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

Abstract

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, 1 H 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 highefficiency 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.

Supramolecular assembly-induced electrochemiluminescence enhancement of gold nanoclusters for hemoglobin detection

“…1c were centered at binding energies of 162.95 eV and 164.05 eV, confirming the presence of Au–S bonds and –SH groups. 27 The C 1s peak attributable to –COO– was observed at 289.02 eV, indicating the presence of carboxyl groups from Arg in the Au NCs, confirming the successful synthesis of Arg/MTU-Au NCs. 39…”

“…20–26 Among them, gold nanoclusters (Au NCs), composed of several to hundreds of gold atoms less than 3 nm in diameter, have great potential as excellent ECL luminophores because of their excellent optical properties, unique catalytic activity, and good biocompatibility. 27–29 However, the low efficiency and poor stability of Au NCs significantly hinder their practical applications. Therefore, improving the efficiency and stability of Au NCs is of central importance in both fundamental research and practical applications.…”

Silver Nanocluster-Tagged Electrochemiluminescence Immunoassay with a Sole and Narrow Triggering Potential Window

“…To the best of our knowledge, the triggering potential window of LPA-AgNCs is much narrower than that of the previously reported ECL from metal NCs, − which can be anticipated to effectively evade the signal cross-talk of luminophores for designing high-throughput ECL bioassays.…”

Intramolecular Charge Transfer of Gold Nanoclusters for pH Indicating

“…13 For example, Yuan's group prepared AuNCs protected by β-cyclodextrin with trimethylamine as coreactant, which exhibited ligand-based shielding effect and achieved "signal off" detection of noradrenaline. 14 Zhang's group synthesized glutathione-coated AuNCs doped with radiometallic nuclides. After accumulating in the tumor's acidic microenvironment, PET/CT imaging was achieved, which facilitated tumor diagnosis and treatment.…”

“…Gold nanoclusters (AuNCs), composed of Au atoms as the core and certain ligands as the shell, have been utilized as fascinating probes with good biocompatibility for biological applications . For example, Yuan’s group prepared AuNCs protected by β-cyclodextrin with trimethylamine as coreactant, which exhibited ligand-based shielding effect and achieved “signal off” detection of noradrenaline . Zhang’s group synthesized glutathione-coated AuNCs doped with radiometallic nuclides.…”