Publications

Conventional gut-on-chip (GOC) models typically represent the epithelial layer of the gut tissue, neglecting other important components such as the stromal compartment and the extracellular matrix (ECM) that play crucial roles in maintaining intestinal barrier integrity and function. These models often employ hard, flat porous membranes for cell culture, thus failing to recapitulate the soft environment and complex 3D architecture of the intestinal mucosa. Alternatively, hydrogels have been recently introduced in GOCs as ECM analogs to support the co-culture of intestinal cells in in vivo-like configurations, and thus opening new opportunities in the organ-on-chip field. In this work, we present an innovative GOC device that includes a 3D bioprinted hydrogel channel replicating the intestinal villi architecture containing both the epithelial and stromal compartments of the gut mucosa. The bioprinted hydrogels successfully support both the encapsulation of fibroblasts and their co-culture with intestinal epithelial cells under physiological flow conditions. Moreover, we successfully integrated electrodes into the microfluidic system to monitor the barrier formation in real time via transepithelial electrical resistance measurements.

JTD Keywords: A-chip, Bioprinted, Caco-2, Cells, Culture, Gut-on-a-chip, Hydrogels, Impedance spectroscopy, Integrated electrodes, Intestinal barrier, Intestinal mucos, Model

Cable bacteria are filamentous, multicellular microorganisms that display an exceptional form of biological electron transport across centimeter-scale distances. Currents are guided through a network of nickel-containing protein fibers within the cell envelope. Still, the mechanism of long-range conduction remains unresolved. Here, we characterize the conductance of the fiber network under dry and wet, physiologically relevant, conditions. Our data reveal that the fiber conductivity is high (median value: 27 S cm-1; range: 2 to 564 S cm-1), does not show any redox signature, has a low thermal activation energy (Ea = 69 +/- 23 meV), and is not affected by humidity or the presence of ions. These features set the nickel-based conduction mechanism in cable bacteria apart from other known forms of biological electron transport. As such, conduction resembles that of an organic semi-metal with a high charge carrier density. Our observation that biochemistry can synthesize an organometal-like structure opens the way for novel bio-based electronic technologies.

JTD Keywords: 'current, Activation energy, Bacteria, Bioelectronic, Bioelectronics, Cable bacteria, Cables, Centimeter-scale, Electrochemical impedance spectroscopy, Electrochemical-impedance spectroscopies, Electron transport, Electron transport properties, Electron-transport, Long -distance electron transport, Long-distance electron transport, Microbial nanowires, Nickel, Nickel containing, Protein conductivity, Protein fibers, Proteins, Sulfur

A new generation of fully bioresorbable metallic Zn-based alloys could be used for stenting applications; however, the initial surface degradation delays stent re-endothelialization. Thus, this work proposes a dual strategy to control the corrosion and accelerate the endothelialization of ZnMg and ZnAg biodegradable alloys. First, a stable polycaprolactone (PCL) coating is obtained and followed by its functionalization with either linear RGD (Arg-Gly-Asp) or REDV (Arg-Glu-Asp-Val) peptides or a dual peptide-based platform combining both sequences (RGD-REDV). Scratching tests showed neither delamination nor detachment of the polymeric coating. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements confirmed the corrosion resistance after PCL coating by revealing lower current density and higher absolute impedance values. X-ray photoelectron spectroscopy (XPS) and fluorescent microscopy confirmed the correct peptide immobilization onto PCL coated Zn alloys. The functionalized samples exhibited enhanced human umbilical vein endothelial cells (HUVEC) adhesion. The higher number of adhered cells to the functionalized surfaces with the RGD-REDV platform demonstrates the synergistic effect of combining both RGD and REDV sequences. Higher corrosion resistance together with enhanced endothelialization indicates that the dual functionalization of Zn alloys with PCL and peptide-based RGD-REDV platform holds great potential to overcome the clinical limitations of current biodegradable metal stents.

JTD Keywords: Binary alloys, Biodegradable metals, Bioresorbable, Cardiovascular applications, Cell adhesive peptides, Corrosion, Corrosion resistance, Corrosion resistant alloys, Corrosion resistant coatings, Degradation, Dual peptide-based platform, Electrochemical corrosion, Electrochemical impedance spectroscopy, Endothelial cells, Endothelialization, Functionalization, Functionalizations, In-vitro, Magnesium alloys, Metallics, Mg alloy, Peptides, Polycaprolactone coating, Polymer-coatings, Rgd-functionalization, Silver alloys, Stents, Surface, X ray photoelectron spectroscopy, Zinc, Zinc alloys, Zn alloys, Zn-based alloys

