Measurement of extracellular pH, K(+), and lactate in ischemic heart

Vacuolar-ATPase-mediated muscle acidification caused muscular mechanical nociceptive hypersensitivity after chronic stress in rats, which involved extracellular matrix proteoglycan and ASIC3

Although widespread pain, such as fibromyalgia, is considered to have a central cause, peripheral input is important. We used a rat repeated cold stress (RCS) model with many characteristics common to fibromyalgia and studied the possible involvement of decreased muscle pH in muscle mechanical hyperalgesia. After a 5-day RCS, the muscle pH and the muscular mechanical withdrawal threshold (MMWT) decreased significantly. Subcutaneously injected specific inhibitor of vacuolar ATPase (V-ATPase), bafilomycin A1, reversed both changes almost completely. It also reversed the increased mechanical response of muscle thin-fibre afferents after RCS. These results show that V-ATPase activation caused muscle pH drop, which led to mechanical hypersensitivity after RCS. Since extracellular matrix proteoglycan and acid sensitive ion channels (TRPV1 and ASIC3) have been considered as possible mechanisms for sensitizing/activating nociceptors by protons, we investigated their involvement. Manipulating the extracellular matrix proteoglycan with chondroitin sulfate and chondroitinase ABC reversed the MMWT decrease after RCS, supporting the involvement of the extracellular mechanism. Inhibiting ASIC3, but not TRPV1, reversed the decreased MMWT after RCS, and ASIC3 mRNA and protein in the dorsal root ganglia were upregulated, indicating ASIC3 involvement. These findings suggest that extracellular mechanism and ASIC3 play essential roles in proton-induced mechanical hyperalgesia after RCS.

GEM-IL: A highly responsive fluorescent lactate indicator

Lactate metabolism has been shown to have increasingly important implications in cellular functions as well as in the development and pathophysiology of disease. The various roles as a signaling molecule and metabolite have led to interest in establishing a new method to detect lactate changes in live cells. Here we report our development of a genetically encoded metabolic indicator specifically for probing lactate (GEM-IL) based on superfolder fluorescent proteins and mutagenesis. With improvements in its design, specificity, and sensitivity, GEM-IL allows new applications compared with the previous lactate indicators, Laconic and Green Lindoblum. We demonstrate the functionality of GEM-IL to detect differences in lactate changes in human oncogenic neural progenitor cells and mouse primary ventricular myocytes. The development and application of GEM-IL show promise for enhancing our understanding of lactate dynamics and roles.

Biocompatible reference electrodes to enhance chronic electrochemical signal fidelity in vivo

In vivo electrochemistry is a vital tool of neuroscience that allows for the detection, identification, and quantification of neurotransmitters, their metabolites, and other important analytes. One important goal of in vivo electrochemistry is a better understanding of progressive neurological disorders (e.g., Parkinson's disease). A complete understanding of such disorders can only be achieved through a combination of acute (i.e., minutes to hours) and chronic (i.e., days or longer) experimentation. Chronic studies are more challenging because they require prolonged implantation of electrodes, which elicits an immune response, leading to glial encapsulation of the electrodes and altered electrode performance (i.e., biofouling). Biofouling leads to increased electrode impedance and reference electrode polarization, both of which diminish the selectivity and sensitivity of in vivo electrochemical measurements. The increased impedance factor has been successfully mitigated previously with the use of a counter electrode, but the challenge of reference electrode polarization remains. The commonly used Ag/AgCl reference electrode lacks the long-term potential stability in vivo required for chronic measurements. In addition, the cytotoxicity of Ag/AgCl adversely affects animal experimentation and prohibits implantation in humans, hindering translational research progress. Thus, a move toward biocompatible reference electrodes with superior chronic potential stability is necessary. Two qualifying materials, iridium oxide and boron-doped diamond, are introduced and discussed in terms of their electrochemical properties, biocompatibilities, fabrication methods, and applications. In vivo electrochemistry continues to advance toward more chronic experimentation in both animal models and humans, necessitating the utilization of biocompatible reference electrodes that should provide superior potential stability and allow for unprecedented chronic signal fidelity when used with a counter electrode for impedance mitigation.

