Person:

Brown, Keith Andrew

We demonstrate atomic force microscope(AFM) imaging using dielectrophoresis(DEP) with coaxial probes. DEP provides force contrast allowing coaxial probes to image with enhanced spatial resolution. We model a coaxial probe as an electric dipole to provide analytic formulas for DEP between a dipole, dielectric spheres, and a dielectric substrate. AFM images taken of dielectric spheres with and without an applied electric field show the disappearance of artifacts when imaging with DEP. Quantitative agreement between our model and experiment shows that we are imaging with DEP.

We demonstrate coaxial atomic force microscope (AFM) tweezers that can trap and place small objects using dielectrophoresis (DEP). An attractive force is generated at the tip of a coaxial AFM probe by applying a radio frequency voltage between the center conductor and a grounded shield; the origin of the force is found to be DEP by measuring the pull-off force versus applied voltage. We show that the coaxial AFM tweezers can perform three-dimensional assembly by picking up a specified silica microsphere, imaging with the microsphere at the end of the tip, and placing it at a target destination.

We present an integrated platform for performing biological and chemical experiments on a chip based on CMOS (complementary metal–oxide–semiconductor) technology. We have developed a hybrid integrated circuit (IC) / microfluidic chip that can simultaneously control thousands of living cells and pL volumes of fluid, enabling a wide variety 25 of chemical and biological tasks. Taking inspiration from cellular biology, phospholipid bilayer vesicles are used as robust picoliter containers for reagents on the chip. The hybrid chip can be programmed to trap, move, porate, fuse, and deform individual living cells and vesicles using electric fields. The IC spatially patterns electric fields in a microfluidic chamber 30 using 128 x 256 (32,768) 11 x 11 μm2 metal pixels, each of which can be individually driven with a radio frequency (RF) voltage. The chip’s basic functions can be combined in series to perform complex biological and chemical tasks and performed in parallel on the chip’s many pixels for high-throughput operations. The hybrid chip operates in two distinct modes, defined by the frequency of the RF voltage applied to the pixels: Voltages at MHz 35 frequencies are used to trap, move, and deform objects using dielectrophoresis and voltages at frequencies below 1 kHz are used for electroporation and electrofusion. This work represents an important step towards miniaturizing the complex chemical and biological experiments used for diagnostics and research into automated and inexpensive chips.