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PD/BD/105876/2014 Electronic skin (e-skin), which is an electronic surrogate of human skin, aims to recreate the multifunctionality of skin by using sensing units to detect multiple stimuli, while keeping key features of skin such as low thickness, stretchability, flexibility, and conformability. One of the most important stimuli to be detected is pressure due to its relevance in a plethora of applications, from health monitoring to functional prosthesis, robotics, and human-machine-interfaces (HMI). The performance of these e-skin pressure sensors is tailored, typically through micro-structuring techniques (such as photolithography, unconventional molds, incorporation of naturally micro-structured materials, laser engraving, amongst others) to achieve high sensitivities (commonly above 1 kPa−1), which is mostly relevant for health monitoring applications, or to extend the linearity of the behavior over a larger pressure range (from few Pa to 100 kPa), an important feature for functional prosthesis. Hence, this review intends to give a generalized view over the most relevant highlights in the development and micro-structuring of e-skin pressure sensors, while contributing to update the field with the most recent research. A special emphasis is devoted to the most employed pressure transduction mechanisms, namely capacitance, piezoelectricity, piezoresistivity, and triboelectricity, as well as to materials and novel techniques more recently explored to innovate the field and bring it a step closer to general adoption by society. publishersversion published

This work was funded by FEDER funds through the COMPETE 2020 Program (POCI-01-0145-FEDER-007728). BV thanks SFRH/BPD/124311/2016. PVB thanksWater JPI Proj TRACE (Ref 281715). Digital Microfluidics (DMF) has emerged as a disruptive methodology for the control and manipulation of low volume droplets. In DMF, each droplet acts as a single reactor, which allows for extensive multiparallelization of biological and chemical reactions at a much smaller scale. DMF devices open entirely new and promising pathways for multiplex analysis and reaction occurring in a miniaturized format, thus allowing for healthcare decentralization from major laboratories to point-of-care with accurate, robust and inexpensive molecular diagnostics. Here, we shall focus on DMF platforms specifically designed for nucleic acid amplification, which is key for molecular diagnostics of several diseases and conditions, from pathogen identification to cancer mutations detection. Particular attention will be given to the device architecture, materials and nucleic acid amplification applications in validated settings. publishersversion published

Mestrado em Engenharia Mecânica Os métodos habitualmente utilizados para a simulação de injecção em moldes envolvem um número considerável de simplificações, originando reduções significativas do esforço computacional mas, nalguns casos também limitações. Neste trabalho são efectuadas simulações de Reaction Injection Moulding (RIM) com o mínimo de simplificações, através da utilização do software de CFD multi-objectivos CFX, concebido para a simulação numérica de escoamentos e transferência de calor e massa. Verifica-se que o modelo homogéneo para escoamentos multifásicos do CFX, geralmente considerado o apropriado para a modelação de escoamentos de superfície livre em que as fases estão completamente estratificadas, é incapaz de modelar correctamente o processo de enchimento. Este problema é ultrapassado através da implementação do modelo não homogéneo juntamente com a condição de fronteira de escorregamento livre para o ar. A reacção de cura é implementada no código como uma equação de transporte para uma variável escalar adicional, com um termo fonte. São testados vários esquemas transitórios e advectivos, com vista ao reconhecimentos de quais os que produzem os resultados mais precisos. Finalmente, as equações de conservação de massa, quantidade de movimento, cura e energia são implementadas conjuntamente para simular os processos simultâneos de enchimento e cura presentes no processo RIM. Os resultados numéricos obtidos reproduzem com boa fidelidade outros resultados numéricos e experimentais disponíveis, sendo necessários no entanto tempos de computação consideravelmente longos para efectuar as simulações. ABSTRACT: Commonly used methods for injection moulding simulation involve considerable number of simplifications, leading to a significant reduction of the computational effort but, in some cases also to limitations. In this work, Reaction Injection Moulding (RIM) simulations are performed with minimum of simplifications, by using the general purpose CFD software package CFX, designed for numerical simulation of fluid flow and heat and mass transfer. The CFX’s homogeneous multiphase flow model, which is generally considered to be the appropriate choice for modelling free surface flows where the phases are completely stratified and the interface is well defined, is shown to be unable to model the filling process correctly. This problem is overcome through the implementation of the inhomogeneous model in combination with the free-slip boundary condition for the air phase. The cure reaction is implemented in the code as a transport equation for an additional scalar variable, with a source term. Various transient and advection schemes are tested to determine which ones produce the most accurate results. Finally, the mass conservation, momentum, cure and energy equations are implemented all together to simulate the simultaneous filling and curing processes present in the RIM process. The obtained numerical results show a good global accuracy when compared with other available numerical and experimental results, though considerably long computation times are required to perform the simulations.