Mechanisms of Small Heat Shock Proteins

Small heat shock proteins (sHSPs) are ATP-independent chaperones that delay formation of harmful protein aggregates. sHSPs' role in protein homeostasis has been appreciated for decades, but their mechanisms of action remain poorly understood. This gap in understanding is largely a consequence of sHSP properties that make them recalcitrant to detailed study. Multiple stress-associated conditions including pH acidosis, oxidation, and unusual availability of metal ions, as well as reversible stress-induced phosphorylation can modulate sHSP chaperone activity. Investigations of sHSPs reveal that sHSPs can engage in transient or long-lived interactions with client proteins depending on solution conditions and sHSP or client identity. Recent advances in the field highlight both the diversity of function within the sHSP family and the exquisite sensitivity of individual sHSPs to cellular and experimental conditions. Here, we will present and highlight current understanding, recent progress, and future challenges.

Recent Progress in Electrochemical pH-Sensing Materials and Configurations for Biomedical Applications

pH-sensing materials and configurations are rapidly evolving toward exciting new applications, especially those in biomedical applications. In this review, we highlight rapid progress in electrochemical pH sensors over the past decade (2008-2018) with an emphasis on key considerations, such as materials selection, system configurations, and testing protocols. In addition to recent progress in optical pH sensors, our main focus in this review is on electromechanical pH sensors due to their significant advances, especially in biomedical applications. We summarize developments of electrochemical pH sensors that by virtue of their optimized material chemistries (from metal oxides to polymers) and geometrical features (from thin films to quantum dots) enable their adoption in biomedical applications. We further present an overview of necessary sensing standards and protocols. Standards ensure the establishment of consistent protocols, facilitating collective understanding of results and building on the current state. Furthermore, they enable objective benchmarking of various pH-sensing reports, materials, and systems, which is critical for the overall progression and development of the field. Additionally, we list critical issues in recent literary reporting and suggest various methods for objective benchmarking. pH regulation in the human body and state-of-the-art pH sensors (from ex vivo to in vivo) are compared for suitability in biomedical applications. We conclude our review by (i) identifying challenges that need to be overcome in electrochemical pH sensing and (ii) providing an outlook on future research along with insights, in which the integration of various pH sensors with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics and prevention.

High-sensitivity ion detection at low voltages with current-driven organic electrochemical transistors

Ions dissolved in aqueous media play a fundamental role in plants, animals, and humans. Therefore, the in situ quantification of the ion concentration in aqueous media is gathering relevant interest in several fields including biomedical diagnostics, environmental monitoring, healthcare products, water and food test and control, agriculture industry and security. The fundamental limitation of the state-of-art transistor-based approaches is the intrinsic trade-off between sensitivity, ion concentration range and operating voltage. Here we show a current-driven configuration based on organic electrochemical transistors that overcomes this fundamental limit. The measured ion sensitivity exceeds by one order of magnitude the Nernst limit at an operating voltage of few hundred millivolts. The ion sensitivity normalized to the supply voltage is larger than 1200 mV V⁻¹ dec⁻¹, which is the largest value ever reported for ion-sensitive transistors. The proposed approach is general and can be extended to any transistor technology, thus opening opportunities for high-performance bioelectronics.

The organic electrochemical transistor is a type of transistor that modulates the channel current by the ion concentration and is thus explored for bio-applications. Here Ghittorelli et al. show a current-driven device configuration to increase the sensitivity by ten times than conventional approaches.

An array of individually addressable micro-needles for mapping pH distributions

This work describes the preparation of an array of individually addressable pH sensitive microneedles which demonstrated suitable for measuring pH distribution during heart ischemia and reperfusion cycles.

In silico ischaemia-induced reentry at the Purkinje-ventricle interface

AIMS

This computational modelling work illustrates the influence of hyperkalaemia and electrical uncoupling induced by defined ischaemia on action potential (AP) propagation and the incidence of reentry at the Purkinje-ventricle interface in mammalian hearts.

METHODS AND RESULTS

Unidimensional and bidimensional models of the Purkinje-ventricle subsystem, including ischaemic conditions (defined as phase 1B) in the ventricle and an ischaemic border zone, were developed by altering several important electrophysiological parameters of the Luo-Rudy AP model of the ventricular myocyte. Purkinje electrical activity was modelled using the equations of DiFrancesco and Noble. Our study suggests that an extracellular potassium concentration [K(+)]o >14 mM and a slight decrease in intercellular coupling induced by ischaemia in ventricle can cause conduction block from Purkinje to ventricle. Under these conditions, propagation from ventricle to Purkinje is possible. Thus, unidirectional block (UDB) and reentry can result. When conditions of UDB are met, retrograde propagation with a long delay (320 ms) may re-excite Purkinje cells, and give rise to a reentrant pathway. This induced reentry may be the origin of arrhythmias observed in phase 1B ischaemia.

