Carbon nanotubes/polyethylenimine/glucose oxidase as a non-invasive electrochemical biosensor performs high sensitivity for detecting glucose in saliva

• FTO-CNTs/PEI/GOx electrochemical saliva glucose sensor is developed. • CNT forest favors the stable immobilization of GOx in considerable quantities. • Electrochemical glucose detection in artificial saliva samples is achieved. • The high sensitivity of 63.38 µA/mMcm 2 (70–700 µM glucose) is achieved. With the aim of improving the life quality for diabetics, we develop a novel electrode for the noninvasive glucose sensor which can determine the glucose levels in saliva. In this work, carbon nanotubes (CNTs) are directly grown on a fluorine-doped tin oxide (FTO) coated glass substrate through chemical vapor deposition, followed by the immobilization of glucose oxidase (GOx) via electrostatic force with the aid of polyethylenimine (PEI). The results confirm that the CNT forest can substantially enhance the charge transferability, and considerable quantities of GOx can be stably immobilized on the rough surface of the electrode because of the networked structure of the CNT forest. With a fast electron transfer rate and short electron transfer distance, both the current difference of the oxygen consumption and enzyme reduction reaction are detected for glucose sensor using the cyclic voltammetry method. The FTO-CNTs/PEI/GOx electrode exhibits the high sensitivity of 63.38 µA/mMcm 2 with a wide linear range of 70–700 µM glucose. Furthermore, the FTO-CNTs/PEI/GOx electrode shows good stability as well as high selectivity towards glucose. Finally, the glucose sensing performance of the FTO-CNTs/PEI/GOx electrode is investigated in artificial saliva, which exhibits great sensitivity even under high-viscosity conditions such as artificial saliva, thus, reveals excellent potential for use in practical applications.