Investigation of relative humidity effects on the response behavior of a pH indicator-based OWG vapor sensor

The response of a pH indicator-based optical waveguide sensor was characterized with respect to the effects of relative humidity (RH) on the magnitude of the sensor response, and on the rate of response to both hydrochloric acid and ammonia/ammonium hydroxide vapors. Water vapor constitutes both a chemical and a systematic (optical) interference for the OWG sensor response to hydrochloric acid. Swelling of the polymer films upon exposure to water vapor results in a decrease in the loss of light at the polymer/air interface, resulting in an increase in the sensor signal. In addition, high RH conditions decrease the bromothymol blue indicator response to hydrochloric acid vapor. In contrast, the bromothymol blue indicator response to ammonia increases as the RH increases. High RH levels also increases the rate of diffusion (transport) of hydrochloric acid into (and out of) Nafion films, but does not affect the diffusion rate for poly(vinyl alcohol) polymer films. The RH does not appear to have any significant effect on the rate of transport of ammonia in any of the polymer films studied.     

Optical fibre sensor for hydrogen sulphide monitoring in mouth air

A reversible optical fibre chemical sensor for hydrogen sulphide monitoring in mouth air based on reflectance measurements has been developed. The active sensing phase has been prepared by immobilising the colorimetric reagent 2,6-dichlorophenolindophenol (DCPI) in a silica gel support. The principle of the determination is based on the increase of reflectance of such solid sensing phase when hydrogen sulphide reduces the colorimetric reagent with the subsequent decolouration process. The addition of 1.26 μg of Cu(II) per gram of solid support improved the response time and reversibility of the sensing phase.The detection limit is 10 ppb (v/v) of hydrogen sulphide. The linear range using the Kubelka-Munk function extends at least up to 1000 ppb (v/v). The sensor exhibits a response time of less than 2 min for hydrogen sulphide concentrations in the linear range and the signal is reversible.The optical sensor has been successfully tested for human malodour monitoring and the results validated by comparison with those obtained for the same individuals using a commercially available electrochemical instrument.     

以Nafion修饰的镀铂玻碳电极为基底的半乳糖传感器的制备

在镀铂的玻碳电极表面,修饰一层全氟代磺酸酯(Nafion)膜,制成基底电极。用化学交联法将半乳糖氧化酶(GAD)固定在基底电极表面,即制成半乳糖传感器。和光亮铂相比,镀铂电极对过氧化氢有更高的响应,而Nafion膜可以消除抗坏血酸,尿酸等电活性物质对测定的影响,提高了酶电极测定的选择性。D-半乳糖测定的线性范围为0.25～4.25 mmol/L,响应时间小于30s。电极连续使用300次,没有明显的电流变化。该电极具有快速、准确,选择性高的特点。     

Sensitive and selective electrochemical detection of carbon monoxide in saline at a Pt-Ru/Nafion/MnO2-modified electrode

We fabricated a sensitive and selective electrochemical carbon monoxide (CO) sensor for physiological conditions based on the Pt-Ru system. At a bare Pt-Ru electrode, a linear amperometric response to CO concentration was obtained in the range of 0.9-9 μM. However, significant current response to model electroactive interferents for physiological conditions, uric acid (UA), ascorbic acid (AA) and hydrogen peroxide (HP), was also recorded at the Pt-Ru electrode. The response to UA and AA was highly suppressed by coating the Pt-Ru electrode surface with a Nafion layer, and the response to HP was almost completely eliminated by the additional coating with a MnO(2)/chitosan layer. Finally, at the Pt-Ru/Nafion/MnO(2) electrode, amperometric CO detection with a sensitivity of 173 nA cm(-2) μM(-1) was obtained in the concentration range of 0.9-9 μM with the UA, AA and HP signal being below 1.7% at the same concentration of CO.     