CONCLUSION

In a defined setting of ischaemia (phase 1B), a small amount of uncoupling between ventricular cells, as well as between Purkinje and ventricular tissue, may induce UDBs and reentry. Hyperkalaemia is also confirmed to be an important factor in the genesis of reentrant rhythms, since it regulates the range of coupling in which UDBs may be induced.

Patient-specific flexible and stretchable devices for cardiac diagnostics and therapy

Advances in material science techniques and pioneering circuit designs have led to the development of electronic membranes that can form intimate contacts with biological tissues. In this review, we present the range of geometries, sensors, and actuators available for custom configurations of electronic membranes in cardiac applications. Additionally, we highlight the desirable mechanics achieved by such devices that allow the circuits and substrates to deform with the beating heart. These devices unlock opportunities to collect continuous data on the electrical, metabolic, and mechanical state of the heart as well as a platform on which to develop high definition therapeutics.

in vivo ischemia monitoring array for endoscopic surgery

An array with all-solid-state, potentiometric, miniaturized sensors for pH and potassium was developed to be introduced into the stomach or other sectors of the digestive tract by means of flexible endoscopy. These sensors perform continuous and simultaneous measurement of extracellular pH and potassium. This detection seeks to sense ischemia in the gastric mucosa inside the stomach, an event indicative of local microvascular perfusion and tissue oxygenation status. Our array is proposed as a medical tool to identify the occurrence of the ischemia after gastrointestinal or gastroesophageal anastomosis. The stability and feasibility of the miniaturized working and reference electrodes integrated in the array were studied under in vitro conditions, and the behavior of the potassium and pH ion-selective membranes were optimized to work under acidic gastric conditions with high concentrations of HCl. The array was tested in vivo in pigs to measure the ischemia produced by clamping the blood flow into the stomach. Our results indicate that ischemic and reperfusion states can be sensed in vivo and that information on tissue damage can be collected by this sensor array. The device described here provides a miniaturized, inexpensive, and mass producible sensor array for detecting local ischemia caused by unfavorable anastomotic perfusion and will thus contribute to preventing anastomotic leakage and failure caused by tissue necrosis.

Stretchable, multiplexed pH sensors with demonstrations on rabbit and human hearts undergoing ischemia

Stable pH is an established biomarker of health, relevant to all tissues of the body, including the heart. Clinical monitoring of pH in a practical manner, with high spatiotemporal resolution, is particularly difficult in organs such as the heart due to its soft mechanics, curvilinear geometry, heterogeneous surfaces, and continuous, complex rhythmic motion. The results presented here illustrate that advanced strategies in materials assembly and electrochemical growth can yield interconnected arrays of miniaturized IrOx pH sensors encapsulated in thin, low-modulus elastomers to yield conformal monitoring systems capable of noninvasive measurements on the surface of the beating heart. A thirty channel custom data acquisition system enables spatiotemporal pH mapping with a single potentiostat. In vitro testing reveals super-Nernstian sensitivity with excellent uniformity (69.9 ± 2.2 mV/pH), linear response to temperature (-1.6 mV °C(-1) ), and minimal influence of extracellular ions (<3.5 mV). Device examples include sensor arrays on balloon catheters and on skin-like stretchable membranes. Real-time measurement of pH on the surfaces of explanted rabbit hearts and a donated human heart during protocols of ischemia-reperfusion illustrate some of the capabilities. Envisioned applications range from devices for biological research, to surgical tools and long-term implants.

Therapeutic angiogenesis: controlled delivery of angiogenic factors

Therapeutic angiogenesis aims at treating ischemic diseases by generating new blood vessels from existing vasculature. It relies on delivery of exogenous factors to stimulate neovasculature formation. Current strategies using genes, proteins and cells have demonstrated efficacy in animal models. However, clinical translation of any of the three approaches has proved to be challenging for various reasons. Administration of angiogenic factors is generally considered safe, according to accumulated trials, and offers off-the-shelf availability. However, many hurdles must be overcome before therapeutic angiogenesis can become a true human therapy. This article will highlight protein-based therapeutic angiogenesis, concisely review recent progress and examine critical challenges. We will discuss growth factors that have been widely utilized in promoting angiogenesis and compare their targets and functions. Lastly, since bolus injection of free proteins usually result in poor outcomes, we will focus on controlled release of proteins.

