Naked-eye cadmium sensor: using chromoionophore arrays of Langmuir-Blodgett molecular assemblies

This study demonstrates the possibility of a reversible naked-eye detection method for submicromolar levels of cadmium(II) using the Langmuir-Blodgett (L-B) technique. Molecular assemblies of 4-n-dodecyl-6-(2-thiazolylazo)resorcinol are transferred on precleaned microscopic glass slides, to act as a sensing probe. Isotherm (pi-A) measurements were performed to ensure the films' structural rigidity and homogeneity during sensor fabrication. The sensor surface morphology was characterized using atomic force microscopy and scanning electron microscopy. The probe membrane exhibits visual color transition, forming a series of reddish-orange to pinkish-purple complexes with cadmium, over a wide concentration range (0.04-44.5 microM). Cadmium response kinetics and the changes in the sensors' intrinsic optical properties were monitored using absorption spectroscopy and further confirmed using X-ray photoelectron spectroscopy. A hybrid L-B film composite of poly(vinyl stearate) and poly(vinyl-N-octadecylcarbamate) were investigated for enhancing sensor performance. The sensor was tested for its practical approach to prove its cadmium selectivity and sensitivity amid common matrix constituents using synthetic mixtures and real water samples. Using the sensor strips, the respective lower limits of cadmium detection and quantification are 0.039 and 0.050 microM, as estimated from a normalized linear calibration plot.     

Bend sensors with direction recognition based on long-period gratings written in D-shaped fiber

The curvature- or bend-sensing response of long-period gratings (LPGs) UV inscribed in D-shaped fiber has been investigated experimentally. Strong fiber-orientation dependence of the spectral response when such LPGs are subjected to bending at different directions has been observed and is shown to form the basis for a new class of single-device sensor with vector-sensing capability. Potential applications utilizing the linear response and unique bend-orientation characteristics of the devices are discussed.     

Rapid analyte recognition in a device based on optical sensors and the olfactory system

We report here the development of a new vapor sensing device that is designed as an array of optically based chemosensors providing input to a pattern recognition system incorporating artificial neural networks. Distributed sensors providing inputs to an integrative circuit is a principle derived from studies of the vertebrate olfactory system. In the present device, primary chemosensing input is provided by an array of fiber-optic sensors. The individual fiber sensors, which are broadly yet differentially responsive, were constructed by immobilizing molecules of the fluorescent indicator dye Nile Red in polymer matrices of varying polarity, hydrophobicity, pore size, elasticity, and swelling tendency, creating unique sensing regions that interact differently with vapor molecules. The fluorescent signals obtained from each fiber sensor in response to 2-s applications of different analyte vapors have unique temporal characteristics. Using signals from the fiber array as inputs, artificial neural networks were trained to identify both single analytes and binary mixtures, as well as relative concentrations. Networks trained with integrated response data from the array or with temporal data from a single fiber made numerous errors in analyte identification across concentrations. However, when trained with temporal information from the fiber array, networks using "name" or "characteristic" output codes performed well in identifying test analytes.     

Iron removal from human plasma based on molecular recognition using imprinted beads

The aim of this study is to prepare ion-imprinted polymers which can be used for the selective removal of Fe³⁺ ions from Fe³⁺-overdosed human plasma. N-Methacryloly-(l)-glutamic acid (MAGA) was chosen as the complexing monomer. In the first step, Fe³⁺ was complexed with MAGA and the Fe³⁺-imprinted poly(HEMA–MAGA) beads were synthesized by suspension polymerization. After that, the template (i.e., Fe³⁺ ions) was removed using 0.1 M EDTA solution. The specific surface area of the Fe³⁺-imprinted poly(HEMA–MAGA) beads was found to be 76.4 m²/g with a size range of 63–140 μm in diameter and the swelling ratio was 75%. According to the elemental analysis results, the beads contained 84.7 μmol MAGA/g polymer. The maximum adsorption capacity was 92.6 μmol Fe³⁺/g beads. The relative selectivity coefficients of imprinted beads for Fe³⁺/Zn²⁺ and Fe³⁺/Cr³⁺ were 17.3 and 48.6 times greater than non-imprinted matrix, respectively. The Fe³⁺-imprinted poly(HEMA–MAGA) beads could be used many times without decreasing their adsorption capacities significantly.     

