Ag-AgCl Electrodes Research Articles

Changes in T-wave amplitude in patients with peripheral edema: implications for patients with congestive heart failure and assessment of the T-wave alternans

developed biopotential fiber sensors (BFSs) will reduce the noise artifacts and thus result in a better ST-segment measurement sensitivity. Methods: We recorded 12-lead ECGs simultaneously from wet gel electrodes and from low-mass, nonmetallic BFS assemblies in routine stress testing of the obese patients. The stress test ECG signals were recorded using the X-Scribe II system and a hi-resolution H-12 Holter, both from Mortara Instruments. In each ECG comprising preexercise, peakexercise, and postexercise phases, we have computed mean sinus rhythm cycles then synchronized them with the raw signal and subtracted. The resulting “residue” (noise) was quantified by computing its SD and rootmean-square of successive differences in each signal. We then computed ST levels and J-ST delays in both ECGs for individual beats and on all 12 mean complexes. We evaluated the results using graphic trends of the computer-generated ST measurements and histograms of the differences between the BFS data–generated ST values and the Ag-AgCl electrode data ST values. Two performance measures, the ST measurement sensitivity and the ST measurement positive predictivity, were used to quantify the performance results of the comparison study. This technique allows for accurate evaluation and quantification of the impact of noise on the performance of the ST measurements in both data sets. Results and conclusions: The root-mean-square of successive differences residuum values were significantly lower with the BFS sensors (16.62 ± 2.71 μV) than with the Ag-AgCl electrodes connected to patient cables (37.47 ± 11.69 μV, P b .001 and P b .002). The ST measurement sensitivity and ST measurement positive predictivity were significantly higher for the BFS signals: 75% vs 52% and 64% vs 46, respectively, for Ag-AgCl electrode signals. We conclude that ECGs from BFS were less noisy than from AgAgCl electrodes, resulting in higher ST-segment measurement sensitivity.

Altered ventricular stretch contributes to initiation of cardiac memory

Cardiac memory is a change in T-wave morphology induced by ventricular pacing or arrhythmias that persist after resumption of normal AV conduction. Changing the pacemaker site from atrium to ventricle alters ventricular activation and the mechanical pattern of ventricular contraction. Either or both alterations affect T-wave configuration. The purpose of this study was to study the role of altered contractile patterns on initiation of cardiac memory. Isolated rabbit hearts were immersed in Tyrode's solution (37 degrees C) and aortically perfused at a constant pressure of 70 mmHg. Three orthogonal quasi-ECG leads were recorded via six Ag-AgCl electrodes located on the walls of the bath. Hearts were paced at a constant cycle length from either the right atrial appendage or left ventricle lateral wall. The pulmonary artery was sealed, and both ventricles contracted isovolumetrically. Cardiac memory was quantified as T-wave vector displacement expressed as distance between T-wave vector peaks during atrial pacing before and after ventricular pacing. Five minutes of ventricular pacing induced significant T-wave vector displacement that returned to control in 5 to 10 minutes. No significant changes in intraventricular pressure occurred during and after ventricular pacing. Interventions that decreased ventricular load (shunting both ventricles to the bath) or contractility (excitation-contraction uncoupler blebbistatin) significantly decreased developed pressure and eliminated T-wave vector displacement. Neither intervention affected ventricular activation during ventricular pacing. Locally applied left ventricular epicardial stretch induced T-wave vector displacement similar to that induced by ventricular pacing. Altered ventricular activation during ventricular pacing initiates cardiac memory via induction of altered contractile patterns and altered stretch.

Use of electrochemical impedance spectroscopy to evaluate resin‐dentin bonds

Electrochemical impedance spectroscopy (EIS) offers a potentially nondestructive quantitative method for measuring the stability of resin films and or resin-bonded dentin over time. The purpose of this study was to measure the electrical impedance of five experimental dental adhesives of increasing hydrophicities as 30-microm films and as resin-bonded coatings on acid-etched dentin. Resin films or resin-coated dentin disks were placed in U-shaped chambers containing pairs of Ag-AgCl electrodes in 0.1M KCl. Electrical impedance spectra were run at day 0, 1, 7, 14, and 21 days. All resin films and resin-bonded dentin showed increases in capacitance during the first day of storage in electrolyte. This was usually associated with an increase in the pore resistance of the resins. Generally, resin-bonded dentin gave lower impedance values than their respective resins (resins 1-4) but solvated resin 5 bonded to water-saturated dentin gave higher capacitance and impedance values than resin 5 films. However, solvated resin 5 films gave higher impedance values than resin 5-bonded dentin. This behavior was confirmed by TEM examinations of silver uptake into films of neat resin 5 vs. ethanol-solvated resin 5, where water tree-like structures seen in the former were not seen in the latter. EIS is useful in examining changes in the capacitance and electrical impedance of very hydrophilic, ionic methacrylate resins. Its utility in detecting degradation in resin-bonded dentin interfaces remains to be determined in longer term studies.

