A liquid-crystal-based DNA biosensor for pathogen detection

A liquid-crystal (LC)-filled transmission electron microscopy (TEM) grid cell coated with the cationic surfactant dodecyltrimethylammonium bromide (DTAB), to which a single-stranded deoxyribonucleic acid probe (ssDNA(probe)) was adsorbed at the LC/aqueous interface (TEM(DTAB/DNA)), was applied for the highly specific detection of target DNA molecules. The DTAB-coated E7 (used LC mixture) in the TEM grid (TEM(DTAB)) exhibited a homeotropic orientation, and changed to a planar orientation upon adsorption of the ssDNA(probe). The TEM(DTAB/DNA) was then exposed to complementary (target) ssDNA, which resulted in a planar-to-homeotropic configurational change of E7 that could be observed through a polarized optical microscope under crossed polarizers. The optimum adsorption density (2 μM) of ssDNA(probe) enabled the detection of ≥0.05 nM complementary ssDNA. This TEM(DTAB/DNA) biosensor could differentiate complementary ssDNA from mismatched ssDNA as well as double-stranded DNA. It also successfully detected the genomic DNAs of the bacterium Erwinia carotovora and the fungi Rhazictonia solani. Owe to the high specificity, sensitivity, and label-free detection, this biosensor may broaden the applications of LC-based biosensors to pathogen detection.