Liquid-crystal based optical sensors for simultaneous detection of multiple glycine oligomers with micromolar concentrations

This paper reports a novel liquid-crystal based method for the optical detection of multiple glycine oligomers simultaneously. The detection principle is based on the disruption of the orientations of a nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) supported on a surface patterned with multiple glycine oligomers. When glycine oligomers with different molecular lengths are immobilized on aldehyde-decorated surfaces under optimized conditions. they form monolayers with different thicknesses corresponding to their molecular lengths. As a result, the orientations of 5CB supported on the surfaces are disturbed when the thickness exceeds 0.5 +/- 0.1 nm. Because liquid crystals are birefringent materials, the disruption of their orientations can cause optical signals visible to the naked eye. This liquid-crystal based detection scheme for glycine oligomers is able to C detect 10 mu M of triglycine, tetraglycine and pentaglycine, 100 mu M of diglycine, and 1 mM of glycine with a sample size as little as 2 mu L. It also provides a good spatial resolution over a large area and is sufficiently simple. (c) 2007 Elsevier B.V. All rights reserved.