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Classification of evoked or event-related potentials is an important prerequisite for many types of brain-computer interfaces (BCIs). To increase classification accuracy, spatial filters are used to improve the signal-to-noise ratio of the brain signals and thereby facilitate the detection and classification of evoked or event-related potentials. While canonical correlation analysis (CCA) has previously been used to construct spatial filters that increase classification accuracy for BCIs based on visual evoked potentials, we show in this paper, how CCA can also be used for spatial filtering of event-related potentials like P300. We also evaluate the use of CCA for spatial filtering on other data with evoked and event-related potentials and show that CCA performs consistently better than other standard spatial filtering methods. [ABSTRACT FROM AUTHOR]

This paper presents an electric circuit model and a dynamic analysis of enzymatic biofuel cells. The model is consistent with classical double-layer capacitance electrode behavior, fuel cell polarization models, and fuel diffusion limits, and may be extracted from commonly used electrochemical measurements. It is shown to accurately predict the observed experimental behavior of implantable enzymatic biofuel cells operating in vivo. The model is analyzed under various power loading conditions to consider runtime and fuel replenishment implications. A case study for powering a pacemaker is considered; and the results and SPICE simulations are shown to be in excellent agreement with experimental observations. The model can be used to identify areas for future biofuel cell improvement and to provide insight into critical electrical interface and system-level issues that must be addressed to advance the adoption of in vivo application of biofuel cells. [ABSTRACT FROM AUTHOR]

Purpose: In microwave breast cancer detection, it is often beneficial to arrange sensors in close proximity to the breast. The resultant coupling generally changes the antenna response. As an a priori characterization of the radio frequency system becomes difficult, this can lead to severe degradation of the detection efficacy. The purpose of this paper is to demonstrate the advantages of adopting an interferometric multiple signal classification (I-MUSIC) approach due to its limited dependence from a priori information on the antenna. The performance of I-MUSIC detection was measured in terms of signal-to-clutter ratio (SCR), signal-to-mean ratio (SMR), and spatial displacement (SD) and compared to other common linear noncoherent imaging methods, such as migration and the standard wideband MUSIC (WB-MUSIC) which also works when the antenna is not accounted for. Methods: The data were acquired by scanning a synthetic oil-in-gelatin phantom that mimics the dielectric properties of breast tissues across the spectrum 1-3 GHz using a proprietary breast microwave multi-monostatic radar system. The phantom is a multilayer structure that includes skin, adipose, fibroconnective, fibroglandular, and tumor tissue with an adipose component accounting for 60% of the whole structure. The detected tumor has a diameter of 5 mm and is inserted inside a fibroglandular region with a permittivity contrast εr-tumor/εr-fibroglandular < 1.5 over the operating band. Three datasets were recorded corresponding to three antennas with different coupling mechanisms. This was done to assess the independence of the I-MUSIC method from antenna characterizations. The datasets were processed by using I-MUSIC, noncoherent migration, and wideband MUSIC under equivalent conditions (i.e., operative bandwidth, frequency samples, and scanning positions). SCR, SMR, and SD figures were measured from all reconstructed images. In order to benchmark experimental results, numerical simulations of equivalent scenarios were carried out by using CST Microwave Studio. The three numerical datasets were then processed following the same procedure that was designed for the experimental case. Results: Detection results are presented for both experimental and numerical phantoms, and higher performance of the I-MUSIC method in comparison with the WB-MUSIC and noncoherent migration is achieved. This finding is confirmed for the three different antennas in this study. Although a delocalization effect occurs, experimental datasets show that the signal-to-clutter ratio and the signal-to-mean performance with the I-MUSIC are at least 5 and 2.3 times better than the other methods, respectively. The numerical datasets calculated on an equivalent phantom for cross-testing confirm the improved performance of the I-MUSIC in terms of SCR and SMR. In numerical simulations, the delocalization effect is dramatically reduced up to an SD value of 1.61 achieved with the I-MUSIC in combination with the antipodal Vivaldi antenna. This shows that mechanical uncertainties are the main reason for the delocalization effect in the measurements. Conclusions: Experimental results show that the I-MUSIC generates images with signal-to-clutter levels higher than 5.46 dB across all working conditions and it reaches 7.84 dB in combination with the antipodal Vivaldi antenna. Numerical simulations confirm this trend and due to ideal mechanical conditions return a signal-to-clutter level higher than 7.61 dB. The I-MUSIC largely outperforms the methods under comparison and is able to detect a 5-mm tumor with a permittivity contrast of 1.5. [ABSTRACT FROM AUTHOR]

Purpose: To validate the use of adaptive nonlinear filters in reconstructing conductivity and permittivity images from the noisy B+ 1 maps in electrical properties tomography (EPT). Methods: In EPT, electrical property images are computed by taking Laplacian of the B+ 1 maps. To mitigate the noise amplification in computing the Laplacian, the authors applied adaptive nonlinear denoising filters to the measured complex B+ 1 maps. After the denoising process, they computed the Laplacian by central differences. They performed EPT experiments on phantoms and a human brain at 3 T along with corresponding EPT simulations on finite-difference time-domain models. They evaluated the EPT images comparing them with the ones obtained by previous EPT reconstruction methods. Results: In both the EPT simulations and experiments, the nonlinear filtering greatly improved the EPT image quality when evaluated in terms of the mean and standard deviation of the electrical property values at the regions of interest. The proposed method also improved the overall similarity between the reconstructed conductivity images and the true shapes of the conductivity distribution. Conclusions: The nonlinear denoising enabled us to obtain better-quality EPT images of the phantoms and the human brain at 3 T. [ABSTRACT FROM AUTHOR]

