A Potentiometric Flow Biosensor Based on Ammonia-Oxidizing Bacteria for the Detection of Toxicity in Water

A flow biosensor for the detection of toxicity in water using the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea as a bioreceptor and a polymeric membrane ammonium-selective electrode as a transducer is described. The system is based on the inhibition effects of toxicants on the activity of AOB, which can be evaluated by measuring the ammonium consumption rates with the ammonium-selective membrane electrode. The AOB cells are immobilized on polyethersulfone membranes packed in a holder, while the membrane electrode is placed downstream in the flow cell. Two specific inhibitors of the ammonia oxidation. allylthiourea and thioacetamide. have been tested. The IC50 values defined as the concentration of an inhibitor causing a 50% reduction in the ammonia oxidation activity have been measured as 0.17 mu M and 0.46 mu M for allylthiourea and thioacetamide, respectively. The proposed sensor offers advantages of simplicity, speed and high sensitivity for measuring toxicity in water.A flow biosensor for the detection of toxicity in water using the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea as a bioreceptor and a polymeric membrane ammonium-selective electrode as a transducer is described. The system is based on the inhibition effects of toxicants on the activity of AOB, which can be evaluated by measuring the ammonium consumption rates with the ammonium-selective membrane electrode. The AOB cells are immobilized on polyethersulfone membranes packed in a holder, while the membrane electrode is placed downstream in the flow cell. Two specific inhibitors of the ammonia oxidation. allylthiourea and thioacetamide. have been tested. The IC50 values defined as the concentration of an inhibitor causing a 50% reduction in the ammonia oxidation activity have been measured as 0.17 mu M and 0.46 mu M for allylthiourea and thioacetamide, respectively. The proposed sensor offers advantages of simplicity, speed and high sensitivity for measuring toxicity in water

Optical Ion Sensing Platform Based on Potential-Modulated Release of Enzyme

We report here on an optical ion sensing platform, in which a polymeric membrane ion-selective electrode (ISE) serves as not only a potentiometric transducer for ion activities in the sample solution but also a reference electrode for the potential-modulated release of enzyme from an iron alginate-horseradish peroxidase (HRP) thin film modified working electrode. The ISE and working electrode are physically separated by a salt bridge: The dissolution of the HRP-embedded thin film can be triggered by the reduction of Fe3+, which is modulated by the potential response of the ISE to the target ion in the sample. The released enzyme induces the, oxidation of its substrate mediated by H2O2, to produce a visual color change. With this setup, an optical ion sensing platform for both cations (e.g., NH4+) and anions,(e.g., Cl-) can be obtained. The proposed platform provides a general and versatile visual-sensing strategy for ions and allows optical ion sensing in colored and turbid solutions

DNA nanostructure-based magnetic beads for potentiometric aptasensing

In this work, a simple, general, and sensitive potentiometric platform is presented, which allows potentiometric sensing to be applied to any class of molecule irrespective of the analyte charge. DNA nanostructures are self-assembled on magnetic beads via the incorporation of an aptamer into a hybridization chain reaction. The aptamer target binding event leads to the disassembly of the DNA nanostructures, which results in a dramatic change in the surface charge of the magnetic beads. Such a surface charge change can be sensitively detected by a polycation-sensitive membrane electrode using protamine as an indicator. With an endocrine disruptor bisphenol A as a model, the proposed potentiometric method shows a wide linear range from 0.1 to 100 nM with a low detection limit of 80 pM (3 sigma). The proposed sensing strategy will lay a foundation for the development of potentiometric sensors for highly sensitive and selective detection of various targets

Potentiometric Aptasensing of Vibrio alginolyticus Based on DNA Nanostructure-Modified Magnetic Beads

A potentiometric aptasensing assay that couples the DNA nanostructure-modified magnetic beads with a solid-contact polycation-sensitive membrane electrode for the detection of Vibrio alginolyticus is herein described. The DNA nanostructure-modified magnetic beads are used for amplification of the potential response and elimination of the interfering effect from a complex sample matrix. The solid-contact polycation-sensitive membrane electrode using protamine as an indicator is employed to chronopotentiometrically detect the change in the charge or DNA concentration on the magnetic beads, which is induced by the interaction between Vibrio alginolyticus and the aptamer on the DNA nanostructures. The present potentiometric aptasensing method shows a linear range of 10-100 CFU mL(-1) with a detection limit of 10 CFU mL(-1), and a good specificity for the detection of Vibrio alginolyticus. This proposed strategy can be used for the detection of other microorganisms by changing the aptamers in the DNA nanostructures

A potentiometric biosensing system based on an isolated degrading bacterium Klebsiella sp MP-6 for the determination of methyl parathion

