Colorimetric/fluorescence dual-mode sensor based on acid phosphatase/peroxidase-mimicking cascade catalysis for ultrasensitive detection of tartaric acid

Nanozymes hold great promise in catalysis-based sensing, however, challenges remain due to their less specificity and unclear catalytic mechanisms, which limited their potential applications. Herein we report an ultrasensitive colorimetric/fluorescence dual-mode tartaric acid (TA) sensor based on hydroxy-iron oxide (FeOOH) nanorods (NRs)@carbon dots (CDs) nanocomposite incorporating with acid phosphatase (ACP). The peroxidase (POD)-like activity of FeOOH can catalyze H 2 O 2 to generate OH, which can further oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to produce blue oxTMB, while the fluorescence of CDs can be quenched by the assembled FeOOH NRs through internal filter effect. The FeOOH@CDs can effectively transfer electron enabling high catalytic activity, which is supported by Cytochrome c as an electron transporter. ACP can hydrolyze trisodium L-ascorbate-2-phosphate salt (AAP) to produce ascorbic acid (AA), which increases colorimetric signal generated by FeOOH@CDs. Interestingly, TA can inhibit ACP activity through strong complexation and reduce the generated AA, by which most ox-TMB could not be restored. Meanwhile, the generated AA could reduce FeOOH to collapse into Fe 2+ , enabling the assembled CDs dropping-off into solution and restored fluorescence. However, TA can inhibit the ACP activity, which prevents fluorescence recovery. A colorimetric/fluorescence dual-mode sensing was established by cascading ACP/POD mimics. The limits of detection are 0.83 μM and 22.8 μM (3σ/S) for the fluorescence mode and colorimetric mode, respectively. The as-proposed method was applied to detect TA in wine samples, consistent well with the results of HPLC. This work not only expands nanozyme’s potential applications in catalysis and sensing, but also provides a potential platform for rapid TA detection for food control.