Nitric oxide-mediated relaxation to lactate of coronary circulation in the isolated perfused rat heart

The objective of this study was to analyze the effects of lactate on coronary circulation. Rat hearts were perfused in a Langendorff preparation, and the coronary response to lactate (3-30 mM) was recorded after precontracting coronary vasculature with 11-dideoxy-1a,9a-epoxymethanoprostaglandin F2α (U46619), in the presence or the absence of the inhibitor of nitric oxide synthesis, N-omega-nitro-l-arginine methyl ester (l-NAME, 10 M), the blocker of Ca-dependent potassium channels, tetraethylammonium (TEA, 10 M), or the blocker of adenosine triphosphate-sensitive potassium channels, glybenclamide (10 M). The effects of lactate were also studied in isolated segments of rat coronary arteries that were precontracted with U46619, with or without endothelium. In perfused hearts, lactate induced concentration-dependent coronary vasodilatation and a reduction in myocardial contractility (left ventricular developed pressure and dP/dt) without altering the heart rate. Coronary vasodilatation in response to lactate was reduced by l-NAME but unaffected by TEA or glybenclamide. The effects of lactate on myocardial contractility were unchanged by l-NAME, TEA, or glybenclamide. In isolated coronary artery segments, lactate also produced relaxation, an effect attenuated by removing the endothelium. Together these findings suggest that lactate exerts coronary vasodilatory effects through the release of endothelial nitric oxide, independently of potassium channels. These findings may be relevant for the regulation of coronary circulation when lactate levels are elevated.

Acid-evoked Ca2+ signalling in rat sensory neurones: effects of anoxia and aglycaemia

Ischaemia excites sensory neurones (generating pain) and promotes calcitonin gene-related peptide release from nerve endings. Acidosis is thought to play a key role in mediating excitation via the activation of proton-sensitive cation channels. In this study, we investigated the effects of acidosis upon Ca²⁺ signalling in sensory neurones from rat dorsal root ganglia. Both hypercapnic (pH_o 6.8) and metabolic–hypercapnic (pH_o 6.2) acidosis caused a biphasic increase in cytosolic calcium concentration ([Ca²⁺]_i). This comprised a brief Ca²⁺ transient (half-time approximately 30 s) caused by Ca²⁺ influx followed by a sustained rise in [Ca²⁺]_i due to Ca²⁺ release from caffeine and cyclopiazonic acid-sensitive internal stores. Acid-evoked Ca²⁺ influx was unaffected by voltage-gated Ca²⁺-channel inhibition with nickel and acid sensing ion channel (ASIC) inhibition with amiloride but was blocked by inhibition of transient receptor potential vanilloid receptors (TRPV1) with (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4] dioxin-6-yl)acrylamide (AMG 9810; 1 μM) and N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl) tetrahydropryazine-1(2H)-carbox-amide (BCTC; 1 μM). Combining acidosis with anoxia and aglycaemia increased the amplitude of both phases of Ca²⁺ elevation and prolonged the Ca²⁺ transient. The Ca²⁺ transient evoked by combined acidosis, aglycaemia and anoxia was also substantially blocked by AMG 9810 and BCTC and, to a lesser extent, by amiloride. In summary, the principle mechanisms mediating increase in [Ca²⁺]_i in response to acidosis are a brief Ca²⁺ influx through TRPV1 followed by sustained Ca²⁺ release from internal stores. These effects are potentiated by anoxia and aglycaemia, conditions also prevalent in ischaemia. The effects of anoxia and aglycaemia are suggested to be largely due to the inhibition of Ca²⁺-clearance mechanisms and possible increase in the role of ASICs.

Potassium Ion Sensing With Nanowire Electrodes on a Flexible Substrate for Early Detection of Myocardial Ischemia

An increase in extracellular potassium levels is a physiological sign of myocardial ischemia and timely sensing with an implantable potassium sensing biosensor could play a significant role in detecting and expediting care. In this paper, unique fabrication techniques for both planar and nanowire structured gold microelectrodes are described along with data showing the enhanced charge transfer capabilities of the nanowire design. Optimization is required for the electrodeposition of polypyrrole onto gold nanowires and processing details along with characterization data are provided for both the polypyrrole layer and ion selective membrane. Cyclic voltammetry and electrochemical impedance spectroscopy results show that the polypyrrole coated gold nanowire electrodes provide stable charge transfer, showing the potential as a potassium sensing device for the early detection of myocardial ischemia applications.

