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 detect 10 μM of triglycine, tetraglycine and pentaglycine, 100 μM of diglycine, and 1 mM of glycine with a sample size as little as 2 μL. It also provides a good spatial resolution over a large area and is sufficiently simple.