Integrated Colorimetric and Fluorescent Assay Using Gold Nanobipyramids and UCNPs for Tyrosinase-based Melanoma Diagnostics

Melanoma, the most lethal form of skin cancer, is closely associated with tyrosinase activity, making it a critical biomarker for early diagnosis. In this study, we developed a dual-mode biosensing platform integrating multicolorimetric and ratiometric fluorometric detection for ultra-sensitive tyrosinase quantification. This platform leverages localized surface plasmon resonance (LSPR) modulation of gold nanobipyramids (AuNBPs) alongside a fluorescence resonance energy transfer (FRET)-based mechanism using upconversion nanoparticles (UCNPs). The tunable LSPR of AuNBPs provided a bidirectional ratiometric multicolor emission improving sensitivity and selectivity. Tyrosinase-mediated oxidation of catechol to quinone inhibits silver (Ag) deposition on AuNBPs, inducing a distinct concentration-dependent color shift for precise visual quantification. This dual-modality assay achieves an exceptional limit of detection (LOD) of 4.13 × 10^–5 and 2.71 × 10^–5 U/mL for colorimetric and fluorometric sensors, respectively, demonstrating high selectivity, robustness in complex biological samples. Additionally, the assay proved effective in screening tyrosinase inhibitors, using kojic acid as a model, and achieved an IC₅₀ value of 61.45 µM, validating its inhibition efficiency.