Papers by Author: Simon Song

Abstract: On-chip cytotoxicity sensing for liquid substances was investigated by using the microbial chemotaxis of Euglena gracilis. The Euglena cells were confined in a closed-type micro-aquarium in a PDMS microchip, and the micro-aquarium was isolated from two microchannels to flow test and reference liquid substances. Small molecules of liquids permeated into PDMS and diffused into the water in the micro-aquarium, and thus, the chemical concentration gradient of test liquids was built in the micro-aquarium. The negative chemotactic movements of Euglena cells were observed for ethanol down to 0.5% within 2-5 min after the injection of diluted ethanol into one of the separated microchannels (counter reference = pure water). On the other hand, when 0.5% H₂O₂ was introduced as a test liquid (counter reference = pure water), the Euglena cells fell into continuous rotation instead of single step turning and/or straight forward swimming. As a result, total swimming activity in the micro-aquarium decreased even after H₂O₂ flow was switched back to water. The observation shows that the types of cytotoxic effects can be identified through the cell movement analysis.

Abstract: We investigated on-chip cytotoxicity gas sensing using the bacterial chemotaxis of Euglena confined in a microaquarium. The sensor chip made from PDMS had one microaquarium and two microfluidic channels passing aside of the microaquarium. The chemotactic microbial cells were confined in the microaquarium, whereas two gases (one sample and one reference) flowed in the two isolated microchannels. Gas molecules move from the microchannels into the microaquarium by permeation through porous PDMS wall, and dissolve into the water in the microaquarium, where Euglena cells are swimming. The chemotactic movements of Euglena were observed with an optical microscope and measured as traces in real time. By injecting CO₂ and air into each microchannel separately, the Euglena cells in the microaquarium moved to air side, escaping from CO₂. This observation showed that the concentration gradient of CO₂ was produced in the water in the microaquarium. The CO₂-avoiding movement of Euglena was increased largely at a CO₂ concentration of 40%, and then moderately increased above 60%. Some Euglena cells stopped swimming at the air side of the microaquarium and remained there even after CO₂ has been removed, which can be used as the indicator of CO₂ history.

Abstract: Nonlinear modeling method for the structural dynamic analysis of a micro cantilever beam actuated by electrostatic force is presented in this study. Static deflection is first obtained by solving nonlinear static equilibrium equation and the modal and the stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly.