Single Molecule Liquid Crystal Detection of Double-Stranded DNA

The utility of liquid crystals lies in the fact that they orient themselves based on the surface chemistry or topography of a substrate due to elastic constraints.  This permits a high level of amplification of surface interactions, which can then be easily characterized with polarized light.  Thermotropic liquid crystals were used to explore the extent of surface passivation of glycidoxypropyltrimethoxysilane self-assembled monolayers.  Low azimuthal anchoring energy was exploited for the detection of double-stranded DNA. Concurrent polarized and fluorescence microscopy was used to simultaneously observe physical alignment of DNA as well as liquid crystal alignment.  The chirality of the molecule, combined with negligible anchoring energy, allowed propagation of the unique alignment of -32±4 when exposed to extended dsDNA.  We observed a minimum threshold for sensitivity has been observed to be 200 molecules per μm²  with theoretical sensitivity as low as 30 molecules per μm² .   Anchoring energies of double and single-stranded DNA are also compared to further quantify disruption of the director field.