Cantilever Array Platform for Quantitative Biological Analysis

RÉSUMÉ L'objectif de ce projet est de développer un réseau de microcapteurs pour collecter des données biologiques quantitatives. Ces types de données peuvent être utilisés dans divers domaines, notamment pour l'analyse cellulaire et moléculaire, la détection d’interactions biologiques spécifiques, la surveillance de maladies et la découverte de médicaments. Les capteurs proposés possèdent des réseaux de « cantilevers » qui convertissent les interactions biologiques en variations mécaniques et électriques. Ces capteurs peuvent avoir une sensibilité élevée et ont montré leurs efficacités dans diverses applications. De plus, leur utilisation permet de concevoir un système à haut débit pour la détection en temps réel de diverses paramètres. Afin de développer ces capteurs, un logiciel multiphysique (COMSOL) a été utilisé pour modéliser les « cantilevers » et plusieurs simulations électromécaniques ont été réalisées pour atteindre une conception appropriée. Deux méthodes de lecture, piezorésistive et capacitive, ont été choisies pour être utilisées avec les capteurs. Les deux capteurs ont été fabriqués par le biais de CMC Microsystems; le processus PolyMUMPs a été employé pour la fabrication de réseaux de capteurs capacitifs, et les capteurs piézorésistifs, quant à eux, ont été développés par le processus de MetalMUMPs. Enfin, les capteurs fabriqués ont été caractérisés suivant différentes étapes incluant l’interferometrie afin d'assurer leur fonctionnalité. Sur la base des résultats de simulation et de caractérisation obtenus, ces capteurs peuvent être utilisés pour élaborer une plateforme haut débit à bas coût pour diverses applications biologiques.----------ABSTRACT The objective of the present project is to develop an array of microsensors for gathering cellular and molecular quantitative biological data. Such data can be used in various fields including cellular and molecular analysis, detection of specific biological interactions, monitoring diseases, and drug discovery. The proposed sensing platform in this project can convert biological interactions into mechanical variations and subsequently converts the mechanical variations to electrical ones. This platform offers the advantage of high sensitivity, real time measurement, high throughput sensing array suitable for fundamental studies as well as clinical applications. We modeled the operation of cantilevers using COMSOL multiphysics software. These simulation techniques can efficiently be used to choose the suitable design and dimensions of cantilevers. Two readout methods, piezoresistive and capacitive, have been chosen to be used along with sensors. Both sensors were fabricated through CMC Microsystems; PolyMUMPs process was employed for fabrication of capacitive sensor array and piezoresistive sensors were developed by MetalMUMPs process. The functionality of cantilevers and their incorporated sensors were characterized through different techniques including interferometry.Based on these simulation and characterization results, the proposed sensors can be good candidate for developing a low cost, high throughput platform for various biological applications

Designing surface chemistries for in situ AFM investigations of biomolecular reactions with proteins at the nanoscale

In situ atomic force microscopy (AFM) characterizations and lithography can be applied to investigate the orientation, reactivity and stability of protein molecules adsorbed on nanostructures of self-assembled monolayers at near-physiological conditions. Automated nanografting was used to fabricate regular arrays of nanopatterns of ù-functionalized n-alkanethiols with designated terminal chemistries. After writing nanopatterns, protein binding occurs selectively on carboxylate-terminated nanopatterns via covalent bonds that are formed using N-ethyl-N\u27(dimethylaminoporpyl)-carbodiimide and N-hydroxysuccinimide activation. The amine groups of lysine residues of proteins bond covalently to nanopatterns of carboxylate-terminated alkanethiol self-assembled monolayers, to form a robust surface attachment for sustained contact-mode AFM imaging during biochemical reactions. Staphylococcal protein A (SpA) furnishes a generic foundation for binding immunoglobulins for nanometer scale sandwich assays. The self-assembly of á,ù-alkanedithiols onto Au(111) was investigated using AFM. When SAMs of 1,8-octanedithiol or 1,9-nonanedithiol are grown naturally from solution, different surface orientations are observed in comparison to methyl-terminated n-alkanethiols. Local views from AFM images reveal a layer of mixed orientations in which the majority of á,ù-alkanedithiol molecules adopt an orientation parallel to the surface with both thiol endgroups bound to Au(111). Results from AFM studies reveal that the chemisorption of thiol endgroups of dithiols inhibits the phase transition from a lying-down to a standing orientation during natural self-assembly. Another method for producing protein nanostructures is particle lithography. Monodisperse mesospheres can be applied to rapidly prepare millions of exquisitely uniform nanometer-sized structures of proteins on flat surfaces using conventional benchtop chemistry steps of mixing, centrifuging, evaporation and drying. The natural self-assembly of monodisperse spheres provides a high throughput and efficient route to prepare circular geometries over millimeter scale areas. The spontaneous assembly of silica or latex mesospheres into organized crystalline layers on flat substrates supplies a structural frame to direct the placement of proteins. Nanopatterns of ferritin, apoferritin, immunoglobulin G and bovine serum albumin were produced with particle lithography. The applicability of particle lithography to generate arrays of protein nanostructures on surfaces such as mica(0001), glass and Au(111) was demonstrated. The morphology and diameter of the protein nanostructures can be tailored by selecting the ratios of protein-to-particles and the diameters of spheres

