Meng Lian

Micropumping of biofluids by alternating current electrothermal effects

Electrokinetics is a preferred technique for microfluidic systems, but it is typically applied on fluids that are not too conductive (lower than 0.02S∕m), which excludes most biological applications. To solve this problem, this letter investigates microfluidic actuation by ac electrothermal (ACET) effect that was largely overlooked by the community. ACET originates from temperature gradients in the fluids, and it becomes more pronounced in more conductive fluids. This letter discusses two ACET pump designs, and pumping was demonstrated with biobuffers (e.g., lysogeny broth at 0.754S∕m).

Ultrafast micropumping by biased alternating current electrokinetics

This paper reports dramatic improvements in flow rate over conventional alternating current (ac) electrokinetic micropumps by exploiting asymmetry in electric potentials over the electrodes. A micropump consisting of a planar asymmetric electrode array was tested using ac signals with and without a direct current (dc) bias. All experiments were done at 100 kHz Vac. The pumping velocity is much faster with a dc voltage, in some cases by an order of magnitude, reaching a linear velocity of up to 2.5 mm/s with only 5.4 Vrms. The discovery presents an exciting opportunity for microfluidics. Future improvement can be anticipated with additional optimization.

Particle Line Assembly/Patterning by Microfluidic AC Electroosmosis

Recently AC electroosmosis has attracted research interests worldwide. This paper is the first to investigate particle line assembly/patterning by AC electroosmosis. Since AC electroosmotic force has no dependence on particle sizes, this technique is particularly useful for manipulating nanoscale substance, and hopefully constructs functional nanoscale devices. Two types of ACEO devices, in the configurations of planar interdigitated electrodes and parallel plate electrodes, and a biased ACEO technique are studied, which provides added flexibility in particle manipulation and line assembly. The paper also investigates the effects of electrical field distributions on generating microflows for particle assembly. The results are corroborated experimentally.

High Sensitivity Particle Detection by Biased AC Electroosmotic Trapping on Cantilever

Real-time detection of low-concentration pathogenic/toxic bioparticles is important for deterring infectious diseases and bioterrorism, which is difficult to achieve for lab-on-a-chip. Currently sensitivity is achieved through time-consuming culturing or sophisticated processing, often unfeasible under field conditions. By microfluidic convection of particles from solution bulk onto sensing electrodes, local cell count can be greatly enriched and sensitivity can be increased significantly. This paper discusses how AC electro-osmosis (ACEO) is applied to trap particles in labs-on-a-chip. A new technique – biased ACEO is developed for effective particle trapping, and its integration with cantilevers is prototyped to reach ultra high detection sensitivity.

Micro/nano- particulate fluid manipulation in AC electro-kinetic lab-on-a-chip

Integrating fluid transport systems on a single chip with micro-scale detectors has significant advantages, including increased resolution, faster response, smaller sample sizes, and increased parallelism of analysis. To realize the detection of low concentration bioparticles, conventional techniques involve sample culturing to increase particle count to a critical mass at the detection sites, which is time-consuming and often unfeasible under field conditions. By attracting target cells from the bulk onto the sensing electrodes to enrich local cell count in real time, sensitivity can be increased by orders of magnitude. Directed line formation of particles on designated electrodes can be realized by our new asymmetric polarization AC electro-osmotic (ACEO) mechanism based on electrochemical reaction, which shows better particle trapping than that of conventional ACEO. This paper also presents a cantilever ACEO particle trap

Ultra Fast Micropumping by Reaction Enhanced AC Electrothermal Effect

AC electrothermal effect generates temperature gradients in the fluids, consequently inducing free charges that move in electric fields, and produce microflows in microchannel. This paper reports dramatic improvements in flow rate over conventional ac electrokinetic micropumps by exploiting asymmetry in electric potentials over the electrodes. A micropump consisting of planar asymmetric electrode array was tested using AC signals with and without a DC bias. The pumping velocity is much faster with a DC voltage, in some cases by an order of magnitude, reaching 3.2 mm/sec linear velocities with only 9 Vrms. Our hypothesis attributes the increase of ACET force to the ion generation near electrode by reactions and the resulting high conductivity gradient. The discovery presents an exciting opportunity for microfluidics, and further improvement can be anticipated with some optimization.Copyright