Gold nanorods with higher aspect ratio as potential contrast agent in optical coherence tomography and for photothermal applications around 1300 nm imaging window

Abstract

Over the past few years, plasmon-resonant nanorods of gold (AuNRs) have been used as the contrast agent in optical imaging and for photothermal applications. However, most of these studies were limited to AuNRs whose spectral peaks fall below 1000 nm. Recently, optical coherence tomography (OCT) imaging around 1300 nm has become one of the niche research areas due to its potential for many diagnostics imaging applications. In this paper, we have investigated plasmon-resonant AuNRs with higher aspect ratio as a potential contrast agent in OCT and for photothermal applications around the 1300 nm window. The AuNRs with an aspect ratio of 8.8, and longitudinal plasmon-resonance peak at 1320 nm have been used for the study. The AuNR used in the study has an average dimension of 88 nm (length) × 10 nm (diameter), and an effective size (Reff) of 11.8 nm. The optical extinction of plasmon-resonant AuNRs has been characterized by OCT using a new cross-correlation approach. The extinction cross-section estimated using the OCT method is in good agreement with the values obtained via finite difference time domain-method and UV–vis–NIR spectroscopy. Both the simulation and phantom based experimental studies have shown that AuNRs exhibit a large absorption to scattering cross-section ratio, making them ideal for absorption based contrast enhancement in OCT imaging around 1300 nm. Ex vivo studies on the pig adipose tissue also illustrate the efficiency of AuNRs with identified aspect ratio as a potential photothermal agent around 1300 nm.