Change In Impedance Magnitude Research Articles

Disposable pH Sensor on Paper Using Screen-Printed Graphene-Carbon Ink Modified Zinc Oxide Nanoparticles

The estimation of pH is vital to assess the biochemical and biological processes in a wide variety of applications ranging from water to soil, health, and environment monitoring. This work reports a screen-printed flexible and disposable pH sensor using the impedimetric method. The pH sensor was fabricated by screen printing graphene-carbon (G-C) modified zinc oxide (ZnO)-based active layer on a paper substrate and shows nearly three orders of change in impedance magnitude in the pH range of 2–9. The sensor was carefully designed using COMSOL Multiphysics software to understand the influence of electrode geometry and the electrical potential developed across the structure. The developed sensor was used for pH monitoring of soil and exhibited high sensitivity of 5.27 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> /pH 2–8 with a correlation coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula> ) of 0.99. Finally, an IoT-enabled smart pH detection system was implemented for continuous pH monitoring for potential application in digital agriculture. The outcome demonstrates that the presented flexible and disposable pH sensor could open new opportunities for monitoring of water, product process, human health, and chemical (or bio) reactions even by using small volumes of samples.

Ultrasensitive and label-free biosensor for the detection of Plasmodium falciparum histidine-rich protein II in saliva

Malaria elimination is a global public health priority. To fulfil the demands of elimination diagnostics, we have developed an interdigitated electrode sensor platform targeting the Plasmodium falciparum Histidine Rich Protein 2 (PfHRP2) protein in saliva samples. A protocol for frequency-specific PfHRP2 detection in phosphate buffered saline was developed, yielding a sensitivity of 2.5 pg/mL based on change in impedance magnitude of the sensor. This protocol was adapted and optimized for use in saliva with a sensitivity of 25 pg/mL based on change in resistance. Further validation demonstrated detection in saliva spiked with PfHRP2 from clinical isolates in 8 of 11 samples. With a turnaround time of ~2 hours, the label-free platform based on impedance sensors has the potential for miniaturization into a point-of-care diagnostic device for malaria elimination.

The effect of precipitation and deposition layer growth on impedance measurements

Abstract The objective of the study was to examine how precipitation and deposition layer growth in an electrochemical cell impact impedance measurements. A measurement system, based on Electrochemical Impedance Spectroscopy (EIS), was used to observe the impedance of an electrochemical cell while precipitation was occurring. The measurement system was also used together with measurements of the solution concentration (in parts per million, ppm) to examine what impact deposition layer growth has on an electrochemical cell. Experimental results indicate a measurable change in the impedance magnitude as the ionic concentration is altered through precipitation. A change in both impedance magnitude and the interfacial capacitance was observed when a deposition layer was established within an electrochemical cell. Results show that impedance measurements are susceptible to changes in solution conductivity and to the presence of a deposition layer in an electrochemical cell. Impedance measurements may be used as an indicator for deposition layer growth, but changes in the solution concentration should be considered when creating a model.

Impedance Sensor to Detect Substance Change at the Needle Tip

AbstractObjective, reliable, accurate and cost‐effective methods for real‐time needle localization within the body are needed for many different clinical applications. Electrical impedance (EI) is a technique used to identify biological tissues and has the potential to provide real‐time needle localization during medical procedures. We have developed a needle integrated with an impedance sensor to enable needle tip impedance measurement and tissue identification. This paper details device performance as it traversed test media, gelatine and lard, at constant speeds and provides analysis of the impedance measurements taken from the needle tip. The average needle speed of forward advancement during ultrasound guided peripheral nerve block was defined and used in these experiments as a clinically relevant needle speed. Impedance was also recorded while the needle was static in bulks of the different substances. Physical change of substance at the needle tip was compared to a change in magnitude of impedance. A delay between the physical substance change and indication of a substance change by impedance was observed. On further investigation using impedance data recorded while the needle was static, limitations of current electrochemical analysers and software were identified as the cause for the delay. Impedance measured by the needle tip electrode accurately determined a change in substance. We conclude that this technology can feasibly provide data to inform substance type at the needle tip. An application in medical procedures will subsequently be evaluated.