Purpose: In this work, a generic recipe for an inexpensive and nontoxic phantom was developed within a range of biologically relevant dielectric properties from 150 MHz to 4.5 GHz. Methods: The recipe includes deionized water as the solvent, NaCl to primarily control conductivity, sucrose to primarily control permittivity, agar-agar to gel the solution and reduce heat diffusivity, and benzoic acid to preserve the gel. Two hundred and seventeen samples were prepared to cover the feasible range of NaCl and sucrose concentrations. Their dielectric properties were measured using a commercial dielectric probe and were fitted to a 3D polynomial to generate a recipe describing the properties as a function of NaCl concentration, sucrose concentration, and frequency. Results: Results indicated that the intuitive linear and independent relationships between NaCl and conductivity and between sucrose and permittivity are not valid. A generic polynomial recipe was developed to characterize the complex relationship between the solutes and the resulting dielectric values and has been made publicly available as a web application. In representative mixtures developed to mimic brain and muscle tissue, less than 2% difference was observed between the predicted and measured conductivity and permittivity values. Conclusions: It is expected that the recipe will be useful for generating dielectric phantoms for general magnetic resonance imaging (MRI) coil development at high magnetic field strength, including coil safety evaluation as well as pulse sequence evaluation (including B+ 1 mapping, B+ 1 shimming, and selective excitation pulse design), and other non-MRI applications which require biologically equivalent dielectric properties. [ABSTRACT FROM AUTHOR]

Microstencils have been utilized in biomedical engineering to pattern cell cultures, engineer tissues, and pattern conductive materials in microelectronics for the measurement of bioelectric activity. However, fabricating these microstencils can be considerably time consuming, expensive, and cleanroom processing or laser micromachining intensive. We present microfabrication strategies for producing stencils rapidly and cost effectively, with minimal use of cleanroom facilities, ideal for prototyping or applications where microfabrication costs need to be conserved. The process utilizes 3-D-printed templates as master structures from, which polydimethylsiloxane (PDMS) microstencils are molded. The entire process, from concept to completed stencil, requires approximately one day; however, the majority of this time is budgeted for PDMS curing cycles, so it requires only ~1-2 person hours to complete. These microstencils were used to pattern metal traces ~160-1000-μm wide, on three commonly used BioMEMS substrate materials- to pattern rat cortical neuronal cell cultures with radii between ~300 and 1000 μm-and to pattern organic materials. With the advancement of 3-D-printing technologies, we anticipate that our presented processes will improve in resolution and gain a greater cost advantage over traditional microstencilling methods. [ABSTRACT FROM AUTHOR]

The cuff electrode provides a stable interface with the peripheral nerve, which has been widely utilized in both basic research and clinical practice over the past few decades. In this paper, we present a microfabricated, parylene-based self-locking cuff electrode. The cuff diameter can be adjusted to accommodate the nerve properly during implantation. This type of cuff electrodes is easy to implant and the cuff was made of the thin, flexible, and biocompatible parylene substrate. Moreover, the integrated parylene cable and pads facilitate the connection with external circuits. Electrochemical properties of electrode sites were characterized by impedance spectroscopy and cyclic voltammetry. The average impedance magnitude and average charge delivery capacity of the Pt electrodes are 8.3 kQ (at 1 kHz) and 2.8 mC/cm2, respectively. Using the proposed cuff electrodes, the evoked compound action potentials of the rat sciatic nerve were successfully recorded. Electrical stimulation tests proved the feasibility of selective stimulation of tibial and peroneal fascicles within the rat sciatic nerve. This type of cuff electrodes induced only a benign foreign body reaction and did not damage the axons within the rat sciatic nerve over 11 weeks of an implantation period. [ABSTRACT FROM AUTHOR]

The hybrid biological/polymeric solid‐state nanopore membrane offers several opportunities to combine the advantage of biological channel (selectivity) and material (robustness). Based on this technology, the challenge is to obtain selective ionic exchange membranes, with no energy intake. The direct insertion of an ionic channel inside a nanopore should be a promise solution. Here, the authors report a hybrid nanopore based on nystatin A1 confinement in commercial nanopore membrane. Ionic transport and selectivity studies show that the hybrid nanopores exhibit mainly an anionic behaviour, on the contrary to biological conditions. However, the order of magnitude between the different ratios of permeation of several cationic species is retained even if the blocking of divalent cation is not totally proved. [ABSTRACT FROM AUTHOR]

We introduce a new 3-D flexible microelectrode array for high performance electrographic neural signal recording and stimulation. The microelectrode architecture maximizes the number of channels on each shank and minimizes its footprint. The electrode was implemented on flexible polyimide substrate using microfabrication and thin-film processing. The electrode has a planar layout and comprises multiple shanks. Each shank is three mm in length and carries six gold pads representing the neuro-interfacing channels. The channels are used in recording important precursors with potential clinical relevance and consequent electrical stimulation to perturb the clinical condition. The polyimide structure satisfied the mechanical characteristics required for the proper electrode implantation and operation. Pad postprocessing technique was developed to improve the electrode electrical performance. The planar electrodes were used for creating 3-D “Waterloo Array” microelectrode with controlled gaps using custom designed stackers. Electrode characterization and benchmarking against commercial equivalents demonstrated the superiority of the Flex electrodes. The Flex and commercial electrodes were associated with low-power implantable responsive neuro-stimulation system. The electrodes performance in recording and stimulation application was quantified through in vitro and in vivo acute and chronic experiments on human brain slices and freely-moving rodents. The Flex electrodes exhibited remarkable drop in the electric impedance (100 times at 100 Hz), improved electrode-electrolyte interface noise (dropped by four times) and higher signal-to-noise ratio (3.3 times). [ABSTRACT FROM AUTHOR]

