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- 摘要
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- 实验方案
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A label-free aptamer-based nanogap capacitive biosensor with greatly diminished electrode polarization effects
摘要： A significant impediment to the use of impedance spectroscopy in bio-sensing is the electrode polarization effect that arises from the movement of free ions to the electrode–solution interface, forming an electrical double layer (EDL). The EDL screens the dielectric response of the bulk and its large capacitance dominates the signal response at low frequency, masking information particularly relevant for biological samples, such as molecular conformation changes and DNA hybridization. The fabrication of nanogap capacitors with electrode separation less than the EDL thickness can significantly reduce electrode polarization effects and provide enormous improvement in sensitivity due to better matching of the sensing volume with the size of the target entities. We report on the fabrication of a horizontal thin-film nanogap capacitive sensor with electrode separation of 40 nm that shows almost no electrode polarization effects when measured with water and ionic buffer solutions, thereby allowing direct quantification of their relative permittivity at low frequencies. Surface modification of the electrodes with thiol-functionalized single strand DNA aptamers transforms the device into a label-free biosensor with high sensitivity and selectivity towards the detection of a specific protein. Using this approach, we have developed a biosensor for the detection of human alpha thrombin. In addition, we also examine frequency dependent permittivity measurements on high ionic strength solutions contained within the nanogap and discuss how these support recent experimental observations of large Debye lengths. A large shift in the Debye relaxation frequency to lower frequency is also found, which is consistent with water molecules being in a rigid-like state, possibly indicating the formation of an ordered ‘‘ice-like’’ phase. Altogether, this work highlights the need for better understanding of fluids in confined, nanoscale geometries, from which important new applications in sensing may arise.
关键词： electrode polarization,aptamer,nanogap,capacitive biosensor,dielectric spectroscopy,thrombin
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE Biomedical Circuits and Systems Conference (BioCAS) - Cleveland, OH, USA (2018.10.17-2018.10.19)] 2018 IEEE Biomedical Circuits and Systems Conference (BioCAS) - Monitoring Red Blood Cell Aggregation Dynamics in Stasis and Under Flow Using a Microfluidic Dielectric Sensor
摘要： This paper reports on monitoring the red blood cell (RBC) aggregation dynamics under flow and in static condition using a microfluidic dielectric sensor. The sensor employs a three-dimensional (3D), parallel-plate, capacitive sensing structure with a floating electrode integrated into a microfluidic channel with a height of 50μm. Using an impedance analyzer, the sensor is shown to measure the real part of complex relative dielectric permittivity of human whole blood in a frequency range of 10kHz–100MHz under flow and in static condition. The dielectric permittivity of human whole blood at 1MHz indicates the formation of RBC aggregate structures called rouleaux under static condition and their complete breakdown under a physiological shear flow rate of 500s-1. This work also demonstrates that the kinetics of RBC aggregation is dependent on fibrinogen concentration of the blood sample and establishes that the sensor is capable of distinguishing this difference in the aggregation process even under physiological shear flow rates. This work demonstrates the potential of dielectric spectroscopy in obtaining information on RBC aggregation dynamics using μL-volumes of whole blood under flow and in stasis.
关键词： red blood cells,capacitive sensor,dielectric spectroscopy,Aggregation,rouleaux formation,microfluidics
更新于2025-09-23 15:23:52
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[IEEE 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Trebic, Czech Republic (2018.9.18-2018.9.20)] 2018 VII. Lighting Conference of the Visegrad Countries (Lumen V4) - Analysis of Liquid Dielectrics by Photometric Instruments
摘要： The liquid dielectrics are used as an electrical insulation or as a medium for heat transfer in the power energy and high voltage devices such as transformers, HV cables or bushings. However dielectric degradations of these liquids are formed in time, most often caused by chemical pollution, thermal destruction or by the electric field influences. Especially electric strength and dissipation factor of insulating oil are affected by these negative influences. The result is the deterioration of devices isolation, which may cause the termination of devices life or even fire or explosion. To avoid loss of the device and further damage, the oil is periodically sampled from the device. The sample of oil is then analyzed, diagnosed and measured in the laboratory. Electrical parameters, mechanical and optical properties are the most common measured quantities. The optical analysis is usually very fast and reliable. There are many commercial analysis devices available on the market. However, none of them can measure all the parameters according to the standards with user settings. The design and realization of optical diagnostic equipment for analysis of liquid dielectrics according ISO 2049 and EN 60422 are the main contribution of this paper. Next monitored parameter is the spectral absorption and transparency of these liquids in the visible and UV spectrum. The proper function and accuracy of the measured methods will be verified in the Light laboratory and in the CVVOZEPower Laboratory in Brno University of Technology.
关键词： spectroradiometer,D-lamp,insulating oil,silicone oil,UV-vis,mineral oil,spectrophotometer,liquid dielectric,spectroscopy,spectrum
更新于2025-09-23 15:21:21
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Dielectric and electro-optic properties of cybotactic nematic phase in hydrogen-bonded liquid crystals
摘要： The new compounds 4-decyloxy-2-fluorobenzoic acid and 4-dodecyloxy-2-fluorobenzoic acid display hydrogen-bonded liquid crystals (HBLC) of smectic and nematic phases. Their phase behavior established using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) consistently occurs as the sequence upon cooling: Isotropic liquid – Nematic – SmC – crystalline solid. The dielectric study in the nematic phase shows a single relaxation process at low frequency characteristic of a cybotactic nematic phase. The optical properties of the nematic phase show a decrease of birefringence as alkyl chain length increases in the high-temperature part of the nematic domain, which reveals a decrease of order parameter for longer chains.
