The increasing interest around imaging and microsurgery techniques based on the photoacoustic effect has boosted active research into the development of exogenous contrast agents that may enhance the potential of this innovative approach.
In this context, plasmonic particles as gold nanorods are achieving resounding interest, owing to their efficiency of photothermal conversion, intense optical absorbance in the near infrared region, inertness in the body and convenience for conjugation with ligands of molecular targets.
On the other hand, the photoinstability of plasmonic particles remains a remarkable obstacle. In particular, gold nanorods easily reshape into nanospheres and so lose their optical absorbance in the near infrared region, under exposure to few-ns-long laser pulses. This issue is attracting much attention and stimulating ad-hoc solutions, such as the addition of rigid shells and the optimization of multiple parameters.
In this contribution, we focus on the influence of the shape of gold nanorods on their photothermal behavior and photostability. We describe the photothermal process in the gold nanorods by modeling their optical absorption and consequent temperature dynamics as a function of their aspect ratio (length / diameter).
Our results suggest that increasing the aspect ratio does probably not limit the photostability of gold nanorods, while shifting the plasmonic peak towards wavelengths around 1100 nm, which hold more technological interest.
Gold nanarods (GNRs) with an aspect ratio equal to 3:1 and 4:1 and a major axis equal to 50 nm, silanized and capped with titania (c-GNRs), were embedded within the 6μ thick semiconductor layer of DSSCs based on an organic D-π-A sensitizer dye (L0 or L1) and a squaraine co-sensitizer (SQ2). These dye cocktails and a transparent titania paste were selected to maximize the transmittance of DSSCs in a region of maximum visual acuity. The thickness of the SiO2 layer was consisted of about 4.0 nm and that of the TiO2 layer of about 2.0 nm in order to maintain high the localized surface plasmon resonance (SPR) effects produced by GNRs and to prevent Au corrosion. The slight thickness of both types of capping was not sufficient to preserve the dimensions of the gold nanorods during sintering at 450 °C. Absorbance, transmittance and reflectance spectra of the films were measured after they were dyed. The plasmonic effects were distinguishable both in absorbance and absorptance spectra for all the types of dyes cocktails and GNRs aspect ratios used. Transmittance values depended on the cocktail used and on the adsorption of the dyes on the semiconductor film blended with c-GNRs. When the mix of L1 and SQ2 was used together with GNRs of a 3:1 aspect ratio, we achieved an increase of 23% in DSSC efficiency (from 3.50% to 4.32%) but transmittance values higher than 50% only between 560 nm and 630 nm.
Photoacoustic imaging and microsurgery have recently attracted attention for applications in oncology. Here, we present a versatile set-up to trigger vapor microbubbles around plasmonic nanoparticles by a combined light-ultrasound excitation. This system enables the detection and parametrization of bubbles as a function of several variables, such us optical fluence, ultrasound intensity, nanoparticles concentration, thus providing useful directions to the development of new strategies for treatments based on optical cavitation.
Imaging and microsurgery procedures based on the photoacoustic effect have recently attracted much attention for cancer treatment. Light absorption in the nanosecond regime triggers thermoelastic processes that induce ultrasound emission and even cavitation. The ultrasound waves may be detected to reconstruct images, while cavitation may be exploited to kill malignant cells. The potential of gold nanorods as contrast agents for photoacoustic imaging has been extensively investigated, but still little is known about their use to trigger cavitation. Here, we investigated the influence of environment thermal properties on the ability of gold nanorods to trigger cavitation by probing the photoacoustic emission as a function of the excitation fluence. We are confident that these results will provide useful directions to the development of new strategies for therapies based on the photoacoustic effect.
Over recent years, gold nanorods (GNRs) have emerged as a promising material in biomedical optics and have been proposed as contrast agents for the photothermal therapy and the photoacoustic imaging of tumors. A pioneering approach to target tumors is the use of cellular vehicles, i.e. cells of the immune system that exhibit an innate tropism to tumors and that can be serve as Trojan horses. This strategy relies on cell types, such as tumor-associated macrophages or T cells, that are recruited by or naturally traffic to the microenvironment of tumors and that can be isolated from a patient and loaded with plasmonic particles in vitro. In this work, GNRs were synthesized and designed to combine high optical and photo-stability and the ability to accumulate into cells of the immuno system. Particles were silanized, PEGylated and conjugated with cationic moieties. Different cationic compounds were tested and the cell viability and uptake of the particles were studied on complementary cell types. The cytotoxicity test was based on a colorimetric WST-8 assay while the intracellular amount of gold and the optical absorbance of the cells were quantified by spectrophotometry. Moreover, we investigated the effect of GNRs on the cell migration and the production of cytokines in the presence of pro-inflammatory stimuli, which provide a functional overview on the feasibility of this approach to target.
Photoacoustic imaging (PAI) and microsurgery are attracting interest for cancer treatment. The absorption of light triggers thermoelastic processes that cause ultrasound emission and even cavitation. The ultrasounds emission is exploited to reconstruct images, the cavitation may be used to destroy malignant cells. Gold nanorods (GNRs) have been investigated as contrast agents for PAI, but still little is known about the trigger of cavitation processes.
Here we study the influence of GNRs parameters, such as their size, coating and environment, on the cavitation threshold.
We expect these results will provide useful indications to develop new theranostics techniques based on light-ultrasound interaction
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