Microfluidic chip integrated with an electrolyte-insulator-semiconductor sensor for pH and glucose level measurement

This paper presents a solid-state sensor, micro-pump, and micro-valve integrated into a microfluidic device that is capable of performing automatic pH level and glucose concentration measurements with small volumes of samples and reagents. Polydimethylsiloxane was used to integrate all of the microfluidic components and was sandwiched between two glass substrate layers with a thin-film metal electrode and reference electrodes. The maximum pumping rate for the pneumatic micro-pump was 74.6 μl min^-1 at a driving frequency of 25 Hz and an air pressure of 16 psi. Over a time period of 50 s, the washing efficiency achieved was 96%, and a washing buffer did not need to be used when changing between two samples being measured because of the use of a micro-scale channel, which shortened the measurement time. The feasibility of the proposed sensor was demonstrated by measuring pH levels and glucose concentrations. The experimental results showed high sensing linearity (0.9996) for the pH measurement with a sensitivity of 49.16 mV pH^-1. With the aid of an entrapped-enzyme alginate bead for enzyme delivery and immobilization, glucose concentration was measured with a sensing linearity of 0.9964 and a sensitivity of 15.05 mV mM^-1, which is higher than using a bulk alginate for enzyme immobilization. In addition, the volume of reagent consumption was greatly reduced to around 200 μl, comparing to the traditional measurement using beaker as a container. With various enzymes encapsulated in the alginate bead, the proposed microfluidic device has the potential to monitor multiple blood indicators at the point of care.