Facile optical quantification of mercury ion concentration using graphene quantum dot coated filter paper disks

Highlights: • Concentrations of mercury (II) ions were optically quantified using graphene quantum dot coated filter paper disks. • The GQDs could be evenly physisorbed by making even contacts between filter paper disks and a well array's bottom surface. • Due to this work's simplicity, small sample volume, cost-effectiveness, it may be developed as mobile devices. There is a high demand for facile on-site mercury ion quantification methods in water due to mercury's serious toxicity. Graphene quantum dot (GQD), fluorescent under ultra-violet (UV) light, can be easily synthesized and used as a mercury ion detection probe because the brightness of GQD's fluorescence decreases with the increase of the number of mercury ions. We developed a facile mercury (II) ion quantification method using GQD coated filter paper disks in a 3D-printed well array. Changes of GQD's fluorescent brightness dependent on mercury ion concentration were measured via optical microscopy image processing. We also observed the dependency of mercury ion detection sensitivity on the amount of GQD and type of GQDs. Our approach may be easily adapted for hand-held mobile mercury ion quantification devices in the future due to its simplicity and small sample size.