Wearable devices, specifically noninvasive attached on skin, provide a very versatile mean of acquiring physiological information about the human body, such as humidity, pH, heartbeat (electrocardiograms) and temperature, as well as are capable of transdermal stimulation and therapeutics. A key challenge in wearable devices, consist in a mismatch between the soft, curvilinear and dynamic skin, and the rigid and fragile silicon wafer-based electronics. Nor- mally, the interfaces between skin and devices are insecure and can severally limit the func- tionality of the wearable devices, as well as increase the amount of motion artifacts and signal to noise ratio. Temporary electronic tattoos (e-tattoos) are an attractive platform for fabricating skin worn and body compliant wearable devices. These e-tattoos allow wearable sensors to mimic the structure of the skin, and conform very well when attached, due to its elasticity properties, while maintaining good sensing performances. In this project, we explore the versatility and advantages of using different polymeric membranes, such as polyimides and parylene for the fabrication of temporary e-tattoos with sensing devices. Additionally, as a proof of concept, we fabricated a wearable and skin confor- mal e-tattoo for temperature sensing. The produced polyimide with aluminum sensors pre- sented resistances of 49.5 Ω and 114.4 Ω and TCR values of 0.0017 ºC-1 for both sensors. The polyimide with gold sensors achieved resistance values of 61.4 Ω and 142.3 Ω with TCR values of 0.0015 ºC-1 and 0.0017 ºC-1. The parylene with gold sensor presented a resistance of 26.4 Ω and TCR of 0.0015 ºC-1. Dispositivos vestíveis, especificamente não-invasivos em contacto com a pele, apresen- tam um método bastante versátil para adquirir informação fisiológica sobre o corpo humano, tal como, humidade, pH, ritmo cardíaco e temperatura, e são também capazes de estimulação e terapia através da pele. Um dos maiores desafios destes dispositivos está na diferença entre a pele, suave e curvilínea, e a eletrónica baseada em bolachas, rígida e frágil. Normalmente, as interfaces entre pele e dispositivo são inseguras e podem limitar seriamente a funcionalidade do dispositivo, bem como podem aumentar os artefactos de movimento e o ratio sinal-ruído. Tatuagens eletrónicas temporárias são uma plataforma atrativa para o fabrico de dis- positivos vestíveis conformáveis à pele. Estas "e-tattoos" permitem ao sensor imitar a estrutura da pele, e conformam-se muito bem quando coladas à pele, devido às suas propriedades elás- ticas, mantendo boas performances sensoriais. Neste projeto, exploramos a versatilidade e vantagens do uso de diferentes membranas poliméricas, nomeadamente poliamida e parileno, para o fabrico de e-tattoos. Adicionalmente, com o uso destas membranas, provámos que é possível fabricar uma tatuagem vestível e con- formal, especificamente para sensor de temperatura. Os sensores de poliamida com aluminio apresentam resistências de 49,5 Ω e 114,4 Ω e valores de TCR de 0,0017 ºC-1 para ambos. OS sensores de poliamida com ouro apresentam resistências de 61,4 e 142,3 Ω com valores de TCR de 0,0015 ºC-1 e 0,0017 ºC-1. O sensor de parileno com ouro apresentou uma resistência de 26,41 Ω e TCR de 0,0015 ºC-1.

