A high yield, controllable process for producing tunable near infrared-absorbing gold nanoplates†
The purpose of this study was to optimize a new synthesis technique, “DiaSynth,” to produce near-infrared (nIR) absorbing gold nanoplates with prescribed localized surface plasmon resonance (LSPR) wavelengths in higher yields over conventional synthesis methods without the need for laborious purification steps. The molecular weight cut off (MWCO; 3.5, 8, 12, 15, 25 & 50 kDa) of the regenerated cellulose membranes (RCM), temperature (25, 37, 50 & 100 °C) and surface area to volume (SA/Vol) ratio (220, 340 & 470 mm2 ml−1) of the RCM to the gold nanoplate solution were varied during the synthesis process to determine the effect of each parameter on gold nanoplates yield, LSPR peak placement and stability. Results indicate the ability of the RCM to remove ∼99% of the contaminant small gold colloid (<10 nm) produced during the synthesis process, while producing a 72% higher yield of gold nanoplates compared to a conventional one-step fabrication process. Increasing the MWCO of the RCM from 3.5 kDa to 15 kDa was found to blue shift the LSPR peak down by 40 nm. Increasing the SA/Vol ratio and temperature blue shifted the LSPR peak wavelength by hundreds of nanometers with the nIR absorbing gold nanoplate LSPR peak occurring within the range of 650–1100 nm. It was also discovered that the gold nanoplates fabricated via the DiaSynth process with dialysis (Process 1) displayed an increase in stability over time without the need of a capping agent. With the increased gold nanoplate stability, further purification and isolation of gold nanoplates was possible through sedimentation over time. This study demonstrated that increasing the temperature, SA/Vol, and MWCO of the RCM allows production of gold nanoplates of increased purity compared to other methods and the ability to tailor the tunability of the LSPR peak to a desired wavelength.