December 11, 2015
Colloquium Speaker: Xuanhong Cheng and James C. M. Hwang
Dr. Xuanhong Cheng is an associate professor in the Dept. of Materials Science and Engineering Department and the Bioengineering Program at Lehigh University. She received her PhD in Bioengineering from University of Washington in 2004, after which she had a postdoctoral training in the surgical department at Massachusetts General Hospital under the guidance of Profs. Mehmet Toner and William Rodriguez. The focus of Xuanhong’s research is to develop microfluidic devices for cell and pathogen diagnostics. In combination with nanomaterials and biosensors, these devices are expected to perform automated sample processing and sensitive analyte detection towards point-of-care uses. She has published ~30 referred technical papers, has 5 patent applications/granted patents and has obtained research funding from ARO, DTRA, NIH, NSF and PA Department of Health. One of the technologies from her postdoctoral work for white blood cell isolation and detection has been licensed to a company Daktari Diagnostics, Inc. for commercial development. Dr. Cheng serves on the scientific advisory board of the company.
Dr. James Hwang is Professor of Electrical Engineering at Lehigh University. He graduated with a B.S. degree in Physics from National Taiwan University in 1970, and completed M.S. (1973) and Ph.D. (1976) studies in Materials Science at Cornell University. After twelve years of industrial experience at IBM, AT&T, GE, and GAIN, he joined Lehigh in 1988. He cofounded GAIN and QED; the latter became a public company (IQE). He has been a Nanyang Professor at Nanyang Technological University in Singapore, as well as an advisory professor at Shanghai Jiao Tong University, East China Normal University, and University of Science and Technology in China. Most recently, he was a Program Officer for GHz-THz Electronics at the Air Force Office of Scientific Research. He is a life fellow of the Institute of Electrical and Electronic Engineers. He has published ~300 refereed technical papers with the impact factor h > 30 and has been granted six U. S. patents.
Traditionally, cell detection is accomplished through chemical or optical means for which sophisticated instruments such as DNA sequencers or flow cytometers are commercially available. DNA sequencers can be very specific, but are slow and destructive. Optical cytometers can be fast and sensitive to single cells and their vitality, but often require labeling which may alter their physiological state. In comparison, electrical cell detection can be label-free and nondestructive with high throughput. To this end, cytometers capable of measuring the electrical properties of single cells are also commercially available as Coulter counters. However, they can suffer from the dilemma of cell clogging or solution parasitics. Cell clogging occurs if a narrow channel is used to increase the cell-to-sample volume ratio, whereas solution parasitics are aggravated if a wide channel is used to prevent cell clogging. Additionally, Coulter counters typically use discrete frequencies on the order of MHz or lower, which made them unduly sensitive to the size and shape variations of individual cells, as well as the polarization layers formed in the solution between the cells and electrodes. For these reasons, Coulter counters are usually optimized for a special purpose such as for counting human blood cells. Recently, to resolve the dilemma encountered by Coulter counters and to evolve a general-purpose electrical detection technique, we used broadband microwave measurement to overcome electrode polarization, AC dielectrophoresis to precisely place cells between narrowly spaced electrodes for maximum cell-to-sample volume ratio, and relatively wide microfluidic channels to prevent cell clogging. This unique combination of approaches resulted in reproducible sensing of single Jurkat and HEK cells, both live and dead, of different cultures at different times.