The antimicrobial and photothermal response of copper sulfide particles with distinct size and morphology

The development of photothermal agents for antibacterial applications has become increasingly attractive. An exciting area for these materials is in the food industry where such materials can be applied to prevent microbial contamination, as an environment-friendly alternative to chemical disinfectants. However, for such applications, there is a need for low-cost photocatalytic materials with easy synthesis procedures and long-term stability. In this regard, copper sulfide (CuS) nanomaterials have gained vast attention for their large antimicrobial response, driven primarily by the photothermal effect resulting from their uniform absorption in the NIR range. However, an important factor for a successful application is the level of the light-to-heat conversion capability of the specific CuS nanomaterial, which highly impacts on the antimicrobial response. Here, different synthesis procedures were investigated to synthesize a variety of CuS particles with distinct sizes and shapes, to demonstrate the large variation in antimicrobial response. The antibacterial activity of the particles was demonstrated on the bacterium Escherichia coli (E. coli) by irradiation with a regular IR lamp, to simultaneously investigate light absorption under a relatively low irradiation power. The results reveal that the light absorption of the CuS particles vary greatly and thus also so does the antibacterial effect. In conclusion, the difference in antimicrobial effect can not only be ascribed to size and morphology, but it is also influenced by crystal size and phase composition.