Lead detection in environmental water sample using an organoclay film-based attenuated total reflectance sensor

A novel, portable and cost-effective optical sensor for lead detection in water has been developed, which combines a miniature sensing platform based on multiple internal reflection attenuated total reflectance (MIR-ATR) with a one-step synthesized thiolated organoclay thin film. This film is highly effective for the sequestration and pre-concentration of Pb²⁺ ions. Lead was detected with high sensitivity achieved through the combination of multiple internal reflections and large Pb²⁺ uptake capacity of the organoclay after forming bright yellow lead-thiolate (PbS_x) complexes within the film. Un-optimized detection limits of 200 ppb Pb²⁺ in deionized water samples and slightly higher in Pb²⁺-spiked natural water samples were measured. The sensor response was reasonably fast and depended on the Pb²⁺ solution flow rate. The Pb²⁺ uptake at equilibrium was greater at slower flow rates, as Pb²⁺ ions require longer times to enter the galleries of the organoclay film and bind to the thiol groups. Operation of the sensor over pH values ranging from 5.0 to 7.0 appeared optimal for maximum sensitivity and longevity of the organoclay films. Lead-loaded films could resist up to 10 recycling treatments with acid before film degradation occurred.     

Sensitive cyclodextrin–polysiloxane gel membrane on EIS structure and ISFET for heavy metal ion detection

Cylodextrin (CD)–polysiloxane gel matrices are used to functionalize EIS (Electrolyte Insulator Semiconductor structure) and ISFET (Ion-Sensitive Field Transistor) devices. Electrochemical measurements were made to study the sensitivity and the selectivity of this sensitive membrane towards heavy metal ions. For both structures, a Nernstian response and good detection limit of an αCD gel membrane towards Cd²⁺ ion and for a βCD towards Pb²⁺ ion were obtained. The selectivity with respect to other cations are given through the potentiometric selectivity coefficients (K_ij).     

Preparation of Cu2O nano-colloid and its application as selective colorimetric sensor for Ag ion

Current work reports a method of preparation of stable yellow copper (I) oxide, nano-colloid by a solution route using Cu (II) salt solution and sodium borohydride. The reduction process was carried out in a controlled manner in air at around 50 °C in the presence of alginate matrix. The nanophase was characterized by techniques such as electronic spectroscopy, infrared spectroscopy, powder X-ray diffraction and transmission electron microscopy. Sensor property of the colloid for the detection of metal ions such as Ag⁺, Na⁺, K⁺, Ca²⁺, Pb²⁺, Cd²⁺, Zn²⁺, Hg²⁺, Mg²⁺ and As⁵⁺ has been studied at room temperature. A distinct color change from yellow to dark brown was noticed in the case of Ag⁺ ion. This is associated with a shift in ‘λ_max’ value from 448 nm to 478 nm. Whereas, no such significant visible color change was noticed on the addition of solutions containing other metal ions. Thus, in the present study Cu₂O nano-colloid was demonstrated as a highly specific and selective liquid colorimetric sensor for Ag⁺ ion.     

A dual functional near infrared fluorescent probe based on the bodipy fluorophores for selective detection of copper and aluminum ions

A new near infrared (NIR) fluorescent 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye with dual functionality was synthesized and characterized. The compound 1 responds to copper ion in NIR region with high selectivity through a photo-induced electron transfer process established between the substituted benzene group in the meso position and the BODIPY core when Cu²⁺ binds with the four oxygen atoms in the structure, and results in the quenching of the fluorescence. The response range to copper ions was from 10 to 50 μM, and other metal ions including Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Pb²⁺, Fe³⁺, Ag⁺, Hg²⁺, Co²⁺, Zn²⁺, Mn²⁺, Cd²⁺, Ni²⁺ and Al³⁺ had no interference. When excited at 520 nm, a new emission peak at 568 nm of compound 1 was used to detect Al³⁺ selectively from 30 μM to 110 μM without any interference from other metal ions including copper ions.     

Polythiophene based fluorescence sensors for acids and metal ions

Poly(thiophene-3-yl-acetic acid 8-quinolinyl ester) is a fluorescent material and it shows fluorescence at 540 nm. The fluorescence of poly (thiophene-3-yl-acetic acid 8-quinolinyl ester) has been studied in the presence of acids, metal ions, nucleotides and protein (l-proline). The fluorescence of polymer is quenched by the addition of HCl which could be recovered by the addition of equivalent amount of alkali. The Stern–Volmer quenching coefficient for HCl is calculated and found to be 141 M⁻¹. Moreover quenching depends on concentration of HCl. Similarly, the fluorescence of polymer is quenched by copper, cadmium and lead metal ions and quenching is sensitive to concentrations of metal ions. The Stern–Volmer quenching coefficient is 2.285 × 10³ M⁻¹ for Cu²⁺ ions, 2.287 × 10³ M⁻¹ for Cd²⁺ ions and 3.7 × 10⁴ M⁻¹ for Pb²⁺ ions. In Al³⁺, Zn²⁺, nucleotides and protein (l-proline), the fluorescence is exorbitantly increased.     

