<p dir="ltr">Microdroplets (typically less than 10 μm in radius) have proven to be unique reaction vessels capable of doing the seemingly impossible: drive the chemistry that could have made life possible. While I am not a biochemist here to explain the intricacies of such a claim, I am a measurement scientist who has worked for the past three and half years to develop new methods which can be used to unveil new chemistries in these droplets. Before electrochemists like me entered the microdroplet realm, mass spectrometrists spent years studying droplets at this scale (typically generated with electrospray methods) and have been able to show that these droplets can promote reaction acceleration by several orders of magnitude, spontaneous generation of reactive species such as water and hydroxide radicals as well as hydrogen peroxide, and other curious chemistries. While these studies have changed the way that scientists view microdroplets, they all require the analysis of thousands of droplets in tandem where values are extrapolated back to the average droplet. The robust correlation of chemistry in an individual droplet of a specific size requires the development of new measurement tools capable of accessing single sub-femtoliter droplets, one at a time. Here, I describe the development of new electrochemical measurement tools which have been used to access this curious chemistry at the single droplet level as well as the implications of the findings from the implementation of these tools. First, stochastic electrochemistry, a method where an electrode effectively “fishes” for droplets suspended in an oil phase, will be outlined and it’s use to probe the spontaneous generation of hydrogen peroxide in such droplets will be presented. Afterwards, a method used for the electroanalysis of droplets in air, or aerosols, where an ionic liquid bubble (suspended by a platinum bubble wand) captures droplets to be analyzed at a carbon fiber wire thread through the middle, will be outlined. The use of these two techniques to correlate enzymatic activity in both droplet types, droplets in oil and aerosols, will then reveal that the gas|liquid interface promotes higher turnover rate acceleration for glucose oxidase. Finally, the fabrication and use of a dual-barrel electrode for the analysis of an acoustically levitated droplet will be presented. These three techniques stand to make electrochemistry a pivotal technique for the analysis of the curious chemistry housed within individual microdroplets. In addition to these methods, methods for extending electrochemistry to the next generation of scientists are presented.</p>

Submitted by Erika Demachki (erikademachki@gmail.com) on 2017-03-02T21:06:32Z No. of bitstreams: 2 Dissertação - Lucas da Costa Duarte - 2016.pdf: 3454791 bytes, checksum: 29ace536ee1c0aefc19dfbcdcec01bbe (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-03-03T11:42:43Z (GMT) No. of bitstreams: 2 Dissertação - Lucas da Costa Duarte - 2016.pdf: 3454791 bytes, checksum: 29ace536ee1c0aefc19dfbcdcec01bbe (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-03-03T11:42:43Z (GMT). No. of bitstreams: 2 Dissertação - Lucas da Costa Duarte - 2016.pdf: 3454791 bytes, checksum: 29ace536ee1c0aefc19dfbcdcec01bbe (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-08-05 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This study describes the assembly and use of a RepRap 3D printer with a modeling technology fused deposition modeling (FDM) for manufacturing microfluidic devices for direct spray ionization mass spectrometry (DS-MS) assisted by paper tip as well as for generation of droplets of water/oil with integrated electrochemical detection. The low-cost 3D printer has been properly assembled and calibrated by means of pieces of kit purchased commercially. The smaller channel width obtained which allowed the uniformity 3D printing without any obstruction was 400 μm. For studies of DS-MS were used microfluidic devices consisting of a single channel (the dimensions 30 mm × 0.5 mm × 0.5 mm) connected to a sample reservoir with 3 mm diameter with low cost (R$ 0.20) and time printing (20 min). A tip paper (5 mm × 0.5 mm) was cut out and inserted at the end of the printed channel to facilitate the formation of the spray. The spraying was promoted by the application of 4 kV in the sample reservoir containing 0.1% formic acid in methanol prepared. This organic medium showed high compatibility with the polymeric material used for the printing of microfluidic chips. Using a glucose solution as a template, the spray formed by the proposed microfluidic device was extremely stable compared to the spray generated by conventional paper devices