Orientation-dependent ionization energies and interface dipoles in ordered molecular assemblies

Although an isolated individual molecule clearly has only one ionization potential, multiple values are found for molecules in ordered assemblies. Photoelectron spectroscopy of archetypical pi-conjugated organic compounds on metal substrates combined with first-principles calculations and electrostatic modelling reveal the existence of a surface dipole built into molecular layers. Conceptually different from the surface dipole at metal surfaces, its origin lies in details of the molecular electronic structure and its magnitude depends on the orientation of molecules relative to the surface of an ordered assembly. Suitable pre-patterning of substrates to induce specific molecular orientations in subsequently grown films thus permits adjusting the ionization potential of one molecular species over up to 0.6 eV via control over monolayer morphology. In addition to providing in-depth understanding of this phenomenon, our study offers design guidelines for improved organic-organic heterojunctions, hole- or electron-blocking layers and reduced barriers for charge-carrier injection in organic electronic devices.     

Antioxidant sensors based on DNA-modified electrodes

TiO2/ITO modified electrodes were developed to quantitatively photooxidize adsorbed ds-DNA and to study the effect of antioxidants as ds-DNA protecting agents. TiO2 films are used for efficient ds-DNA immobilization, for ds-DNA oxidation through photogenerated hydroxyl radicals, and as electrodes for amperometric sensing. The films, prepared by a sol-gel process, are deposited on ITO glass electrodes. Damages occurring after ds-DNA oxidation by ROS are detected by adding MB as an intercalant probe and by monitoring the electrochemical reduction current of the intercalated redox probe. The MB electrochemical signal is found to be sensitive enough to monitor ds-DNA structure changes, and the electrochemical sensor has been applied to the evaluation of the antioxidant properties of glutathione and gallic acid.     

Chemical sensors based on nano-polymer films

A procedure is described for formation of a nano-structured organic-organic interface with increased conductivity at the interface of two polymer films. It is established that conductivity is determined by the type and degree of external action. It is shown that on the basis of this interface it is possible to create chemical sensors, and in fact sensors for the relative humidity of air, ethanol vapor pressure, and pH readings. Translated from Izmeritel’naya Tekhnika, No. 4, pp. 62–64, April, 2009.     

Enantioselective sensors based on antibody-mediated nanomechanics

The use of microfabricated cantilevers as bioaffinity sensors was investigated. Since many bioaffinity interactions involve proteins as receptors, we conducted studies of the magnitude, kinetics, and reversibility of surface stresses caused when common proteins interact with microcantilevers (MCs) with nanostructured (roughened) gold surfaces on one side. Exposure of nanostructured, unfunctionalized MCs to the proteins immunoglobulin G and bovine serum albumin (BSA) resulted in reversible large tensile stresses, whereas MCs with smooth gold surfaces on one side produced reversible responses that were considerably smaller and compressive. The response magnitude for nanostructured MCs exposed to BSA is shown to be concentration dependent, and linear calibration over the range of 1-200 mg/L is demonstrated. Stable, reusable protein bioaffinity phases based on unique enantioselective antibodies are created by covalently linking monoclonal antibodies to nanostructured MC surfaces. The direct (label-free) stereoselective detection of trace amounts of an important class of chiral analytes, the alpha-amino acids, was achieved based on immunomechanical responses involving nanoscale bending of the cantilever. The temporal response of the cantilever (delta deflection/delta time) is linearly proportional to the analyte concentration and allows the quantitative determination of enantiomeric purity up to an enantiomeric excess of 99.8%. To our knowledge, this is the first demonstration of chiral discrimination using highly scalable microelectromechanical systems.     

基于MXene的电化学传感研究进展EI北大核心CSCD

MXene是一种早期过渡金属碳化物、氮化物或碳氮化物组成的二维(2D)层状材料。由于MXene具有独特的层状形态、高电导率、高比表面积、优异的亲水性和良好的热稳定性等特性,在物理、化学和纳米技术领域具有广阔的应用前景,可应用于催化、储能和传感器等多种科学领域。本文主要综述基于MXene的电化学传感器的研究进展,介绍电化学传感器的原理、构成,传感界面修饰和MXene制备方法,着重讨论MXene在电化学酶传感器、电化学非酶传感器、电化学免疫传感器、电化学适体传感器和电化学分子印迹传感器方面的研究进展,指出MXene电化学传感领域工业化和商业化利用不足、新种类MXene开发的挑战,对其在各类分析物检测、更多潜在领域的应用进行展望。     

