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Quantum-dot-tagged microbeads for multiplexed optical coding of biomolecules


Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots (zinc sulfide–capped cadmium selenide nanocrystals) into polymeric microbeads at precisely controlled ratios. Their novel optical properties (e.g., size-tunable emission and simultaneous excitation) render these highly luminescent quantum dots (QDs) ideal fluorophores for wavelength-and-intensity multiplexing. The use of 10 intensity levels and 6 colors could theoretically code one million nucleic acid or protein sequences. Imaging and spectroscopic measurements indicate that the QD-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.

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Figure 1: (A) Schematic illustration of optical coding based on wavelength and intensity multiplexing.
Figure 2: Fluorescence micrograph of a mixture of CdSe/ZnS QD-tagged beads emitting single-color signals at 484, 508, 547, 575, and 611 nm.
Figure 3: Quantitative analysis of single-bead signal intensities, uniformity and reproducibility of QD incorporation.
Figure 4: Multicolor QD-tagged beads with precisely controlled fluorescence intensities.
Figure 5: Schematic illustration of DNA hybridization assays using QD-tagged beads.
Figure 6: DNA hybridization assays using multicolor encoded beads.


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We are grateful to Warren C.-W. Chan for help in quantum dot synthesis and for stimulating discussions. This work was supported in part by the National Institutes of Health and the Department of Energy. S.N. acknowledges the Whitaker Foundation for a Biomedical Engineering Award and the Beckman Foundation for a Beckman Young Investigator Award.

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Correspondence to Shuming Nie.

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Han, M., Gao, X., Su, J. et al. Quantum-dot-tagged microbeads for multiplexed optical coding of biomolecules. Nat Biotechnol 19, 631–635 (2001).

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