Bioresponsive Release and Multiple Signal Amplification Induce a Strong Signal-On Mode for Hydrocortisone Ultrasensitive Detection.

Enhancing the sensitivity of electrochemiluminescence (ECL) sensors can reduce the false-negative risk. A pronounced signal change in the presence of the target provides an effective idea to achieve high sensitivity. In this work, a competitive immunoreaction-triggering release strategy was constructed based on the specific interaction between hydrocortisone (HC), antibody, and HC antigen. Cu2S snowflakes (SFs) exhibited strong catalytic ability for K2S2O8 and were sequentially modified with antibody and ssDNA 1 (S1). Additionally, carbon quantum dots (C QDs) as luminophores were encapsulated in mesoporous silica spheres (MSS). The pores of MSS were blocked by the Ag nanoparticles (NPs)-ssDNA 2 (S2)-antigen compound (Ag-S2-antigen). Upon antigen-antibody recognition, the pores of MSS were opened, leading to the release of C QDs to generate the signal-on mode. Simultaneously, Ag nanoparticles were introduced to the sensing interface via the S1-S2 hybridization. They could promote the conversion of S2O82- into SO4•- to further increase the ECL signal change. Overall, the strong signal-on mode induced via multiple signal amplification can improve the sensitivity of the sensor. The resulting sensor showed excellent analytical performance with a broad dynamic range from 100 fg/mL to 1 μg/mL. The low limit of detection (LOD) was 25.3 fg/mL. This design provided a new direction for ultrasensitive monitoring of HC in the environment.