基于叶片状氧化铜纳米材料的无酶葡萄糖传感电极

将Nafion交联剂与纳米材料修饰至玻碳电极基底制备一种无酶葡萄糖传感器,通过循环伏安曲线、时间-电流曲线检测该电极电化学特性. 氧化铜纳米复合膜具有高比表面积和多活性点位的优点. 实验结果表明,氧化铜纳米电极对葡萄糖的检测线性响应范围0.01 ~ 0.3 mmol·L^-1,灵敏度1783.58 μA·L·mmol^-1·cm^-2,检测限0.80 μmol·L^-1 (S/N=3),稳定性较好,能抵抗抗坏血酸、多巴胺和尿酸干扰.     

Starch-iodine films respond to water vapor

Starch-iodine indicator films were found to have useful spectroscopic properties for the detection of water vapor. The large colorimetric response of these easily prepared films was easily detected by the absorption of 632.8 nm HeNe laser light, using a planar integrated optical waveguide (IOW) platform. The detection limit of a prototype sensor was found to be below 5% relative humidity (RH), with response times of the order of seconds.     

A Novel Hybrid Nano‐composite Grafted Electrochemically Reduced Graphene Oxide Based Sensor for Sensitive Determination of Efavirenz

A novel, facile fabrication, based on electrochemically reduced graphene oxide (ErGO), grafted with Pt nanoparticles and Nafion hybrid nano‐composite (ErGO‐Pt/Nafion) on the surface of edge plane pyrolytic graphite (EPPG) has been reported. The fabricated sensor has been used for the sensitive and selective determination of efavirenz (EFZ), a well‐known drug for HIV infections. The ErGO‐Pt/Nafion film was characterized by Field Emission Scanning Electron Microscopy (FE‐SEM), Energy‐dispersive X‐ray spectrometry (EDS) and Electrochemical Impedance Spectroscopy (EIS). The experimental results reveal that the modified sensor displays an excellent electrocatalytic activity towards the oxidation of EFZ and exhibits a large linear dynamic relationship in the range of 0.05 μM to 150 μM, with a detection limit of 1.8 nM. Practical utility of the developed sensor has been demonstrated by determining the EFZ in biological fluids and pharmaceutical samples and a low detection limit with high sensitivity observed makes it valuable for the clinical diagnosis.     

Cuprous Oxide/Nitrogen-doped Graphene Nanocomposites as Electrochemical Sensors for Ofloxacin Determination

Cu₂O/nitrogen-doped grapheme(NG) nanocomposite material was prepared via a facile one step chemical reduction and characterized by means of X-ray diffraction(XRD) and scanning electron microscopy(SEM). A new electrochemical sensor was then fabricated by coating Cu₂O/nitrogen-doped graphene nanocomposite with Nafion on glassy carbon electrode(Cu₂O/NG/Nafion/GCE). The electrochemical response of this modified electrode toward ofloxacin was examined by cyclic voltammetry. The results indicate that Cu₂O/NG/Nafion composite-modified electrode exhibits higher catalytic activity in the electrochemical oxidation of ofloxacin compared with glassy carbon electrode(GCE), Cu₂O/Nafion modified electrode(Cu₂O/Nafion/GCE), and N-doped graphene/Nafion modified electrode(NG/Nafion/GCE). Under optimal conditions, the peak current was found to be linearly proportional to the concentration of ofloxacin in the 0.5-27.5 μmol/L and 27.5-280 μmol/L ranges with a lower detection limit of 0.34 μmol/L, higher sensitivity of 39.32 μA·L·mmol^-1 and a shorter reaction time of less than 2 s. In addition, Nafion can enhance the stability of the modified electrode and prevent some negative species. Thus the modified electrode exhibits good selectivity and a long working life. The Cu₂O/NG/Nafion composite modified electrode shows promising application in electrochemical sensors, biosensors, and other related fields because of its excellent properties.     