DNA-barcode directed capture and electrochemical metabolic analysis of single mammalian cells on a microelectrode array

A microdevice is developed for DNA-barcode directed capture of single cells on an array of pH-sensitive microelectrodes for metabolic analysis. Cells are modified with membrane-bound single-stranded DNA, and specific single-cell capture is directed by the complementary strand bound in the sensor area of the iridium oxide pH microelectrodes within a microfluidic channel. This bifunctional microelectrode array is demonstrated for the pH monitoring and differentiation of primary T cells and Jurkat T lymphoma cells. Single Jurkat cells exhibited an extracellular acidification rate of 11 milli-pH min(-1), while primary T cells exhibited only 2 milli-pH min(-1). This system can be used to capture non-adherent cells specifically and to discriminate between visually similar healthy and cancerous cells in a heterogeneous ensemble based on their altered metabolic properties.

Glucose and lactate biosensors for scanning electrochemical microscopy imaging of single live cells

We have developed glucose and lactate ultramicroelectrode (UME) biosensors based on glucose oxidase and lactate oxidase (with enzymes immobilized onto Pt UMEs by either electropolymerization or casting) for scanning electrochemical microscopy (SECM) and have determined their sensitivity to glucose and lactate, respectively. The results of our evaluations reveal different advantages for sensors constructed by each method: improved sensitivity and shorter manufacturing time for hand-casting, and increased reproducibility for electropolymerization. We have acquired amperometric approach curves (ACs) for each type of manufactured biosensor UME, and these ACs can be used as a means of positioning the UME above a substrate at a known distance. We have used the glucose biosensor UMEs to record profiles of glucose uptake above individual fibroblasts. Likewise, we have employed the lactate biosensor UMEs for recording the lactate production above single cancer cells with the SECM. We also show that oxygen respiration profiles for single cancer cells do not mimic cell topography, but are rather more convoluted, with a higher respiration activity observed at the points where the cell touches the Petri dish. These UME biosensors, along with the application of others already described in the literature, could prove to be powerful tools for mapping metabolic analytes, such as glucose, lactate, and oxygen, in single cancer cells.

Differential pH measurements of metabolic cellular activity in nl culture volumes using microfabricated iridium oxide electrodes

In this paper we describe a new approach to measure pH differences in microfluidic devices and demonstrated acidification rate measurements in on-chip cell culture systems with nl wells. We use two miniaturized identical iridium oxide (IrOx) thin film electrodes (20 micromx400 microm), one as a quasi-reference electrode, the other as a sensing electrode, placed in two confluent compartments on chip. The IrOx electrodes were deposited onto microfabricated platinum (Pt) electrodes simultaneously using electrodeposition. Incorporating the electrodes into a microfluidic device allowed us to expose each electrode to a different solution with a pH difference of one pH unit maintaining a confluent connection between the electrodes. In this configuration, we obtained a reproducible voltage difference between the two IrOx thin film electrodes, which corresponds to the electrode sensitivities of -70 mV/pH at 22 degrees C. In order to measure the acidification rate of cells in nl cell culture volumes we placed one IrOx thin film electrode in the perfusion channel as a quasi-reference electrode and the other in the cell culture volume. We obtained an acidification rate of 0.19+/-0.02 pH/min for fibroblast cells using a stop flow protocol. These results show that we can use two identical miniaturized microfabricated IrOx electrodes to measure pH differences to monitor the metabolic activity of cell cultures on chip. Furthermore, our approach can also be applied in biosensor or bioanalytical applications.

Effects of ischaemia-mimetic factors on isolated rat ventricular myocytes

Conventional ischaemia-mimetic solutions contain several key components for inducing hypoxia, glucose deficiency, acidosis, lactate accumulation and hyperosmosis. The effect of each component on myocyte contractility during cardiac ischaemia was investigated in this study. A video-based edge-detection system was used to monitor single ventricular myocytes isolated from the rat. The effect of each factor was compared by preparing the following ischaemia-mimetic solutions: solution A, containing all of the above-mentioned factors; and solutions B, C, D, E and F, each with one of the factors excluded. The solutions that contained lactate severely reduced the contractility of the cardiomyocytes, but cell contraction did not differ significantly between the cardiomyocytes in these solutions. The effect of the solution without the acidosis-inducing component was weaker than that of the conventional ischaemia-mimetic solution. The solution lacking lactate produced the least depression of cell contractility. Lactate impaired cardiomyocyte contractility in a concentration-dependent manner. Our observations suggest that lactate is the main contributor to cardiac ischaemic injury and that its effects are attributable to acidosis and are concentration dependent. Imposition of hypoxia, glucose deficiency and hyperosmosis had little impact on the cardiomyocytes.

