Photoenhancement of lifetimes in CdSe/ZnS and CdTe quantum dot-dopamine conjugates.

The response of water-soluble, mercaptocarboxylic acid-capped fluorescent semiconductor nanoparticles, or quantum dots (QDs), to extended visible-light irradiation is variable and poorly described. Here we use time-resolved spectroscopy to investigate the photoluminescence intensities and lifetimes of CdSe/ZnS and CdTe QDs as a function of blue light illumination. Conjugates of the particles to the electron donor dopamine were also investigated, and the effect of the antioxidant beta-mercaptoethanol was explored.

Fluorescence intensity and intermittency as tools for following dopamine bioconjugate processing in living cells.

CdSe/ZnS quantum dots (QDs) conjugated to biomolecules that quench their fluorescence, particularly dopamine, have particular spectral properties that allow determination of the number of conjugates per particle, namely, photoenhancement and photobleaching. In this work, we quantify these properties on a single-particle and ensemble basis in order to evaluate their usefulness as a tool for indicating QD uptake, breakdown, and processing in living cells. This creates a general framework for the use of fluorescence quenching and intermittency to better understand nanoparticle-cell interactions.

Effect of ligand density on the spectral, physical, and biological characteristics of CdSe/ZnS quantum dots.

Chemical modification of the surface of CdSe/ZnS quantum dots (QDs) with small molecules or functional ligands often alters the characteristics of these particles. For instance, dopamine conjugation quenches the fluorescence of the QDs, which is a property that can be exploited for sensing applications if the conjugates are taken up into living cells. However, different sizes and/or preparations of mercaptocarboxylic acid solubilized QDs show very different properties when incubated with cells.

Photophysics of dopamine-modified quantum dots and effects on biological systems.

Semiconductor quantum dots (QDs) have been widely used for fluorescent labelling. However, their ability to transfer electrons and holes to biomolecules leads to spectral changes and effects on living systems that have yet to be exploited. Here we report the first cell-based biosensor based on electron transfer between a small molecule (the neurotransmitter dopamine) and CdSe/ZnS QDs.