Evaporation-based Microfluidic Pump Using Super-Hydrophilic Diatom Biosilica Thin Films

Diatoms are a group of single-celled photosynthetic algae that use biochemical pathways to bio-mineralize and self-assemble three-dimensional photonic crystals with unique photonic and micro- & nano-fluidic properties. In recent years, diatom biosilica has been used in surface-enhanced Raman scattering (SERS) based optofluidic sensors for detection of a variety of chemical and biological molecules. In this paper, we present a study to develop a microfluidic pumping system using super-hydrophilic diatom thin films. The desire to develop such a system stems from the requirement to create a low-cost, self-powered microfluidic pumping system that can sustain a continuous flow over an extended period of time. The diatom biosilica acts not only as the driving force behind the flow, but also serves as ultra-sensitive SERS substrates that allows for trace detection of various molecules. Liquid is drawn from a reservoir to the tip of a 150 mu m inner diameter capillary tube positioned directly over the diatom film. A thin and long horizontal reservoir is used to prevent flooding on the diatom film when the liquid is initially drawn to the diatom film through a capillary tube from the reservoir. The connection of the meniscus from the capillary to the film was maintained from a horizontal reservoir for a recorded time of 20 hours and 32 minutes before the partially filled reservoir emptied. Flow rates of 0.38, 0.22 and 0.16 mu L/min were achieved for square biosilica thin films of 49mm(2), 25mm(2), and 9mm(2) at a temperature of 63 degrees F and 45% relative humidity respectively. A temperature-controlled system was introduced for the 49mm(2) substrate and flow rates of 0.60, 0.82, 0.93, and 1.15 mu L/min were observed at 72, 77, 86, and 95 degrees F at 21% relative humidity respectively. More testing and analysis will be performed to test the operation limits of the proposed self-powered microfluidic system.