Photoacoustic characterization of photothermal nanoparticles containing metal-bis(dithiolene) complexes: in vitro validation

Recent advances in nanotechnology and imaging have improved the efficacy of chemotherapy while reducing side effects. However, creating nano-compounds with high imaging contrast, targeted selectivity, biocompatibility, and suitable administration remains challenging. To address this, metal-bis(dithiolene) complexes were encapsulated into water-soluble polymer nanoparticles (NPs) to develop effective and biocompatible contrast agents for photoacoustic (PA) imaging. These complexes, which exhibit excellent photothermal properties under laser irradiation, were tested for their potential as PA imaging contrast agents. Three suspensions were tested, each containing nickel, palladium, or platinum-bis(dithiolene) complexes encapsulated into poly(malic acid) block-copolymer. After verifying optical absorption, the NPs were injected into agar phantoms to evaluate their PA response. The performance was assessed by decreasing the complex concentration and testing on a research platform and a commercial Vevo-LAZR system. Results showed that the NPs provided a detectable PA response at minimal concentrations of dithiolene complex around 9 µg/mL with the research platform and a 1064 nm excitation. However, higher concentrations were required for the commercial system. These findings indicate that the NPs have potential as therapeutic and imaging agents.