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

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 S₂O₈^2- 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.