Fabrication of polyaniline/graphene oxide composites for implementation in humidity sensing

This work reports the measurement of impedance variations under various humidity conditions at frequency ranges between 100 Hz and 5 MHz. An electrochemical polymerization process has been used in the synthesis including varying the mass ratios of graphene oxide (GO) in polyaniline. An electrochemical deposition method has been used to produce a sample film on an indium tin oxide glass slide. The percentage relative humidity (RH%) of the samples has been estimated to be 20–90%. Impedance and humidity had an inverse relationship, i.e. the impedance value decreased with an increase in humidity. In contrast with platinum capacitive humidity sensors (HS), the GO-based HS had a sensitivity of 75–99%, which was ~10-fold more than that of traditional sensors. With three different parameter weight % of GO, the frequency range have been 100 Hz to 5 MHz and RH% has been found to 20–90%. The HS showed a fast response and recovery time. Therefore, GO appears to be a useful material for building HS with high sensitivity for a comprehensive approach.     

Nanoindentation and storage of teeth

This study determined changes in nanomechanical properties of dentin and enamel during storage in deionized water, calcium chloride buffered saline solution and Hank's balanced salts solution (HBSS). Atomic force microscopy based nanoindentation showed that storing teeth in deionized water or CaCl(2)-solution resulted in a large decrease in elastic modulus and hardness. At 1 day a decrease in the mechanical properties values of up to 20% and 30% was observed for enamel and dentin, respectively. After 1 week, mechanical properties dropped below 50% of their starting values, which is attributed to a demineralization process during storage. In contrast, storing teeth in HBSS did not significantly alter the mechanical properties for a time interval of 2 weeks. The use of HBSS for storage of samples from teeth is recommended.     

面向血液葡萄糖测量的生物组织阻抗模型

本文推导了细胞膜电容与血糖浓度之间的关系,并将这种关系应用到Pauly和Schwan提出的弛豫模型中,再将弛豫模型应用于多重Cole-Cole介电模型,最后通过介电模型得出阻抗模型,建立起人体血糖浓度与组织介电谱,阻抗谱之间的联系。通过分析发现,细胞膜电容随着血糖浓度增加而增大,且当血糖浓度趋于无穷大时,细胞膜电容等于血糖浓度为0时细胞膜电容的1.53倍。对介电谱的仿真得出,当外加信号频率小于1 MHz时,介电常数实部随着葡萄糖浓度改变而发生明显变化。阻抗谱的研究结果表明,随着葡萄糖浓度的升高,阻抗的实部减小,阻抗虚部模增大,且分别在频率为1.48 MHz和0.55 MHz时变化得最快。本文建立的模型为血糖无创检测提供了一种新的方法和手段。     

Assessment of composition and anisotropic elastic properties of secondary osteon lamellae

Measurement of the elastic properties of single osteon lamellae is still one of the most demanding tasks in bone mechanics to be solved. By means of site-matched Raman microspectroscopy, acoustic microscopy and nanoindentation the structure, chemical composition and anisotropic elasticity of individual lamellae in secondary osteons were investigated. Acoustic impedance images (911-MHz) and two-dimensional Raman spectra were acquired in sections of human femoral bone. The samples were prepared with orientations at various observation angles theta relative to the femoral long axis. Nanoindentations provided local estimations of the elastic modulus and landmarks necessary for spatial fusion of the acoustic and spectral Raman images. Phosphate nu(1) (961 cm(-1)) and amide I (1665 cm(-1)) band images representing spatial distributions of mineral and collagen were fused with the acoustic images. Acoustic impedance was correlated with the indentation elastic modulus E(IT) (R(2)=0.61). Both parameters are sensitive to elastic tissue anisotropy. The lowest values were obtained in the direction perpendicular to the femoral long axis. Acoustic images exhibit a characteristic bimodal lamellar pattern of alternating high and low impedance values. Since this undulation was not associated with a variation of the phosphate nu(1)-band intensity in the Raman images, it was attributed to variations of the lamellar orientation. After threshold segmentation and conversion to elastic modulus the orientation and transverse isotropic elastic constants were derived for individual ensembles of apparent thin and thick lamellae. Our results suggest that this model represents the effective anisotropic properties of an asymmetric twisted plywood structure made of transverse isotropic fibrils. This is the first report that proves experimentally the ability of acoustic microscopy to map tissue elasticity in two dimensions with micrometer resolution. The combination with Raman microspectroscopy provides a unique way to study bone and mineral metabolism and the relation with mechanical function at the ultrastructural tissue level.     

