Defect-Engineering-Induced Vacancy-Rich Bi₂S_3–<i>x</i>@AuNPs with Enhanced Photothermal Activity for Sensitive Bimodal-Type Gentamicin Monitoring

One of the most promising approaches to effectively modulate the performance of immunochromatography (ICA) is the rational design of nanomaterials. It is anticipated to facilitate highly sensitive ICA analysis by introducing and controlling the internal defect structures of nanomaterials. Herein, we designed Bi₂S_3-<i>x</i>@AuNPs with deep-level defect properties, revealing that these deep defects act as electron-hole nonradiative complex centers to promote phonon production, ultimately leading to photothermal analytical performance in ICA. By effectively regulating the defect density, the assay showed extraordinary colorimetric intensity, photothermal performance, and stability, which were conducive to constructing sensitive ICA. With a proof-of-concept for gentamicin (Gen), the limit of detection (LOD) was determined to be 0.0358 ng mL^-1, with overall recoveries ranging from 84.40% to 108.30% in both milk and milk powder samples. It demonstrates the importance of the rational design of internal defect structures to improve analytical performance and broaden the application of ICA.