High-resolution high-voltage sensor based on SAW

A surface acoustic wave (SAW)-based high-voltage sensor is described. The sensor consists of a SAW oscillator fabricated on a 10 mm × 10 mm 128° rotated Y-cut, X-propagating LiNbO₃ substrate. The voltage is applied to electrodes on the substrate, and the resulting electric field changes the propagation time of the SAW. The propagation time is directly related to the output frequency of the SAW oscillator. The high-voltage sensor offers a small-sized high-voltage measurement device with several attractive features: a high resolution (better than 0.2 V up to 2.4 kV, better than 0.4 V for higher voltages), a large range (−10 to +10 kV), a high input impedance (> 10¹³ ω) and a low input capacitance (< 10 pF). The sensitivity amounts to 16 Hz V⁻¹.     

Simulation and fabrication of piezoresistive membrane type MEMS strain sensors

Two piezoresistive (n-polysilicon) strain sensors on a thin Si₃N₄/SiO₂ membrane with improved sensitivity were successfully fabricated by using MEMS technology. The primary difference between the two designs was the number of strips of the polysilicon patterns. For each design, a doped n-polysilicon sensing element was patterned over a thin 3 μm Si₃N₄/SiO₂ membrane. A 1000×1000 μm² window in the silicon wafer was etched to free the thin membrane from the silicon wafer. The intent of this design was to fabricate a flexible MEMS strain sensor similar in function to a commercial metal foil strain gage. A finite element model of this geometry indicates that strains in the membrane will be higher than strains in the surrounding silicon. The values of nominal resistance of the single strip sensor and the multi-strip sensor were 4.6 and 8.6 kΩ, respectively. To evaluate thermal stability and sensing characteristics, the temperature coefficient of resistance [TCR=(ΔR/R₀)/ΔT] and the gage factor [GF=(ΔR/R₀)/] for each design were evaluated. The sensors were heated on a hot plate to measure the TCR. The sensors were embedded in a vinyl ester epoxy plate to determine the sensor sensitivity. The TCR was 7.5×10⁻⁴ and 9.5×10⁻⁴/°C for the single strip and the multi-strip pattern sensors. The gage factor was as high as 15 (bending) and 13 (tension) for the single strip sensor, and 4 (bending) and 21 (tension) for the multi-strip sensor. The sensitivity of these MEMS sensors is much higher than the sensitivity of commercial metal foil strain gages and strain gage alloys.     

Pyroelectric thin-film sensor array

Pyroelectric thin-film point detectors and 1 × 12 arrays have been fabricated and characterized. They consist of sol-gel-deposited PZT thin-film elements on micromachined Si₃N₄/SiO₂ membranes. The measured current and voltage response as a function of modulation frequency of a 1 × 12 array element is compared with finite-element calculations. Voltage responsivities of almost 3000 V W⁻¹ in vacuum and 800 V W⁻¹ in air have been achieved for 0.4 mm × 0.9 mm elements. Some point detectors have been completely packaged and correct operation in a movement detection system has been demonstrated.     

Development of a highly sensitive and selective optical chemical sensor for batch and flow-through determination of mercury ion

A very sensitive, highly selective and reversible optical chemical sensor (optode) for mercury ion is described. The sensor is based on the interaction of Hg²⁺ with 2-mercapto-2-thiazoline (MTZ) in plasticized PVC membrane incorporating a proton-selective chromoionophore (ETH5294) and lipophilic anionic sites (sodium tetraphenylborate, NaTPB). The membranes were cast onto glass substrates and used for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The sensor could be used in the range 2.0 × 10⁻¹⁰ to 1.5 × 10⁻⁵ M (0.04 ng mL⁻¹ to 3 μg mL⁻¹) Hg²⁺ with a detection limit of 5.0 × 10⁻¹¹ M and a response time of <40 s. It can be easily and completely regenerated by dilute nitric acid solution. The sensor has been incorporated into a home-made flow-through cell for determination of mercury ion in flowing streams with improved sensitivity, precision and detection limit. The sensor showed excellent selectivity for Hg²⁺ with respect to several common alkali, alkaline earth and transition metal ions. The results obtained for the determination of mercury ion in river water samples using the proposed optode was found to be comparable with the well-established cold-vapor atomic absorption method.     

