Ion-selective Microelectrodes Research Articles

Single-cell calcium monitoring of Caco-2 cell co-cultured with intestinal microbiome through carbon fiber based potentiometric microelectrode

The Caco-2 cells were used as intestinal epithelial cell model to illustrate the hyperuricemia (HUA) mechanism under the co-culture of the imbalanced intestinal microbiome in this work. The uric acid (UA) concentration in the HUA process was monitored, and could be up to 425 μmol/L at 8 h co-cultured with the imbalanced intestinal microbiome. Single-cell potentiometry based on ion-selective microelectrode was used to study extracellular calcium change, which is hypothesized to play an important role in the UA excretion. The potential signal of the calcium in the extremely limited microenvironment around single Caco-2 cell was recorded through the single-cell analysis platform. The potential signal of sharp decrease and slow increase followed within a few seconds indicates the sudden uptake and gradually excretion process of calcium through the cell membrane. Moreover, the value of the potential decrease increases with the increase of the time co-cultured with the imbalanced intestinal microbiome ranging from 0 to 8 h. The Ca2+ concentration around the cell membrane could decrease from 1.3 mM to 0.4 mM according to the potential decrease of 27.0 mV at the co-culture time of 8 h. The apoptosis ratio of the Caco-2 cells also exhibits time dependent with the co-culture of the imbalanced intestinal microbiome, and was 39.1 ± 3.6 % at the co-culture time of 8 h, which is much higher than the Caco-2 cells without any treatment (3.9 ± 2.9 %). These results firstly provide the links between the UA excretion with the apoptosis of the intestinal epithelial cell under the interaction of the imbalanced intestinal microbiome. Moreover, the apoptosis could be triggered by the calcium signaling.

A Photoelectrochemical Sensor for Real-Time Monitoring of Neurochemical Signals in the Brain of Awake Animals.

Metal ion homeostasis is imperative for normal functioning of the brain. Considering the close association between brain metal ions and various pathological processes in brain diseases, it becomes essential to track their dynamics in awake animals for accurate physiological insights. Although ion-selective microelectrodes (ISMEs) have demonstrated great advantage in recording ion signals in awake animals, their intrinsic potential drift impairs their accuracy in long-term in vivo analysis. This study addresses the challenge by integrating ISMEs with photoelectrochemical (PEC) sensing, presenting an excitation-detection separated PEC platform based on potential regulation of ISMEs. A flexible indium tin oxide (Flex-ITO) electrode, modified with MoS2 nanosheets and Au NPs, serves as the photoelectrode and is integrated with a micro-LED. The integrated photoelectrode is placed on the rat skull to remain unaffected by animal activity. The potential of ISME dependent on the concentration of target K+ serves as the modulator of the photocurrent signal of the photoelectrode. The proposed design allows deep brain detection while minimizing interference with neurons, thus enabling real-time monitoring of neurochemical signals in awake animals. It successfully monitors changes in extracellular K+ levels in the rat brain after exposure to PM2.5, presenting a valuable analytical tool for understanding the impact of environmental factors on the nervous system.

Inward Operation of Sodium-Bicarbonate Cotransporter 1 Promotes Astrocytic Na+ Loading and Loss of ATP in Mouse Neocortex during Brief Chemical Ischemia.

Ischemic conditions cause an increase in the sodium concentration of astrocytes, driving the breakdown of ionic homeostasis and exacerbating cellular damage. Astrocytes express high levels of the electrogenic sodium-bicarbonate cotransporter1 (NBCe1), which couples intracellular Na+ homeostasis to regulation of pH and operates close to its reversal potential under physiological conditions. Here, we analyzed its mode of operation during transient energy deprivation via imaging astrocytic pH, Na+, and ATP in organotypic slice cultures of the mouse neocortex, complemented with patch-clamp and ion-selective microelectrode recordings and computational modeling. We found that a 2 min period of metabolic failure resulted in a transient acidosis accompanied by a Na+ increase in astrocytes. Inhibition of NBCe1 increased the acidosis while decreasing the Na+ load. Similar results were obtained when comparing ion changes in wild-type and Nbce1-deficient mice. Mathematical modeling replicated these findings and further predicted that NBCe1 activation contributes to the loss of cellular ATP under ischemic conditions, a result confirmed experimentally using FRET-based imaging of ATP. Altogether, our data demonstrate that transient energy failure stimulates the inward operation of NBCe1 in astrocytes. This causes a significant amelioration of ischemia-induced astrocytic acidification, albeit at the expense of increased Na+ influx and a decline in cellular ATP.