A unique pathway of cardiac myocyte death caused by hypoxia-acidosis

Chronic hypoxia in the presence of high glucose leads to progressive acidosis of cardiac myocytes in culture. The condition parallels myocardial ischemia in vivo, where ischemic tissue becomes rapidly hypoxic and acidotic. Cardiac myocytes are resistant to chronic hypoxia at neutral pH but undergo extensive death when the extracellular pH (pH[o]) drops below 6.5. A microarray analysis of 20 000 genes (cDNAs and expressed sequence tags) screened with cDNAs from aerobic and hypoxic cardiac myocytes identified >100 genes that were induced by >2-fold and approximately 20 genes that were induced by >5-fold. One of the most strongly induced transcripts was identified as the gene encoding the pro-apoptotic Bcl-2 family member BNIP3. Northern and western blot analyses confirmed that BNIP3 was induced by 12-fold (mRNA) and 6-fold (protein) during 24 h of hypoxia. BNIP3 protein, but not the mRNA, accumulated 3.5-fold more rapidly under hypoxia-acidosis. Cell fractionation experiments indicated that BNIP3 was loosely bound to mitochondria under conditions of neutral hypoxia but was translocated into the membrane when the myocytes were acidotic. Translocation of BNIP3 coincided with opening of the mitochondrial permeability pore (MPTP). Paradoxically, mitochondrial pore opening did not promote caspase activation, and broad-range caspase inhibitors do not block this cell death pathway. The pathway was blocked by antisense BNIP3 oligonucleotides and MPTP inhibitors. Therefore, cardiac myocyte death during hypoxia-acidosis involves two distinct steps: (1) hypoxia activates transcription of the death-promoting BNIP3 gene through a hypoxia-inducible factor-1 (HIF-1) site in the promoter and (2) acidosis activates BNIP3 by promoting membrane translocation. This is an atypical programmed death pathway involving a combination of the features of apoptosis and necrosis. In this article, we will review the evidence for this unique pathway of cell death and discuss its relevance to ischemic heart disease. The article also contains new evidence that chronic hypoxia at neutral pH does not promote apoptosis or activate caspases in neonatal cardiac myocytes.

A wire-based dual-analyte sensor for glucose and lactate: in vitro and in vivo evaluation

Continuous measurement of lactate is potentially useful for detecting physical exhaustion and for monitoring critical care conditions characterized by hypoperfusion, such as heart failure. In some conditions, it may be desirable to monitor more than one metabolic parameter concurrently. For this reason, we designed and fabricated twisted wire-based microelectrodes that can measure both lactate and glucose. These dual-analyte sensors were characterized in vitro by measuring their response to the analyte of interest and to assess whether they were susceptible to interference from the other analyte. When measured in stirred aqueous buffer, lactate sensors detected a very small amount of crosstalk from glucose in vitro, although this signal was less than 3% of the response to lactate. Glucose sensors did not detect crosstalk from lactate. Sensors were implanted subcutaneously in rats and tested during infusions of lactate and glucose. Each sensing electrode responded rapidly to changes in its analyte concentration, and there was no evidence of in vivo crosstalk. This study constitutes proof of the concept that oxidase-based, amperometric wire microsensors can detect changes in glucose and lactate during subcutaneous implantation in rats.

Design and performance of some microflow-cell potentiometric transducers

The paper presents and compares the design of three potentiometric transducers: ion-selective field effect transistor (ISFET), solid-state Ag/AgCl electrode and miniaturized classical Ag/AgCl electrode. The reported transducers were fabricated using different, less or more complicated and expensive, technologies. The transducers were constructed to be compatible with the sensor housing of the flow-cell, designed previously. Moreover, the back-side contact structures of the two planar devices, where electrical connectors and the sensing layer are on the opposite sides, facilitated their application in the flow analysis. Exemplary potassium-selective microsensors based on developed transducers were prepared, applying plasticized PVC and polysiloxane membranes containing valinomycine. The determined microsensor performances allowed comparison of their usefulness for multiparameter flow analysis.