Tunable Ultrasmall Visible-to- Extended Near-Infrared Emitting Silver Sulfide Quantum Dots for Integrin-Targeted Cancer Imaging

Abstract

luorescent nanoparticles, especially quantum dots (QDs), are widely used in biological imaging because their unique properties can overcome many drawbacks of conventional organic fluores-cent dyes. These QD properties include broad absorption for ease of excitation at multiple wavelengths, narrow emission bands for multicolor imaging, high photo-stability for longitudinal imaging in cells and in vivo, and polyvalency for multifunctional applications.17 Although cadmium- and indium-based QDs exhibit the above desir-able properties, concerns remain about the use of these nanomaterials in biological imaging applications.8,9 To mitigate poten-tial toxicity and provide functionalizable anchors for these QDs, polymer coating has been successfully employed. Not only does this approach significantly increase hydrodynamic diameter (>20 nm), but it also complicates the synthesis procedure and occasionally employs reagents that could induce systemic toxicity. Another un-intended consequence of large QDs is that they are generally confined to the vascular space, hindering extravasation from blood vessels and subsequent diffusion to cells distant from the vessels. The combination of large size and prolonged retention in the vascular system favors opsonization and enhanced uptake by the reticuloendothelial system (RES) in the liver. These effects can induce cytotoxicity or reduce QD efficiency and sensitivity in imaging studies.10 Recent efforts to overcome size limita-tions without using toxic materials have resulted in the development of diverse nanoparticle formulations and constructs for in vivo applications. Of particular interest * Address correspondence t