Purpose: Pulsed RF (PRF) is a nonablative technique for treating neuropathic pain. Bipolar PRF application is currently aimed at creating a "strip lesion" to connect the electrode tips; however, the electrical and thermal performance during bipolar PRF is currently unknown. The objective of this paper was to study the temperature and electric field distributions during bipolar PRF. Methods: The authors developed computer models to study temperature and electric field distributions during bipolar PRF and to assess the possible ablative thermal effect caused by the accumulated temperature spikes, along with any possible electroporation effects caused by the electrical field. The authors also modeled the bipolar ablative mode, known as bipolar Continuous Radiofrequency (CRF), in order to compare both techniques. Results: There were important differences between CRF and PRF in terms of electrical and thermal performance. In bipolar CRF: (1) the initial temperature of the tissue impacts on temperature progress and hence on the thermal lesion dimension; and (2) at 37℃, 6-min of bipolar CRF creates a strip thermal lesion between the electrodes when these are separated by a distance of up to 20 mm. In bipolar PRF: (1) an interelectrode distance shorter than 5 mm produces thermal damage (i.e., ablative effect) in the intervening tissue after 6 min of bipolar RF; and (2) the possible electroporation effect (electric fields higher than 150 kV m-1) would be exclusively circumscribed to a very small zone of tissue around the electrode tip. Conclusions: The results suggest that (1) the clinical parameters considered to be suitable for bipolar CRF should not necessarily be considered valid for bipolar PRF, and vice versa; and (2) the ablative effect of the CRF mode is mainly due to its much greater level of delivered energy than is the case in PRF, and therefore at same applied energy levels, CRF, and PRF are expected to result in same outcomes in terms of thermal damage zone dimension. [ABSTRACT FROM AUTHOR]

Next generation neural interfaces for upper-limb (and other) prostheses aim to develop implantable interfaces for one or more nerves, each interface having many neural signal channels that work reliably in the stump without harming the nerves. To achieve real-time multi-channel processing it is important to integrate spike sorting on-chip to overcome limitations in transmission bandwidth. This requires computationally efficient algorithms for feature extraction and clustering suitable for low-power hardware implementation. This paper describes a new feature extraction method for real-time spike sorting based on extrema analysis (namely positive peaks and negative peaks) of spike shapes and their discrete derivatives at different frequency bands. Employing simulation across different datasets, the accuracy and computational complexity of the proposed method are assessed and compared with other methods. The average classification accuracy of the proposed method in conjunction with online sorting (O-Sort) is 91.6%, outperforming all the other methods tested with the O-Sort clustering algorithm. The proposed method offers a better tradeoff between classification error and computational complexity, making it a particularly strong choice for on-chip spike sorting. [ABSTRACT FROM AUTHOR]

Human joint impedance is the dynamic relationship between the differential change in the position of a perturbed joint and the corresponding response torque; it is a fundamental property that governs how humans interact with their environments. It is critical to characterize ankle impedance during the stance phase of walking to elucidate how ankle impedance is regulated during locomotion, as well as provide the foundation for future development of natural, biomimetic powered prostheses and their control systems. In this study, ankle impedance was estimated using a model consisting of stiffness, damping and inertia. Ankle torque was well described by the model, accounting for 98 ±1.2% of the variance. When averaged across subjects, the stiffness component of impedance was found to increase linearly from 1.5 to 6.5 Nm/rad/kg between 20% and 70% of stance phase. The damping component was found to be statistically greater than zero only for the estimate at 70% of stance phase, with a value of 0.03 Nms/rad/kg. The slope of the ankle's torque-angle curve-known as the quasi-stiffness-was not statistically different from the ankle stiffness values, and showed remarkable similarity. Finally, using the estimated impedance, the specifications for a biomimetic powered ankle prosthesis were introduced that would accurately emulate human ankle impedance during locomotion. [ABSTRACT FROM AUTHOR]

A fundamental goal in systems neuroscience is to assess the individual as well as the synergistic roles of single neurons in a recorded ensemble as they relate to an observed behavior. A mandatory step to achieve this goal is to sort spikes in an extracellularly recorded mixture that belong to individual neurons through feature extraction and clustering techniques. Here, we propose an approach for approximating the often nonlinear and time varying decision boundaries between spike-derived feature classes based on a simple, yet optimal thresholding mechanism. Because thresholding is a binary classifier, we show that the complex nonlinear decision boundaries required for spike class discrimination can be achieved by adequately fusing a set of weak binary classifiers. The thresholds for these binary classifiers are adaptively estimated through a learning algorithm that maximizes the separability between the sparsely represented classes. Based on our previous work, the approach substantially reduces the computational complexity of extracting, aligning and sorting multiple single unit activity early in the data stream. Here, we also show its ability to track changes in spike features over extended periods of time, making it highly suitable for basic neuroscience studies as well as for implementation in miniaturized, fully implantable electronics in brain-machine interface applications. [ABSTRACT FROM AUTHOR]

Miniaturisation of microchip capillary electrophoresis (MCE) is becoming an increasingly important research topic, particularly in areas related to micro total analysis systems or lab on a chip. One of the important features associated with the miniaturised MCE system is the portable power supply unit. In this work, a very low electric field MCE utilising an amperometric detection scheme was designed for use in DNA separation. The device was fabricated from a glass/polydimethylsiloxane hybrid engraved microchannel with platinum electrodes sputtered onto a glass substrate. Measurement was based on a three‐electrode arrangement, and separation was achieved using a very low electric field of 12 V/cm and sample volume of 1.5 µl. The device was tested using two commercial DNA markers of different base pair sizes. The results are in agreement with conventional electrophoresis, but with improved resolution. The sensitivity consistently higher than 100 nA, and the separation time approximately 45 min, making this microchip an ideal tool for DNA analysis. [ABSTRACT FROM AUTHOR]

We describe the construction of a model of the electrode-electrolyte interface and surrounding electrolyte in the case of a platinum-electrode array intended for spinal-cord stimulation (SCS) application. We show that a finite, two-dimensional, resistor array provides a satisfactory model of the bulk electrolyte, and we identify the complexity required of that resistor array. The electrode-electrolyte interface is modelled in a fashion suitable for commonly-available, compact simulators using a nonlinear extension of the model of Franks (IEEE Trans. Biomed. Eng., vol. 52 , no. 7 , pp. 1295–1302, Jul. 2005) that incorporates diodes and a memristor. The electrode-electrolyte interface model accounts for the nonlinear current-overpotential characteristic and diffusion-limiting effects. We characterise a commercial, implantable, electrode array, fit the model to it, and show that the model successfully predicts subtle operational characteristics. [ABSTRACT FROM PUBLISHER]

