Individual Single-Crystalline Irregular In₂O₃ Microcavity for Ultrasensitive Semiconductor-Based SERS Biosensor

Surface-enhanced Raman spectroscopy (SERS) achieves ultrahigh sensitivity at the molecular level and enables water-interference-free detection. However, the development of single-particle semiconductor substrates that do not rely on gap-enhanced electromagnetic fields remains challenging. Herein, capitalizing on the dual merits of morphology-induced prolonged light accumulation and structure-improved interfacial charge transfer, we developed an ultrasensitive semiconductor-based individually SERS system based on a highly crystalline irregular hexagonal prism In₂O₃ (I-In₂O₃) microcavity. Finite-difference time-domain simulations and photoluminescence spectra confirmed the successful establishment of a whispering-gallery-mode microcavity on the I-In₂O₃ platform. This microcavity enables the long-term confinement and oscillation of resonant photons, thereby significantly enhancing light-matter interactions. Aberration-corrected electron microscopy demonstrated that although I-In₂O₃ single crystals were isostructural to regular hexagonal prisms, they exhibit contracted lattice parameters. Density functional theory calculations further revealed that atomic-scale compressive lattice strain induces electronic band restructuring, enhancing the interfacial interactions between individual particle substrates and adsorbed molecules at the atomic level. In addition, the I-In₂O₃ SERS system demonstrates quantitative and multiplexing capabilities for rapid antibiotic detection. This work presents new perspectives for constructing supersensitive semiconductor SERS sensors using a micron-scale single-particle platform.