The Absence of an Na+/Ca2+Exchanger (NCX) in Bullfrog Proximal Tubules and Cellular pH is More Influential Than Cellular Ca2+ on Proximal Na Transport.

The functional significance of the Na+/Ca2+ exchanger (NCX) in basolateral membranes in the proximal tubule remains controversial. The key factor in crosstalk between the apical and basolateral sides is not known. We investigated the basolateral membranes, using double-barreled Ca2+ or pH ion-selective microelectrodes. We used doubly perfused bullfrog kidneys in vivo, and switched the basolateral solution (renal portal vein) to experimental solutions. In the control, cellular pH (pHi) was 7.33 ± 0.032 (mean ± SE, n = 7) and in separate experiments, cellular Ca2+ activity (aCai) was 249.6 ± 35.54 nM (n = 28). Changing to respiratory acidosis, pHi was significantly acidified by 0.123 pH units on average and the change of aCai was +53.1 nM (n = 9 ns). In metabolic acidosis, pHi was reduced by 0.151 while aCai was reduced by 143.4. Using the 30 mM K+ solution, pHi was increased by 0.233 while aCai was reduced by 203.9, with depolarization. Both ionomycin and ouabain caused aCai to increase. In the 0.5 mM Na+ solution (replaced with BIDAC Cl), pHi was reduced by 0.177. No changes in aCai (+49.8 ns) were observed although we recorded depolarization of 15.2 mV. In the 0.5 mM Na+ solution, replaced with raffinose, no changes in aCai (-126.4 ns) were observed with depolarization (6.5 ns). Our results suggest that thermodynamic calculations of cellular Na+ concentration led to the conclusion that either a Na+/HCO3- exchanger (NBC) or NCX could be present in the same basolateral membrane. H+ ions are the most plausible key factor in the crosstalk.

Biodegradable Microelectrodes for Monitoring the Dynamics of Extracellular Ca2+ in Rat Brain.

In vivo electrochemical analysis is of great significance in understanding the dynamics of various physiological and pathological activities. However, the conventional microelectrodes for electrochemical analysis are rigid and permanent, which comes with increased risks for long-term implantation and secondary surgery. Here, we develop one biodegradable microelectrode for monitoring the dynamics of extracellular Ca2+ in rat brain. The biodegradable microelectrode is prepared by sputtering gold nanoparticles (AuNPs) on a wet-spun flexible poly(l-lactic acid) (PLLA) fiber for conduction and transduction and coating a Ca2+ ion-selective membrane (ISM) with a PLLA matrix on the PLLA/AuNPs fiber, forming PLLA/AuNPs/Ca2+ISME (ISME = ion-selective microelectrode). The prepared microelectrode shows excellent analytical properties including a near-Nernst linear response toward Ca2+ over the concentration range from 10 μM to 50 mM, good selectivity, and long-term stability for weeks as well as biocompatibility and biodegradability. The PLLA/AuNPs/Ca2+ISME can monitor the dynamics of extracellular Ca2+ following spreading depression induced by high potassium even if in the fourth day. This study provides a new design strategy for the biodegradable ISME and promotes the development of biodegradable microelectrodes for long-term monitoring of chemical signals in brain.

Identification of RhBG Mutations that Impair NH3/NH4+ Transport in Patients with Chronic Kidney Disease

