27 research outputs found
OPTICAL DETECTION OF MOLECULAR INTERACTIONS ON THE SURFACE OF MATERIALS INDEX-MATCHED TO WATER.
The idea to have highly effective autonomous sensors able to measure and share information
about the quality of our environment, and particularly water, in our lakes and
rivers, our water supply system and the outputs of municipal and industrial wastewater
treatment systems is revolutionary and fascinating. These sensors could be densely deployed
at multiple locations, and the information may be available to citizens through
the Internet. This idyllic vision, nowadays, is far away from being reality, despite the
huge effort made to develop innovative molecular sensors. The main challenges related
to the realization of these autonomous sensors network are the biofouling, power supply
and compactness. In fact, despite thousands of papers in literature about development
of novel nanostractured materials for sensing, for instance, there is still not a single
example of any of these device being used in direct contact with water for long-term
environmental monitoring.
The work presented in this thesis proposes a new kind of optical sensor that combines
a fast and low cost method to detect water pollutant with good performance and robustness.
In particular, this work is focused on the detection of small molecular pollutants,
as oils compounds and surfactants. An innovative aspect of the proposed approach relies
on the use of a novel class of materials as sensing substrate which have peculiar and
fascinating optical properties: these are amorphous perfluorinated polymers with refractive
index similar to that of water. When immersed in aqueous solutions, they provide
extremely low reflection or scattering of light, hence they become barely visible. For this
reason, this class of materials is called phantom. In this limit, when a thin molecular layer
spontaneously adsorbs on the surfaces of these materials, the reflected or scattered light
increases, providing the basis for optical detection of molecules.
In this work, three different phantom materials made of perfluorinated polymers
are exploited in the framework of the detection of water contaminants: a prism, microporous
membranes and micro-beads, that represent the building blocks for the assembly
of an invisible chromatography column. The membrane and the micro-beads were produced
for the first time during this work. The use of fluoropolymer prism substrate for
molecular detection was already proposed in recent works to realize label-free biosensors
based on the functionalization of the surface with antibodies. Here I extend the
exploitation of this system to the detection of molecular pollutant through their adsorption
on the bare surface of the fluoropolymer materials, without the need of any surface
treatment. Despite the lack of surface functionalization, a selectivity in the adsorption of
various classes of molecules is demonstrated
Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures
The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2ÂœD structures [2â4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 ”m at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. PiquĂ© and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. PiquĂ© (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513â519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ât Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087â4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553
Optical feedback interferometry sensing technique for flow measurements in microchannels
Le phĂ©nomĂšne dâinterfĂ©romĂ©trie par rĂ©injection optique, ou effet self-mixing dans un laser permet de concevoir des capteurs non-invasifs, auto-alignĂ©s, ne nĂ©cessitant que peu dâĂ©lĂ©ments optiques et simples Ă implĂ©menter. Ce type de capteur permet de mesurer avec la prĂ©cision propre Ă lâinterfĂ©romĂ©trie laser le dĂ©placement, la vitesse ou la position de cibles dite coopĂ©ratives (cibles rĂ©flĂ©chissantes ou fortement diffusantes). Dans cette Ă©tude, ce type de capteurs est appliquĂ© Ă la mesure de profil dâĂ©coulement des fluides dans des microcanaux. Le faible coĂ»t et la polyvalence des capteurs Ă rĂ©injection optique sont dâun grand intĂ©rĂȘt dans lâindustrie biomĂ©dicale et chimique, ainsi que pour la recherche en mĂ©canique des fluides. Dans un premier temps, et en se basant sur les Ă©tudes rĂ©alisĂ©es dans des macro-canaux, nous avons proposĂ© un modĂšle dâinterferomĂ©trie par rĂ©injection optique dans une diode laser lorsque la cible est constituĂ© de particules en mouvement, en suspension dans un liquide. A partir de ce modĂšle, nous avons Ă©tudiĂ© expĂ©rimentalement lâimpact du volume de mesure ainsi que du type de particules (taille et concentration) sur le signal mesurĂ©. Nous avons ensuite proposĂ© des mĂ©thodes de traitement du signal permettant de calculer le calcul du dĂ©bit du fluide, ainsi que sous certaines conditions identifiĂ©es, la vitesse locale en tout point dâun microcanal. Ces Ă©tudes prĂ©liminaires nous ont permis de reconstruire le profil dâĂ©coulement de diffĂ©rents liquides dans des canaux de 320”m de diamĂštre. Enfin, nous avons comparĂ© les performances du capteur dĂ©veloppĂ© dans cette thĂšse avec un capteur basĂ© sur la technique du Dual-Slit, technique dĂ©jĂ validĂ©e pour la microfluidique, en mesurant le profil dâĂ©coulement dans un canal Ă section rectangulaire de 100x20”m. ABSTRACT : The phenomenon of optical feedback interferometry (OFI) or self-mixing effect in a laser is used to design non-invasive and self-aligned sensors, requiring only few optical elements and simple to implement. This type of sensor is used to measure the displacement, velocity or position of cooperative targets (reflective or strongly scattering