Signal-off electrochemiluminescence immunosensors based on the quenching effect between curcumin-conjugated Au nanoparticles encapsulated in ZIF-8 and CdS-decorated TiO2 nanobelts for insulin detection.

A new strategy for the highly sensitive electrochemiluminescence (ECL) detection of insulin was developed based on curcumin-conjugated Au nanoparticles wrapped in zeolitic Zn²⁺-imidazolate cross-linked framework nanoparticles (Au-Cur/ZIF-8) quenching the ECL of CdS-decorated TiO₂ nanobelts (CdS@TiO₂). Curcumin-conjugated Au nanoparticles were embedded in ZIF-8 through epitaxial growth or nucleus coalescence. Herein, dual coreactants H₂O₂ and K₂S₂O₈ were employed to enhance the ECL emission of CdS@TiO₂, and the enhancing mechanism may be due to the electrogenerated hydroxyl radical (OH˙) strengthening the amount of sulfate radical anion (SO₄˙⁻), which was the main species of generating ECL signals. In order to sensitively detect insulin, Au-Cur/ZIF-8 labels were used to anchor secondary antibodies via amidation reaction and inhibit the ECL intensity of CdS@TiO₂. Moreover, the possible mechanism of quenching between Au-Cur/ZIF-8 and CdS@TiO₂ was ascribed to the poor conductivity of ZIF-8, the consumption of OH˙ and the ECL resonance energy transfer between CdS@TiO₂ and Au-Cur. Under optimal conditions, a sandwich immunosensor was prepared to determine insulin with a good linear range from 0.3 pg mL⁻¹ to 20 ng mL⁻¹ and a low detection limit of 0.09 pg mL⁻¹ (S/N = 3). [ABSTRACT FROM AUTHOR]