Colorimetric paper-based device for gaseous hydrogen cyanide quantification based on absorbance measurements

Hydrogen cyanide is a highly toxic compound employed for applications such as electroplating, production of organic solvents, fish stunning, and even as a chemical weapon. In this work, we describe a new microfluidic paper-based assay for selective cyanide determination, based on the reaction of the cyanide anion with palladium dimethylglyoximate (DMG) followed by colorimetric reaction of DMG with nickel. Quantification was performed by measuring the absorbance of light passing through the paper, employing an LED emitting at 525 nm and a log ratio amplifier circuit emulating Lambert-Beer's law. This offers an alternative to the smartphone-based methodologies for signal treatment usually employed in colorimetric μPAD-based methods The technique enabled linear calibration within the range 100-500 ppb of HCN, as well as a detection limit of 10 ppb for HCN in gaseous samples. The sampling time used for this concentration range was 5 min. The method was also tested for the quantification of cyanide in aqueous samples by adding H3PO4 to the sample, followed by exposure of the paper sensor to the gaseous HCN generated. A detection limit of 1 μM was achieved, which makes the method also suitable for detection of cyanide in liquid samples.