Sarah Lai

A multifunctional organosilica cross-linker for the bio-conjugation of gold nanorods

We report on the use of organosilica shells to couple gold nanorods to functional peptides and modulate their physiochemical and biological profiles. In particular, we focus on the case of cell penetrating peptides, which are used to load tumor-tropic macrophages and implement an innovative drug delivery system for photothermal and photoacoustic applications. The presence of organosilica exerts subtle effects on multiple parameters of the particles, including their size, shape, electrokinetic potential, photostability, kinetics of endocytic uptake and cytotoxicity, which are investigated by the interplay of colorimetric methods and digital holographic microscopy. As a rule of thumb, as the thickness of organosilica increases from none to ∼30nm, we find an improvement of the photophysical performances at the expense of a deterioration of the biological parameters. Therefore, detailed engineering of the particles for a certain application will require a careful trade-off between photophysical and biological specifications.

The role of silanized and capped with TiO2 gold nanorods of different aspect ratios in co-sensitized DSSCs for transparent windows applications

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.

Light-activated microbubbles around gold nanorods for photoacoustic microsurgery

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.

Ready-to-use protein G-conjugated gold nanorods for biosensing and biomedical applications

BackgroundGold nanorods (GNRs) display unique capacity to absorb and scatter near infrared light, which arises from their peculiar composition of surface plasmon resonances. For this reason, GNRs have become an innovative material of great hope in nanomedicine, in particular for imaging and therapy of cancer, as well as in photonic sensing of biological agents and toxic compounds for e.g. biomedical diagnostics, forensic analysis and environmental monitoring. As the use of GNRs is becoming more and more popular, in all these contexts, there is emerging a latent need for simple and versatile protocols for their modification with targeting units that may convey high specificity for any analyte of interest of an end-user.ResultsWe introduce protein G-coated GNRs as a versatile solution for the oriented immobilization of antibodies in a single step of mixing. We assess this strategy against more standard covalent binding of antibodies, in terms of biocompatibility and efficiency of molecular recognition in buffer, serum and plasma, in the context of the development of a direct immunoenzymatic assay. In both cases, we estimate an average of around 30 events of molecular recognition per particle. In addition, we disclose a convenient protocol to store these particles for months in a freezer, without any detrimental effect.ConclusionsThe biocompatibility and efficiency of molecular recognition is similar in either case of GNRs that are modified with antibodies by covalent binding or oriented immobilization through protein G. However, protein G-coated GNRs are most attractive for an end-user, owing to their unique versatility and ease of bioconjugation with antibodies of her/his choice.

Light activated microbubbles for imaging and microsurgery

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.

Light and ultrasound activated microbubbles around gold nanorods for photoacoustic microsurgery

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.

Optically induced microbubbles around gold nanorods: The influence of particle parameters and environment on cavitation threshold

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