关键词： Polarized optical microscopy,Dielectric spectroscopy,Nematic,Hydrogen-bonded liquid crystal
更新于2025-09-23 15:19:57
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[IEEE 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Budapest (2018.7.1-2018.7.5)] 2018 IEEE 2nd International Conference on Dielectrics (ICD) - Estimation of Frequency Dependent Dielectric Behavior of PP-SiO2 Nanocomposite Interphase at Different Temperatures
摘要： This work aims to emphasize the frequency dependent dielectric response of the interface region of a PP-SiO2 nanodielectric at different temperatures. The approach is that of an inverse problem technique, i.e. a numerical model was built and the frequency dependent dielectric properties of the interphase were estimated so that the modeling results in terms of effective permittivity (real part) and loss tangent be close to the dielectric spectroscopy results. The numerical results show that the proposed procedure provides a good estimation of the dielectric response of the interphase, which dominates the dielectric response of the whole nanodielectric.
关键词： dielectric spectroscopy,interface,nanodielectric,numerical modeling
更新于2025-09-23 15:19:57
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Dielectric Properties of γ‐Iirradiated, Stretched, and Poled PVDF Thin Films
摘要： The e?ects of ??-irradiation on the dielectric properties of stretched and poled polyvinylidene ?uoride thin ?lms synthesized by solvent cast method are reported. The ?lms are subjected to ??-irradiation with di?erent doses (25, 50, and 75 kGy). XRD pattern is obtained to identify the presence of ??/?? phases. Dielectric constant and loss values of the stretched and poled ?lms have been measured, before and after irradiation, and their nature of variation has been studied. ?? phase is retained even after the irradiation thereby con?rming that the radiation damage is not signi?cant. The dielectric loss is minimum in the frequency range 102 to104 Hz, giving the preferable frequency range of operation for devices.
关键词： ??-irradiation,dielectric spectroscopy,polyvinylidene?uoride thin ?lms
更新于2025-09-19 17:13:59
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Liquid crystal-based capacitive, electro-optical and dielectric biosensors for protein quantitation
摘要： 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.
关键词： bovine serum albumin,biosensing,dielectric spectroscopy,Electro-optical measurement,protein,capacitance
更新于2025-09-16 10:30:52
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Terahertz Dielectric Spectroscopic Analysis of Polypropylene Aging Caused by Exposure to Ultraviolet Radiation
摘要： Terahertz dielectric spectroscopy is shown to be an effective tool for bench-marking ultraviolet aging of polypropylene. In this, thin-film polypropylene samples exposed to standard artificial ultraviolet radiation in accelerated aging from 1 day to 30 days are closely monitored by a terahertz time-domain spectroscopy system and analyzed using an effective data processing method. It is found that the terahertz absorption of the polypropylene samples is generally weak and the terahertz dielectric constant varies slightly though discernibly during the aging process, with the refractive index decreasing slightly with increasing length of ultraviolet exposure. Nonetheless, the rate of variation of the polypropylene refractive index with increasing terahertz frequency exhibits a drastic inflection around the 15-days aging point and the rate changes suddenly from positive value to negative value. Based on this prominent and consistent THz dielectric spectroscopic feature of the aging process, an efficient judging criterion is established to distinguish the early-term, mid-term, and late-term phases as well as the degree of polypropylene ultraviolet aging, corresponding to the fundamental transformation of the polymer material from a nonpolar to a polar substance at a critical level of oxidation induced by ultraviolet radiation.
关键词： ultraviolet aging,polypropylene,THz dielectric spectroscopy
更新于2025-09-12 10:27:22
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Investigations of dual-frequency nematic liquid crystals doped with dichroic dye
摘要： In this work, we studied and analysed a particular variety of liquid crystals, the so-called dual-frequency nematic liquid crystals (DFNLCs). The interest was to perform dielectric spectroscopy and optical characterisation with two pure and doped mixtures of DFNLCs. By means the dielectric spectroscopy we observed a low value of crossover frequency at room temperature for one dye doped mixture. Additionally, in the spectra studies, a scattering of light at cross-frequency, and a stable and unstable focal conical state was observed, respectively, for the investigated mixtures.
关键词： relaxation frequency,crossover frequency,dielectric spectroscopy,optical characterisation,Dual-frequency liquid crystal
更新于2025-09-10 09:29:36
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Effective permittivity of liquid crystal nanodispersions and composites with different pore structure
摘要： The volume filling fraction dependence of the effective permittivity of the nematic liquid crystal 4-n-pentyl-4’-cyanobiphenyl embedded in different porous membranes and dispersed with aerosil nanoparticles was determined using broadband dielectric spectroscopy in the frequency range from 106 to 109 Hz. The experimental data were analyzed and compared with some existing theories based on the effective medium approximation and their modifications. The obtained effective permittivities as a function of the volume filling fraction lie between the lower limits of the Wiener and Hashin–Shtrikman bounds. The observed shift of the experimental points reflects the changes in the structure of the investigated composites.
关键词： Hashin–Shtrikman bounds,Dielectric spectroscopy,nematic liquid crystal,Maxwell Garnett theory,Wiener bounds
更新于2025-09-09 09:28:46