Fig. 6

a Schematic representation of the construction and utilization of H–Mn–Cu-NFs-incorporated paper microfluidic device for the visual determination of phenolic neurotransmitters. b Selectivity of H–Mn–Cu NFs-incorporated paper microfluidic device for simultaneous detection of dopamine (D) and epinephrine (E). Both dopamine and epinephrine were used at a concentration of 20 µM, whereas all control samples were used at a concentration of 200 µM. Sensitivity of H–Mn–Cu NFs-incorporated paper microfluidic device for detecting c dopamine and d epinephrine. Dose–response curves, the corresponding linear calibration plots, as well as the real photographs of the devices were presented for detecting each target phenolic neurotransmitter at seven representative concentrations (1, 3, 5, 10, 25, 50, and 100 µM)