Polymeric membranes exhibit unique and modulate transport properties when they are properly functionalised, which make them ideal for ions transport, molecules separation and molecules interactions. The present work proposes the design and fabrication of nanostructured membranes, composed by biodegradable poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG), incorporating a lipophilic molecule (cholesterol) covalently bonded, were especially designed to provide even more application opportunities in sensors field. Electrochemical studies, by means of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV), revealed important differences regarding the functionalised and non-functionalised PLA systems. PEGcholesterol building block units showed a clear affinity with ascorbic acid (vitamin C) and Trolox (R) (a watersoluble analogue of vitamin E), both hydrophilic in nature, with a limit of detection capacity of 8.12 mu M for AA and 3.53 mu M for AA and Trolox, respectively, in aqueous salt solution. The bioinspired polymer may be used to incorporate antioxidant property that allow the design of anti-stress biosensors, electrodes for the detection of vitamin C or vitamin E in biomedical nutrition programs, among other applications.

JTD Keywords: Antioxidant molecules, Antioxidants, Application programs, Ascorbic acid, Biomimetics, C (programming language), Capacity, Chemical detection, Cholesterol, Cyclic voltammetry, Electrochemical detection, Electrochemical impedance spectroscopy, Functional polymers, Functionalized, Lactic acid, Molecules, Nanomembranes, Poly ethylene glycols, Poly lactic acid, Poly(ethylene glycol), Poly(ethyleneglycol), Poly(lactic acid), Polyethylene glycols, Vitamin-e

A fundamental task of the respiratory system is to operate as a mechanical gas pump ensuring that fresh air gets in close contact with the blood circulating through the lung capillaries to achieve O2 and CO2 exchange. To ventilate the lungs, the respiratory muscles provide the pressure required to overcome the viscoelastic mechanical load of the respiratory system. From a mechanical viewpoint, the most relevant respiratory system properties are the resistance of the airways (R aw), and the compliance of the lung tissue (C L) and chest wall (C CW). Both airflow and lung volume changes in spontaneous breathing and mechanical ventilation are determined by applying the fundamental mechanical laws to the relationships between the pressures inside the respiratory system (at the airway opening, alveolar, pleural, and muscular) and R aw, C L, and C CW. These relationships also are the basis of the different methods available to measure respiratory mechanics during spontaneous and artificial ventilation. Whereas a simple mechanical model (R aw, C L, and C CW) describes the basic understanding of ventilation mechanics, more complex concepts (nonlinearity, inhomogeneous ventilation, or viscoelasticity) should be employed to better describe and measure ventilation mechanics in patients.Thieme. All rights reserved.

JTD Keywords: airway-resistance, alveolar, compliance, dilution, elastance, flow, inhomogeneous ventilation, input impedance, lung-volume, mechanical ventilation, monitoring, pendelluft, pleural pressure, respiratory-distress-syndrome, viscoelasticity, Chest-wall mechanics, Resistance

Breathing pattern has been shown to be different in chronic obstructive pulmonary disease (COPD) patients compared to healthy controls during rest and walking. In this study we evaluated respiratory parameters and the breathing variability of COPD patients as a function of their severity. Thoracic bioimpedance was acquired on 66 COPD patients during the performance of the six-minute walk test (6MWT), as well as 5 minutes before and after the test while the patients were seated, i.e. resting and recovery phases. The patients were classified by their level of airflow limitation into moderate and severe groups. We characterized the breathing patterns by evaluating common respiratory parameters using only wearable bioimpedance. Specifically, we computed the median and the coefficient of variation of the parameters during the three phases of the protocol, and evaluated the statistical differences between the two COPD severity groups. We observed significant differences between the COPD severity groups only during the sitting phases, whereas the behavior during the 6MWT was similar. Particularly, we observed an inverse relationship between breathing pattern variability and COPD severity, which may indicate that the most severely diseased patients had a more restricted breathing compared to the moderate patients.

JTD Keywords: 6mwt, activation, breathing pattern, burden, chronic obstructive pulmonary disease, exercise, muscles, pressure, pulmonary, signals, variability, volumes, wearables, Bioimpedance, Impedance pneumography

The design of catalysts with controlled selectivity at will, also known as catalytic plasticity, is a very attractive approach for the recycling of carbon dioxide (CO2). In this work, we study how catalytically active hydroxyapatite (HAp) and brushite (Bru) interact synergistically, allowing the production of formic acid or acetic acid depending on the HAp/Bru ratio in the catalyst. Raman, wide angle X-ray scattering, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy studies, combined with an exhaustive revision of the crystalline structure of the catalyst at the atomic level, allowed to discern how the Bru phase can be generated and stabilized at high temperatures. Results clearly indicate that the presence of OH– groups to maintain the crystalline structural integrity in conjunction with Ca2+ ions less bonded to the lattice fixate carbon into C1, C2 and C3 molecules from CO2 and allow the evolution from formic to acetic acid and acetone. In this way, the plasticity of the HAp-Bru system is demonstrated, representing a promising green alternative to the conventional metal-based electrocatalysts used for CO2 fixation. Thus, the fact that no electric voltage is necessary for the CO2 reduction has a very favorable impact in the final energetic net balance of the carbon fixation reaction. © 2021

