Photothermal optical coherence tomography for investigation and imaging photothermal trapping of gold nano-rods in clear media and biological tissue

Abstract

A quantitative spectrometer-based photothermal optical coherence tomography (PT-OCT) system is employed to investigate and image the photothermal trapping of gold nano-rods (GNRs) in clear and biological media. The PT-OCT system is calibrated through dynamic phase measurements of piezo motion with known driving parameters. We measure and compare the displacement sensitivities of the PT-OCT system at different camera exposure time settings in two configurations: with a distinct reference path; and with a common path. The displacement sensitivity of the system in the common path configuration is improved from 1.5 to 0.17 nm by performing Fourier analysis on the output phase. The minimum Ti:Sa power capable of inducing a detectable photothermal response of GNRs is measured to be 0.5 mW. This value agrees with the latest reported minimum Ti:Sa power for photothermal trapping GNRs. The PT-OCT system is used to generate en-face images of photothermal trapped GNRs in the water solution and in the biological tissue. By displaying the difference between successive en-face phase images, spatial distribution patterns of the aggregated GNRs, resulted from the photothermal trapping, are clearly outlined with great contrast. The photothermal trapping of GNRs in tissue shows a greater complexity than in the clear media. The limitation of the PT-OCT technology is discussed. The study proves the potential of PT-OCT for imaging the photothermal trapping of GNRs.

Molecular Contrast Optical Coherence Tomography and Its Applications in Medicine

“…All kinds of gold nanoparticles are the most popular molecular contrast agents for PT-OCT scanning due to their resonance in the NIR optical window. They are biocompatible, optical absorption tunable and can easily be used for photothermal therapy [ 104 , 106 , 107 , 112 , 113 , 115 , 116 , 172 , 173 ]. A discussion of different gold nanostructures can be found in Cho’s review [ 174 ].…”

“…Because human tissues only contain a few effective light endogenous absorbers, many nanomaterials have been developed as contrast agents for PT-OCT scans. At first, in vitro and ex vivo research with targeted gold nanospheres [ 104 ], non-targeted gold nanoshells [ 103 , 106 ], gold nanorods [ 111 , 112 ], gold nanoroses [ 105 ], and carbon nanotubes [ 113 ]. These nanoparticles showed little signal in standard OCT scans but clearly showed their distribution in photothermal OCT scans.…”

Label-free photothermal optical coherence microscopy to locate desired regions of interest in multiphoton imaging of volumetric specimens

“…Among these technologies, PT-OCT has attracted significant research attention for the evaluation of the thermal fluctuations of samples and the resulting changes in their physical and optical properties. In PT-OCT systems, nanoparticles, photothermal responsive exogenous contrast agents, and absorbers have been utilized to generate and measure the photothermal effects within the sample 42 – 45 . To date, studies using endogenous contrast agents instead of external contrast agents have been limited due to the lack of usefulness and the difficulty in measuring weak photothermal response signals.…”

Analysis of performance improvement in a swept source for optical coherence tomography applications

“…The imaging quality of the OCT system is affected by the stability, spectral region, and dispersion matching rate of each device in the system. 24,25) Therefore, to construct a frequency sweep system with high imaging quality, it is critical to model each device in the system.…”