In Situ Controllable Generation of Copper Nanoclusters Confined in a Poly-l-Cysteine Porous Film with Enhanced Electrochemiluminescence for Alkaline Phosphatase Detection

Copper nanoclusters (Cu NCs) as emerging luminescent metal NCs are gaining increasing attention owing to the comparatively low cost and high abundance of the Cu element in nature. However, it remains challenging to manipulate the optical properties of Cu NCs. Unlike most dispersed Cu NCs, whose luminescence efficiency was restricted by nonexcited relaxation, the Cu NCs confined in a porous poly-l-cysteine (poly-l-Cys) film were generated controllably with enhanced electrochemiluminescence (ECL) by in situ electrochemical reduction. Specifically, poly-l-Cys provided a porous structure to regulate the generation of Cu NCs within its holes, which not only increased the restriction on the intramolecular vibration and rotation of the ligands but also expedited the electron transfer near the electrode surface, reflecting in an enhancement of the ECL signal and efficiency. As an application of the confined Cu NCs, an ECL biosensor with high performance was constructed skillfully for highly sensitive detection of alkaline phosphatase (ALP), which adopted Cu NCs as the ECL luminophore and poly-l-Cys as a coreaction accelerator in a novel ECL ternary system (Cu NCs/S₂O₈^2-/poly-l-Cys). Furthermore, an ingenious target amplification based on the combination of a DNA walker and click chemistry was developed to convert ALP to DNA strands efficiently, achieving great improvement in the recognition efficiency. As a result, the biosensor had a low detection limit (9.5 × 10^-7 U·L^-1) and a wide linear range (10^-8-10^-2 U·L^-1) for ALP detection, which showed great promise for the detection of non-nucleic acid targets and the diagnosis of diseases.