targets). In this study, this phenomenom is applied to the measurement of fluid flow profile in microchannels. The low cost and versatility of optical feedback sensors are of great interest in biomedical and chemical industry as well as research in fluid mechanics. Based on studies in macro-channels, we proposed first a theoretical model of OFI in a laser diode when the target consists of moving particles suspended in a liquid. Based on this model, we then studied experimentally the impact of the sensorâs sensing volume and the type of particles (size and concentration) on the OFI signal. We then proposed signal processing methods for calculating the fluid flow rate, as well as the local velocity at any point in a microchannel. These preliminary studies allowed us to reconstruct the flow profile of different liquids flowing in a circular channel of 320ÎŒm diameter. Finally, we compared the performance of the sensor developed in this thesis with a sensor based on the Dual-Slit technique, which has been already validated for microchannels, by measuring the flow profile in a rectangular shaped channel (100x20”m)
Single molecule detection and fluorescence correlation spectroscopy on surfaces
In this thesis a new approach for single molecule detection and analysis is explored. This approach is based on the combination of two well established methods, fluorescence correlation spectroscopy (FCS) and total internal reflection fluorescence microscopy (TIRFM). In contrast to most existing fluorescence spectroscopy techniques, the subject of primary interest in FCS is not the fluorescence intensity itself but the random intensity fluctuation around the mean value. Intensity fluctuations are induced by thermal noise in a minute observation volume, which is in classical FCS the confocal volume of a confocal microscope. E.g. FCS is commonly utilized to investigate diffusion. In this case, diffusing fluorescent molecules entering or leaving the observation volume cause intensity fluctuations, which are analyzed by calculating the temporal autocorrelation of the observed signal. The autocorrelation is a measure for the self-similarity of a signal and contains information about the average fluctuation strength and duration. The confocal observation volume, i.e. the measurement volume that is actually seen by the detector is approximately given by the product of the optical transfer function with the fluorescence exciting intensity distribution of a focused laser beam. To achieve a high signal-to-background ratio a small observation volume is absolutely essential, first of all because the background from e.g. scattered light increases with the size of the observation volume. Second, a small volume assures for a small average number of fluorophores inside the observation volume and therefore for a high fluctuation amplitude i.e. FCS signal. This thesis proposes and discusses an alternative to confocal FCS specially conceived for measurements on surface-bound molecular systems, such as biological receptors or immobilized enzymes. In contrast to confocal FCS, fluorescence is excited within an evanescent field generated by total internal reflection (TIR) of a laser beam at the interface between a microscope coverslip and the sample. This is achieved by focusing the laser beam off-axis at the back focal plane of a high NA oil-immersion objective. The collimated beam that emerges from the objective is incident at an oblique angle at the coverslip-sample interface and totally internal reflected. In contrast to confocal FCS, the generated observation volume is completely confined to the surface and background fluorescence as well as scattered light from the bulk is efficiently suppressed. Our method, called objective-type TIR-FCS in the following, features an increased collection efficiency compared to existing techniques that combine evanescent wave excitation and FCS. Existing techniques use total internal reflection on the surface of a prism to generate an evanescent field. This leads to a configuration where the choice of objectives is limited to air or water-immersion objectives. In our system we use a high NA oil-immersion objective, specially conceived for TIR applications, which collects light efficiently. The collection efficiency is further enhanced by a naturally occurring change of the emission properties of fluorophores close to interfaces between dielectric media. The presence of the interface favors emission into the optically denser medium so that about 60% of the emitted light can be collected. These factors, together with a reduced observation volume lead to a very sensitive method with a high potential for applications in single molecule detection and analysis. The performance of the proposed method was experimentally shown for measurements on molecules subject to Brownian motion and binding to modified coverslips. In particular, it was experimentally shown that objective-type TIR-FCS features high signal-to-background ratio on a single molecule level. In this thesis, concise derivations of analytical expressions for autocorrelation functions for diffusion and most important, the case of ligands reversibly binding to a single and localized binding site are presented. The derived model allows for the quantitative determination of binding rates for a single receptor. We strongly believe that the application of these results in the context of investigations of receptor-ligand binding kinetics will allow for deeper understanding of cellular signaling. Moreover, this thesis discusses the applicability of the proposed method in enzymology. Enzymes, as most proteins are subject to continuous changes of their structure or conformation. These conformational changes are correlated with the function of