Polymethine fluorophores for in vivo shortwave infrared imaging

Optical detection of biological function in living cells, model organisms, and humans is a powerful approach for studying physiology and disease. The amount of information that can be gained noninvasively, however, is limited in penetration depth and resolution by unfavorable interactions between light and tissue. Optical imaging with detection in the shortwave infrared (SWIR, 1,000–2,000 nm) region enables the observation of structure and function in deep tissue. With low scattering coefficients and few naturally occurring molecules with SWIR absorption or emission, SWIR light has minimal competing optical phenomena within biology. While rapid development of contrast agents has followed the decade-old discovery of SWIR detection as a noninvasive imaging technique, improved bright and biocompatible contrast agents are vital for imaging with minimal biological perturbation. In this dissertation, long wavelength absorbing and emitting polymethine dyes are established, optimized, and applied, in combination with imaging methodology, to advance SWIR imaging in mice.Chapter One is a perspective on the growth and application of polymethine dyes as shortwave infrared contrast agents. Chapter Two describes the initial development and in vivo SWIR imaging application of 7-dimethylamino flavylium polymethine dyes. Chapters Three and Four establish excitation multiplexing with shortwave infrared detection as an effective method to obtain real-time multicolor images in vivo, noninvasively. In Chapter Three, flavylium heptamethine dyes with absorption wavelengths matched to excitation lasers enable two- and three-color imaging in anesthetized and awake animals. Chromenylium penta- and heptamethine dyes which display increased brightness are offered in Chapter Four as improved labels for fast and multicolor SWIR imaging using near infrared excitation wavelengths. Chapter Five details strategies taken to facilitate delivery of polymethine dyes to biological systems. The approaches include encapsulation in phospholipid, organic polymer-based, and perfluorocarbon nanomaterials, as well as appending lipophilic, fluorophilic, and hydrophilic solubilizing tags to the chromophores. Chapter Six explores the use of hollow mesoporous silica nanoparticles (HSMNs) to stabilize J-aggregates for SWIR imaging. Chapter Seven is a study of the photophysical properties of indocyanine green (ICG) relevant to benchmarking SWIR imaging experiments