This paper presents a low power neural signal amplifier with tunable cut-off frequencies. The presented compact amplifier, which is used for sensing various types of neural signals, reduces the size and the power consumption of the whole circuit. The distinguishing features of this solution are the large time constant, linearity, and small achievable area, which are realized with a configurable series of pseudo resistances. The proof of concept has been manufactured on TSMC 90 nm technology. [ABSTRACT FROM PUBLISHER]

When extracellular action potentials (spikes) from cultured neurons are recorded using microelectrode arrays in open wells, their amplitudes are usually quite small (often below the noise level) despite the extracellular currents originating from the relatively large surface area of neural cell somata. In this paper rat cortical neurons were seeded into one well of a two well system separated by 3 ×10 μm microtunnels and then seven days later into the second well forming a feed-forward network between two small neuronal assemblies. In contrast to measurements in the open well spikes recorded from axons within the restricted volumes imposed by the microtunnels are often several orders of magnitude larger than in the open well, with high signal to noise ratio, despite the currents originating in the much smaller surface area of the axon. Average signal amplitudes exceeding 250 μV are typical, with some signals as large as 4.5 mV (signal-to-noise ratio up to 450), 20 times greater than the maximum recorded from electrodes in adjacent but open wells. We confirm the dependence of signal amplitude on the impedance of the microtunnel and discuss possible reasons for the phenomenon. [ABSTRACT FROM AUTHOR]

Although the subject of some scrutiny over the years, the mechanism of conduction in DNA has not yet been resolved, with competing theories suggesting either electronic and ionic conduction mechanisms. In this paper we use dielectrophoresis to determine the electrical properties of poly(dG)-poly(dC) (GC) and poly(dA)-poly(dT) (AT) DNA in solution. The molecules show different conduction mechanisms; GC DNA exhibits conduction primarily through the molecule, whereas in AT DNA conduction through the counterion cloud surrounding the molecule in solution is more significant. [ABSTRACT FROM PUBLISHER]

Induced current density in the human body is the basic restriction of the electromagnetic field protection guidelines for frequencies <10~MHz. Due to the difficulty of measurement, numerical methods are often used for assessment of basic restrictions. In this paper, induced current distributions are calculated in the high-resolution 3-D adult and child models exposed to magnetic fields between 100 kHz and 10 MHz, which is the frequency range of the resonant wireless power transfer (WPT) systems. For this frequency range, it is difficult to apply the conventional finite-difference time-domain (FDTD) method for bioelectric field computation. Thus, the quasi-static FDTD method is used to reduce the number of time steps. The results are analyzed according to different human models, grounding conditions, organs, frequencies, and orientations of the incident magnetic field. In addition, the plane wave exposure is compared with exposure to magnetic field of transmit coil of WPT system. Using the calculation results, the feasibility of the magnetic field reference level in the International Commission on Non-Ionizing Radiation Protection guideline is analyzed. [ABSTRACT FROM AUTHOR]

Purpose: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an imaging modality to reconstruct the electrical conductivity of biological tissue based on the acoustic measurements of Lorentz force induced tissue vibration. This study presents the feasibility of the authorsˈ new MAT-MI system and vector source imaging algorithm to perform a complete reconstruction of the conductivity distribution of real biological tissues with ultrasound spatial resolution. Methods: In the present study, using ultrasound beamformation, imaging point spread functions are designed to reconstruct the induced vector source in the object which is used to estimate the object conductivity distribution. Both numerical studies and phantom experiments are performed to demonstrate the merits of the proposed method. Also, through the numerical simulations, the full width half maximum of the imaging point spread function is calculated to estimate of the spatial resolution. The tissue phantom experiments are performed with a MAT-MI imaging system in the static field of a 9.4 T magnetic resonance imaging magnet. Results: The image reconstruction through vector beamformation in the numerical and experimental studies gives a reliable estimate of the conductivity distribution in the object with a ∼1.5 mm spatial resolution corresponding to the imaging system frequency of 500 kHz ultrasound. In addition, the experiment results suggest that MAT-MI under high static magnetic field environment is able to reconstruct images of tissue-mimicking gel phantoms and real tissue samples with reliable conductivity contrast. Conclusions: The results demonstrate that MAT-MI is able to image the electrical conductivity properties of biological tissues with better than 2 mm spatial resolution at 500 kHz, and the imaging with MAT-MI under a high static magnetic field environment is able to provide improved imaging contrast for biological tissue conductivity reconstruction. [ABSTRACT FROM AUTHOR]

In this paper, a novel method for evaluating antioxidant activity against low density lipoprotein (LDL) oxidation (anti-LDLox) using a carbon nanotube (CNT) based electrode was investigated. Although ORAC and DPPH are known methods to evaluate antioxidant activity, they do not directly reflect the capacities of anti-LDLox. A method has been reported for measuring oxidized LDL using a CNT electrode. We evaluated anti-LDLox by measuring the amount of oxidized LDL using the electrode after incubation of LDL with antioxidants during copper-mediated oxidation. Thiobarbituric acid reactive substances (TBARS) were also determined for comparison with the CNT electrode. There was a correlation of the CNT electrode with the TBARS and the ORAC, whereas no correlation was found between the CNT electrode and the DPPH. We demonstrate here that a CNT electrode method has a potential for the determination of the antioxidant activity of various natural and synthetic compounds by detecting oxidized LDL. [ABSTRACT FROM PUBLISHER]

