Multifunctional Fe3O4@CuS nanoparticle-driven colorimetric and photothermal immunochromatographic test strip for the sensitive detection of Salmonella typhimurium in milk

Magnetic nanoparticles are widely employed as signal labeling reporters in immunochromatographic test strips (ICTS) for detecting foodborne pathogens due to their outstanding anti-interference and magnetic enrichment performance. However, the insufficient colorimetric signal brightness of magnetic nanoparticles results in poor sensitivity, hindering their ability to meet the growing demand for advanced ICTS. Herein, we synthesized Fe3O4@CuS 3 O 4 @CuS core-shell structure nanoparticles using a facile in-situ growth method. These Fe3O4@CuS 3 O 4 @CuS nano- particles exhibit a superior photothermal conversion efficiency of 42.12 % and a magnetization strength of 35 emu/g. We developed a dual-readout format ICTS based on Fe3O4@CuS, 3 O 4 @CuS, incorporating both colorimetric and photothermal formats to enhance sensitivity for Salmonella typhimurium detection. The limit of detection for Fe3O4@CuS-ICTS 3 O 4 @CuS-ICTS in the colorimetric and photothermal format was 5 x 104 4 CFU/mL and 7.7 x 103 3 CFU/mL, respectively. Additionally, the average recoveries ranged from 91.25 % to 103.39 %, with variations from 2.2 % to 11.1 %, demonstrating good accuracy and precision. Therefore, this work suggests that Fe3O4@CuS 3 O 4 @CuS nano- particles, with their superior magnetic, optical, and photothermal properties, can serve as promising signal labeling reporters to improve the detection performance of ICTS and hold potential for constructing more accurate and sensitive point-of-care testing platforms.