A composite sensor array impedentiometric electronic tongue Part I. Characterization

A study aimed at the characterization of five compounds with different chemical characteristics and gustative perceptions by measuring the variations of the electrical impedance of a composite sensor array is presented. The array was composed of five sensors of three different types based on carbon nanotubes or carbon black dispersed in polymeric matrices and doped polythiophenes. Measurements were carried out by evaluating the electrical impedance of the sensor array at a frequency of 150 Hz, and the data acquisition process was automated; a mechanical arm and a rotating platform controlled by a data acquisition card and a dedicated software allowed the sequential dipping of sensors in the test solutions. Fifty different solutions eliciting the 5 basic tastes (sodium chloride, citric acid, glucose, glutamic acid and sodium dehydrocholate for salty, sour, sweet, umami and bitter, respectively) at 10 concentration levels comprising the human perceptive range were analysed. More than 100 measurements were carried for each sample in a 4-month period to evaluate the system repeatability and robustness. The impedentiometric composite sensor array is shown to be sensitive, selective and stable for use in an electronic tongue.     

Dielectric Properties Based Detection of Heavy Metal Contaminated Soil in the Frequency Range from 10 MHz to 1 GHz

Physical parameters based electromagnetic methods are promising technologies to detect contaminated sites. In these methods, the dielectric property is a key parameter. In this paper, we studied the dielectric characteristics of heavy metal contaminated soil. The chromium contaminated soil was made into samples, and the open-ended coaxial line was adopted as the measurement method. Experiments were conducted in the frequency band between 10 MHz and 1 GHz. The results showed that the complex permittivity, including the real part and the imaginary part, changes as the ionic content changes. Especially, at low frequencies (<50 MHz), the complex permittivity increases significantly with the increase of ionic content. In addition, it also could be seen that the water content of the soil also affects the complex permittivity. We proposed to adopt the drying method or the Time Domain Reflection method to determine the water content. The dielectric parameters are most affected by the ionic content after knowing the water content. Therefore, it is feasible to detect heavy metal contaminated sites based on dielectric properties.     

Physicochemical properties of structured water in human albumin and gammaglobulin solutions.

The physicochemical properties of the different phases of water molecules were studied in concentrated solutions (132 g/L) of human serum albumin and gammaglobulin by (1)H NMR relaxometry. Spin-lattice (T1) relaxation times of total water and structured water (non-freezable water) were measured at 40 MHz above and below the freezing point of bulk water (ordinary, liquid water) at different temperatures. Analysis of the temperature dependence of the T1 demonstrated that total water differed qualitatively while structured water characteristics changed both quantitatively and qualitatively in the two protein solutions. Comparison of the temperature dependence of the structured water's T1 in the two solutions in the presence of an increasing concentration of manganese chloride allowed two main conclusions to be drawn. Firstly, the differences observed in total water and structured water physicochemical properties are directly related to protein structure and three-dimensional arrangement. Secondly, the motion of structured water determines the motion of the total water in the system through the values of the translational diffusion and chemical exchange correlation times tau(D) and tau m.     

