Read-by-eye quantification of aluminum (III) in distance-based microfluidic paper-based analytical devices

Herein we report the first two distance-based microfluidic paper-based analytical devices (μPADs) using fluorescence to quantify aluminum. In addition to their read-by-eye quantification, the devices are simple to fabricate, require no sample pretreatment or preconcentration, and have a shelf life of >5 months. The first device is designed in a "chemometer" format where the length of a fluorescent band linearly responds to an Al(III) concentration. The second device uses a radial design where the fluorescent diameter also linearly responds to an Al(III) concentration. The chemometer device has a detection limit of 2.5 ppm (100 μM) and a linear range from 2 to 54 ppm Al(III) (100 μM-1 mM), R² = 0.989). The radial device has a detection limit of 0.9 ppm (33 μM) and a linear range from 2 to 24 ppm Al(III) (100-900 μM, R² = 0.968). The utility of the μPADs were successfully demonstrated by measuring Al(III) in two water effluent samples from the Gold King Mine near Silverton, CO.