Graphene oxide-mediated copper reduction allows comparative evaluation of oxygenated reactive residues exposure on the materials surface in a simple one-step method

Graphene Oxide (GO) is the oxidized form of graphene rich in surface groups comprising carbonyl, carboxyl, hydroxyl, and epoxy residues. The solubility in water makes GO an ideal material in the biomedical field though the plethora of synthesis methods available can modify the balance of oxygen groups and, consequently, the effects on eukaryotic and prokaryotic cells. For this reason, GO materials are always characterized with spectroscopic methods such as X-ray photoelectron and Fourier-transform Infrared spectroscopy. However, these techniques have some limitations, being disruptive and not clearly indicating oxygen functionalities available to react with polymers or biological media. In this work, we exploit GO reactivity with copper ions to develop a colorimetric method for the facile evaluation of surface oxidation degree and accessibility in polymeric samples. In the presence of GO, Cu2+ is reduced to Cu1+ and can react with bicinchoninic acid and induce light absorption at 562 nm. We observed that this reaction is dependent both on concentration and oxidation degree, and can be used to estimate GO exposure in thick composite samples. This technique will be fundamental in the future for scaffold characterization in tissue engineering and all the surface science studies analyzing GO-related materials' interactions with biological entities.