The photoluminescence dynamics of colloidal CdSe/ZnS/streptavidin quantum dots were studied using time-resolved single-molecule spectroscopy. Statistical tests of the photon-counting data suggested that the simple "on/off" discrete state model is inconsistent with experimental results. Instead, a continuous emission state distribution model was found to be more appropriate. Autocorrelation analysis of lifetime and intensity fluctuations showed a nonlinear correlation between them. These results were consistent with the model that charged quantum dots were also emissive, and that time-dependent charge migration gave rise to the observed photoluminescence dynamics.

Nanostructures of colloidal CdSe/ZnS core/shell quantum dots (QDs) surrounded by a discrete number of Au nanoparticles were generated via DNA hybridization and purified by gel electrophoresis. Statistics from TEM analysis showed a high yield of designed structures. The distance between Au particles and QD, the number of Au around the central QD, and the size of Au and QD can be adjusted. Rationally designed structures such as these hold great promise for researching the physical interactions between semiconductor and Au nanoparticles and for developing more efficient nanoprobes.

We report two cDNA microarray-based applications of DNA-nanocrystal conjugates, single-nucleotide polymorphism (SNP) and multiallele detections, using a commercial scanner and two sets of nanocrystals with orthogonal emissions. We focus on SNP mutation detection in the human p53 tumor suppressor gene, which has been found to be mutated in more than 50% of the known human cancers. DNA-nanocrystal conjugates are able to detect both SNP and single-base deletion at room temperature within minutes, with true-to-false signal ratios above 10. We also demonstrate microarray-based multiallele detection, using hybridization of multicolor nanocrystals conjugated to two sequences specific for the hepatitis B and hepatitis C virus, two common viral pathogens that inflict more than 10% of the population in the developing countries worldwide. The simultaneous detection of multiple genetic markers with microarrays and DNA-nanocrystal conjugates has no precedent and suggests the possibility of detecting an even greater number of bacterial or viral pathogens simultaneously.