/AgCl),respectively.The hole-injected state around 0.94 V can bring out efficient oxidative-reduction ECL with a similar color to Ru(bpy)32+ in the presence of tri-n-propylamine(TPrA)and enable CIS/ZnS NCs promising ECL tags with L-glutathione as linker for labeling.The ECL of CIS/ZnS NCs/TPrA can be utilized to determine vascular endothelial growth factor(VEGF)from 0.10 to 1000 pM with the limit of detection at 0.050 pM(S/N = 3).Although the hole injected state around 0.55 V is generated ahead of oxidation of TPrA and fails to bring out coreactant ECL,annihilation ECL proves that both hole-injected states generated,at 0.55 and 0.94 V,can be involved in electrochemical redox-induced radiative charge transfer by directly stepping CIS/ZnS NCs from electron-injecting potential to hole-injecting potential.CIS/ZnS NCs are promising nontoxic electrochemiluminophores with lowered ECL triggering potential around 0.55 V for less electrochemical interference upon the development of coreactant.3.Copper indium sulfide(CIS)nanocrystals(NCs)are a promising solution to the toxicity issue of Cd-and Pb-based NCs.The CIS/ZnS NCs can be oxidized to hole-injected-states(Ox1 and Ox2)via electrochemically injecting holes into valence band at 0.55 V and 0.94 V(vs Ag/AgCl)in Tris-HCl buffer solution.The hole-injected-states Oxl can bring out efficient oxidative-reduction ECL with ultra-low electrochemiluminescence(ECL)emission potential in the presence of N2H4 H2O.CIS/ZnS NCs are promising non-toxic electrochemiluminophores with ultra-low ECL triggering potential around 0.52 V for less electrochemical interference.