Graphene Meets Microbubbles: A Superior Contrast Agent for Photoacoustic Imaging

Abstract

Coupling graphene with a soft polymer surface offers the possibility to build hybrid constructs with new electrical, optical, and mechanical properties. However, the low reactivity of graphene is a hurdle in the synthesis of such systems which is often bypassed by oxidizing its carbon planar structure. However, the defects introduced with this process jeopardize the properties of graphene. In this paper we present a different approach, applicable to many different polymer surfaces, which uses surfactant assisted ultrasonication to exfoliate, and simultaneously suspend, graphene in water in its intact form. Tethering pristine graphene sheets to the surfaces is accomplished by using suitable reactive functional groups of the surfactant scaffold. We focused on applying this approach to the fabrication of a hybrid system, made of pristine graphene tethered to poly(vinyl alcohol) based microbubbles (PVA MBs), designed for enhancing photoacoustic signals. Photoacoustic imaging (PAI) is a powerful preclinical diagnostic tool which provides real time images at a resolution of 40 μm. The leap toward clinical imaging has so far been hindered by the limited tissues penetration of near-infrared (NIR) pulsed laser radiation. Many academic and industrial research laboratories have met this challenge by designing devices, each with pros and cons, to enhance the photoacoustic (PA) signal. The major advantages of the hybrid graphene/PVA MBs construct, however, are (i) the preservation of graphene properties, (ii) biocompatibility, a consequence of the robust anchoring of pristine graphene to the bioinert surface of the PVA bubble, and (iii) a very good enhancement in a NIR spectral region of the PA signal, which does not overlap with the signals of PA active endogenous molecules such as hemoglobin.

Toward an Understanding of the Microstructure and Interfacial Properties of PIMs/ZIF-8 Mixed Matrix Membranes

“…Sonication has been widely used for the synthesis and/or dispersion of a wide range of organic and inorganic particles or filaments at the nano-or mesoscale. 53,54,55 It was also implemented for the functionalization of materials 56 The impact of the molecular structure of the polymer on the compatibility with the ZIF-8 NPs was also investigated by using the PIM-EA-TB polymer (see Scheme 1). Similar results were obtained with the ZIF-8/PIM-EA-TB system for a ZIF-8 content ranging from 50, 30, and 20 wt%, showing the coexistence of PIM-EA-TB particles and compact aggregates of ZIF-8 NPs with a diameter of a few hundreds of nanometers (see Figure S16).…”

Long-term physical evolution of an elastomeric ultrasound contrast microbubble

“…In this respect, the strict interconnection between some pivotal multifunctional applications of our PVA MBs and their own peculiar crosslinked-PVA structure has been proven (e.g. the possibility of modifying the external surface of the shell, the targeting ability, and the biodistribution) [7,21]. From the compelling translational opportunities that the class of micro-structured PVA materials offers in biomedical engineering and theranostics, what emerged was the essential need to clarify how ageing affects the acoustic and structural properties of PVA-shelled MBs.…”

Photoacoustic Imaging: Contrast Agents and Their Biomedical Applications

“…Two main categories of carbon‐based nanomaterials, namely, carbon nanotubes (CNTs) and graphene‐based nanomaterials, have been extensively investigated as contrast agents. Both categories have a distinct absorption in the NIR window.…”