Electrochemical performances of B doped and undoped diamond-like carbon (DLC) films deposited by femtosecond pulsed laser ablation for heavy metal detection using square wave anodic stripping voltammetric (SWASV) technique

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets.In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd²⁺, Pb²⁺, Ni²⁺ and Hg²⁺, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at −1.3 V deposition potential, and 90 s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si₃N₄ electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 μg/L or 2 μg/L and a dynamic range from 1 or 2 to 25 μg/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 μA/ppb or μA μg⁻¹ L for Cd²⁺, Pb²⁺, Ni²⁺ and Hg²⁺, respectively.     

A highly selective triphenylamine-based indolylmethane derivatives as colorimetric and turn-off fluorimetric sensor toward Cu detection by deprotonation of secondary amines

A new triphenylamine-based fluorogenic probe bearing an indolylmethane unit (R1) was developed as a fluorescent chemosensor with high selectivity toward Cu²⁺ over other cations tested. The new probe R1 only sensed Cu²⁺ among heavy and transition metal (HTM) ions in CH₃CN/H₂O (70/30, v/v) solution. The capture of Cu²⁺ by the receptor resulted in deprotonation of the secondary amine conjugated to the triphenylamine, so that the electron-donation ability of the “N” atom would be greatly enhanced; thus sensor showed a 250 nm change in the new absorption band (from 291 nm to 541 nm) and a large colorimetric response, it also exhibited the large decrease in fluorescence intensity at 378 nm and affinity to Cu²⁺ over other cations such as Hg²⁺, Fe³⁺, Pb²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Mn²⁺ make this compound a useful chemosensor for Cu²⁺ detection in CH₃CN/H₂O (70/30, v/v) mixture. The probe R1 (c = 1.0 × 10⁻⁶ M) displayed significant fluorescence change and colorimetric change upon addition of Cu²⁺ among the metal ions examined.     

Cu2+-ISFET type microsensors based on thermally evaporated p-tert-butylcalix[9 and 11]arene thin films

Large size odd-numbered calixarenes were used for the first time as ionophoric agents for the functionalization of ISFET microsensors and EIS structures through thermal evaporation process. Both calixarenes have shown a nernstian sensitivity over three decades towards only copper (II) activities. Very low selectivity coefficients were observed for K⁺ and Ca²⁺ whereas Cd²⁺ and Pb²⁺ (less than 10⁻³) can be considered as interfering ions. Lifetime of around three months for the microsensors were obtained.     

Potassium ion sensing using a self-assembled calix[4]crown monolayer by surface plasmon resonance

The precise detection of K⁺ ion is crucial because K⁺ ion plays a leading role in membrane transport. Current K⁺ ion detection methods suffered low resolution and detection limit. Calix[4]crown-5 derivatives are well known as K⁺ ionophores. We described here a K⁺ ion-sensing system using a self-assembled monolayer of calix[4]crown-5 derivative (calix[4]crown) modified gold chip based on surface plasmon resonance (SPR). The calix[4]crown sensing layer was characterized by atomic-force microscopy (AFM), SPR, Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) and cyclic voltammetry (CV). It was found calix[4]crown was assembled as a monolayer on Au surface. The SPR angle was found to be modulated by various concentrations of K⁺ ion due to the interaction between the calix[4]crown and K⁺ ion. This calix[4]crown monolayer showed a more sensitive and selective binding toward potassium ion over other alkali and alkaline earth metal ions. From the simple SPR spectroscopic analysis, we were able to monitor K⁺ ion concentration with a wide range of 1.0 × 10⁻¹² to 1.0 × 10⁻² M in an aqueous solution with a pH 6–8. These experimental results showed a useful method for the design of simple and precise potassium ion biosensors.     

A review of the use of the potentiometric electronic tongue in the monitoring of environmental systems

This paper introduces electronic tongue systems for remote environmental monitoring applications. This new approach in the chemical sensor field consists of the use of an array of non-specific sensors coupled with a multivariate calibration tool which may form a node of a sensor network. In our work, the proposed arrays were made up of potentiometric sensors based on polymeric membranes, and the subsequent cross-response processing was based on a multilayer artificial neural network model. Two cases are described: the environmental monitoring of ammonium pollutant plus alkaline ions at different measuring sites in the states of Mexico and Hidalgo (Mexico), and the monitoring of heavy metals (Cu²⁺, Pb²⁺, Zn²⁺ and Cd²⁺) in open air waste streams and rivers heading down the Gulf of Mexico.     

