Investigations into the use of gold nanorods (Au-NRs) for biological applications are growing exponentially due to their distinctive physicochemical properties, which make them advantageous over other nanomaterials. Au-NRs are particularly renowned for their plasmonic characteristics, which generate a robust photothermal response when stimulated with light at a wavelength matching their surface plasmon resonance. Numerous reports have explored this nanophotonic phenomenon for temperature driven therapies; however, to date there is a significant knowledge gap pertaining to the kinetic heating profile of Au-NRs within a controlled physiological setting. In the present study, the impact of environmental composition on Au-NR behavior and degree of laser actuated thermal production was assessed. Through acellular evaluation, we identified a loss of photothermal efficiency in biologically relevant fluids and linked this response to excessive particle aggregation and an altered Au-NR spectral profile. Furthermore, to evaluate the potential impact of solution composition on the efficacy of nano-based biological applications, the degree of targeted cellular destruction was ascertained in vitro and was found to be susceptible to fluid-dependent modifications. In summary, this study identified a diminution of Au-NR nanophotonic response in artificial physiological fluids that translated to a loss of application efficiency, pinpointing a critical concern that must be considered to advance in vivo, nano-based bio-applications.

Near infrared (NIR) light, which spans wavelengths from ~700-1100 nm holds particular promise in bionanotechnology-enabled applications because both NIR light and nanoparticles (NPs) have the potential for remote activation leading to exquisite localization and targeting scenarios. In this study, aqueous solutions of carbon and metal-based NPs (carbon black, single-walled carbon nanotubes, silver nanoparticles and copper nanoparticles) were exposed to continuous NIR laser (λ = 1064 nm) irradiation at powers of 2.2W and 4.5W. The differential heating of bulk aqueous suspension of NPs with varying physicochemical properties revealed maximum temperatures of 67 °C with visible evidence of condensation and bubble formation. The basis of the NP heating is due to the strong intrinsic optical absorbance in the NIR spectral window and the transduction of this NIR photon energy into thermal energy. In this regard, UV-vis measurements can accurately predict NP heating kinetics prior to NIR irradiation. Further, a uniform thermodynamic heating model demonstrates close agreement with the experimental data for the low NIR-absorbing NPs. However, the uniform thermodynamic heating model used in this study does not accurately portray the energy release upon localized NP heating because of bubble formation for the highly absorbing NPs. Therefore, this study reveals the differential heating kinetics of NPs excited with NIR with implications in the development of novel NIR-NP-based systems.

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