Low-Background Cardiac Troponin I Detection via In Situ Self-Color-Changing Lateral Flow Immunoassay Enabled by H 2 O 2 -Triggered Cerium Oxide Nanoprobes

Conventional lateral flow immunoassay (LFIA) based on gold nanoparticles (AuNPs) often suffer from low detection sensitivity. Current signal enhancement strategies, such as metal in situ growth and enzyme catalysis, still face challenges, including poor stability of exogenous chromogenic reagents (prone to aggregation/degradation), uncontrollable enhancement processes, and strong background interference. To address these critical limitations, we developed an in situ, controllable, and background-free self-color-changing enhanced LFIA (SCCE-LFIA) utilizing novel cerium oxide nanoparticles coated with a polydopamine layer (CeO 2 @PDA NPs). The core of this method involves the H 2 O 2 -triggered oxidation of Ce 3+ to Ce 4+ on the nanoprobe surface, inducing a distinct colorimetric signal change from colorless/light brown to yellow/orange directly at the test line (T line). This intrinsic chemical-state-transition-driven signal enhancement fundamentally circumvents issues of uncontrollable enhancement processes, diffusion of chromogenic products, and nonspecific adsorption, thereby eliminating severe background interference. It strongly enables rapid and sensitive detection of cardiac troponin I (cTnI), a crucial clinical biomarker, with a low visual limit of detection (vLOD) of 0.8 ng/mL with only 30 s of coloration. This work establishes a precedent for the design of in situ, controllable, and background-free signal enhancement strategies, confirms the effectiveness of CeO 2 @PDA NPs as substitutes for traditional chromogenic substrates, and paves the way for the development of accurate and reliable point-of-care testing (POCT) in analytical chemistry and clinical diagnostics.