Integration of Myrica rubra–based N-doped carbon dots with Fe3S4 as excellent peroxidase mimics for colorimetric assay and smartphone-based intelligent sensing of p-aminophenol in waters

To realize the reutilization of waste Myrica rubra in the analytical field, we synthesized Myrica rubra –based N-doped carbon dots (MN-CDs) and further anchored them onto the surface of Fe 3 S 4 to fabricate Fe 3 S 4 @MN-CD nanocomposites. The as-fabricated nanocomposites possessed higher peroxidase-mimetic activity than its two precursors, resulting from the synergistic effect between them, and could catalyze colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into deep blue oxTMB with a strong 652-nm absorption. Under optimized conditions (initial solution pH, 3.5; incubation temperature, 35 ℃; Fe 3 S 4 @MN-CD concentration, 50 µg mL −1 , and 652-nm absorption), Fe 3 S 4 @MN-CDs were employed for colorimetric assay of p -aminophenol ( p -AP) with wide linear range (LR, 2.9–100 µM), low detection limit (LOD, 0.87 µM), and satisfactory recoveries (86.3–105%) in environmental waters. Encouragingly, this colorimetric assay provided the relative accuracy of 97.0–99.4% as compared with  conventional HPLC-UV detection. A portable smartphone-based colorimetric application was developed by combining the Fe 3 S 4 @MN-CD-based visually chromogenic reaction with a “Thing Identify” APP software. Besides, we engineered an image-capturing device feasible for field use, in which the internal-compact sealing prevented external light source from entering photography chamber, thereby reducing light interference, and also the bottom light source enhanced the intensity of blue imaging. This colorimetric platform exhibited satisfactory LR (1–500 µM), low LOD (0.3 µM), and fortification recoveries (86.6–99.6%). In the chromogenic reaction catalyzed by Fe 3 S 4 @MN-CDs, ·O 2 − played a key role in concomitant with the participation of •OH and h + . Both the colorimetric assay and smartphone-based intelligent sensing show great promising in on-site monitoring of p -AP under field conditions. Graphical Abstract