JTD Keywords:

ethanol production & nbsp, brushite, co2 reduction, conversion, electrocatalytic reduction, electrode, formate, heterogeneous catalysis & nbsp, hydrogen evolution, insights, monetite, polarized hydroxyapatite,

JTD Keywords: amino-acids, catalysis, dopant-free hydroxyapatite, electrical properties, electrophotosynthesis, nitrogen, thermally-stimulated polarization, Advanced materials, Biocompatibility, Biomedical applications, Brushite, Doped hydroxyapatites, Electric voltage, Electrical characterization, Electrochemical impedance spectroscopy, Equivalent circuits, Future perspectives, Highest temperature, Hydroxyapatite, Interfaces (materials), Material interfaces, Medical applications, Polarization, Polarization conditions, Surface-charges, Technological applications

© 2021 Elsevier B.V. The blood-brain barrier (BBB) is a dynamic cellular barrier that regulates brain nutrient supply, waste efflux, and paracellular diffusion through specialized junctional complexes. Finding a system to mimic and monitor BBB integrity (i.e., to be able to assess the effect of certain compounds on opening or closing the barrier) is of vital importance in several pathologies. This work aims to overcome some limitations of current barrier integrity measuring techniques thanks to a multi-layer microfluidic platform with integrated electrodes and Multi-frequency Trans-Endothelial Electrical Resistance (MTEER) in synergy with machine learning algorithms. MTEER measurements are performed across the barrier in a range of frequencies up to 10 MHz highlighting the presence of information on different frequency ranges. Results show that the proposed platform can detect barrier formation, opening, and regeneration afterwards, correlating with the results obtained from immunostaining of junctional complexes. This model presents novel techniques for a future biological barrier in-vitro studies that could potentially help on elucidating barrier opening or sealing on treatments with different drugs.

JTD Keywords: blood-brain barrier, cellular barrier integrity monitoring, impedance sensors, machine learning, microelectrodes, mteer, rapid prototyping, Blood-brain barrier, Cellular barrier integrity monitoring, Electrical impedance spectroscopy, Impedance sensors, Machine learning, Microelectrodes, Mteer, Rapid prototyping

Flexible hydrogels are attracting significant interest as solid-like electrolytes for energy storage devices, especially for supercapacitors, because of their lightweight and anti-deformation features. Here, we present a comparative study of four ionic conductive hydrogels derived from biopolymers and doped with 0.1 M NaCl. More specifically, such hydrogels are constituted by κcarrageenan (κC), carboxymethyl cellulose (CMC), poly-γ-glutamic acid (PGGA) or a phenylalaninecontaining polyesteramide (PEA). After examining the morphology and the swelling ratio of the four hydrogels, which varies between 483% and 2356%, their electrical and capacitive behaviors were examined using electrochemical impedance spectroscopy. Measurements were conducted on devices where a hydrogel film was sandwiched between two identical poly(3,4-ethylenedioxythiophene) electrodes. The bulk conductivity of the prepared doped hydrogels is 76, 48, 36 and 34 mS/cm for PEA, PGGA, κC and CMC, respectively. Overall, the polyesteramide hydrogel exhibits the most adequate properties (i.e., low electrical resistance and high capacitance) to be used as semi-solid electrolyte for supercapacitors, which has been attributed to its distinctive structure based on the homogeneous and abundant distribution of both micro-and nanopores. Indeed, the morphology of the polyestermide hydrogel reduces the hydrogel resistance, enhances the transport of ions, and results in a better interfacial contact between the electrodes and solid electrolyte. The correlation between the supercapacitor performance and the hydrogel porous morphology is presented as an important design feature for the next generation of light and flexible energy storage devices for wearable electronics.

JTD Keywords: biopolymers, electrochemical impedance spectroscopy, flexible hydrogels, supercapacitor, Biopolymers, Electrochemical impedance spectroscopy, Flexible hydrogels, Supercapacitor

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by a functional deterioration of the brain. Currently, there are selected biomarkers for its diagnosis in cerebrospinal fluid. However, its extraction has several disadvantages for the patient. Therefore, there is an urgent need for a detection method using sensitive and selective blood-based biomarkers. Kynurenic acid (KYNA) is a potential biomarker candidate for this purpose. The alteration of the KYNA levels in blood has been related with inflammatory processes in the brain, produced as a protective function when neurons are damaged. This paper describes a novel electrochemical immunosensor for KYNA detection, based on successive functionalization multi-electrode array. The resultant sensor was characterized by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The proposed biosensor detects KYNA within a linear calibration range from 10 pM to 100 nM using CA and EIS, obtaining a limit of detection (LOD) of 16.9 pM and 37.6 pM in buffer, respectively, being the lowest reported LOD for this biomarker. Moreover, to assess our device closer to the real application, the developed immunosensor was also tested under human serum matrix, obtaining an LOD of 391.71 pM for CA and 278.8 pM for EIS with diluted serum.

