No description available.

Photonic crystal waveguide (PCW) based device has been used in many applications in recent years due to its unique slow light effect. In this work, the application of PCW on sensing is presented. First, we present a PCW structure based Infrared (IR) spectroscopy combining with slot structure which has a large electric field enhancement for light-matter interaction for chemical sensing. The slow light effect and the electric field enhancement of our designed structure greatly enhance the absorption factor of chemical analytes by 1000. We then use multimode interference (MMI) optical splitter and Y junction combiner to connect two PCWs to show multiplexed detections of two chemicals on a single chip. Our results show the detection is down to 1 ppb for xylene in water and 100ppm for methane in nitrogen. We also present PCW microcavities structure for biological sensing in our work. Due to its high quality factor and easier immobilization of biomaterials, we are able to use ink jet printing method to bind the biomaterials on top of our chip. We choose linear-type 13 (L13, missing 13 holes) microcavities to do the biosensing for antibodies and cancer cell lysates because of its higher sensitivity combining with slow light effect. Our work achieves the cancer cell lysates detection down to 2 cells/μl., and further applications will be presented in our group in the future. / text

The thickness shear mode acoustic wave (TSM) sensor, operated in a flow-through format, has been widely used in bioanalytical research. My research is mainly focused on the study of surface-attached biomolecules and cells using the TSM sensor, including lesions in DNA, conformational change of calmodulin, as well as the properties and attachment of rat aortic smooth muscle cells. Aldehydic apurinic or apyrimidinic sites (AP sites) that lack a nucleobase moiety are one of the most common forms of toxic lesions in DNA. In this work, synthesized oligodeoxyribonucleotides containing one, two, or three abasic sites were hybridized to complementary sequences immobilized on the gold electrode of the TSM device by affinity binding. The influence of AP sites on local base stacking energy and geometry caused a dramatic destabilization of the DNA duplex structure, which was detected by the TSM sensor. The signals detected by TSM correlated well with the thermostability of DNA duplexes in solution. The results indicate that both the number of sites and their localization in the double-stranded structure influence the stability of a 19 b.p. duplex. TSM was also used to detect the binding of ions or peptides to surface-attached calmodulin. The interaction between calmodulin and ions induced an increase in resonant frequency and a decrease in motional resistance. In addition, these signal changes were reversible upon washing with buffer. The response was interpreted as a decrease in surface coupling induced by exposure of hydrophobic domains on the protein, and an increase in the length of calmodulin by approximately 3 Å. In addition, the interaction of the protein with peptide together with calcium ions was detected successfully, despite the relatively low molecular mass of the 2-kDa peptide. In addition, the attachment of smooth muscle cells to various surfaces has been monitored by TSM. These surfaces include laminin, fibronectin and bare gold. The results of these experiments in terms of changes of frequency (fs) and resistance (Rm) were analyzed. The responses of the surface-bound cells to the introduction of various ions, depolarisation events and damage subsequent to exposure to hydrogen peroxide were also observed. Morphological changes in the cells, as confirmed by atomic force microscopy and scanning electron microscopy, are correlated with results from the TSM sensor.

The thickness shear mode acoustic wave (TSM) sensor, operated in a flow-through format, has been widely used in bioanalytical research. My research is mainly focused on the study of surface-attached biomolecules and cells using the TSM sensor, including lesions in DNA, conformational change of calmodulin, as well as the properties and attachment of rat aortic smooth muscle cells. Aldehydic apurinic or apyrimidinic sites (AP sites) that lack a nucleobase moiety are one of the most common forms of toxic lesions in DNA. In this work, synthesized oligodeoxyribonucleotides containing one, two, or three abasic sites were hybridized to complementary sequences immobilized on the gold electrode of the TSM device by affinity binding. The influence of AP sites on local base stacking energy and geometry caused a dramatic destabilization of the DNA duplex structure, which was detected by the TSM sensor. The signals detected by TSM correlated well with the thermostability of DNA duplexes in solution. The results indicate that both the number of sites and their localization in the double-stranded structure influence the stability of a 19 b.p. duplex. TSM was also used to detect the binding of ions or peptides to surface-attached calmodulin. The interaction between calmodulin and ions induced an increase in resonant frequency and a decrease in motional resistance. In addition, these signal changes were reversible upon washing with buffer. The response was interpreted as a decrease in surface coupling induced by exposure of hydrophobic domains on the protein, and an increase in the length of calmodulin by approximately 3 Å. In addition, the interaction of the protein with peptide together with calcium ions was detected successfully, despite the relatively low molecular mass of the 2-kDa peptide. In addition, the attachment of smooth muscle cells to various surfaces has been monitored by TSM. These surfaces include laminin, fibronectin and bare gold. The results of these experiments in terms of changes of frequency (fs) and resistance (Rm) were analyzed. The responses of the surface-bound cells to the introduction of various ions, depolarisation events and damage subsequent to exposure to hydrogen peroxide were also observed. Morphological changes in the cells, as confirmed by atomic force microscopy and scanning electron microscopy, are correlated with results from the TSM sensor.