Background: Acid-base disturbances are common in many illnesses, and metabolic acidosis is a major complication in patients with chronic kidney disease (CKD). The kidneys respond to acidosis by increasing urinary excretion of total ammonia (NH 3 /NH 4 + ) and to a lesser extent titratable acids. In the collecting duct, total ammonia is secreted by the NH 3 /NH 4 + transporters, RhBG and RhCG. RhBG transports NH 3 and NH 4 + at the basolateral membrane of intercalated cells. In CKD patients, the increase in ammonium excretion in response to acidosis is markedly impaired. Recent studies suggest that the reduced ability of the kidney to excrete ammonium is likely a cause of detrimental renal outcome in CKD and faster progression towards end-stage renal disease. Hypothesis: This study aims to identify loss of function mutations of RhBG (nsSNPs) that impair NH 3 /NH 4 + transport which may contribute to the deleterious effect of acidosis in CKD. Methods: We used Chronic Renal Insufficiency Cohort (CRIC) study to select SNPs of RhBG that are present in CKD patients but not in controls, or have a significant odds ratio (OR). Transport studies were conducted on Xenopus oocytes expressing Rh proteins or mutants. Wild-type RhBG (RhBG-WT) or RhBG-mutants were expressed by microinjecting oocytes with respective mRNA. H 2 O-injected oocytes served as negative controls. Each oocyte was perfused with solutions containing 5 mM NH 3 /NH 4 + or 5 mM MA/MA + (methylamine/methylammonium, a surrogate of NH 3 /NH 4 + ) to test RhBG function. Using ion-selective microelectrodes, we measured changes in intracellular pH, whole cell currents or surface pH to assess transport of NH 3 or NH 4 + . Results: Two RhBG mutations, G148R and G148W, which are only present in the patient group from CRIC cohort, significantly inhibited transport of NH 3 and NH 4 + (and MA/MA + ) compared with RhBG-WT (p<0.05) in Xenopus oocytes. Two other mutations, G86S and G86C, positively associated with CKD patients (OR=4.65, p<0.05), showed different inhibition patterns: G86S maintained the ability to transport NH 4 + , NH 3 and MA + while G86C inhibited NH 3 and NH 4 + transport but MA + transport was less affected compared with RhBG-WT. Both G86S and G86C showed a 50% decrease in MA transport (p<0.05) that was still significantly higher than negative control. Conclusions: We discovered two RhBG mutations, G148R and G148W, in CKD patients that completely inhibited the transport of NH 3 /NH 4 + . The other two mutations, G86S and G86C, partially inhibited transport, and G86C was more deleterious than G86S in its inhibitory effect on NH 4 + and NH 3 transport. Significance: This study is the first to identify, in a cohort of CKD patients, 4 mutations with functional effects on NH 3 /NH 4 + transport. This work provides the foundation to further investigate whether naturally occurring genetic variations that impair ammonia secretion are associated with fast CKD progression under acidosis conditions. Funding grants: NIH-U54 GM104940, Paul Teschan Research, NIH-R01, Carol Lavin Bernick, Tulane institutional This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Real-time calcium uptake monitoring of a single renal cancer cell based on an all-solid-state potentiometric microsensor.

Introduction: In addition to many cellular processes, Ca2+ is also involved in tumor initiation, progression, angiogenesis, and metastasis. The development of new tools for single-cell Ca2+ measurement could open a new avenue for cancer therapy. Methods: The all-solid-state calcium ion-selective microelectrode (Ca2+-ISμE) based on carbon fiber modified with PEDOT (PSS) as solid-contact was developed in this work, and the characteristics of the Ca2+-ISμE have also been investigated. Results: The Ca2+-ISμE exhibits a stable Nernstian response in CaCl2 solutions in the active range of 1.0 × 10-8 - 3.1 × 10-3 M with a low detection limit of 8.9 × 10-9M. The Ca2+-ISμE can be connected to a patch clamp to fabricate a single-cell analysis platform for in vivo calcium monitoring of a single renal carcinoma cell. The calcium signal decreased significantly (8.6 ± 3.2mV, n = 3) with severe fluctuations of 5.9 ± 1.8mV when the concentration of K+ in the tumor microenvironment is up to 20mM. Discussion: The results indicate a severe cell response of a single renal carcinoma cell under high K+ stimuli. The detection system could also be used for single-cell analysis of other ions by changing different ion-selective membranes with high temporal resolution.

Deep isoflurane anesthesia is associated with alterations in ion homeostasis and specific Na+/K+-ATPase impairment in the rat brain.