Construction of a highly selective PVC-based membrane sensor for Ce(III) ions

A highly Ce(III) ion-selective poly vinyl chloride (PVC) membrane sensor based on N′-[(2-hydroxyphenyl)methylidene]-2-furohydrazide (NHMF) as an excellent sensing material is successfully developed. The electrode shows a good selectivity for Ce(III) ions with respect to most common cations including alkali, alkaline earth, transition and heavy metal ions. The proposed sensor exhibits a wide linear response with a slope of 19.4 ± 0.3 mV/decade over the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, and a detection limit of 7.6 × 10⁻⁶ M of Ce(III) ions. The sensor response is independent of pH in the range of 3.5–10.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of Ce(III) ions with EDTA and C₂O₄². It was also successfully applied in the determination of cerium ions in aqueous samples.     

Manganese(II)-selective PVC membrane electrode based on a pentaazamacrocyclic manganese complex

Manganese(II) complex of 14,16-dimethyl-1,4,7,10,13-pentaazacyclohexadeca-13,16-diene [Me₂(16)dieneN₅] (I) was synthesized and used in the fabrication of Mn²⁺-selective ISE membrane in PVC matrix. The membrane having Mn(II) macrocyclic complex as electroactive material along with sodium tetraphenylborate (NaTPB) as anion discriminator and dioctylphthalate (DOP) as plasticizer in poly(vinylchloride) (PVC) matrix was prepared for the determination of Mn²⁺. The best performance was observed by the membrane having Mn(II) complex–PVC–NaTPB–DOP in the ratio 1:5:1:3. The sensor worked well over a concentration range of 1.25 × 10⁻⁵ to 1.0 × 10⁻¹ M between pH 3.0 and 8.0 and had a fast response time of 20 s with a lifetime of 4 months. Their performance in partially non-aqueous medium was found satisfactory up to 30% (v/v) alcoholic content. Electrodes exhibited excellent selectivity for Mn²⁺ ion over other mono-, di-, trivalent cations. It can also be used as indicator electrode in the potentiometric titration of Mn²⁺ against EDTA.     

A novel potentiometric membrane sensor for determination of Co based on 5-amino-3-methylisothiazole

A new poly(vinylchloride) (PVC) membrane electrode for trace level determination of Co²⁺ ions has been developed based on 5-amino-3-methylisothiazole as an ionophore, o-nitrophenyloctylether as a plasticizer and oleic acid (OA) as a good lipophilic additive. The electrode exhibits a Nernstian slope of 29.5 ± 0.2 mV/decade in a linear range of 1.0 × 10⁻¹ to 6.3 × 10⁻⁷ M for Co²⁺ ions. The detection limit of this electrode is 3.9 × 10⁻⁷ M. It has a fast response time of 12 s and can be used for a period of 4 months without any divergence in potentials. The proposed electrode reveals a good selectivity for Co (II) over a wide variety of other tested cations and could be used in the pH range 3.3–9.0. The electrode was successfully applied as an indicator electrode for the potentiometric titration of cobalt ions with EDTA as well as for the direct determination of Co (II) in real samples.     

Fabrication of a highly selective Eu(III) membrane sensor based on a new S–N hexadentates Schiff''s base

A novel potentiometric membrane Eu (III) ion sensor is described based on a new S–N hexadentates Schiff's base, bis(thiophenol)butane2,3-dihydrazone (SNSB). The sensor exhibited a Nernstian response over a concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻² M, with a detection limit of 5.0 × 10⁻⁶ M. The best performance was achieved with a membrane composition of 30% PVC, 63% o-nitrophenyloctyl ether (NPOE), 5% SNSB, and 5% (0.010 mmol) potassium tetrakis(p-chlorophenyl) borate (KTpClPB). It was found that in the pH range of 3.0–8.5, the potential response of the sensor was not affected by the pH. Furthermore, the electrode presented satisfactory reproducibility, very fast response time (<5 s), and relatively good discriminating ability for Eu(III) ions with respect to many common cations and lanthanide ions, including sodium, potassium, magnesium, calcium, copper, nickel, cobalt, zinc, lead, lanthanum, cerium, gadolinium, samarium, ytterbium, presidium, terbium, neodymium, holmium, erbium, thulium, lutetium, dysprosium, iron and chromium metal ions. The sensor was applied to the determination of fluoride ions in two mouth wash preparations and binary mixtures.     

