Carbon post-microarrays for glucose sensors

A novel design and fabrication method of glucose sensors based on high aspect ratio carbon post-microarrays is reported in this paper. Apart from the fact that carbon has a wide electrochemical stability window, a major advantage of using carbon post-microarrays as working electrodes for an amperometric glucose sensor is the large reactive surface per unit footprint substrate area, improving sensitivity of the glucose sensor. The carbon post-microarrays were fabricated by carbon-microelectromechanical systems (C-MEMS) technology. Immobilization of enzyme onto the carbon post-electrodes was carried out through co-deposition of glucose oxidase (GOx) and electrochemically polymerized polypyrrole (PPy). Sensing performance of the glucose sensors with different post-heights and various post-densities was tested and compared. The carbon post-glucose sensors show a linear range from 0.5 mM to 20 mM and a response time of about 20 s, which are comparable to the simulation result. Sensitivity per unit footprint substrate area as large as 2.02 mA/(mM cm²) is achieved with the 140 μm high (aspect ratio around 5:1) carbon post-samples, which is two times the sensitivity per unit footprint substrate area of the flat carbon films. This result is consistent with the hypothesis that the number of reaction sites scales with the reactive surface area of the sensor. Numerical simulation based on enzymatic reaction and glucose diffusion kinetics gives the optimum geometric design rules for the carbon post-glucose sensor. Glucose sensors with even higher sensitivity can be achieved utilizing higher carbon post-microarrays when technology evolution will permit it.