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Current Research of Dr. Hsueh-Chia Chang

Rapid and Selective Molecular Sensing by Electrokinetics/Hydrodynamics

We develop new DC ad AC electrokinetic technologies to concentrate and detect a small number of molecular targets in microfluidics. The new techniques are invented in our group and include dielectrophoresis, field-enhanced molecular stretching/pairing, electrochemical carbon nanotube sensing, nanoslot-induced ion selectivity, micro-vortex molecular mixer/concentrator etc.

Integrated Pathogen/Molecular Detection Chips

We integrate microfabrication and nanoetching technologies to develop portable chips that allow rapid (<15 minutes), selective (one mismatch discrimination in DNA hybridization) and robust (heterogeneous medical and environmental samples) genetic detection of pathogens in the field. We work with the Great Lakes and EPA scientist on developing new field-detection protocols that are being developed by start-ups.

Nanofluidics and Electrokinetics

Complementing experiments with matched asymptotics, molecular dynamics simulation and CFD, we examine some fundamental issues in nanoscale electrokinetics that are important and yet poorly understood. Topics include (over)-limiting current in membrane ion transport, redox agent transport limitation in solar cells, activation barriers for molecular hybridization, aerosol electrostatics due to induced polarization, conducting Stern layer in nanocolloid (di)electrophoresis, hydrodynamic/transport homogenization at nanoscale (slip, Helmholtz and Debye length scales) etc.

Single Cell Analysis with Signal Protein Detection

With collaborators in biology and medicine, we are developing new technologies for confining blood cells, immune cells, mammalian cells, both in stationary traps and flowing streams, and detect the transport of proteins and viral particles across the cells in response to hydrodynamic, electrical and chemical stimuli. The cells are confined and manipulated by dielectrophoresis and the molecular detection by the rapid and selective molecular sensing techniques.

Nanocolloid Mass Spectrometry and Nanoaerosol Dynamics

We have discovered novel aerosol ejection dynamics dictated by the singular Laplace harmonics of the electric field near geometric singularities like cones and wedges. The liquid and solid aerosols are directed and sorted into surfaces and lines corresponding to the eigenfunctions of these discrete harmonics. These new aerosol dynamics governed by geometric singularities are used to direct nanocolloids into mass spectrometry with minimum loss and to sort nanocolloids by size for molecular detection applications.

Two-Phase Micro-Cooling with Nanofoam Pumping

We are studying the feasibility of using electric Maxwell pressure to compress nanofoam in micro-cooling devices for electronic cooling. Our earlier work indicates that nano-electroosmotic pumping can achieve the high pressure, in excess of 20 atm, to compress two-phase refrigerants to achieve high-efficiency cooling in a small unit. This concept is being developed to produce a micro-refrigeration cycle with two-phase nanofoam fluids.

AC Electrospray and Genomic Mass Spectrometry

We have discovered the AC analog of the DC Taylor cone. The AC cone has a half angle of 11 degrees, in contrast to 49 degrees of the Taylor cone. We found that the difference in angle is due to the different polarization mechanisms---space charge entrainment for the AC cone and dielectric polarization for the DC cone. Since the space charge entrained is the low-mobility product of field-induced ionization at the cone tip, we are able to entrain, concentrate, ionize and spray DNA and protein molecules without fragmentation. We are working towards a new mass spectrometry paradigm based on this soft-ionization technique.