JTD Keywords: alzheimer’s disease (ad), blood analysis, chronoamperometry (ca), electrochemical biosensor, electrochemical impedance spectroscopy (eis), immunosensor, in vitro diagnosis (ivd), kynurenic acid (kyna), Alzheimer’s disease (ad), Blood analysis, Chronoamperometry (ca), Electrochemical biosensor, Electrochemical impedance spectroscopy (eis), Immunosensor, In vitro diagnosis (ivd), Kynurenic acid (kyna), Point of care diagnosis (poc)

© 1964-2012 IEEE. Chronic Obstructive Pulmonary Disease (COPD) is one of the most common chronic conditions. The current assessment of COPD requires a maximal maneuver during a spirometry test to quantify airflow limitations of patients. Other less invasive measurements such as thoracic bioimpedance and myographic signals have been studied as an alternative to classical methods as they provide information about respiration. Particularly, strong correlations have been shown between thoracic bioimpedance and respiratory volume. The main objective of this study is to investigate bioimpedance and its combination with myographic parameters in COPD patients to assess the applicability in respiratory disease monitoring. We measured bioimpedance, surface electromyography and surface mechanomyography in forty-three COPD patients during an incremental inspiratory threshold loading protocol. We introduced two novel features that can be used to assess COPD condition derived from the variation of bioimpedance and the electrical and mechanical activity during each respiratory cycle. These features demonstrate significant differences between mild and severe patients, indicating a lower inspiratory contribution of the inspiratory muscles to global respiratory ventilation in the severest COPD patients. In conclusion, the combination of bioimpedance and myographic signals provides useful indices to noninvasively assess the breathing of COPD patients.

JTD Keywords: Bioimpedance, Chronic obstructive pulmonary disease, Inspiratory threshold protocol, Myographic signals, Wearables

Many studies have focused on novel noninvasive techniques to monitor respiratory rate such as bioimpedance. We propose an algorithm to detect respiratory phases using wearable bioimpedance to compute time parameters like respiratory rate, inspiratory and expiratory times, and duty cycle. The proposed algorithm was compared with two other algorithms from literature designed to estimate the respiratory rate using physiological signals like bioimpedance. We acquired bioimpedance and airflow from 50 chronic obstructive pulmonary disease (COPD) patients during an inspiratory loading protocol. We compared performance of the algorithms by computing accuracy and mean average percentage error (MAPE) between the bioimpedance parameters and the reference parameters from airflow. We found similar performance for the three algorithms in terms of accuracy (>0.96) and respiratory time and rate errors (<3.42 %). However, the proposed algorithm showed lower MAPE in duty cycle (10.18 %), inspiratory time (10.65 %) and expiratory time (8.61 %). Furthermore, only the proposed algorithm kept the statistical differences in duty cycle between COPD severity levels that were observed using airflow. Accordingly, we suggest bioimpedance to monitor breathing pattern parameters in home situations.Clinical relevance - This study exhibits the suitability of wearable thoracic bioimpedance to detect respiratory phases and to compute accurate breathing pattern parameters. © 2021 IEEE.

JTD Keywords: algorithms, copd, signals, Algorithm, Algorithms, Bioimpedance, Breathing rate, Chronic obstructive lung disease, Electronic device, Human, Humans, Lung, Pulmonary disease, chronic obstructive, Respiratory rate, Wearable electronic devices

Bioimpedance is an unobtrusive noninvasive technique to measure respiration and has a linear relation with volume during normal breathing. The objective of this paper was to assess this linear relation during inspiratory loading protocol and determine the best electrode configuration for bioimpedance measurement. The inspiratory load is a way to estimate inspiratory muscle function and has been widely used in studies of respiratory mechanics. Therefore, this protocol permitted us to evaluate bioimpedance performance under breathing pattern changes. We measured four electrode configurations of bioimpedance and airflow simultaneously in ten healthy subjects using a wearable device and a standard wired laboratory acquisition system, respectively. The subjects were asked to perform an incremental inspiratory threshold loading protocol during the measurements. The load values were selected to increase progressively until the 60% of the subject's maximal inspiratory pressure. The linear relation of the signals was assessed by Pearson correlation (r ) and the waveform agreement by the mean absolute percentage error (MAPE), both computed cycle by cycle. The results showed a median greater than 0.965 in r coefficients and lower than 11 % in the MAPE values for the entire population in all loads and configurations. Thus, a strong linear relation was found during all loaded breathing and configurations. However, one out of the four electrode configurations showed robust results in terms of agreement with volume during the highest load. In conclusion, bioimpedance measurement using a wearable device is a noninvasive and a comfortable alternative to classical methods for monitoring respiratory diseases in normal and restrictive breathing.

