Miniaturized differential scanning calorimeter with an integrated mass sensing system: first steps

In this paper, the first steps towards integrating a mass sensing system into an existing miniaturized ceramic DSC (differential scanning calorimetry) chip are presented. A vibration setup is developed based on the mass-dependent change in frequency of the DSC chip as an oscillating cantilever. A simulation model reveals that the resolution of the measurement can be improved by reducing the chip thickness. In this study, different measurement methods (acoustic, optical, and piezoresistive) are investigated. Three complete measurement systems are set up and evaluated with regard to their integration in the DSC chip. All presented measurement methods show promising results and already allow mass measurements with a resolution of 100 µg.</p

MICROMANIPULATOR-RESONATOR SYSTEM FOR SELECTIVE WEIGHING OF INDIVIDUAL MICROPARTICLES

Over the past decade, MEMS-based cantilever sensors have been widely used in the detection of biomolecules, environmental pollutants, chemicals and pathogens. Cantilever-based sensors rely on attachment of target entities on their surface. The attachment causes either change in surface stress or resonance frequency of the cantilever, which is detected using various schemes that range from optical to piezoelectric. The majority of these sensors rely on probabilistic attachment of multiple target entities to the sensor surface. This introduces uncertainties since the location of the adsorbed target entity can modify the signal generated by the sensor. In addition, it does not allow the measurement of individually selected target entities. The goal of this dissertation is to exploit the cantilever-based sensors\u27 mass sensing capability to develop a supermarket weight scale for the micro world: a scheme that can enable the user to pick an individual target entity and weigh only that particular entity by precisely positioning it on a micro- weight scale

Integrated microcantilever fluid sensor as a blood coagulometer

The work presented concerns the improvement in mechanical to thermal signal of a microcantilever fluid probe for monitoring patient prothrombin time (PT) and international normalized ratio (INR) based on the physical measurement of the clotting cascade. The current device overcomes hydrodynamic damping limitations by providing an internal thermal actuation force and is realised as a disposable sensor using an integrated piezoresistive deflection measurement. Unfortunately, the piezoresistor is sensitive to thermal changes and in the current design the signal is saturated by the thermal actuation. Overcoming this problem is critical for demonstrating a blood coagulometer and in the wider field as a microsensor capable of simultaneously monitoring rheological and thermal measurements of micro-litre samples. Thermal, electrical, and mechanical testing of a new design indicates a significant reduction in the thermal crosstalk and has led to a breakthrough in distinguishing the mechanical signal when operated in moderately viscous fluids (2-3 cP). A clinical evaluation has been conducted at The Royal London Hospital to measure the accuracy and precision of the improved microcantilever fluid probe. The correlation against the standard laboratory analyser INR, from a wide range of patient clotting times(INR 0.9-6.08) is equal to 0.987 (n=87) and precision of the device measured as the percentage coefficient of variation, excluding patient samples tested < 3 times, is equal to 4.00% (n=64). The accuracy and precision is comparable to that of currently available point-of-care PT/INR devices. The response of the fluid probe in glycerol solutions indicates the potential for simultaneous measurement of rheological and thermal properties though further work is required to establish the accuracy and range of the device as a MEMS based viscometer

Damping of piezoelectric MEMS oscillators – fundamentals and applications

A limiting parameter for the performance of micromechanical oscillators is the damping induced by the surrounding medium. In this work, the damping losses of micromechanical oscillators with piezoelectric actuation and detection are investigated in nine different gas atmospheres over a pressure range of six decades. In addition, the influence of the distance to a spatial boundary is examined, covering a range from narrow gaps with squeeze film damping to an almost freely oscillating structure. This reveals a superposition of four different damping mechanisms, which occur in varying strength depending on pressure, distance and eigenmode. Using an analytical approach, the individual damping phenomena can be separated from each other and subsequently evaluated in a targeted manner. Based on these results, new insights are gained for the molecular flow regime as well as the transitional flow regime, which include the impact of the number of active degrees of freedom of the gas molecules as well as thermal resonance effects. In addition, an electrical equivalent circuit was designed for the entire measurement range, which shows very good agreement with the experimental data. Finally, the damping effects are exploited for applications in sensor technology and a wide range pressure sensor using the nonlinear regime of the oscillators as well as a concept for the measurement of the oxygen concentration are presented.Eine für die Leistungsfähigkeit mikromechanischer Oszillatoren limitierende Größe stellt die Dämpfung durch das umgebende Medium dar. In dieser Arbeit werden daher die Dämpfungsverluste mikromechanischer Oszillatoren mit piezoelektrischer Anregung und Detektion in neun verschiedenen Gasatmosphären über einen Druckbereich von sechs Dekaden untersucht. Zusätzlich wird der Einfluss des Abstandes zu einer räumlichen Begrenzung betrachtet und dabei ein Bereich von engen Spalten mit Squeeze Film Dämpfung bis hin zu fast frei schwingenden Strukturen untersucht. Dabei ergibt sich eine Überlagerung von vier verschiedenen Dämpfungsmechanismen, welche in Abhängigkeit von Druck, Abstand und Eigenmode in unterschiedlich starker Ausprägung auftreten. Durch einen analytischen Ansatz lassen sich die einzelnen Dämpfungsphänomene voneinander separieren und in der Folge gezielt auswerten. Anhand dieser Ergebnisse wurden für den molekularen sowie den Übergangsbereich neue Erkenntnisse gewonnen, welche die Anzahl aktiver Freiheitsgrade der Gasmoleküle sowie thermische Resonanzeffekte miteinbeziehen. Darüber hinaus wurde für den gesamten Messbereich ein elektrisches Ersatzschaltbild konzipiert, das eine sehr gute Übereinstimmung mit den experimentellen Daten zeigt. Abschließend werden die Dämpfungseffekte für Anwendungen in der Sensorik erschlossen und ein Mehrbereichsdrucksensor mit Hilfe des nichtlinearen Bereichs der Oszillatoren sowie ein Konzept zur Messung des Sauerstoffgehaltes präsentiert.German Research Foundation (DFG

