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Now showing 1 - 10 of 87

Liquid crystal-based capacitive, electro-optical and dielectric biosensors for protein quantitation
(2020-06-20)
Lee, Mon-Juan
;
Lee, Wei
;
光電學院
;
College of Photonics
The electrical, electro-optical and dielectric properties of liquid crystals (LCs) are routinely manipulated in liquid-crystal display (LCD) devices, but their potential application in the development of biosensors is still in a nascent stage. In this review, utilising the electrical properties, electro-optical effect and dielectric anisotropy in LCs, we provide insights into several possible modes of label-free biodetection and describe how capacitance, electro-optical and dielectric measurements of various LCs assist in quantitative analysis of biomolecules. It is concluded that the electrically induced biosensing techniques proposed here provides new incentives for researchers to study the interaction between LCs and biomolecules and to resolve technical hurdles facing the development of LC-based biosensors.
Color tuning in thermo-sensitive chiral photonic liquid crystals based on the pseudo-dielectric heating effect
(2019-12-15)
Yeh, Min-Chih
;
Yang, Sheng-Hsiung
;
Lee, Wei
;
照明與能源光電研究所
;
影像與生醫光電研究所
The ability of electro-thermal tuning in center wavelength (X,) of the Bragg reflection band is promoted in cholesteric liquid crystal (CLC) containing a positive-dielectric-anisotropy liquid crystal host (E7) and a binary chiral dopant (R-811 and R-5011). In the CLC mixtures with a fixed R-811 content of 30 wt%, the transition temperature of the smectic-A phase to CLC phase decreases when the R-5011 loading increases. The CLC systems are temperature-sensitive, each exhibiting a temperature range of about 9-12 degrees C in the CLC phase. Optimization of the content of R-5011 at 1.5 wt% allows for the remarkably effective thermal tuning in lambda(c )from 780 nm to 380 nm in response to a temperature increase of merely 3 degrees C from the room temperature. Under the mechanism of pseudo-dielectric heating, the tunable lambda(c) can shift in the entire visible spectrum by an applied voltage as low as 7 V-rms at a frequency of 2 MHz across the cell gap of a 4.8-mu m-thick cell. Furthermore, a multifunctional and operation-reversible device is demonstrated by the control of the applied AC voltage, yielding an optical device in which the reflection band can be tuned and the mode can be switched among the reflection, scattering, and transparent states. (C) 2019 Elsevier B.V. All rights reserved.
Chiral Optical Tamm States at the Interface between an All-Dielectric Polarization-Preserving Anisotropic Mirror and a Cholesteric Liquid Crystal
(2019-10-01)
Rudakova, Natalya, V
;
Timofeev, Ivan, V
;
Bikbaev, Rashid
;
Pyatnov, Maxim, V
;
Vetrov, Stepan Ya
As a new localized state of light, the chiral optical Tamm state exists at the interface between a polarization-retaining anisotropic mirror and a substance with optical activity. Considering a hybrid structure comprising a metal-free polarization-preserving mirror and a cholesteric liquid crystal, we highlight the high Q factor arising from the all-dielectric framework. The intensity of localized light decreases exponentially with increasing distance from the interface. The penetration of the field into the cholesteric liquid crystal is essentially prohibited for wavelengths lying in the photonic bandgap and close to the cholesteric pitch length. The dielectric mirror has its own photonic bandgap. The energy transfer along the interface can be effectively switched off by setting the tangential wave vector to zero. The spectral behavior of the chiral optical Tamm state is observed both as reflection and transmission resonance. This Fano resonance is analogous to the Kopp-Genack effect. Our analytics are well in line with precise calculations, which may pave a new route for the future development of intelligent design for laser and sensing applications.
Pseudo-dielectric relaxation-enabled electrothermal tuning of reflective color in a soft chiral photonic crystal
(2019-01-01)
Wu, Po-Chang
;
Wu, Guan-Wei
;
Lee, Wei
;
照明與能源光電研究所
;
影像與生醫光電研究所
Many published papers bear flaw information caused by misinterpreting the pseudo-dielectric relaxation in liquid crystal (LC) confined in thin cells. The pseudo-dielectric relaxation stems from the cell geometries or parameters, which should not be misrecognized as an inherent material property of the LC. In this work, we explored the pseudo-dielectric relaxation and demonstrated an unconventional tuning means to electrically manipulate the reflective color of a typical cholesteric LC cell based on the heating due to the pseudo-dielectric relaxation. A tuning range in the full-color spectrum can be easily achieved by a limited temperature change of merely a few degrees Celsius.