Electrogenerated chemiluminescence sensor for itopride with Ru(bpy)3-doped silica nanoparticles/chitosan composite films modified electrode

A electrogenerated chemiluminescence (ECL) sensor for itopride was developed based on tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)-doped silica (RuDS) nanoparticles/biopolymer chitosan composites membrane modified glassy carbon electrode (GCE). The RuDS nanoparticles (52 ± 5 nm) were prepared by a modified Stőber synthesis method and were characterized by electrochemical, fluorometric and transmission electron microscopy technology. The Ru(bpy)₃²⁺ encapsulation interior of the silica nanoparticle maintains its electrochemical activities and also reduces Ru(bpy)₃²⁺ leaching from the silica matrix when immersed in water due to the electrostatic interaction. The ECL analytical performances of this ECL sensor for itopride based on its enhancement ECL emission of Ru(bpy)₃²⁺ were investigated in details. Under the optimum condition, the enhanced ECL intensity was linear with the itopride concentration in the range of 1 × 10⁻⁸ to 2 × 10⁻⁵ g/mL (R = 0.9978). The detection limit was 3 × 10⁻⁹ g/mL, and the relative standard deviation was 2.3% for 8 × 10⁻⁸ g/mL itopride (n = 11). The method was successfully applied to the determination of itopride in pharmaceutical and human serum samples with satisfactory results. The as-prepared ECL sensor for the determination of itopride displayed good sensitivity and stability.     

Nano levels detection of beryllium by a novel beryllium PVC-based membrane sensor based on 2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetra oxacyclododecine-12-carbaldehyde-12-(2,4-dinitrophenyl)hy

A novel poly(vinyl chloride)-based 2,3,5,6,8,9-hexahydro-1,4,7,10-benzotetra oxacyclododecine-12-carbaldehyde-12-(2,4-dinitrophenyl)hy (PBC) with sodium tetraphenyl borate (NaTPB) as an anion excluder, benzyl acetate (BA), acetophenon (AP) and o-nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators was prepared and investigated as a beryllium selective sensor. The best performance was observed with the membrane having the PVC–NaTPB–NPOE–PBC composition 30%:3%:62%:5%, which worked well over a very wide concentration range (1.0×10⁻⁷ M to 1.0×10⁻¹ M). The sensor exhibits a Nernstian slope of 29.9 mV per decade of Be²⁺ activity. The detection limit of the sensor is 7.0×10⁻⁸ M (630 ppt). The proposed electrode shows excellent discriminating ability toward Be²⁺ ion with regard to alkali, alkaline earth, transition and heavy metal ions. It was successfully applied to the determination of beryllium in a mineral sample.     

Fluorescence quenching of benzo[k]fluoranthene in poly(vinyl alcohol) film: a possible optical sensor for nitro aromatic compounds

Benzo[k]fluoranthene (BkF) is a condensed multi-ring compounds with high fluorescence quantum yield and Stokes’ shift. Nitro aromatic compounds (NACs) are known to be good electron acceptors and quenchers. The fluorescence quenching of benzo[k]fluoranthene in poly(vinyl alcohol) film by different NACs, e.g. nitrobenzene, m-dinitrobenzene, o-nitrotoluene, m-nitrotoluene, p-nitrobromobenzene, o-nitroaniline, p-nitrophenol, etc. has been studied. The BkF film shows a strong quenching in the NACs concentration range from 1×10⁻⁴ to 1×10⁻³ M. The Stern–Volmer plots for NACs are found to be non-linear, but regular in this concentration range, which can be used for estimation of these compounds. The typical response time of the sensing film is found to be 2–10 s. The sensor film also shows minimal interference from different organic molecules and has good reversibility and reproducibility. The sensor gives a sensitivity of 1×10⁻⁵ M for p-nitrophenol.     

Perchlorate selective membrane electrodes based on synthesized platinum(II) complexes for low-level concentration measurements

Three synthesized platinum(II) complexes, [PtR₂(NN)] (R = Me, p-MeC₆H₄ and p-MeOC₆H₄; NN = 2,2′-bipyridyl), were studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with [Pt(p-MeOC₆H₄)₂(NN)] showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO₄⁻ ions over a wide concentration range from 5 × 10⁻⁷ to 4.0 × 10⁻¹ M for PME and 1.5 × 10⁻⁷ to 2.7 × 10⁻¹ M for CGCE with low detection limits (4.0 × 10⁻⁷ M for PME and 1.0 × 10⁻⁷ M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO₄⁻ relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.5–9.5. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water, urine samples and also samples containing interfering anions. The interaction of the ionophore with perchlorate ions was shown by UV–vis spectroscopy.     

