Artificial Cilia for Capture and Sampling

Abstract

There is a need for improved methods of pre-concentration and detection of bacteria in food safety. The sample preparation is necessary to increase the number of target bacteria in a fluid sample to improve the limit of detection. We show the use of metallic thin films as artificial cilia for applications in sample manipulation in microfluidics and biosensors. We use evaporated alloy of nickel-iron on a glass substrate which are actuated magnetically by varying the external magnetic field. These hair like synthetic structures actuated by the magnetic field have a highly asymmetric bending patterns in an oscillatory cycle. This asymmetry is important for creating any microfluidic transport. In this work, we exploit this asymmetry in the strokes and demonstrate microfluidic transport phenomenon of pumping, rapid mixing and capture of micro-particles in a microchannel. To characterize the microfluidic pumping capabilities of the artificial cilia, we incorporate the cilia inside a PDMS microchannel loop and analyze the flow in produces. We vary important parameters such as the cilia width, spacing, number of rows and channel dimensions and establish its influence on the pumping efficiency. We observe low pumping rates at very high and very low operating frequencies, and establish an optimum operating frequency for maximized pumping efficiency. Further, we demonstrate the use of such cilia for microfluidic mixing. For this, we use a PDMS Y-channel with cilia on its bottom wall. Two fluids dyed with different fluorescent colors are introduced into the two inlet channels. And the ability of the cilia to mix the two streams of fluid is characterized by imaging the fluorescent intensity of the fluid stream downstream from the cilia. Again, we show the dependence of mixing efficiency on several parameters of the system. We also demonstrate particle capture with these artificial cilia. To do this, we functionalize the cilia with streptavidin protein, and introduce particles coated with biotin into the microchannel. The cilia is then oscillated so as to produce mixing in the microchannel. The mixing effect increases the probability of particles coming in contact with the cilia. The biotin coated particles stick to the cilia when they come into contact. This demonstrates capture of particles in a microfluidic channel. These microfluidic functions find varied application in many lab on a chip devices where active fluid transport is needed.