Low-cost Microfluidic LOC System for Separation of Microalgae and Cells

Abstract

Material and fabrication at low-cost used for lab-on-a-chip (LOC) system and the ease of operation without expensive and complicated instruments are crucial for wide application in our daily life. The current low-cost LOC material could be categorized as two types: paper-based LOC and polymer like polydimethylsiloxane (PDMS) based device. Paper-based devices enable the advantages of easy fabrication, disposable nature and least cost. Using an office laser printer to create a carbon powder pattern on the filter paper, we created a microwell pattern area of which the uncovered carbon powder enables a flow rate greater than that where covered with carbon powder along the filter; the flow can carry and localize single microalgae into the microwell separately. The separation process only takes 30 seconds and the separation performance of isolating single microalgae could be over 37% in average. The open-structure design of the paper device makes it operable with a common laboratory micropipette for sample retrieval and transfer. The paper-device can also function as an incubator for microalgae growth on simply rinsing the paper with a growth medium. In this research, we developed PDMS based filter LOC devices to separate microalgae and detect circulating tumor cells (CTCs). Clogging always becomes a main issue on filter based separation; cross-flow system was proven to reduce this drawback. We develop a centrifugally driven, multilayer, concentric filter device, a small bench-top centrifuge, which is commonly available in biochemical laboratories, was employed as part of our centrifugal microfluidic separation system. The cross-flow in our separation system was simply generated on altering the rate of rotation, as revolutions per minute (RPM), instantly through the relative motion of the device and the fluid. This strong cross-flow can wash away the particle and microalgae clogs at the filter pores, so increasing the filtration performance over 13.7 % without complicated control and expensive equipment. The use of the PDMS filter device enabled variously sized microparticles and environmentally collected microalgae samples to be readily separated in a few minutes. This device was also applied to detect CTCs. By using the anti–human EpCAM antibody coated polystyrene (PS) beads to capture CTCs which could enlarge the size of CTCs to create significant size different from normal cell like white blood cells (WBCs). With a concentric filter device and centrifugation, the unbound PS beads and WCBs would flow to the outer layer of the device; the targeted CTCs bound with PS beads would be retained in the inner filter layer. The inner filter layer is designed as a detection zone in which the bound cells are easily observed by microscope because of the small area of the inner channel and the enrichment effect. We successfully demonstrate that CTCs could be separated and detected in the concentration of one CTC per million of WBCs by this device and method.