Solvothermal Synthesis of Indium Tin Oxide (ITO) Nanoparticles: From Infrared Localized Surface Plasmon Resonance Absorption to Spontaneous Antibacterial Properties

A series of cubic-phase indium tin oxide (ITO) nanoparticles (NPs) with varying tin (Sn) doping ratios were synthesized via a solvothermal method. By precisely controlling the dopant concentration, the resulting ITO NPs of approximately 15 nm with excellent crystallinity achieved tunable infrared localized surface plasmon resonance (LSPR) absorption across the 1000-6000 nm wavelength range. For the first time, the antibacterial properties of ITO NPs under dark conditions were systematically investigated, revealing a strong correlation between their infrared LSPR absorption characteristics and antibacterial efficacy. Notably, ITO NPs with 5% Sn doping ratio exhibited the highest LSPR quality factor and the strongest antibacterial activity, producing an inhibition zone diameter 3.33 times larger than that of the control. In contrast, undoped, lightly doped, or excessively doped samples showed either diminished plasmonic quality factors, weak antibacterial activity, or a complete absence of antibacterial effects. This study represents the first demonstration of exploiting infrared LSPR-active ITO NPs for spontaneous antibacterial activity in darkness. The observed functionality is attributed to the NPs' ability to absorb and convert ambient background radiation into localized energy. In summary, this work establishes ITO NPs as a novel class of inorganic antibacterial materials for dark environments with promising potential for coating and surface protection applications.