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.     

Development of a new fluorescent sensor based on a triazolo-thiadiazin derivative immobilized in polyvinyl chloride membrane for sensitive detection of lead(II) ions

A new sensor membrane based on a novel triazolo-thiadiazin derivative immobilized in polyvinyl chloride has been developed for the determination of Pb(II) ions that displays excellent performance. The parameters involved in the preparation of the optode and determination of Pb(II) were optimized. Under the optimal conditions, the proposed sensor displays a calibration response for Pb(II) over a wide concentration range of 5.0 × 10⁻⁸ to 3.8 × 10⁻⁴ M with the detection limit of 2.2 × 10⁻⁸ M. In addition to high reproducibility and reversibility of the fluorescence signal, the sensor also exhibits good selectivity over common metal ions. The optode membrane developed is easily prepared, stable, rapid, and simple for the determination of Pb(II). The accuracy of the proposed sensor was confirmed by analyzing standard reference materials of natural water and surface water. The sensor was successfully used for the determination of Pb(II) ions in water samples with satisfactory results.     

Optical fiber chemical sensing of Hg(II) ions in aqueous samples using a microfluidic device containing a selective tripodal chromoionophore-PVC film

A novel methodology for the determination of Hg(II) ions was developed based on optical fiber chemical sensing in a microfluidic device containing a selective tripodal chromoionophore (i.e. tris[2-(4-phenyldiazenyl)phenylamino)ethoxy]cyclotriveratrylene/TPPECTV)-PVC film. Absorbance detection was performed by incorporating a single optical fiber on the top and the bottom of the detection zone of the microfluidic device. In this micro-sensing system, the intensity of the absorption maximum at 495 nm of the TPPECTV-Hg(II) complex linearly increases as a function of the Hg(II) ion concentration in the range 1.0 × 10⁻⁶ to 2.5 × 10⁻⁴ M, with a detection limit of 0.5 μM. Interference from other heavy metal ions was not observed at significant levels. The absorbance results of the detection of Hg(II) ions in environmental water samples (river water) are in good agreement with those obtained by a macro-scale system (cold vapor atomic absorption spectrometry/CVAAS).     

Development of an optical hydrogen sulphide sensor

A hydrogen sulphide (H₂S)-sensitive optode film has been fabricated by immobilising tetraoctylammonium fluorescein mercury(II) acetate (TOFMA) and tri-n-butyl phosphate in a poly(vinyl chloride) (PVC) matrix. The optode film, coated on an overhead transparency film, was employed as a sensing device for fluorimetric detection of H₂S. The fluorescence intensity monitored at 553 nm (excitation at 503 nm) increased with increasing H₂S concentrations. The optode film showed a good, linear and reversible response to H₂S from 0 to 15 ppm (v/v). It was optically stable and the reproducible response of the film on exposure to 10 ppm (v/v) H₂S was extremely good. There was no sign of degradation after 8 h of continuous use. The response to H₂S levelled off at about 27.5 ppm The response and recovery times of the optical H₂S sensor were fast and less than 2 and 5 s, respectively. An optically-based sensor for H₂S determination was successfully developed. It was anticipated that the system could be used to monitor H₂S with a concentration range of 0–25 ppm (v/v) with satisfactory results. A proposed mechanism for the detection of H₂S by the optode films is described.     

Preconcentration and voltammetric analysis of mercury(II) at a carbon paste electrode modified with natural smectite-type clays grafted with organic chelating groups

This study is devoted to the evaluation of a carbon paste electrode modified by a natural 2:1 phyllosilicate clay functionalized with either amine or thiol groups as a sensor for mercury(II). Functionalization was achieved by grafting the pristine clay via its reaction with 3-aminopropyltriethoxysilane (APTES) or 3-mercaptopropyltrimethoxysilane (MPTMS), respectively. The electroanalytical procedure comprises two steps: the chemical accumulation of the analyte under open-circuit conditions followed by the electrochemical detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The different parameters that govern the two steps (accumulation time, concentration of the analyte, composition of the detection medium, potential and duration of electrolysis) were studied in detail. After optimization, a linear response was obtained in the concentration range from 0.1 to 0.7 μM Hg(II). In these conditions, the detection limits of the method were found to be 8.7 × 10⁻⁸ and 6.8 × 10⁻⁸ M, respectively, for the amine- and thiol-functionalized clays, on the basis of a signal-to-noise ratio of 3. The effect of potential interference on the determination of Hg(II) by the carbon paste electrode modified with the thiol-functionalized clay was also studied and the applicability of the method to real sample analysis was evaluated.     

Highly sensitive and linear calibration optical fiber oxygen sensor based on Pt(II) complex embedded in sol-gel matrix

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ORMOSIL composite xerogel films film sequestered with luminophore platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) prepared by a sol-gel process. The composite xerogels studied are 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or n-propyltrimethoxysilane (n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS). Results show that, expect for PtTFPP-doped TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels show the high sensitivity and linear Stern-Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivities of the two oxygen sensors are quantified in terms of the ratio I_N2/I_O2, where I_N2 and I_O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped TFP-TriMOS/TEOS/Octyl-triEOS and n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensors have sensitivities of 101 and 155, respectively. The experimental results confirm that the current oxygen sensors exhibit the linear Stern-Volmer plots and high-sensitive based on the oxygen indicator embedded in TFP-TriMOS or n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels.     

