A novel optical sensor for uranium determination

A metal ion indicator, Alizarin Red S, was tested for its potential use in uranium selective optode membrane. The water-soluble indicator was lipophilized in the form of an ion pair with tetraoctylammonium bromide, and subsequently immobilized on a triacetyl cellulose membrane. The membrane responds to uranium ions, giving a color change from yellow to violet in acetate buffer pH 5. This optode has a linear range of (1.70-18.7) × 10⁻⁵ M of UO₂²⁺ ions with a limit of detection of 5 × 10⁻⁶ M. The response time of optode was within 6 min depending on the concentration of UO₂²⁺ ions. The sensor can readily be regenerated with hydrochloric acid solution (0.01 M). The optode is fully reversible.     

A novel ion selective membrane potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II)

A new PVC membrane potentiometric sensor that is highly selective to Fe(III) ions was prepared by using 2-[(2-hydroxy-1-propenyl-buta-1,3-dienylimino)-methyl]-4-p-tolylazo-phenol [HPDTP] as a suitable carrier. The electrode exhibits a linear response for iron(III) ions over a wide concentration range (3.5 × 10⁻⁶ to 4.0 × 10⁻²) with a super Nernstian slope of 28.5 (±0.5) per decade. The electrode can be used in the pH range from 4.5 to 6.5. The proposed sensor shows fairly a good discriminating ability towards Fe³⁺ ion in comparison to some hard and soft metals such as Fe²⁺, Cd²⁺, Cu²⁺, Al³⁺ and Ca²⁺. It has a response time of <15 s and can be used for at least 2 months without any measurable divergence in response characteristics. The electrode was used in the direct determination of Fe³⁺ in aqueous samples and as an indicator electrode in potentiometric titration of Fe(III) ions.     

A graphene-based electrochemical sensor for sensitive and selective determination of hydroquinone

Graphene was prepared by electrochemical reduction of exfoliated graphite oxide at cathodic potentials, and used to fabricate a graphene-modified glassy carbon electrode (GCE) which was applied in a sensor for highly sensitive and selective voltammetric determination of hydroquinone (HQ). Compared to a bare (conventional) GCE, the redox peak current for HQ in pH 5.7 acetate buffer solution is significantly increased, indicating that graphene possesses electrocatalytic activity towards HQ. In addition, the peak-to-peak separation is significantly improved. The modified electrode enables sensing of HQ without interference by catechol or resorcinol. Under optimal conditions, the sensor exhibits excellent performance for detecting HQ with a detection limit of 0.8?μM, a reproducibility of 2.5% (expressed as the RSD), and a recoveries from 98.4 to 101.2%.

Metal ion based chiral fluorescence sensor selective for dihydrogenphosphate

A Cu(II) based conformationally restricted chiral fluorescence sensor (receptor 2) has been designed and synthesized for selective sensing of anions. The anion recognition property of the Cu²⁺-complex has been studied in acetonitrile by fluorescence methods which show remarkable sensitivity toward dihydrogen phosphate via fluorescence modulation of the Cu²⁺-complex over the other anions examined.     

A PVC-based 1,8-diaminonaphthalen electrode for selective determination of vanadyl ion

A PVC membrane vanadyl (VO²⁺) ion-selective electrode was constructed using 1,8-diaminonaphthalen (DAN) as a neutral carrier. The electrode shows good Nernstian response for VO²⁺ ions over a wide concentration range (1.0×10⁻¹-1.0×10⁻⁵ M). The optimum composition of the membrane was 55 wt.% poly(vinylchloride), 35 wt.% 2-nitrophenyl octyl ether (NPOE), 5 wt.% ionophore, and 5 wt.% potassium tetrakis(p-chlorophenyl)borate (KTpClPB). It has relatively fast response time and can be used at least for 5 weeks without any considerable divergence in potentials. The proposed electrode revealed relatively good selectivity for VO²⁺ over wide variety of other metal ions. The electrode was used for the potentiometric titration of VO²⁺ ions with EDTA.     

A novel ferroin membrane sensor for potentiometric determination of iron

A novel potentiometric approach for both batch and flow injection determination of iron(II) and/or iron(III) is described. It is based on the formation and monitoring of ferroin with a PVC membrane sensor containing ferroin-TPB as an electroactive component plasticized with 2-nitrophenyl phenyl ether. The sensor exhibits fast Nernstian response for ferroin with a cationic calibration slope of 30 +/- 0.2 mV/concentration decade down to 4 x 10(-7)M ferroin (0.03 ppm Fe) at pH 3-9. Interferences from common inorganic cations are negligible or can be eliminated by a pretreatment with DDC. The ferroin sensor was successfully applied to the determination of iron contents in water, alloys, rocks and pharmaceuticals. The results show good correlation with data obtained by the standard spectrophotometric ferroin method, the coefficient of correlation is better than 0.7%.     

