Selective and Rapid Biosensor Integrated into a Commercial Hand‐Held Instrument for the Measurement of Ammonium Ion in Sewage Effluent

Modified electrode decorated with silver as a novel non-enzymatic sensor for the determination of ammonium in water

Ammonium is an essential component of the nitrogen cycle, which is essential for nitrogen cycling in ecosystems. On the other hand, ammonium pollution in water poses a great threat to the ecosystem and human health. Accurate and timely determination of ammonium content is of great importance for environmental management and ensuring the safety of water supply. Here we report a highly sensitive electrochemical sensor for ammonium in water samples. The modified electrode is based on the incorporation of silver nitrate (AgNO3) into a carbon paste embedded with 1-aminoanthraquinone and supported by multi-walled carbon nanotubes, which are commercially available. A potential of 0.75 V is applied to the modified electrode, followed by activation in hydrochloric acid. The modified electrode was used for square wave voltammetry of ammonium in water in the potential range of - 0.4-0.2 V. The performance of ammonium analysis was determined in terms of square wave frequency, square wave amplitude and concentration of electrolyte solution (sodium sulphate). The calculation of the surface area according to the Randles-Sevcik equation resulted in the largest surface area for the Ag/pAAQ/MWCNTs/CPE. The modified electrode exhibited a linear range of 5-100 µM NH4+ in 0.1 M Na2SO4 with a detection limit of 0.03 µM NH4+ (3σ). In addition, the modified electrode showed high precision with an RSD value of 9.93% for 10 repeated measurements. No interfering effect was observed at twofold and tenfold additive concentrations of foreign ions. Good recoveries were obtained in the analysis of tap and mineral water after spiking with a concentration of ammonium ions.

Overview of Immobilized Enzymes' Applications in Pharmaceutical, Chemical, and Food Industry

The use of immobilized enzymes in industry is becoming a routine process for the manufacture of many key compounds in the pharmaceutical, chemical, and food industry. Some enzymes like lipases are naturally robust and efficient, can be used for the production of many different molecules, and have found broad industrial applications. Some more specific enzymes, like transaminases, have required protein engineering to become suitable for applications in industrial manufacture. For all enzymes, the possibility to be immobilized and used in a heterogeneous form brings important industrial and environmental advantages such as simplified downstream processing or continuous process operations. Here, we present a series of large-scale applications of immobilized enzymes with benefits for the food, chemical, pharmaceutical, cosmetics, and medical device industries, some of them hardly reported before.

A promising voltammetric biosensor based on glutamate dehydrogenase/Fe3O4/graphene/chitosan nanobiocomposite for sensitive ammonium determination in PM2.5

A novel NH₄⁺ voltammetric electrochemical biosensor was constructed by immobilizing glutamate dehydrogenase (GLDH)/Fe₃O₄/graphene (GR)/chitosan (CS) nanobiocomposite onto a glassy carbon electrode (GCE). On the GLDH/Fe₃O₄/GR/CS/GCE, GLDH catalyzed the reversible reaction, i.e., the reductive amination of α-ketoglutaric acid and the oxidative deamination of L-glutamate. The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the [Fe(CN)₆]^3-/4- couple, which helped for the amplification of the electrochemical signal. The electrochemical detection of NH₄⁺ was based on the fact that the enhanced response current was proportional to the NH₄⁺ concentration. Owing to the combination of the advantages of the synergistic effects of Fe₃O₄ nanospheres, GR and CS, a promising platform for NH₄⁺ sensing was provided. Under optimum conditions, the introduced biosensor had a linear range of 0.4-2.0 μM for NH₄⁺ with the detection and quantification limits of 0.08 and 0.27 μM, respectively. Moreover, the biosensor exhibited good sensitivity and excellent reproducibility. It could retain 91.8% of its original response after two weeks of storage at 4 °C, suggesting satisfactory stability. Additionally, the proposed biosensor was successfully applied to detect NH₄⁺ levels in PM_2.5 samples, indicating its feasibility for application in NH₄⁺monitoring in the environmental fields.

A flow injection system, comprising a biosensor based on a screen-printed carbon electrode containing Meldola's Blue-Reinecke salt coated with glucose dehydrogenase, for the measurement of glucose

A biosensor for the measurement of glucose in serum has been developed, based on a screen-printed carbon electrode modified with Meldola's Blue-Reinecke salt, coated with the enzyme glucose dehydrogenase (from Bacillus sp.), and nicotinamide adenine dinucleotide coenzyme (NAD+). A cellulose acetate layer was deposited on top of the device to act as a permselective membrane. The biosensor was incorporated into a commercially available, thin-layer, amperometric flow cell operated at a potential of only +0.05 V versus Ag/AgCl. The mobile phase consisted of 0.2 M phosphate buffer (pH 7.0) containing 0.1 M potassium chloride solution, and a flow rate of 0.8 ml min(-1) was used throughout the investigation. The biosensor response was linear over the range of 0.075-30 mM glucose, with the former representing the detection limit. The precision of the system was determined by carrying out 20 repeat injections of a 5-mM glucose standard, and the calculated coefficient of variation was 3.9%. It was demonstrated that this biosensor system could be applied to the direct measurement of glucose in serum without pretreatment. Therefore, this would allow high-throughput analysis, at low cost, for this clinically important analyte.

Recent advances in NADH electrochemical sensing design

NADH electrochemical sensor development has been one of the most studied areas of bioelectroanalysis because of the ubiquity of NAD(P)H based enzymatic reactions in nature. The different solutions proposed are still far from the realisation of the "ideal" NADH sensor and the research area is still challenging. The principles and the recent approaches in NADH electrochemical sensing design are reported in this review. An overview of selected examples and novel sensor materials for the electrocatalysis of NADH is given with emphasis on the appropriate design to obtain improved performances. The literature data taken in consideration has been grouped depending on the strategy used in: surface modified electrodes for NADH sensing, surface redox mediated NADH probes, and bulk modified electrodes for the electrocatalytic oxidation of NADH. A list of already reported dehydrogenase-based biosensors is also given.

Biosensors based on screen-printing technology, and their applications in environmental and food analysis

This review summarizes scientific research activity on biosensors, especially screen-printed, electrode-based biosensors. The basic configurations of biosensors based on screen-printing technology are discussed and different procedures for immobilization of the biorecognition component are reviewed. Theoretical aspects are exemplified by practical environmental and food-analysis applications of screen-printed, electrode-based biosensors.