Previous studies have indicated that electrodes placed between fascicles can provide nerve recruitment with high topological selectivity if the areas of interest in the nerve are separated with passive elements. In this study, we investigated if this separation of fascicles also can provide topologically selective nerve recordings and compared the performance of mono-, bi-, and tripolar configurations for stimulation and recording with an intra-neural interface. The interface was implanted in the sciatic nerve of 10 rabbits and achieved a median selectivity of Ŝ=0.98-0.99 for all stimulation configurations, while recording selectivity configurations was in the range of Ŝ=0.70-0.80 with the monopolar configuration providing the lowest and the average reference configuration the highest recording selectivity. Interfascicular electrodes could provide an interesting addition to the bulk of peripheral nerve interfaces available for neural prosthetic devices. The separation of the nerve into chambers by the passive elements of the electrode could ensure a higher selectivity than comparable cuff electrodes and the intra-neural location could provide an option of targeting mainly central fascicles. Further studies are, however, still required to develop biocompatible electrodes and test their stability and safety in chronic experiments. [ABSTRACT FROM AUTHOR]

Particular attention has recently been paid to bioassay systems that allow the responses of living organisms to be monitored to support water quality evaluation. This technology can complement traditional chemical inspection methods, which have limitations in terms of chemical substance coverage and inspection frequency. This paper proposes a bioassay system that can be used to detect the water contamination by monitoring the behavior and ventilatory signals of zebrafish. Rather than engaging an optical device, the system extracts behavioral information from the ventilatory signals measured via an electrode array, thereby providing advantages in terms of robustness against changes in environmental light. This paper then describes the capacity of the proposed system to detect contamination with ethanol (a low-toxicity substance) as an example. [ABSTRACT FROM PUBLISHER]

Oxidized-low-density lipoprotein (ox-LDL), which is generated by LDL oxidation, is a risk factor of cardiovascular disease development. LDL has positive charges on the surface attributable to amino groups of lysine moieties on Apo B-100. Its positive charge is decreased by oxidation. For this paper, the topography and surface potential of LDL and ox-LDL are measured using atomic force microscopy and Kelvin probe force microscopy (KPFM). Although it is difficult to ascertain a difference between topographic images of LDL and ox-LDL, the KPFM images of ox-LDL differ from those obtained using LDL. The averaged potential of the surface decreases concomitantly with increasing oxidation time of the LDL. We demonstrate a method to evaluate the oxidation level of LDL using KPFM. [ABSTRACT FROM PUBLISHER]

This paper provides an overview on graphene solution-gated field-effect transistors (SGFETs) and their applications in bioelectronics. The fabrication and characterization of arrays of graphene SGFETs is presented and discussed with respect to competing technologies. To obtain a better understanding of the working principle of solution-gated transistors, the graphene–electrolyte interface is discussed in detail. The in vitro biocompatibility of graphene is assessed by primary neuron cultures. Finally, bioelectronic experiments with electrogenic cells are presented, confirming the suitability of graphene to record the electrical activity of cells. [ABSTRACT FROM PUBLISHER]

The electrocardiogram (ECG) is a non‐invasive and widely used technique for cardiac electrophysiological assessment. Although the ECG has traditionally only been used for functional diagnostic and evaluation, several advances in electrophysiological sensing have made available robust signal acquisition devices, particularly suited for ambulatory conditions, widening its range of applications. In particular, recent work has shown the potential of the ECG as a biometric trait, both for human identification and authentication. This study sets the ground for an ECG‐based real‐time biometric system. The authors describe an experimental setup and the evaluation of new fiducial and non‐fiducial approaches, including data acquisition, signal processing, feature extraction and analysis and classification methodologies, showing the applicability of the ECG as a real‐time biometric. Performance evaluation was done in clinical‐grade ECG recording from 51 healthy control individuals (of a publicly available benchmark dataset) as well as on data collected from 26 healthy volunteers performing computer activities without any posture or motion limitations, thus simulating a regular computer usage scenario. [ABSTRACT FROM AUTHOR]

Purpose: Prostate cancer ranks as one of the most common malignancies and currently represents the second leading cancer-specific cause of death in men. The current use of single modality transrectal ultrasound (TRUS) for biopsy guidance has a limited sensitivity and specificity for accurately identifying cancerous lesions within the prostate. This study introduces a novel prostate cancer imaging method that combines TRUS with electrical impedance tomography (EIT) and reports on initial clinical findings based on in vivo measurements. Methods: The ultrasound system provides anatomic information, which guides EIT image reconstruction. EIT reconstructions are correlated with semiquantitative pathological findings. Thin plate spline warping transformations are employed to overlay electrical impedance images and pathological maps describing the spatial distribution of prostate cancer, with the latter used as reference for data analysis. Clinical data were recorded from a total of 50 men prior to them undergoing radical prostatectomy for prostate cancer treatment. Student's t-tests were employed to statistically examine the electrical property difference between cancerous tissue and benign tissue as defined through histological assessment of the excised gland. Results: Example EIT reconstructions are presented along with a statistical analysis comparing EIT and pathology. An average transformation error of 1.67% is found when 381 spatially coregistered pathological images are compared with their target EIT reconstructed counterparts. At EIT signal frequencies of 0.4, 3.2, and 25.6 kHz, paired-testing demonstrated that the conductivity of cancerous regions is significantly greater than that of benign regions ( p < 0.0304). Conclusions: These preliminary clinical findings suggest the potential benefits electrical impedance measurements might have for prostate cancer detection. [ABSTRACT FROM AUTHOR]

Automatic seizure detection is of great significance for epilepsy long-term monitoring, diagnosis, and rehabilitation, and it is the key to closed-loop brain stimulation. This paper presents a novel wavelet-based automatic seizure detection method with high sensitivity. The proposed method first conducts wavelet decomposition of multi-channel intracranial EEG (iEEG) with five scales, and selects three frequency bands of them for subsequent processing. Effective features are extracted, such as relative energy, relative amplitude, coefficient of variation and fluctuation index at the selected scales, and then these features are sent into the support vector machine for training and classification. Afterwards a postprocessing is applied on the raw classification results to obtain more accurate and stable results. Postprocessing includes smoothing, multi-channel decision fusion and collar technique. Its performance is evaluated on a large dataset of 509 h from 21 epileptic patients. Experiments show that the proposed method could achieve a sensitivity of 94.46% and a specificity of 95.26% with a false detection rate of 0.58/h for seizure detection in long-term iEEG. [ABSTRACT FROM AUTHOR]