Fabrication of a highly selective and sensitive Gd(III)-PVC membrane sensor based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea

In this work we report the development of a highly selective and sensitive Gd(III) membrane based on N-(2-pyridyl)-N′-(4-nitrophenyl)thiourea (PyTu4NO₂) as an excellent neutral ion carrier. The Gd(III) sensor exhibits a Nernstian slope of 19.95 ± 0.3 mV per decade over the concentration range of 3.0 × 10⁻⁷ to 1.0 × 10⁻¹ M, and a detection limit of 3.0 × 10⁻⁷ M of Gd(III) ions. The potentiometric response of the sensor is independent of the solution pH in the range of 4.0–9.0. It manifests advantages of low detection limit, fast response time (10 s), and most significantly, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, and Eu ions). It can be used at least for a period of 8 weeks without any significant divergences in its potential response. To assess its analytical applicability the proposed Gd(III) sensor was successfully applied as an indicator electrode in the titration of Gd(III) ion solutions with EDTA and for the determination of the fluoride ion in two mouth wash preparations. It was also used for the direct monitoring of Gd(III) ions in binary mixtures.     

Simultaneous determination of lead and cadmium at a glassy carbon electrode modified with Langmuir–Blodgett film of p-tert-butylthiacalix[4]arene

A glassy carbon electrode (GCE) modified with a Langmuir–Blodgett (LB) film of p-tert-butylthiacalix[4]arene (TCA) has been investigated as a disposable sensor for measuring the trace levels of lead and cadmium. The possibility of determining lead and cadmium at trace levels was examined with differential pulse stripping voltammetry in the measurement step. The electrochemical response was characterized with respect to supporting electrolyte, pH of solution, accumulation time, accumulation potential, layers of the LB films, and possible interferences. Calibration plots were found to be linear in the range 2 × 10⁻⁷ to 5 × 10⁻⁵ mol l⁻¹ (Cd²⁺) and 1 × 10⁻⁷ to 2.5 × 10⁻⁵ mol l⁻¹ (Pb²⁺); the detection limits were 2 × 10⁻⁸ mol l⁻¹ (Cd²⁺) and 8 × 10⁻⁹ mol l⁻¹ (Pb²⁺). Possible recognition mechanism was also discussed. From the analysis of real samples (river, lake and tap water) it can be concluded that the method is sensitive and reproducible in determining of these elements and can be used in the analysis of natural water samples.     

High sensitivity ethanol gas sensor integrated with a solid-state heater and thermal isolation improvement structure for legal drink-drive limit detecting

The paper reports the successful fabrication of ethanol gas sensors with tin-dioxide (SnO₂) thin films integrated with a solid-state heater, which is realized with technologies of micro-electro-mechanical systems (MEMS), and are compatible with VLSI processes. The main sensing part with dimensions of 450×400 μm² in this developed device is composed of a sensing SnO₂ film, which is fabricated by electron-gun evaporation with proper annealing in ambient oxygen gas to yield fine particles and good structure. An integrated solid-state heater with a 4.5 μm-thick cantilever bridge (1000×500 μm²) structure is made of silicon carbide (SiC) material by MEMS technologies. The sensitivity for 1000 ppm ethanol gas reaches as high as 90 with 10 s and 2 min for the response and recovery time, respectively, at an operating temperature of 300°C. Those experimental results also exhibit a much superior performance to that of a popular commercial ethanol gas sensor TGS-822. Therefore, the developed sensor with high performance is a good candidate for some specific application in automobile to detect drink-drive limit and allows an array integration available with various films for controlling each element at separate resistance.     

A selective modified bentonite–porphyrin carbon paste electrode for determination of Mn(II) by using anodic stripping voltammetry

A novel voltammetric sensor based on chemically modified bentonite–porphyrin carbon paste electrode (MBPCE) has been introduced for the determination of trace amount of Mn(II) in wheat flour, wheat rice and vegetables. In this method Mn(II) gives well-defined voltammetric peak at the pH range of 3.5–7.5. For the preliminary screening purpose, the catalyst was prepared by modification of bentonite with porphyrin and characterized by thermogravimetric method (TG) and UV–vis spectroscopy. The detection limit (three times signal-to-noise) with 4 min accumulation is 1.07 × 10⁻⁷ mol L⁻¹ Mn(II). The peak currents increases linearly with Mn(II) concentration over the range of 6.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹ (r² = 0.9959). Statistical treatment of the results gave a relative standard deviation lower than 2.30%. The chemical and instrumental parameters have been optimized and the results showed that 1000-fold excess of the additive ions had not interferences on the determination of Mn(II).     

