Enzyme-free, metal oxide-based amperometric-colorimetric dual-mode functional glucose sensor

To address the urgent need for glucose level detection in the human body, several affordable, lightweight, and skin-mounted glucose sensors have been developed. Enzymatic sensors are frequently utilized, but they have challenges of enzyme degradation and indirect charge transfer through a redox mediator, which affect their reusability and shelf life. Here, enzyme-free nickel oxide thin film electrode in an alkaline medium is used to enable direct charge transfer with glucose. A chemical reaction between glucose and the electrode surface occurs, leading to an additional oxidation (Ni+2/Ni+3) of the electrode under external bias. Additionally, the colorimetric analysis further validated this reaction through the transformation of a dark-colored NiO (Ni+3) electrode into a bleached color state (reduced from Ni+3 to Ni+2 through the oxidation of glucose. As the glucose concentrations increase to 5mM, the color of the electrode is no longer optically readable (ΔT% ∼ 66%). The corresponding amperometric response is determined with a detection limit of 2 μM and a 3579 μA mM−1 cm−2 sensitivity, and it also recognizes a passive response to other interfering species and facilitates its one-month shelf life. Additionally, a two-electrode electrochemical colorimetric liquid cell-type glucose sensor has been designed to pave the way for future applications.