Electrode Potentials of a Silver-Silver Chloride Electrode vs. Temperature for Biosensors

The aim of this study is to make clear the effect of temperature on the potentials of silver-silver chloride(Ag-AgCl) electrodes in potassium chloride(KCl) and sodium chloride(NaCl) solutions for micro biosensor applications. Non-isothermal coefficients, or thermal coefficient of Ag-AgCl electrodes in the concentrations of 0.1 to 1.0[mol/kg] were experimentally measured in the range of 15 to 45[°C]. The electrode was prepared by electrolytical process in KCl or NaCl solutions. The length and diameter of the electrode are 20[mm] and 3[mm], respectively. The coefficients in KCl solutions were 0.42[mV/°C] in 0.1[mol/kg] and 0.26[mV/°C] in 1.0[mol/kg] and almost the same in NaCl solutions. Isothermal coefficients were also measured. Although the coefficients must theoretically be zero by definition for all temperatures, the difference of potentials between a pair of electrodes which is called as offset voltage appears practically. They were 3∼4[μV/°C] in 0.1[mol/kg] and 0.3[μV/°C] in 1[mol/kg] at the steady state of temperature. The values were depending on the degree of the uniformity of electrode surface.

A Novel Dry Active Electrode for EEG Recording

The design and testing of a "dry" active electrode for electroencephalographic recording is described. A comparative study between the EEG signals recorded in human volunteers simultaneously with the classical Ag-AgCl and "dry" active electrodes was carried out and the reported preliminary results are consistent with a better performance of these devices over the conventional Ag-AgCl electrodes.

ECG measurement on a chair without conductive contact

For the purpose of long-term, everyday electrocardiogram (ECG) monitoring, we present a convenient method of ECG measurement without direct conductive contact with the skin while subjects sat on a chair wearing normal clothes. Measurements were made using electrodes attached to the back of a chair, high-input-impedance amplifiers mounted on the electrodes, and a large ground-plane placed on the chair seat. ECGs were obtained by the presented method for several types of clothing and compared to ECGs obtained from conventional measurement using Ag-AgCl electrodes. Motion artifacts caused by usual desk works were investigated. This study shows the feasibility of the method for long-term, convenient, everyday use.

Evaluation of the effect of water-uptake on the impedance of dental resins

Electrical impedance spectroscopy (EIS) offers a quantitative method of measuring the stability of resin films in aqueous solution over time. Purpose The purpose of this study was to measure the EIS of five experimental dental adhesive films (ca. 17 μm thick) of increasing hydrophilicity (ranked by their Hoy's solubility parameters), and how much these values change over 3 weeks in aqueous buffer. Methods The resin films were placed in a U-shaped chamber and a pair of Ag–AgCl electrodes was used for EIS. The EIS results were confirmed by immersing the films in 50% AgNO 3 for 24 h to trace the distribution of any water absorption into the resins by TEM observations. Results The resistance ( R r) of the resins 1–4 films increased most during the first day, and varied from 1×10 11 ohm for resin 1, to 40 Ω for resin 5 at day 1. The day 1 R r values of resins 1–4 were inversely proportional to their Hoy's solubility parameter for hydrogen bonding forces. Electrical impedance values of resins 1–3 and 5 varied widely but were relatively constant over time, while those of resin 4 decreased more than 99% from day 1 to 21 ( p < 0.05 ). Capacitance ( C r) of films of resins 1–4 all increased over the first day and then were relatively unchanged over the 20 days (except for resin 4 that continued to increase) and were between 0.01 and 1 nF. Silver uptake by TEM revealed the development of water-filled branching structures that formed in resins 4 and 5 over time.

