The device consisted of three layers; (i) a layer of patterned paper containing a 7 mm diameter hydrophilic area for sample preconcentration,(ii) a 50 mm ×25 mm transparency film connector layer with two 5-mm diameter holes 5 mm apart, the second of which contains the selective, SDS-modified, transfer paper to wick the sample to (iii) a commercial SPCE for electrochemical detection of DA (Fig. 1a). The two holes in the transparency were designed to allow for sample preconcentration by repeated 20 L sample applications and drying in the first hole followed by selective sample transfer through the second hole containing treated filter paper to the SPCE (third layer) (Fig. 1b).