Selectivity characteristics of ammonia-gas sensors based on a polymer membrane electrode

Rapid and sensitive detection of ammonia in water by a long period fiber grating sensor coated with sol-gel silica

A sensitive ammonia sensor based on long-period fiber grating (LPFG) is designed and manufactured for the detection of ammonia concentration in water. Femtosecond laser direct writing technology is used to write LPFGs on standard single-mode silica fiber. A thin layer doped with basic dyes is coated on the optical fiber for sensing by using the sol-gel method. The thicknesses of sol-gel layers, which play a key role in the sensitivity of the LPFG sensor, were carefully studied. Experimental results show that LPFG with a functional layer of ∼340 nm has the best sensing performance, and the detection limit is 0.08 ppm. The response time of the sensor is less than one minute, and the sensor has good repeatability with a short recovery time. Compared with other organic molecules and ions in water, the proposed LPFG sensor has not only good reusability, but also selectivity for the detection of ammonia.

An electronic tongue for simultaneous determination of Ca2+, Mg2+, K+ and NH4+ in water samples by multivariate calibration methods

In this study, a multi ion-selective electrode system was developed for simultaneous determination of Ca²⁺, Mg²⁺, K⁺ and NH₄⁺ ions. The system, called electronic tongue, was used for the quantitative determination of these ions in different water samples. The measurement system was comprised of sixteen ion-selective electrodes, an Ag/AgCl double-junction reference electrode, and a sixteen-channel multi-potentiometer. In the fabrication process of the electronic tongue, an electrode body, which comprised eight ion-selective electrodes together on it, was designed. The obtained data were evaluated by using multivariate calibration methods such as Classical Least Squares (CLS), Principal Component Regression (PCR) and Partial Least Squares (PLS1). The parameters that influence the electronic tongue performance were investigated. Analyses were conducted in synthetic water samples and real water samples. Percentage recovery values in synthetic samples, which were calculated via PLS1, were found 101.35%, 102.41%, 100.04% and 99.23% for Ca²⁺, Mg²⁺, K⁺ and NH₄⁺ respectively. The results, obtained from the electronic tongue and other analytical techniques, were compared and no significant difference was found between the results at 95% confidence level.

Synthesis and characterization of ammonia-responsive polymer microgels

We report a polymer microgel that can undergo rapid, reversible, and highly-sensitive volume phase transitions upon varying ammonia concentrations in milieu.

Electronic Materials in Biological Applications

Decisions concerning patient care, which are routinely made by the attending physician, based on experience and clinical laboratory analyses, will eventually be supplemented or even replaced by real-time, quantified, health assessments from cutaneous and indwelling multisensor probes. These probes will employ a multitude of technologies including optical and solid state techniques for the precise measurement of body analytes such as blood gases, electrolytes, pH, glucose, etc. In addition to clinical monitoring, these sensors will also be used to provide feed-back for closed-loop therapeutic systems.

Currently, there are rapid advances being made in sensor technology and its application for the determination of various analytes. However, a major problem still remains at the device/body interface, especially when chronic implantation is required.

Polymer membrane-based ion-, gas- and bio-selective potentiometric sensors

Recent progress in the design of new polymer membrane-based potentiometric ion-, gas- and bio-selective electrodes in chemistry laboratories at the University of Michigan (Ann Arbor) is reviewed. Emphasis is placed on describing the performance of devices for measuring anions (e.g., salicylate, thiocyanate, chloride and heparin) and gases (e.g., ammonia, carbon dioxide and oxygen) in biological samples, both in vitro and in vivo. Beyond direct measurement of key ions and gases in complex matrices, some of the new membrane electrode systems reported can serve as base transducers for the development of biosensors containing integrated biological reagents, including enzymes and antibodies. New approaches for mass fabricating solid-state ion and biosensor devices as well as future directions for research in the entire field of polymer membrane sensors are also described.

Potentiometric (bioselective electrodes) assay systems: utility and limitations

Numerous potentiometric assays utilizing bioselective electrodes are fast revolutionizing many areas of biotechnology. Adequately discussing the utility and limitations of these electrochemical systems is the purpose of this review. A general overview introduces bioselective potentiometry by presenting basic concepts, historical background, and current developments. Essentially, the review consists of several sections describing electrode architecture, operational concepts, different biosensors, assay systems, applications, and future trends. Advantages and disadvantages of the different bioselective assay systems discussed are included throughout each section. Electrode design discussion covers conventional liquid probes and the newer solid-state transitor biosensors. Limitations and advantages of different chemoreceptors, biocatalysts, and potentiometric transducers are presented. Operational characteristics include: linear behavior, sensitivity, stability, specificity, response, recovery, and the influence of interfering factors. Enzyme, organelle, tissue, and microbial biocatalytic sensors are discussed. Bioligand systems include: affinity, immunoselective enzyme, and liposome sensors. Potentiometric bioselective drug, microbial, and immunoassay systems are also included.