Gold nanorod reshaping in vitro and in vivo using a continuous wave laser

Abstract

Gold nanorods (GNRs) are increasingly being investigated for cancer theranostics as they possess features which lend themselves in equal measures as contrast agents and catalysts for photothermal therapy. Their optical absorption spectral peak wavelength is determined by their size and shape. Photothermal therapy using GNRs is typically established using near infrared light as this allows sufficient penetration into the tumour matrix. Continuous wave (CW) lasers are the most commonly applied source of near infrared irradiation on GNRs for tumour photothermal therapy. It is perceived that large tumours may require fractionated or prolonged irradiation. However the true efficacy of repeated or protracted CW irradiation on tumour sites using the original sample of GNRs remains unclear. In this study spectroscopy and transmission electron microscopy are used to demonstrate that GNRs reshape both in vitro and in vivo after CW irradiation, which reduces their absorption efficiency. These changes were sustained throughout and beyond the initial period of irradiation, resulting from a spectral blue-shift and a considerable diminution in the absorption peak of GNRs. Solid subcutaneous tumours in immunodeficient BALB/c mice were subjected to GNRs and analysed with electron microscopy pre- and post-CW laser irradiation. This phenomenon of thermally induced GNR reshaping can occur at relatively low bulk temperatures, well below the bulk melting point of gold. Photoacoustic monitoring of GNR reshaping is also evaluated as a potential clinical aid to determine GNR absorption and reshaping during photothermal therapy. Aggregation of particles was coincidentally observed following CW irradiation, which would further diminish the subsequent optical absorption capacity of irradiated GNRs. It is thus established that sequential or prolonged applications of CW laser will not confer any additional photothermal effect on tumours due to significant attenuations in the peak optical absorption properties of GNRs following primary laser irradiation.

Laser‐induced optothermal response of gold nanoparticles: From a physical viewpoint to cancer treatment application

“…The consequence of using CW laser on the morphology of GNRs was demonstrated in the in vitro and in vivo study by Harris‐Birtill et al [178]. They compared the absorbance and the spectral peak for GNRs with different optical density before and after exposure to the laser beam.…”

The Combined Use of Gold Nanoparticles and Infrared Radiation Enables Cytosolic Protein Delivery

“…Also, UV‐VIS‐NIR spectra recorded after irradiation revealed a minor shift in the case of unmodified AuNRs (Figure S5B) and no shift in the case of the modified ones, which is explained by the stabilizing effect of PEG modification (Figure 2 B). The conservation of the UV‐VIS‐NIR spectra of this sample confirms the photothermal stability of the system, suggesting no re‐shaping of the AuNRs [41–43] …”

Monte Carlo Simulations of Heat Deposition during Photothermal Skin Cancer Therapy Using Nanoparticles

“…In our work, the aim was to develop and validate a theoretical approach to thermal dose deposition within tissue, so that: (i) the spatial and temporal distributions of thermal dose within the tissue could be analysed —which is technically unfeasible with most experimental set-ups; (ii) offer a predictive tool which allows researchers to estimate likely thermal effects of concentrations and spatial profiles of nanoparticles as well as irradiation dose that could influence tumour treatment efficacy; and (iii) give an estimate of the concentration of gold nanorods that is needed to give a heat rise that results in adequate cell kill within the tumour (many experimental reports do not measure the concentration of GNRs in the tumour at the point of irradiation—rather they only know the injected concentration). Another factor that could effectively lower the concentration of nanorods is a sintering effect where localized heat deforms the nanoparticles such that they no longer exhibit plasmonic absorption at the irradiation wavelength [26].…”