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.