Searching for optimal sensitivity of single-mode D-type optical fiber sensor in the phase measurement

To improve the sensitivity of a single-mode D-type optical fiber sensor, we selected a D-type optical fiber sensor with 4 mm long and 4 μm core thickness made of a single-mode fiber, a Au-coating on the sensor with a thickness range of 15–32 nm, a light wavelength of 632.8 nm, and an incident angle of 86.5–89.5° for different refractive index (1.33–1.40) sensing. These simulations are based on the surface plasmon resonance (SPR) theory using the phase method which shows that the sensitivity is proportional to the refractive index, Au film thickness and lower incident angle on the sensing interface. The sensitivity is higher than 4000 (degree/RIU), and the resolution is better than 2.5 × 10⁻⁶(RIU) as the minimum phase variation is 0.01°. This device is used to detect the refractive index or gas or liquid concentration in real-time. The proposed sensor is small, simple, inexpensive, and provides an in vivo test.     

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.     

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.     

Simultaneous determination of Zn(II), Cd(II) and Hg(II) in water

The use of artificial neural networks (ANNs) as a tool for simultaneous determination of Zn(II), Cd(II) and Hg(II) in water has been investigated, by employing an optode based on the 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (Br-PADAP) complex immobilised on Amberlite XAD-4 resin.

Studies were performed with binary and ternary mixtures of Zn(II), Cd(II) and Hg(II) ions in the 0–3.0 mg l⁻¹ range (prepared in pH 8.0 NH₄Cl solution), in order to avoid sensing phase saturation. A 0.1 mol l⁻¹ HCl solution was employed to regenerate the optode after each measurement. Reflectance measurements were recorded in the 400–800 nm region after pumping metal ion solution for 1, 1.5, 2.0, 2.5 and 3.0 min. Spectra were smoothed by employing a weighted sliding average of three reflectance intensities (weights of 1:3:1) and normalised to the reflectance intensities of the immobilised reagent in the NH₄Cl solution. A feed-forward ANN with error back-propagation training algorithm was employed for data treatment. The ANN was initially fed through seven inputs neurons, corresponding to reflectance intensities at 558, 568, 583, 590, 605, 615 and 623 nm, and optimised with respect to the number of hidden neurons, momentum and learning rate. Binary mixtures of Zn(II) and Cd(II), and Hg(II) and Cd(II) were employed to evaluate the capability of prediction by the ANN. Measurements were carried out in triplicate leading to standard deviations (expressed in mg l⁻¹) better than 0.29 for Cd(II), 0.38 for Hg(II) and 0.35 for Zn(II) and absolute errors better than 0.14 for Cd(II), 0.31 for Hg(II) and 0.36 for Zn(II). Similar results were obtained when solution mixtures containing all three metal ions were employed in the studies.

These results indicate that ANN can be employed for simultaneous determination of metal ions in water. However, attention must be given to the leaching and to the saturation of the sensing phase, which limit the lifetime and analytical range of the sensor, respectively.     

Azo dyes featuring a pyrene unit: New selective chromogenic and fluorogenic chemodosimeters for Hg(II)

Three new chemodosimeters 1–3 were prepared, and their chromogenic and fluorogenic behaviors toward various metal cations were investigated. Receptors 1–3 show exclusive response toward Hg²⁺ ion and also distinguish Hg²⁺from other metal cations by different color changes in DMSO aqueous solution (DMSO/H₂O = 9/1). Among them, receptor 1 also exhibits a pronounced Hg²⁺-induced fluorescence enhancement. Thus, the receptor 1 can be used as a colorimetric and fluorescent chemodosimeter for the determination of Hg²⁺ ion. The use of the test strip of the receptor 1 to detect Hg²⁺ was also reported.     

Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber

A novel wavelength modulation-based fiber-optic surface plasmon resonance (SPR) sensor is reported which utilizes both polarization separation and broad band radiation depolarization in polarization-maintaining fibers to enhance sensor stability. Theoretical analysis of the sensing structure with ideally separated polarizations based on the mode of expansion and propagation method is presented. The effect of polarization cross-coupling was also analyzed in the approximation of an equivalent bulk optic structure. A laboratory prototype of the fiber-optic SPR sensor was characterized in terms of sensitivity and resolution. Experimental results indicate that this fiber-optic SPR sensor is able to resolve refractive index changes as low as 4×10⁻⁶ under moderate fiber deformations.     

