Gas Sensors Based On Locally Heated Multiwall Carbon Nanotubes Decorated With Metal Nanoparticles

We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2 substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μ m and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μ m wide and 5 μ m deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μ L volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10-5 to 10-2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity.2015Tanaka, K., Yamabe, T., Fukui, K., (1999) The Science and Technology of Carbon Nanotubes, , Elsevier Science, Oxford, UKWilson, S.A., Jourdain, R.P.J., Zhang, Q., New materials for micro-scale sensors and actuators: An engineering review (2007) Materials Science and Engineering: R: Reports, 56 (1-6), pp. 1-129Loiseau, A., Launois, P., Petit, P., Roche, S., Salvetat, J.-P., (2006) Understanding Carbon Nanotubes, Vol. 677 of Lecture Notes in Physics, , Springer, Berlin, GermanyCao, Q., Rogers, J.A., Ultrathin films of single-walled carbon nanotubes for electronics and sensors: A review of fundamental and applied aspects (2009) Advanced Materials, 21 (1), pp. 29-53Gelamo, R.V., Rouxinol, F.P., Verissimo, C., Vaz, A.R., De Moraes, M.A.B., Moshkalev, S.A., Low-temperature gas and pressure sensor based on multi-wall carbon nanotubes decorated with Ti nanoparticles (2009) Chemical Physics Letters, 482 (4-6), pp. 302-306Gelamo, R.V., Rouxinol, F.P., Verissimo, C., De Bica Moraes, M.A., Moshkalev, S.A., Gas and pressure sensors based on multi-wall carbon nanotubes: Study of sensing mechanisms (2010) Sensor Letters, 8 (3), pp. 488-492Abgrall, P., Nguyen, N.T., Nanofluidic devices and their applications (2008) Analytical Chemistry, 80 (7), pp. 2326-2341Mubeen, S., Lim, J.-H., Srirangarajan, A., Mulchandani, A., Deshusses, M.A., Myung, N.V., Gas sensing mechanism of gold nanoparticles decorated single-walled carbon nanotubes (2011) Electroanalysis, 23 (11), pp. 2687-2692Li, K., Wang, W., Cao, D., Metal (Pd, Pt)-decorated carbon nanotubes for CO and NO sensing (2011) Sensors and Actuators B: Chemical, 159 (1), pp. 171-177Koós, A.A., Nicholls, R.J., Dillon, F., Tailoring gas sensing properties of multi-walled carbon nanotubes by in situ modification with Si, P, and N (2012) Carbon, 50 (8), pp. 2816-2823Shin, W.C., Besser, R.S., A micromachined thin-film gas flow sensor for microchemical reactors (2006) Journal of Micromechanics and Microengineering, 16 (4), pp. 731-741Dai, L., Soundarrajan, P., Kim, T., Sensors and sensor arrays based on conjugated polymers and carbon nanotubes (2002) Pure and Applied Chemistry, 74 (9), pp. 1753-1772Savu, R., Silveira, J.V., Flacker, A., Micro-reactors for characterization of nanostructure-based sensors (2012) Review of Scientific Instruments, 83 (5)Dresselhaus, M.S., Jorio, A., Filho, A.G.S., Saito, R., Defect characterization in graphene and carbon nanotubes using Raman spectroscopy (2010) Philosophical Transactions of the Royal Society A, 368 (1932), pp. 5355-5377Ponce, M.A., Parra, R., Savu, R., Impedance spectroscopy analysis of TiO2 thin film gas sensors obtained from waterbased anatase colloids (2009) Sensors and Actuators, B: Chemical, 139 (2), pp. 447-452Galstyan, V., Comini, E., Faglia, G., Sberveglieri, G., TiO2 nanotubes: Recent advances in synthesis and gas sensing properties (2013) Sensors (Switzerland), 13 (11), pp. 14813-1483

Gas Sensors Based on Locally Heated Multiwall Carbon Nanotubes Decorated with Metal Nanoparticles