Assessment of medical disorders is often aided by objective diagnostic tests which can lead to early intervention and appropriate treatment. In the case of brain dysfunction caused by head injury, there is an urgent need for quantitative evaluation methods to aid in acute triage of those subjects who have sustained traumatic brain injury (TBI). Current clinical tools to detect mild TBI (mTBI/concussion) are limited to subjective reports of symptoms and short neurocognitive batteries, offering little objective evidence for clinical decisions; or computed tomography (CT) scans, with radiation-risk, that are most often negative in mTBI. This paper describes a novel methodology for the development of algorithms to provide multi-class classification in a substantial population of brain injured subjects, across a broad age range and representative subpopulations. The method is based on age-regressed quantitative features (linear and nonlinear) extracted from brain electrical activity recorded from a limited montage of scalp electrodes. These features are used as input to a unique “informed data reduction” method, maximizing confidence of prospective validation and minimizing over-fitting. A training set for supervised learning was used, including: “normal control,” “concussed,” and “structural injury/CT positive (CT+).” The classifier function separating CT+ from the other groups demonstrated a sensitivity of 96% and specificity of 78%; the classifier separating “normal controls” from the other groups demonstrated a sensitivity of 81% and specificity of 74%, suggesting high utility of such classifiers in acute clinical settings. The use of a sequence of classifiers where the desired risk can be stratified further supports clinical utility. [ABSTRACT FROM AUTHOR]

Microsecond-duration electric pulses are widely used for research and therapeutic purposes. The most commonly used device for in vitro exposure to electric pulses is a standard electroporation cuvette. The use of nanosecond-duration electric pulses [nanosecond pulsed electromagnetic fields (nsPEFs) or nanopulses] is an emerging technology. For microsecond pulses, some dedicated generators with voltage regulation have been developed and allow one to easily impose a well-known voltage during biological experiments. However, it is not the case for nsPEF. The application of nsPEF thus requires considering the output impedance of the generator used and the impedance of the biological load because both impose the magnitude and the shape of the applied pulses. The model proposed here describes the behavior of the biological sample on a large frequency band (100 Hz to 3 GHz), including or not the exposure device. This model allows predicting the real electric pulses applied to biological samples and highlights the limitations induced by the use of standard electroporation cuvettes. Considering this kind of application device and the use of 10-ns-duration trapezoidal electric pulses, we evaluate the distortion of the pulses and also the impact of the output impedance of the generator on the steepness of the pulse rising and falling edges. This study is then transposed to potato tuber, a model currently used as a homogeneous biological tissue. [ABSTRACT FROM PUBLISHER]

A lateral-flow immunobiosensor is developed based on electrospun nanofibers and conductive magnetic nanoparticles (MNPs) for rapid detection of Escherichia coli O157:H7 bacteria. The magnetic nanoparticles are bioconjugated with antibody specific to E. coli O157:H7 to act as immunomagnetic separator to extract and purify the target from the sample solution. The cellulose nitrate nanofibers are synthesized using electrospinning technique to form unwoven biocompatible membrane with optimized nanoporous structure and excellent capillary properties. The nanofibrous membrane is biochemically functionalized with E. coli antibody to act as biosensor capture pad. Due to high surface area and unique nanostructure, the conductive pathogen/nanoparticle complex in the purified solution is effectively captured on the nanofiber membrane by antibody–antigen binding. The unbound nanoparticles and impurities are absorbed in the following cellulose membrane by capillary action. When the flow equilibrium is achieved, the resistance signal of the electrospun membrane is measured by a portable sensing platform, which indicates the pathogen concentration in the sample solution. This novel biosensor was capable to detect E. coli O157:H7 bacteria as low as 67 CFU/mL in a total detection time of 8 min. The test results demonstrate linear sensing response range of 10^1–10^4 CFU/mL, which is higher than that using nitrocellulose porous membrane under the same analytical conditions. This sensitive and low-cost biosensor fabricated using electrospun technology is fast and reliable, which can be used for on-field biodefense and food and water safety applications. [ABSTRACT FROM PUBLISHER]

A novel microdevice for electrical impedance spectroscopy is presented to differentiate between normal and cancerous cells at the single cell level with a high sensitivity. The device utilizes a microfluidic tunnel structure, whose height is smaller than the cell diameters, to squeeze the target cells. Thus, the tight contact between the cells and electrodes allows the device to measure the intrinsic electrical properties of the cells with a higher sensitivity than through noncontact methods. Three-dimensional interdigitated electrodes (3-D IDE) are also employed to confine most of the electric field into the cell membrane, which contains the meaningful electrical properties. Consequently, the variance of the measured values could be reduced because the position of target cells is almost the same in every cell assay. The device well distinguishes normal human breast cells (MCF-10A) from early-stage human breast cancer cells (MCF-7) by means of electrical impedances at 500 kHz; the average differences of the real part and phase angle between the target cells are 44.4 and 1.41 , respectively. The proposed device also shows a high repeatability for the deionized (DI) water test conducted before and after each cell assay; the variances of the real part and phase angle of electrical impedance at 500 kHz are as small as 9.07 and 0.27 , respectively. [ABSTRACT FROM PUBLISHER]