Force sensors based on distortion in delay lines

The principle of operation of force sensors based on distortion in delay lines type of sensor is the distortion of an acoustic signal, in a pulse-excited magnetostrictive delay line due to a force applied at any point between the point where the pulse is generated and the receiving coil. A conductor orthogonal to the delay line is used for pulsed current transmission and its distance is fixed with respect to the delay line. The input and the output of the system are the applied force on the delay line support and the amplitude of the detected output V _o, respectively. Under fixed amplitude of the pulsed current, V_o has a maximum value under zero input and decreases as the applied force increases. Experimental results show that the response of the sensor is a monotonic, exponential function of the applied force. A method is also proposed, according to which an integrated sensor array could be made based on this principle     

Biomimetic bone scaffolds based on chitosan and calcium phosphates

This paper reports a novel biomimetic technique for obtaining chitosan-calcium phosphate composite scaffolds (Cs-CP) by calcium phosphate precipitation from its precursors,CaCl₂ and NaH₂PO₄ in the presence of ammonia and Cs, followed by product freeze-drying. The structural and morphological analysis showed the arrangement of CP onto Cs fibers, while Cs acting as glue to bind together the CP crystals. The presence of different forms of CP was evidenced, including hydroxyapatite, which is known to be involved in the formation of the new bone tissue in living organisms. Great mechanical properties of the scaffolds indicate their potential use in bone tissue engineering.     

Chemical sensor based on surface acoustic wave resonator using Langmuir-Blodgett film

A one-port surface acoustic wave (SAW) resonators incorporating Langmuir-Blodgett (LB) films has been investigated. SAW sensors are one potential applications of SAW devices. Most of the work reported on SAW sensor concerns delay lines. In this paper we characterize the mass loading effects of one-port resonators by depositing successive monolayers of LB films onto the surface. A 90 MHz SAW gas-phase sensor has been fabricated on an ST cut quartz substrate, and one-port resonator configurations have been used as the sensing element. Ultra thin monolayers of arachidic acid and arachidic acid ethyl ester have been deposited using the LB method. The resonant frequencies and the Q values have been measured as sensor response. Experimental results show that the Q values and the resonant frequencies of the one-port SAW resonator vary with film mass loading on the SAW device surface.     

Theoretical study of molecular aggregation in Langmuir-Blodgett films using a dipolar interaction model

We present a dipole-dipole interaction model based on the classical electrostatic theory in the Langmuir-Blodgett (LB) films to calculate the state of aggregation of rod-like molecules with permanent electronic dipole moment. The dependence of the molecular aggregation spectral properties on the structure parameters in the Z-type LB films, such as the intra-layer molecular separation distance, the adjacent layer separation distance, the molecular orientation angle and the layer number of LB films have been studied. It is found that the H-J-type transition of the aggregation could be realized by modulating the structure parameters of the LB films. The theoretical results show a qualitative agreement with experimental data.     

Kirigami-inspired strain-insensitive sensors based on atomically-thin materials

This work reports kirigami-inspired architectures of graphene for strain-insensitive, surface-conformal stretchable multifunctional electrodes and sensors. The kirigami-inspired graphene electrode exhibits strain-insensitive electrical properties up to 240% applied tensile strain and mixed strain states, including a combination of stretching, twisting, and/or shearing. Moreover, a multitude of kirigami designs of graphene are explored computationally to predict deformation morphologies under different strain conditions and to achieve controllable stretchability. Notably, strain-insensitive graphene field-effect transistor and photodetection under 130% stretching and 360° torsion are achieved by strategically redistributing stress concentrations away from the active sensing elements via strain-responsive out-of-plane buckling at the vicinity of the kirigami notches. The combination of ultra-thin form factor, conformity on skin, and breathable notches suggests the applicability of kirigami-inspired platform based on atomically-thin materials in a broader set of wearable technology.     

Reference instruments based on industrial pressure sensors

A high precision pressure transducer with a reduced error of 0.03% is created. The possibility of using a reference instrument with a relative error of 0.02% is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 31–33, January, 2008.     

Thin-film sensors based on evaporated chalcogenide glasses

Thin-film sensors based upon evaporated layers of chalcogenide glasses and sensitive to silver, copper, and lead ions have been developed. The optimal contents of the membranes were established and the electrochemical characteristics were investigated. It was shown that the sensitivity, detection limit, response time, reproducibility, and selectivity to interfering ions are in good agreement with those for traditional bulk ion-selective electrodes.     

Nonequilibrium processes in capacitive sensors based on porous silicon

The response of a capacitive sensor of the Al/por-Si/n-Si type to the presence of ammonia and water vapor in the gas phase was studied. It was found that illumination affects the process of capacitance relaxation.