Photonic immunosorbent assay PHISA for specific detection of label-free biomolecules

Detecting small amounts of specific biomolecules with high precision is a cornerstone of environmental monitoring, medical diagnostics, and biochemical research. Consolidated biochemical immunoassays offer established protocols and high reliability but suffer from complex procedures, expensive reagents, invasive labeling, and prolonged timescales. We functionalized ultrasensitive whispering gallery mode (WGM) spherical microlasers to obtain a highly accurate immunosorbent assay for label-free interferon-γ antigen. Analysis of WGM spectra reveals small amounts of proteins that gradually stick to the spheres; the estimated lower limit of detection is 10 pg mL−1. We validated our results through enzyme-linked immunosorbent assay tests on the same samples. Our photonic biosensing strategy requires only a few microliters of sample, decreasing the number of process steps and chemical reagents typical of chemoluminescence assays. Its micrometric size allows for easy integration and operation in different kinds of specimens, and label-free operation ensures no need for antigen tagging or modification.