Visual and colorimetric detection of ethylene glycol based on freeze-thawing induced aggregation of silver nanoparticles

The authors report on a simple colorimetric method for the determination of ethylene glycol (EG) in aqueous solution. It is based on the finding that EG prevents the aggregation of silver nanoparticles (AgNPs) on freezing-thawing. In the absence of EG, AgNPs aggregate after freeze-thawing because their surface were disrupted by ice crystals. This causes the solution to become colorless. However, in the presence of EG, ice crystals are not formed, and aggregation and decoloration do not occur. Under optimized conditions, the photometric assay, best performed at a wavelength of 395 nm, works in the 10 to 400 mM EG concentration range, and the detection limit is 3 mM (at a signal-to-noise ratio of 3). Concentrations down to 100 mM can be even detected visually.