Spatially Controlled Microfluidics Using Low-Voltage Electrokinetics

Most electrokinetic microfluidic devices currently require high voltages (>50 V) to generate sustained electric fields. However, two long-standing limitations remain, namely: (i) the resulting electrolysis of water produces bubbles, forcing electrodes to be placed in reservoirs outside the channels, and (ii) direct integration with low-voltage microelectronics cannot be achieved. A further limitation is the lack of spatial control within the microchannel. This work presents a method to achieve low-voltage (/spl les/1 V) electrokinetic transport using micropatterned Ag-AgCl electrode arrays, which allows spatial flow control within microchannels. We demonstrate bidirectional electrophoretic control of microparticles within microfluidic channels using /spl plusmn/1 V.

Analysis of Root Growth by Impedance Spectroscopy (EIS)

Electrical impedance spectroscopy (EIS) is investigated as a non-destructive method for monitoring root growth of tomato. This paper aims to (i) review the basic principles of EIS applied to the characterisation of the different parts of the soil–root–stem-electrode continuum, (ii) experiment the validity of the relationship between root weight and root capacitance taking into account the influence of the soil and plant electrodes position, (iii) describe an EIS analysis of the root growth of tomato plants. All experiments were carried out in 50 dm 3 containers either in hydroponics at 930 lS for the test of root fresh or dry weight and root capacitance relationships, or in a potting mix (oxisol) for electrode placement tests and EIS estimation of root growth. Electrical measurements of the soil–root–stem-electrode continuum were done with a twoelectrode measuring system using unpolarisable Ag–AgCl electrodes. A ‘root cutting’ and a ‘progressively immersed root system’ experiments were carried out in order to validate the relationship between root capacitance and root mass at 1 kHz. The effects of soil electrode and plant electrode placement were also tested, pointing out the sensitivity of the method to the insertion height of the ‘‘plant electrode’’ into the stem. For the root growth experiment, Impedance Spectra (IS) measurements were made just before harvesting the roots for dry weight and length determination. Measurements were made 14, 22, 26 and 39 days after planting, until flowering. The IS of the soil–root–stem-electrode continuum was modelled by a lumped electric circuit consisting of a series resistor R0 for the soil and of four parallel resistance (Ri)capacitance (Ci) circuits for the other components of the circuit. The model had nine parameters whose values were estimated by Complex Nonlinear Least Squares curve fitting. A stepwise ascendant regression was used to identify the electrical parameters that better correlated with root dry mass or length increment: C3 and C4 were well correlated with root dry mass with a r 2 of 0.975, whereas root length was explained by the combination of 1/R3, C3 ,1 / R2 and 1/R1 with a r 2 of 0.986. This work may be considered as a new methodological contribution to the understanding of root electrical properties in the non-destructive diagnosis of root systems.

Microanalysis system for pO/sub 2/, pCO/sub 2/, and pH constructed with stacked modules

A miniaturized analysis system for online monitoring of pO/sub 2/, pCO/sub 2/, and pH was constructed by stacking a reference electrode module, a sensing module, and a sampling module. The liquid-junction reference electrode module used durable thin-film Ag-AgCl electrodes with pinholes to use an internal solution saturated with KCl. A Clark-type pO/sub 2/ sensor, a Severinghaus-type pCO/sub 2/ sensor, and an indicator electrode for a pH sensor were integrated on a sensing module. The sampling module used reversible growth or shrinkage of a hydrogen bubble on a platinum black working electrode. The volume change of the gas was converted to the movement of the solution in a flow channel reproducibly by a silicone rubber diaphragm. An external solution could be introduced into the system successfully by the sampling mechanism. Clear responses were observed with the three sensors upon sampling of standard solutions. Calibration plots were linear in clinically important ranges for the respective analytes.

Recurrent spreading depression (SD) causes early opening of the blood-brain barrier (BBB)