Maintenance of ion homeostasis is essential for normal brain function. Inhalational anesthetics are known to act on various receptors but their effects on ion homeostatic systems, such as the Na+/K+-ATPase, remain largely unexplored. Based on reports demonstrating global network activity and wakefulness modulation by interstitial ions, we hypothesized that deep isoflurane anesthesia affects ion homeostasis and the key mechanism for clearing extracellular K+, the Na+/K+-ATPase. Using ion-selective microelectrodes, we assessed isoflurane-induced extracellular ion dynamics in cortical slices of male and female Wistar rats in the absence of synaptic activity, the presence of two-pore-domain K+ channel antagonists, during seizures, and spreading depolarizations. We measured specific isoflurane effects on Na+/K+-ATPase function using a coupled enzyme assay and studied the relevance of our findings in vivo and in silico. Isoflurane concentrations clinically relevant for burst suppression anesthesia increased baseline [K+]o (mean±SD: 3.0 ± 0.0 versus 3.9 ± 0.5mM, p<0.001, n=39) and lowered [Na+]o (153.4 ± 0.8 versus 145.2 ± 6.0mM, p<0.001, n=28). Similar changes in [K+]o, [Na+]o, and a substantial drop in [Ca2+]o (1.5 ± 0.0 versus 1.2 ± 0.1mM, p=0.001, n=16) during inhibition of synaptic activity and two-pore-domain K+ suggested a different underlying mechanism. Following seizure-like events and spreading depolarization, isoflurane greatly slowed [K+]o clearance (63.4 ± 18.2 versus 196.2 ± 82.4s, p<0.001, n=14). Na+/K+-ATPase activity was markedly reduced after isoflurane exposure (>25%), affecting specifically the α2/3 activity fraction. In vivo, isoflurane-induced burst suppression resulted in impaired [K+]o clearance and interstitial K+ accumulation. A computational biophysical model reproduced the observed effects on [K+]o and displayed intensified bursting when Na+/K+-ATPase activity was reduced by 35%. Finally, Na+/K+-ATPase inhibition with ouabain induced burst-like activity during light anesthesia in vivo. Our results demonstrate cortical ion homeostasis perturbation and specific Na+/K+-ATPase impairment during deep isoflurane anesthesia. Slowed K+ clearance and extracellular accumulation might modulate cortical excitability during burst suppression generation while prolonged Na+/K+-ATPase impairment could contribute to neuronal dysfunction after deep anesthesia.

Welding and galvanic coupling effects on the electrochemical activity of dissimilar AA2050 and AA7050 aluminum alloys welded by Friction Stir Welding (FSW)

In this work, the effects of friction stir welding (FSW) on the microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys have been investigated. Local electrochemical tests supported by surface analytical characterization were used to study the local electrochemical activities developed along the weld zones of the dissimilar alloys. The investigation was carried out on the cross-section of the welded Al alloys. The results showed that the friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the electrochemical behavior of the different regions (HAZ, TMAZ, SZ) formed by the welding process. Scanning vibrating electrode technique (SVET) and micropotentiometry by using an ion-selective microelectrode showed that TMAZ was the zone with the highest electrochemical activity. This zone corresponded to the transition region between the two welded alloys. The high electrochemical activity observed in this region was associated with the effect of welding on the microstructure and, also, with the galvanic coupling between the two alloys, where the alloy AA7050 acted as an anode and the AA2050 as a cathode. Preferential corrosion attack on the AA7050 alloy was also evident.

An all-solid-state potentiometric microsensor for real-time monitoring of the calcification process by Bacillus subtilis biofilms

A robust all-solid-state potentiometric microsensor using carbon nanotube fibers was designed. The ion-selective microelectrodes provide a simple and versatile tool for real-time monitoring of the calcification process by Bacillus subtilis biofilms.

Surface finishing effects on the corrosion behavior and electrochemical activity of 2098-T351 aluminum alloy investigated using scanning microelectrochemical techniques

The effects of surface finishing on the corrosion behavior and electrochemical activity of AA2098-T351 (Al–Cu–Li alloy) were investigated on the basis of the correlation between surface chemistry, microstructure and electrochemical activity. The alloy was evaluated in the as-received and polished conditions. The morphology of the two types of surfaces was investigated using confocal laser scanning microscopy (CLSM), optical microscopy and optical 3D profilometry. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). Scanning microelectrochemical techniques (namely, localized electrochemical impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM) in potentiometric mode) were used to examine the electrochemical activity of the surfaces. The results showed that on the as-received surface, the near surface deformed layer (NSDL), which is composed of Mg-rich bands, influenced the corrosion activity of the alloy. Higher electrochemical activity and greater susceptibility to severe localized corrosion were related to the polished surface condition compared to the as-received one. • Surface finishing effects on chemical activity of 2098-T351 Al–Cu–Li alloy studied using scanning microelectrochemical techniques. • The effect of the near-surface deformed layer (NSDL) on 2098-T351 Al–Cu–Li was investigated for different surface finishes. • A solid contact magnesium ion-selective microelectrode (Mg 2+ ISME) employed to monitor Mg 2+ distributions over the surfaces. • SVET, LEIS, and SECM in potentiometric operation produced high spatial resolution images of reactive sites on the surfaces. • The surface chemistry, microstructure and electrochemical activity of the alloy with and without NSDL were correlated.