Planar Integrated Optical Waveguide Sensor for Isopropyl Alcohol in Aqueous Media

An attenuated total reflection (ATR) sensor for water-miscible organic solvents was constructed using a combination of sol-gel processing and integrated optical waveguide (IOW) technologies. The sensor consisted of single-mode, sol-gel based planar waveguide coated with a 40 nm thick, porous sol-gel indicator layer prepared from methyltriethoxysilane and doped with methyl red. The response of the senor to aqueous isopropyl alcohol (IPA) was investigated. Solvation of the indicator dye by IPA causes the absorbance spectrum to undergo a blue shift coupled with an increase in molar absorptivity. IPA was detected by measuring changes in ATR of the guided mode at 488 nm. A response curve extending from 1 to 100% (v/v) IPA in water was constructed for the sensor, from which a detection limit of 0.7% (v/v) IPA/water was estimated. Response and reversal times were typically less than one minute, making this sensor potentially attractive for on-line monitoring applications. The rapid response characteristics are attributable to relatively weak, reversible interactions between the indicator and analyte.     

Electrochemistry and voltammetric determination of L-tryptophan and L-tyrosine using a glassy carbon electrode modified with a Nafion/TiO2-graphene composite film

We describe a glassy carbon electrode (GCE) modified with a film composed of Nafion and TiO₂-graphene (TiO₂-GR) nanocomposite, and its voltammetric response to the amino acids L-tryptophane (Trp) and L-tyrosine (Tyr). The incorporation of TiO₂ nanoparticles with graphene significantly improves the electrocatalytic activity and voltammetric response compared to electrodes modified with Nafion/graphene only. The Nafion/TiO₂-GR modified electrode was used to determine Trp and Tyr with detection limits of 0.7 and 2.3 μM, and a sensitivity of 75.9 and 22.8 μA mM^?1 for Trp and Tyr, respectively.

Sensitive and Selective Sensing of Hydrogen Peroxide with Iron‐Tetrasulfophthalocyanine‐Graphene‐Nafion Modified Screen‐Printed Electrode

We developed a novel iron‐tetrasulfophthalocyanine‐graphene‐Nafion (FeTSPc‐GR‐Nafion) modified screen‐printed electrode to determine hydrogen peroxide (H₂O₂) with high sensitivity and selectivity. The nanocomposite film (FeTSPc‐GR‐Nafion) exhibits an excellent electrocatalytic activity towards oxidation of H₂O₂ at a potential of +0.35 V in the absence of enzyme. A comparative study reveals that the FeTSPc‐GR complexes play a dual amplification role. Amperometric experiment indicates that the sensors possess good sensitivity and selectivity, with a linear range from 2.0×10^?7 M to 5.0×10^?3 M and a detection limit of 8.0×10^?8 M. This sensor has been successfully used to develop the glucose biosensor and has also been applied to determine H₂O₂ in sterile water.     

Amperometric biosensors based on the immobilization of oxidases in a Prussian blue film by electrochemical codeposition

Prussian blue has been formed by cyclic voltammetry onto the basal pyrolytic graphite surface to prepare a chemically modified electrode which provides excellent electrocatalysis for both oxidation and reduction of hydrogen peroxide. It is found for the first time that glucose oxidase or -amino oxidase can be incorporated into a Prussian blue film during its electrochemical growth process. Two amperometric biosensors were fabricated by electrochemical codeposition, and the resulting sensors were protected by coverage with a thin film of Nafion. The influence of various experimental conditions was examined for optimum analytical performance. The glucose sensor responds rapidly to substrates with a detection limit of 2 × 10⁻⁶ M and a linear concentration range of 0.01–3 mM. There was no interference from 2 mM ascorbic acid or uric acid. Another ( -amino acid) sensor gave a detection limit of 3 × 10⁻⁵ M -alanine, injected with a linear concentration range of 7.0 × 10⁻⁵-1.4 × 10⁻² M. Glucose and -amino acid sensors remain relatively stable for 20 and 15 days, respectively. There is no obvious interference from anion electroactive species due to a low operating potential and excellent permselectivity of Nafion.     