SD is a depolarization wave propagating at a rate of about 3 mm/min in the cerebral cortex. It is characterized by an amplitude reduction of the electrocorticographic activity, a rise of the extracellular potassium to 60 mM and a reduction of the extracellular volume. Typical changes of cerebral blood flow (CBF) accompany SD, which consist of a short lasting spreading hyperemia followed by a long lasting spreading oligemia. SD is triggered by electrical, mechanical or toxic factors and is probably involved in the pathogenesis of migraine, focal ischemia, head trauma and cerebral hemorrhage. SD is assumed to be the pathophysiological correlate of the migraine aura. We have recently observed a patient with familial hemiplegic migraine (FHM) type II and a long-lasting migraine aura with fluctuating neurological symptoms. Quantitative analysis of early gadolinium-enhanced MR images revealed a left-hemispheric, cortical blood brain-barrier (BBB) disruption preceding delayed cortical edema in this ATP1A2 mutation carrier. As we know from the work by Strong et al. repetitive SDs can occur in the human brain tissue, which could explain the fluctuating symptoms in our FHM patient. Additionally, a recent publication by Gursoy-Ozdemir et al. showed a delayed enhancement of BBB permeability and subsequent cortical oedema following a single SD. Based on these observations, we studied here whether recurrent SD causes early BBB disruption in the rat cortex in vivo. We triggered SD with artificial cerebrospinal fluid (ACSF) containing a potassium concentration ([K+]ACSF) of 130 mM at an open parietal cranial window. SDs were monitored with an intracortical potassium sensitive microelectrode and laser-Doppler flowmetry. We also recorded the propagation of SDs to a distant closed frontal cranial window using an epidural Ag-AgCl electrode. BBB integrity was evaluated quantitatively by analyzing fluorescence in brain sections following the peripheral injection of Evan's Blue or Lucifer yellow. At the occipital window, [K+]ACSF evoked several SDs in all animals. In the first group (n = 10), one or more SDs propagated to the frontal window. In contrast, in the second group (n = 9), pretreatment with MK-801 (5 mg/kg BW i.v.), abolished SD propagation. Within two hours after the onset of the first SD, significantly enhanced fluorescence intensity at the frontal cortex was only measured in animals from group 1 with multiple propagated SDs. In conclusion, we provide evidence that repetitive SDs significantly increase blood-brain barrier permeability within two hours after the onset.

Sympathetic skin response recorded from the genital region in normal and diabetic women

Aim of the study. – An electrophysiological technique assessing the sympathetic skin activity related to sudomotor function from the genital skin has been described previously in normal adult man. The problems of the genitourinary tracts and the sexual disorders are difficult to analyse in women. In this paper, a method for recording the genital sympathetic skin responses (g-SSR) has been described in normal women and the objective changes were demonstrated in female patients with diabetes mellitus. Material and method. – Our study comprised 20 healthy adult women (mean age 42.5 years) and 20 diabetic women (mean age 52.8 years). We examined both left hand sympathetic skin responses (SSR) and genital region SSR by electrophysiological methods. Superficial Ag–AgCl electrodes were placed on perineum in front of the anal sphincter and 1–1.5 cm lateral to right labia majora for recording after the stimulation of the right median nerve. All g-SSRs from both recording sites were analysed, latency and amplitudes were compared in normal subjects and patients. Results. – It has been clearly demonstrated that the g-SSR is easily obtained from all normal female subjects in labia majora-perineum montage. In seven of 20 diabetic patients g-SSR could not be elicited. Mean amplitude was significantly reduced in diabetic group according to normal subjects ( P < 0.05). Conclusion. – It was concluded that the method described in this study is easily applied and objectively evaluated for the female patients with genitourinary and sexual problems.

Study of thermodynamic properties of quaternary mixture RbCl + Rb 2SO 4 + CH 3OH + H 2O by EMF measurement at 298.15 K

The electromotive force (EMF) measurements of the cell: Rb-ion selective electrode (ISE)/RbCl ( m A), Rb 2SO 4 ( m B), CH 3OH ( X), H 2O (1 − X)/Ag AgCl with X = 10 wt.% on the quaternary system RbCl + Rb 2SO 4 + CH 3OH + H 2O were carried out at 298.15 K and over total ionic strengths from 0.0050 mol kg −1 up to near saturated concentration 2.5000 mol kg −1. The Rb-ISE and Ag AgCl electrodes used in this work were prepared in our laboratory and exhibited reasonably good Nernst response. The activity coefficients of RbCl in the mixture were directly determined. The experimental data were analyzed by using the Harned rule and Pitzer ion interaction model, and the corresponding model parameters required in the two equations for this system have been evaluated. It was found that the experimental results obey the Harned rule and the Pitzer model can be used to describe the system satisfactorily. The activity coefficients of Rb 2SO 4, the osmotic coefficients of the mixtures and the excess Gibbs free energy were also calculated.

New method using multi-regression analysis on evoked electromyography during movement to adjust stimulation conditions.

