Ali Vahedi

In this study, biosensors based on dielectric/metal/dielectric triple photonic crystals containing a defect layer (sample) were proposed. With assumed parameters such as some triple photonic crystal layers, the refractive index of samples and viruses, the thickness of photonic crystal, metal and, defect layers, and also by selecting the appropriate wavelength area, the transmittance matrix of the system is calculated, then transmittance is simulated as a function of wavelength. The simulations show good results for N= 3 periodic layers, with 150 nm dielectric layer and 5000 nm defect layer thicknesses. Also, among the four metals gold, silver, copper, and aluminum, the intensity of the transmission spectrum of copper and the FWHM of gold was the highest. The simulation of the standard sample and samples infected with viruses and microbes show that the sensitivity of this structure increases almost linearly in the higher wavelength regions and is more favorable than the lower wavelength regions. Compared to similar biosensors, this structure has a high sensitivity for the low number of photonic crystal layers and the low thickness of the samples.

Breast cancer (BC) is one of the most commonly diagnosed cancers and the second leading cause of cancer mortality among women around the world. The purpose of this study is to present a non-labeled liquid crystal (LC) biosensor, based on the inherent feature of nematic LCs, for the evaluation of BC using the human epidermal growth factor receptor-2 (HER-2) biomarker. The mechanism of this sensing is supported by surface modification with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) encouraging the long alkyl chains that induce a homeotropic orientation of the LC molecules at the interface. To enhance the binding efficacy of more HER-2 antibody (Ab) on LC aligning agents, a simple ultraviolet radiation-assisted method was also used to increase functional groups on the DMOAP coated slides, thereby improving binding affinity and efficiency onto HER-2 Abs. The designed biosensor makes use of the specific binding of HER-2 protein to HER-2 Ab and disruption of the orientation of LCs. This orientation change leads to a transition of the optical appearance from dark to birefringent, enabling the detection of HER-2. This novel biosensor exhibits a linear optical response to HER-2 concentration in the wide dynamic range of 10^–6–10² ng/mL, with an ultra-low detection limit of 1 fg/mL. As a proof of concept, the designed LC biosensor was successfully investigated for the quantification of HER-2 protein in patients suffering from BC. Owing to the sensitivity, selectivity, and label-free detection, this biosensor may amplify the application of LC-based biosensors for the detection of most types of cancers.

MgO nanoparticles (NPs) have been dispersed in pure 5CB in three various concentrations. It was found that by incrementing NPs concentration, dielectric permittivities (ε_∥ and ε_⊥) and dielectric anisotropy (Δε) continuously decrease. Real dielectric permittivities of pure and doped liquid crystals in terms of frequency in the range 50–500Hz were obtained. The influence of nano doping on physical and optical parameters, i.e. threshold voltage, ac electric conductivity, phase transition temperature, light transmission, splay elastic constant and refractive index anisotropy was investigated. The temperature-dependent dielectric properties have been improved in the frame of a novel six-parameter dielectric permittivity model.

Recent progress has shown that a minor concentration of nanoparticles in liquid crystals can have an important effect on the electrical and optical properties of liquid crystals. In this study, the temperature-dependent dielectric and electro-optical properties of planar and homeotropic oriented 6CHBT nematic liquid crystals doped with MgO nanoparticles were investigated. MgO nanoparticles were dispersed in pure 6CHBT in various concentrations. It was established that the dielectric permittivity (ε_|| and ε_⊥) and the dielectric anisotropy (Δε) are decreased by adding nanoparticles up to a certain concentration, and then it increased. The effect of doping nanoparticles on the physical and optical parameters, namely, the ac electric conductivity, absorption, emission, threshold voltage, splay elastic constant, and anisotropic refractive index were investigated. In the frame of the new six-parameter dielectric permittivity model, the temperature-dependent dielectric properties were improved. Graphical Abstract