Recent advances in photoacoustic contrast agents for in vivo imaging.

Photoacoustic imaging (PAI) is a noninvasive hybrid imaging modality offering rich optical contrast and high depth-to-resolution ratio deep-tissue imaging. Endogenous chromophores present in the body such as hemoglobin, lipid, melanin, and so on provide strong photoacoustic contrast due to their strong light absorption in certain optical window. To enhance the performance of PAI further, researchers have developed several exogenous contrast agents such as metallic nanoparticles, carbon-based nanomaterials, quantum dots, organic small molecules, semiconducting polymer nanoparticles, and so on. These exogenous contrast agents not only help improving the imaging contrast, but also make targeted molecular imaging possible. In this review article, we first discuss the state-of-the-art PAI techniques with endogenous contrast mechanism. Later, we provide an overview of recent progress in the development of exogenous photoacoustic contrast agents for in vivo imaging applications. Finally, we present the pros/cons of the existing PA contrast agents along with future challenges of contrast agent-based PAI for biomedical applications. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.