Noninvasive Salivary Sensor Based on Ferrocene/ZnO/Nitrogen-Incorporated Nanodiamond/Si Heterojunction Nanostructures for Glucose Sensing in Neutral Conditions

Abstract

The development of a simple and convenient noninvasive salivary glucose sensor to replace the needle-prick blood collection process can not only enhance early detection and diagnosis but also reduce excess medical care costs due to delayed treatment. This study presents a noninvasive sensor based on a ferrocene/ZnO/nitrogen-incorporated nanodiamond/Si heterojunction structure to measure glucose in saliva. The sensing electrode based on a heterojunction structure composed of ferrocene (FC), Bidens-like zinc oxide (b-ZnO), and nitrogen-incorporated ultra-nanocrystalline diamond (NUNCD) films, which is a kind of nitrogen-incorporated nanodiamond, was constructed on a silicon (Si) substrate. Herein, FC and b-ZnO act as a mediator and a specific surface area promoter, respectively, and NUNCD provides a good nucleation site and conducting path. Glucose oxidase (GOx) was introduced into the system to play the role of enzyme to catalyze the reaction and increase the electrode selectivity. The FC/b-ZnO/NUNCD/Si sensor exhibited superior performance in glucose measurements within the linear ranges (1) 20–100 μM (R2 = 0.9717) with a sensitivity of 1125.18 μA/(mM cm2) and (2) 20–600 μM (R2 = 0.9926) with a sensitivity of 804.11 μA/(mM cm2). Additionally, the sensor has a sensitivity of 1012.35 μA/(mM cm2) within the range 50–400 μM (R2 = 0.9912) for artificial saliva.