for at least 10 min. The analytical devices for viability of the printed DS-MS was successfully demonstrated by qualitative analysis of ball pens inks, caffeine, xylose and lysozyme. The DS-MS devices exhibited significant repeatability and reproducibility, making it possible to reuse. For the generation of droplets of oil/water it was built with a device channel in the T-junction configuration with 0.75 mm × 50.0 mm × 0.7 mm and containing two integrated electrodes (1.5 mm × 2.0 mm and spacing 0.5 mm) in antiparallel arrangement. These electrodes consisting of a mixture of ABS and carbon nanotubes were used for conductivity detection capacitively coupled contact (C4D). The droplets were generated by varying the flow rate of continuous phase comprised of oil + Span80/water + Triton between 10 to 60 μL/min. Through the printed electrodes it was possible to employ the system C4D system to detect the droplets generated with a satisfactory response. The intensity and width of peaks obtained exponentially decrease the extent that it increases the flow of the continuous phase. Moreover, it was possible to correlate the length of the droplet generated from the signals obtained with C4D, indicating potential as a new technique for droplet measures. Finally, the 3D printer made possible the manufacture of parts contributed to other works in cooperation to include the construction of an electrochemical cell for by batch injection analysis, a support for Snitrosothiols decomposition, a cover for conductivity detection cell, micromixers, devices for ELISA assays and mold for manufacturing zones for colorimetric analysis. / modelagem por fusão e deposição (fused deposition modeling, FDM) para fabricar dispositivos microfluídicos para ionização direta por spray em espectrometria de massas (DS-MS) assistida por ponta de papel, bem como para geração de gotículas de água/óleo com detecção eletroquímica integrada. A impressora 3D de baixo custo foi devidamente montada e calibrada por meio do kit de peças adquirido comercialmente. A menor largura de canal obtida que permitiu a uniformidade de impressão 3D sem qualquer obstrução foi de 400 μm. Para os estudos de DS-MS, foram utilizados dispositivos microfluídicos constituídos de um único canal (nas dimensões 30 mm × 0,5 mm × 0,5 mm) conectado a um reservatório de amostra com 3 mm de diâmetro com baixo custo (R$ 0,20) e tempo de impressão (20 min). Uma ponta de papel (5 mm × 0,5 mm) foi cortada e inserida na extremidade do canal impresso para facilitar a formação do spray. A pulverização foi promovida através da aplicação de 4 kV no reservatório de amostra contendo 0,1% de ácido fórmico preparada em metanol. Este meio orgânico demonstrou grande compatibilidade com o material polimérico utilizado para a impressão dos chips microfluídicos. Usando-se uma solução de glicose como modelo, o spray formado pelo dispositivo microfluídico proposto foi extremamente estável quando comparado com o spray gerado pelos dispositivos convencionais de papel por pelo menos 10 min. A viabilidade analítica dos dispositivos impressos para DS-MS foi demonstrado com sucesso por meio de análise qualitativa de tintas de canetas esferográficas, cafeína, xilose e lisozima. Os dispositivos de DS-MS exibiram repetitividade e reprodutibilidade significativa, tornando possível a sua reutilização. Para a geração de gotículas de óleo/água foi construído um dispositivo com canais na configuração junção em T com 50,0 mm × 0,75 mm × 0,7 mm contendo dois eletrodos integrados (1,5mm × 2,0 mm e espaçamento de 0,5 mm) na disposição antiparalela. Estes eletrodos, constituídos de uma mistura de ABS e nanotubos de carbono, foram utilizados para detecção condutométrica sem contato capacitivamente acoplada (C4D). As gotículas foram geradas variando a vazão de fase contínua formadas por óleo+Span80/ água+Triton de 10 a 60 μL/min. Por meio dos eletrodos impressos foi possível empregar o sistema C4D para detecção das gotas geradas com resposta satisfatória. A intensidade e largura dos picos obtidos diminuem exponencialmente a medida em que se aumenta a vazão da fase contínua. Além disso, foi possível correlacionar o comprimento da gota gerada com os sinais obtidos com C4D, indicando potencialidade como uma nova técnica para medidas de gotículas. Por fim, a impressora 3D possibilitou a fabricação de peças que contribuíram para outros trabalhos em colaboração que incluem a construção de uma célula eletroquímica para análise por injeção em batelada, um suporte para decomposição de S-nitrosotióis, uma tampa para cela de detecção condutométrica, micromisturadores, dispositivos para ensaios de ELISA, e molde para fabricação de zonas para análises colorimétrica.

