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.     

Development of an optical ammonia sensor based on polyaniline/epoxy resin (SU-8) composite

Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Experimental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films.     

Luminescence Quenching Behavior of Oxygen Sensing ORMOSIL Films Based on Ruthenium Complex

An organically modified silicate(ORMOSIL) based optical sensor response to gaseous O2 or O2 dissolved in water is presented. The oxygen sensing film mechanism is based on the principle of fluorescence quenching of tris(4,7-diphenyl-l , 10-phenanthroline) ruthenium ( ) ([Ru(dpp)3]2+), which has been entrapped in a porous ORMOSIL film. In order to establish optimum film-processing parameters, comprehensive investigations, including the effects of the polarity and the hydrophobicity of the sensing film on oxygen quenching response and response time, were carried out. The film hydrophobicity increased as a function of dimethyl-dimethoxysilane (DiMe-DMOS) content, which is correlated with enhanced oxygen sensor performance. The sensor developed in the present work exhibits the advantages of fast response time and good reversibility. The detection limits are 0. 5 % and 0. 3 g/mL for O2 in the gaseous and the aqueous phases, respectively.     

Plasmophore sensitized imaging of ammonia release from biological tissues using optodes

A plasmophore sensitized optode was developed for imaging ammonia (NH(3)) concentrations in muscle tissues. The developed ammonia sensor and an equivalent non plasmophore version of the sensor were tested side by side to compare their limit of detection, dynamic range, reversibility and overall imaging quality. Bio-degradation patterns of ammonia release from lean porcine skeletal muscle were studied over a period of 11 days. We demonstrate that ammonia concentrations ranging from 10nM can be quantified reversibly with an optical resolution of 127 μm in a sample area of 25 mm × 35 mm. The plasmophore ammonia optode showed improved reversibility, less false pixels and a 2 nM ammonia detection limit compared to 200 nM for the non-plasmophore sensor. Main principles of the sensing mechanism include ammonia transfer over a gas permeable film, ammonia protonation, nonactin facilitated merocyanine-ammonium coextraction and plasmophore enhancement. The vast signal improvement is suggested to rely on solvatochroism, nanoparticle scattering and plasmonic interactions that are utilized constructively in a fluorescence ratio. In addition to fundamental medicinal and biological research applications in tissue physiology, reversible ammonia quantification will be possible for a majority of demanding imaging and non imaging applications such as monitoring of low ammonia background concentrations in air and non-invasive medicinal diagnosis through medical breath or saliva analysis. The nanoparticle doped sensor constitutes a highly competitive technique for ammonia sensing in complex matrixes and the general sensing scheme offers new possibilities for the development of artificial optical noses and tongues.     

Fiber-optic dual Fabry-Pérot interferometric carbon monoxide sensor with polyaniline/Co3O4/graphene oxide sensing membrane

An optical fiber dual Fabry-Pérot interferometric carbon monoxide gas sensor based on PANI/Co₃O₄/GO (PCG) sensing membrane coated on the end face of the optical fiber is proposed and fabricated. One end face of photonic crystal fiber (PCF) without cut-off wavelength is fused with a single-mode fiber (SMF), and the other end face of the PCF is coated with PCG sensing membrane. The collapsed layer formed during the air hole fusion of PCF is used as the first reflector, the interface between PCF and sensing membrane is used as the second reflector, and the interface between the sensing membrane and the air is used as the third reflector, thus the dual Fabry-Pérot structure sensor is formed. The results show that the sensor has excellent sensitivity and selectivity to carbon monoxide. With the increasing concentration of carbon monoxide gas in the range of 0−60 ppm, the intensity of interference spectrum decreases. The sensitivity of the sensor is 0.3473 dB m/ppm, and its linearity is good. The response time and recovery time are 68 s and 106 s, respectively. The sensor has the advantages of the compact size, low cost, high sensitivity, strong selectivity and simple structure. It is suitable for the sensing detection of low concentration carbon monoxide gas.     

Polyaniline coated micro-capillaries for continuous flow analysis of aqueous solutions

The inner walls of fused silica micro-capillaries were successfully coated with polyaniline nanofibres using the “grafting” approach. The optical response of polyaniline coatings was evaluated during the subsequent redoping–dedoping processes with hydrochloric acid and ammonia solutions, respectively, that were passed inside the micro-capillary in continuous flow. The optical absorbance of the polyaniline coatings was measured and analysed in the wavelength interval of [300–850 nm] to determine its optical sensitivity to different concentrations of ammonia. It was found that the optical properties of polyaniline coatings change in response to ammonia solutions in a wide concentration range from 0.2 ppm to 2000 ppm. The polyaniline coatings employed as a sensing material for the optical detection of aqueous ammonia have a fast response time and a fast regeneration time of less than 5 s at room temperature. The coating was fully characterised by scanning electron microscopy, Raman spectroscopy, absorbance measurements and kinetic studies. The response of the coatings showed very good reproducibility, demonstrating that this platform can be used for the development of micro-capillary integrated sensors based on the inherited sensing properties of polyaniline.     