A new method of stimulation of the lower extremities was devised that automatically adjusts the stimulation conditions at any angle of the knee joint. An M-wave is considered to indicate the stimulation conditions, because it is the waveform that results from direct stimulation to the axon of the alpha motor neuron. The present device adjusted the stimulation intensity, using multi-regression analysis to evoke an M-wave of preset amplitude. Participants included five people without any neuromuscular impairment. The subjects sat on a chair during the test. The hip joint was fixed at a flexion angle of 90 degrees, and the ankle joint was fixed at the midposition. During passive knee joint movement ranging from 0 degrees to 135 degrees, M-waves were measured. Electrodes were attached at the popliteal fossa and the patella to stimulate the tibial nerve. Ag-AgCl electrodes were put on the belly of the right soleus muscle for the M-wave measurement. The device was set to give M-waves close to the preset value, 10% Mmax. According to previous research, the allowable limit of M-wave amplitude deviations was reported to be about 5% Mmax. The M-wave amplitudes evoked by the device were in the allowable range (9.2 +/- 2.5% Mmax). The device enabled control of the M-wave amplitude over the entire range of motion of the joint. Using this device, it was possible to examine the excitability of the alpha motor neuron pool more precisely.

Determination of thermodynamic properties of aqueous mixtures of RbCl and Rb 2SO 4 by the EMF method at T=298.15 K

The thermodynamic properties, including activity coefficients, osmotic coefficients and excess Gibbs free energy for RbCl and Rb 2SO 4 aqueous mixtures at T=298.15 K and in 0.01 mol · kg −1 to 5 mol · kg −1 ionic strength, were determined by emf measurements. The Rb–ISE and Ag–AgCl electrodes used in this work were prepared in our laboratory and had a reasonably good Nernst response. The experimental data were fitted by using the Harned rule and Pitzer model. The Harned coefficients and the Pitzer binary and ternary interaction parameters for the system have been evaluated. The experimental results obey the Harned rule. The Pitzer model can be used to describe this aqueous system satisfactorily.

Investigation into the origin of the noise of surface electrodes.

In the recording of biomedical signals, a significant noise component is introduced by the electrode. The magnitude of this noise is considerably higher than the equivalent thermal noise from the electrode impedance. As the noise in surface electrodes limits the resolution of biopotential recordings, it is important to understand its origin. It was found that the noise mainly originates in the electrolyte-skin interface and that it is highly dependent on the electrode gel used and the skin properties of the test subject. Depending on skin treatment, magnitudes between 1 and 20 microVrms were measured among subjects. When the metal-electrolyte interface was allowed time to stabilise, electrodes of different metals measured face to face all showed a negligibly small noise magnitude (< 1 microVrms). In pre-gelled electrodes, where the metal-electrolyte interface has stabilised, no difference in noise properties was found between Ag-AgCl electrodes and other metals when measured on the skin. In subjects at rest, the contribution of EMG signals to the total noise level was shown to be negligibly small compared with the noise contribution of the electrolyte-skin interface. The magnitude of the noise of electrodes appeared to be inversely proportional to the square root of the area of the electrode on the skin.

Quantification of topically delivered 5-aminolevulinic acid by lontophoresis across ex vivo human stratum corneum.

Iontophoretic transport of the prodrug 5-aminolevulinic acid (ALA), which is used for photodynamic therapy (PDT), across human stratum corneum (SC) was studied quantitatively in vitro. The experiments were carried out in a three-compartment iontophoresis cell consisting of two electrode chambers equipped with Ag-AgCl electrodes, each separated from a central acceptor chamber by a sheet of SC, supported by a dialysis membrane, to mimic the side-by-side configuration normally used in vivo. Acceptor fluid samples were collected every hour for a period of 30 h in a fraction collector and analyzed by high-performance liquid chromatography-fluorometry after derivatization of the ALA. The iontophoretic ALA flux was studied as a function of the applied current density and the ALA concentration in the donor solution (1, 2.5 or 10% ALA). Depending on the ALA concentration in the donor cell, iontophoresis enhances the flux from close to the detection limit of 0.23 nmol cm(-2) h(-1) at zero current density (passive diffusion) to several hundred or thousand nanomoles per square centimeter per hour at current densities ranging from 100 to 1000 microA cm(-2). For example, interpolating our data we find that with an ALA concentration of 2% in the donor chamber, a current density of 0.255 mA cm(-2) transports 0.065 micromol cm(-2) ALA across the SC in 10 min (conditions of Rhodes et al. (1997), J. Invest. Dermatol. 108, 87-91). For passive diffusion we find that a 5 h topical application of 20% ALA results in the transport of 0.05 micromol cm(-2). Thus, the amount of ALA that passively diffuses through the SC in several hours, leading to therapeutic levels of protoporphyrin IX (PpIX) in the epidermis, can be delivered by iontophoresis in 10 min or less. However, because the formation of sufficient PpIX also requires several hours and also because the SC overlying skin lesions such as basal cell carcinoma (BCC) is not intact, the clinical benefit of topical ALA delivery by iontophoresis for PDT of BCC is yet to be established.