Tuning,coupling and matching of a resonant cavity in microwave exposure system for biological objects

A new microwave exposure system for biological experiments with well-defined exposure conditions and improved control of the exposure parameters consisting of variable frequency power source, coaxial to waveguide transition, matching network and single-mode resonant cavity with movable shorting plunger was fabricated and characterized. The introduction of a biological sample into a resonant cavity has a large impact on its field configuration and port impedance. As such, the properties, geometry and position of the biological sample become a part of the electrical properties of the microwave circuit. With that change, the electrical properties of the resonant cavity, such as impedance, quality factor and resonant frequency, also change. In this study, an appropriate coupling system with effective power transfer and an algorithm to tuning and coupling of resonant cavity in resonance before and after the introduction of biological sample have been proposed. This procedure will lead to a known dose distribution within the biological sample and allow a better comparison with other studies. Coupling of the electromagnetic energy into a resonant cavity was experimentally investigated. Graphical representation of cavity impedance in case of undercoupled, critically coupled and overcoupled cavity has been presented. Critical coupling of an empty resonant cavity has been accomplished at voltage standing wave ratio (VSWR) 1.01, at resonance frequencies 900 and 947.5 MHz. Critical coupling with the introduction of a biological sample has been accomplished at VSWR ≤ 1.07 for frequency bandwidth 1 MHz and VSWR ≤ 1.5 for frequency bandwidth up to 5 MHz with central frequency 947.5 MHz.     

Measuring electrical impedance of organs--instrumental equipment for research and clinical use

An apparatus for measuring the impedance of intact biological organs or parts of organs in the frequency range of 10 Hz to 10 MHz is described. In this range impedance exhibits a large dispersion, which is dependent on tissue structures. The time course of alterations of electrical impedance such as occur during ischemia can be recorded with this equipment. Five specimens in five measuring chambers can be examined simultaneously at different temperatures. In the second part of the article, a portable impedance meter for measuring the modulus of impedance near 200 Hz, the phase of impedance at 5 kHz and the local temperature at the measuring point, is described. These parameters permit an intra-operative evaluation of the changing state of ischemic organs. Sterilizable probes with four surface electrodes and an integrated temperature sensor permit atraumatic measurements at the organ surface. The measurement itself is harmless to the tissue.     

Correlation of second virial coefficient with solubility for proteins in salt solutions

In this work, osmotic second virial coefficients (B(22)) were determined and correlated with the measured solubilities for the proteins, α-amylase, ovalbumin, and lysozyme. The B(22) values and solubilities were determined in similar solution conditions using two salts, sodium chloride and ammonium sulfate in an acidic pH range. An overall decrease in the solubility of the proteins (salting out) was observed at high concentrations of ammonium sulfate and sodium chloride solutions. However, for α-amylase, salting-in behavior was also observed in low concentration sodium chloride solutions. In ammonium sulfate solutions, the B(22) are small and close to zero below 2.4 M. As the ammonium sulfate concentrations were further increased, B(22) values decreased for all systems studied. The effect of sodium chloride on B(22) varies with concentration, solution pH, and the type of protein studied. Theoretical models show a reasonable fit to the experimental derived data of B(22) and solubility. B(22) is also directly proportional to the logarithm of the solubility values for individual proteins in salt solutions, so the log-linear empirical models developed in this work can also be used to rapidly predict solubility and B(22) values for given protein-salt systems.     

A dielectric analysis of liquid and glassy solid glucose/water solutions

Dielectric relaxation data covering a temperature range from above room temperature to below the glass transition for 40% (w/w) and 75% (w/w) glucose/water solutions in the frequency range between 5 and 13 MHz are presented. These data are used to obtain correlation times for the dielectric relaxation in the viscous liquid and the glass and are compared with correlation times determined from deuterium nuclear spin relaxation times [J. Chem. Phys., 110 (1999) 3472-3483]. The two sets of results have the same temperature dependence, but differ in magnitude by a factor of 3, implying that the relaxation is a small-step rotational diffusion. Both the structural relaxation (alpha process) and the slow beta process are present. In the 40% glucose/water sample, there is a dielectric relaxation attributable to the ice that forms at low temperature. It is shown that the reciprocal of the viscosity, the correlation time derived from the dielectric relaxation, and the dc conductivity have a similar dependence on temperature.     