An All-solid-state Cd-selective electrode with a low detection limit

A new all-solid-state Cd²⁺-selective electrode with a low detection limit was prepared by using conjugated thiophene oligomer α-sexithiophene (α-6T) as solid contact deposited between an ionophore-doped poly(vinyl chloride) membrane and a gold disc substrate. The electrode exhibited a Nernstian response for Cd²⁺ ions over a wide concentration range of 10⁻³-10⁻⁷ M with a detection limit as low as 1.3 × 10⁻⁸ M. Results showed that the fabricated potentiometric sensor was suitable for use within the pH range of 2.0-9.0 and exhibited good reproducibility for long-term measurements.     

Detection of heavy metal ions in aqueous solution by P(MBTVBC-co-VIM)-coated QCM sensor

A novel copolymer P(MBTVBC-co-VIM) was designed and successfully synthesized for the fabrication of copolymer-coated QCM sensors to detect the heavy metal ions in aqueous solution. The copolymer P(MBTVBC-co-VIM) contains many nitrogen (N) and sulfur (S) atoms in the side groups as electron donors, which can easily form complexes with heavy metal ions. The strong interaction between the S atom and Au electrode of quartz crystal further assures the stability of copolymer thin films on the quartz crystal surface in aqueous media. The QCM results indicated that the P(MBTVBC-co-VIM)-coated sensor exhibited high sensitivity, stability and selectivity for the detection of Cu²⁺ in aqueous solution. The lowest detection limit can reach 10 ppm Cu²⁺ in aqueous solution, which resulted in the frequency shift of 3.0 Hz (ΔF₃/3). The P(MBTVBC-co-VIM)-coated QCM sensors had porous surface morphologies as revealed by AFM investigation. Such porous structures enhanced the surface areas of the copolymer thin films, which increased the contacting probability of N and S atoms with heavy metal ions in solution and improved the detection sensitivity of the copolymer-coated QCM sensors.     

Large nanoparticle-induced enhancement of recognition selectivity for Cu ion

A new fluorescent excited state intramolecular proton transfer compound, 2-(2-hydroxy-4-carbaldehydephenyl)benzoxazole (HCPBO), has been synthesized for the detection of Cu²⁺, based on its fluorescence quenching. In molecular monodispersed solution, the recognition selectivity for Cu²⁺ was poor as Co²⁺ and Ni²⁺ gave similar results in fluorescence quenching. However, the nanoparticles of HCPBO, prepared in ethanol-water (1:4, v/v), greatly enhanced the recognition selectivity for Cu²⁺. The mechanism was discussed as energy transfer (ET), energy migration (EM) and the more quantity of formed HCPBO-Cu²⁺ complex than other metal ions in the nanoparticle conditions enhanced the recognition selectivity for Cu²⁺ together.     

A new acridine derivative as a highly selective ‘off-on’ fluorescence chemosensor for Cd in aqueous media

A new acridine fluoroionophore containing two diethanolamine ligands, 4,5-bis(N,N-di (2-hydroxyethyl)iminomethyl)acridine (BHIA), was designed and synthesized based on the fluorophore-spacer-receptor format. And its fluorescent sensing behavior towards metal ions was investigated in buffered aqueous media. The presence of Cd²⁺ induces the formation of a 1:1 ligand/metal complex at neutral pH, which exhibits enhanced emission at 454 nm. The fluorescence intensity is linear with the Cd²⁺ concentration in the range of 1.0 × 10⁻⁶ to 3.0 × 10⁻⁵ M (R = 0.9967). Experimental results show a low interference response towards other metal ions. The selective switch-on fluorescence response of BHIA to Cd²⁺ makes it suitable for sensing of Cd²⁺ in aqueous solution. The detection limit is 1.3 × 10⁻⁷ M. Moreover, the results indicated that BHIA was a reversible chemosensor for Cd²⁺, which makes it attractive for sensing applications.     