Electronic skin (e-skin) is a hot topic due to its enormous potential for health monitoring, functional prosthesis, robotics, and human-machine-interfaces (HMI). For these applications, pressure and temperature sensors and energy harvesters are essential. Their performance may be tuned by their films micro-structuring, either through expensive and time-consuming photolithography techniques or low-cost yet low-tunability approaches. This PhD thesis aimed to introduce and explore a new micro-structuring technique to the field of e-skin – laser engraving – to produce multifunctional e-skin devices able to sense pressure and temperature while being self-powered. This technique was employed to produce moulds for soft lithography, in a low-cost, fast, and highly customizable way. Several parameters of the technique were studied to evaluate their impact in the performance of the devices, such as moulds materials, laser power and speed, and design variables. Amongst the piezoresistive sensors produced, sensors suitable for blood pressure wave detection at the wrist [sensitivity of – 3.2 kPa-1 below 119 Pa, limit of detection (LOD) of 15 Pa], general health monitoring (sensitivity of 4.5 kPa-1 below 10 kPa, relaxation time of 1.4 ms, micro-structured film thickness of only 133 µm), and robotics and functional prosthesis (sensitivity of – 6.4 × 10-3 kPa-1 between 1.2 kPa and 100 kPa, stable output over 27 500 cycles) were obtained. Temperature sensors with micro-cones were achieved with a temperature coefficient of resistance (TCR) of 2.3 %/°C. Energy harvesters based on micro-structured composites of polydimethylsiloxane (PDMS) and zinc tin oxide (ZnSnO3) nanowires (NWs; 120 V and 13 µA at > 100 N) or zinc oxide (ZnO) nanorods (NRs; 6 V at 2.3 N) were produced as well. The work described herein unveils the tremendous potential of the laser engraving technique to produce different e-skin devices with adjustable performance to suit distinct applications, with a high benefit/cost ratio.

In the last decades the development in miniaturization of devices has become a very important topic for the future of technology. Although the miniaturization of devices has been successful in de-creasing the size of devices, the same can not be said about their energy sources. Recent work in the nanomaterials filed has started to show some progress in the towards self-powered energy sources that generate power form the environment that surrounds them. This energy can be scavenged from solar, thermal, mechanical, etc. The advances in this area shows that is possible to generate this environmental energy using nanomaterials with different architectures: nanowires, nanofibers and films. In this work nanofibrous membranes produced by electrospinning were used as nanogenerators. Electrospinning is a low-cost, easy and scalable methods to produce nanofibers. The fibres and mem-branes produced can have different morphologies, thicknesses and are lightweight, therefore being good candidates for miniaturized devices and wearables, etc. The nanofiber membranes were produced with Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-co-TrFE)), which is a polymeric electroactive material with good piezoelectric and pyroelec-tric properties, and is commonly used has an energy generator. The energy generation is highly associ-ated with the crystalline structure of its β-phase. Three different materials (Carbon Paint, PEDOT:PSS and Aluminium), were used to create the electric contacts of this nanogenerator. The contacts where deposited by electrospinning (PEDOT.PSS), airbrush (Carbon Paint and PEDOT:PSS) and by thermal evaporation (Aluminium). DSC, XRD, FTIR, Pyroelectric Constant, Impedance spectroscopy, Tensile Strength, etc. were used to characterize the behaviour and properties of the materials and device. The electrospinning process did not show any increase in β-phase fraction and the dipoles do-mains orientation. Airbrush deposition of PEDOT:PSS was the only process that produced an electric contact capable of being used on a device. After poling, the device displayed a pyroelectric response, thus showing that the poling process improved the electroactive properties of the polymer.

This work is focussed on using additive manufacturing (AM) to produce electroactive structures using fused deposition modelling (FDM) and P(VDF-TrFE) as a ferroelectric polymer which will confer electroactive properties to printed structures. The FDM, commonly called 3D printing, was chosen due to its emergence in the industry segment with low-cost production and the capability of projecting prototypes without shape limitations, converting a digital design in a physical object. Beyond these features, the possibility of using functional materials and their properties in the production of sensors and actuators was one of the main reasons for the increased interest in this technology. The boundaries of 3D printing process were explored during the production in order to obtain a uniform and homogenous thin film. It was used a P(VDF-TrFE) filament that was previously extruded to make possible the use of additive manufacturing process. Subsequently, a commercial conductive PLA filament was used to produce electrodes for the electrical characterization of the electroactive films. P(VDF-TrFE) films with 65 μm and aluminium electrodes yielded the best results with a pyroelectric coefficient of 3 μC m-2 K-1. The aforementioned sample was used to produce a fully 3D printable pyroelectric sensor. This sensor was made of P(VDF-TrFE), commercial conductive PLA and conventional PLA. The P(VDF-TrFE) provides electroactive properties, conductive PLA enables the creation of conductive tracks and the conventional PLA gave structural basis to the device.