Numerous applications in the present day ranging from testing humidity in air to detecting miniscule quantities of potentially hazardous chemical and biological agents in the air or water supplies require the development of chemical sensors capable of analyte detection with high sensitivity and selectively. Further, it has become desirable to create lab-on-chip systems that can detect multiple chemical agents and allow for sampling and testing of environments at locations distant from conventional laboratory facilities. Current challenges in this area include design, development and characterization of low detection limit sensors, development of low-noise readout methods, positive identification of analytes and, identification and reduction of the effect of various noise sources - both intrinsic and extrinsic to the sensor. The current work examines the performance limits of a 10-cantilever piezoresistive microcantilever array (PµCA) sensor. The microcantilevers measure analyte concentration in terms of the surface stress associated with analyte binding to the functionalized cantilever surface. The design, fabrication, characterization and testing of this measurement platform is presented. A novel aspect of the sensors developed is the use of n-type doping which increases the sensitivity of the device by one order of magnitude. In addition, design rules for surface stress-based chemical sensors have been developed. Extensive thermal characterization of the piezoresistive microcantilevers has been performed for DC and AC electrical excitation and values of heat transfer coefficient for the associated microscale phenomena are reported. Further, a method of low-noise measurement of cantilever resistance has been developed based on phase-sensitive detection techniques and this has been integrated with a multiplexing circuit to measure piezoresistance change in multiple cantilevers. Finally, the two novel techniques of chemical sensing- double-sided sensing and thermal array-based sensing have been investigated. These methods are presented as a means of extending the applicability and functionality of piezoresistive microcantilever sensors for chemical sensing.

abstract: A wireless hybrid device for detecting volatile organic compounds (VOCs) has been developed. The device combines a highly selective and sensitive tuning-fork based detector with a pre-concentrator and a separation column. The selectivity and sensitivity of the tuning-fork based detector is optimized for discrimination and quantification of benzene, toluene, ethylbenzene, and xylenes (BTEX) via a homemade molecular imprinted polymer, and a specific detection and control circuit. The device is a wireless, portable, battery-powered, and cell-phone operated device. The device has been calibrated and validated in the laboratory and using selected ion flow tube mass spectrometry (SFIT-MS). The capability and robustness are also demonstrated in some field tests. It provides rapid and reliable detection of BTEX in real samples, including challenging high concentrations of interferents, and it is suitable for occupational, environmental health and epidemiological applications. / Dissertation/Thesis / M.S. Electrical Engineering 2011

abstract: This work demonstrates the integration of a wearable particulate detector and a wireless chemical sensor into a single portable system. The detection philosophy of the chemical sensor is based on highly selective and sensitive microfabricated quartz tuning fork arrays and the particle detector detects the particulate level in real-time using a nephelometric (light scattering) approach. The device integration is realized by carefully evaluating the needs of flow rate, power and data collection. Validation test has been carried out in both laboratory and in field trials such as parking structures and highway exits with high and low traffic emissions. The integrated single portable detection system is capable of reducing the burden for a child to carry multiple devices, simplifying the task of researchers to synchronize and analyze data from different sensors, and minimizing the overall weight, size, and cost of the sensor. It also has a cell phone for data analysis, storage, and transmission as a user-friendly interface. As the chemical and particulate levels present important exposure risks that are of high interests to epidemiologists, the integrated device will provide an easier, wearable and cost effective way to monitor it. / Dissertation/Thesis / M.S. Electrical Engineering 2012

No description available.