Technology assessment and feasibility study of high-throughput single cell force spectroscopy

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 72-83).In the last decade, the field of single cell mechanics has emerged with the development of high resolution experimental and computational methods, providing significant amount of information about individual cells instead of the averaged characteristics provided by classical assays from large populations of cells. These single cell mechanical properties correlate closely with the intracellular organelle arrangement and organization, which are determined by load bearing cytoskeleton network comprised of biommolecules. This thesis will assess the feasibility of a high throughput single cell force spectroscopy using an atomic force microscopy (AFM)-based platform. A conventional AFM set-up employs a single cantilever probe for force measurement by using laser to detect the deflection of the cantilever structure, and usually can only handle one cell at a time. To improve the throughput of the device, a modified scheme to make use of cantilever based array is proposed and studied in this project. In addition, to complement the use of AFM array, a novel cell chip design is also presented for the fine positioning of cells in coordination with AFM cantilevers. The advantages and challenges of the system are analyzed too. To assess the feasibility of developing this technology, the commercialization possibility is discussed with intellectual property research, market analysis, cost modeling and supply chain positioning. Conclusion about this technology and its market prospect is drawn at the end of the thesis.by He Cheng.M.Eng

Surface studies of organic thin films using scanning probe microscopy and nanofabrication

Porphyrins and metalloporphyrins have unique chemical and electronic properties and thus provide useful model structures for nanoscale studies of the role of chemical structure for electronic properties. Porphyrins have been proposed as viable materials for molecular-based information-storage devices, gas sensors, photovoltaic cells, organic light-emitting diodes and molecular wires. The function and efficiency of porphyrins in devices is largely attributable to molecular architecture and how the molecules are self-organized. Modifications of the porphyrin macrocycle, peripheral groups or bound metal ions can generate a range of electrical, photoelectrical or magnetic properties. The conductive properties are greatly influenced at the molecular level by the organization of porphyrins into supramolecular arrays, aggregates, and nanocrystals on surfaces. Conductive-probe atomic force microscopy (CP-AFM) has been used extensively for studies of alkanes, phenylalkanes and arenethiols; however, the conductive properties of porphyrins have not been studied as rigorously. Characterizations with CP-AFM are becoming prevalent for molecular electronics studies because of the dual capabilities for obtaining physical measurements and structural information with unprecedented sensitivity. For CP-AFM, the tip is placed directly on the sample surface, at a designated force. To acquire current-voltage (I-V) spectra, a conductive tip is grounded, and a bias is applied to the substrate. For this dissertation, cobaltcarborane porphyrins were synthesized using a ring-opening zwitterionic reaction to produce isomers with different numbers of carborane clusters per macrocycle. Particle lithography was used to prepare regular arrangements of well-defined nanopatterns of porphyrin nanocrystals on conductive substrates. Nanopatterned SAMs of alkanethiols and organosilanes were used successfully to direct the nanocrystals of porphyrins on the surface and characterized with contact and tapping mode imaging of AFM. Our goals were to elucidate the role of molecular structure, packing and orientation for the conductive properties of porphyrins. Understanding how the self-organization and surface assembly influence electrical properties and reliable measurements of conductive properties when these molecules are coordinated to different metals and surfaces will provide information for developing predictive models

Nanoscale resolution immersion scanning thermal microscopy

Nanoscale thermal properties are becoming of extreme importance for modern electronic circuits that dissipate increasing power on the length scale of few tens of nanometers, and for chemical and physical properties sensors and biosensors using nanoscale sized features. While Scanning Thermal Microscopy (SThM) is known for its ability to probe thermal properties and heat generation with nanoscale resolution, until today it was perceived impossible to use it in the liquid environment due to dominating direct heat exchange between microfabricated thermal probe and surrounding liquid that would deteriorate spatial resolution. Nonetheless, our theoretical analysis of SThM in liquids showed that for certain design of SThM probe with resistive heater located near the probe tip, their thermal signal is only moderately affected, by less than half on immersion in a dodecane environment. More significantly, its spatial resolution, surprisingly, would remain practically unaffected, and the thermal contact between the tip apex and the studied sample would be beneficially improved. Our experimental trials of such immersion SThM, or iSThM, were fully successful and here we report for the first time nanoscale SThM measurements of thermal conductivity of Ultra Large Scale Integration polymerceramic metal interconnects with the spatial thermal resolution down to 50 nm. Further studies of heat transport in nanoscale graphite flakes in iSThM suggested, in particular, that highly anisotropic thermal conductivity in graphene layers may play significant role in the nanoscale thermal transport in liquid environment. New iSThM opens a wide range of applications from noncontact measurements of thermal transport in semiconductor devices to exploring graphene energy storage, catalytic reactions and heat generation in biological systems