Several oxides present a severe and reversible resistance changes with the application of an external stimulus such as an electrical field, temperature, optical or magnetic properties. Among them there are two groups, those who recover for the initial stage after the stimulus is finished and those who keeps the final stage, despite the stimulus is over. In the first group, vanadium dioxide (VO2), present a sharp and reversible metal-to-insulator transition, induced by temperature near 68 °C. Since is a low transition temperature and presents a high speed and volatile change. In this project we optimize the crystallization of VO2 thin film produced by e-beam evaporation and produced a versatile X-Ray Diffractometer (XRD) holder, capable to be adapted to several other characterization equipment. This holder has the capability to heat and control the temperature applied on the oxide and at the same time perform the electric characterization of the oxide in situ, during the XRD measurement. This holder will be very helpful in characterization of several material due to its ability to have a uniform heating behavior in many equipments, thus ensuring that the process is the same regardless of the equipment used.

The ever-growing global market for smart wearable technologies and Internet of Things (IoT) has increased the demand for sustainable and multifunctional nanomaterials synthesized by low-cost and energy-efficient processing technologies. Zinc oxide (ZnO) is a key material for this purpose due to the variety of facile methods that exist to produced ZnO nanostructures with tailored sizes, morphologies, and optical and electrical properties. In particular, ZnO nanostructures with a porous structure are advantageous over other morphologies for many applications because of their high specific surface area. In this chapter, a literature review on the latest progress regarding the synthesis and applications of ZnO with a porous morphology will be provided, with special focus on the synthesis by microwave hydrothermal method of these nanomaterials and their potential for application in energy harvesting devices. Nanogenerators of a composite made by polydimethylsiloxane (PDMS) and porous ZnO nanostructures were explored and optimized, with an output voltage of (4.5 ± 0.3) V being achieved for the best conditions. The daily life applicability of these devices was demonstrated by lighting up a commercial LED, by manually stimulating the nanogenerator directly connected to the LED.

Digital Microfluidics (DMF) is a technology capable of maneuvering picoliter to microliter droplets in an independent and individual manner, with a wide variety of uses for bioassays and biosensing. These systems are advantageous for their small volumes, higher portability and multiplex assay capabilities, proving to be very capable of lab-on-chip and point-of-care applications. One of these applications are DNA amplification assays, of which, Loop Mediated Isothermal Amplification (LAMP), that has received increased interest from the scientific community. This method is a sensitive and simple diagnostic tool for fast detection and identification of molecular biomarkers enabling real-time monitoring. Nevertheless, sensing methods coupled with DMF devices are still uncapable of measuring the progress of said reaction in real-time. This work explores two real-time LAMP measurement approaches to be coupled with a DMF system. The first approach uses an H-shaped device, where human c-Myc proto-oncogene and human 18S housekeeping gene are amplified and measured in real-time through fluorescence methods. The second approach uses interdigitated electrodes, where human c-Myc proto-oncogene is amplified and measured in real-time through Electrochemical Impedance Spectroscopy (EIS). Following development and characterization of both techniques, fluorescence measuring devices show 49% fluorescence signal difference between positive and negative controls end-points. EIS measuring devices indicate significant differences between commercial solutions with pH 4, 7 and 10, by Ciclic Voltammetry. This suggests that such devices could be used for real-time, label free, LAMP monitoring, since significant pH changes occur during a LAMP reaction

