Recent Progress and Perspectives on Polyurethane Membranes in the Development of Gas Sensors.

In today's technology, gas sensors are of great importance in areas such as assessing environmental impacts, monitoring gas production facilities, measuring natural gas, controlling mines and gas leaks. Improving sensor sensitivity and decreasing the determination time is among the subjects that are continuously investigated. The use of polymeric membranes to make such improvements is common practice in the gas sensor field. By the development of polymeric membrane-based gas sensors and increasing the measurement sensitivity, accurate, sensitive, precise and fast measurements of toxic gases, volatile organic gases, and trace gases have been possible. Therefore, polyurethane membranes have been promising in the development of next-generation gas sensors based on membrane diffusion to ensure real-time and continuous monitoring of gases in industry and academic studies. This study aims to evaluate, compare and discuss the recent developments in the use of polyurethane membranes in existing gas detection technologies with chemical, electrical and optical measurement methods. In these measurement methods, polyurethane structures act as a selectively permeable membrane, an ideal matrix material for conductive additives or a suitable film structure for coating the conductive polymeric films. Conductive additives or conductive film structures for gas sensors play an important role in the detection of the gas structure with the change in electrical properties during the passage of gas molecules. This review has focused on important properties such as selectivity, detection time and measurement sensitivity concerning gas detection technology containing polyurethane, which has been used so far.

Antidepressant effect of Gentiana olivieri Griseb. in male rats exposed to chronic mild stress.

Background: The flowering parts of Gentiana olivieri, known as 'Afat' in the southeastern Anatolia region of Turkey, are used as a tonic, an appetizer, and for the treatment of several mental disorders, including depression. The purpose of this study is to investigate the antidepressant effect of G. olivieri ethanol extract (GOEE) in a chronic mild stress-induced rat model, which was used to mimic a depressive state in humans, and to compare the effect with that of imipramine.Methods: Male Sprague-Dawley rats were randomly divided into six groups: control, stress, treated with imipramine (positive control) and treated with GOEE at three different (200, 500, 1000 mg/kg) doses groups. The rats in all groups, except the control group, were exposed to chronic mild stress. At the end of the 3-week experimental period, biochemical and behavioral parameters were examined.Results: The results showed that treatment with GOEE or imipramine significantly improved rats' sucrose consumption which was diminished by chronic mild stress, restored serum levels of corticosterone and proinflammatory cytokines (interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α)), prevented the increase of liver index of rats. Moreover, in the hippocampus tissue, decreased serotonin and noradrenaline levels were significantly increased by treatment with GOEE or imipramine, and antioxidant parameters (thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), and glutathione (GSH)) were significantly improved by treatment with GOEE though not with imipramine.Conclusion: The data demonstrate that G. olivieri may exert its antidepressant activity by improving monoaminergic system disorders, and by favorably affecting the antioxidant, inflammatory and the endocrine mechanisms.

Investigation of the Voltammetric Behavior of Methyldopa at a Poly (p-Aminobenzene Sulfonic Acid) Modified Sensor.

OBJECTIVES: The aim was to modify carbon electrodes with (p-aminobenzene sulfonic acid) and use them as a sensor for sensitive and reliable detection of methyldopa (MD) and ascorbic acid. MATERIALS AND METHODS: Electropolymerization was performed by cyclic voltammetry in 0.1 M KCl solution. The modified sensor has a high electrocatalytic effect for oxidation of MD, which appeared in the pH range of 2-11 by differential pulse voltammetry (DPV) techniques. RESULTS: For the voltammetric determination of MD, the best results were acquired by DPV in phosphate buffer solution (PBS) (pH 3). The calibration plot of the proposed sensor is linear in two concentration ranges of 1.0-30 and 30.0-300.0 µM. The calibration equations over these ranges are Ipa (µA)=1.21×C (µM)+30.81, R2 =0.994 and Ipa (µA)=0.53×C (µM)+53.30, R2 =0.9975, respectively. In the sensitivity studies, the limit of quantification and the limit of detection were 10.6 nM and 5.0 nM, respectively. The modified sensor was used for the simultaneous determination of interfering substances such as MD and ascorbic acid in real samples. CONCLUSION: The obtained results revealed that the prepared modified electrode and the proposed method have good sensitivity, repeatability, reproducibility, and stability.