Abstract-Opticaldielectrophoresis(ODEP)has been explored experimentally with success in manipulating microscale objects in the last 5 years. However, not much theoretical analyses have been performed to understand its operating principles in depth and also determine its limitations as a tool to manipulate micro-and nano-scale objects. In this paper, we present our work on establishing an equivalent electrical model to analyze the important physical interactions when optically induced dielectrophoretic force is used to manipulate micron-sized polystyrene beads. Simulation results show that the ODEP manipulation of microbeads is frequency-dependent and that the electrothermal effect is negligible. Furthermore, the relationship between the frequency of the applied voltage and the maximum manipulation velocity of the microbeads obtained from simulation is consistent with our experimental measurements. In addition, simulation results also show that the minimum radius of a bead that can be manipulated exponentially decreases with respect to the size of the illuminated spot. For instance, when the illuminated spot size is -indicating that ODEP can be extended to manipulate nano-scale objects if the illuminated spot size can be significantly reduced.
This paper presents the development of a chemical sensor employing electronic-grade carbon nanotubes (EG-CNTs) as the active sensing element for sodium hypochlorite detection. The sensor, integrated in a PDMS-glass microfluidic chamber, was fabricated by bulk aligning of EG-CNTs between gold microelectrode pairs using dielectrophoretic technique. Upon exposure to sodium hypochlorite solution, the characteristics of the carbon nanotube chemical sensor were investigated at room temperature under constant current mode. The sensor exhibited responsivity, which fits a linear logarithmic dependence on concentration in the range of 1/32 to 8 ppm, a detection limit lower than 5 ppb, while saturating at 16 ppm. The typical response time of the sensor at room temperature is on the order of minutes and the recovery time is a few hours. In particular, the sensor showed an obvious sensitivity to the volume of detected solution. It was found that the activation power of the sensor was extremely low, i.e. in the range of nanowatts. These results indicate great potential of EG-CNT for advanced nanosensors with superior sensitivity, ultra-low power consumption, and less fabrication complexity.
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