Application of polyamide 56 nanofiber membrane loaded with coffee grounds carbon dots in Fe³⁺ detection

One novel nanofiber membrane was fabricated which could detect Fe³⁺ with the help of either fluorescence spectrometer or smartphone. Coffee grounds carbon dots (CCDs) were prepared by the solvent-thermal method, followed by the fabrication of CCDs/polyamide 56 (PA56) composite nanofiber membrane through electrospinning process. The 4 % CCDs/PA56 composite nanofiber membrane (FNM4) maintained good fluorescence performance (λ_em = 554 nm, λ_ex = 470 nm) even after 5-runs quenching-recovery cycles. Its fluorescence could be quenched by Fe³⁺ with the limit of detection (LOD) of 0.74 μM when the fluorescence spectrometer was used. In addition, FNM4 could also detect Fe³⁺ by reading its RGB values using one smartphone and the lowest LOD was 4.31 μM when one Apple smartphone was used. The second method is portable to operate and eliminates the constraints of bulky laboratory equipment.