Effect of recess dimensions on performance of the needle-type dissolved oxygen microelectrode sensor

In this work, needle-type recessed dissolved oxygen (DO) microelectrode sensors with different recess dimensions were fabricated and characterized to investigate the relationship between recess dimensions and sensor performance. The square-ring type cathode geometry inside the recess was formed by wet etching, with the recess length ranging from ∼35 to ∼247 μm and the average length to hydraulic diameter (Lave/Dh) ratio ranging from 3.0 to 12.3. Sensor performance was characterized by three concentrations of dissolved oxygen (0, 4.1, and 8.7 mg/L O2) in 0.85% saline solution. Response time, stirring effect (e.g., sensitivity to physical interference), and current sensitivity were investigated. The longer recess increased sensor sensitivity. Sensors with recesses dimensions of Lave/Dh > 5 were found to be stable, exhibiting performance without stirring effect, and sensitivities in excess of 500 pA/mg/L. This work will permit better understanding of DO sensor performance with recessed structure for the accurate DO measurements.