Ratiometric electrochemical biosensing based on double-enzymes loaded on two-dimensional dual-pore COFETTA-TPAL

Herein, a covalent organic framework with dual-pore sizes prepared by ammonia-aldehyde condensation reaction (COFETTA-TPAL) was proposed to load microperoxidase-11 (MP-11) and glucose oxidase (GOD) for ratiometric electrochemical glucose biosensing. The COFETTA-TPAL were flexible two-dimensional (2D) nanosheets with highly ordered crystalline conjugated structure and dual-pores of 3.06 nm and 0.87 nm. The size of MP-11 and GOD matched with its large and small pore well and accordingly they could be embedded into the pores of COFETTA-TPAL through pore encapsulation and hydrogen bond between N-doped skeleton of COFETTA-TPAL and −COOH of MP-11 and GOD. The good flexibility allowed them to be firmly attached to the electrode surface, just like chitosan and nafion which were usually used to modify electrode. The GOD-MP-11−COFETTA-TPAL modified electrode exhibited the reduction peak of COFETTA-TPAL near 0.15 V (j0.15 V) and the reduction peak of MP−11 at −0.4 V (j−0.4 V). The j−0.4 V was decreased gradually and the j 0.15 V was kept constant with the adding of glucose. The j−0.4 V/j0.15 V linearly reduced with the glucose concentration varied from 0.017 mM to 3 mM, and the detection limit was 4.97 μM. The biosensor also displayed good selectivity, stability and reproducibilty. The work successfully proved the application of COF as support platform to load enzymes/proteins for electrochemical biosensors.