Ultrasensitive Detection and Cellular Photothermal Therapy via a Self‐Photothermal Modulation Biosensor

Abstract The use of light, which is s a powerful tool for imaging and sensing, has also become one of the most prospective strategies in tumor treatment. Optical microfibers, which have engineerable waveguiding properties, are highly attractive for optical sensing and photothermal therapy on the micro/nanoscale. However, for their real‐world application, the sensitivity limit needs to be addressed, as does the issue of improving the intrinsic photothermal performance of silica microfibers. Herein, a nanointerface consisting of triangular Au@Ag₂S nanoplates and VO₂ nanoparticles on an optical microfiber is designed to fabricate a structurally resilient hierarchical microfiber sensor with well‐distributed plasmonic hotspot enhancement. The nanointerface enhances the evanescent field with temperature tunability, adding a self‐photothermal modulation function to the sensor. The sensor exhibits a temperature‐tunable sensitivity to alpha‐fetoprotein with a limit of detection of 0.62 × 10⁻¹⁸ m. It differentiates hepatoma carcinoma cells from normal cells and provides photothermal therapy aimed at the former. Quantitative evaluation of the sensor indicates that photothermal therapy kills more than 82% of cancer cells using a lower power. This work provides a new opportunity for selective evanescent field modulation for evanescent biosensors as well as a potential approach to the integration of cellular diagnosis and therapy.