Magnetically Retrievable Platinum Nanoreporters for Efficient Lateral Flow Immunoassay in Complex Bio‐Samples

Abstract Lateral flow immunoassays (LFIAs) are widely used for point‐of‐care diagnostics, but their development is challenged by the complexity and variability of patient samples. In particular, LFIAs often exhibit reduced sensitivity and specificity when used with patient samples, compared to their performance with analyte‐spiked idealized matrices. Patient samples are inherently complex, with variations in physical and biochemical properties between patients. This complexity has consequences for the performance of LFIAs, and can result in non‐specific binding on the test line, discoloration of the nitrocellulose membrane, and incomplete sample flow along the test strip. To address these challenges, a magnetically retrievable platinum nanoreporter (termed Pt@Fe ₃ O ₄ ) is developed for LFIAs. Leveraging the magnetic properties of the Fe ₃ O ₄ core, magnetic separation is utilized to enable the purification and concentration of target antigens from complex human matrices, including serum, saliva, and even stool samples. This also eliminates assay inconsistencies caused by inter‐sample variability. Further, the suitability of Pt@Fe ₃ O ₄ nanoreporters has been explored for use as detection probes in LFIAs. Signal enhancement is demonstrated by the utilization of the magnetic and enzyme‐mimicking activity of the nanoreporter, resulting in a marked improvement in sensitivity, as evidenced by a 2‐ to 4‐fold decrease in the visual limit of detection.