Experimental and theoretical investigation of sensing parameters in carbon nanotube‐based DNA sensor

Nowadays, sensitive biosensors with high selectivity, lower costs and short response time are required for detection of DNA. The most preferred materials in DNA sensor designing are nanomaterials such as carbon and Au nanoparticles, because of their very high surface area and biocompatibility which lead to performance and sensitivity improvements in DNA sensors. Carbon nanomaterials such as carbon nanotubes (CNTs) can be considered as a suitable DNA sensor platform due to their high surface‐to‐volume ratio, favourable electronic properties and fast electron transfer rate. Therefore, in this study, the CNTs which are synthesised by pulsed AC arc discharge method on a high‐density polyethylene substrate are used as conducting channels in a chemiresistor for the electrochemical detection of double stranded DNA. Moreover, the response of the proposed sensor is investigated experimentally and analytically in different temperatures, which confirm good agreement between the presented model and experimental data.Inspec keywords: electrochemical sensors, polymers, arcs (electric), biological techniques, nanosensors, carbon nanotubes, DNAOther keywords: C, chemiresistor, double stranded DNA detection, CNT, electronic properties, surface‐to‐volume ratio, nanoparticles, biosensors, electrochemical detection, high‐density polyethylene substrate, pulsed AC arc discharge method, electron transfer rate, carbon nanomaterials, carbon nanotube‐based DNA sensor     

Effect of solution pH on structure and electrochemical performance of MoS2

Journal of Materials Science: Materials in Electronics - As energy demand continues to increase, the development of energy storage devices is imminent. Due to its unique structure, molybdenum...     

Investigation of graphene‐on‐metal substrates for SPR‐based sensor using finite‐difference time domain

In this study, the authors investigated the effects of a single layer graphene as a coating layer on top of metal thin films such as silver, gold, aluminum and copper using finite‐difference time domain method. To enhance the resolution of surface plasmon resonance (SPR) sensor, it is necessary to increase the SPR reflectivity and decrease the full‐width‐half maximum (FWHM) of the SPR curve so that there is minimum uncertainty in the determination of the resonance dip. Numerical data was verified with analytical and experimental data where all the data were in good agreement with resonance angle differing in <10% due to noise present in components such as humidity and temperature. In further analysis, reflectivity and FWHM were compared among four types of metal with various thin film thicknesses where graphene was applied on top of the metal layers, and data was compared against pure conventional metal thin films. A 60 nm‐thick Au thin film results in higher performance with reflectivity of 92.4% and FWHM of 0.88° whereas single layer graphene‐on‐60 nm‐thick Au gave reflectivity of 91.7% and FWHM of 1.32°. However, a graphene‐on‐40 nm‐thick Ag also gave good performance with narrower FWHM of 0.88° and reflection spectra of 89.2%.Inspec keywords: graphene, surface plasmon resonance, finite difference time‐domain analysis, reflectivity, metallic thin films, silver, gold, aluminium, copper, chemical sensors, biological techniquesOther keywords: graphene‐on‐metal substrates, SPR‐based sensor, finite‐difference time domain, metal thin films, surface plasmon resonance sensor, SPR curve, resonance angles, reflectivity, C, Ag, Au, Al, Cu     

An optical fiber sensor for remote pH sensing and imaging

A fiber-optical probe for pH sensing and real-time imaging is successfully fabricated by connecting a polymer imaging fiber and a gradient index (GRIN) lens rod which was modified with a sensing film. By employing an improved metallographic microscope, an optical system is designed to cooperate with the probe. This novel technique has high-quality imaging capabilities for observing remote samples while measuring pH. The linear range of the probe is pH 1.2-3.5. This technique overcomes the difficulty that high-quality images cannot be obtained when directly using conventional imaging bundles for pH sensing and imaging. As preliminary applications, the corrosion behavior of an iron screw and the reaction process of rust were investigated in buffer solutions of pH 2.0 and 2.9, respectively. The experiment demonstrated that the pH values of the analytes' surface were higher than that of buffer solutions due to the chemical reaction. It provides great potential for applications in optical multifunctional detection, especially in chemical sensing and biosensing.     

