Atomic-shell engineering in manganese-doped palladium@iridium nanozymes: d-Band optimization for enhanced peroxidase-like activity in ultrasensitive lateral flow immunoassays

Lateral flow immunoassay (LFIA) has been widely used in clinical diagnosis, food safety, and environmental protection due to the simple operation and high detection efficiency. However, the sensitivity of LFIA still falls short of the requirements when dealing with low levels of biomarkers. In this work, a type of manganese-doped core-shell nanozyme (Pd@Ir-Mn) with an ultrathin iridium (Ir) shell (~2 nm) was synthesized and utilized for the signal amplification of LFIA. By doping with other metals (Mn, Fe, Co, Ni, Cu, and Zn), the d-band center of Ir was tuned. The relationship between the d-band center and the conversion coefficient followed a volcano plot, with Mn-doped Pd@Ir located at the peak of the volcano. The as-prepared Pd@Ir-Mn was finally applied to LFIA (HT-Pd@Ir-Mn-LFIA) for the detection of hCG, the sensitivity was improved by 41 times compared to the traditional gold nanoparticles based LFIA (AuNPs-LFIA). Moreover, this method exhibited good specificity, stability, precision, and accuracy, making it suitable for clinical detection.