Sodium chloride affects propidium monoazide action to distinguish viable cells

Propidium monoazide (PMA) is a DNA-intercalating agent used to selectively detect DNA from viable cells by polymerase chain reaction (PCR). Here, we report that high concentrations (>5%) of sodium chloride (NaCl) prevents PMA from inhibiting DNA amplification from dead cells. Moreover, Halobacterium salinarum was unable to maintain cell integrity in solutions containing less than 15% NaCl, indicating that extreme halophilic microorganisms may not resist the concentration range in which PMA fully acts. We conclude that NaCl, but not pH, directly affects the efficiency of PMA treatment, limiting its use for cell viability assessment of halophiles and in hypersaline samples.     

Contribution of electrogenic ion transport to impedance of the algae Valonia utricularis and artificial membranes.

The cell membrane of Valonia utricularis contains an electrogenic carrier system for chloride (Wang et al., Biophys J. 59:235-248 (1991)). The electrical impedance of V. utricularis was measured in the frequency range between 1 Hz and 50 kHz. The analysis of the impedance spectra from V. utricularis and its comparison with equivalent circuit models showed that the transport system created a characteristic contribution to the impedance in the frequency range between 10 Hz and 5 kHz. The fit of the impedance spectra with the formalism derived from the theory of carrier-mediated transport allowed the determination of the kinetic parameters of chloride transport through the cell membrane of V. utricularis, and its passive electrical properties. Simultaneous measurements of the kinetic parameters with the charge pulse method demonstrated the equivalence of both experimental approaches with respect to the evaluation of the translocation rate constants of the free and the charged carriers and the total density of carriers within the membrane. Moreover, the impedance spectra of the protonophor-mediated proton transport by FCCP (carbonylcyanide p-trifluoromethoxyphenyl-hydrazone) were measured in model membranes. The carrier system made a substantial contribution to the impedance of the artificial membranes. The analysis of the spectra in terms of a simple carrier system (Benz and McLaughlin, 1983, Biophys. J. 41:381-398) allowed the evaluation of the kinetic and equilibrium parameters of the FCCP-mediated proton transport. The possible application of the measurement of impedance spectra for the study of biological transport systems is discussed.     

Micro hole-based cell chip with impedance spectroscopy

Electric fields can be used for the characterisation and manipulation of single biological cells. One approach to avoid the effect of electrode polarisation is to position cells on micro holes and to apply the electrical fields via the micro holes. For a correct characterisation and optimal manipulation, the electrical properties of the micro hole/cell interface must be understood. In this article, the electrical characteristics of a micro hole-based cell chip were investigated. By FEM simulation, it was estimated that the impedance measurement with micro hole-based chip is most dependent on the cell adhesion/spread rather than the intra-cellular space (contribution of intra-cellular space to the total impedance: 0.07% at 1 kHz, 0.3% at 1 MHz). The effective frequency range in which the impedance related with cell state on the hole considerably influences total measured impedance was below several kiloHertz. From the experiments, it was shown that the impedance of cell cultured on the hole at the low frequency range is increased during the increase of cultivation period, but is sensitively decreased after applying only several nanolitres of culture medium including 5% dimethlysulfoxide. This micro hole-based chip has a potential for monitoring the cell growth and the membrane integrity of even single cell without any labelling.     

