A highly sensitive and stable lateral flow immunoassay for carcinoembryonic antigen using weakly-ionized AuNPs and a cationic polymer control line.

Lateral flow immunoassay (LFIA) is widely used for point-of-care testing due to its simplicity, rapid results, and low cost. However, conventional gold nanoparticles (AuNPs) with limited antibody conjugation efficiency and colloidal stability often restrict detection sensitivity, making accurate analysis of low-abundance biomarkers in complex serum matrices challenging. To address these limitations, we developed a novel LFIA strategy based on weakly ionized AuNPs (WIAu) (AA-AuNPs) as detection probes and a poly dimethyl diallyl ammonium chloride (PDDA)-based control line (PCL), which is simply referred to as WIAu/PCL-LFIA. Using tumor biomarker carcinoembryonic antigen (CEA) as the model target analytes, AA-AuNPs allowed highly efficient antibody conjugation via electrostatic adsorption, significantly improving labeling efficiency and colloidal stability. Simultaneously, a non-biological control line (C-line) was constructed by immobilizing PDDA on the nitrocellulose membrane, which effectively captures free probes through multi-site cooperative capture interactions, thereby overcoming the denaturation risk and batch-to-batch variability associated with conventional protein-based C-line. The developed WIAu/PCL-LFIA platform achieved a detection limit of 1.49 ng/mL for CEA in serum samples, well below the clinical threshold of 5 ng/mL, demonstrating high sensitivity, excellent storage stability, and low cost. This newly designed WIAu/PCL-LFIA platform provides a reliable and commercially viable tool for at-home monitoring of colorectal cancer prognosis, exhibiting great potential in the rapid detection of disease-related biomarkers.