Prototypenentwicklung eines oberflächen-integrierten Mikrosensor Systems für 3D Traktionskraftmessungen durch DHM/DIC

In times of a rapid development and growing market in robotics, high-tech protheses and the personalization of medicine, biomimicking natural materials like artificial tissue are of central interest within research and industry. To fully understand the structure-function relations within living systems, comprehensive knowledge about the smallest living block, the cell, and its biomechanics are a central topic in world-wide research. However, there is so far no comprehensive technique established that can measure 3D cell forces simultaneously and quantitatively. In this project, a novel surface-integrated mechano-optical microsensor system has therefore been conceptualized, prototyped and tested, which allows for the record of pico- to micronewton traction forces in three dimensions simultaneously. First, adequate microsensor elements were designed via topology optimization and linear static finite element analysis. These designs were fabricated by micromachining processes of biocompatible thin films of nickel-titanium and amorphous silicon. Furthermore, a plasma etching process was developed to fabricate polydimethylsiloxane sensor elements. For accurate and quantitative traction force measurements, AFM cantilever based calibrations of the out-of-plane and in-plane sensor element spring constants were established. For the first time, a diamagnetic levitation force calibrator was used as an adequate pre-calibration method for the sensor elements with a high accuracy of 1 %. For the cost-efficient, simple, compact, variable and sensitive mechano-optical readout, a setting was conceptualized and tested based on the combination of digital holography and digital image correlation. To control cell adhesion, a high-throughput micro-nano structuring method was developed based on the fusion of ink-jet printing with the established method of diblock-copolymer micelle nanolithography.In Zeiten schneller Entwicklung und wachsender Märkte in der Robotik, der high-tech Prothetik und der personalisierten Medizin ist die Biomimetik natürlicher Materialien wie beispielsweise künstliche Haut von zentralem Interesse in Forschung und Industrie. Um die Struktur-Funktions-Beziehungen in lebenden Systemen umfassend zu verstehen ist die umfangreiche Wissenserweiterung hinsichtlich des kleinsten lebenden Bausteins, der Zelle, und seiner Biomechanik Gegenstand weltweiter Forschungsprojekte. Dennoch gab es bis jetzt keine Methode, die 3D Zellkräfte simultan und quantitativ messen kann. In diesem Projekt wurde ein neuartiges, oberflächen-integriertes, mechano-optisches Mikrosensorsystem konzeptioniert, prototypisiert und getestet, das die Messung piko-bis mikronewton kleiner Zugkräfte gleichzeitig in alle drei Dimensionen ermöglicht. Die Sensorelemente wurden mittels Topologieoptimierung und linear statischer Finite Elementanalyse konzipiert. Diese Designs wurden in Mikromaterialbearbeitungsprozessen aus biokompatiblen Nickel-Titan und amorphen Silizium-Dünnschschichten hergestellt. Desweiteren wurde ein Prozess entwickelt, um Polydimethylsiloxan basierte Sensorelemente herzustellen. Für genaue, quantitative Zugkraftmessungen wurden AFM-Cantilever basierte Kalibrierungen der axialen und lateralen Sensorelement-Federkonsten etabliert. Zum ersten Mal wurde dabei ein diamagnetischer Levitationskraftkalibrator mit einer Genauigkeit von 1% als geeignete Kalibrierungsmethode für die Sensorelemente genutzt. Für eine günstige, einfache, kompakte, variable und im Nanometerbereich empfindliche mechano-optische Datenauslesung wurde ein Aufbau konzeptioniert und getestet, in dem digitale Holographie und digitale Bildkorrelation kombiniert werden. Zur Zell-Adhäsionskontrolle wurde eine Hochdurchsatz-Mikro-Nanostrukturierungsmethode entwickelt, die auf der Kombination von Ink-Jet Drucken mit der etablierten Methode der Diblock-Copolymer Mizellen Nanolithographie basiert

