应机械工程学院邀请，美国田纳西大学(The University of Tennessee, Knoxville)吴杰副教授于2017年6月19~21日访问我校，并做微尺度传感与检测、微流控芯片技术等微机电系统领域的系列学术报告。
报告题目：A Passive and Wireless Lab-on-a-Film for Disposable and Wearable Microfluidics
报告时间：2017 年 6月19日（星期一）上午9:00-10:00
报告人：吴杰（Jayne Jie Wu）副教授（美国田纳西大学）
A wirelessly powered and controlled biased-AC electroosmotic (biased-ACEO) lab-on-a-film (LOF) is presented here for particle and fluid manipulation. Amplitude modulation (AM) and inductive coupling are used for wireless transmission of low frequency signals required for excitation of biased-ACEO effects employed by the LOF for microfluidic functions. The LOF consists of a receiving coil (for receiving inductively transmitted high frequency signals), surface mounted devices (for recovering a low frequency AC signal) and an array of interdigitated electrodes (IDE, for excitation of biased-ACEO effects). Unlike existing wireless lab-on-a-chip devices that have cumbersome set-ups, require high voltages and perform only one microfluidic function, the presented LOF has a compact and flexible structure, works at very low voltage ranges, and can perform several microfluidic operations corresponding to a wirelessly-controlled voltage. When the level of the demodulated signal over the IDE is about 0.7 V, the IDE performs particle enrichment over designated electrodes. The IDE functions as an active mixer at about 2 V; and as a pump when the voltage reaches 3 V. The LOF is prototyped rapidly on a flexible substrate at low cost using inexpensive benchtop equipment with an overall dimension of 10 × 20 mm2. Though the electrode definition is limited to micro-scales, the LOF prototype has successfully demonstrated desired microfluidic functions. In addition to inductive transmission of low frequency signals, the printed circuit board-based LOF device offers a low cost and effective solution for using small, flexible microfluidic systems in nontraditional clinical diagnostic tools, disposable devices and heath care settings.
报告题目：Thermally biased AC electrokinetic pumping effect for Lab-on-a-chip based delivery of biofluids
报告时间：2017 年 6月20日（星期二）下午14:30-15:30
报告人：吴杰（Jayne Jie Wu）副教授（美国田纳西大学）
One major motivation for microfluidic research is to develop point of care diagnostic tools, which often demands a solution for chip-scale pumping that is of low cost, small size and light weight. Electrokinetics has been extensively studied for disposable pumping since only electrodes are needed to induce microflows. However, it encounters difficulties with conductive biofluids because of the associated high salt content. In electrokinetic pumps, electrodes are in direct contact with fluid, so high salt content will compress the electric double layer that is essential to electroosmostic flows. Alternating current electrothermal (ACET) effect is the only electrokinetic method found viable for biofluid actuation. While high frequency (>10 kHz) operation can suppress electrochemical reactions, electrical potential that could be applied over biofluids is still limited within several volts due to risk of electrolysis or impedance mismatch. Since ACET flow velocity has a quartic dependence on the voltage, ACET flows would be rather slow if electric field alone is used for actuation. This work studies the effect of a thermal bias on enhancing AC electrokinetic pumping. With proper imposition of external thermal gradients, significant improvement in flow velocity has been demonstrated by numerical simulation and preliminary experiments. Both showed that with 4 Vrms at 100 kHz, flow velocity increased from ~10 μm/s when there was no thermal biasing to ~112 μm/s when a heat flux was applied.
报告题目：Interactions of Electrical Fields with Fluids: Biotechnological Applications
报告时间：2017 年 6月21日（星期三）上午9:00-10:00
报告人：吴杰（Jayne Jie Wu）副教授（美国田纳西大学）
A microfluidic chip should have following functions: mixing, pumping, concentration step to assist detection, etc., as shown schematically here. As device dimension scales down, pressure driven flow becomes increasingly inefficient due to high surface-volume ratio. In contrast, electrokinetics is gaining popularity as a microfluidic actuation mechanism, due to its no moving parts and easy implementation. Traditional electrokinetic pumping requires applying high DC voltage across the microchannel, and the electric field drives the mobile charges at the fluid/channel interface (i.e. electroosmosis) to transport fluid. High voltage causes bubble generation and pH gradients from electrochemical reactions. To minimize these adverse effects, AC electrokinetics (ACEK) has emerged recently for on-chip pumping and particle manipulation for its low voltage operation.
ACEK investigates the behavior of particles in fluid and the motion of electrolytic fluids when they are subjected to AC electrical fields. Charges are induced in the bulk of the fluids where there is an interface (e.g. electroosmosis) or gradients in fluid attributes (e.g. electrothermal effect). Because the electric fields and induced charges in fluid change polarity simultaneously, steady (not oscillatory) fluid motion can be generated in ACEK. There are mainly three types of ACEK phenomena, dielectrophresis (studied since 1991), AC electroosmosis (since 1999, our group initiated “biased ACEO”) and AC electrothermal effect (our group is the first to have developed ACEK micropumps). ACEO is mainly effective for low-conductivity fluid (e.g. water), thus limiting its application in lab-chips. We have developed capabilities for conductive fluids, making an important step towards practical EK devices.
ACEK can also manipulate micro/nano particles in the fluid, which include DNA, protein molecules, virus, bacteria, plant and animal cells, and inorganic particles. To detect low concentration bioparticles, a concentration step is necessary to increase particle count to a critical mass at the detection sites. ACEK is the only known on-chip method to collect particles in a short time. My group prototyped a first in-situ microcantilever particle trap (experimented on 200nm to 1µm particles), and we are extending it to protein and DNA concentrating.
吴杰（Jayne Jie Wu），1999年和2004年分别获中国科学院应用物理和美国圣母大学(Notre Dame)电子工程学的博士学位，现任美国田纳西大学副教授，主要从事交流电动力学(Alternating Current Electrokinetics)与微流控芯片(Microfluidics, Lab-on-a-chip)技术的基础与应用研究，目前兼任田纳西大学及时诊断与纳米生物传感技术中心(Initiative for PON/POC Nanobiosensing)主任。独立主持田纳西大学微系统课题组，是国际上最早开展微流体交流电热(Alternating Current Electrothermal)效应理论和应用研究的几个研究组之一。
所主持的美国国家科学基金项目“非对称极化交流电渗实验室芯片研究”获Career奖，课题组专注于微尺度颗粒的介电泳(dielectrophoresis, DEP)技术，生物流体的智能传感与控制、微驱动与微实行器件的开发等研究。近五年来，吴杰教授课题组致力于解决开发新型微流控生物传感器所面临的基础科知识题。目前在生物传感器与微机电系统领域的主流期刊Biosensors and Bioelectronics, Microfluidics and Nanofluidics, Biomicrofluidics, Biomedical Microdevice, Sensors and actuators等发表SCI学术论文60余篇，总被引用1300余次，H因子为21。兼任IEEE可穿戴生物力学传感与系统学会高级会员，Austin Journal of Biosensors and Bioelectronics，Journal of Mechanics in Medicine and Biology等期刊编委。
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