Papers by Author: Kazunari Ozasa

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Authors: Kazunari Ozasa, Jee Soo Lee, Simon Song, Masahiko Hara, Mizuo Maeda
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.
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Authors: Alex Mason, Kazunari Ozasa, Olga Korostynska, Ismini Nakouti, Montserrat Ortoneda-Pedrola, Mizuo Maeda, Ahmed Al-Shammaa
Abstract: Euglena is a naturally occurring algae which can be found in any fresh water source.It is non-toxic, easy to handle, visualize and relatively resilient to variation in environment.This, along with the relatively large size of Euglena, means it can be readily used as a modelfor environmental monitoring of other smaller pathogenic micro-organisms (e.g. Escherichiacoli ). Currently the behavior of Euglena is observed through the use of an optical microscopefor sensing purposes. However, this method su ers from following major pitfalls: (1) the sizeand expense of the microscope; (2) the small observation volume (approx. 1 L); (3) the imageprocessing requirements and (4) need for a skilled human operator to acquire those images. Byusing electromagnetic (EM) wave technology in the GHz frequency range we seek to overcomethese challenges, since it has been demonstrated by the authors to be cost e ective, have alarge sensing volume (> 100L) and produce comparatively simple output data. Furthermoreit is possible to use simple software algorithms to process the sensor output data, and providereal-time information on Euglena gracilis viability and quantity. This paper shows proof ofconcept work to verify the feasibility of the proposed EM wave technology as an alternative tothe current optical microscopy methods.
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Authors: Kazunari Ozasa, Jee Soo Lee, Simon Song, Masahiko Hara, Mizuo Maeda
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.
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