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Ultrastable calixarene-coated gold nanorods as promising candidates for contrast agents in photoacoustic imaging

par Lepeintre, Victor ;Bruylants, Gilles ;Jabin, Ivan
Référence SFNano Meeting 2022 (5-7 December 2022: Strasbourg, France)
Publication Non publié, s.d.

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Résumé :

Gold nanorods (AuNRs) have emerged as extremely promising material for thedevelopment of biomedical in vivo applications. In addition to the already outstandingproperties of gold nanoparticles, such as good biocompatibility or the existence ofvarious well-established surface chemistries, AuNRs present easily tunable opticalproperties. Indeed, they display two distinct LSPR bands, a transverse and alongitudinal one, whose maximum absorbance wavelength can be tuned through theaspect ratio of the rod. For high aspect ratios, the longitudinal band lies in the nearinfrared(NIR) region, which is often referred as the “optical tissue transparencywindow” as absorbance by water, hemoglobin and other endogenous molecules isminimal in that region, leading to increased light penetration in tissues. Gold is alsoone of the most chemically inert metals and has a high electron density: it is thereforepossible to locate gold nanostructures in complex environments, such as tissues,making them ideal candidates as bioimaging contrast agents. Photoacoustic imaginghas recently emerged as one of the most promising imaging techniques that combinesthe high contrast of optical imaging with the spectral and temporal resolution ofultrasound. It is a “light in/sound out” technique compared to the conventional “soundin/sound out” ultrasound technique. AuNRs possess several qualities that make themexcellent photoacoustic contrast agents: they have a high biocompatibility, longcirculation times, and intense optical absorption cross-sections and extinctioncoefficients in the NIR region which, as already stated, allows a deeper tissuepenetration with a lower background absorption than visible light. However, onelimitation of the AuNRs is their anisotropic structure that is susceptible to deformationupon illumination: pulsed-laser irradiation has been shown to lead to the spherificationof AuNRs, leading to a rapid decrease of their NIR absorption.An efficient strategy for the building of robust and thin organic coatings on varioussurfaces consists in the use of calix[4]arene-tetradiazonium salts. Indeed, thesemolecular platforms can be irreversibly and strongly grafted on surfaces through thereduction of their diazonium groups. We have adapted this calixarene-based coatingtechnology to produce ultrastable AuNRs (AuNRs-calix), more stable thanconventional AuNRs. These calixarene-coated AuNRs were then used as contrastagents in photoacoustic imaging. Our preliminary results indicate that these AuNRscalixremain stable for longer periods of time under pulsed laser irradiation thancommonly used AuNRs coated with citrate or thiols. Increasing the stability of AuNRsunder laser irradiation, allowing longer analysis time, could lead to significant advancesin the field.