Au/Pt@PEG Nanozymes Probe for Ultrasensitive and Matrix-Robust Lateral Flow Immunoassay of Cardiac Troponin I.

Early diagnosis of acute myocardial infarction (AMI) critically depends on the ultrasensitive, interference-resistant, point-of-care detection of cardiac troponin I (cTnI). However, conventional lateral flow immunoassays (LFIA) are fundamentally limited by insufficient signal output for trace amounts of cTnI and nonspecific protein adsorption from complex serum matrices, which elevate background noise and undermine both sensitivity and specificity. To simultaneously address these challenges, this study developed SH-PEG-COOH functionalized Au/Pt bimetallic nanoparticles (Au/Pt@PEG NPs) as a dual-functional LFIA probe. The heterobifunctional molecule SH-PEG-COOH integrates a metal-thiol anchoring terminus, a PEG antifouling spacer, and a carboxyl conjugation terminal within a single architecture, enabling one-step self-assembly of a well-defined "anchor-antifouling-conjugation" trilayer interface. The PEG brush suppresses nonspecific protein adsorption through cooperative steric hindrance, hydration repulsion, and conformational entropic repulsion independent of ionic strength, while uniformly exposed carboxyl termini enable orientation-specific antibody immobilization via EDC/NHS chemistry. Meanwhile, accessible Pt sites catalyze TMB/H2O2 oxidation at the test line for in situ colorimetric signal amplification. The platform achieves a limit of detection of 5.2 pg mL-1, representing a 712-fold improvement over conventional AuNP-based LFIA. Systematic evaluation against 13 interfering substances confirms matrix interference elimination, with recovery rates of 92.70%-109.80% in 60% fetal bovine serum. The covalent metal-thiol anchoring maintains PEG brush integrity and antibody conjugation density throughout the probe lifetime, evidenced by stable T/C signal values over 35 days at room temperature. Clinical validity was confirmed across 30 patient samples with strong agreement against commercial ELISA (R2 = 0.998).