A potentiometric sensing system for the sensitive and selective detection of methyl parathion (MP) is described in this paper. The system is based on a degrading bacterium Klebsiella sp. MP-6 as recognition element and a polymeric membrane anion-sensitive electrode as a transducer. Klebsiella sp. MP-6 can be isolated from long-term organophosphorus pesticide contaminated soils, which is capable of biodegrading MP to produce p-nitrophenol. The product can be deprotonated under basic conditions and thus detected by using the anion exchanger based membrane electrode. The bioreactor is prepared by packing the bacterial cells between two polyether sulfone membranes placed in a holder. Molecularly imprinted solid-phase extraction using the MP imprinted polymer as a sorbent enables accumulation and separation of MP from real samples. Under the optimized experimental conditions, the potential response of the biosensing system is linear with the MP concentration in the range of 5-100 nM. The detection limit is 1 nM. The electrode exhibits an excellent selectivity towards other organophosphorus pesticides. The sensing system has been evaluated with spiked water samples and shows good recovery and high accuracy. This methodology is promising to develop potentiometric sensors for detecting organophosphorus pesticides at trace levels in the environment.A potentiometric sensing system for the sensitive and selective detection of methyl parathion (MP) is described in this paper. The system is based on a degrading bacterium Klebsiella sp. MP-6 as recognition element and a polymeric membrane anion-sensitive electrode as a transducer. Klebsiella sp. MP-6 can be isolated from long-term organophosphorus pesticide contaminated soils, which is capable of biodegrading MP to produce p-nitrophenol. The product can be deprotonated under basic conditions and thus detected by using the anion exchanger based membrane electrode. The bioreactor is prepared by packing the bacterial cells between two polyether sulfone membranes placed in a holder. Molecularly imprinted solid-phase extraction using the MP imprinted polymer as a sorbent enables accumulation and separation of MP from real samples. Under the optimized experimental conditions, the potential response of the biosensing system is linear with the MP concentration in the range of 5-100 nM. The detection limit is 1 nM. The electrode exhibits an excellent selectivity towards other organophosphorus pesticides. The sensing system has been evaluated with spiked water samples and shows good recovery and high accuracy. This methodology is promising to develop potentiometric sensors for detecting organophosphorus pesticides at trace levels in the environment

A chronopotentiometric flow injection system for aptasensing of E. coli O157

In this research, we demonstrate a simple flow injection analysis system for chronopotentiometric aptasensing of E. coli O157. The sensing protocol is based on using an aptamer as a bioreceptor and the current-driven-release of protamine from a polyion-sensitive membrane electrode as a signal reporter

Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs

Solid-contact K+-selective electrode based on three-dimensional molybdenum sulfide nanoflowers as ion-to-electron transducer

Three-dimensional (3D) molybdenum sulfide (MoS2) nanoflowers have been synthesized via a novel hydrothermal method and applied as ion-to-electron transducer for solid-contact ion-selective electrodes (SC-ISEs). The morphology and elemental composition of the prepared nanomaterials have been characterized. The performance of the developed K+-SC-ISE has been demonstrated by determining K+ in solution with a polymeric membrane containing valinomycin as the ionophore. A Nernstian slope of 55.8 mV/decade with a detection limit of 10(-5.5) M can be obtained. Using the 3D flowerlike MoS2 as solid contact, the fabricated K+-SC-ISE exhibits a smaller impedance and more stable potential response than the coated-wire electrode. In addition, the novel SC-ISE behaves well in the water layer test and shows good resistance to interferences from light, O-2 and CO2. It is believed that the 3D MoS2 nanoflowers can be a good alternative as solid contact in SC-ISEs. (C) 2016 Elsevier B.V. All rights reserved

An enzyme-free glucose sensor based on a difunctional diboronic acid for molecular recognition and potentiometric transduction

On the basis of the unusual anionic potential response of a diboronic acid and its ability to specifically recognize glucose, a highly selective enzyme-free potentiometric glucose sensor was developed

Determination of hydroxylated polychlorinated biphenyls by offline solid-phase extraction-liquid chromatography-tandem mass spectrometry using a molecularly imprinted polymer as a sorbent for sample preconcentration

Hydroxylated polychlorinated biphenyls (OH-PCBs) can be detected by liquid chromatography-mass spectrometry coupled to solid-phase extraction (SPE) using a dummy molecularly imprinted polymer (DMIP) as a sorbent. The DMIP is prepared by using an analogue of OH-PCBs (i.e., 4, 4-dihydroxybiphenyl) as a dummy template, to avoid the leakage of the target molecules. The DMIP-SPE sorbent shows good recoveries for OH-PCBs at pH 11 due to the charge-assisted hydrogen bondings between OH-PCBs and the DMIP. It has been found that the DMIP is much more effective and selective than the traditional C-18-SPE method. The sample pH, polymer dosage, elution solvent and volume have been optimized for higher recoveries. Under the optimum experimental conditions, OH-PCBs can be detected in the linear concentration range of 0.05-1.0 pM, with the detection limits ranging from 11 fM to 82 fM for 4'-OH-CB 9, 4'-OH-CB 30, 4'-OH-CB 61, 4'-OH-CB 106 and 4'-OH-CB 112. The proposed system has been successfully applied to the determination of trace OH-PCBs in spiked water samples with recoveries in the range of 89-110%. (C) 2015 Elsevier B.V. All rights reserved