High sensitive optode for selective determination of Ni based on the covalently immobilized thionine in agarose membrane

A novel Ni²⁺ optode was prepared by covalent immobilization of thionine, 3,7-diamine-5-phenothiazoniom thionineacetate, in a transparent agarose membrane. Influences of various experimental parameters on Ni²⁺ sensing, including the reaction time, the solution pH and the concentration of reagents were investigated. Under the optimized conditions, a linear response was obtained for Ni²⁺ concentrations ranging from 1.00 × 10⁻¹⁰ to 1.00 × 10⁻⁷ mol l⁻¹ with an R² value of 0.9985. The detection limit (3σ) of the method for Ni²⁺ was 9.30 × 10⁻¹¹ mol l⁻¹. The influence of several potentially interfering ions such as Ag⁺, Hg²⁺, Cd²⁺, Zn²⁺, Pb²⁺, Cu²⁺, Mn²⁺, Co³⁺, Cr³⁺, Al³⁺ and Fe³⁺ on the determination of Ni²⁺ was studied and no significant interference was observed. The membrane showed a good durability and short response time with no evidence of reagent leaching. The membrane was successfully applied for the determination of Ni²⁺ in environmental water samples.     

A Hg fluorescent chemosensor without interference from anions and Hg-imaging in living cells

A fluorescent chemosensor, B2, for Hg²⁺ containing a BODIPY fluorophore and carboxyl-thiol metal-bonding moieties was described. B2 exhibits selective fluorescence enhancement (123-fold) toward Hg²⁺ over other metal ions. Especially, the fluorescence enhancement was unaffected by anions existing in environment and organism. B2 shows high sensitivity to Hg²⁺ in a concentration of ppb range with detection limit of 77 nM. B2-ester, the membrane-permeable ethyl ester, is able to be hydrolyzed to B2 in vivo, and successfully applied to image intracellular Hg²⁺ in living cells.     

Effect of alkali metal ions co-doping on the structure and luminescent properties of phosphor Zn3(BO3)2:Eu3+

A series of the Zn₃(BO₃)₂:Eu³⁺ without or with alkali metal ions doping at a low sintering temperature were synthesized by the solid-state reaction method. The XRD pattern shows that all samples exhibit Zn₃(BO₃)₂ crystalline phase. The samples co-doped with alkali metal ions have better crystallinity compared with the un-compensated ones. The different charge compensation approaches have no influence on the shape and position of the emission and excitation spectra. However, the luminescent intensity of samples has been obviously enhanced with different alkali metal ions co-doping. The introduction of Li⁺ can increase the red emission of Eu³⁺ compared with the others. Thus, the volume compensation and the equilibrium of mole number can be taken into consideration by charge compensated (CC) approaches.     

Lead (II) carbon paste electrode based on derivatized multi-walled carbon nanotubes: Application to lead content determination in environmental samples

For the first time a novel derivatized multi-walled carbon nanotubes-based Pb²⁺ carbon paste electrode is reported. The electrode with optimum composition, exhibits an excellent Nernstian response to Pb²⁺ ion ranging from 5.9 × 10⁻¹⁰ to 1.0 × 10⁻² M with a detection limit of 3.2 × 10⁻¹⁰ M and a slope of 29.5 ± 0.3 mV dec⁻¹ over a wide pH range (2.5-6.5) with a fast response time (25 s) at 25 °C. Moreover, it also shows a high selectivity and a long life time (more than 3 months). Importantly, the response mechanism of the proposed electrode was investigated using AC impedance technique. Finally, the electrode was successfully applied for the determination of Pb²⁺ ion concentration in environmental samples, e.g. soils, waste waters, lead accumulator waste and black tea, and for potentiometric titration of sulfate anion.     

Fe-selective fluorescent probe based on rhodamine B and its application in bioimaging

A Rhodamine-based fluorescent and colorimetric chemosensor for Fe³⁺ ion, acetyl rhodamine-hydroxamate (ARH), was designed and synthesized. Upon mixed with Fe³⁺ in CH₃CN-H₂O (1:1, v/v), the spirolactam of ARH was opened, which resulted in the dramatic enhancement of both fluorescence and absorbance intensity as well as the color change of the solution. Background metal ions showed small or no interference with the detection of Fe³⁺. The Job's plot indicated the formation of 1:1 complex between ARH and Fe³⁺. Confocal laser scanning microscopy experiments showed that ARH could be used to detect Fe³⁺ in living cells.     

Novel pyrazoline-based selective fluorescent sensor for Zn in aqueous media

This work describes the preparation of a novel pyrazoline compound and the properties of its UV-vis absorption and fluorescence emission. Moreover, this compound can be used to determine Zn²⁺ ion with high selectivity and a low detection limit in the HEPES (20 mM HEPES, pH = 7.2, 50% (v/v) CH₃CN) buffer solution. This sensor forms a 1:1 complex with Zn²⁺ and shows a fluorescent enhancement by chelation enhanced fluorescence effect with good tolerance of other metal ions. In addition, this sensor is very sensitive with fluorometric detection limit of 0.12 μM.