Hg2 + 离子传感器的最新研究进展

综述了汞离子传感器的最新研究进展，主要介绍了利用光化学传感器、离子选择电极和生物传感器检测汞离子的状况，重点分析比较了功能材料和传感器特性。在此基础上，介绍了我们的研究情况，通过两个阶段的固相反应合成了汞离子传感器，并且通过激光脉冲沉积(PLD)技术把靶材(汞离子传感器)制备在光寻址电位传感器(LAPS)的表面上，形成薄膜，实现了汞离子传感器的微型化。     

Designing of MIP-based QCM sensor for the determination of Cu(II) ions in solution

A novel quartz crystal microbalance (QCM) sensor with a high selectivity and sensitivity has been developed for the determination of Cu(II) ions, based on the modification of Cu(II) ion-imprinted polymer (Cu(II)-IIP) film onto a quartz crystal. The performance of the developed MIP-QCM sensor was evaluated and the results indicated that a sensitive MIP-QCM sensor could be fabricated. The obtained MIP-QCM sensor presents high-selectivity monitoring of Cu(II) ions, better reproducibility, shorter response time (6 min), wider linear range (0.001–50 μM) and lower detection limit (8 × 10⁻⁴ μM). The practical analysis of the MIP-QCM sensor confirms the feasibility of Cu(II) determination in wastewater.     

A mid-infrared optical fibre sensor for the detection of carbon monoxide exhaust emissions

An optical fibre presented is capable of monitoring the presence of carbon dioxide and carbon monoxide in the exhaust system of petrol engines. At present there exists no commercial sensor, which is capable of providing online measurements of these exhaust gases as required by European legislation. The design of this sensor using low cost and compact mid-infrared components, which make it suitable for insertion into a vehicle, is presented. Results are presented for 200 ppm step changes in concentration of carbon monoxide supplied from a laboratory controlled supply is presented.     

基于K~+交换平面光波导气体传感器检测丙酮蒸气

利用旋转甩涂法K+交换玻璃光波导元件表面上固定甲基绿/聚乙烯醇敏感膜,成功地研制出一种丙酮光学传感器。实验结果表明:传感器对浓度在25~650mg/m3范围内的丙酮蒸气具有良好的线性响应,相关系数为0.991 15(n=5),检出限达到11mg/m3(S/N=3),响应时间小于3 s。该传感器具有较好的可逆性、重复性和成本低等特点。     

Electrochemical copper (II) sensor based on self-assembled 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate

A 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate (AHMP)-based self-assembled monolayer (SAM) was formed on the gold electrode surface. Ellipsometric measurements evidenced the SAM formation on the gold electrode surface. The structural integrity of the modified gold electrode was also characterized by insulating properties of the SAM that were detected by cyclic voltammetry. The results of cyclic voltammetry showed that the SAM, which was formed by assembly of AHMP, was stable but did not completely block the redox-activity of ferrocene and K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. In contrast completely blocked redox-activity was observed after the treatment of AHMP-based SAM with saturated solution of 4-formylphenylboronic acid in 1,4-dioxan. The modified electrodes exhibited a selective response towards Cu(II) ions in the presence of some interfering ions such as Cd(II), Co(II), Fe(II), Ni(II) and Pb(II). This study is the first scientific report on the application of AHMP-modified electrode as a selective Cu(II) sensor in the presence of some interfering cations.     

Potential of 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) for a multifunctional sensor

An organic compound 5,10,15,20-Tetrakis(3′,5′-di-tertbutylphenyl)porphyrinatocopper(II) (TDTPPCu) is synthesized and studied as an active material for multifunctional capacitive sensor. The capacitance of the device as a function of illumination, humidity and temperature has been investigated. It is observed that the capacitance increases by 4.7 times from the dark condition under an illumination of 3850 lx. The capacitance is also changed 9.5 times with the increase in relative humidity (RH) from 30% to 95%. No change in capacitance appeared below critical temperature 120 °C. Based on the experimental results for the multifunctional sensor a mathematical model has been developed. The model is mainly based on the assumption that the capacitive response of the sensor is associated with dielectric polarization. The sensors are simulated using this model. The simulated results match well with experimental results.     

Optical VOCs detection using poly(3-alkylthiophenes) with different side-chain lengths

The use of conjugated polymers in the gas and volatile organic compounds (VOCs) detections represents an advance in the development of the electronic noses. Polythiophenes show good thermal and environmental stability, are easily synthesized and they have been studied as gas and VOCs sensors using different principles or transduction techniques. Among these techniques, optical sensing has been attracted attention, mainly due to its versatility. However, conjugated polymer-based optical sensors are still less studied. This paper describes the use of two poly(3-alkylthiophenes) for VOCs optical detection. The sensing measurements were carried out using visible spectroscopy. Both polymers showed good sensitivity to the VOCs, showing fast and reversible responses with some hysteresis, and were unable to detect hydroxylated samples. Furthermore, it was demonstrated that the thickness of polymer films influences the intensity of the optical response. Although there is similarity in the superficial composition of the polymers films, demonstrated by their surface energies, they showed significant differences in their optical properties upon exposure to the VOCs.     

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.