DETERMINATION OF MERCURY IN TRACE LEVEL USING MODIFIED GOLD NANOPARTICLES

Abstract

Highly sensitive methods for trace level mercury(II) ions detection was developed. Two methods are proposed in this research; the use of L-cysteine modified gold nanoparticles (cys-AuNPs) solution and the use of L-cysteine modified gold nanoparticles supported silica (cys-AuNPs-Si). In the solution system, the aggregation of cys-AuNPs was induced by mercury(II) ions resulting in the change of solution color from red to blue. The phenomenon was investigated by UV-Visible spectrophotometer at 670 and 520 nm. The effect of parameters affecting mercury(II) determination including modification time, NaCl concentration, detection time, sample volume and co-existing ions were investigated. The linear range of this method was obtained in a range of 5 to 40 µg/L and detection limit was as low as 4.5 µg/L. In the solid system, gold nanoparticles were coated on silica and further modified with L-cysteine (cys-AuNPs-Si) for mercury(II) ions extraction and sensing. To improve the selectivity of mercury(II) detection, the extracted mercury(II) ions on cys-AuNPs-Si phase were reduced with tin(II) chloride. The color of the solid phase changed from pink to purple and blue depending on mercury(II) concentration. The effect of parameters affecting mercury(II) determination including AuNPs concentration, coating time, L-cysteine concentration, extraction time, tin(II) chloride concentration, co-existing ions were studied. The proposed method could detect mercury by naked eyes in a range of 2 to 100 µg/L. Finally, these methods were applied to the analysis of drinking and tap water.