ELECTROKINETICS-ASSISTED ELECTRICAL SENSORS FOR RAPID DETECTION OF BACTERIA

Department of Mechanical Enginering (Mechanical Engineering)An array of microfabricated interdigitated electrodes (IDEs) is the most commonly used form of electrode geometry for dielectrophoretic manipulation of biological particles in microfluidic biochips owing to simplicity of fabrication and ease of analysis. However, the dielectrophoretic force dramatically reduces as the distance from the electrode surface increasestherefore, the effective region is usually close to the electrode surface for a given electric potential difference. Here, I present a novel two-dimensional computational method for generating planar electrode patterns with enhanced volumetric electric fields, which I call the ???microelectrode discretization (MED)??? method. It involves discretization and reconstruction of planar electrodes followed by selection of the electrode pattern that maximizes a newly defined objective function, factor S, which is determined by the electric potentials on the electrode surface alone. In this study, IDEs were used as test planar electrodes. Two arrays of IDEs and respective MED-optimized electrodes were implemented in microfluidic devices for the selective capture of Escherichia coli against 1-??m-diameter polystyrene beads, and I experimentally observed that 1.4 to 35.8 times more bacteria were captured using the MED-optimized electrodes than the IDEs (p < 0.0016), with a bacterial purity against the beads of more than 99.8%. This simple design method offered simplicity of fabrication, highly enhanced electric field, and uniformity of particle capture, and can be used for many dielectrophoresis-based sensors and microfluidic systems. Dielectrophoresis (DEP) is usually effective close to the electrode surface. Several techniques have been developed to overcome its drawbacks and to enhance dielectrophoretic particle capture. Here a simple technique was presented of superimposing alternating current DEP (high-frequency signals) and electroosmosis (EOlow-frequency signals) between two coplanar electrodes (gap: 25 ??m) using a lab-made voltage adder for rapid and selective concentration of bacteria, viruses, and proteins, where the voltages and frequencies of DEP and EO were controlled separately. This signal superimposition technique enhanced bacterial capture (Escherichia coli K-12 against 1-??m-diameter polystyrene beads) more selectively (>99 %) and rapidly (~30 s) at lower DEP (5 Vpp) and EO (1.2 Vpp) potentials than those used in the conventional DEP capture studies. Nanometer-sized MS2 viruses and troponin I antibody proteins were also concentrated using the superimposed signals, and significantly more MS2 and cTnI-Ab were captured using the superimposed signals than the DEP (10 Vpp) or EO (2 Vpp) signals alone (p < 0.035) between the two coplanar electrodes and at a short exposure time (1 min). This technique has several advantages, such as simplicity and low cost of electrode fabrication, rapid and large collection without electrolysis. Electrokinetic technologies such as AC electro-osmosis (EO) and dielectrophoresis (DEP) have been used for effective manipulation of bacteria to enhance the sensitivity of an assay, and many previously reported electrokinetics-enhanced biosensors are based on stagnant fluids. An effective region for positive DEP for particle capture is usually too close to the electrode for the flowing particles to move toward the detection zone of a biosensor against the flow directionthis poses a technical challenge for electrokinetics-assisted biosensors implemented within pressure-driven flows, especially if the particles flow with high speed and if the detection zone is small. Here, a microfluidic single-walled carbon nanotubes (SWCNTs)-based field-effect transistor immunosensor was presented with electrohydrodynamic (EHD) focusing and DEP concentration for continuous and label-free detection of flowing Staphylococcus aureus in a 0.01?? phosphate buffered saline (PBS) solution. The EHD focusing involved AC EO and negative DEP to align the flowing particles along lines close to the bottom surface of a microfluidic channel for facilitating particle capture downstream in the detection zone. For feasibility, 380-nm-diameter fluorescence beads suspended in 0.001?? PBS were tested, and 14.6 times more beads were observed to be concentrated on the detection area with EHD focusing. Moreover, label-free, continuous, and selective measurement of S. aureus in 0.01?? PBS was demonstrated, showing good linearity between the relative changes in electrical conductance of the SWCNTs and logarithmic S. aureus concentrations, a capture/detection time of 35 min, and limit of detection of 150 CFU/mL, as well as high specificity through electrical manipulation and biological interaction.ope