JTD Keywords: Bioimpedance, Chronic respiratory diseases, Electrode configurations, Inspiratory threshold protocol, Wearable

Bioimpedance is known for its linear relation with volume during normal breathing. For that reason, bioimpedance can be used as a noninvasive and comfortable technique for measuring respiration. The goal of this study is to analyze the temporal behavior of bioimpedance measured in four different electrode configurations during inspiratory loaded breathing. We measured four bioimpedance channels and airflow simultaneously in 10 healthy subjects while incremental inspiratory loads were imposed. Inspiratory loading threshold protocols are associated with breathing pattern changes and were used in respiratory mechanics studies. Consequently, this respiratory protocol allowed us to induce breathing pattern changes and evaluate the temporal relationship of bioimpedance with volume. We estimated the temporal delay between bioimpedance and volume respiratory cycles to evaluate the differences in their temporal behavior. The delays were computed as the lag which maximize the cross-correlation of the signals cycle by cycle. Six of the ten subjects showed delays in at least two different inspiratory loads. The delays were dependent on electrode configuration, hence the appearance of the delays between bioimpedance and volume were conditioned to the location and geometry of the electrode configuration. In conclusion, the delays between these signals could provide information about breathing pattern when breathing conditions change.

JTD Keywords: Bioimpedance, Delays, Electrodes, Protocols, Loading, Electrocardiography, Atmospheric measurements

We present a novel lab-on-a-chip (LOC) device for the simultaneous detection of multiple biomarkers using simple voltage measurements. The biosensor functionalization is performed in-situ, immediately before its use, facilitating reagents storage and massive devices fabrication. Sensitivity, limit of detection (LOD) and limit of quantification (LOQ) are tunable depending on the in-chip flown sample volumes. As a proof-of-concept, the system has been tested and adjusted to quantify two proteins found in blood that are susceptible to be used combined, as a screening tool, to diagnose prostate cancer (PCa): prostate-specific antigen (PSA) and spondin-2 (SPON2). This combination of biomarkers has been reported to be more specific for PCa diagnostics than the currently accepted but rather controversial PSA indicator. The range of detection for PSA and SPON2 could be adjusted to the clinically relevant range of 1 to 10. ng/ml. The system was tested for specificity to the evaluated biomarkers. This multiplex system can be modified and adapted to detect a larger quantity of biomarkers, or different ones, of relevance to other specific diseases.

JTD Keywords: Adjustable sensing, Impedance measurements, In situ functionalization, Microfluidics, Prostate specific antigen, Self-assembled monolayers

Bacteria concentration and detection is time-consuming in regular microbiology procedures aimed to facilitate the detection and analysis of these cells at very low concentrations. Traditional methods are effective but often require several days to complete. This scenario results in low bioanalytical and diagnostic methodologies with associated increased costs and complexity. In recent years, the exploitation of the intrinsic electrical properties of cells has emerged as an appealing alternative approach for concentrating and detecting bacteria. The combination of dielectrophoresis (DEP) and impedance analysis (IA) in microfluidic on-chip platforms could be key to develop rapid, accurate, portable, simple-to-use and cost-effective microfluidic devices with a promising impact in medicine, public health, agricultural, food control and environmental areas. The present document reviews recent DEP and IA combined approaches and the latest relevant improvements focusing on bacteria concentration and detection, including selectivity, sensitivity, detection time, and conductivity variation enhancements. Furthermore, this review analyses future trends and challenges which need to be addressed in order to successfully commercialize these platforms resulting in an adequate social return of public-funded investments.

JTD Keywords: Bacteria, Dielectrophoresis, Impedance, Microfluidics, On-chip

Abstract Here we describe the fabrication of a highly sensitive and label-free ITO-based impedimetric immunosensor for the detection of pathogenic bacteria Escherichia coli O157:H7. Anti-E. coli antibodies were immobilized onto ITO electrodes using a simple, robust and direct methodology. First, the covalent attachment of epoxysilane on the ITO surface was demonstrated by Atomic Force Microscopy and cyclic voltammetry. The immobilization of antibody on the epoxysilane layer was quantified by Optical Waveguide Lightmode Spectroscopy, obtaining a mass variation of 12 ng cm− 2 (0.08 pmol cm− 2). Microcontact printing and fluorescence microscopy were used to demonstrate the specific binding of E. coli O157:H7 to the antibody-patterned surface. We achieved a ratio of 1:500 Salmonella typhimurium/E. coli O157:H7, thus confirming the selectivity of the antibodies and efficiency of the functionalization procedure. Finally, the detection capacity of the ITO-based immunosensor was evaluated by Electrochemical Impedance Spectroscopy. A very low limit of detection was obtained (1 CFU mL− 1) over a large linear working range (10–106 CFU mL− 1). The specificity of the impedimetric immunosensor was also examined. Less than 20% of non-specific bacteria (S. typhimurium and E. coli K12) was observed. Our results reveal the applicability of ITO for the development of highly sensitive and selective impedimetric immunosensors.

