Novel enzyme-functionalized covalent organic frameworks for the colorimetric sensing of glucose in body fluids and drinks

Abstract

Covalent organic frameworks (COFs) are promising platforms for use in enzyme immobilization. However, whether from the perspective of structural design or functional expansion, more enzyme-COF composite materials, which combine the advantages of COFs and enzymes, and may create new features, need to be developed. A colorimetric sensor is simple, cost-effective and easy to operate, and can transform targeted analytic events to visual color changes. How to detect the concentration of glucose simply and practically is of great significance for the control of diabetes mellitus. Herein, an enzyme-coupling COF (COF_HD–GOX) colorimetric biosensor was fabricated by covalent connection of a new carboxyl-contained COF (COF_HD) and glucose oxidase (GOX), which was the first colorimetric sensor for glucose, based on a COF–enzyme composite. Compared with other reported colorimetric sensors for glucose detection, this method displayed a relatively wider linear range from 0.005 to 2 mM and a relatively lower detection limit, which was 0.54 μM. The operability and accuracy of the COF_HD–GOX biosensor was confirmed by the quantitative determination of glucose in real samples, such as serum, diabetic urine and drinks. Moreover, the COF_HD–GOX based colorimetric biosensor showed good selectivity, recoverability and storage stability, and it could be reused for glucose detection at least five times. Even after 100 days of storage, the relative activity was still more than 85%. This study used enriched enzyme-linked COF materials and demonstrated that COF–enzyme matrices are promising for applications in colorimetric biosensing and medical diagnostics.