Birtwell, S., Galitonov, G.S., Whitton, A., Morgan, H. and Zheludev, N.
Diffraction bar-codes as high capacity optical microtags for chemical and biological applications
At QEP-17 at Photon06.
04 - 07 Sep 2006.
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The rapid advances in high throughput screening, combinatorial chemistry, genomic and proteomic sciences have stimulated dramatic development of new encoding strategies for bead-based assays. Several optical encoding methods are currently used in these applications, including fluorescence, Raman and magnetic tagging on microbeads. Here we describe a new method for encoding small beads which allows for non-contact reading and offer potentially millions of distinguishable tags. The tagging technique is based on fabricating a nano-structured pattern on the surface of the particle, which is only a few microns in size, read by detecting the spatial distribution of laser light diffracted by the tag. In the simplest implementation, the pattern is no more than a miniature diffraction grating, where information is coded in the pitch or spatial dimensions of the grating, read by detecting the angle of the diffracted orders. A huge increase in capacity has been achieved by using a number of superimposed gratings with different pitch and by employing two dimensional gratings. Distinguishing of tens of thousands of tags has been demonstrated on a chromium-on-glass chip library of 50 µm long tags. The technique has also been proved with biologically compatible gratings manufactured on metal nanoparticle doped SU8 photo-polymer.
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