Controllably tuning the near-infrared plasmonic modes of gold nanoplates for enhanced optical coherence imaging and photothermal therapy

Abstract

Tuning the localized surface plasmon modes of gold nanostructures to be in resonance with near-infrared incident light is desirable in various applications such as biosensing, biomedicine/therapy and opto-electronic devices. Unfortunately, current methods for regulating the plasmon modes of gold nanoparticles still suffer from poor controllability and reproducibility. Here, we developed a facile and effective method to precisely tailor the plasmon mode of gold triangular nanoprisms (GTNPs) by simply exposing them to O₃ atmosphere. The resonant wavelength of the plasmon mode sustained by the GTNPs can be steadily tuned over a broad spectral range varying from 1010 nm to 780 nm (within the bio-window region), along with their shapes gradually changing from triangular nanoprism into circular nanoplate. By controlling the concentrations of O₃, exposure duration, the concentrations of surfactant in suspension and the reaction temperature, GTNPs with various plasmon modes could be efficiently obtained from one original GTNPs sample. To demonstrate the potential applications of these GTNPs, we applied this method to obtain gold nanoplates as-needed for enhanced optical coherence tomography (OCT) and photothermal therapy. The plasmon mode of GTNPs was tuned to match the excitation wavelength of the OCT laser source, and was applied to enhance the signal of OCT imaging. The plasmon mode of GTNPs was also precisely tuned to 808 nm which was well resonant with the wavelength of a near-infrared excitation laser (λ_ex = 808 nm); when the as-obtained GTNPs were used as a photothermal agent, they displayed an enhanced effect of photothermal therapy on Hela cancer cells compared to those without the tuning of the plasmon mode. Considering the simplicity and high controllability of the method for fine-tuning the plasmonic mode of GTNPs, this work has great potential in a wide range of applications such as biomedical imaging and thermotherapy, chemical/biological sensing, surface-enhanced spectroscopy and solar energy harvesting, etc.