Photonics for the Biosciences and Health: In Vivo and Microscopic Information

While photonics has entered the mainstream of research in the biosciences and health, the related revolutions are still in their infancies. I describe our recent accomplishments and directions along three lines: in vivo optical molecular imaging, coherent optical imaging, and optical nanotweezers and forces. We have shown that it is possible to image molecular information through fluorescence resonance energy transfer (FRET) parameters and related fluorescence information in vivo. This means that it is in principle possible to determine spatial maps of protein folding in vivo. Using fluorescence information, it also becomes possible to achieve neural network maps of the whole brain using direct information for the first time, and to determine drug kinetic information that has been unavailable in pharmacology. I describe our recent efforts along these lines that are made possible by our ability to relate heavily scattering optical measurements to a parameterized forward model in cost function, leading to computed images. We recently showed that speckle intensity correlations over object position lead to information about the field incident on a heavily scattering random medium and also a means to image objects moving within the scattering medium. This indicates that it is in principle possible to image objects based upon motion deep in tissue. Interestingly, the measurements are sensitive to far-subwavelength motion, and this is motion in a structured (speckled) field. Expanding this notion, I describe an imaging method to achieve far-subwavelength resolution information based on motion with structured illumination that does not require fluorescent labeling. Our basic and applied work on nanophotonics leads to a means to trap nanoparticles and hence study biological molecules without the need for large beads, and to a way to apply local forces over tens of nanometers. I describe our recent theoretical and experimental work related to nanotweezers and optical forces, offering some fundamental perspectives on the relevant physics. I also highlight key aspects of nanostructured materials in relation to the illuminating light.