Electrochemical characterization of alloy segregation in the near-surface deformed layer of welded zones of an Al−Cu−Li alloy using scanning electrochemical microscopy

The development of heterogeneous electrochemical activity in the welded zones of aluminum alloy 2098-T351 by friction stir welding (FSW) associated with the formation of a near-surface deformed layer (NSDL) upon exposure to an aqueous chloride-containing solution was characterized using scanning electrochemical microscopy (SECM) in potentiometric operation. A solid-contact Mg2+ ion-selective microelectrode allowed in situ monitoring of the corrosion reactions sites for magnesium dissolution from different zones of the FSW weld upon exposure to a chloride-containing aqueous environment. In this way, localized corrosion reactions developing in the galvanically coupled joint/heat affected zones (WJ/HAZ) of the weld were detected and imaged with spatial resolution. The most active domains for local Mg2+ concentrations were associated with the HAZ of the retreating side (RS), and these corresponded to Mg oxidation from the Mg-enriched oxide bands in NSDL.

H2S in Horticultural Plants: Endogenous Detection by an Electrochemical Sensor, Emission by a Gas Detector, and Its Correlation with L-Cysteine Desulfhydrase (LCD) Activity.

H2S has acquired great attention in plant research because it has signaling functions under physiological and stress conditions. However, the direct detection of endogenous H2S and its potential emission is still a challenge in higher plants. In order to achieve a comparative analysis of the content of H2S among different plants with agronomical and nutritional interest including pepper fruits, broccoli, ginger, and different members of the genus Allium such as garlic, leek, Welsh and purple onion, the endogenous H2S and its emission was determined using an ion-selective microelectrode and a specific gas detector, respectively. The data show that endogenous H2S content range from pmol to μmol H2S · g−1 fresh weight whereas the H2S emission of fresh-cut vegetables was only detected in the different species of the genus Allium with a maximum of 9 ppm in garlic cloves. Additionally, the activity and isozymes of the L-cysteine desulfhydrase (LCD) were analyzed, which is one of the main enzymatic sources of H2S, where the different species of the genus Allium showed the highest activities. Using non-denaturing gel electrophoresis, the data indicated the presence of up to nine different LCD isozymes from one in ginger to four in onion, leek, and broccoli. In summary, the data indicate a correlation between higher LCD activity with the endogenous H2S content and its emission in the analyzed horticultural species. Furthermore, the high content of endogenous H2S in the Allium species supports the recognized benefits for human health, which are associated with its consumption.

Microelectrodes for measurement of intracellular [K+] and [Na+]in the choroid plexus epithelium and cerebrospinal fluid

The choroid plexus epithelium (CPE) has recently gained increasing interest as a potential target tissue to manipulating cerebrospinal fluid (CSF) production (1). It is therefore crucial to identify the basolateral Na+ transport mechanisms that are involved in CSF secretion, as it would be accessible from the blood side and thereby hold promise for pharmacological intervention. The sodium‐bicarbonate transporter Ncbe has been identified as a basolateral Na+ importer in the CPE (2,3). Currently, there is no direct intracellular cation measurements in choroid plexus and this information is needed to establish Ncbe as the main basolateral Na+ importer. The aim of this project is to measure the [Na+] and [K+] concentration in CSF and in CPE in vivo with double‐barreled microelectrodes. Ion selective double‐barreled microelectrodes are the tool to measure directly the different ion concentrations. The reference barreled was filled with 500 mM KCl solution and the tip of ion sensitive barrel was filled with Na+ or K+ionophore and then backfilled with KCl solution. In this ongoing project, we were able to estimate extracellular [K+] to 4.08 ± 1.06 mM in CSF of mice in vivo (n=7). The study is in progress.References1: Damkier HH, Brown PD, Praetorius J. Cerebrospinal fluid secretion by the choroid plexus. Physiol Rev. 2013;93:1847‐92.2: Praetorius J, Nejsum LN, Nielsen S. A SLC4A10 gene product maps selectively to the basolateral plasma membrane of choroid plexus epithelial cells. Am J Physiol Cell Physiol. 2004;286:C601‐10.3: Damkier HH, Nielsen S, Praetorius J. Molecular expression of SLC4‐derived Na+‐dependent anion transporters in selected human tissues. Am J Physiol Regul Integr Comp Physiol. 2007;293:R2136‐46.