Scanning-laser-beam semiconductor pH-imaging sensor

We have constructed a two-dimensional (2-D) pH-imaging sensor that enables us to observe th H⁺ distribution produced by living cells. The pH-sensing principle is similar to that of thelight-addressable potentiometric sensor. The electrolyte-insulator-semiconductor (EIS) structure (electrolyte---Si₃N₄---SiO₂---Si) is illuminated by a focused (1 μm) and modulated (1–10 kHz) He—Ne laser bean from the backside of the semiconductor, and the a.c. photocurrent flowing through the EIS structure is measured. By scanning the laser beam, 2-D pH images can be obtained. By using this sensor, pH distributions of colonies of yeast (Saccharomyces cerevisiae) have been observed. The spatial resolution of this sensor could be improved by thinning the Si wafer.     

An organically modified sol–gel membrane for detection of lead ion by using 2-hydroxy-1-naphthaldehydene-8-aminoquinoline as fluorescence probe

A fluorescent reagent, 2-hydroxy-1-naphthaldehydene-8-aminoquinoline (HNAAQ) was synthesized, and an organically modified sol–gel membrane for detection of lead ion by using HNAAQ as fluorescence probe was fabricated. Under the optimum conditions, by a coplanar effect and the degree of molecular conjugation due to the complexation of Pb²⁺ with HNAAQ the relative fluorescence intensity I₁₀₀/I₀ of the sensing membrane is linearly increased over the Pb²⁺ concentration range of 1.9 × 10⁻⁷ to 1.9 × 10⁻⁴ mol/L with the detection limit of 8.3 × 10⁻⁸ mol/L. The preparation of this organically modified sol–gel membrane and its characteristics were investigated in detail.     

Perchlorate-selective membrane sensors based on two nickel-hexaazamacrocycle complexes

The perchlorate salts of nickel(II) complexes of 1,3,5,8,10,13-hexaazacyclotetradecane (1) and 1,8-tert-butyl-1,3,5,8,10,13-hexaazacyclotetradecane (2) were used in construction of PVC based membrane electrodes. These sensors show very good selectivity for ClO₄⁻ ions over a wide variety of anions. These electrodes exhibit Nernstian behavior with the slopes of 59.5 and 59.3 mV per decade for (1) and (2), respectively. The working concentration ranges of the sensors are 1.0 × 10⁻¹–9.0 × 10⁻⁷ M (1) and 1.0 × 10⁻¹–5.0 × 10⁻⁷ M (2) with the detection limits of 6.0 × 10⁻⁷ and 2.0 × 10⁻⁷ M, respectively. The response time of the both sensors is very fast, and can be used for 2 (I) and 12 (II) weeks in a pH range of 3.0–11.0. These electrodes were applied to the determination of perchlorate ions in wastewater and cattle urine samples.     

A wireless, remote-query sensor for real-time detection of Escherichia coli O157:H7 concentrations

This paper describes the real-time detection of Escherichia coli O157:H7 concentrations using a remote-query (wireless, passive) magnetoelastic sensor. The resonance frequency of a liquid immersed magnetoelastic sensor, measured through magnetic field telemetry, changes mainly in response to bacteria adhesion to the sensor and the liquid properties (viscosity, density, elasticity, etc.) of the culture medium. In the described application, during its growth and reproduction we find E. coli consumes nutrients from a liquid culture medium that decreases the solution viscosity, and in turn changes the resonance frequency of the medium-immersed magnetoelastic sensor. Using the described technique we are able to directly quantify E. coli O157:H7 concentrations of 2 × 10² to 3 × 10⁶ cells ml⁻¹, and quantify the effect of gentamycin sulfate injection (GSI) on proliferation of the bacteria. The lack of any physical connections between the sensor and the monitoring electronics facilitates aseptic operation, and makes the sensor platform ideally suited for monitoring bacteria from within, for example, sealed food containers.