Study of the performance of an optochemical sensor for ammonia

An optical sensor for ammonia based on ion pairing has been investigated. A pH-sensitive dye (bromophenol blue) was immobilized as an ion pair with cetyltrimethylammonium in a silicone matrix. The colour of the dye changes reversibly from yellow to blue with increasing concentration of ammonia in the sample. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam, solid state photometer. The measurement range is from 6 × 10⁻⁷ to 1 × 10⁻³ M (0.01 to 17 μg ml⁻¹) in 0.1 M sodium phosphate buffer, pH 8. The 90% and 100% response times at a flow rate of 2.5 ml min⁻¹ are 4 min and 10 min, respectively, for a change from 41.9 to 82.5 μM ammonia, or 12 min and 48 min, respectively, for change from 160 to 0 μM ammonia. A continuous drift in signal baseline and ammonia sensitivity limited the measurement stability. The sensor was useful over a period of a few days. The storage stability is more than 10 months (dry). No interference due to pH was observed in the range from pH 5 to pH 9. Sensor performance is seriously affected by amines and cationic detergents. The sensor could be sterilized with 3% hydrogen peroxide or dry heat (90 °C).     

Development of an aminocarboxylic acid-modified infrared chemical sensor for selective determination of tyrosine in urine

An infrared (IR) chemical sensor based on immobilization of an acidified tris(2-aminoethyl)amine (ATAA) for the detection of tyrosine in urine is described. The sensing phase (i.e., coating) was saturated with nickel ions so that it would interact with tyrosine molecules in aqueous solution through the formation of stable ATAA-Ni²⁺-tyrosine complexes. Investigation of the signals of nine amino acids shows that only the three containing phenyl groups could be detected by this sensor system. A unique spectral feature located at 1515 cm⁻¹ allowed tyrosine to be discriminated from the other two amino acids. To examine the performance of the ATAA sensing phase in the quantitative analysis of tyrosine, the effects of several factors were examined. pH affected the ability of tyrosine to form complexes; the optimal signal occurred at ca. pH 8. The concentration of ammonia buffer also affected the analytical signals through a competition effect; lower concentrations of ammonia buffer provided higher intensity signals. It was found that nickel ions are the most useful for detection of tyrosine. Although the concentration of nickel ions had less influence on the analytical signal than did the concentration of the ammonia buffer, the signal intensity was optimal when the nickel ions and the target molecule had similar concentrations. The detected time profiles indicated that the ATAA sensor phase functioned via a surface adsorption mechanism. The linear range of signal intensities was up to 600 μM with a detection limit of 30 μM.     

Thiourea-treated graphene aerogel as a highly selective gas sensor for sensing of trace level of ammonia

As a result of this study, a new and simple method was proposed for the fabrication of an ultra sensitive, robust and reversible ammonia gas sensor. The sensing mechanism was based upon the change in electrical resistance of a graphene aerogel as a result of sensor exposing to ammonia. Three-dimensional graphene hydrogel was first synthesized via hydrothermal method in the absence or presence of various amounts of thiourea. The obtained material was heated to obtain aerogel and then it was used as ammonia gas sensor. The materials obtained were characterized using different techniques such as Fourier transform infra red spectroscopy (FT-IR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thiourea-treated graphene aerogel was more porous (389 m² g⁻¹) and thermally unstable and exhibited higher sensitivity, shorter response time and better selectivity toward ammonia gas, compared to the aerogel produced in the absence of thiourea. Thiourea amount, involved in the hydrogel synthesis step, was found to be highly effective factor in the sensing properties of finally obtained aerogel. The sensor response time to ammonia was short (100 s) and completely reversible (recovery time of about 500 s) in ambient temperature. The sensor response to ammonia was linear between 0.02 and 85 ppm and its detection limit was found to be 10 ppb (3S/N).     

Optochemical Sensor for Ammonia Based on a Lipophilized pH Indicator in a Hydrophobic Matrix

Abstract

An optical sensor for the determination of ammonia in water based on ion pairing has been investigated. A pH-sensitive dye is immobilized as an ion pair in a silicone matrix. The colour of the dye changes from yellow to blue depending on the concentration of ammonia in the sample solution. This change is reversible. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength.