電流刺激による皮膚受容感覚の安定化のための絶対しきい値と皮膚インピーダンスの関連性の検討

This study focused on stabilizing the sensations elicited by electrical stimulation applied to the skin through surface electrodes, a technique widely used in sensory feedback research. The relationship between absolute threshold (the minimum stimulus amplitude that causes sensation) and the parameters of an electrical equivalent circuit for skin impedance was examined with neurologically intact subjects. Electric current pulse stimulation at 100 Hz frequency and pulse widths between 0.08 and 0.5 ms was used to elicit a cutaneous sensation. The electrical equivalent circuit for skin impedance consisted of resistance Rp and capacitance Cp connected in parallel, plus resistance Rs connected in series to both.First, we estimated the parameters of the equivalent circuit by the skin impedance measured with sinusoidal signals (Rps and Cps), and we examined their relevance to the absolute threshold. For Ag-AgCl electrodes used with electroconductive paste, variations over time of the frequency characteristics of Rps and Cps were found to be similar to the changes caused by repeatedly stripping the skin. Values of Cps and Rps at 10 Hz were found to relate to the absolute threshold with high correlation coefficients. For a solid-gel Ag-AgCl electrode, changes of absolute threshold, Rps and Cps caused by increasing size of the solid-gel electrode were similar to variations over time obtained using electrodes with electroconductive paste. Correlations between the threshold and values of Rps and Cps at 10 Hz were also observed.Next, we estimated the parameters of the equivalent circuit by measuring stimulus pulse current and voltage waves of square-wave stimulus pulses using solid-gel electrodes (Rps and Cpr). We then examined their relevance to the absolute threshold. The absolute threshold increased with repeated electrical stimulation to the skin and decreased after adequate rest with no electrical stimulation. The value of Rpr decreased with repeated electrical stimulation and increased after rest, while the value of Cpr did not change. These variations became minor after preparation of the skin for removing the stratum corneum. A significant correlation between Rpr and the absolute threshold was observed. These results show that electrical stimulation to the stratum corneum affects both absolute threshold and skin impedance; they also indicate that real-time evaluation is important for stabilizing cutaneous sensation elicited by electrical stimulation.The relevance of Rp to the threshold was shown in both methods that were used to estimate the parameters. Possible reasons for decreasing Rp were an increase of ionic conductivity due to osmosis of electroconductive paste into the stratum corneum or an increase of electric charge in the stratum corneum due to charge transfer by electrical stimulation through the skin. The increase of the threshold amplitude was considered to be the result of broadened current path due to increases of ionic or electric conductivities in the stratum corneum. It is necessary to clarify the mechanism of the relationship between the threshold and impedance parameters in order to develop a technique for stabilizing electrocutaneous sensation.

Solid-state hydrogen sensor based on acid-doped polybenzimidazole

A solid-state potentiometric hydrogen sensor for hydrogen determination in air is described. The device incorporates a protonic polymer electrolyte based on polybenzimidazole, an E-TEK gas diffusion electrode as sensing electrode and an Ag-AgCl electrode as reference electrode. The sensing mechanism of E-TEK can be explained by the mixed potential model. The stability of the reference system is demonstrated. The reference system is assumed to operate properly because of the existence of a thin hydrated layer containing chlorine ions. The sensor performances are reported.

Microsensor based on NASICON for the analysis of Na + in the gingival fluid

A miniaturized electrochemical sensor for in vivo determination of Na + in the gingival fluid is described. The device includes a NASICON type ceramic as the ion-sensitive membrane and a polyethylene-oxide-based polymer as the internal reference system. The device was successfully used for the direct determination of Na + activity in gingival fluid. The response time was as short as 10 s. Measurements were performed with an external miniaturized calomel electrode located in the vestibular cavity. Some tests were also performed with an integrated Ag–AgCl electrode. The recordings clearly demonstrate that such a Na + probe can be used to make in vivo diagnosis.