Size-focusing results in highly photoluminescent sulfur quantum dots with a stable emission wavelength that can be used for bioanalysis.

Screening high-performance anodic electrochemiluminescence (ECL) systems with low triggering potential is a promising way to broaden their applications. In addition to electrochemiluminophore, co-reactant also plays an important role in the ECL process, since the oxidation of co-reactants is one of the most important steps in the anodic ECL process. Herein, a novel co-reactant-mediated high-performance low-potential Au nanocluster (AuNC)-based ECL system has been successfully developed. Benefiting from the isopropyl substitution and hydroxyl addition to the triethylamine (TEA), the BSA-AuNC/2-(diisopropylamino)­ethanol (DIPEA-OH) ECL system achieved higher energy efficiency at a lower potential of 0.75 V. In addition, compared with the BSA-AuNC/TEA system, the ECL intensity and quantum yield (Φ ECL) with DIPEA-OH as a co-reactant increased 22.34-fold and 13-fold (as high as 68.17%), respectively. Based on the low potential, high Φ ECL of the AuNC/DIPEA-OH ECL system, a sandwich-type immunosensor has been constructed for a highly selective SARS-CoV-2 N protein assay. In the absence of any complex signal amplification strategies, the ECL immunosensor for the SARS-CoV-2 N protein detection showed a linear range of 0.001–100 ng/mL and a detection limit of 0.35 pg/mL. Moreover, the ECL platform had good reproducibility and stability and exhibited acceptable detection performance in the detection of actual serum samples. This work established a framework for in-depth design and study of anode ECL co-reactants for AuNCs and other luminophores, and expanded the potential application of ECL sensors in the clinical diagnosis of COVID-19.

Electrochemiluminescence (ECL) is a widely used light output mechanism from electrochemical excitation. Understanding the intrinsic essence for ideal ECL generation remains a fundamental challenge. Here, based on the molecular orbital theory, we reported an energy level engineering strategy to regulate the ECL performance by using ligand-protected gold nanoclusters (AuNCs) as luminophores and N,N-diisopropylethylamine (DIPEA) as a coreactant. The energy level matching between the AuNCs and DIPEA effectively promoted their electron transfer reactions, thus improving the excitation efficiency and reducing the trigger potential. Simultaneously, the narrow band gap of the AuNCs further enabled enhanced emission efficiency. Using the energy level engineering theory developed here, a dual-enhanced strategy was proposed, and β-CD-AuNCs were designed to further verify this mechanism. The β-CD-AuNCs/DIPEA system resulted in highly stable near-infrared ECL with an unprecedented ECL efficiency (145-fold higher than that of the classic Ru(bpy) 3 2+ /tetra-n-butylammonium perchlorate system) and a low trigger potential of 0.48 V. A visual NIR-ECL based on this ECL system was successfully realized by an infrared camera. This work provides an original mechanistic understanding for designing efficient ECL systems, which promises to be a harbinger for broad applicability of this strategy for other ECL systems and ECL sensing platforms.

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