Unary Au Nanocrystal with Prestored Electrons and\nIntrinsic Low Hole-Injected Potential for Low-Triggering Potential\nElectrochemiluminescence

Screening\na novel electrochemiluminescence (ECL) system and lowering\nthe ECL triggering potential are essential to ECL evolution. Herein,\nthe near-infrared (NIR) ECL system with low-triggering potential ECL\nwas constructed with weakly reductive <i>tert</i>-butylamine\nborane as coreactant and mercaptosuccinic acid/citrate (MSA/Cit)-capped\nAu (MSA/Cit@AuNCs) as luminophores. Toxic-element-free and dual-ligand\nMSA/Cit@AuNCs were prepared via ligand exchange and utilized as a\nmodel for developing unary metal NCs-based luminophores with more\nenhanced ECL performance than monoligand Au nanocrystals (AuNCs),\nwhich exhibited a two hole-injected process at around 0.48 and 0.80\nV, respectively. Beneficial to the intrinsic low hole-injected potential\nof AuNCs, MSA/Cit@AuNCs exhibited similar low-triggering ECL potential\nat around 0.57 V with the participation of series coreactants or not,\noriginating from the recombination of an internal prestored electron\nwithin the conduction band (CB) and electroinjected holes at around\n0.25 V. Furthermore, the enhanced low-triggering potential around\n0.57 V and NIR ECL around 835 nm of MSA/Cit@AuNCs was eventually obtained\nwith the reductive <i>tert</i>-butylamine borane or N<sub>2</sub>H<sub>4</sub>·H<sub>2</sub>O containing a −C–N\nsingle-bond structure merely as coreactant. The low-triggering potential\nECL of MSA/Cit@AuNCs/<i>tert</i>-butylamine borane system\nat 0.57 V can be harnessed to selectively determine a carcinoembryonic\nantigen (CEA) with one linear range spanning from 2 to 20000 fg/mL\nand a limit of detection of 0.33 fg/mL (S/N = 3). This study will\ncontribute to a more comprehensive understanding of the ECL mechanism\nin terms of both regulating NCs and selecting coreactants.