Papers by Keyword: Chemical Sensing

Abstract: We developed the real-time analysis of chemotactic motion of microbial cells (Euglena gracilis), for on-chip cytotoxicity sensing for environmental chemical substances. The Euglena cells were confined in a closed-type micro-aquarium in a PDMS microchip, and their movements were taken by a CMOS video camera. When 1.5%-H₂O₂ was introduced into a microchannel running aside of the micro-aquarium, the H₂O₂ molecules permeated into the micro-aquarium by diffusion through porous PDMS wall, and the cells fell into continuous rotation instead of single step turning and/or straightforward swimming. Such an abnormal swimming behavior is the result of metabolic disturbing effects evoked by radical oxygen species released from H₂O₂. In order to sensing the metabolic disturbing effects, we achieved real-time categorization of the swimming traces into straightforward swimming or continuous rotation; firstly the swimming traces in the video image were sectioned into squares, and then the aspect ratio and filling factor for each square were calculated. High aspect ratio or small filling factor corresponded to straightforward swimming, whereas low aspect ratio and high filling factor to continuous rotation. This motion analysis enables to measure the metabolic disturbing effects on swimming Euglena cells quantitatively, which is important to detect unidentified toxic substances in environments.

Abstract: Triphenylamine derivative is one of the multifunctional materials which has attracted considerable interest of research for their unique radical properties containing triphenylamine unit with higher holes mobility, excellent photoelectric conversion capability. The three benzyl rings of triphenylamine unit can connect different functional groups which can display different activity in the fields of organic solar cells, electroluminescence, electrochromism, optical limiting and chemical sensors. Moreover， the developing prospects of triphenylamine derivative are also briefly discussed.

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 the chemical sensing mechanism of epitaxial graphene grown on 6H-SiC (0001) to different polar solvents and their behavior at higher temperatures. We show that at 300 K the sensitivity of the graphene sensor increases exponentially with the dipole moment of a solvent and decreases significantly as the temperature increased to 425 K. Using electrical measurements, we also show that graphene can effectively discriminate between polar protic and polar aprotic solvents with the shift in device electrical resistance at 300 K.

Abstract: Modern resistive chemical sensors include discontinuous nano/mesostructures. Sensing performances are then governed by the chemical nature of the nanostructure gap as well as by the sensor design at the nanogap scale. Various top-down, bottom-up and hybrid fabrication routes of discontinuous/nanogaped metal nano and mesostructures have been developed. These structures are assembled/organized on insulating surfaces for integration of resistor based devices for the specific sensing of chemicals in gaseous as well as in liquid media. Hydrogen sensing based on discontinuous/gaped palladium nano/mesostructures is a chosen case-study for the evaluation of various nano/mesogap fabrication methods.

Abstract: Chemical sensing is a key application of bio-inspired smart materials. Artificial nanostructured layers mimicking biorecognition are synthetically accessible e.g. by imprinting techniques or affinity material nanoparticles. Hence, for detecting extremely malodorous organic thiols (butane/octance thiol), we designed molybdenum disulphide nanoparticles. In contrast to soft metals (e.g. gold) they interact with the SH-group fully reversibly leading to one of the first real QCM sensors for these compounds. Rationally varying the surface of the recognition material allows for optimizing the interaction properties. Electrolyzed gold e.g. shows sensor effects being about an order of magnitude higher than screen printed electrodes. Furthermore, molecular imprinting leads to highly selective cavities in polymers (polyurethanes, -styrenes, -acrylates) for detecting odorous compounds, e.g. aliphatic alcohols, ethyl acetate and limonene. With these materials, we designed an electronic nose for monitoring plant degradation processes based on a six-electrode QCM (quartz crystal microbalance) array. With a variety of degrading materials (grass, fruit, conifers), it determines the above analytes down to some ppm directly on-line. The concentration data can be extracted from the E-nose frequency shifts by Neural Networks and validated by GC-MS.