High-Sensitivity Cell-Based Plasmonic Biolayer Interferometry with a Two-Tiered Enhancement for Clinical Autoimmunity Surveillance of Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a chronic, often fatal autoimmune blistering disorder that affects the skin and body-wide mucous membranes, imperatively urging for accurate detection of characteristic autoantibodies. To overcome the sensitivity constraint, we report here a serological avidity test for complex PV autoantibodies, relying on cell-based plasmonic biolayer interferometry (cpBLI) with two-tiered enhancement of light interference by gold nanostars (AuNSs). High-surface-area, clean-surface AuNSs with abundant tips and grooves can enhance interference patterns and promote intrinsic and extrinsic catalysis of 3,3'-diaminobenzidine by themselves and conjugated peroxidase, enabling a dual hierarchical signal amplification of 26.8-fold over conventional BLI at a limit of detection of 0.36 pM. The cpBLI responses correlate well with diagnostic ELISA from clinical laboratories, precisely differentiating PV from normal and other epithelial antibody-associated immunobullous cutaneous diseases such as bullous pemphigoid. In a simple dip-and-read format with real-time readouts, the efficacy was verified in a masked validation cohort and multicenter patient samples. The cpBLI effectively assesses PV prognosis and precisely stratifies severity in good association with the Pemphigus Disease Area Index (PDAI). Notably, live cells on the biosensor surface facilitate drug screening by responding to PV therapeutics. Therefore, the cpBLI immunodiagnostic assay is promising for diagnosing, staging, and therapeutic monitoring PV in clinical settings and can be generalized for other autoimmune diseases.