Smart-Dust-Nanorice for Enhancement of Endogenous Raman Signal, Contrast in Photoacoustic Imaging, and T2-Shortening in Magnetic Resonance Imaging

Recent Advances in Photoacoustic Tomography

Photoacoustic tomography (PAT) that integrates the molecular contrast of optical imaging with the high spatial resolution of ultrasound imaging in deep tissue has widespread applications in basic biological science, preclinical research, and clinical trials. Recently, tremendous progress has been made in PAT regarding technical innovations, preclinical applications, and clinical translations. Here, we selectively review the recent progresses and advances in PAT, including the development of advanced PAT systems for small-animal and human imaging, newly engineered optical probes for molecular imaging, broad-spectrum PAT for label-free imaging of biological tissues, high-throughput snapshot photoacoustic topography, and integration of machine learning for image reconstruction and processing. We envision that PAT will have further technical developments and more impactful applications in biomedicine.

A smart theranostic platform for photoacoustic and magnetic resonance dual-imaging-guided photothermal-enhanced chemodynamic therapy

The use of smart theranostic agents in multimodal imaging and treatment is a promising strategy to overcome the limitations of single mode diagnosis and treatment, and can greatly improve the diagnosis and effects of treatment. In this study, a gold@manganese dioxide (Au@MnO2) core-shell nanostructure was designed as a glutathione (GSH)-triggered smart theranostic agent for photoacoustic and magnetic resonance (MR) dual-imaging-guided photothermal-enhanced chemodynamic therapy. Both in vitro and in vivo experiments demonstrated not only that the photoacoustic and MR imaging function of Au@MnO2 could be activated by a high endogenous GSH concentration, but also that after being triggered by the endogenous GSH, Au@MnO2 had an excellent synergistic treatment effect in photothermal-enhanced chemodynamic therapy under the guidance of photoacoustic and MR imaging. This study demonstrated that the use of GSH-triggered Au@MnO2 in photoacoustic and MR dual-imaging-guided photothermal-enhanced chemodynamic therapy is a smart theranostic nanoplatform for the accurate diagnosis and efficient treatment of cancer.

Recent Advances in Molecular Imaging with Gold Nanoparticles

Gold nanoparticles (AuNP) have been extensively developed as contrast agents, theranostic platforms, and probes for molecular imaging. This popularity has yielded a large number of AuNP designs that vary in size, shape, surface functionalization, and assembly, to match very closely the requirements for various imaging applications. Hence, AuNP based probes for molecular imaging allow the use of computed tomography (CT), fluorescence, and other forms of optical imaging, photoacoustic imaging (PAI), and magnetic resonance imaging (MRI), and other newer techniques. The unique physicochemical properties, biocompatibility, and highly developed chemistry of AuNP have facilitated breakthroughs in molecular imaging that allow the detection and imaging of physiological processes with high sensitivity and spatial resolution. In this Review, we summarize the recent advances in molecular imaging achieved using novel AuNP structures, cell tracking using AuNP, targeted AuNP for cancer imaging, and activatable AuNP probes. Finally, the perspectives and current limitations for the clinical translation of AuNP based probes are discussed.

A Gold Nanocage/Cluster Hybrid Structure for Whole-Body Multispectral Optoacoustic Tomography Imaging, EGFR Inhibitor Delivery, and Photothermal Therapy

Gold nanocages (AuNCs) and gold nanoclusters (AuClusters) are two classes of advantageous nanostructures with special optical properties, and many other attractive properties. Integrating them into one nanosystem may achieve greater and smarter performance. Herein, a hybrid gold nanostructure for fluorescent and optoacoustic tomography imaging, controlled release of drugs, and photothermal therapy (PTT) is demonstrated. For this nanodrug (EA-AB), an epidermal growth factor receptor (EGFR) inhibitor erlotinib (EB) is loaded into AuNCs, which are then capped and functionalized by biocompatible AuCluster@BSA (BSA = bovine serum albumin) conjugates via electrostatic interaction. Upon cell internalization, the lysosomal proteases and low pH cause the release of EB from EA-AB, and also induce fluorescence restoration of the AuCluster for imaging. Irradiation with near-infrared light further promotes the drug release and affords a PTT effect as well. The AuNC-based nanodrug is optoacoustically active, and its biodistribution and metabolic process have been successfully monitored by whole-body and 3D multispectral optoacoustic tomography imaging. Owing to the combined actions of PTT and EGFR pathway blockage, EA-AB exhibits marked tumor inhibition efficacy in vivo.

Current concepts in nanostructured contrast media development for in vivo photoacoustic imaging

To overcome the endogenous photoacoustic contrast arising from endogenous species, specific contrast agents need to be developed, allowing PAI to successfully identify targeted contrast in the range of wavelength in which the interference from the biomatrix is minimized.