L'objectif de ce travail de recherche est la réalisation de dispositifs à base de nanofils de silicium, réalisés par la méthode des espaceurs. La synthèse des nanofils est effectuée à partir d'une couche de silicium polycristallin, déposée par la technique LPCVD (Low Pressure Chemical Vapor Deposition). Ces nanofils sont ensuite intégrés dans les dispositifs électroniques tels que des résistances ou des transistors réalisés suivant deux configurations différentes « bottom-gate » et « step-gate ». Les caractéristiques électriques de ces deux types de transistors ont mis en évidence des propriétés électriques suffisantes pour leur utilisation en tant que capteurs. Une simulation permet d'expliquer l'effet de l'apport de charges électriques à la surface des nanofils sur la concentration d'électrons dans la couche active. Les dispositifs sont tout d'abord utilisés pour la mesure du pH, et montrent une sensibilité de détection supérieure à la sensibilité nernstienne. Pour une utilisation du dispositif en tant que biocapteur, une fonctionnalisation de la surface des nanofils est nécessaire pour permettre l'accrochage de sondes d'ADN. La détection électronique de l'hybridation sondes/cibles de brins d'ADN complémentaires est démontrée avec un faible seuil de détection. Enfin, afin d'augmenter la surface d'échange entre le nanofil et les espèces chargées, un procédé de fabrication de résistances à base de nanofils suspendus est développé. Des tests de détection en présence d'ammoniac ont mis en évidence une réponse linéaire sur une gamme de concentrations. Les résistances à base de nanofils suspendus présentent une plus grande sensibilité que celles à base de nanofils non suspendus, mettant en avant l'effet important de la surface des nanofils. Tous ces résultats permettent de démontrer la faisabilité de capteurs chimiques et biologiques à base de nanofils de silicium à partir des techniques conventionnelles de la microélectronique en utilisant un procédé de fabrication « bas-coût ». / The goal of this research work is the realization of devices based on silicon nanowires, realized using sidewall spacer formation technique. Nanowires are synthesized form a polycrystalline silicon layer deposited by LPCVD technique (Low Pressure Chemical Vapor Deposition). These nanowires are then integrated into electronic devices such as resistors and transistors made using two different configurations “bottom-gate” and “step-gate”. The electrical characteristics of these two types of transistors have shown adequate electrical properties for their use as sensors. A simulation is made, to explain how additional electrical charges on the surface of the nanowires, affect the electron concentration inside the active layer. The devices are firstly used for the pH measurement, and have shown sensitivity higher than the Nernstian sensitivity detection. For a use as biosensor, nanowires are functionnalized to allow the binding of DNA probes. Electronic detection of hybridization complementary probe/target DNA strands is demonstrated with a low detection limit. Finally, in order to increase the exchange surface between the nanowires and charged species, resistors based on suspended nanowires were developed. Different tests were performed in the presence of ammonia and showed a linear response over a range of concentrations. Resistors based on suspended nanowires highlighted greater sensitivity than those based on unsuspended nanowires, bringing out the important effect of the surface of the nanowires. All these results demonstrate the feasibility of chemical and biological sensors based on silicon nanowires compatible with conventional microelectronics techniques using a low-cost process.

