Individual Single‐Crystalline Irregular In 2 O 3 Microcavity for Ultrasensitive Semiconductor‐Based SERS Biosensor

ABSTRACT 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 In 2 O 3 (I‐In 2 O 3 ) microcavity. Finite‐difference time‐domain simulations and photoluminescence spectra confirmed the successful establishment of a whispering‐gallery‐mode microcavity on the I‐In 2 O 3 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‐In 2 O 3 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‐In 2 O 3 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.