The tremendous impact that cardiovascular diseases have in modern society is motivating the research of novel imaging techniques that would make possible early diagnosis and, therefore, efficient treatments. Cardiovascular optical coherence tomography (CV-OCT) emerged as a result of such a demand, and it has already been used at the clinical level. Full utilization of CV-OCT requires the development of novel contrast molecular agents characterized by a large scattering efficiency in the infrared (800-1400 nm). Gold nanoparticles (GNPs) seem to be the best candidates, but their scattering properties in the infrared are hardly known. In most of the cases, scattering properties are extracted from numerical simulations. This knowledge gap here is covered by providing an experimental evaluation of the infrared scattering properties of different GNPs (nanoshells, nanostars, and nanorods). These GNPs display remarkable extinction coefficients in the first and second biological windows, including the particular CV-OCT wavelength. We use a unique combination of techniques (thermal loading experiments, infrared optical coherence tomography, infrared dark field microscopy, and optoacoustic spectroscopy) to experimentally determine the scattering efficiency at three different near-infrared wavelengths (808 nm, 980 nm, and 1280 nm), lying in the first and second biological windows. Consequently, this work determines experimentally the influence of particle morphology on the infrared scattering efficiency of GNPs and evidences the existence of remarkable discrepancies between experimental data and numerical simulations.

This work was supported by the Spanish Ministerio de Economía y Competitividad under Project No. MAT2016-75362-C3-1-R. J.A.S.-G. and D.R.A. acknowledge the partial financial support from the Spanish Ministerio de Economía y Competitividad through the grant LENSBEAM (No. FIS2015-69295-C3-2-P), Ministerio de Educación, Cultura y Deporte through a Ph.D. Fellowship (No. FPU15/03566), and also Consejo Superior de Investigaciones Científicas (i-COOP LIGHT 2015CD0011). J.H. acknowledges the scholarship from the China Scholarship Council (CSC, No. 201506650003). D.T. and P.R.G. acknowledge the Mineco and MdM Excellence Intiative (Nos. FJCI-2014-22398, RYC-2012-10059, CTQ2013-45433-P[FEDER], and MDM-2014-0370-04).