Este trabalho descreve o desenvolvimento de um biossensor contendo transdução condutométrica sem contato (C4D, capacitively coupled contactless conductivity detection) e ácido fólico (FA) como biorreceptor em microchip, uma nova alternativa que poderá ser utilizada na determinação do biomarcador tumoral FR-α. Essa espécie exibe interações com FA altamente específicas, com constantes de formação da ordem de 109-1010. Os dispositivos microfluídicos, os quais consistiram de uma lâmina de vidro (integrando os eletrodos), dielétrico (contendo a fase biossensora) e substrato de poli(dimetilsiloxano) (PDMS, incorporando os microcanais), foram fabricados utilizando-se processos de fotolitografia e deposição de filmes finos em fase vapor. Objetivando melhorias nos níveis de detecção da C4D, estudos de sensibilidade com base em parâmetros da curva analítica foram conduzidos alterando-se a natureza do dielétrico e a configuração dos eletrodos. Posteriormente, estudos de caracterização foram realizados para as superfícies modificadas com os intermediários de imobilização; condições reacionais distintas (reagente, concentração, solvente e tempo) foram consideradas. As técnicas de microscopia eletrônica de varredura e espectroscopia de fotoelétrons excitados por raios-X foram usadas, respectivamente, a fim de se verificar a possível formação de aglomerados e permitir determinações qualitativas e quantitativas sobre as composições químicas das superfícies. Como resultado dos experimentos de sensibilidade e caracterização de superfície, adotamos os parâmetros seguintes para os ensaios de interações biomoleculares posteriores: filme de SiO2 como dielétrico, eletrodos seletivos à C4D com formato retangular e orientação antiparalela e monocamadas automontadas do reagente 3-aminopropil(trietoxisilano) como intermediário de imobilização de FA. As duas etapas finais do trabalho foram: otimização do tempo de funcionalização com FA (3, 5 e 7 h) e caracterização da fase biossensora, realizada a partir de medidas de C4D e microscopia de força atômica (AFM). Para o primeiro caso, os microchips foram aplicados a um padrão de anticorpo monoclonal específico a FA (α-FA). Os ensaios biomoleculares indicaram uma adsorção efetiva de FA junto à superfície de SiO2 silanizada, sem a ocorrência (ao menos em níveis significativos) de impedimentos estéricos de sua espécie bioativa. Dentre os tempos de funcionalização investigados, 3 h foi aquele que resultou em uma maior sensibilidade do método. Em termos da etapa de caracterização eletroquímica da fase biossensora, seus resultados mostraram haver correlação entre a resposta analítica e as interações FA/α-FA. Em adição, conforme indicaram as medidas de AFM, não houve alterações drásticas na morfologia do substrato (SiO2) em função dos processos de modificação química de superfície. Por fim, o uso da C4D como uma técnica de transdução em biossensores mostrou-se uma alternativa promissora para a análise do biomarcador tumoral FR-α. Dentre outros aspectos, essa plataforma analítica requer uma instrumentação simples, barata e portátil, não apresenta inconvenientes relacionados ao contato eletrodo/solução, dispensa o uso de mediadores redox e permite a determinação simultânea de multianalitos. Neste ínterim, alterações no transdutor devem ser implementadas visando um aumento na sensibilidade do método, o qual representa seu fator limitante principal. / This work describes the development of a biosensor containing capacitively coupled contactless conductivity transduction (C4D) and folic acid (FA) as bioreceptor in microchip, a new alternative that can be used in FR-α tumor biomarker analysis. FR-α exhibits highly specific interactions with FA, showing formation constants of the order of 109-1010. The microfluidic devices consisted of a glass layer (integrating the electrodes), dielectric (containing the biosensor phase), and poly(dimetilsiloxane) substrate (PDMS, incorporating microchannel). The microfabrication stage evolved photolithography processes, metal adsorption via sputtering, and plasma-enhanced vapor film deposition. In order to improve detection levels of C4D, sensitivity studies were conducted by changing the dielectric nature and electrode configuration. Through flow analysis with given electrolyte standards, the limits of detection and quantification were calculated based on analytical curve parameters. Subsequently, researches were performed to characterize the modified surfaces with immobilization intermediate considering reaction conditions distinct (reagent, concentration, solvent, and time). The techniques of scanning electron microscopy and X-ray photoelectron spectroscopy were employed, respectively, aiming to verify the clusters formation and allow qualitative and quantitative determinations about the surfaces chemical composition. From the results of sensitivity experiments and surface characterization, we adopt the following parameters for the biomolecular interactions assays: SiO2 film as dielectric, C4D selective electrodes with rectangular shape and antiparallel orientation, and self-assembled monolayers of 3-aminopropyl(triethoxysilane) as intermediary for immobilization of FA. The two final steps of the work were: optimizing the FA functionalization time (3, 5, and 7 h) and phase biosensor characterization, made from measures of C4D and atomic force microscopy (AFM). For the first case, due to the absence of FR-α standard for purchase, the microchips were applied to FA specific monoclonal antibody (α-FA). The biomolecular assay indicated effective adsorption of FA, without occurrence (at least in significant levels) of steric hindrance of its bioactive specie. Among the investigated times of functionalization, 3 h resulted in a higher sensitivity of the method. In terms of biosensor phase electrochemical characterization stage, their results evidenced correlation between analytical response and FA/α-FA interactions. Additionally, as the AFM measurements showed, drastic changes in the morphology of the substrate (SiO2) with the surface modification processes did not occur. Finally, the use of the C4D as transduction technical in biosensors proved to be a promissory alternative for FR-α tumor biomarker analysis. Among other features, this platform has not drawbacks related to the electrode/solution contact, dispenses the use of redox mediators, allows the simultaneous determination of multianalytes, and employs an instrumentation that is simple, cheap, and portable. Nevertheless, changes in the transducer should be implemented to increase the method sensitivity, which represents its main limiting factor.