Seed-Mediated Galvanic Synthesis of CuS–Au Nanohybrids for Photo-Theranostic Applications

Copper sulfide nanoparticles (CuS) have received attention as a potential photothermal therapy (PTT) and photoacoustic imaging contrast agent for cancer theranostics. Prior studies suggest that functionalized gold (Au) nanoparticles show anticancer effects. Hence, CuS/Au nanohybrids are being explored for various imaging and therapy operations. However, the relatively bigger size of such nanohybrids limits their applications for deep tumor applications. This study specifically focuses on developing ultrasmall CuS–Au (TSP–CA) nanohybrid using seed-mediated galvanic reduction of gold precursors on the surface of CuS nanoparticles. Tannic acid (TA) and sodium citrate were used as reducing agents to form Au nanoseeds and to impart its anticancer effect. Polyvinylpyrrolidone (PVP) was used as a stabilizing agent to form small PVP–CuS NPs. Furthermore, the hydrogen-bonding properties of TA and PVP were utilized, followed by galvanic reduction to form the TSP–CA nanohybrids. These particles were expected to show reactive oxygen species (ROS) effect, and PTT influenced anticancer effects. The photoacoustic (PA) properties of the nanohybrids were also studied for their potential as an exogenous contrast agent. The proposed nanohybrids attained a mean size of 8 nm and retained their crystalline nature. The X-ray photoelectron spectroscopy studies revealed the presence of Cu and Au. PA experiments indicated a higher signal-to-noise ratio. PTT efficiency was estimated to be 25%, and the nanohybrid showed good photo stability. In vitro experiments suggest ROS-mediated anticancer effects on lung cancer cells. The nanohybrid was evaluated for PTT and PA signal generation using ex vivo chicken breast studies at depths of 1 and 1.5 cm, respectively. PA signal was measured using an ultrasound transducer of 2.25 MHz center frequency and the laser operating at 960 nm at depths of 1 cm. Additionally, the ROS and apoptosis studies revealed the enhanced anticancer effect of the hybrid nanoparticles compared to the individual nanoparticle category.