Sliding‐mode‐based controllers for automation of blood glucose concentration for type 1 diabetes

Destruction of β‐cells in pancreas causes deficiency in insulin production that leads to diabetes in the human body. To cope with this problem, insulin is either taken orally during the day or injected into the patient''s body using artificial pancreas (AP) during sleeping hours. Some mathematical models indicate that AP uses control algorithms to regulate blood glucose concentration (BGC). The extended Bergman minimal model (EBMM) incorporates, as a state variable, the disturbance in insulin level during medication due to either meal intake or burning sugar by engaging in physical exercise. In this research work, EBMM and proposed finite time robust controllers are used, including the sliding mode controller (SMC), backstepping SMC (BSMC) and supertwisting SMC (second‐order SMC or SOSMC) for automatic stabilisation of BGC in type 1 diabetic patients. The proposed SOSMC diminishes the chattering phenomenon which appears in the conventional SMC. The proposed BSMC is a recursive technique which becomes robust by the addition of the SMC. Lyapunov theory has been used to prove the asymptotic stability of the proposed controllers. Simulations have been carried out in MATLAB/Simulink for the comparative study of the proposed controllers under varying data of six different type 1 diabetic patients available in the literature.     

基于pH响应的氨传感器的研究

本文研究利用二甲基二甲氧基硅烷(DiMe-DMOS)和正硅酸甲酯(TMOS)掺杂,获得具有好柔韧和透明性的基质材料,并利用该材料对pH指示剂溴酚蓝(BPhB)、溴百里酚蓝(BCB)进行包埋。所获得的敏感膜对水体中的氨浓度的响应范围为0～20μg/mL,响应时间为5min。     

High-resolution position sensor based on two sensing elements

A high-resolution optical position sensor based on two sensing elements is described. The important system nonlinearities and error sources are identified, and correction methods are presented. An autozeroing scheme is employed to obtain an accurate center point and to reduce the effects of temperature variations and component tolerances on the overall system. The predicted results are verified experimentally using commercial parts     

Effect of adsorbent concentration to the adsorption of phenol on hexadecyl trimethyl ammonium-bentonite

In this work, it is intended to study the effect of adsorbent concentration on the adsorption of phenol by hexadecyl trimethyl ammonium-bentonite. The experiments were conducted in two groups. The adsorption of hexadecyl trimethyl ammonium bromide (HDTMA) on bentonite was studied in the first group of experiments. It was observed that the all HDTMA was adsorbed by the bentonite, even when the amount used exceeded 100% of cation exchange capacity (CEC). After the modification of bentonite by using HDTMA in an amount equivalent to 100% of CEC, the adsorption experiments were performed at five different adsorbent concentrations ranging from 2 to 10 g/L. A type V isotherm and a non-linear increase in percent removal with adsorbent concentration were observed. The observation of the non-linear relation between the percent removal and adsorbent concentration was attributed to the effect of intra particle interactions and it was represented by a second order polynomial. Several adsorption isotherm equations were applied to the experimental data. Although, the Freundlich equation fitted fairly well, it failed to represent the plateau and the second region that appeared in the isotherm. Therefore, an equation giving the equilibrium concentration as a function of initial and adsorbent concentrations was suggested.     