A microfluidic platform for drug screening in a 3D cancer microenvironment

Development of resistance to chemotherapy treatments is a major challenge in the battle against cancer. Although a vast repertoire of chemotherapeutics is currently available for treating cancer, a technique for rapidly identifying the right drug based on the chemo-resistivity of the cancer cells is not available and it currently takes weeks to months to evaluate the response of cancer patients to a drug. A sensitive, low-cost diagnostic assay capable of rapidly evaluating the effect of a series of drugs on cancer cells can significantly change the paradigm in cancer treatment management. Integration of microfluidics and electrical sensing modality in a 3D tumour microenvironment may provide a powerful platform to tackle this issue. Here, we report a 3D microfluidic platform that could be potentially used for a real-time deterministic analysis of the success rate of a chemotherapeutic drug in less than 12h. The platform (66mm×50mm; L×W) is integrated with the microsensors (interdigitated gold electrodes with width and spacing 10µm) that can measure the change in the electrical response of cancer cells seeded in a 3D extra cellular matrix when a chemotherapeutic drug is flown next to the matrix. B16-F10 mouse melanoma, 4T1 mouse breast cancer, and DU 145 human prostate cancer cells were used as clinical models. The change in impedance magnitude on flowing chemotherapeutics drugs measured at 12h for drug-susceptible and drug tolerant breast cancer cells compared to control were 50,552±144 Ω and 28,786±233 Ω, respectively, while that of drug-susceptible melanoma cells were 40,197±222 Ω and 4069±79 Ω, respectively. In case of prostate cancer the impedance change between susceptible and resistant cells were 8971±1515 Ω and 3281±429 Ω, respectively, which demonstrated that the microfluidic platform was capable of delineating drug susceptible cells, drug tolerant, and drug resistant cells in less than 12h.

Microfluidic Chip with Integrated Electrical Cell-Impedance Sensing for Monitoring Single Cancer Cell Migration in Three-Dimensional Matrixes

Cell migration has been recognized as one hallmark of malignant tumor progression. By integrating the method of electrical cell-substrate impedance sensing (ECIS) with the Boyden chamber design, the state-of-the-art techniques provide kinetic information about cell migration and invasion processes in three-dimensional (3D) extracellular matrixes. However, the information related to the initial stage of cell migration with single-cell resolution, which plays a unique role in the metastasis-invasion cascade of cancer, is not yet available. In this paper, we present a microfluidic device integrated with ECIS for investigating single cancer cell migration in 3D matrixes. Using microfluidics techniques without the requirement of physical connections to off-chip pneumatics, the proposed sensor chip can efficiently capture single cells on microelectrode arrays for sequential on-chip 2D or 3D cell culture and impedance measurement. An on-chip single-cell migration assay was successfully demonstrated within several minutes. Migration of single metastatic MDA-MB-231 cells in their initial stage can be monitored in real time; it shows a rapid change in impedance magnitude of approximately 10 Ω/s, whereas no prominent impedance change is observed for less-metastasis MCF-7 cells. The proposed sensor chip, allowing for a rapid and selective detection of the migratory properties of cancer cells at the single-cell level, could be applied as a new tool for cancer research.

Gellan gum doped polypyrrole neural prosthetic electrode coatings

Surface modification of neural prosthetic electrodes with polymeric materials, in particular, conducting polymers and hydrogels, has the potential to circumvent many problems associated with currently used electrode platforms. These problems include the disparity in mechanical properties between implanted electrodes and host neural tissue and the lack of biofunctionality at the electrode surface, both of which dissuade favourable reception of the implanted device. We have developed conducting polymer electrode coatings doped with the polysaccharide gellan gum, as a platform for improved functionality of neural prosthetic electrodes. Our electrode coatings, prepared by galvanostatic electropolymerisation, significantly reduced the impedance magnitude at frequencies relevant to neural cells, relative to uncoated gold Mylar electrodes (24 ± 3 Ω at 1 kHz). Cyclic voltammetry was used to explore the electrochemical stability of the coatings, which lose only 23 ± 2% charge carrying capacity when subjected to 400 redox cycles. The coatings show no change in impedance magnitude at 1 kHz when subject to 32 h of clinically relevant charge balanced current stimulation.

Determination of the location and magnitude of synaptic conductance changes in spinal motoneurons by impedance measurements.

The relation between impedance change and the location and magnitude of a tonic synaptic conductance was examined in compartmental motoneuron models based on previously published data. The dependency of motoneuron impedance on system time constant (tau), electrotonic length (L), and dendritic-to-somatic conductance ratio (rho) was examined, showing that the relation between impedance phase and rho differed markedly between models with uniform and nonuniform membrane resistivity. Dendritic synaptic conductances decreased impedance magnitude at low frequencies; at higher frequencies, impedance magnitude increased. The frequency at which the change in impedance magnitude reversed from a decrease to an increase-the reversal frequency, F(r)-was a good estimator of electrotonic synaptic location. A measure of the average normalized impedance change at frequencies less than F(r), cuDeltaZ, estimated relative synaptic conductance. F(r) and cuDeltaZ provided useful estimates of synaptic location and conductance in models with nonuniform (step, sigmoidal) and uniform membrane resistivity. F(r) also provided good estimates of spatial synaptic location on the equivalent cable in both step and sigmoidal models. Variability in relations between F(r), cuDeltaZ, and conductance location and magnitude between neurons was reduced by normalization with rho and tau. The effects on F(r) and cuDeltaZ of noise in experimental recordings, different synaptic distributions, and voltage-dependent conductances were also assessed. This study indicates that location and conductance of tonic dendritic conductances can be estimated from F(r), cuDeltaZ, and basic electrotonic motoneuron parameters with the exercise of suitable precautions.

