Development of a Highly Sensitive Electrochemical Detection of Salivary Glucose and pH Sensors Based on Glucose Oxidase Using Interdigitated Microelectrodes
Authors: Adib Md Ridwan , Barrett Colm , Kennedy Emer , O'Riordan Alan 
Published: August 2024

The use of electrochemical nanosensors has seen a significant uptick in recent years, largely due to the improved chemical and physical properties that result from the modification of nano or microelectrode devices with nanomaterials.[1] These electrodes play a crucial role in enhancing electrochemical-based nanosensors, offering benefits such as a higher signal-to-noise ratio, lower detection limits, cost-effectiveness, ease of fabrication, and the ability to achieve steady-state currents. The interest in electrochemical nanosensors is considerable, given their broad application spectrum, which includes areas like animal health, human health, environmental monitoring, and bioprocess monitoring.[2] The focus of this research is the development of on-chip salivary glucose and pH sensors that are integrated on silicon wafers. These sensors are specifically designed to identify two frequently occurring bovine diseases: bovine respiratory disease (BRD) and scour. Both of these diseases are highly contagious, often resulting in fatal outcomes for calves, and cause economic losses amounting to millions of euros across Europe. Therefore, early detection of BRD and scour is essential to prevent, oversee, or delay the progression of the disease and its related complications. However, the current methods of blood glucose testing for calves have a significant disadvantage, as they require regular invasive blood sampling. Encouragingly, the analysis of saliva has surfaced as a non-invasive and convenient alternative for monitoring glucose levels in calves with above-mentioned disease.[3] Thus, it is necessary to develop a highly sensitive electrochemical nanosensor for early detection of BRD and scour by using biomarkers (glucose, pH) in a calf's saliva. The proposed electrochemical nanosensor is based on a micro fabricated device that integrates a silicon microelectrode, reference electrode, and counter electrode with six individual sensor that can be used for the detection of six different biomarkers i.e. glucose, pH, lactate, electrolytes, etc. The sensing mechanism is based on the measurement of changes in current that occur because of glucose and pH interactions with the modified silicon surface. The sensors are designed to detect small changes in glucose and pH concentrations that can be indicative of the onset of BRD and scour. The main advantage of the proposed electrochemical nanosensor is its ability to provide rapid and accurate detection of BRD and scour in calves. Early detection of these diseases can significantly improve treatment outcomes and reduce the risk of transmission to other animals. In addition, the low cost and ease of fabrication of these sensors make them an attractive option for large-scale deployment in agricultural settings. In conclusion, the development of on-chip electrochemical nanosensors for the early detection of bovine respiratory disease and scour by using saliva as a medium is a promising approach for improving animal health and reducing economic losses. The proposed sensors offer high sensitivity, low cost, and easy fabrication, making them an attractive option for widespread deployment in agricultural settings. Future research can focus on optimizing the sensor design for improved performance and expanding the range of biomarkers that can be detected.
This work represents the microfabrication and characterization of gold interdigitated electrodes (IDE) on silicon using standard microfabrication methods i.e., lithography and etching techniques. The sensor have six individual working electrodes (WEs) along with on-chip gold counter and platinum reference electrodes and can be modified individually for glucose and pH sensor. A two-step electrodeposition process was carried out for platinum platting thus incorporating glucose oxidase (GOx) onto a platinum-modified gold IDE with an o-phenylenediamine (o-PD). The enzymatic based nanosensor demonstrated a linear reduction response to wider range of glucose from 0.02-7mM using chronoamperometric measurements in artificial saliva (Figure 1a,b). In addition, real calf samples have been used to detect the glucose level in calf saliva and compared with commercial glucometer (Figure 1c). Furthermore, at gold IDE, the sensor exhibits linear responses for pH ranging from pH 5-8 using cyclic voltammetric analysis (Figure 1d,f).
References:
[1] S. Berry and A. O‘Riordan, Electrochemical nanosensors: advances and applications, Reports in Electrochemistry, 2016, 6, 1-14.
[2] J. Madden, C. Barrett, F. R. Laffir, M. Thompson, P. Galvin and A. O’Roirdan, On-Chip Glucose Detection Based on Glucose Oxidase Immobilized on a Platinum-Modified, Gold Microband Electrode, Biosensors, 2021, 11(8), 249.
[3] A. Ko, C. Liao, Salivary glucose measurement: A holy ground for next generation of non-invasive diabetic monitoring, Hybrid Advances, 2023, 3, 100052.

Figure 1