Covalent Functionalization of Graphene Oxide with a Presynthesized Metal–Organic Framework Enables a Highly Stable Electrochemical Sensing

This paper reports the covalent functionalization of graphene oxide (GO) by a presynthesized metal–organic framework NH2-MIL-101(Fe) via ultrasonication of the two components. The formation of Fe–O covalent bonding in the NH2-MIL-101(Fe)-GO nanohybrid is clearly evidenced, and the covalent bonding still remains after electrochemical reduction. The morphology and structure of the nanohybrid are characterized via scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. The electrode based on electrochemically reduced NH2-MIL-101(Fe)-GO shows ultrastable and high-sensitive performance in simultaneous electrochemical sensing of three purine metabolic derivatives (uric acid, xanthine, and hypoxanthine); in particular, no signal fading is seen even after running for 120 times. The covalent bonding within the nanohybrid is obviously the key to maintain such a stability.