We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2 substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μm and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μm wide and 5 μm deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μL volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10−5 to 10−2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity

Microfluidic devices development for bioprocesses characterization

Orientadores: Stanislav Moshkalev, Jacobus Willibrordus SwartDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A fermentação alcoólica para produção de etanol brasileiro apresenta muitas perdas e sofre com falta de monitoramento. Os tanques contêm um ambiente microbiológico complexo e de intervenção limitada, pois dados em tempo real sobre o bioprocesso não são levantados. A microfluídica tem se mostrado uma grande ferramenta de sensoriamento que poderia ser utilizada para monitoramento local de fatores relevantes que poderiam levar à correção e à otimização desse processo. Com todos os avanços alcançados nas últimas três décadas, é plausível imaginar que grande parte da caracterização de bioprocesso que, atualmente, é realizada em laboratório tradicional, também possa ser realizada em campo, usando um dispositivo microfluídico eficiente e de custo acessível. O conhecimento dos elementos químicos presentes, bem como a saúde dos microrganismos envolvidos deve ajudar no aprimoramento do bioprocesso industrial de larga escala utilizado. A implementação eficiente de dispositivos microfluídicos na caracterização da fermentação industrial pode levar à operação com amostras coletadas e analisadas em tempo real, permitindo a correção de processo em andamento com provável redução de perdas. Existe, portanto, boas condições para a aproximação entre a microfluídica e a fermentação, uma ação multidisciplinar por natureza que só se concretizará com equilíbrio e sintonia entre as diversas áreas fundamentais de atuação: microbiologia, química, engenharia industrial, engenharia dos materiais e engenharia de microconstrução. Nesta tese mostramos, pela primeira vez no Brasil, como desenvolver dispositivos microfluídicos complexos utilizando moldes construídos com escrita a laser. A técnica, originalmente empregada na microeletrônica, permite a confecção de moldes precisos, rápidos e de fácil alteração de padrão resultando em estruturas similares à alcançada com litografia tradicional. Os dispositivos foram desenvolvidos para ter diferentes geometrias que atenderão as diversas necessidades encontradas na prática. Os quatro dispositivos foram aplicados, com sucesso, para a caraterização inicial da levedura saccharomyces cerevisiae e também na difusão de corantes em diversos meiosAbstract: Sugar cane fermentation for the production of Brazilian ethanol has many losses and suffers from lack of monitoring. The processing tank contains a complex microbiological environment with limited intervention, as they are not collected real time data about the bioprocess conditions. Microfluidics has been proved to be a good tool for sensing and monitoring, which can be used for low cost local monitoring of relevant factors that might be used for the correction and optimization of this process. The effective implementation of microfluidic devices in the characterization of industrial fermentation can lead to real time samples gathering and analyzed, allowing the correction of the underway process with likely loss reduction. With all the advances achieved in the last three decades, it is plausible to imagine that much of the characterization of bioprocess, which is currently held in a traditional laboratory, can also be performed on the field using an efficient and inexpensive microfluidic device. Knowledge of the chemical elements present as well as the health of microorganisms involved should help in the improvement of the large-scale industrial bioprocess used. Therefore, there are good conditions for the forthcoming between microfluidic and fermentation. This process is multidisciplinary and involves finding the balance and the harmony between the various fundamental areas involved: microbiology, chemistry, industrial engineering, materials engineering and microfabrication engineering. In this thesis we show, for the first time in Brazil, the development of complex microfluidic devices using molds built by laser writing. We also show that thick SU-8 can be successfully sensitized by laser writing, showing characteristics similar to SU-8 made by traditional lithography. The technique developed allows making precise molds, with fast and easy patterns change, using a technology that was originally used in microelectronics. The devices were designed to have different geometries so that can meet the diverse needs find in practice. The four devices were applied successfully for the initial characterization of saccharomyces cerevisiae yeast and diffusion of dyes in various mediumsMestradoEletrônica, Microeletrônica e OptoeletrônicaMestre em Engenharia Elétric