Modelling, implementation and validation of polymeric planar spring mechanisms

This thesis explores, by means of modelling and physical experiments, variant designs for triskelion devices, a type of planar exure mechanism widely considered for use in micro-probe suspensions and, more recently, force transfer artefacts. The accurate measurement of low force is challenging problem that has wide range of force related applications. A lot of attention has been paid worldwide during last decade within and beyond the National Metrology Institutes (NMIs) to measuring low forces. A major concern is how to provide traceability for micro- to nanonewton level forces that is highly reliable and could be used for real machine calibration. The current consensus is that this process requires special secondary standards and novel artefacts to transfer such standards to working systems. The latter provides the motivation for this thesis, which makes the following main contributions. A published linear elastic model has been considerably enhanced and generalised to enable the study of a wide range of variants from the one widely-used design of triskelion device. Triskelion and tetraskelion software programs implement this new model, providing a new tool for computing forces, moments, stress, strain, axial stiffness and torsional stiffness for devices before their fabrication. It has been used to explore widely the sensitivity of the devices to changes in design parameters such as suspension leg geometry and 'elbow' angles. To provide essential physical verification of the practicality of a linear model, a low-cost technique has been developed for making small triskelion test samples. This was used with a new test-rig configuration to measure polymeric triskelion devices under loads in the 1 mN to 1N region with deflections up to around 1 mm. Experiments have determined the onset and characteristics of non-linear spring behaviour in typical devices and have verified the general predictions from the new model. The overall conclusion to be drawn is that at large de ection the spring characteristics follow a cubic law (stiffening). However, during the initial stages of the de ection the linear term dominates over a range that is quite sufficiently wide for practical use as force test artefacts. The polymeric test devices performed well, behaving reasonably closely to predicted values in the linear (model) region. The promising results indicate its prospects for use in low force technology in the future

Micromechanical resonators with sub-micron gaps filled with high-k dielectrics

Scaled microelectromechanical (MEMS) resonating devices have generated a great interest for their use in RF front-end architectures for wireless communication, channel-select filters, on-chip signal processing and timing and extreme mas sensing applications thanks to their robustness, low power consumption, easy integration with CMOS and multimode reconfigurability. Therefore, MEMS resonators are a promising alternative to various discrete electrical components, offering excellent figures of merit at in the HF/VHF frequency range. However, there are many remaining open challenges for the research on MEMS resonators such as high quality factor at high frequency, thermal stability, reduced motional resistance, frequency precision and stability, low phase noise and appropriate hermetical and low cost packaging. Many advanced MEMS resonators use deep sub-micron air gaps (<100 nm) in order to improve the electrostatic coupling and, thus, to obtain low motional impedance levels. The lower limit to the gap size is set by fabrication methods, by vibration amplitude and/or by nonlinear effects such as intermodulation distortion. The free space electrode gap offers the advantage to nearly achieve perfect acoustic isolation due to large impedance discontinuity. To overcome the inherent limitations of capacitive transductions, the use of gaps filled with high permittivity materials has been proposed as a way to enhance the electrostatic coupling. Solid and partially-filled high-k dielectric gap resonators have attracted a certain interest in comparison to the air-gap electrostatic transduction since they enhance the transduction efficiency and the electrical resonance current, reduce motional resistance and may even strengthen the suspended structures, making them more reliable for mass sensing applications. During the course of this work, diverse microfabrication processes have been developed and realized in order to obtain air and partially-filled flexural and bulk resonators working in the HF/VHF range from frequencies between 5MHz and 70MHz. Benefiting from gap transduction enhancement coming from the gap-filling with high-k material such as hafnium oxide, the motional resistance has been reduced up to hundreds of Ohms and f0 x Q products of the order of 5 x 1011 have been accomplished. A remarkable improvement in output signals has been obtained by the novel combination of high-k dielectric gap-filling and piezoresistive detection. We have reported some of the first experiments with partially-filled gaps flexural double-ended tuned fork (DETF) resonators and bulk wine-glass disk resonators, piezoresistively sensed. Moreover, mass sensing experiments have been carried out by means of resonator mass loading with controlled Atomic Layer Deposition (ALD) of HfO2 and experimental mass sensitivities up to 4.8 kHz/pg- have been derived. These preliminary results suggest that partially-filled gap MEMS resonators can be utilized to realize mass sensors in large range of masses and frequencies

Recent Progress in Electrospun Nanofibres: Reinforcement Effect and Mechanical Performance

Composite materials are becoming increasingly important as structural materials for aeronautical and space engineering, naval, automotive, and civil engineering, sporting goods, and other consumer products. Fiber-based reinforcement represents one of the most effective manufacturing strategies for enhancing the mechanical strength and other properties of composite materials. Electrospinning has gained widespread interest in the last two decades because of its ability to fabricate continuous ultrafine nanofibers with unique characteristics. The impact of electrospinning on fiber synthesis and processing, characterization, and applications in drug delivery, nanofiltration, tissue scaffolding, and electronics has been extensively studied in the past. In this article, the authors have focused on a comprehensive review of the mechanical performance and properties of electrospun nanofibers as potential reinforcements as well as their advanced nanocomposites