β-Cyclodextrin protected gold nanoparticle based cotton swabs as an effective candidate for specific sensing of trace levels of cyanide

In this paper, a rapid colorimetric and easy visual determination of cyanide ions (CN − ions) in water, based on gold nanoparticles (AuNPs) stabilized with β-cyclodextrin (β-CD), is described. Optical detection of CN − ions is carried out using β-CD-AuNPs by tracking the changes in the surface plasmon resonance band and colorimetric nature of the β-CD AuNPs. This colorimetric nanosensor easily and with ultra-sensitivity identifies the CN − ions because of their capacity to etch the surface of the β-CD AuNPs and form a stable water soluble Au–CN complex. Under experimental conditions, the colorimetric assay demonstrated a steady response for CN − ions over a concentration ranges from 4.50 × 10 −6 to 99.00 × 10 −6 mol dm −3 with R = 0.994. The lowest limit of detection of this inexpensive, visual with the naked eye, approach is 93.00 × 10 −9 mol dm −3 , which is under the tolerance limit value (1.90 × 10 −6 mol dm −3 ) set by the World Health Organization for drinking water. The specificity of the β-CD-AuNPs based optical platform for the detection of CN − ions is superb when evaluated with various potential interfering anions. Furthermore, the proposed β-CD-AuNPs nanoprobe is effectively applied to quantify the CN − ions in tap and drinking water samples. For convenient use, a very stable cotton swab containing the β-CD-AuNPs has been designed and it revealed good sensitivity against CN − ions in the environment using the naked eye.