Effect of ZnO doping on morphology and electrochemical properties of sub-micron RuO2 sensing electrode of DO sensor

Thick-film 20 mol% ZnO-doped RuO₂ sensing electrodes (SEs) were fabricated by screen-printing technique on the platinised alumina substrate of the planar electrochemical dissolved oxygen (DO) sensor. The effect of ZnO doping on morphology, electrochemical properties and sensing characteristics of the sensor was investigated. It was found that ZnO doping has not only improved the SE structure, but has also enhanced selectivity of the DO sensor. Selectivity testing exhibited that the presence of Cl⁻, Li⁺, SO₄²⁻, NO³⁻, Ca²⁺, PO₄³⁻, Mg²⁺, Na⁺ and K⁺ with a concentration range of 10⁻⁷ to 10⁻¹ mol/L in the solution had practically no effect on the sensor's emf. The reason in enhancement of the sensor characteristics could be related to the establishment of the better structured SE as more advanced crystallization is achieved for the doped RuO₂-SE.     

Synthesis and sensing properties of triphenylamine based dye sensor

We have designed and synthesized a triphenylamine-based new dye sensor and corresponding selective and sensitive detection functions for heavy metal ions were investigated. The complex potentials for heavy metal ions were characterized by the measurements of optical properties using UV-Vis spectrophotometer and spectrofluorophotometer. Furthermore, the molecular energy levels of the designed dye sensors were also computationally optimized and calculated by the density function theory (DFT) with exchange correction functional of local density approximation (LDA) based on the Perdew-Wang (PWC) set and cyclic voltammetry.     

An electrochemical sensor based on the human estrogen receptor ligand binding domain

Three different conformations of the ligand binding domain of the human estrogen receptor (ER-LBD) are observed for the native state when binding an agonist and when binding an antagonist. By conjugating ER-LBD conformation specific peptides to CdS nanoparticles, the three different states can be identified by anodic stripping voltammetry. This electrochemical sensor can detect and distinguish the binding of different ligands to the human estrogen receptor.     

Fabrication,calibration, and preliminary testing of microcantilever‐based piezoresistive sensor for BioMEMS applications

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantilever‐based sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self‐assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever‐based biosensor is a crucial design parameter for the low‐pressure range and also influence the sensitivity of the microelectromechanical system‐based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra‐sensitive and selective towards Hg²⁺ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml).Inspec keywords: molecular biophysics, bioMEMS, chemical sensors, microfabrication, cantilevers, microsensors, self‐assembly, monolayers, gold, piezoresistive devices, calibration, chromium, thin film sensors, mercury (metal), silicon compoundsOther keywords: microcantilever‐based piezoresistive sensor, BioMEMS application, biomedical microelectromechanical system application, targeted biomolecules, piezoresistive technique, cantilever‐based biosensor, microelectromechanical system‐based sensor, microcantilever fabrication, calibration, surface modification, surface alteration, self‐assembled monolayer, SAM, coating, thin films, HMI, heavy metal ion, Au‐Cr‐SiO₂ , Hg     

Improved electrochemical capacitive characteristics by controlling the carbon nanotube morphology and electrolyte solution concentration

Carbon nanotubes (CNTs) have been used as the electrochemical double layer in capacitor (EDLC) electrodes. CNTs were synthesized using thermal chemical vapor deposition (CVD) at a growth temperature of 750 °C by flowing C₂H₂. The surface morphology of the synthesized CNTs could be controlled with or without Al film deposition between the stainless (SUS) sheet and Fe catalyst film. Electrochemical measurements were performed in a three-electrode arrangement. H₂SO₄ with different concentrations was used as the electrolyte solution. The relation between the specific capacitance and the surface morphology of the CNTs and the electrolyte concentration were investigated. The results showed that the electrode formed using vertically aligned CNTs with higher electrolyte concentration exhibited higher specific capacitance.     

Low-cost electrochemical sensor based on montmorillonite for antibiotic tetracycline hydrochloride detection

Journal of Materials Science: Materials in Electronics - Tetracycline hydrochloride (TC(HCl)) has been extensively used as veterinary drugs and food additives in feed, but the abuse of TC(HCl)...     

