Double signal ratiometric electrochemical riboflavin sensor based on macroporous carbon/electroactive thionine-contained covalent organic framework

Riboflavin (RF) is one of the necessary vitamins. If human body lacks RF, it will lead to inflammation and dysfunction of mouth, lips and skin. Thus sensitive and accurate determination of RF is necessary. Here, an electroactive covalent-organic framework nanobelt (COF TFPB-Thi ) with thickness of 1.4 nm was prepared by amine-aldehyde condensation reaction between thionine and 1, 3, 5-tris (p-formylphenyl) benzene, which was then grown vertically on three-dimensional porous carbon derived from kenaf stem (3D-KSC) for double signal ratiometric electrochemical detection of RF. The resulted 3D-KSC/COF TFPB-Thi showed two reduction peaks at −0.08 V and −0.23 V, which came from the reduction of COF TFPB-Thi and the conjugated structure of COF TFPB-Thi , respectively . In the presence of RF, those RF molecules near the electrode surface were oxidized at 0.6 V. Then some oxidized RF (RF ox ) adsorbed on COF TFPB-Thi would oxidize COF TFPB-Thi into COF TFPB-Thi (ox) while other RF ox adsorbed on 3D-KSC kept unchanged. When the potential was scanned from 0.6 V to −0.6 V, both COF TFPB-Thi (ox) and RF ox adsorbed on 3D-KSC were reduced at −0.08 V and −0.45 V accordingly, while the reduction peak of −0.23 V of the conjugated structure of COF TFPB-Thi kept constant. When j -0.45 /j -0.23 was used as the response signal, the detection limit was 44 nM and the linear range was 0.13 μM −0.23 mM. By using j -0.08 /j -0.23 as the response signal, a detection limit of 90 nM and a linear range of 0.30 μM-0.23 mM (S/N = 3) were obtained. By using double signals, the measurement results can be corrected to make the results more accurate and reliable. The sensor also showed good selectivity, reproducibility and stability, which provided a good application prospects.