Showing papers by "Michael G. Pollack published in 2003"

Electrowetting-based droplet mixers for microfluidic systems

Abstract: Mixing of analytes and reagents is a critical step in realizing a lab-on-a-chip. However, mixing of liquids is very difficult in continuous flow microfluidics due to laminar flow conditions. An alternative mixing strategy is presented based on the discretization of liquids into droplets and further manipulation of those droplets by electrowetting. The interfacial tensions of the droplets are controlled with the application of voltage. The droplets act as virtual mixing chambers, and mixing occurs by transporting the droplet across an electrode array. We also present an improved method for visualization of mixing where the top and side views of mixing are simultaneously observed. Microliters of liquid droplets are mixed in less than five seconds, which is an order of magnitude improvement in reported mixing times of droplets. Flow reversibility hinders the process of mixing during linear droplet motion. This mixing process is not physically confined and can be dynamically reconfigured to any location on the chip to improve the throughput of the lab-on-a-chip.

Electrowetting-based on-chip sample processing for integrated microfluidics

Abstract: In this work, results and data are reported on key aspects of sample processing protocols performed on-chip in a digital microfluidic lab-on-a-chip We report the results of experiments on aspects of sample processing, including on-chip preconcentration and dilution, on-chip sample injection or dispensing, and sample mixing It is shown that high speed transport and mixing of analytes and reagents can be performed using biological solutions without system contamination

A digital microfluidic biosensor for multianalyte detection

Abstract: A microfluidic lab-on-chip (LoC) for measuring the concentration of human body metabolites, using submicroliter droplets as reaction chambers, is presented in this paper. The device is based on the manipulation of droplets using the principle of electrowetting and is integrated with an optical absorbance measurement system for detection. We have demonstrated the detection of glucose using a colorimetric enzyme-kinetic assay in less than 40 seconds. The sensor response is linear in the range of 25mg/dl to 300mg/dl, with less than 5% deviation from linearity at the upper limit. In addition to glucose, we have also demonstrated the feasibility of lactate, glutamate, and pyruvate assays using our system.

3-d imaging of moving droplets for microfluidics using optical coherence tomography

Abstract: VVe present the use of optical coherence tomography (OCT), an interferometric 3-D imaging technique, to visualize microdroplets in an electrowetting-based microfluidic device. Vertical cross-sectional images of stationary and moving microdroplets are obtained using this technique, to provide information on static and dynamic contact angle changes and flow profiles inside the microdroplet during transport. The initial results are encouraging and OCT appears to be a promising method to study fundamental, yet poorly understood electrowetting phenomena such as contact angle saturation and contact angle hysteresis. OCT can also be used in visualizing 3-D flow profiles in droplet-based microfluidics.

Automated electrowetting based droplet dispensing with good rei'roducibility

Abstract: Electrowetting based droplet on-chip dispensing is presented. On-chip reservoir and droplet formation channel are designed to facilitate droplet creation. The mechanism and conditions in which droplet can be formed are analyzed. The droplet volume variations are tested over a range of interfacial tension and number of pinch off electrode. The results show that droplet volume reproducibility is degraded significantly when liquid-oil interfacial tension is reduced. And droplet volume is a fimction of number of pinch off electrode and the timing of control sequence. Keyword: droplet dispensing, electrowetting, volume reproducibility

Method for splitting droplets by electrowetting-based techniques

Abstract: A method for splitting a droplet into two or more droplets includes providing a starting droplet on a surface comprising an array of electrodes and a substantially co-planar array of reference elements. The electrode array comprises at least three electrodes comprising a first outer electrode, a medial electrode adjacent to the first outer electrode, and a second outer electrode adjacent to medial electrode. The starting droplet is initially disposed on at least one of the three electrodes and at least partially overlaps at least one other of the three electrodes. The method further includes activating each of the three electrodes to spread the starting droplet across the three electrodes, and de-activating the medial electrode to split the starting droplet into first and second split droplets. The first split droplet is thereby disposed on the first outer electrode and the second split droplet is disposed on the second outer electrode.