Size-dependent trajectories of DNA macromolecules due to insulative dielectrophoresis in submicrometer-deep fluidic channels.

In this paper, we demonstrate for the first time that insulative dielectrophoresis can induce size-dependent trajectories of DNA macromolecules. We experimentally use lambda (48.5 kbp) and T4GT7 (165.6 kbp) DNA molecules flowing continuously around a sharp corner inside fluidic channels with a depth of 0.4 mum. Numerical simulation of the electrokinetic force distribution inside the channels is in qualitative agreement with our experimentally observed trajectories. We discuss a possible physical mechanism for the DNA polarization and dielectrophoresis inside confining channels, based on the observed dielectrophoresis responses due to different DNA sizes and various electric fields applied between the inlet and the outlet. The proposed physical mechanism indicates that further extensive investigations, both theoretically and experimentally, would be very useful to better elucidate the forces involved at DNA dielectrophoresis. When applied for size-based sorting of DNA molecules, our sorting method offers two major advantages compared to earlier attempts with insulative dielectrophoresis: Its continuous operation allows for high-throughput analysis, and it only requires electric field strengths as low as approximately 10 Vcm.

A temperature sensor from a self-assembled carbon nanotube microbridge

Recent studies show that carbon nanotubes (CNTs) can be used as temperature sensors, and offer great opportunities towards extreme miniaturization, high sensitivity, low power consumption, and rapid response. Previous CNT based temperature sensors are fabricated by either dielectrophoresis or piece-wise alignment of read-out electronics around randomly dispersed CNTs. We introduce a new deterministic and parallel microsensor fabrication method based on the self-assembly of CNTs into three-dimensional microbridges. We fabricated prototype microbridge sensors on patterned electrodes, and found their sensitivity to be better than -0.1 %/K at temperatures between 300K and 420K. This performance is comparable to previously published CNT based temperature sensors. Importantly, however, our research shows how unique sensor architectures can be made by self-assembly, which can be achieved using batch processing rather than piecewise assembly. ©2010 IEEE.