Presented is a noncontact model and radiometric sensor developed to facilitate core body temperature extraction. The system has been designed as a close-proximity sensor to detect thermal emissions radiated from deep inside the human body. The radiometer uses a cavity-backed slot antenna (CBSA) designed to account for performance degradation which occurs in the near field of the human body. Tissue-simulating materials with electrical properties similar to the human body have been identified, and layered configurations of these phantoms are used to mimic the electromagnetic characteristics of a human stomach volume: hence, defines the core model. Positioned approximately 7 mm from the core model, the sensor tracks the change in brightness temperature as the subsurface physical temperature is varied. A mathematical noncontact model (NCM) is subsequently used to correlate the observed brightness temperature to the subsurface temperature, accounting for artifacts induced by the sensor's remote positioning from the specimen. The accuracy of the NCM is validated through an analysis of the measurement data extracted from the test bed before and after applying the model. The results illustrate that the measurement is highly sensitive to the antenna impedance match and atmospheric temperature. The measurement is less sensitive to the physical temperature of the instrument and emissivity of the specimen. The results of this study demonstrate that radiometric sensors are capable of close proximity, subsurface extraction of biological data given that certain parameters are closely monitored. [ABSTRACT FROM PUBLISHER]

In this paper, some recent results obtained with film-type sensor materials polyvinylidenefluoride (PVDF) and electromechanical film (EMFi) are presented. The materials generate a voltage when they are mechanically deformed, however, because of their capacitive nature only the change of an external force can be measured. Hence, the sensors made of these materials are useful especially in the measurements of physiological pulsatile signals (e.g., heart rate and respiration). The entire measurement process with the PVDF and EMFi sensors is considered here; from the design and construction of the sensors and measurement electronics to the analysis of the measured data. The paper also presents some examples of the physiological signals (heart rate, respiration, and heart sounds) measured with the PVDF and EMFi sensors. Flexible and thin sensor materials are useful especially in physiological applications where the sensor is integrated into clothing or into daily life objects (e.g., a chair or a bed). The sensor attachments to human can be minimized and the measurement systems can be designed to be unobtrusive and comfortable for the user. [ABSTRACT FROM PUBLISHER]

Weakly electric fish sense their surroundings in complete darkness by active electrolocation. In a biomimetic approach, we designed catheter-based technical sensor systems working according to the same biological principles that could be used for medical diagnostics of arteriosclerosis. Several measurements using artificial blood vessels, computer simulations, and a physical test bed showed that it is possible to detect and analyze vulnerable plaques in blood vessels and that our method of signal production and analysis is principally suitable for medical diagnostics. [ABSTRACT FROM PUBLISHER]

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices. [ABSTRACT FROM AUTHOR]

Electrical stimulation of arm and hand muscles can be a functional tool for patients with motor dysfunction. Sufficient stimulation of finger and thumb musculature can support natural grasping function. Yet it remains unclear how different grasping movements can be selectively supported by electrical stimulation. The goal of this study is to determine to what extent activation of individual fingers is possible with surface electrical stimulation for the purpose of rehabilitation following stroke. The extensor digitorum communis (EDC) muscle, flexor pollicis longus (FPL) muscle, and the thenar muscle group, all involved in grasp and release, were selected for stimulation. The evoked forces in individual fingers were measured. Stimulation thresholds and selective ranges were determined for each subject. Electrode locations where the highest selective range occurred were compared between subjects and influences of different isometric wrist positions were assessed. In all subjects selective stimulation of middle finger extension and thumb flexion was possible. In addition, selective stimulation of index and ring finger extension was possible in most cases. In nine out of the ten EDC subjects we were able to stimulate three or all four fingers selectively. However, large variability in electrode locations for high selectivity was observed between the subjects. Within the designs of grasping prostheses and grasping rehabilitation devices, the variability of electrode locations should be taken into account. The results of our study facilitate the optimization of such designs and favour a design which allows individualized stimulation locations. [ABSTRACT FROM AUTHOR]

This study investigates whether signals obtained from an implantable pressure sensor placed in the urinary bladder wall could be used to detect the onset of bladder contractions. The sensor assembly was custom made using a small piezoresistive sensor die. The die was mounted on ceramic substrate (8 mm × 8 mm) and encapsulated in silicone by a two-part moulding process. The final sensor was lens shaped with a diameter of 13.6 mm and height of 2.0 mm. Experiments were performed in six pigs that had one or more sensors placed in the bladder wall. An external reference sensor was used to simultaneously monitor intravesical pressure via a transurethral catheter. Bladder contractions were evoked by unilateral electrical stimulation of the pelvic nerve. Onset latency was computed using both signals. In addition, the correlation between wall pressure and intravesical pressure was calculated. On average, the onset latency was -307 ms using the wall sensors compared to the intravesical pressure, i.e., the detection occurred earlier using the wall sensors than the intravesical sensor. In 91 of 114 recordings the correlation coefficient was above 0.90. In conclusion, the implantable sensor performs similar to the reference sensor when used to detect the onset of bladder contractions. [ABSTRACT FROM AUTHOR]

The brain-computer interface (BCI) system has been developed to assist people with motor disability. To make the system more user-friendly, it is a challenge to reduce the electrode preparation time and have a good reliability. This study aims to find a minimal set of electrodes for an individual stroke subject for motor imagery to control an assistive device using functional electrical stimulation for 20 sessions with accuracy higher than 90%. The characteristics of this minimal electrode set were evaluated with two popular algorithms: Fisher's criterion and support-vector machine recursive feature elimination (SVM-RFE). The number of calibration sessions for channel selection required for robust control of these 20 sessions was also investigated. Five chronic stroke patients were recruited for the study. Our results suggested that the number of calibration sessions for channel selection did not have a significant effect on the classification accuracy. A performance index devised in this study showed that one training day with 12 electrodes using the SVM-RFE method achieved the best balance between the number of electrodes and accuracy in the 20-session data. Generally, 8-36 channels were required to maintain accuracy higher than 90% in 20 BCI training sessions for chronic stroke patients. [ABSTRACT FROM AUTHOR]