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

A review of sensing technologies for gas nerve agents, through the use of agent mimics in the gas phase: future needs

The aim of the work presented in this review is to present a detailed summary of the current sensing technology available within the scientific literature for the detection of nerve agent simulants in the gas phase, focussing on the recognised sarin surrogate: dimethyl methylphonate (DMMP). The use of simulants for the development of sensing technology has been widely established for nerve agents to reduce the potential risk to personnel and to offer a realistic, simple molecule to try and test the technology. The present review compiles a comparison of different sensors and their respective sensing mechanisms. These sensing technologies are then compared to the U.S environmental protection agencies standard for concentration of Sarin at 15 ppb (known lethal dose). Only some work developed using semiconductor detectors present a reliable system able to detect DMMP with low LoD (0.05 ppb), fast response time (0.02 mins) and good recovery times (0.5 min)

Ioonsete elektromehaaniliselt aktiivsete polümeeride deformatsioonist sõltuv elektroodi impedants

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Elektromehaaniliselt aktiivsed materjalid on polümeeridel põhinevad mitmekihilised komposiitmaterjalid, mis muudavad oma välist kuju, kui neid elektriliselt stimuleerida; tihti nimetatakse neid ka tehislihasteks. Taolistest materjalidest valmistatud täiturid pakkuvad huvi nii mikrolaborseadmetes kui ka loodust matkivas robootikas, sest võimaldavad luua keerukaid ülipisikesi ajameid. Võrreldes tavapäraste elektrimootoritega võimaldavad EAP-d (elektromehaaniliselt aktiivsed polümeerid) helitut liigutust ning neid saab lõigata konkreetse rakenduse jaoks sobivasse suurusesse. EAP-d jagunevad kahte põhiklassi: elektron- ja ioon-EAP. Doktoritöös käsitletakse kahte erinevat ioon-EAP materjali, kus mehaaniline koste on tingitud ioonide ümberpaigutumisest kolmekihilises komposiitmaterjalis. Kuna EAP-de elektromehaanilised omadused sõltuvad lisaks sisendpinge amplituudile ja sagedusele ka tugevasti ümbritseva keskkonna parameetritest (nt niiskus ja temperatuur), siis on nendest materjalidest loodud täiturite juhtimiseks tarvilik kasutada tagasisidet. Täiendav tagasisideallikas võib oma omaduste tõttu aga vähendada EAP-de rakendusvõimalusi ning seetõttu on eesmärgiks luua n-ö isetundlik EAP ajam, mis funktsioneerib samaaegselt nii täituri kui ka liigutusandurina. Doktoritööd esitatakse uuritud materjalide elektroodi impedantsi ja deformatsiooni vaheline seos ning kirjeldatakse vastav elektriline mudel. Eraldamaks andursignaali täituri sisendpingest pakutakse välja elektroodikihi piires täituri ja anduri elektriline eraldamine. Loobudes ainult elektroodimaterjalist säilitab polümeerkarkass täituri ja anduri mehaanilise ühendatuse – seega taolises süsteemis järgib sensor täituri kuju, kuigi need on elektriliselt lahti sidestatud. Elektroodimaterjali valikuliseks eemaldamiseks kasutatakse mitmeid erinevaid meetodeid (freesimine, laserablatsioon jne) ning ühtlasi uuritakse nende kasutusmugavust ja protsessi mõju kogu komposiitmaterjalile.Electromechanically active materials are polymer-based composites exhibiting mechanical deformation under electrical stimulus, i.e. they can be implemented as soft actuators in variety of devices. In comparison to conventional electromechanical actuators, their key characteristics include easy customisation, noiseless operation, straightforward mechanical design, sophisticated motion patterns, etc. Ionic EAPs (electromechanically active polymers) are one of two primary classes of electroactive materials, where actuation is caused mostly by the displacement of ions inside polymer matrix. Mechanical response of ionic EAPs is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore a major challenge lies in achieving controlled actuation of these materials. Due to their size and added complexity, external feedback devices inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators—capable for simultaneous actuation and sensing—are desired. In this thesis, sensing based on deformation-dependent electrochemical impedance is demonstrated and modelled for two types of trilayer ionic EAPs—ionic polymer-metal composite and carbon-polymer composite. Separating sensing signal from the input signal of the actuator is achieved by patterning the electrode layers of an IEAP material in a way that different but mechanically coupled sections for actuation and sensing are created. A variety of concepts for pattering the electrode layers (machining, laser ablation, masking, etc.) are implemented and their applicability is discussed