On the Synthesis of Novel Dyes for Biomedical Imaging using Surface-Enhanced Raman Spectroscopy
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The syntheses and applications of dye molecules has fascinated chemists for over a century. Applications of synthetic dyes are vast, and are of interest to textile industry, molecular imaging, and renewable imaging. Recent developments in biomedical imaging and materials chemistry has necessitated the synthesis of tailored designer dyes. Specifically, Surface-Enhanced Raman Scattering (SERS) requires spectroscopically unique chromophores to permit multiplexing of convoluted biological tissues. Currently, the user is limited to a handful of commercially available dyes, precluding the true multiplexing capabilities of SERS from being realized. The pyrylium dye class has long been known, and possess several functionalizable moieties that enable control over photophysical and photochemical properties. Namely, the incorporation of heavy chalcogen atoms confer affinity for gold and silver nanopoarticles typically used in SERS assays. Subsequent studies have demonstrated that these dyes can be tailored to incorporate alkyne and cyano functional groups, which display stretching in the Raman silent region of biological tissue. An additional benefit is that the absorption of these pyrylium dyes can be tuned from the near infrared to infrared. This permits deep tissue penetration and minimizes scattering from biological tissue. Herein, the synthesis of novel near-infrared absorbing pyrylium will be described, and applications towards clinically-translatable imaging agents will be discussed.