In situ pH-Controlled electrochemical sensors for glucose and pH detection in calf saliva

Electrochemical biosensors have been extensively researched and employed across diverse fields from environmental monitoring to clinical diagnostics. Detecting biomarkers like saliva pH and glucose are crucial indicators of the health and well-being of animals and opens the door for development of new non-invasive calf health measurements. Herein, we introduce a highly sensitive and stable electrochemical sensor for detection of pH and glucose in artificial and calf saliva. Pristine gold electrodes were employed for pH measurement using the voltage where the minimum of the gold oxide reduction peak occurred as a pH indicator. For glucose sensing, we utilized an effective in-situ pH control method enabled by interdigitated microelectrodes (IDEs) to optimize pH for accurate detection of glucose in artificial and calf saliva. Glucose oxidase (GOx) was first immobilized onto a platinum black modified gold IDE array through an electrodeposition process, which involved a mixture of o-phenylenediamine (o-PD) and β-cyclodextrin (β-CD). 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 -166 mV.pH^-1 was recorded for the pH sensor within the pH range of 5-9. These multiplexed sensors successfully detected glucose and pH levels in calf saliva noninvasively, which is particularly significant for meeting the frequent and continuous monitoring requirements of biomarkers (glucose, pH) associated with Bovine respiratory disease (BRD) and diarrhoetic calves.