Le développement de différentes formes colloïdales pour la thérapie et le diagnostic médical ultrasonore connait un intérêt croissant depuis de nombreuses années. En particulier, les microbulles de perfluorocarbone (PFC) sont des agents de contraste intéressants, car le gaz est un puissant réflecteur des ultrasons. Plus récemment, les gouttelettes de PFC ont été proposées pour de nouvelles applications acoustiques. Suite à une impulsion acoustique, les ultrasons induisent un changement de phase de l’état liquide à l’état gazeux. Ce phénomène est appelé la vaporisation acoustique de gouttelettes. Parallèlement à l’étude de nouvelles applications, le développement de nouvelles techniques de préparation offrant un meilleur contrôle lors de la production, reste un enjeu primordial. Ainsi, de nouvelles méthodes de préparation basées sur des dispositifs membranaires semblent être particulièrement intéressantes. L’objectif de la thèse porte donc sur le développement de nouvelles techniques à membrane pour la formulation de microbulles et de microgouttelettes de taille contrôlée pour des applications en imagerie et thérapie ultrasonore. Dans ce travail, l’émulsification membranaire directe avec un module membranaire de type cross-flow a été utilisé pour la préparation de microbulles stabilisées par des tensioactifs solubles, tandis qu’un module de type microkit a permis l’obtention de microbulles stabilisées par des phospholipides. Dans un second temps, l’émulsification membranaire par prémix a permis de formuler des microgouttelettes de PFC monodispersées. Pour les différentes formes colloïdales préparées, nous avons observé l’influence des paramètres du procédé (pression, débit et contrainte de cisaillement), des paramètres de formulation (molécules stabilisatrices, type de PFC de la phase dispersée) et des paramètres de la membrane (taille des pores) sur la formation des microbulles/ microgouttelettes. Par la suite, la caractérisation acoustique des microbulles/microgouttelettes a montré que ces systèmes présentent les propriétés nécessaires pour être utilisés comme agents de contraste ultrasonores / The development of various colloidal forms for therapy and diagnosis in ultrasound medical present a great interest for many years. In particular, microbubbles of perfluorocarbon (PFC) are interesting as contrast agents because the gas is a high ultrasound reflector. More recently, PFC droplets have been proposed for news acoustic applications. Indeed, after an acoustic pulse, the ultrasound waves induce a phase change from the liquid state to the gaseous state. This phenomenon is called the acoustic vaporization of droplets. In parallel with the study of new applications, the development of new process offering a better control during production, remains a key issue.Thus, the preparation using news methods based on membrane devices seem to be particularly interesting. The aim of the thesis is the development of new membrane process for the formulation of microbubbles and droplets with a size controlled for ultrasound applications in imaging and therapy. In this work, the direct membrane emulsification with a cross-flow membrane module was used for the preparation of microbubbles stabilized by soluble surfactants, while a microkit module allowed to obtain microbubbles stabilized by phospholipids. In a second step, the membrane emulsification by premix allowed to formulate monodispersed droplets of PFC. For the various colloidal forms prepared, we observed the influence of the process parameters (pressure, flow rate and shear stress), the formulation parameters (surfactants, type of PFC of the dispersed phase) and the membrane parameters (pore size) on the formation of microbubbles/droplets. Subsequently, the acoustic characterization of microbubbles/droplets has shown that these systems have the properties to be used as ultrasonic contrast agents

Des composites polyamide-6 renforcés fibres de verre obtenus par injection réactive ont été caractérisés afin de remplacer ces fibres synthétiques par des fibres biosourcées de viscose haute ténacité. La première étape a été l’étude physico-chimique des fibres et de la matrice polymère thermoplastique par des techniques multiples : DSC, ATG, essais mécaniques, FTIR, RMN et mesure d’angle de contact. Afin d’améliorer l’interface entre la viscose haute ténacité et le polyamide-6, les fibres de viscose ont été fonctionnalisées en deux étapes. Premièrement, un traitement plasma oxygène a permis le nettoyage de la surface de ces fibres. Elles ont été ensuite fonctionnalisées par un agent de couplage silane. Une nouvelle méthode de dépôt de microgouttes de polymère sur les fibres a été développée, dans des conditions représentatives de l’injection réactive, afin de vérifier l’avantage d’un traitement de surface des fibres. Cette approche permet de déterminer la résistance au cisaillement interfacial entre les fibres et le polyamide-6, par déchaussement des microgouttes. Par la suite, des composites polyamide-6 renforcé viscose traitée ou non traitée ont été obtenus. / Polyamide-6 / glass fibers composites were studied in order to replace glass fibers with high tenacity viscose as a reinforcement, using a reactive injection process. The first step was the physico-chemical characterization of fibers and matrix using different techniques such as: DSC, TGA, mechanical testing, FTIR, NMR and contact angle measurements. In order to improve the interface between high tenacity viscose and polyamide-6, the viscose fibers were functionalized using a two step method. First, oxygen plasma was applied as a cleaning process to remove impurities. Secondly, the fibers were functionalized using an aminosilane. A new deposition technique of polymer microdroplets onto fibers, in conditions similar to these of reactive injection process, was developed in order to confirm the advantages of the silane treatment. Moreover, a pull-out test of these microdroplets led to the determination of the interfacial shear strength between polyamide-6 and high tenacity viscose fibers. Then, polyamide-6 composites reinforced with high tenacity viscose were obtained.