A novel fluorescence-scattering ratiometric sensor based on Fe-N-C nanozyme with robust oxidase-like activity

Numerous ratiometric fluorescence nanozyme sensors are developed, though, fluorescence-scattering ratiometric sensors based on nanozymes are hardly reported. First-order scattering (FOS) could be quenched due to inner filter effect of quenchers on scattering signals. Meanwhile, Second-order scattering (SOS) depended on FOS. Based on the principle, we designed a novel nanozyme sensor by coupling fluorescence (FL) and SOS. Specifically, Fe-N-C nanozyme (Fe-HCNP) was fabricated by doping Fe into carbon-nitrogen polymers via formamide condensations . Fe-HCNP possessed robust oxidase-like activity, effectively transforming O 2 into ·O 2 - and ·OH. Then, Fe-HCNP and o-phenylenediamine (OPD) severed as a hybrid system to construct an FL-SOS ratiometric sensor for ascorbic acid (AA). Fe-HCNP with large size possessed strong SOS. After being added into the Fe-HCNP/OPD system, AA could fast be oxidized to dehydroascorbic acid (DAA) due to Fe-HCNP as oxidase mimics. Subsequently, fluorescent quinoxaline derivative (DFQ) was produced after condensation reactions between DAA and OPD, causing an increase in fluorescence. Meanwhile, the intensity of FOS was reduced because FOS peaks of Fe-HCNP overlapped absorption bands of DFQ, causing a decrease in SOS. The FL-SOS ratiometric sensor for AA showed outstanding advantages of high specificity and fast. Overall, this work provided a new strategy for nanozyme ratiometric sensors.