8 November 2007 Nanocrystal coated beads for optical coding and whispering gallery modes
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Proceedings Volume 6796, Photonics North 2007; 67962Z (2007); doi: 10.1117/12.779084
Event: Photonics North 2007, 2007, Ottawa, Canada
Abstract
Semiconductor quantum dot nanocrystals (QDs) have unique optical properties such as size tunable photoluminescence (PL) wavelength and a chemically functionalized sufrace. Our CdSe/ZnS quantum dot nanocrystals have been made water-soluble by encapsulation in a micelle of positively charged amphiphilic copolymers. Layer-by-layer deposition of these QDs was done on sub-micrometer silica beads as well as magnetic and polymeric micro-sized beads. The negative surface charge of these various beads allowed successive stacking of cationic polyethylnimine, anionic polyacrylic acid sodium salt and the cationic encapsulated QDs. Multiple QD layers can be added by repeating the stacking process. The PL spectral of green QDs is moduoated by whispering galley mode resonances when the QDs arecoating a singe 3 μm bead. Depending on the quality factor of this microsphere, it can also be possible to detect perturbations caused by sufficient adsorption of biomolecules or even living microorganisms on a bead's surface by observing spectral shifts of the resonances. If different colorsof QDs are used to coat smaller beads where the modes are not spectrally resolved, an optical coating system can be devised base on the relative emission intensity for each color. The uniformity of a bead ensemble coded with 2 QD colors has been invesetigated, revealing a ~20% relataive standard deviation for various intensity levels. Better control of photobleaching through QD passivation reduced this number to ~8%, which would allow us to differentiate up to 2.6x1010 optical codes on our setup. Labelling large amount of molecules in solution, e.g. DNA sequences, then becomes possible with an appropriate biofunctionalization of bead surfaces.
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Claudine Nì Allen, Nicolas Lequeux, Christophe Chassenieux, Guillaume Cyr, Gilles Tessier, Benoit Dubertret, "Nanocrystal coated beads for optical coding and whispering gallery modes", Proc. SPIE 6796, Photonics North 2007, 67962Z (8 November 2007); doi: 10.1117/12.779084; https://doi.org/10.1117/12.779084
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KEYWORDS
Zinc

Cadmium

Adsorption

Silica

Luminescence

Refractive index

Nanocrystals

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