Capacitive detection of living microalgae in a microfluidic chip

Capacitive detection of living microalgae from the sample suspension in a microfluidic chip is presented in this paper. A three-dimension capacitance sensor was designed by placing two cylindrical copper wires across the microfluidic channel. The frequency-dependent capacitive changes for both living and dead Dunaliella Salina were analyzed with Maxwell mixture theory and measured experimentally in this study. The results show that the amplitude of capacitive change is mainly influenced by algaeʹs size, living status and the applied alternative current frequency. Specifically, capacitive change increases with the increase in algae size and decreases with the increase in frequency. For the same kind of algae, the capacitance change caused by the living algal, however, is larger than that of the dead one under the same frequency, which can be used to differentiate the living algae from the sample suspension. The method of frequency-dependent capacitive detection of live algae described in this paper is simple and sensitive. The experimentally determined frequency window can serve as a guideline to differentiate the living algal from the dead one.