Defect-Engineering-Induced\nVacancy-Rich Bi<sub>2</sub>S<sub>3–<i>x</i></sub>@AuNPs with Enhanced Photothermal\nActivity for Sensitive Bimodal-Type Gentamicin Monitoring

One of the most promising approaches to effectively modulate\nthe\nperformance of immunochromatography (ICA) is the rational design of\nnanomaterials. It is anticipated to facilitate highly sensitive ICA\nanalysis by introducing and controlling the internal defect structures\nof nanomaterials. Herein, we designed Bi<sub>2</sub>S<sub>3–<i>x</i></sub>@AuNPs with deep-level defect properties, revealing\nthat these deep defects act as electron–hole nonradiative complex\ncenters to promote phonon production, ultimately leading to photothermal\nanalytical performance in ICA. By effectively regulating the defect\ndensity, the assay showed extraordinary colorimetric intensity, photothermal\nperformance, and stability, which were conducive to constructing sensitive\nICA. With a proof-of-concept for gentamicin (Gen), the limit of detection\n(LOD) was determined to be 0.0358 ng mL<sup>–1</sup>, with\noverall recoveries ranging from 84.40% to 108.30% in both milk and\nmilk powder samples. It demonstrates the importance of the rational\ndesign of internal defect structures to improve analytical performance\nand broaden the application of ICA.