Photoluminescence of CdSe/ZnS quantum dots in nematic liquid crystals in electric fields

Concentration-dependent dielectric and electro-optical properties of composites based on nematic liquid crystals and CdS:Mn quantum dots

Composites in a wide concentration range of 0-0.6 wt% based on a nematic liquid crystal mixture and CdS quantum dots doped with manganese ions (Mn 6%) are presented. The effect of the CdS:Mn quantum dots on the phase diagram and electronic structure of composites was studied using differential scanning calorimetry and fluorescence analysis. Nonmonotonic concentration-dependent changes in the clearing point, which correlate with the fluorescence quenching behavior of the main CdS:Mn peak, were found. Dielectric spectroscopy and electro-optic studies revealed a corresponding increase in the dielectric permittivity anisotropy and birefringence in the 0.2-0.4 wt% range, where thermodynamic changes occur. The initiating factors behind this effect are supposed to be the self-assembly of quantum dots, and the distortion of the orientation order of liquid crystal molecules at a higher mass concentration of quantum dots.

Highly sensitive distance-based liquid crystalline visualization for paper-based analytical devices

We successfully report on the first demonstration of a highly sensitive distance-based liquid crystalline visualization for paper-based analytical devices. The construction of this paper sensor was achieved by immobilizing 4-cyano-4'-pentylbiphenyl (5CB) as liquid crystalline molecules (LCs) onto a paper strip substrate. The sensing mechanism is based on the ultrasound-assisted decomposition of 5CB by the hydroxyl radical (^•OH) which is generated from the oxidase enzymatic reaction of the analyte, this then results in the change of texture and color of paper. The utility of our devices was then demonstrated with the determination of bilirubin (BR) in biological samples using a bilirubin oxidase enzymatic reaction. The quantification of BR can be achieved by dipping the tip of the paper strips into the analyte solutions and then by measuring the length of color which has been changed on the paper, by the naked eye. Under optimized conditions, this paper sensor offered the linear range of BR detection from 2.0 to 30.0 pmol/L (R² = 0.9945) with the limit of detection (LOD) of 0.80 pmol/L. In addition, the results of this sensor were highly reproducible, with a relative standard deviation (RSD) of less than 3.50%. The recoveries of spiked BR in human urine and serum samples were in the range of 99.09-107.89%, which demonstrates the high accuracy of this paper sensor. Overall, this work presents a simple method to determine the concentration of H₂O₂ and BR at pmol levels with an instrument-free length-measuring readout, so it could be suitable for quantitative analysis of other biomarkers based on oxidase enzymatic reaction, which can provide important information about early disease diagnosis and patient prognosis.

Molecular origin of the heterogeneity in the nematic and smectic liquid crystals: Elastic constants, gradients of order parameters, and visualization of small objects

The formation of heterogeneous nematic and smectic liquid crystals in the general case of an arbitrary geometry is investigated in the framework of molecular-statistical approach [Emelyanenko and Khokhlov, J. Chem. Phys. 142, 204905 (2015)JCPSA60021-960610.1063/1.4921684]. The molecular aspects of the orientational and translational orderings at the curved surfaces of small solid objects dispersed in liquid crystal are considered, and the differential equations for gradients of the order parameters in vicinities of the small objects are presented in the general form. The five elastic constants are obtained within the same approach, from which we were able to predict that a significant space variations of the order parameters can be observed within the 0.5-0.8μm area around any small object, almost independently of its own dimension. Therefore, the liquid crystals can be a simple tool for the optical visualization of nano-objects. It is also demonstrated that the kind of molecular self-organization (smectic, nematic or conventionally isotropic) at the surfaces of small solid objects can be different from that in the bulk of mesogenic material. Totally we predict eight various combinations of simple states at the surfaces and in the bulk depending on the solid objects' size and temperature. It is also shown that the surfaces of 10μm-size solid objects and larger act almost as flat surfaces, while the surfaces of 1μm-size solid objects and smaller act almost as point defects.