Ligand-Based Shielding Effect Induced Efficient Near-Infrared Electrochemiluminescence of Gold Nanoclusters and Its...

Preparing high-efficiency ECL gold nanoclusters (Au NCs) still faces a serious challenge due to the poor stability of co-reactant radicals in aqueous media. Herein, we report a ligand-based shielding effect induced record near-infrared (λ_max = 786 nm) ECL efficiency of β-cyclodextrin-protected Au NCs (β-CD-Au NCs) with triethylamine (TEA) as co-reactant. The ligand of β-CD-Au NCs with a matched hydrophobic cavity could encapsulate TEA driven by host-guest chemistry, which not only allows the generation of TEA^• in the cavity to diminish environmental exposure, thus reducing the quenching by dissolved oxygen, water, etc., but also shortens the charge transfer pathway without extensive chemical modification. Density functional theory, ¹H NMR spectra, electron paramagnetic resonance, and differential pulse voltammetry studies revealed that the β-CD ligand-based shielding effect significantly increased the reactivity efficiency of TEA. More importantly, in stark contrast to those of traditional ligand-protected Au NCs, the ECL efficiency of β-CD-Au NCs enhanced 321-fold versus BSA-Au NCs, 153-fold versus ATT-Au NCs, and 19-fold versus GSH-Au NCs with 1 mM TEA. Therefore, this work provides an in-depth understanding of the crucial role of ligands in enhancing the active co-reactant radical stability for high-efficiency ECL metal NCs to immensely stimulate their promising applications. Using the β-CD-Au NCs as emitters, a "signal off" ECL sensing platform was constructed to detect noradrenaline as a model target with a lower detection limit of 0.91 nM.