(ENG) In recent years, the advancement of science and technology tends to evolve towards the exploitation of electronic skin (e-skin) and functional prosthetic devices, enabling innovating applications in various fields such as biomedical systems, sports health-monitoring and healthcare. Owing to their significant role in health monitoring, pressure sensors come as essential components in the development of artificial systems that can mimic the impressive human skin. The development of such sensors comprises the search for flexible and stretchable materials suitable for implementation in robust devices that enable the integration of multiple sensingfunctionalities. To quantitatively monitor pressure, these sensors use transduction methods based on piezoresistivity, capacity, piezoelectricity, and triboelectricity. In this work, piezoresistive devices were chosen over others due to their ease in structure design and readout mechanism. The mechanism of such piezoresistive pressure sensor relies on the transduction of a pressure change into a change in resistance that, in this case derives from variations in the contact area. In the approach presented in this work, a semi-sphere microstructuring patterning made by laser engraving on hard-poly(dimethylsiloxane) (h-PDMS) was introduced. h-PDMS works as a mold from which standard-poly(dimethylsiloxane) (s- PDMS) microstructured membranes with approximately 200 μm thickness are peeled off. Carbonink, working as active material, was deposited on top of the microstructured s-PDMS membranes. The fabrication of such pressure sensors based on organic membranes combines advantages such as the production in a low-cost and fast way, device flexibility, and tunability of the sensor’s design. Moreover, sensitivities of 2.4 × 10-1 kPa-1 were reached for the sensors developed. (PT) Nos últimos anos, o avanço da ciência e da tecnologia tende a evoluir para a exploração da pele eletrónica (e-skin) e próteses funcionais, possibilitando aplicações inovadoras em vários campos, nomeadamente sistemas biomédicos, saúde desportiva, e monitorização da saúde. Devido ao seu papel significativo na monitorização da saúde, os sensores de pressão são componentes essenciais no desenvolvimento de sistemas artificiais que conseguem imitar a impressionante pele humana. O desenvolvimento destes sensores requer a procura por materiais flexíveis e extensíveis adequados para implementação em dispositivos robustos que permitam a integração de múltiplas funcionalidades de detecção. Para monitorizar a pressão, estes sensores usam métodos de transdução baseados em piezoresistividade, capacidade, piezoelectricidade e triboeletricidade. Neste trabalho, dispositivos piezoresistivos foram escolhidos em detrimento dos outros devido à sua fácil implementação e mecanismo de leitura. Este mecanismo consiste na transdução de uma diferença de pressão numa diferença de resistência que, neste caso, deriva de variações na área de contato. Na nova abordagem apresentada neste trabalho, introduziu-se um método de microestruturação de semi-esferas baseado na gravação a laser em poli(dimetilsiloxano)-duro (h-PDMS). O h- PDMS funciona como um molde a partir do qual se retiram membranas microestruturadas de poli(dimetilsiloxano)-standard (s-PDMS) com aproximadamente 200 μm de espessura. O material ativo em cima do domínio microestruturado é tinta de carbono. A fabricação destes sensores de pressão com base em membranas orgânicas combina vantagens como a produção de forma rápida, fabricação de baixo custo, flexibilidade do dispositivo e flexibilidade na mudança do design do sensor. Para além disso, para estes sensores foram conseguidas sensibilidades de 2.4 × 10-1 kPa-1.

Digital Microfluidics (DMF) is an innovative technology for liquid manipulation at microliter- to picoliter-scale, with tremendous potential of application in biosensing. DMF allows maneuvering single droplets over an electrode array, by means of electrowetting-on-dielectric (EWOD), that allows changing the contact angle of a droplet over a dielectric. Each droplet is thus considered a microreactor, with an unparalleled potential to perform chemical and biological reactions. Several aspects inherent to DMF platforms, such as multiplex assay capability and integration capability, make them promising for lab-on-chip and point-of-care (PoC) applications, e.g. DNA amplification assays or disease detection. DNA detection strategies for PoC have been profiting from recent development of isothermal amplification schemes, of which Loop-mediated Isothermal Amplification (LAMP) is a major methodology, allowing a 109-fold amplification efficiency in one hour. Here, I demonstrate for the first time the effective coupling of DMF and LAMP, resulting in a DMF device capable of performing LAMP reactions. This novel DMF platform has been developed and characterised, which allows successful amplification of a c-Myc gene fragment by LAMP. Precise temperature control is achieved by using a transparent heating element, connected to a looping feedback control system. This platform is able to amplify just 0.5 ng/μL of the target DNA, in only 45 minutes, for a device temperature of 65 °C and a reaction volume of 1.62 μL, one of the lowest volumes ever reported. Moreover, the electrophoretic analysis indicates that the amplification efficiency of the on-chip LAMP is considerably higher than that from the bench-top reaction.

