Fluorescent nanoparticles (NPs) are promising optical probes for biological and biomedical applications, thanks to their excellent photophysical properties, color tunability and facile bioconjugation. It still remains unclear, however, how fluorescent NPs behave in the complex biological environment. Our group has quantified interactions of different fluorescent NPs (i.e., semiconductor quantum dots and metal nanoclusters) with serum proteins and living cells by the combined use of different spectroscopic and microscopic techniques. Our studies show that (1) interactions with proteins may significantly alter the photophysical properties of the NPs as well as the responses of cells internalizing them; (2) protein surface charge distributions play an important role in the interactions of NPs with proteins and cells; (3) ultrasmall NPs (diameter less than 10 nm) show a cellular internalization behavior that is distinctly different from the one observed with larger particles (diameter ~100 nm).
Fluorescent metal nanoclusters (NCs) have many attractive features, including ultrasmall size, good biocompatibility and
large Stokes shift, thus making them promising alternatives as fluorescent markers for biological applications. We have
developed a facile method of synthesizing water-soluble, near-infrared (NIR) luminescent AuNCs. By virtue of the long
fluorescence lifetime of these AuNCs, we explored their application in cellular fluorescence lifetime imaging (FLIM).
Furthermore, the interaction of AuNCs with biomolecules such as proteins has been investigated. Upon protein
association, the fluorescence of AuNCs was found to be enhanced and their luminescence lifetime was prolonged. Our
studies underline the importance of studying the behavior of AuNCs within the complex biological environment for their
application as novel cellular imaging probes.
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