A novel ratiometric electrochemical biosensor for sensitive detection of ascorbic acid

In this work, a novel ascorbic acid (AA) ratiometric biosensor was prepared by using the PCN-333 (Al) metal-organic frameworks (MOFs) (PCN stands for porous coordination network) to encapsulate Ketjen black (KB) as catalyst for catalyzing oxidation of AA and thionine (Thi) as an internal reference signal simultaneously. The encapsulation of KB and Thi in the pores of PCN-333 (Al) MOFs not only improved efficiency of KB and Thi greatly because PCN-333 (Al) MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly. Furthermore, PCN-333 (Al) MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors. The oxidation peak current of AA catalyzed by KB at −0.05   V increased with the increasing concentration of AA, while the oxidation peak current of Thi at −0.24   V kept constant, which resulted in a novel ratiometric biosensor for AA detection. The ratiometric biosensor exhibited a wider linear range from 14.1   ±   0.2 to (5.5   ±   0.1) х10 3   μM (R 2   =   0.998) and a lower detection limit of 4.6   ±   0.1   μM with high accuracy, selectivity, reproducibility and sensitivity. The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.