A new form of deep brain stimulation (DBS) electrode was proposed that was made of carbon nanotube yarns (CNTYs). Electrode interface properties were examined using cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS). The CNTY electrode interface exhibited large charge storage capacity (CSC) of 12.3 mC/cm2 which increased to 98.6 mC/cm2 after acid treatment, compared with 5.0 mC/cm2 of Pt-Ir. Impedance spectrum of both untreated and treated CNTY electrodes showed that finite diffusion process occurred at the interface due to their porous structure and charge was delivered through capacitive mechanism. To evaluate stability electrical stimulus was exerted for up to 72 h and CV and EIS results of CNTY electrodes revealed little alteration. Therefore CNTY could make a good electrode material for DBS. [ABSTRACT FROM AUTHOR]

Surface electromyogram (sEMG) signals, a noninvasive bioelectric signal, can be used for the rehabilitation and control of artificial extremities. Current sEMG pattern-recognition systems suffer from a limited number of patterns that are frequently intensified by the unsuitable accuracy of the instrumentation and analytical system. To solve these problems, we designed a multistep-based sEMG pattern-recognition system where, in each step, a stronger more capable relevant technique with a noticeable improved performance is employed. In this paper, we utilized the sEMG signals to classify and recognize six classes of hand movements. We employed an adaptive neuro–fuzzy inference system (ANFIS) to identify hand motion commands. Training the fuzzy system was performed by a hybrid back propagation and least-mean-square algorithm, and for optimizing the number of fuzzy rules, a subtractive-clustering algorithm was utilized. Furthermore, this paper employed time and time–frequency domains and their combination as the features of the sEMG signal. The proposed recognition scheme utilizing the combined features with an ANFIS classification provided the best result in identifying complex hand movements. The maximum identification accuracy rate of 100% and an average classification accuracy of the proposed ANFIS system of 92% proved to be superior in comparison with relevant studies to date. [ABSTRACT FROM AUTHOR]

The element-free Galerkin method is applied to the study of the electrostatic behavior of a biomolecule inside a ionic solvent. To this aim, the attention is focused on the solution of the linearized Poisson–Boltzmann equation. The numerical results put in evidence the capability of the proposed approach to approximate the steep gradients of the electrostatic potential arising in the molecular region. [ABSTRACT FROM PUBLISHER]

This paper deals with contact currents that may occur when the human body is in contact with two electrodes at different electrical potentials, e.g., an electrical/electronic device and the floor. Actually, any device must comply not only with electromagnetic compatibility and safety requirements, but also with specific electromagnetic field exposure recommendations in order to prevent health hazards for the occupational and general public population. Since the contact currents depend on the applied voltage and on the human body impedance, this last parameter has been measured for several configurations in a broadband frequency range, from 40 Hz to 110 MHz. From the measurement results, a new equivalent circuit of the human body impedance is derived by using a vector-fitting procedure. This equivalent circuit is very easy and can be adopted for compliance tests against contact currents. [ABSTRACT FROM AUTHOR]

There is a lack of noninvasive pulmonary function measurement techniques suitable for continuous long-term measurement of tidal breathing in mobile subjects, although tidal breathing analysis has been shown to contain information that relates to the level airway obstruction. This paper is the first to assess the suitability of impedance pneumography (IP) for measurement of continuous pulmonary flow and volume signals instead of only the respiration rate (RR) or tidal volume (VT ). We measured pneumotachograph (PNT) and IP signals simultaneously from 20 healthy male subjects in erect, dorsal supine, and lateral supine positions while voluntarily varying VT. IP was measured using five different impedance lead configurations with electrodes integrated into a textile chest belt. The IP signals were compared with PNT signals to assess agreement of IP with a more well-established measurement method. The pulmonary flow signal wave form agreement was assessed with standard error of measurement (SEM) between the time-differentiated IP signal and the PNT signal as ρ=1-SEM. Additionally, we assessed the agreement of IP and PNT in VT estimation and the magnitude of the cardiogenic oscillation present in the impedance signal. The agreement in the pulmonary flow signal waveform shapes was found excellent at all tidal volumes and postures (mean ρ > 0.90). The agreement between the PNT-derived and the IP-derived VT estimates was very high when IP values were calibrated per subject and posture (mean difference <3%). The main source of error in visual inspection of the IP signal was the cardiogenic distortion. From the five novel electrode configurations tested, the lateral ones were found clearly better than the anteroposterior ones. IP potentially enables the development of a noninvasive ambulatory measurement device for long-term studies of certain tidal breathing parameters in mobile subjects. [ABSTRACT FROM AUTHOR]

We have studied the effect of cell geometry on propagation velocity of the cardiac impulse using a subcellular computer model of myocardium. Variation of cell size has only small effects on longitudinal and transverse conduction velocities, when the ratio of cell length/width is constant, for cell sizes (length \times width) between (60 \mum \times 20 \mum) and (120 \mum \times 40 \mu m). The results were not dependent on gap-junction conductance (range 0.25–1 \muS), gap-junction distribution, or the specific tissue architecture. Longitudinal conduction velocity increased with the cell length/width ratio and transverse velocity decreased. The cell length/width ratio was a good estimator of the anisotropic ratio. In conclusion, cell length/width ratio is more important than cell size in determining conduction velocity. [ABSTRACT FROM PUBLISHER]

This study presents a model to simulate the electrophysiological activities of multiple Michigan Cancer Foundation-7 (MCF-7) cells, the most studied breast cancer cell line. The intercellular spacing of MCF-7 cells is estimated using the effective diffusion coefficient. Nonuniform finite-difference discretization is implemented to accommodate for the contrast in size between the intercellular spacing and the cell dimension. The model computes the amplitude and the spatiotemporal patterns of biopotentials and electric current densities at different cell division stages. The results show that the biopotentials increase proportionally to the number of cells, especially when all cells are in the hyperpolarization stage. Also, the results show significant electric current density in the intercellular gap between the cells. [ABSTRACT FROM AUTHOR]