In the present study, a carbon dot/hemoglobin (CD/Hb) complex is used as a bio-receptor in an optical cholesterol biosensor. This optical sensor detects cholesterol through fluorescence enhancement of CD, which is normally quenched via π–π interactions between CD and Hb in the CD/Hb complex. CD is released from the CD/Hb complex because hydrophobic interactions between Hb and cholesterol are more favorable than π–π interactions between CD and Hb. The CD/Hb complex enabled selective detection of cholesterol within a linear range from 0 to 800 μM, with a limit of detection of 56 μM and a response time of ≤5 minutes in human blood plasma. Compared with other cholesterol sensors, a CD/Hb complex-based biosensor is simple, highly sensitive, selective, rapid, eco-friendly, and cost-effective for cholesterol detection in both biological and environmental samples.

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.