All measurements were performed with a dual-beam optical meter. The measurement range was from 5.9 × 10^?7 to 1 × 10^?3 M (0.01 to 17 mg/l) in 0.1 M phosphate buffer of pH 8. The detection limit was 10 μg/l. The response times at a flow rate of 2.5 ml/min were 4 min for t₉₀ and 10 min for t₁₀₀ at a change from 41.9 to 82.5 μM ammonia and 12 min for t₉₀ and 48 min for t₁₀₀ at a change from 160 to 0 μM ammonia. The operational lifetime of the ammonia sensor was limited to a period of a few days only. A continuous decrease in baseline signal and relative signal change was observed over the whole measurement. The storage stability was more than 10 months (dry). With respect to possible application of the ammonia sensor to environmental analysis, the influence of pH, typical interferences, such as amines and various detergents on the sensor response was investigated. No interference due to pH was observed in the range from pH 5 to pH 9. With methyl- and ethylamine the response was not completely reversible. The sensor was affected by cationic detergents, but not by anionic or neutral detergents.     

基于钌配合物荧光猝灭原理的新型氟化有机改性溶胶-凝胶氧传感膜的研究

选用3,3,3-三氟丙基三甲氧基硅烷为前驱体,制备氧光化学传感膜材料.利用4,7-二苯基-1,10-邻菲咯啉钌(Ⅱ)([Ru(dpp)3(ClO4)2])为氧荧光猝灭指示剂,通过优化制备条件获得对氧浓度变化具有敏感响应的传感膜.研究结果表明:所制备的氧传感膜对水体中的溶解氧的线性响应范围为0.5～16.0 mg/L,最...     

Detection of Amines in Lamb Spoilage by Optical Waveguide Sensor Based on Bromophenol Blue-Silicon Composite Film

We herein report the development of a bromophenol blue(BPB)-silicone composite film/K^+-exchange glass optical waveguide(OWG)sensor for the detection of amines produced during the spoilage of lamb.the optical and structural properties of the sensitive thin film were studied by ultra violet-visible(UV-Vis)spectroscopy,and the light source of the OWG detecting system was selected.Gas sensing measurements showed that the sensor exhibited a good selectivity,higli sensitivity,and short response-recovery time towards volatile amine gases in the 0.00117一11.72 mg/g range.The as-prepared optical waveguide device was subsequently applied in the determination of gases(namely trimethylamine,dimethylamine,and ammonia)emitted from the lamb samples(5g)stored at room temperature(25℃)and in a refrigerator(5℃)for 0—4 d,and the total volatile basic nitrogen(TVB-N)contents were detected by UV-Vis spectroscopy,and the results were compared witli those obtained using our detector.It was found that the sensing element was capable of detecting mixed gases produced by the decomposition of lamb samples in a refrigerator for 0.5 h,where the TVB-N content was lower than 35μg/g.     

Air-gap fiber-optic ammonia gas sensor

A novel fiber-optic gas sensing arrangement based on an air-gap design is evaluated. In this arrangement, a small gap of air separates the internal solution from the sample. In addition, a second air-gap separates the internal solution from a fiber-optic probe which measures the fluorescence of the internal solution. A series of gas sensors for ammonia is used to investigate several critical design parameters. The length of the air-gap between the internal solution and the fiber-optic probe affects the magnitude of response. The length of the air-gap separating the internal and sample solutions has minimal effect on either magnitude or rate of response. As with membrane-type gas sensors, thickness of the internal solution and concentration of the indicator dye are the most important sensor parameters to consider when designing a fiber-optic gas sensor.     

Miniaturized Optical System for Detection of Ammonia Nitrogen in Water Based on Gas-Phase Colorimetry

A small-size gas-tight optical measuring system for detection of ammonia nitrogen in water was prepared based on gas-phase ammonia induced color change of the sensing element that was made by loading bromothymol blue (BTB) in a transparent porous glass fiber membrane. The gas-tight optical measuring system consists of a gas-testing and a liquid-sample chamber connected with each other by means of tubes and a mini-pump that cycles the gas between the two chambers. A 625-nm light emitting diode (LED), a photodetector and a sensing element were mounted in the gas-testing chamber for optical response to ammonia gas released from the water in the liquid-sample chamber. Release of ammonia gas was realized by alkalinizing the water sample with NaOH. Owing to the amount accumulation of ammonia gas in the sealing system, the ammonia nitrogen detection limit of the device can be very low. A small concentration of ammonia nitrogen, as low as 0.05 mg/L, was detected. The two linear-response ranges from 0.05 mg/L to 0.26 mg/L and from 0.26 mg/L to 2.62 mg/L were obtained. A relative standard deviation of ≤1% was determined by multiple measurements of the same sample.     