Determination of carboxylic acid vapour by a thickness-sheer-mode acoustic wave sensor coated with crown ethers

The frequency response sensitivities for 39 organic vapours by thickness-sheer-mode (TSM) acoustic wave sensors coated with monobenzo-15-crown-5 (B15C5), monobenzo-18-crown-6 (B18C6) and dibenzo-30-crown-10 (DB30C10) have been reported. It shows that crown ethers are the most efficient adsorptively active material for sensing carboxylic acid vapour, particularly B15C5 can be used for sensing formic acid vapour. The B15C5 based sensor possesses good reproducibility, high stability and short response time with wide linear detection range and a low detection limit down to 0.0201 mg l(-1) (about 5.70 ppm, V/V) of formic acid vapour while coating with 12 mug of B15C5. There is no significant interference from other organic vapours except for some nitrogen containing compounds such as diethylamine, pyridine and N,N-dimethylformamide, and carboxylic acid homologues such as acetic and propionic acids. The effect of humidity is easily controllable. Compared with acid-base titration method, the sensor can be used for the determination of HCOOH vapour with recovery rate of 98.4 approximately 103.8%, the analytical results are in good agreement with those obtained by the more time consuming acid-base titration method.     

Influence of Analyte Flow Rate on Signal and Response Time of the Amperometric Gas Sensor with Nafion Membrane

This paper presents results of an investigation on influence of volumetric flow rate on the signal and response time of a prototype of sulfur dioxide gas sensor with Nafion membrane. The sensors differing in type of working electrode and composition of internal electrolyte were compared. We used Au and Pt working electrodes obtained via vacuum sublimation deposition on a Nafion membrane surface. The electrolytes were aqueous solutions of sulfuric acid of the summary concentration 5 mol dm^?3 (electrolyte A). The electrolyte B contained an addition of dimethylsulfoxide (DMSO); the water/DMSO molar ratio was 2 : 1. Based on a proposed equation, which takes diffusion resistance into account, the obtained sensor signals were analyzed for the flow rate within a range of 0–100 cm³ min^?1. The sensor response time was also determined for the above flow rate range.     

Towards a hybrid micro-device allowing the selective detection of hydrogen fluoride vapours in a complex mixture

In this work, design and fabrication of a hybrid micro-device dedicated to the selective detection of hydrogen fluoride vapours is reported. This micro-device is composed by a gas chromatographic micro-column positioned in front of a tin dioxide-based gas sensor. The efficiency of this hybrid micro-system regarding to reproducibility and reversibility for various HF concentrations was investigated. The influence of the HF concentration on the electrical responses of the sensor is also studied. The experimental results show that this hybrid micro-system is efficient since it allows the elution, separation and detection of hydrogen fluoride at a low temperature close to ambient.     

Detection of trace organophosphorus vapor with a self-assembled bilayer functionalized SiO2 microcantilever piezoresistive sensor

Using piezoresistive SiO₂ microcantilever technology, we present an ultra-sensitive chemical sensor for trace organophosphorus vapor detection. A self-assembled composite layer of Cu²⁺/11-mercaptoundecanoic acid is modified on the surface of the sensing cantilever as a specific coating to capture PO containing compounds. Experimental results indicate that the sensor can be quite sensitive to DMMP vapor (well known as a simulant of nerve agent). The signal-noise-limited detection resolution of the sensor is experimentally obtained as low as several parts per billion. Besides that the sensor can yield reversible and repeatable response to DMMP vapor, adsorption of DMMP on the self-assembled composite layer is well fit to the Langmuir isotherm model.     

Amperometric sensing of hydrogen peroxide vapor for security screening

Rapid detection of the hydrogen peroxide precursor of peroxide explosives is required in numerous security screening applications. We describe a highly sensitive and selective amperometric detection of hydrogen peroxide vapor at an agarose-coated Prussian-blue (PB) modified thick-film carbon transducer. The sensor responds rapidly and reversibly to dynamic changes in the level of the peroxide vapor, with no apparent carry over and with a detection limit of 6 ppbv. The remarkable selectivity of the PB-based screen-printed electrode towards hydrogen peroxide leads to effective discrimination against common beverage samples. For example, blind tests have demonstrated the ability to selectively and non-invasively identify concealed hydrogen peroxide in drinking cups and bottles. The attractive performance of the new microfabricated PB-based amperometric peroxide vapor sensor indicates great potential for addressing a wide range of security screening and surveillance applications. Figure Experimental setup (left) with three electrode electrochemical Hydrogen Peroxide sensor hanging above container of “unknown” liquid. Schematic (right) demonstrating fundamental principles of operation of the sensor.     

