High Yield Seedless Synthesis of Mini Gold Nanorods: Partial Silver Decoupling Enabling Effective Nanorods Elongation With Tunable Surface Plasmon Resonance Beyond 1000 nm and CTAB-Free Functional Coating for mTHPC Conjugation

Gold nanorods with reduced dimensions possess better cellular uptake and absorption efficiency. The ability to synthesize gold nanorods while maintaining tunability of the aspect ratio towards an increased value is challenging, as it requires careful control of the reaction conditions, often employing additional parameters such as pH modification or the use of polymeric additives. We demonstrate a seedless approach for the synthesis of mini (width<10 nm) gold nanorods with tunable longitudinal surface plasmon resonance from ~700 nm to >1000 nm with aspect ratios ranging from ~3 to ~7 without the use of any polymeric additives or pH modification. A single mild reduction agent, hydroquinone, allows for up to ~98% reaction yield from the gold precursor. A mechanism for the elongation is proposed based on partial silver decoupling from the reaction. Finally, the particles are coated with various capping agents to allow functionalization and conjugation of mTHPC drug molecules used in photodynamic treatments and the cytotoxic CTAB is removed to increase their biocompatibility.