An optical method is described for the ratiometric fluorometric determination of cyanide ions. It is based on the use of a mixture of aqueous solutions of blue-emitting carbon dots (CDs) and red-emitting gold nanoclusters (AuNCs). The presence of cyanide reduces the red fluorescence of the AuNCs through the formation of a stable complex [Au(CN)2-]. The blue emission of the CDs, in contrast, stays constant. Hence, the color of fluorescence changes from red to purple to blue. The ratio of the fluorescence intensities located at 612 and 438 nm varies over a wide range, with 2 linear responses ranges (from 8 nM to 12.5 μM, and from 12.5 to 75 μM). The method was applied to the determination and visual discrimination of cyanide in food and drink samples. Graphical abstract A ratiometric method for determination of cyanide detection is described that is based on mixing carbon dots (CDs) and gold nanoclusters (AuCNs). The presence of cyanide reduces the red fluorescence of the AuNCs through the formation of a stable complex Au(CN)2-. The blue emission of the CDs, in contrast, stays constant. The fluorescence intensity ratios show linear response to cyanide with a concomitant red-purple-blue fluorescence color change.
Keywords: Cyanide nanoprobe; Elsner reaction; Ratiometric determination; Stern−Volmer plot; Two linear response ranges; Visual discrimination.