Seedless co-surfactant-based dimensional and optical tunability of gold nanorods with simultaneous pH regulation

Intense electromagnetic fields generated by the gold nanorods (GNRs) owing to their strong plasmon resonance make them promising candidate for applications in cancer diagnostics, photothermal therapy, single-molecule detection, drug delivery, etc. Use of GNRs in these applications as plasmon resonance probes depends on the extent to which their plasmon resonance band can be tuned into NIR region. In this study, we propose a facile seedless approach to synthesize GNRs in a cetyltrimethyammonium bromide (CTAB)–benzyledimethylhexadecylammonium chloride (BDAC) co-surfactant system with simultaneous pH regulation that yields GNRs with tunable plasmon resonance in tissue transparent NIR region. The role of binary co-surfactants, pH of the growth solution, and influence of the volume of the reducing agent on GNRs growth has been studied. Under optimized conditions, the longitudinal plasmon resonance band of GNRs can be tuned from 780–1300 nm by regulating the pH of the growth solution from 2.5 to 1.3. The role of co-surfactants and pH in the regulation of dimensions and thus plasmonic properties of GNRs synthesized by single-step seedless approach has been evaluated.