Changes in Astroglial K+ upon Brief Periods of Energy Deprivation in the Mouse Neocortex.

Malfunction of astrocytic K+ regulation contributes to the breakdown of extracellular K+ homeostasis during ischemia and spreading depolarization events. Studying astroglial K+ changes is, however, hampered by a lack of suitable techniques. Here, we combined results from fluorescence imaging, ion-selective microelectrodes, and patch-clamp recordings in murine neocortical slices with the calculation of astrocytic [K+]. Brief chemical ischemia caused a reversible ATP reduction and a transient depolarization of astrocytes. Moreover, astrocytic [Na+] increased by 24 mM and extracellular [Na+] decreased. Extracellular [K+] increased, followed by an undershoot during recovery. Feeding these data into the Goldman–Hodgkin–Katz equation revealed a baseline astroglial [K+] of 146 mM, an initial K+ loss by 43 mM upon chemical ischemia, and a transient K+ overshoot of 16 mM during recovery. It also disclosed a biphasic mismatch in astrocytic Na+/K+ balance, which was initially ameliorated, but later aggravated by accompanying changes in pH and bicarbonate, respectively. Altogether, our study predicts a loss of K+ from astrocytes upon chemical ischemia followed by a net gain. The overshooting K+ uptake will promote low extracellular K+ during recovery, likely exerting a neuroprotective effect. The resulting late cation/anion imbalance requires additional efflux of cations and/or influx of anions, the latter eventually driving delayed astrocyte swelling.

Contributions of Microelectrochemical Scanning Techniques for the Efficient Detection of Localized Corrosion Processes at the Cut Edges of Polymer-Coated Galvanized Steel

Spatially resolved information on corrosion reactions operating at the cut edges of coated metals can be obtained using microelectrochemical scanning techniques using a suitable selection of operation modes and scanning probes. The scanning vibrating electrode technique (SVET) provides current density maps with a spatial resolution of the order of the dimensions of the sample, which allows the temporal evolution of the corrosion reactions to be followed over time. This leads to the identification and localization of cathodic and anodic sites, although the technique lacks chemical specificity for the unequivocal identification of the reactive species. The application of scanning electrochemical microscopy (SECM) was previously limited to image cathodic reaction sites, either due to oxygen consumption in the amperometric operation or by the alkalinisation of the electrolyte in potentiometric operation. However, it is shown that anodic sites can be effectively monitored using an ion-selective microelectrode (ISME) as a probe. The ISME probes detected differences in the local concentrations of Zn2+ and OH− ions from the cut edges of a complete coil coating system compared to the same system after the polymeric layers were removed. In this way, it has been shown that the inhibitor loading in the polymer layers effectively contributes to reducing the corrosion rates at the cut edge, thus helping to extend the useful life of the sacrificial galvanized layer bonded directly to the steel matrix. Additionally, these two probe configurations can be integrated into a multi-electrode tip for potentiometric operation to simultaneously monitor localized changes in pH values and metal ion dissolution in a single scan. Spatial and temporal distributions were further investigated using different rastering procedures, and the potential of constructing pseudomaps for 2D-imaging is described.

