In Situ pH-Controlled Electrochemical Sensors for Glucose and pH Detection in Saliva

Electrochemical biosensors have been extensively researched and employed across diverse fields from environmental monitoring to clinical diagnostics. The determination of biomarkers such as glucose and pH, which are crucial for the health and well-being of animals, has led to a widespread use of these specific biosensors. Herein, we introduced a highly sensitive and stable electrochemical non-invasive detection of glucose and pH biosensors in artificial and real saliva utilizing an effective in-situ pH control method by interdigitated microelectrodes. Utilizing the on-chip platinum reference and gold counter electrodes, glucose oxidase (GOx) was immobilized onto a platinum black modified, gold interdigitated electrode through an electrodeposition process, which involved a mixture of o-phenylenediamine (o-PD) and β-cyclodextrin (β-CD). The fabricated electrodes were then examined using various techniques including optical microscopy, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). An electrochemical in-situ pH control technique was utilized for accurate detection of glucose in artificial and real saliva. This method provides an opportunity for localized pH adjustment at the detection point, eliminating the requirement for extra reagents. To assist with experimental design concerning both electroanalysis and in-situ pH control of the solution, COMSOL simulations were conducted on interdigitated electrodes. Glucose and pH detection were performed in a multiplexed fashion utilizing GOx modified and gold interdigitated array electrodes, respectively. The enzymatic based glucose sensor showed an exceptional sensitivity of -0.46 nA.mM-1 in artificial saliva at a wide range of concentrations from 0.02 mM to 7 mM, with a LOD of 0.3 µM. Simultaneously, a sensitivity of -0.20 nA.pH⁻¹ was recorded for the pH sensor within the pH range of 5 to 8. The multiplexed sensors were utilized to noninvasively detect glucose and pH levels in real saliva, effectively demonstrating their successful application. This capability is particularly significant for meeting the frequent and continuous monitoring requirements of biomarkers (glucose, pH) associated with Bovine respiratory disease (BRD) and diarrhoetic calves.