A portable smartphone platform with FeNPs@g-C3N4 nano-enzyme for visual and on-site sensing of F− and Al3+ in tea

A portable platform for the visual determination of F− and Al3+ was developed by combining FeNPs@g-C3N4 nano-enzyme and a smartphone. The FeNPs@g-C3N4 nano-enzyme with excellent peroxidase activity was synthesized through the in situ growth of Fe nanoparticles (FeNPs) on graphite-phase carbon nitride nanosheets (g-C3N4), which could catalyze H2O2 to oxidize TMB to blue oxide (oxTMB). The peroxidase activity of the FeNPs@g-C3N4 nano-enzyme could be inhibited by F−, and then restored by Al3+ because of the coordination reaction between Fe3+/Al3+ and F−. Furthermore, the solution color could be dynamically manipulated by changing the concentrations of F− and Al3+. Under optimal conditions, the developed method gave low detection limits of 2.43 nM for F− and 7.66 μM for Al3+. The cooperation of nano-enzyme and smartphone has greatly shortened the detection time and reduced the cost of detection, providing a new strategy for the on-site and convenient detection of F− and Al3+ in tea, and showed significant application potential in food safety evaluation.