Highly Enhanced Luminol Electrochemiluminescence Based on L-Cysteine Film for Ultrasensitive Immunoassay

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Abstract
A novel label free electrochemiluminescence (ECL) immunosensor based on the ECL of luminol for detection of α-1-fetoprotein (AFP) has been developed. For this proposed immunosensor, gold nanoparticles (nano-Au) were firstly electrodeposited on the glass carbon electrode (GCE) surface, which promoted the electron transfer and largely enhanced the ECL signal of luminol. Subsequently, L-cysteine self-assembled monolayer (SAM) was formed on the nano-Au modified electrode to further enhance the ECL signal and improve the absorption capacity of antibody. Then, EDC/NHS was used to activate the reaction between the −COOH/−NH2 of L-cysteine and the NH2/−COOH of anti-AFP. At last bovine serum albumin (BSA) was used to block the nonspecific binding sites. As a result, the ECL of luminol enhanced by L-cysteine film was firstly developed for ultrasensitive immunosensor. The developed immunosensor performed high sensitivity and wide linear range for detection of AFP in the linear range of 0.001–20 ng mL−1, with a low detection limit of 0.33 pg mL−1 (defined as S/N = 3). Moreover, the immunosensor showed good fabrication and detection reproducibility.

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