JTD Keywords: E. coli O157:H7, Electrochemical Impedance Spectroscopy, Immunosensor, Indium tin oxide, Label-free detection

The present paper reports a bacteria autonomous controlled concentrator prototype with a user-friendly interface for bench-top applications. It is based on a micro-fluidic lab-on-a-chip and its associated custom instrumentation, which consists in a dielectrophoretic actuator, to pre-concentrate the sample, and an impedance analyser, to measure concentrated bacteria levels. The system is composed by a single micro-fluidic chamber with interdigitated electrodes and a instrumentation with custom electronics. The prototype is supported by a real-time platform connected to a remote computer, which automatically controls the system and displays impedance data used to monitor the status of bacteria accumulation on-chip. The system automates the whole concentrating operation. Performance has been studied for controlled volumes of Escherichia coli (E. coli) samples injected into the micro-fluidic chip at constant flow rate of 10 μL/min. A media conductivity correcting protocol has been developed, as the preliminary results showed distortion of the impedance analyser measurement produced by bacterial media conductivity variations through time. With the correcting protocol, the measured impedance values were related to the quantity of bacteria concentrated with a correlation of 0.988 and a coefficient of variation of 3.1%. Feasibility of E. coli on-chip automated concentration, using the miniaturized system, has been demonstrated. Furthermore, the impedance monitoring protocol had been adjusted and optimized, to handle changes in the electrical properties of the bacteria media over time.

JTD Keywords: Autonomous Device, Bacteria Concentrator, Dielectrophoresis, Escherichia coli, Impedance Analysis

We present a procedure for calibrated complex impedance measurements and dielectric quantification with scanning microwave microscopy. The calibration procedure works in situ directly on the substrate with the specimen of interest and does not require any specific calibration sample. In the workflow tip-sample approach curves are used to extract calibrated complex impedance values and to convert measured S11 reflection signals into sample capacitance and resistance images. The dielectric constant of thin dielectric SiO2 films were determined from the capacitance images and approach curves using appropriate electrical tip-sample models and the εr value extracted at f = 19.81 GHz is in good agreement with the nominal value of εr ∼ 4. The capacitive and resistive material properties of a doped Si semiconductor sample were studied at different doping densities and tip-sample bias voltages. Following a simple serial model the capacitance-voltage spectroscopy curves are clearly related to the semiconductor depletion zone while the resistivity is rising with falling dopant density from 20 Ω to 20 kΩ. The proposed procedure of calibrated complex impedance measurements is simple and fast and the accuracy of the results is not affected by varying stray capacitances. It works for nanoscale samples on either fully dielectric or highly conductive substrates at frequencies between 1 and 20 GHz.

JTD Keywords: Complex impedance, Dielectric constant, Nanotechnology: calibration, Resistivity, Scanning microwave microscopy

Here we describe a high-throughput impedance flow cytometer on a chip. This device was built using compact and inexpensive electronic instrumentation. The system was used to count and size a mixed cell sample containing red blood cells and white blood cells. It demonstrated a counting capacity of up to ~500 counts/s and was validated through a synchronised high-speed optical detection system. In addition, the device showed excellent discrimination performance under high-throughput conditions.

JTD Keywords: Electronics, Impedance, Microcytometry, Microfluidics, Red blood cells (RBCs), White blood cells (WBCs)

In this work we report the fabrication and characterization of a label-free impedimetric immunosensor based on a silicon nitride (Si 3N 4) surface for the specific detection of human serum albumin (HSA) proteins. Silicon nitride provides several advantages compared with other materials commonly used, such as gold, and in particular in solid-state physics for electronic-based biosensors. However, few Si 3N 4-based biosensors have been developed; the lack of an efficient and direct protocol for the integration of biological elements with silicon-based substrates is still one of its the main drawbacks. Here, we use a direct functionalization method for the direct covalent binding of monoclonal anti-HSA antibodies on an aldehyde-functionalized Si-p/SiO 2/Si 3N 4 structure. This methodology, in contrast with most of the protocols reported in literature, requires less chemical reagents, it is less time-consuming and it does not need any chemical activation. The detection capability of the immunosensor was tested by performing non-faradaic electrochemical impedance spectroscopy (EIS) measurements for the specific detection of HSA proteins. Protein concentrations within the linear range of 10 -13-10 -7M were detected, showing a sensitivity of 0.128ΩμM -1 and a limit of detection of 10 -14M. The specificity of the sensor was also addressed by studying the interferences with a similar protein, bovine serum albumin. The results obtained show that the antibodies were efficiently immobilized and the proteins detected specifically, thus, establishing the basis and the potential applicability of the developed silicon nitride-based immunosensor for the detection of proteins in real and more complex samples.

