Site-Specific Antigen Immobilization Improves Autoantibody Binding Efficiency on the Luminex Platform

Autoantibodies (AABs) are valuable biomarkers for diagnosing and monitoring autoimmune diseases and cancer. Conventional AAB profiling methods, such as enzyme-linked immunosorbent assay and immunoblot, are time-consuming, labor-intensive, and limited in multiplexing capacity. Luminex xMAP technology overcomes these limitations by enabling high-throughput, multiplexed AAB detection via bead-based immunoassays. However, the random immobilization of antigens on Luminex beads can lead to suboptimal epitope exposure, reduced binding sensitivity, and inconsistent assay performance. This study examines whether oriented antigen immobilization via genetic code expansion and click chemistry enhances binding sensitivity on the Luminex platform compared to random immobilization via conventional amine coupling. We selected three human antigenic proteins, HDAC3, RPS17, and RPS4Y1, and incorporated the noncanonical amino acid (ncAA) N ^ε-((2-azidoethoxy)-carbonyl)-l-lysine (AzK) at a genetically defined position using the stop codon suppression method. This enabled site-specific conjugation of the antigens to dibenzocyclooctyne (DBCO)-functionalized beads via strain-promoted azide-alkyne cycloaddition (SPAAC). Binding sensitivity was assessed using serum samples from 88 individuals (22 healthy and 66 lung carcinoma patients). Oriented immobilization of RPS4Y1 AzK on DBCO-beads resulted in a 2.5-fold increase in binding sensitivity compared to random immobilization on COOH-beads, demonstrating that controlled antigen orientation improves epitope accessibility and enhances AAB detection sensitivity. These findings establish site-specific antigen immobilization via genetic code expansion and click chemistry as a superior alternative to conventional amine coupling. This immobilization approach significantly improves AAB detection and holds broad potential for applications such as antibody profiling, diagnostics, and drug screening on the Luminex and other biosensing and diagnostics platforms, where high sensitivity and accuracy are essential.