One-pot synthesis of multifunctional sliver nanoparticles with controlled size for sensitive colorimetric and electrochemiluminescent immunoassay of SARS-CoV-2.

Silver nanoparticles (AgNPs) have great potential in a broad range of applications because of their biochemical functionality, unique physical and optical properties. However, it is still a great challenge to synthesize small-size AgNPs with good stability and high performance for biosensors. In this work, triethanolamine and polyacrylic acid modified AgNPs (TEOA@AgNPs-PAA) with controllable size and high catalytic activity for sensitive detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are reported. Monodisperse TEOA@AgNPs-PAA are prepared by the one-pot synthesis using the TEOA and PAA as reducing agent and surfactant, respectively. The size of TEOA@AgNPs-PAA (the average size of 8.65 nm) is 6 times smaller than that of the TEOA@AgNPs (52 ± 1.5 nm) without PAA. The as-prepared TEOA@AgNPs-PAA possess catalytic activity and present mimicking property of horseradish peroxidase, which are employed to fabricate colorimetric biosensors by catalyzing the reaction between H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue oxTMB for sensitive detection of SARS-CoV-2 spiking proteins. Significantly, the small-size TEOA@AgNPs-PAA can catalyze electroreduction process of K2S2O8 to enhance the cathodic ECL signal, and their surface cap abundant TEOA molecules, which can also act as a coreactant to enhance the anodic ECL of Ru(bpy)32+. Under optimal conditions, the fabricate immunosensors for anodic and cathodic ECL determination of SARS-CoV-2 present the detection limits of 9.2 fg/mL and 14.3 fg/mL (S/N = 3), respectively. This work exhibits a promising novel strategy for the development of multifunctional AgNPs as an efficient sensing platform for the clinical diagnosis and biosensing application.