Inertial force-driven synthesis of near-infrared plasmonic nanosphere composites

Near-infrared (NIR) responsive nanoparticles (NPs) like gold nanorods (GNRs) are important in biomedical fields because of their transparency for biological tissues. Although GNRs are sought after as contrast agents for theranostics in cancer studies, capping ligands like cetyl trimethyl ammonium bromide (CTAB) used for the GNR synthesis are toxic for biological tissues. This work aimed to develop a physical method as an alternative to toxic GNR chemical process. The synthesis process, using colloidal citrate capped gold as model NP, was simple, cost-effective, and did not require the use of a toxic chemical like CTAB. The inertial (g-) force-driven synthesis of nanosphere composites (NSCs) resulted in composites of two NPs combined together with little or no gaps between them. The formed NSCs showed rod-like characteristics, which are typified by the evolution of absorption spectra from the transverse to longitudinal mode, similar to GNRs. The new nanomaterials by the g-force-driven technique showed high potential to be an effective alternative to many existing toxic NPs, particularly GNRs.