Recent developments in urea biosensors

Membrane-dialyzer injection loop for enhancing the selectivity of anion-responsive liquid-membrane electrodes in flow systems Part 2. A selective sensing system for salicylate

Enzymatic electrocatalysis as a strategy for electrochemical detection in heterogeneous immunoassays.

3D hierarchical Nano-ZnO/TiO 2 on conductive fluorinated-tin oxide (FTO) layer was fabricated by reactive direct current (DC) magnetron sputtering of ZnO, at the optimized instrumental deposition conditions, on a pre-covered TiO 2 surface with Polyvinyl Alcohol (PVA) as an omissible polymer in a pattern of parallel strips (Nano-ZnO/PVA/TiO 2 /FTO) following by PVA omission via annealing process, which resulted in an efficient porous media for urease (Urs) enzyme immobilization (Urs/Nano-ZnO/TiO 2 /FTO) designed for urea biosensing. The criteria for TiO 2 selection as substrate was based on: (i) its ability to promote electron transfer between ZnO to FTO substrate, (ii) affording high electronic density to the biosensor surface as an electrostatic repulsion layer for the anionic interferents at the biological media, and (iii) enhancement of urea biosensing by the formation of heterojunctions with ZnO. Characterization of the surface morphology of 3D hierarchical Nano-ZnO/TiO 2 film by field emission-scanning electron microscopy (FE-SEM) exhibits cavities of nanoporous ZnO film as an effective biosensing area for Urs enzyme immobilization. Step by step monitoring of Urs/Nano-ZnO/TiO 2 /FTO biosensor fabrication was performed using electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fabricated Urs/Nano-ZnO/TiO 2 /FTO biosensor was used for urea determination using impedimetric assessment. The impedimetric results show high sensitivity for urea detection within 5–205 mg dl −1 and limit of detection as 2 mg dl −1 . A fast response of fabricated biosensor can usually allow a real-time analysis.

Development of sensitive impedimetric urea biosensor using DC sputtered Nano-ZnO on TiO2 thin film as a novel hierarchical nanostructure transducer

A method is described for the determination of total ammoniacal
nitrogen in waters using an ammonium ion-selective sensor based on
nonactin. The flow injection method relies on the measurement of the
potential of the sensor at two pH values, 6.0 and 9.4, and the use of a
mathematical expression to calculate the total ammoniacal nitrogen
concentration. The method also compensates for the interference from
moderate concentrations of other cations such as potassium and sodium.

Determination of Ammonia in Waste Waters by a Differential pH Method Using Flow Injection Potentiometry and a Nonactin-Based Sensor

The analytical response properties of two types of flow-through ammonia gas sensing electrode systems are examined and directly compared under the same experimental conditions. Both detection systems involve the use of continous flow gas dialysis in conjuction with tubular polymer membrane electrode detectors. In one method, the pH of the flowing recipient stream leaving the dialyser is monitored; in the second, ammonium ions are detected. For each of five sample diluents studied, the latter method is shown to offer a greater than 100-fold improvement in detection limits over the more classical pH monitoring technique. Further studies clearly show that the ammonium electrode detection mode also offers superior selectivity over volatile amines (e.g., methylamine, ethylamine, etc.). The reasons for these enhanced analytical characteristics are discussed in terms of ammonia flux through the gas-permeable membrane of the dialyser and appropriate solution equilibria.

Comparison of tubular polymeric pH and ammonium ion electrodes as detectors in the automated determination of ammonia

Enzyme electrodes for amperometric measurement of ammonia was prepared by immobilization of L-glutamate dehydrogenase on an Immobilon-AV Affinity membrane and attachment to a glassy carbon electrode. Reduced nicotinamide adenine dinucleotide (NADH) was used as the electroactive species. The electrochemical oxidation of NADH was monitored at ＋1.0 volt vs. Ag/AgCl. Response was linear from M. The detection limit was 2.0 M. Response time, the optimum pH and life time of enzyme immobilized membrane were 2 min, pH 7.3∼7.6 (Dulbecco's buffer solution) and about 25 days respectively. When the enzyme electrode was applied to the determination with amperometric method, other physiological materials had no interference.

Amperometric Enzyme Electrode for the Determination of $NH_4^+$

Purification and properties of acetylacetone as a solvent for electrochemical studies

The dependence of voltammetric parameters on the pressure for the reduction of Cu(II) in 0.5M KCl aqueous solution has been studied. In this system micro platinum electrode, standard calomel electrode and a helix type of platinum wire were used as the working, the reference and the auxilary electrode, respectively. With increasing the pressure from 1 to 1,800 bars, the half wave potentials of first reduction wave are shifted to the more negative potentials. And the diffusion currents of first and second reduction wave become considerably larger with increase in pressure from 1 to about 1,000 bars but are getting smaller beyond 1,000 bars. The good linear relationships between diffusion current and the concentrations of Cu(II) are established over all pressure range( bars). The reversibility of the each reduction step is not changed with increasing pressure.

Effect of High Pressure of Voltammetric Parameters of Copper

The effect of high pressure on the stability of copper(II), cadmium(II) and zinc (II) complex ions with ethylenediamine, propylenediamine, diethylenetriamine has been investigated polarographically. 0.10M KN solution was used as a supporting electrolyte. The concentration of chelating agents was varied from 0.01M to 1.00M. The dissociation constants of metal complex ions were increased with increasing the pressure from 1 atmosphere to 1,500 atmospheres. The increment of the dissociation constant per unit atmosphere varied from 1.1 % for Cu(dien) to 5.0 % for Zn(en).

Heung Lark Lee

Papers

Comparison of tubular polymeric pH and ammonium ion electrodes as detectors in the automated determination of ammonia

Amperometric Enzyme Electrode for the Determination of $NH_4^+$

Purification and properties of acetylacetone as a solvent for electrochemical studies

Effect of High Pressure of Voltammetric Parameters of Copper

Effect of High Pressure on the Stability of Metal Complex Ion by Polarographic Method