Simultaneous detection of ammonium and nitrate in environmental samples using on ion-selective electrode and comparison with portable colorimetric assays

Simple, robust, and low-cost nitrate-and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting linear concentration range between 5.0 × 10−6 and 2.5 × 10−3 M with a detection limit of 5.5 × 10−7 M. On the other hand, MMA-DMA—based membranes showed suitability for both ammonium-and nitrate-selective electrodes, and were successfully applied to detect NO3− and NH4+ in water and soil samples. The proposed ISEs exhibited near-Nernstian potentiometric responses to NO3− and NH4+ with the linear range concentration between 5.0 × 10−5 and 5.0 × 10−2 M (LOD = 11.3 µM) and 5.0 × 10−6 and 1.0 × 10−3 M (LOD = 1.2 µM), respectively. The power of ISEs to detect NO3− and NH4+ in water and soils was tested by comparison with traditional, portable colorimetric techniques. Procedures required for analysis by each technique from the perspective of a non-trained person (e.g., farmer) and the convenience of the use on the field are compared and contrasted

Simultaneous detection of ammonium and nitrate in environmental samples using on ion-selective electrode and comparison with portable colorimetric assays

Simple, robust, and low-cost nitrate-and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting linear concentration range between 5.0 × 10−6 and 2.5 × 10−3 M with a detection limit of 5.5 × 10−7 M. On the other hand, MMA-DMA—based membranes showed suitability for both ammonium-and nitrate-selective electrodes, and were successfully applied to detect NO3− and NH4+ in water and soil samples. The proposed ISEs exhibited near-Nernstian potentiometric responses to NO3− and NH4+ with the linear range concentration between 5.0 × 10−5 and 5.0 × 10−2 M (LOD = 11.3 µM) and 5.0 × 10−6 and 1.0 × 10−3 M (LOD = 1.2 µM), respectively. The power of ISEs to detect NO3− and NH4+ in water and soils was tested by comparison with traditional, portable colorimetric techniques. Procedures required for analysis by each technique from the perspective of a non-trained person (e.g., farmer) and the convenience of the use on the field are compared and contrasted

โพเทนชิโอเมทริกและคาพาซิทีฟแอฟฟินิตีไบโอเซนเซอร์

Thesis (Ph.D., Chemistry)--Prince of Songkla University, 200

A Novel Microfluidic-Based OMC-PEDOT-PSS Composite Electrochemical Sensor for Continuous Dopamine Monitoring

Fast and precise analysis techniques using small sample volumes are required for next-generation clinical monitoring at the patient’s bedside, so as to provide the clinician with relevant chemical data in real-time. The integration of an electrochemical sensor into a microfluidic chip allows for the achievement of real-time chemical monitoring due to the low consumption of analytes, short analysis time, low cost, and compact size. In this work, dopamine, used as a model, is an important neurotransmitter responsible for controlling various vital life functions. The aim is to develop a novel serpentine microfluidic-based electrochemical sensor, using a screen-printed electrode for continuous dopamine detection. The developed sensor employed the composite of ordered mesoporous carbon (OMC) and poly (3,4 ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT-PSS). The performance of a microfluidic, integrated with the sensor, was amperometrically evaluated using a computer-controlled microfluidic platform. The microfluidic-based dopamine sensor exhibited a sensitivity of 20.2 ± 0.6 μA μmol L−1, and a detection limit (LOD) of 21.6 ± 0.002 nmol L−1, with high selectivity. This microfluidic-based electrochemical sensor was successfully employed to determine dopamine continuously, which could overcome the problem of sensor fouling with more than 90% stability for over 24 h. This novel microfluidic sensor platform provides a powerful tool for the development of a continuous dopamine detection system for human clinical application

Disposable Polyaniline/<i>m</i>-Phenylenediamine-Based Electrochemical Lactate Biosensor for Early Sepsis Diagnosis

Lactate serves as a crucial biomarker that indicates sepsis assessment in critically ill patients. A rapid, accurate, and portable analytical device for lactate detection is required. This work developed a stepwise polyurethane–polyaniline–m-phenylenediamine via a layer-by-layer based electrochemical biosensor, using a screen-printed gold electrode for lactate determination in blood samples. The developed lactate biosensor was electrochemically fabricated with layers of m-phenylenediamine, polyaniline, a crosslinking of a small amount of lactate oxidase via glutaraldehyde, and polyurethane as an outer membrane. The lactate determination using amperometry revealed the biosensor’s performance with a wide linear range of 0.20–5.0 mmol L−1, a sensitivity of 12.17 ± 0.02 µA·mmol−1·L·cm−2, and a detection limit of 7.9 µmol L−1. The developed biosensor exhibited a fast response time of 5 s, high selectivity, excellent long-term storage stability over 10 weeks, and good reproducibility with 3.74% RSD. Additionally, the determination of lactate in human blood plasma using the developed lactate biosensor was examined. The results were in agreement with the enzymatic colorimetric gold standard method (p > 0.05). Our developed biosensor provides efficiency, reliability, and is a great potential tool for advancing lactate point-of-care testing applications in the early diagnosis of sepsis

Capacitive biosensor for quantification of trace amounts of DNA

A flow injection capacitive biosensor system to detect trace amounts DNA has been developed based on the affinity binding between immobilized histone and DNA. Histones from calf thymus and shrimp were immobilized on gold electrodes covered with self-assembled monolayer (SAM) of thioctic acid. Each of these histones was used to detect DNA from calf thymus, shrimp and Escherichia coli. The studies indicated that histones can bind better with DNA from the same source and give higher sensitivity than the binding with DNA from different sources. Under optimum conditions, both histones from calf thymus and shrimp provided the same lower detection limit of 10(-5) ng l(-1) for DNA from different sources, i.e., calf thymus, shrimp and E. coli. The standard curve for the affinity reaction between calf thymus histone and DNA shows sigmoidal behavior and two linear ranges, 10(-5) to 10(-2) ng l(-1) and 10(-1) to 10(2) ng l(-1), could be obtained. The immobilized histones were stable and after regeneration good reproducibility of the signal could be obtained up to 43 times with a %R.S.D. of 3.1. When applied to analyze residual DNA in crude protein extracted from white shrimp recoveries were obtained between 80% and 116%. (c) 2009 Elsevier B.V. All rights reserved

Interference Compensation for Thin Layer Coulometric Ion-Selective Membrane Electrodes by the Double Pulse Technique

Ion-selective membranes operated in a thin layer coulometric detection mode have previously been demonstrated to exhibit attractive characteristics in view of realizing sensors without the need for frequent recalibration. In this methodology, the analyte ion is exhaustively removed across an ion-selective membrane by an applied potential, and the resulting current is integrated to yield the coulomb number and hence the amount of analyte originally present in the sample. This exhaustive process, however, places greater demands on the selectivity of the membrane compared to direct potentiometry, since the level of interference will increase as the analyte depletes. We evaluate here a double pulse protocol to reduce the level of interference, in which the sample is electrolyzed once again after the initial coulometric detection pulse. Since the analyte ion is no longer present at significant concentrations during the second pulse, but an interfering ion of high concentration did not appreciably deplete, the second electrolysis step may be used to partially compensate for undesired interference. These processes are here evaluated by numerical simulation for ions of the same charge, demonstrating that the resulting coulomb number may indeed be reduced for systems of limited selectivity. The improvement in operational selectivity relative to uncompensated coulometry is found to be ca. 6-fold. The methodology is successfully demonstrated experimentally with a calcium selective membrane and tetraethylammonium as a model interfering agent, and the observed relative errors after background compensation can be favorably compared to that in direct potentiometry where no sample depletion occurs