Ammonia detection using nanoporous alumina resistive and surface acoustic wave sensors

The effect of pore size and uniformity on the response of nanoporous anodized alumina to ammonia at room temperature, 23 °C, is reported. Pore sizes examined range from 13.6 to 48 nm, with pore size standard deviations ranging from 2.6 to 7.8 nm. The nanoporous alumina films were used in conjunction with 98.5 and 32.5 MHz surface acoustic wave (SAW) devices, and as impedance-based sensors, both of which were found sensitive to ammonia. The SAW devices showed a frequency shift of approximately 0.001% per percentage change in ammonia concentration. Similarly, at 5 kHz an alumina sensor with an average pore size of 13.6 nm, standard deviation 2.6 nm, exhibits a factor of two change in impedance magnitude as it is cycled between an ammonia and argon environment. The nanoporous alumina-based sensors demonstrated a fast response time (≈30–40 s) and recovery time (≈60–80 s), and complete recovery upon removal from an ammonia ambient. We believe the enhanced physisorption of ammonia on alumina films due to the large surface area, provided by the mesoporous topology, is responsible for the sensing behavior.

Highly Ordered Nanoporous Alumina Films: Effect of Pore Size and Uniformity on Sensing Performance

The effect of pore size and uniformity on the humidity response of nanoporous alumina, formed on aluminum thick films through an anodization process, is reported. Pore sizes examined range from approximately 13 to 45 nm, with a pore size standard deviations ranging from 2.6 to 7.8 nm. The response of the material to humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm (standard deviation 2.6 nm) exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Increasing pore size decreases the humidity range over which the sensors have high sensitivity and shifts the operating range to higher humidity values. Cole–Cole plots of 5 to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of water adsorption and ion migration within the adsorbed water layer. The presence of impurity ions within the highly ordered nano-dimensional pores, accumulated during the anodization process, appear highly beneficial for obtaining a substantial variation in measured impedance over a wide range of humidity values.

Room Temperature Ammonia and Humidity Sensing Using Highly Ordered Nanoporous Alumina Films

The effect of pore size and uniformity on the response of nanoporous alumina, formed on aluminum thick films through an anodization process, to ammonia and humidity at room temperature is reported. Pore sizes examined range from 13 nm to 48 nm, with pore size standard deviations ranging from 2.6 nm to 7.8 nm. The response of the material to ammonia and humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm, standard deviation 2.6 nm, exhibits a factor of two change in impedance magnitude as it is cycled between an ammonia and argon environment. At 5 kHz the same sensor exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Cole-Cole plots of the 5 Hz to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of adsorption and ion migration.

Electrical impedance in the subicular area of rats during paradoxical sleep

A four-electrode method of chronically measuring impedance of less than 1 mm 3 parts of brain in unrestrained rats is described. The method is usually good from about 1.5 to 3,000 cycle/sec for the absolute value of phase angle, and relative changes in magnitude of impedance can be measured from about 1.5 to 10,000 cycle/sec. Testing current of 2 × 10 −8 amp is used, which produces a signal of about 20 μv. Stability for hours and days is sometimes, but not always, achieved. In the subicular area, there is invariably an increase in magnitude of impedance of up to 25% during paradoxical sleep. In the same animal, this increase is the same during all episodes of paradoxical sleep lasting longer than 1 min, and is the same at 32 to 10,000 cycle/sec. The phase angle at 100 to 1,000 cycle/sec becomes 1 or 2 deg more negative during paradoxical sleep. There are no changes or very small changes in Ammon's horn and the fascia dentata. Because these data are fairly complete, the mechanisms which might possibly be responsible for these impedance changes can be stated specifically in semiquantitative form. Among several possibilities, a single one cannot be chosen on the basis of these impedance data alone, but from other considerations, a decreased size of interstitial space seems by far the most likely.

CALIBRATION OF AN IMPEDANCE PNEUMOGRAPH.

An experimental calibration of an electrical impedance pneumograph is presented over a range of tidal volumes from 250 to 4,000 ml. Transthoracic impedance measurements were made on four subjects using 1-in. cup electrodes, and at a frequency of 100 kc/sec. A 1-ohm change of impedance magnitude corresponding to an average tidal volume of 830 ml was observed, based on a total of 1,063 measurements. The standard deviation of these data was approximately 50% for low tidal volumes and 30% for the larger tidal volumes. Data from individual subject trials indicated significant variations in the calibration constants and regions of apparent linearity, both between subjects and between trials on each subject. Experimental records of the change in impedance magnitude as a function of inspired air volume during inspiration are included to illustrate typical variations. plethysmography, impedance; impedance, transthoracic; tidal volume, measurement of; respiration meter Submitted on July 29, 1963