Electrical frequency dependent characterization of DNA hybridization

The hybridization of oligomeric DNA was investigated using the frequency dependent techniques of electrochemical impedance spectroscopy (EIS) and quartz crystal microgravimetry (QCM). Synthetic 5'-amino terminated single stranded oligonucleotides (ssDNA) were attached to the exposed glass surface between the digits of microlithographically fabricated interdigitated microsensor electrodes using 3-glycidoxypropyl-trimethoxysilane. Similar ssDNA immobilization was achieved to the surface of the gold driving electrodes of AT-cut quartz QCM crystals using 3-mercaptopropyl-trimethoxysilane. Significant changes in electrochemical impedance values (both real and imaginary components) (11% increase in impedance modulus at 120 Hz) and resonant frequency values (0.004% decrease) were detected as a consequence of hybridization of the bound ssDNA upon exposure to its complement under hybridization conditions. Non-complementary (random) sequence sowed a modest decrease in impedance and a non-detectable change in resonant frequency. The possibility to detect the binding state of DNA in the vicinity of an electrode, without a direct connection between the measurement electrode and the DNA, has been demonstrated. The potential for development of label-free, low density DNA microarrays is demonstrated and is being pursued.     

Nerve membrane electrical characteristics near the resting state

Summary An experimental analysis of the squid axon membrane impedance in the vicinity of the resting state and as a function of frequency is presented. Particular attention was devoted to the measurement of theresonance frequency, for which the absolute magnitude of the impedance attains its maximum value, in different, extracellular solutions, at various temperatures and in the presence of constant depolarizations or hyperpolarizations.The variations in the concentration of sodium, potassium and divalent ions and the addition of tetrodotoxin, changed markedly the maximum impedance but had little effect, at a fixed temperature, on the resonance frequency, whose temperature dependance is described by aQ ₁₀ variable from 3.7 (around 4 °C) to 1.9 (around 15 °C). Substitution of heavy water decreased the resonance frequency by a factor 1.25, fairly independent of temperature. Steady depolarizations or hyperpolarizations produced large variations of the resonance frequency, with strong temperature dependance.The results indicate that the resonance frequency is directly related to the membrane permeability changes which take place quite independently of the composition of the extra cellular solution and are governed by the electric field existing within the membrane structure rather than by the total membrane potential, to which membrane-solution boundary potentials can give a large contribution.     

Minimally invasive silicon probe for electrical impedance measurements in small animals

It is commonly accepted that electrical impedance provides relevant information about the physiological condition of living tissues. Currently, impedance measurements are performed with relatively large electrodes not suitable for studies in small animals due to their poor spatial resolution and to the damage that they cause to the tissue. A minimally invasive needle shaped probe for electrical impedance measurements of living tissues is presented in this paper. This micro-probe consists of four square platinum electrodes (300 microm x 300 microm) on a silicon substrate (9 mm x 0.6 mm x 0.5 mm) and has been fabricated by using standard Si microelectronic techniques. The electrodes are not equally spaced in order to optimise the signal strength and the spatial resolution. Characterisation data obtained indicate that these probes provide high spatial resolution (measurement radius <4 mm) with a useful wide frequency band going from 100 Hz to 100 kHz. A series of in vivo experiments in rat kidneys subjected to ischemia was performed to demonstrate the feasibility of the probes and the measurement system. The impedance modulus and phase were measured at 1 kHz since this frequency is sufficiently low to permit the study of the extracellular medium. The extracellular pH and K+ were also simultaneously measured by using commercial miniaturised Ion Selective Electrodes. The induced ischemia period (45 min) resulted in significant changes of all measured parameters (Delta/Z/ approximately 65%; DeltapH approximately 0.8; DeltaK+ approximately 30 mM).     

Intensities and other spectral parameters of infrared amide bands of polypeptides in the β- and random forms

The intensities and other spectral parameters of the main components of infrared amide bands for the random and anti-parallel pleated sheet forms have been determined for poly-S-carbobenzoxymethylcysteine, poly-S-carboxymethylcysteine, polylysine and silk fibroin of Bombyx mori in heavy water solutions and in organic solvents. Assuming that the optical spectra of these two types of structure are additive, the method was proposed for determining relative contents and molar absorption coefficients of amide I band. Integral intensity and maximum frequency values of the main components of the amide I band for all the samples in the β-form turned out to be specific. In contrast to this the integral intensity of the band of amide I in the random coil form varied within certain limits, while the main maximum frequency for all samples remained the same.