Biocompatibility of a droplet-mixing device using an electro-conjugate fluid

An electro-conjugate fluid (ECF) is a type of functional fluid that produces a jet flow under a non-unifoun electric field. We use an ECF to generate a rotational flow in a tiny cylindrical chamber. When multiple droplets are dripped into the rotational flow of the ECF, they may be subjected to a centripetal force because of the difference in density between the droplets and ECF. This causes the droplets to move to the center of the chamber and mix with each other. In this paper, we conducted luminance measurements using a bioluminescence reaction to verify the suitability of this device for biological applications. We observed the luminescence produced by mixing droplets of luciferin and luciferase, and measured luminance maxima and area to assess the mixing ability of the device. In addition, because the enzyme luciferase can be deactivated by surroundings, we confirmed whether the proposed mixing method has any harmful influence on biological samples or not. To better understand the properties of the device, we conducted control experiments with two other set of conditions; i.e., without ECF and with still ECF. Our results confirmed that there was no difference in mixing ability between the three systems, and the influence of an electric- and centrifugal-field generated in the device on mixing might be negligible for biological applications.