Center for Functional Nanomaterials Seminar

Quantum dot nanocrystals [QDs] have a number of unique fluorescent properties that overcome the limitations of conventional organic dyes: (1) QDs exhibit long fluorescence lifetimes, (2) narrow emission spectra, and (3) are not susceptible to conventional photo-degradation. QDs not only exhibit higher fluorescence quantum yields than organic dyes, but also their longer fluorescence lifetime allows temporal “gating” with respect to background auto-fluorescence. Reduction of the auto-fluorescence is important for biological imaging and sensing applications. Only a few nanometers in diameter, QDs are usually composed of a semiconductor core of CdSe capped with a ZnS shell. CdSe QDs fluoresce with a very broad absorption and narrow emission spectra. By adjusting the core size, the emission wavelength can be finely tuned. The ZnS shell helps in stabilizing the core, makes the light emission more intense, and keeps the NC from degrading. For biological applications, the surfaces of QDs can be conjugated with biological molecules (such as protein antibodies, antigens, DNA, and RNA), so they can be readily incorporated into specific sites of complex biological and biomimetic systems for in vivo and in vitro imaging.

The highly specific linkage of QD to the engineered phage and to the biological target such as bacteria (streptavidin-coated-QD---biotin-coated-phage-bacteria complex) provides a unique fluorescent signal at the single copy sensitivity. This new detection strategy based on phage-QD complexes enables a simple, diffraction-limited fluorescence optical microscopy be used for highly precise quantitative measurements with the sensitivity to the single copy number of bacteria, phage or QD. We will discuss our results on transmission electron microscopy, flow cytometry, and fluorescence optical microscopy. The phage-QD nanocomplex can be used to specifically identify biological targets including bacterial strain(s) or cells from clinical or environmental isolat