JTD Keywords: Aldehyde, Electrochemical impedance spectroscopy, Human serum albumin, Immunosensor, Silicon nitride, Bovine serum albumins, Chemical reagents, Complex samples, Covalent binding, Detection capability, Electrochemical impedance, Electrochemical impedance spectroscopy measurements, Functionalizations, Human serum albumins, Impedimetric immunosensors, Label free, Limit of detection, Linear range, Protein concentrations, Silicon-based, Specific detection, Aldehydes

The synthesis and self-assembled monolayer (SAM) formation of a calix[4]crown-5 derivative are reported. Several techniques, including electrochemistry, atomic force microscopy (AFM), Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle measurements have been applied to characterise the monolayer film designed for chemical sensor applications. The recognition properties of this SAM for metal cations has been investigated using impedance spectroscopy (IS) showing an electrochemical response proportional to calcium ion concentration in the range from 10(-7) M to 10(-2) M. This response is related to microscopic changes at the gold surface induced by selective binding by the immobilised calixarene.

JTD Keywords: Calixarenes, Self assembled monolayer, Micro-contact printing, Atomic force microscopy, Impedance spectroscopy

In this work, we report the detection of proteins by means of simultaneous fluorescence and impedance measurements in a cyclo olefin polymer (COP) chip containing an ordered pillar array column, used for reversed-phase liquid chromatography, with integrated microband gold electrodes at the end of the channel.

JTD Keywords: Cyclo olefin polymer, Gold microelectrodes, Impedance, Pillar array, Protein detection

Worsening of respiratory mechanics during a spontaneous breathing trial (SBT) has been traditionally associated with weaning failure, although this finding is based on studies with chronic obstructive pulmonary disease patients only. The aim of our study was to assess the course of respiratory impedance non-invasively measured by forced oscillation technique (FOT) during a successful and failed SBT in a mixed population. Thirty-four weaning trials were reported in 29 consecutive mechanically ventilated patients with different causes of initiation of ventilation. During the SBT, the patient was breathing through a conventional T-piece connected to the tracheal tube. FOT (5 Hz, +/- 1 cm H2O, 30 s) was applied at 5, 10, 15, 20, 25, and 30 min. Respiratory resistance (Rrs) and reactance (Xrs) were computed from pressure and flow measurements. The frequency to tidal volume ratio f/V-t was obtained from the flow signal. At the end of the trial, patients were divided into two groups: SBT success and failure. Mixed model analysis showed no significant differences in Rrs and Xrs over the course of the SBT, or between the success (n=16) and the failure (n=18) groups. In contrast, f/V-t was significantly (P < 0.001) higher in the failure group. Worsening of respiratory impedance measured by FOT is not a common finding during a failed SBT in a typically heterogeneous intensive care unit population of mechanically ventilated patients.

JTD Keywords: Ventilation, High frequency oscillation, Ventilation, Mechanical, Ventilation, Respiratory impedance

Electrochemical impedance spectroscopy (EIS) is applied to detect pathogenic E. coli O157:H7 bacteria via a label free immunoassay-based detection method. Polyclonal anti-E.coli antibodies (PAb) are immobilized onto gold electrodes following two different strategies, via chemical bond formation between antibody amino groups and a carboxylic acid containing self-assembled molecular monolayer (SAM) and alternatively by linking a biotinylated anti-E. coli to Neutravidin on a mixed-SAM. Impedance spectra for sensors of both designs for increasing concentrations of E. coli are recorded in phosphate buffered saline (PBS). The Nyquist plots can be modeled with a Randle equivalent circuit, identifying the charge transfer resistance RCT as the relevant concentration dependent parameter. Sensors fabricated from both designs are able to detect very low concentration of E. coli with limits of detection as low as 10-100 cfu/ml. The influence of the different immobilization protocols on the sensor performance is evaluated in terms of sensitivity, dynamic range and resistance against nonspecific absorption.

JTD Keywords: Bacteria detection, Biosensors, E-coli, Impedance spectroscopy

Nanometric films of a thiomacrocyclic ionophore, 4-phenyl-4-sulfide-11(1- oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane (ThM), have been deposited on the surface of a Glassy Carbon Electrode (GCE) by the Langmuir-Blodgett (LB) technique. The films have been characterised by using AFM. The influence of these modified electrodes (GCE-ThM) on the reduction of Cu(II) ions has been investigated by using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS), and its sensor response has been checked. The CV and EIS responses of LB films on GCE indicate that these ThM films are sensitive to Cu(II) ions. The analysis by EIS of the interference of some other cations, as Mg(II) and Co(II), shows that LB films of ThM can be used for specific Cu(II) sensing applications.

