High contrast 3-D optical bioimaging using molecular and nanoprobes optically responsive to IR light

Biophotonics is a convergent field which integrates biological physics, neurosciences, optical physics, and nanoscience for optical diagnostics, bioimaging and light activated therapies, with no tissue invasion and free of ionizing radiation. It is expected to play an important role in advancing the emerging field of molecular medicine by yielding detailed information on structures and dynamics at subcellular levels. This review, truly interdisciplinary and unique in its scope, highlights the integrated roles of the above-named disciplines for advancing IR bioimaging, aiming to attract a broad cross-section of readership of Physics Reports, and is written with multinational authorship to bring out a global perspective. A unique feature of this review is its comprehensive coverage of a multitude of the various optical bioimaging modalities, their physics principles, their relative merits, and their complementarity. Specifically covered themes are fluorescence imaging, nonlinear optical imaging, photoacoustic imaging, optical coherence tomography (OCT) and hyperspectral imaging. The review first discusses light propagation and bio-optics of processes of light absorption, scattering and transmission in biological media. It describes the various biological spectral windows of maximum optical transparencies which are suitable for optical imaging. Then, we introduce the different optical imaging modalities and their features in bioimaging both in vitro and in vivo. The role of molecular and nano-probes to serve as contrast agents for different modalities of imaging is described. A unique aspect also discussed in this review is the physics of manipulation of excitation dynamics that can make them selectively nanoemitters for fluorescence imaging; nonlinear optical probes for imaging; nano-photothermal heaters and nanothermometry for photoacoustic imaging; and nanoscatterers for OCT. As selected emerging applications, we describe imaging-guided theranostics as well as applications in novel areas of neurophotonics and nanodentistry. Finally, the review concludes by presenting current challenges and our views on future opportunities aimed to stimulate further research in this field of high societal impact.