基于差压传感器的溶液密度检测方法

为了实现对溶液密度的简单、精确测量,建立了溶液压力与溶液密度之间的关系,推导出溶液密度的计算公式,确定了利用差压传感器来实现对溶液密度的间接测量,指出了测量的难点和解决的方法.为了提高测量精度,还对传感器量程的选取方法和原则,以及在安装环境下对传感器的零点校正和量程设定方法、求取位差的方法进行了阐述和分析.该测量方法简单、可行,技术成熟,在溶液配比和质量监测上有其十分重要的地位.     

Effect of heterogeneous oxidation on electrochemical properties of tailored Cu0.4Ru3.4O7 + RuO2 sensing electrode of potentiometric DO sensor

Effect of heterogeneous oxidation of the thick-film Cu_0.4Ru_3.4O₇ + RuO₂ sensing electrode (SE) of the planar potentiometric dissolved oxygen (DO) sensor on its electrochemical properties has been investigated by field emission beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltametry (CV) and electrochemical impedance spectroscopy (EIS) techniques. It was found that the most of heterogeneous oxidation has occurred during the first week of SE exposure to the aqueous environment leading to the partial oxidation Ru^IV to Ru^III occurred mostly on the grain boundaries of SE. The presence of the “inner” active surfaces in the bulk of the developed complex oxide SE has been reaffirmed. It was also found that heterogeneous oxidation caused the increase of the Cu 2p peaks intensity on the surface of SE after the water treatment for one month, which has been confirmed by XPS measurement.     

Construction and investigation of breast‐cancer‐specific ceRNA network based on the mRNA and miRNA expression data

It has been proved and widely acknowledged that messenger RNAs can talk to each other by competing for a limited pool of miRNAs. The competing endogenous RNAs are called as ceRNAs. Although some researchers have recently used ceRNAs to do biological function annotations, few of them have investigated the ceRNA network on specific disease systematically. In this work, using both miRNA expression data and mRNA expression data of breast cancer patient as well as the miRNA target relations, the authors proposed a computational method to construct a breast‐cancer‐specific ceRNA network by checking whether the shared miRNA sponges between the gene pairs are significant. The ceRNA network is shown to be scale‐free, thus the topological characters such as hub nodes and communities may provide important clues for the biological mechanism. Through investigation on the communities (the dense clusters) in the network, it was found that they are related to cancer hallmarks. In addition, through function annotation of the hub genes in the network, it was found that they are related to breast cancer. Moreover, classifiers based on the discriminative hubs can significantly distinguish breast cancer patients’ risks of distant metastasis in all the three independent data sets.Inspec keywords: cancer, genetics, medical computing, molecular biophysics, RNAOther keywords: breast‐cancer specific ceRNA network construction, miRNA expression data, mRNA expression data, gene pairs, computational method, dense clusters, cancer hallmarks, biological mechanism, discriminative hub genes     

巨磁阻抗传感器敏感材料的选择

利用巨磁阻抗(GMI)效应来研制传感器,敏感材料的选择非常关键,其GMI性能的好坏直接决定了GMI磁传感器的灵敏度水平.讨论了GMI材料的选择标准,列出了能够产生GMI效应的各种材料,并分析和评述了这些GMI材料的软磁特性、GMI效应及其在传感器上的可能应用,提供了设计高性能GMI传感器的候选材料,这些材料以及新型材料的开发为GMl传感器的研制创造了有利的条件,将会促进GMI传感器的发展与应用.     

pH值和温度对镀锌钢在模拟锈层溶液中电化学腐蚀行为的影响

应用极化曲线和电化学阻抗技术,结合扫描电子显微镜方法,测试镀锌钢在模拟锈层溶液中pH值和温度对镀锌钢电化学腐蚀行为的影响作用。结果表明,镀锌钢在强碱性的模拟锈层溶液中处于钝态,其耐蚀性能随着pH值的升高而增大。温度为0～40℃时,镀锌钢的腐蚀速率变化不大,当温度升高到60℃时,腐蚀速率急剧增大。