A novel palygorskite-modified carbon paste amperometric sensor for catechol determination

A palygorskite-modified carbon paste electrode (CPE) was constructed using graphite powder mixed with palygorskite particles. Compared with the unmodified CPE, the resulting palygorskite-modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the palygorskite exhibits catalytic activity to catechol and significantly improves the determining sensitivity. The electrocatalytic activity of palygorskite is attributed to its high adsorption capability and the –OH groups on its surface, which plays an important role in the electron transfer between the modified CPE and the catechol in the solution. The sensor shows a linear response range between 5 and 100 μM catechol with a correlation coefficient of 0.998. The detection limit was calculated as 0.57 μM (s/n = 3).     

A novel chemiluminescence flow-through sensor for the determination of analgin

A novel chemiluminescence (CL) flow-through sensor for the determination of analgin with flow-injection analysis (FIA) based on the auto-oxidation of analgin in the presence of Tween 80 sensitized by Rhodamine 6G immobilized on a cation-exchange column is described. This sensor responds linearly to the analgin concentration in the range of 0.4 ∼ 10 mg/L, with a detection limit (3σ) of 0.15 mg/L. A complete analysis, including sampling and washing, takes 1 min with a relative standard deviation of < 5%. The sensor is stable for over 200 determinations and has successfully been applied to the determination of analgin in pharmaceutical preparations. Received: 1 October 1998 / Revised: 19 April 1999 / Accepted: 6 May 1999     

A novel piezo-optical styrene sensor incorporating polymer-supported tribromide ion

Encapsulation of Amberlyst A-26 supported tribromide in a 10,000 MW polyethylene glycol matrix gives a robust colour-sensitive reagent matrix which can be deposited on indium-tin oxide coated polyvinylidene fluoride (PVDF) piezoelectric film for the detection of styrene (and other alkene) vapours.     

A novel amperometric sensor and chromatographic detector for determination of parathion

A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10^–9–2.0×10^–5 mol L^–1. The detection limit was 1.0×10^–9 mol L^–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10^–9 mol L^–1. Application of the method for determination of parathion in rice was satisfactory.     

Conducting polymer ion sensor electrodes-III. Potentiometric sulfide ion selective electrode

A new potentiometric sensor electrode for sulfide based on conducting polymer films is introduced. The electrode is formed by electrochemically depositing a film of poly(3-methylthiophene) and poly(dibenzo-18-crown-6) onto an alloy substrate. Different methods were used for the electrode preparations. The alloy used has a low melting point, which allowed its use for manufacturing a microsize version of this electrode. The electrode response is stable for 3 days. The working temperature range for this electrode is between 10 and 40 degrees C. The linear dynamic range is 1.0x10(-7)-1.0x10(-2) M and measures total sulfide concentration over a range of pH from 1 to 13. The polymer electrode showed high selectivity for sulfide in the presence of many common interfering anions. The electrode is useful for the measurement of total sulfide in biological environments and can be manufactured in the micron scale. Therefore, it will be useful for the measurement within biofilms.     

A novel barium polymeric membrane sensor for selective determination of barium and sulphate ions based on the complex ion associate barium(II)-Rose Bengal as neutral ionophore

A simple, long life, rapid response and sensitive barium(II)-PVC membrane sensor that typically follows Nernstian behavior has been developed for the assay of barium(II) ions. The developed sensor has been made by incorporating the complex ion associate of barium(II)-Rose Bengal (Ba-RB) as an ionophore into a plasticized PVC matrix. The sensor is stable and exhibited fast potential response of 20 s and gave a good linear response with a Nernstian slope of 28.5 ± 0.4 mV/decade of activity within the concentration range 5 × 10⁻⁵ to 10⁻¹ M over a wide range of pH 4.5-10.0 for barium(II) ions. The developed sensor showed comparatively good selectivity for barium(II) ions with respect to other alkali, alkaline earth, transition and heavy metal ions. The plasticizer o-nitrophenyloctyl ether controlled significantly the calibration slope and the lifetime of the fabricated sensor. The proposed sensor was used successfully for the analysis of barium(II) ions in wastewater samples and in lithophone pigment with excellent recovery percentages in the range 98.9-99.8 ± 1.6%. The determination of sulphate in fresh and potable water samples with the developed sensor has been also achieved successfully. The described sensor provides a reliable means with good correlation with the data obtained by atomic absorption spectrometry (AAS) and other spectrophotometric methods for the analysis of trace amounts of barium(II) and/or sulphate ions in different matrices.     

A highly selective and sensitive perylenebisimide-based fluorescent PET sensor for Al determination in MeCN

A novel ‘turn-on’ fluorescent probe with perylene tetracarboxylic bisimide (PBI) as the fluorophore and di(2-(salicylideneamino))ethylamine (DSEA) as the metal ion receptor was designed. The capability of the prepared probe to detect metal ions was evaluated by the changes in its emission intensity. The probe demonstrated a considerable emission enhancement (ca. 110-fold) in the presence of Al³⁺ in MeCN with high selectivity and sensitivity. Furthermore, the considerably ‘off–on’ fluorescence response concomitantly led to the apparent color change from colorless to brilliant yellow, which could also be identified by naked eye easily under UV lamp.     