This thesis is one of the first reports of digital microfluidics on paper and the first in which the chip’s circuit was screen printed unto the paper. The use of the screen printing technique, being a low cost and fast method for electrodes deposition, makes the all chip processing much more aligned with the low cost choice of paper as a substrate. Functioning chips were developed that were capable of working at as low as 50 V, performing all the digital microfluidics operations: movement, dispensing, merging and splitting of the droplets. Silver ink electrodes were screen printed unto paper substrates, covered by Parylene-C (through vapor deposition) as dielectric and Teflon AF 1600 (through spin coating) as hydrophobic layer. The morphology of different paper substrates, silver inks (with different annealing conditions) and Parylene deposition conditions were studied by optical microscopy, AFM, SEM and 3D profilometry. Resolution tests for the printing process and electrical characterization of the silver electrodes were also made. As a showcase of the applications potential of these chips as a biosensing device, a colorimetric peroxidase detection test was successfully done on chip, using 200 nL to 350 nL droplets dispensed from 1 μL drops.

Dissertação para obtenção do Grau de Mestre em Biotecnologia No presente trabalho foi desenvolvido um sistema de imunodeteção, baseado num biossensor capacitivo que integra um par de microelétrodos interdigitais (transdutor). À superfície dos microeléctrodos testaram-se dois tipos de matrizes de suporte diferentes para imobilização de anticorpos – membrana comercial de Fluoreto de Polivinilideno (PVDF) e camada de nanopartículas de Óxido de Zinco (nanobastonetes de ZnO). O objetivo da utilização destas matrizes específicas foi maximizar a distribuição dos anticorpos detetores ao longo da região de interação do campo elétrico criado pelo transdutor. A abordagem inovadora deste trabalho (maximizar a distribuição dos anticorpos através da utilização de matrizes de suporte sobre o transdutor) pretende ser uma alternativa simples e económica à utilização de nanoelétrodos, mais dispendiosos e de fabrico complexo. As membranas de PVDF foram alvo de estudo sobre a influência de um pré-tratamento com álcool na capacidade de difusão dos antigénios na membrana, bem como do processo de bloqueamento da membrana com Albumina do soro bovino e leite magro em pó – habitualmente usados em imunoensaios para aumentar a especificidade de ligação do antigénio ao anticorpo. A deposição da camada de nanobastonetes de ZnO foi realizada durante quatro intervalos de tempo diferentes (1,5, 3, 5 e 7 horas), de forma a selecionar as condições para maior revestimento da área superficial do transdutor. Como modelos representativos das interações anticorpo/antigénio foram utilizados dois sistemas distintos: anticorpo anti-PfHsp70 e respetivo antigénio PfHsp70 (Plasmodium falciparum Heat Shock Protein 70); anticorpo anti-HRP e respetivo antigénio HRP (Peroxidase de Rábano). Cada sensor foi analisado por Espectroscopia de Impedância (de 40 Hz a 110 MHz), de forma a detetar alterações de capacidade e impedância resultantes da interação anticorpo/antigénio. Os sensores com membrana de PVDF registaram variações de capacidade baixas (inferiores a 1 pF), mas foram capazes na sua maioria de distinguir entre soluções sem e com antigénio. Nos sensores com nanobastonetes de ZnO, a presença do antigénio HRP produziu um sinal distinto em relação aos controlos negativos (solução tampão e antigénio não-específico). Em todos os sensores (com PVDF e ZnO), a maior variação da capacidade na presença do antigénio foi observada entre 1 e 10 kHz, sugerindo que este intervalo de frequências é ideal para imunodeteção por Espectroscopia de Impedância.

Digital Microfluidics (DMF) is a second generation technique, derived from the conventional microfluidics that instead of using continuous liquid fluxes, it uses only individual droplets driven by external electric signals. In this thesis a new DMF control/sensing system for visualization, droplet control (movement, dispensing, merging and splitting) and real time impedance measurement have been developed. The software for the proposed system was implemented in MATLAB with a graphical user interface. An Arduino was used as control board and dedicated circuits for voltage switching and contacts were designed and implemented in printed circuit boards. A high resolution camera was integrated for visualization. In our new approach, the DMF chips are driven by a dual-tone signal where the sum of two independent ac signals (one for droplet operations and the other for impedance sensing) is applied to the electrodes, and afterwards independently evaluated by a lock-in amplifier. With this new approach we were able to choose the appropriated amplitudes and frequencies for the different proposes (actuation and sensing). The measurements made were used to evaluate the real time droplet impedance enabling the knowledge of its position and velocity. This new approach opens new possibilities for impedance sensing and feedback control in DMF devices.

