| Semiconductor quantum dots are of considerable interest not only because of their unique size-tunable properties, but also their dimensional similarities with biological macromolecules (e.g., nucleic acids and proteins). These similarities could allow an integration of nanotechnology and biology, leading to major advances in medical diagnostics, targeted therapeutics, molecular and cell biology.; In this context, we have synthesized highly fluorescent ZnS-capped CdSe dots, and developed novel surface coating methods to make the dots water-soluble and stable in complicated biological environments. After linking to biomolecules, these fluorescent nanoparticles are excellent fluorophores for multicolor optical imaging and ultrasensitive detection. In particular, we have achieved immunostaining of single cells and clinical tissue specimens, as well as tumor imaging and targeting in live animals. In comparison to organic dyes, the advantages of using quantum dots include size-tunable fluorescence emission, narrow and symmetrical emission spectra, broad excitation profiles and photostability.; We have also developed an optical encoding technology for high-throughput biomolecule analysis by embedding multicolor quantum dots into microbeads at precisely controlled ratios. The use of 10 intensity levels and 6 colors could theoretically code one million nucleic acid and protein sequences. Spectroscopic and flow cytometric measurements indicate that the quantum-dot tagged beads are highly uniform and reproducible, yielding bead identification accuracies as high as 99.99% under favorable conditions. DNA hybridization studies demonstrate that the coding and target signals can be simultaneously read at the single-bead level. This spectral coding technology is expected to open new opportunities in gene expression studies, high-throughput screening, and medical diagnostics. |
