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David Bradley ISSUE #61
December 2006
Zhongze Gu
Zhongze Gu
Biomolecules Out on a Wing

Photonic crystals give butterflies their beautiful colors and synthetic versions are now being developed for a range of technological applications. Most recently, Zhongze Gu, Deputy Director of the State Key Laboratory of Bioelectronics at Southeast University, Nanjing, China, has published details of a photonic crystal that can be used to carry biomolecules, such as proteins and nucleic acids for sophisticated diagnostic tests and multiassays, as well as carrying smaller molecules for high-throughput pharmaceutical screening.

Until now, the only commercial approach to encoding biomolecular carriers was to use fluorescent dyes. In order to distinguish the attached biomolecules, these carriers are doped or labeled with dyes. However, fluorescent molecules suffer from some serious drawbacks, such as background noise and photo-bleaching in which the light used to trigger the fluorescence for detecting the labeled molecules bleaches the dyes, thus rendering them useless. Such problems complicate what would otherwise be a simple procedure, adding time and expense to diagnostics and lab tests.

Credit: Gu et al/Wiley

Gu and his colleagues suggest that photonic crystals, which are not intrinsically pigmented, produce different colors because their surfaces reflect light of different wavelengths to different degrees&mdashthey are iridescent, like the surface of a butterfly's wing. Because their color is due to solid state features rather than a photochemical response, they cannot be bleached nor can their color be masked by or confused with other fluorescent signals from a sample.

Gu and his colleagues have now developed tiny photonic crystal beads with stable colors, on which biomolecular probes can be immobilized and used to detect multiplex components of interest in the same sample.

"In multiplex bioanalysis and high-throughput screening, encoded supports are needed in order to allow lots of individual assays to be performed simultaneously within the same sample," Gu told Reactive Reports. "Our method uses colloidal photonic crystal beads as the supports, which means that the encoding element is stable, the nanostructure of the beads endows the high surface-to-volume ratio, the readout of the codes is simple." He adds that photonic crystals might also be used in conjunction with fluorescent labels to enhance the fluorescent signal and protect them from photo-bleaching.

Angew Chem Int Edn, 2006, 45, 6835-6838; http://dx.doi.org/10.1002/anie.200601302