The need for mass scale testing in areas such as microbiology and chemistry requires faster processing times, multiplexing capability, and reduced reagent requirements. To achieve this, the volumes processed must be reduced. This work intends to produce a microfluidic chip capable of producing increasingly smaller droplets that serve as testing vessels, by taking advantage of the dynamics of two immiscible fluids. The purpose of the present chip is to be used in the future in a digital Polymerised Chain Reaction (dPCR) for DNA amplification and detection. The microfluidic device was first simulated using COMSOL Multiphysics to understand the different behaviours of the droplet generator junctions. Glass sealed devices were produced using soft-lithography, composed of two different parts, a glass substrate and a top PDMS slab fabricated by photolithography of a SU-8 mould on a Si wafer that was used to mould the PDMS. Devices were tested with two immiscible fluids, which were injected at a constant flow rate into two inlets that lead to the junction were the droplets were formed. We were able to obtain droplets as small as 1 nL in devices with a channel size of 50 μm. We concluded that reducing the entry section to the main channel until the junction point, will decrease droplet size keeping the same size of the channels after the junction. Faster droplet generation rate was also obtained, using side channels width smaller (50 μm) than the main channel (100 μm).

Recently, research in health care improved the creation of devices that accurately monitor various physiological stimuli (wearable devices) which provide better health care and help to predict possible diseases through continuous data collection. However, wearable devices are at an early stage of development and several improvements must be made, both at structural and materials level. Some examples of devices on the market such as smartwatches or fitness bands are still very bulky and the goal is to make them as small and functional as possible. This work focuses on the improvement of fabrication process steps of pressure sensors, based on micro-structured thin polymeric films of Polydimethylsiloxane (PDMS) or Parylene C, namely micro-structuration techniques and electrode deposition. To create domeshaped structures, Polystyrene (PS) microspheres were deposited by Langmuir-Blodgett (LB) process over Parylene C and then subjected to a Reactive Ion Etching (RIE) process to create the mold. Pyramidal structures were made by anisotropic etching of silicon with potassium hydroxide (KOH) to make molds. Both molds were further used to produce micro-structured PDMS films by soft lithography. Through these techniques, PDMS domes with diameters between 2.3 m and 3.0 m and heights between 1.6 m and 1.7 m, and PDMS pyramids with a size of 50 m to 100 m and a height of 34.3 m to 66.4 m were achieved. To work as a piezoresistive pressure sensor, the micro-structures must be covered with a conductive layer that will play the role of electrode. To overcome adhesion issues between PDMS and some metals, the possibility of using a thin film of Parylene C on top of PDMS was studied. The metals explored were aluminium, copper, and titanium with gold, where the latter presented better adhesion and electrical properties. The developed micro-structured films were assembled and tested as piezoresistive or capacitive pressure sensors achieving sensitivities up to -1.1 10􀀀2 kPa􀀀1 and 3.1 10􀀀2 kPa􀀀1 respectively.

Digital microfluidics (DMF) is a field which has emerged in the last decade as a re-liable and versatile tool for sensing applications based on liquid reactions. DMF allows the discrete displacement of droplets, over an array of electrodes, by the application of voltage, and also the dispensing from a reservoir, mixing, merging and splitting fluidic operations. The main drawback of these devices is due to the need of high driving volt-ages for droplet operations. In this work, alternative dielectric layers combinations were studied aiming the reduction of these driving voltages. DMF chips were designed, pro-duced and optimized according to the theory of electrowetting-on-dielectric, adopting different combinations of parylene-C and tantalum pentoxide (Ta2O5) as dielectric ma-terials, and Teflon as hydrophobic layer. With both devices’ configurations, i.e., Parylene as single dielectric, and multilayer chips combining Parylene and Ta2O5, it was possible to perform all the fluidic opera-tions in the microliter down to hundreds of nanoliters range. Multilayer chips presented significant reduction on driving voltages for droplet op-erations in silicone oil filler medium: from 70 V (parylene only) down to 30 V (parylene/Ta2O5) for dispensing; and from 50 V (parylene only) down to 15 V (parylene/Ta2O5) for movement. Peroxidase colorimetric reactions were successfully performed as proof-of-concept, using multilayer configuration devices.