基于荧光内滤效应的荧光增强型钠离子光纤传感器

在吸收型钠离子光化学传感器的敏感膜中加入合适的荧光试剂,应用荧光内滤效应研制成的荧光增强型光纤传感器,在测量灵敏度和抗背景干扰能力方面均有较大的改善,对血清和矿泉水样品中的钠离子含量进行了分析,获得了满意的结果。     

Electrospun Nanofibers from a Tricyanofuran‐Based Molecular Switch for Colorimetric Recognition of Ammonia Gas

A chromophore based on tricyanofuran (TCF) with a hydrazone (H) recognition moiety was developed. Its molecular‐switching performance is reversible and has differential sensitivity towards aqueous ammonia at comparable concentrations. Nanofibers were fabricated from the TCF–H chromophore by electrospinning. The film fabricated from these nanofibers functions as a solid‐state optical chemosensor for probing ammonia vapor. Recognition of ammonia vapor occurs by proton transfer from the hydrazone fragment of the chromophore to the ammonia nitrogen atom and is facilitated by the strongly electron withdrawing TCF fragment. The TCF–H chromophore was added to a solution of poly(acrylic acid), which was electrospun to obtain a nanofibrous sensor device. The morphology of the nanofibrous sensor was determined by SEM, which showed that nanofibers with a diameter range of 200–450 nm formed a nonwoven mat. The resultant nanofibrous sensor showed very good sensitivity in ammonia‐vapor detection. Furthermore, very good reversibility and short response time were also observed.     

Optical ammonia gas sensor based on a porous silicon rugate filter coated with polymer-supported dye

An ammonia gas sensor chip was prepared by coating an electrochemically-etched porous Si rugate filter with a chitosan film that is crosslinked by glycidoxypropyltrimethoxysilane (GPTMS). The bromothylmol blue (BTB), a pH indicator, was loaded in the film as ammonia-sensing molecules. White light reflected from the porous Si has a narrow bandwidth spectrum with a peak at 610 nm. Monitoring reflective optical intensity at the peak position allows for direct, real-time observation of changes in the concentration of ammonia gas in air samples. The reflective optical intensity decreased linearly with increasing concentrations of ammonia gas over the range of 0–100 ppm. The lowest detection limit was 0.5 ppm for ammonia gas. At optimum conditions, the full response time of the ammonia gas sensor was less than 15 s. The sensor chip also exhibited a good long-term stability over 1 year. Therefore, the simple sensor design has potential application in miniaturized optical measurement for online ammonia gas detection.     

Highly sensitive and selective room temperature NH3 gas microsensor using an ionic conductor (CuBr) film

A new ammonia gas microsensor was developed, based on the large resistance change of an ionic conductor (CuBr) film when exposed to low NH₃ concentrations. The detection is based on specific interactions between ammonia molecules contained in the gas atmosphere and mobile copper ions in the copper(I) bromide layer. The sensor is operating at ambient temperature and allows highly sensitive and specific ammonia detection. The sensor works at ammonia concentrations between 1 and 500 ppm. There are no significant cross-effects to acetylene and carbon monoxide and only a weak cross-sensitivity to hydrogen sulfide gas (200 ppm). The selectivity was experimentally compared with commercial tin dioxide sensors (TGS 826). The sensor fabrication is a simple process, allowing low cost device production.     

Novel fused-LEDs devices as optical sensors for colorimetric analysis

The development of a novel, low power optical sensing platform based on light emitting diodes (LEDs) is described. The sensor is constructed from a pair of LEDs fused together at an angle where one LED functions as the light source and the other LED is reverse biased to function as a light detector. Sensor function is based on the level of light received by the detector diode, which varies with the reflectance of the interface between the device and its environment, or the chemochromic membrane that covers the device. A simple microprocessor circuit is used to measure the time taken for the photon-induced current to discharge the detector LED from an initial 5 V (logic 1) to 1.7 V (logic zero). This sensing device has been successfully used for colour and colour-based pH measurements and offers extremely high sensitivity, enabling detection down to the sub micro molar level of dyes.     

Fiber-Optic biosensor for urea based on sensing of ammonia gas

A fiber-optic biosensor for urea is described. This biosensor is based on the immobilization of urease at the sensing tip of a fluorescence-based ammonia gas-sensing fiber-optic chemical sensor. Urease is immobilized on a Teflon membrane by the well known bovine serum albumin (BSA)/glutaraldehyde cross-linking method. The indicator solution for this biosensor is composed of 0.145 M sodium chloride, 5.00 mM ammonium chloride, 9.4 μM 2′,7′-bis(carboxyethyl)-5 (and 6)-carboxyfluorescein and 0.9 μM 5 (and 6)-carboxyfluorescein. The steady-state and dynamic response properties of the sensor have been established. Results show that the urease/BSA protein layer has a significant effect on sensor response and recovery times. Also, the fluorescence-based sensor has been found to be faster than a conventional potentiometric ammonia gas-sensing electrode. In addition, the fluorescence sensor responds significantly quicker than a similar absorbance-based fiber-optic urea biosensor. The utility of the resulting urea biosensor for the determination of urea in diluted serum samples is demonstrated.