Automatic isotope gas analysis of tritium labelled organic materials

An analytical procedure and an automatic apparatus are described for the determination of tritium in organic compounds by gas counting. The sample is pyrolysed in hydrogen atmosphere at 1000°C, then, with hydrogen, the decomposition products are rinsed through a column of molecular sieve-5A heated to 550°C. Tritium in water, hydrogen sulphide, ammonia and hydrogen cyanide is transferred into the hydrogen stream by isotope exchange completed on the column. The inactive water vapor, hydrogen sulphide, ammonia and hydrogen cyanide as well as carbon dioxide are removed from the gas stream by appropriate absorbents, and the radioactive hydrogen together with tritiated methane, carbon monoxide and nitrogen included in the pyrolytic products is led into an internal proportional counter tube for radioactivity measurement. The method provides quantitative recovery, it is free of memory effect and suitable for the rapid assay of a wide variety of organic compounds containing C, H, N, O, S in addition to tritium.     

Molecularly imprinted polymer-based electrochemical sensor for the sensitive detection of glyphosate herbicide

A sensitive electrochemical molecularly imprinted sensor was developed for the detection of glyphosate (Gly), by electropolymerisation of p-aminothiophenol-functionalised gold nanoparticles in the presence of Gly as template molecule. The extraction of the template leads to the formation of cavities that are able to specifically recognise and bind Gly through hydrogen bonds between Gly molecules and aniline moieties. The performance of the developed sensor for the detection of Gly was investigated by linear sweep voltammetry using a hexacyanoferrate/hexacyanoferrite solution as redox probe, the electron transfer rate increasing when concentration of Gly increases, due to a p-doping effect. The molecularly imprinted sensor exhibits a broad linear range, between 1 pg/L and 1 µg/L and a quantification limit of 0.8 pg/L. The selectivity of the proposed sensor was investigated towards the binding of Gly metabolite, aminomethylphosphonic acid, revealing excellent selectivity towards Gly. The developed sensor was successfully applied to detect Gly in tap water samples.     

Differential selectivity in electrochemical oxidation of ascorbic acid and hydrogen peroxide at the surface of functionalized ormosil-modified electrodes

Functionalized ormosil-modified electrodes have been developed for electroanalytical applications. The functionalized ormosil-modified electrodes are made by encapsulating potassium ferricyanide/potassium ferrocyanide within ormosil film derived from an optimum composition of 3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium in absence of Nafion/crown ether (system 1), in the presence of Nafion (system 2) and in the presence of dibenzo-18-crown-6 (system 3). Another modified electrode (system 4) is also developed using the reaction product of potassium ferricyanide, 3-aminopropyltrimethoxysilane and either tetrahydrofuran (THF) or cyclohexanone followed by ormosil formation in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium. The electrochemical oxidation of hydrogen peroxide and ascorbic acid conducted at the surface of these four types of functionalized electrodes shows very interesting observations on the selective sensing of ascorbic acid and peroxide. The results based on cyclic voltammetry justify the relative performances on the kinetics of hydrogen peroxide oxidation and reduction. System 3 shows relatively much better oxidation kinetics of hydrogen peroxide as compared to other three systems with relatively weak reduction kinetics whereas system 4 shows relatively faster reduction kinetics of hydrogen peroxide as compared to other three systems. Similarly system 4 shows excellent response to ascorbic acid whereas system 3 shows insensitivity to ascorbic acid under similar experimental conditions. Typical response curve for the analysis of hydrogen peroxide and ascorbic acid using system 3 and system 4 respectively are reported. The results show that system 3 is the best for probing hydrogen peroxide with lowest detection limit of 0.5 μM without any interference from ascorbic acid as commonly encountered using many conventional and chemically modified electrodes.