Application of L–cysteine modified silver nanoparticles as a colorimetric sensor for the determination of Barium ions

The identification and quantification of the mineral elements play a significant role in environmental and biological sciences. According to the reports, barium (Ba2+) is considered to be an accompanying element to calcium, which is essential at trace levels. However, at higher concentrations, barium compounds exhibit serious taxological effects on various living systems, and is considered as a physiological antagonist of K+ ion.According to the recent opinion, Ba2+ ion can block K+ ion channels of the Na K pump in the membranes of cells, increasing active influx and inhibiting passive efflux of K+ ions. It acts as a muscle poison that causes cardiac and gastrointestinal irregularities, and paralysis. In view of this, several research groups have been explored analytical protocols for the detection of Ba2+ ion in environmental samples using various analytical techniques such as graphite furnace atomic absorption spectrometry, UV-visible spectrometry, ion-chromatography, inductively coupled plasma-mass spectrometric, inductively coupled plasma atomic emission spectrometry. Unfortunately, most of these methods are rather expensive, complicated and time-consuming. Considering the attractive features of nanotechnology, development of new nanoparticles-based sensors has been one of the most important issues in various fields of science and technology in recent years. Hence a colorimetric method based on the shift in the maximum of plasmon resonance band of AgNPs is proposed as an alternative approach for the determination of Barium levels in engine oil samples. The strategy used in this work was based on three main steps, (a) preparation of AgNp Sol, (b) modification of silver nanoparticles with cysteine, and (c) Study of the effect of the barium cations on the L – cysteine modified silver nanoparticles. Aggregation of nanoparticles would be the final result, which could be used as a colorimetric sensor for selective determination of Barium ions. In the presence of cysteine molecules, color of the AgNp solution was changed from yellow to pink on the addition of certain amounts of Ba2+. Effective parameters including time, L – cysteine concentration and pH of solution were studied. Calibration curve obtained by this method at 530nm has a linear range of 20 – 70 with 8μM detection limit for barium. The probable interferences in the measurement process due to the presence of other species present in real samples were studied. the effect of the studied interferences could be overcome by addition of appropriate amounts of EDTA at pH =7.