A novel potassium ion membrane sensor based on rifamycin neutral ionophore

A novel potentiometric membrane sensor for potassium ion based on the use of rifamycin as a neutral ionophore is described. The sensing membrane is formulated with 2 wt.% rifamycin-SV, 69 wt.% dibutylsebacate plasticizer and 29 wt.% PVC. Linear and stable potential response with near-Nernstian slope of 56.7 +/- 0.2 mV decade(-1) are obtained over the concentration range 1 x 10(-1)-3 x 10(-5) M K(+). The detection limit is 0.3 microg ml(-1) K(+), the response time is 10-30 s and the working pH range is 4-11. Responses of the sensor toward alkali and alkaline earth metal ions are in the order K(+) > Rb(+) > Cs(+) > Na(+) > NH(4)(+) > Ba(2+) > Mg(2+) > Ca(2+) > Sr(2+) > Li(+). The selectivity coefficient data reveal negligible interference from transition metal ions. Direct potentiometric determination of K(+) in the presence of 10-50-fold excess of alkali and alkaline earth metals gives results with an average recovery of 99.1%, and a mean standard deviation of 1.2%. The data agree fairly well with those obtained by flame photometry.     

A selective supramolecular photochemical sensor for dopamine

Dopamine (DA) is an important biomarker for diseases and biological disorders. Existing techniques for DA detection suffer from drawbacks including low sensitivity and selectivity as well as interfering signals from non-target molecules. A simple and selective photochemical sensor for the determination of DA in a supramolecular manner is presented. This approach utilises the complexation properties of a highly fluorescent water-soluble complex of perylene bis(diimide) dye with the macrocyclic host cucurbit[8]uril. The method can be used for the determination of DA in aqueous media, with detection limits below 2 × 10^? 5 M, even in the presence of known interferents including ascorbic acid and the catecholamines epinephrine and norepinepherine.     

A novel sensor of cysteine self-assembled monolayers over gold nanoparticles for the selective determination of epinephrine in presence of sodium dodecyl sulfate

A novel sensor of cysteine self-assembled monolayers over gold nanoparticles modified gold electrode has been constructed for the determination of epinephrine in presence of sodium dodecyl sulfate (Au/Au(nano)-CysSDS). Electrochemical investigation and characterization of the modified electrode are achieved using cyclic voltammetry, linear sweep voltammetry, and scanning electron microscopy. The Au/Au(nano)-CysSDS electrode current signal is remarkably stable via repeated cycles and long term stability, due to the strong Au-S bond, compared to the Au/Au(nano) electrode. The catalytic oxidation peak currents obtained from linear sweep voltammetry (LSV) increased linearly with increasing epinephrine concentrations in the range of 2 to 30 μmol L(-1) and 35 to 200 μmol L(-1) with correlation coefficients of 0.9981 and 0.9999 and a limit of detection of 0.294 nmol L(-1) and 1.49 nmol L(-1), respectively. The results showed that Au/Au(nano)-CysSDS can selectively determine epinephrine in the coexistence of a large amount of uric acid and glucose. In addition, a highly selective and simultaneous determination of tertiary mixture of ascorbic acid, epinephrine, and acetaminophen is explored at this modified electrode. Excellent recovery results were obtained for determination of epinephrine in spiked urine samples at the modified electrode. Au/Au(nano)-CysSDS can be used as a sensor with excellent reproducibility, sensitivity, and long term stability.     

Liquid membrane potentiometric sensor for determination of Fe3+ ion

Solution studies showed a selective interaction between the new synthesized ionophore, 2-[(thiophen-2-yl)methyleneamino]isoindoline-1,3-dione (TMID) and Fe(III) ion. Therefore, TMID was used as an iron selective ion-carrier in a plasticized liquid membrane sensor. The linear response range of the proposed electrode was 1.0 × 10^?6–1.0 × 10^?2 M. The Nernstian slope of 20.1 ± 0.3 mV/decade, and a detection limit of 5 × 10^?7 M was obtained. The sensor could be used in the pH range of 2.3–4.8, and the response time was about 10 s. The lifetime of the electrode was at least 7 weeks. The sensor accuracy was investigated in two ways: (i) with the potentiometric titration of a Fe³⁺ solution with EDTA and (ii) with Fe(III) monitoring in some cationic mixtures. Finally, the newly fabricated electrode was effectively applied as an indicator electrode for the direct Fe³⁺ determination in real samples.     

A "turn-on" fluorescent sensor for the selective detection of mercuric ion in aqueous media

A water-soluble turn-on fluorescent sensor for Hg(II) is described. Incorporation of soft thioether donors into an aniline-derived ligand framework that can be linked to a fluorescein platform affords sensor MS1, which shows a approximately 5-fold increase in integrated emission upon addition of 1 equiv of Hg(II). The synthesis and metal-binding properties of MS1 are discussed, and its ability to detect environmentally relevant concentrations of Hg(II) is demonstrated.     

A microchip sensor for calcium determination

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca²⁺ ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g⁻¹ polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca²⁺ determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 × 10⁻⁵ – 5.71 × 10⁻⁴ M Ca²⁺, with a limit of detection (LOD) of 2.68 × 10⁻⁵ M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.