Frequency-modulated textural formation and optical properties of a binary rod-like/bent-core cholesteric liquid crystal
(2019-11-01)
Lin, Yueh-Chern
;
Wu, Po-Chang
;
Lee, Wei
;
照明與能源光電研究所
;
影像與生醫光電研究所
We explore the mechanisms of voltage-induced textural switching and the corresponding electro-optical responses of a binary cholesteric liquid crystal (CLC) composed of the rod-like nematic LC E7 with positive dielectric anisotropy and the bent-core LC dimer CB7CB with large flexoelectric coefficients. Our results indicate that the minimal voltage (V-H) required for retaining the CLC in the homeotropic state and the optical transparency of the CLC after treating with decreasing voltage (from V-H to zero) are dependent on the voltage frequency. The observed frequency modulated electro-optical properties are characterized by the frequency regimes separated by the critical frequencies of flexoelectric polarization and dielectric relaxation in dielectric dispersion. These unusual features, specific to the CB7CB-doped CLC, are explained by the dielectric and frequency-dependent flexoelectric responses of LC molecules to an external AC voltage. Accordingly, in addition to the known Grandjean planar and focal conic states, the uniform lying helix as a third stable state can be feasibly generated in the binary CLC with 45 wt% CB7CB by two pathways. The first one is to treat the cell directly with a sufficient voltage lower than V-H ; the other is to decrease the voltage gradually from V-H to zero in the low-frequency regime, where the flexoelectric strength is significant. Manifested by its optical tristability, frequency-controllable optical transparency, and fast flexoelectro-optical response, the proposed binary rod-like/bent-core CLC system is promising for developing a variety of memory- and dynamic-mode photonic and optoelectronic devices. (C) 2019 Chinese Laser Press
Electric-field-assisted signal amplification for label-free liquid-crystal-based detection of biomolecules
(2019-10-01)
Hsu, Wei-Liang
;
Lee, Mon-Juan
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
The fundamental principle of liquid-crystal (LC)-based biosensing is the sensitive response of LC orientation to external stimuli. Biomolecules such as proteins or DNAs immobilized on the glass substrate of a LC cell are detected through disrupting the LC alignment and, in turn, altering the birefringence, resulting in changes in the optical texture that can be readily observed under a polarizing optical microscope. With an additional weak electric field across a sandwiched LC cell, we demonstrate in this study a novel label-free biodetection technique with amplified signal and improved detection limit. By applying the binarization analysis as the quantitative approach, the increase in the light leakage area in the optical texture of LCs with increasing amount of biomolecules can be quantitated with a bright-area-ratio (BAR)-versus-concentration curve. The reported biosensing technique exploits both the optical and electrical properties of LCs and is potentially applicable to other LC-based rapid screening and bioassays. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Liquid crystal-based capacitive, electro-optical and dielectric biosensors for protein quantitation
(1970-01-01)
Lee, Mon-Juan
;
Lee, Wei
;
光電學院
;
College of Photonics
The electrical, electro-optical and dielectric properties of liquid crystals (LCs) are routinely manipulated in liquid-crystal display (LCD) devices, but their potential application in the development of biosensors is still in a nascent stage. In this review, utilising the electrical properties, electro-optical effect and dielectric anisotropy in LCs, we provide insights into several possible modes of label-free biodetection and describe how capacitance, electro-optical and dielectric measurements of various LCs assist in quantitative analysis of biomolecules. It is concluded that the electrically induced biosensing techniques proposed here provides new incentives for researchers to study the interaction between LCs and biomolecules and to resolve technical hurdles facing the development of LC-based biosensors.
Voltage-induced pseudo-dielectric heating and its application for color tuning in a thermally sensitive cholesteric liquid crystal
(1970-01-01)
Wu, Po-Chang
;
Wu, Guan-Wei
;
Yu, Chia-Hua
;
Lee, Wei
;
照明與能源光電研究所
We previously proposed an electrical approach enabling the tuning of the center wavelength lambda(c) of the cholesteric liquid crystal (CLC) bandgap in the full-color visible spectrum based on the electro-thermal effect. The idea involved the design of a negative CLC with a thermally sensitive bandgap feature and the use of a sandwich-type cell with finite electrode conductivity, allowing the control of cell temperature by applied voltage via pseudo-dielectric heating. It has been demonstrated experimentally that the induced pseudo-dielectric heating is predominated by the pseudo-dielectric relaxation originating from the designated cell geometry. On the basis of this technique, key factors determining the tuning efficacy of the temperature and thus lambda(c) are primarily investigated in this study. Our results suggest that lowering the electrode resistivity and the specific heat conductivity of the cell can promote the maximum tunable temperature range. Expectedly, optimizing the electrode area, cell gap and dielectric permittivity of the CLC favors a decreased relaxation frequency and, in turn, reducing the voltage as well as the frequency required for lambda(c) tuning.
Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell
(2019-04-01)
Yu, Chia-Hua
;
Wu, Po-Chang
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f(1) and, subsequently, f(2), which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 V-rms at f(1) = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 V-rms and f(1) = 55 kHz, our results indicate that switching of the voltage frequency from f(1) to f(2) enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f(2) = 1 kHz or by the electrohydrodynamic effect at f(2) = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.
Electrothermo-optical effect in liquid crystals and its applications
(2017-01-01)
Hsiao, Yu-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
Electro-optical effects in liquid crystals (LCs) have been widely utilized in many optical components and photonic devices, thanks to the anisotropic media that can be easily manipulated by an electric field to modulate the light. In general, dielectric heating in LC applications is negligible because their orientational dielectric relaxations occur at high frequencies. Here we focus on a dual-frequency LC characterized by its much lower relaxation frequency. The field-induced heat strongly affects the LC ordering and optical properties. The electrothermo-optical effect reveals an unusual behavior compared with the well-known electro-optical effect in regular LCs. Based on the electrothermo-optical effect, some applications such as optical modulators or tunable optical shutters are demonstrated.

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