Plasmonic colorimetric sensor based on alpha-cyclodextrin-functionalized silver nanoparticles for the selective detection of arsenic(<sc>iii</sc>) in aqueous media

The optical detection of arsenic (As) in human biological fluids and environmental water samples is presented using alpha-cyclodextrin-modified silver nanoparticles (alpha/CyD-AgNPs) at the trace level. This method is based on the measurement of a red shift of the LSPR band of alpha/CyD-AgNPs in the region of 200-800 nm. The color of alpha/CyD-AgNPs was changed from yellow to colorless by the addition of As(iii). The mechanism for the detection of As(iii) is based on the electrostatic interaction between the positively charged As(iii), which causes the red shift of the LSPR band from 410 nm to 580 nm. As(iii) ions specifically interact with alpha/CyD-AgNPs to form As(iii)-alpha/CyD-AgNPs and cause a remarkable decrease in the absorbance peak of AgNPs at 410 nm, which enables the determination of As(iii) with high selectivity and sensitivity. The interaction between alpha/CyD-AgNPs and As(iii) is theoretically explored by density functional theory (DFT) using LANL2DZ basis sets with the help of the Gaussian 09 (C.01) program. The developed colorimetric method provides a detection limit of 12.5 ppm with a detection range of 20-500 mu g mL-1 for As(iii) determination. The advantages of using alpha/CyD-AgNPs as a chemical sensor in colorimetry assays are that they are simple, low-cost and selective for the detection of As(iii) from human blood, serum, urine, and environmental river and tap water samples.