In this study, we developed a liquid crystal (LC)-based immunoassay incorporating copper nanoparticles (CuNPs) as signal amplifiers for the highly sensitive and selective detection of human serum albumin (HSA). The detection mechanism relies on specific immunobinding between HSA and anti-HSA/CuNPs complexes immobilized on a DMOAP-coated glass surface, which perturbs the homeotropic alignment of 4-cyano-4′-pentylbiphenyl (5CB) and induces a dark-to-bright optical transition observable under polarized light. A detection limit as low as 0.05 μg·mL−1 was achieved, representing a nearly 300-fold improvement over conventional LC-based immunoassays without CuNPs amplification. The sensor exhibited excellent selectivity, showing no significant interference from bovine serum albumin (BSA), avidin, biotin, or unrelated antibodies. Comparative studies further demonstrated that CuNPs outperform gold nanoparticles (AuNPs), not only by increasing the effective immunocomplex volume but also through specific interactions between copper atoms and the cyano groups of 5CB, which facilitate LC reorientation. This dual amplification mechanism underscores the unique role of CuNPs in LC-based biosensors and offers a simple, label-free, and ultrasensitive platform for biomarker detection with promising applications in early disease diagnostics and point-of-care testing.
