Smartphone-Based Immune Response Measurement Using a Colorimetric Self-Assembled Plasmonic Biosensor

We present a point-of-care, cost-effective colorimetric nanosensor that leverages gap-plasmon dispersion of self-assembled aluminum nanoparticles on a phase-matched near-field cavity for antibody Immunoglobulin G (IgG) detection. The sensor achieves a broad dynamic range of 10 μg/mL to 5 mg/mL with a limit of detection (LOD) of ∼5.9 μg/mL, ensuring reliable performance across physiologically relevant concentrations. Its tunable optical response in the visible spectrum arises from the structural configuration of gap-plasmon coupled nanoparticles. We evaluated both colorimetric and spectroscopic sensitivities in controlled affinity biosensing assays and established a robust framework for colorimetric analysis. To demonstrate the translational potential, we developed a smartphone application that processes user-captured sensor images and estimates the analyte concentration, eliminating the need for bulky optics, spectrometers, or trained personnel. This biosensing strategy paves the way for low-cost, rapid, and user-friendly diagnostics, empowering individuals to combat infectious diseases and outbreaks more effectively.