Optothermal properties of plasmonic inorganic nanoparticles for photoacoustic applications

Abstract

Plasmonic systems are becoming a favourable alternative to dye molecules in the generation of photoacoustic signals for spectroscopy and imaging. In particular, inorganic nanoparticles are appealing because of their versatility. In fact, as the shape, size and chemical composition of nanoparticles are directly correlated with their plasmonic properties, the excitation wavelength can be tuned to their plasmon resonance by adjusting such traits. This feature enables an extensive spectral range to be covered. In addition, surface chemical modifications can be performed to provide the nanoparticles with designed functionalities, e.g., selective affinity for specific macromolecules. The efficiency of the conversion of absorbed photon energy into heat, which is the physical basis of the photoacoustic signal, can be accurately determined by photoacoustic methods. This review contrasts studies that evaluate photoconversion in various kinds of nanomaterials by different methods, with the objective of facilitating the researchers' choice of suitable plasmonic nanoparticles for photoacoustic applications.

NIR-Absorbing Mesoporous Silica-Coated Copper Sulphide Nanostructures for Light-to-Thermal Energy Conversion

“…In the past decades theoretical studies [ 1 , 2 , 3 ], as well as in vitro and in vivo investigation [ 4 , 5 , 6 , 7 , 8 ], have demonstrated the great potential of colloidal plasmonic nanoparticles (NPs) as nanoheaters in targeted photothermal (PT) therapy, and are suggested as an alternative approach to chemotherapy for cancer treatment [ 9 , 10 , 11 ]. Photoexcitation of the NP surface plasmon oscillations by a resonant laser light results in NP light absorption and, due to subsequent nonradiative relaxation, thermal energy is released through the NP interface into the environment [ 1 , 2 ].…”

“…A similar laser light-activated process can be also investigated on plasmonic NPs that behave as exogenous contrast agents for non-invasive photoacoustic imaging (PAI). Upon excitation with appropriate short-pulsed light, NPs convert the absorbed incident photons into heat, generating a thermoacoustic wave, which can be detected by an ultrasound transducer for image reconstruction [ 3 ].…”

“…Compared to visible light, the NIR radiation can penetrate deeper into biological tissues, with minimal attenuation by water and hemoglobin and other biological components, and thus, reduced interference due to cell constituents. Such features, in turn, enhance NP absorption, improve PT efficiency, and increase therapeutic efficacy for subcutaneous tumor treatments [ 1 , 3 , 15 ]. Moreover, the anisotropic plasmonic NPs are valuable in PT therapy not only for their NIR absorbing properties.…”

“…Moreover, the anisotropic plasmonic NPs are valuable in PT therapy not only for their NIR absorbing properties. Theoretical simulations [ 1 , 3 , 16 ] and experimental studies demonstrate an electrical field enhancement, occurring at the sharp edges or vertices in anisotropic NPs, due to hot spot generation, which is reflected by a strong increase in temperature [ 17 ]. Localization of the electric field intensity on the tips leads to a strong dephasing of coherently oscillated surface electrons, whose energy is transferred to the atomic lattice effusing a strong flux of heat at the particle−dielectric interface [ 18 ].…”

Acid-triggered in vivo aggregation of Janus nanoparticles for enhanced imaging-guided photothermal therapy

“…Particularly, the light absorption of Au NPs can be shied to the red or near-infrared (NIR) region by modulating their size, which makes Au NPs ideal not only for photothermal therapy (PTT) but also for use in photoacoustic imaging (PAI) promising candidates. Aggregation of Au NPs promotes the formation of interparticle "hot spots" and signicantly increases the localized surface plasmon resonance coupling of Au NPs, 27,28 enhancing the self-PAI signal and PTT efficacy. 29,30 In this study, we describe the development of gold-iron oxide Janus (GIJ) NPs by a one-pot method.…”