JTD Keywords: Cu(II) sensor, Cyclic voltammetry, Electrochemical impedance spectroscopy, Langmuir-blodgett films

This article presents the fabrication and characterisation of a high-speed detection micro-Coulter counter with two-dimensional (2D) adjustable aperture and differential impedance detection. The developed device has been fabricated from biocompatible and transparent materials (polymer and glass) and uses the principle of hydrodynamic focusing in two dimensions. The use of a conductive solution for the sample flux and non-conductive solutions for the focalising fluxes provides an adjustable sample flow where particles are aligned and the resistive response concentrated, consequently enhancing the sensitivity and versatility of the device. High-speed counting of 20 mu m polystyrene particles and 5 mu m yeast cells with a rate of up to 1000 particles/s has been demonstrated. Two-dimensional focusing conditions have been used in devices with physical cross-sectional areas of 180 mu m x 65 mu m and 100 mu m x 43 mu m, respectively, in which particles resulted undetectable in the absence of focusing. The 2D-focusing conditions have provided, in addition, increased detection sensitivity by a factor of 1.6 as compared to 1 D-focusing conditions.

JTD Keywords: Impedance, Chip, Microfluidics

Obstructive sleep apnea, which is the most prevalent sleep breathing disorder, is characterized by recurrent episodes of upper airway collapse and reopening. However, the mechanical properties of the upper airway are not directly measured in routine polysomnography because only qualitative sensors (thermistors for flow and thoraco-abdominal bands for pressure) are used. This review focuses on two techniques that quantify upper airway obstruction during sleep. A Starling model of collapsible conduit allows us to interpret the mechanics of the upper airway by means of two parameters: the critical pressure (Pcrit) and the upstream resistance (Rup). A simple technique to measure Pcrit and Rup involves the application of different levels of continuous positive airway pressure (CPAP) during sleep. The forced oscillation technique is another non-invasive procedure for quantifying upper airway impedance during the breathing cycle in sleep studies. The latest developments in these two methods allow them to be easily applied on a routine basis in order to more fully characterize upper airway mechanics in patients with sleep breathing disorders.

JTD Keywords: Obstructive sleep apnea, Upper airway, Airway resistance, Critical pressure, Respiratory impedance

Thin films of silicon nitride (Si3N4) can be used in several kinds of micro-sized biosensors as a material to monitor fine environmental changes related to the process of bone formation in vitro. We found however that Si3N4 does not provide optimal conditions for osseointegration as osteoblast-like MG-63 cells tend to detach from the surface when cultured over confluence. Therefore Si3N4 was modified with self-assembled monolayers bearing functional end groups of primary amine (NH2) and carboxyl (COOH) respectively. Both these modifications enhanced the interaction with confluent cell layers and thus improve osseointegration over Si3N4. Furthermore it was observed that the NH2 functionality increased the adsorption of fibronectin (FN), promoted cell proliferation, but delayed the differentiation. We also studied the fate of pre-adsorbed and secreted FN from cells to learn more about the impact of above functionalities for the development of provisional extracellular matrix on materials interface. Taken together our data supports that Si3N4 has low tissue integration but good cellular biocompatibility and thus is appropriate in cellular biosensor applications such as the ion-sensitive field effect transistor (ISFET). COOH and NH2 chemistries generally improve the interfacial tissue interaction with the sensor and they are therefore suitable substrates for monitoring cellular growth or matrix deposition using electrical impedance spectroscopy.

JTD Keywords: Adsorption, Amines/chemistry, Biocompatible Materials/ chemistry, Biosensing Techniques, Cell Differentiation, Cell Line, Cell Proliferation, Electric Impedance, Extracellular Matrix/metabolism, Fibronectins/chemistry, Humans, Materials Testing, Osteoblasts/ cytology, Silicon Compounds/ chemistry, Surface Properties

A novel microfluidic chip able to detect a wide range of different cell sizes at very high rates is reported. The device uses two-dimensional hydrodynamic focusing [1] of the sample (conducting) flow by three non-conducting flows and high-speed differential impedance detection electronics. High-speed counting of 15μm polystyrene particles and 5μm yeast cells with a rate of up to 1000 particles/s has been demonstrated. Using of two-dimensional focusing effect turn out to be essential in a device with very large cross-sectional area (100x43 μm2) in which particles result undetectable in the absence of focusing.

JTD Keywords: Coulter-counter, Impedance, Microfluidics, Polydimethylsiloxane