Development of an Al3+ ion-selective microelectrode for the potentiometric microelectrochemical monitoring of corrosion sites on 2098−T351 aluminum alloy surfaces

A novel potentiometric Al3+−ion selective microelectrode (ISME), with internal solid contact, based on the use of a neutral carrier morin as ionophore is reported. The ability of the ISME to image local ion concentration distributions was tested on aluminum alloy surfaces freely corroding in an aqueous solution containing chloride ions. The microelectrode was then used as the sensing tip for scanning electrochemical microscopy (SECM) in potentiometric operation to monitor the reactive sites associated with the dissolution of aluminum that developed in the 2098−T351 Al−Cu−Li alloy as a result of welding by the Friction Stir Welding (FSW) process. The ISME detected differences in the local concentrations of Al3+ species arising from the 2098−T351 Al−Cu−Li alloy (base material) and from the coupled weld joint/heat affected zones (WJ/HAZ) of the alloy produced by the FSW process. More active domains for Al3+ dissolution were found in the HAZ regions coupled to WJ, more specially in the HAZ of the advancing side (AS). These results demonstrate that the Al3+−ISME presented in this work can be used to monitor corrosion sites on aluminum alloys surfaces with combined chemical and spatial resolution.

Ion Selective Electrode Mediated by Transfer Layer of Graphene Oxide for Detection of Ca2+ with Highly Sensitivity and Selectivity

A Ca2+ selective microelectrode was proposed through electrodepositing graphene oxide (GO) on carbon fiber as an efficient ion-electron transfer layer. The gold leaves were further synthesized at GO surface to increase the specific surface area, and provide a substrate for assembly of the specific ligands for Ca2+. GO with negatively charges greatly facilitated the electron transfer process from the recognition center to electrode surface, resulting in the apparently enhanced sensitivity towards Ca2+. Moreover, the developed ion-selective microelectrode exhibited good selectivity to Ca2+, and a good linear range from 10 μM to 10 mM with a detection limit of 5.91 ± 0.46 μM.

In vivo monitoring of calcium ions in rat cerebrospinal fluid using an all-solid-state acupuncture needle based potentiometric microelectrode

Acupuncture needles are regarded as ideal materiel for the development of microelectrodes for in vivo sensing. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating a calcium ion-selective membrane on an acupuncture needle tip with a diameter of less than 80 μm, which is modified with poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) as solid contact. The proposed Ca2+-ISμE shows a Nernstian response toward Ca2+ in the range from 1.0 × 10−6 to 3.1 × 10−3 M with a slope of 30.8 ± 0.9 mV/decade (R2 = 0.999), and the detection limit is 1.2 × 10−7 M. The Ca2+-ISμE has been used for in vivo monitoring of the calcium changes in rat cerebrospinal fluid (CSF) under the injury of spinal cord transection. The results demonstrate that the calcium concentration in CSF increases sharply from the normal level of 20.6 ± 1.72 μM (n = 3) to 133.2 ± 7.63 μM (n = 3) with a severe fluctuation after spinal cord damage. Thus, the proposed Ca2+-ISμE is available for in vivo monitoring of calcium ions with high temporal resolution and flexibility. The detection system can be extended to measure other ions in CSF by changing different ion-selective membranes.

Studying the Activity of Neuropeptides and Other Regulators of the Excretory System in the Adult Mosquito.

Studies of insect physiology, particularly in those species that are vectors of pathogens causing disease in humans and other vertebrates, provide the foundation to develop novel strategies for pest control. Here, a series of methods are described that are routinely utilized to determine the functional roles of neuropeptides and other neuronal factors (i.e., biogenic amines) on the excretory system of the mosquito, Aedes aegypti. The Malpighian tubules (MTs), responsible for primary urine formation, can continue functioning for hours when removed from the mosquito, allowing for fluid secretion measurements following hormone treatments. As such, the Ramsay assay is a useful technique to measure secretion rates from isolated MTs. Ion-selective microelectrodes (ISME) can sequentially be used to measure ion concentrations (i.e., Na+ and K+) in the secreted fluid. This assay allows for the measurement of several MTs at a given time, determining the effects of various hormones and drugs. The Scanning Ion-selective Electrode Technique uses ISME to measure voltage representative of ionic activity in the unstirred layer adjacent to the surface of ion transporting organs to determine transepithelial transport of ions in near real time. This method can be used to understand the role of hormones and other regulators on ion absorption or secretion across epithelia. Hindgut contraction assays are also a useful tool to characterize myoactive neuropeptides, that may enhance or reduce the ability of this organ to remove excess fluid and waste. Collectively, these methods provide insight into how the excretory system is regulated in adult mosquitoes. This is important because functional coordination of the excretory organs is crucial in overcoming challenges such as desiccation stress after eclosion and before finding a suitable vertebrate host to obtain a bloodmeal.