the enzyme. In the discussed example the enzyme catalyzes an oxidation where the product is fluorescent but the substrate is not. The function of the enzyme i.e. the recurring product formation leads to observable intensity fluctuations. Since function and conformational states are correlated, conformational fluctuations can be investigated by means of FCS as was already shown for confocal FCS. A technique closely related to FCS is fluorescence lifetime spectroscopy (where lifetime refers to the mean lifetime of the electronic excited state). Whereas in FCS the relaxation after random deviations from thermal equilibrium is investigated, relaxation of excited fluorophores towards their electronic ground-state is investigated in lifetime spectroscopy. The technique is used for e.g. discrimination between fluorophores with different lifetimes. Lifetime spectroscopy combined with imaging is used in many domains of life-science, including microarray reading and medical diagnostics. In preliminary work we developed a novel approach to perform lifetime imaging that is based on a multiplexing technique. The proposed method requires no mechanical scanning stage and only a single-point detector. Furthermore, noise is reduced under certain circumstances if the signal is low. Characteristics of this technique as well as advantages and disadvantages are shortly discussed
Advanced Image Acquisition, Processing Techniques and Applications
"Advanced Image Acquisition, Processing Techniques and Applications" is the first book of a series that provides image processing principles and practical software implementation on a broad range of applications. The book integrates material from leading researchers on Applied Digital Image Acquisition and Processing. An important feature of the book is its emphasis on software tools and scientific computing in order to enhance results and arrive at problem solution
Novel Biosensing Approaches for Detection of Exosomal Proteins
Exosomes are endocytic lipid membrane-bound bodies that have been shown to carry proteins associated with cancer and neurodegenerative disease. This has led to an exponential rise in research that looks to incorporate exosomal proteins as disease biomarkers within diagnostic assays. Furthermore, ubiquitous presence of exosomes in nearly all biological fluids creates the possibly of minimally invasive liquid biopsies for the patient. However, the heterogeneity of exosomes and complexity of biological source materials requires a consideration of optimal isolation protocols. More importantly, the development of effective exosome based assays is limited by the scarcity of translational characterization approaches that are capable of determining their molecular composition and physical properties in physiological fluids. The key objectives of this doctoral research was to establish a robust exosome isolation protocol from complex media, prior to sensing the exosomes on an immunosensor transduced by acoustic wave and electrochemical measurements. This work also looked to enhance these platforms from their current baseline performance, through the implementation of various surface structure modifications. A size exclusion chromatography approach was developed for the isolation of exosomes expressing CD63, Alix, CD81 and CD9 proteins, and allowed them to be extracted effectively from cell culture media, human serum and urine. Isolated exosomes were subsequently detected on a quartz crystal microbalance with dissipation (QCM-D) monitoring, after the optimisation of an affinity-based immunofunctionalisation approach. This technique displayed high sensitivity and specificity towards exosomal CD63 at clinically relevant concentrations in complex media. The QCM-D sensor was also used as a working electrode, as part of an electrochemical cell, to enable additional impedance spectroscopy analysis of exosome binding in tandem with the QCM-D response, collectively termed EQCM-D. The combination of these approaches offers a label-free, sensitive and real-time approach to exosome detection. The sensitivity of the EQCM-D platform was improved through surface formation of tuneable gold nanoparticle arrays from selective impregnation of block-copolymer templates, taking advantage of their segregation behaviour. This presented a versatile approach to tune sensor surfaces in order to improve ligand orientation and subsequent analyte binding. Similar advancements were made on silica detection surfaces through the formation of silica inverse opal crystals, with differing thicknesses, using a single-step co-assembly approach that combines a sol-gel matrix with poly(methyl methacrylate) (PMMA) spheres. Porous networks atop the sensors increased the internal surface area significantly, translating to a higher binding capacity of exosomes notwithstanding a higher degree of artefact entrapment. The results achieved through this work offer a potential for multi-modal analysis of exosomal proteins in diagnostics, underpinned by acoustic wave methodologies and nanostructured materials
Microelectromechanical Systems and Devices
The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators
A study of SNARE-mediated autophagosome clearance using fluorescence lifetime microscopy
Cell survival requires the turnover of toxic cellular material and recycling of
biomolecules in low nutrient conditions. An efficient degradation system is
therefore essential for disease prevention and its dysfunction has been linked to
both neurodegeneration and oncogenesis. Bulk degradation is accomplished
through the collection of cytoplasmic material in a unique sequestration vesicle,
which forms de novo and subsequently deposits cargo in the lysosome for
degradation. This process, known as autophagy, therefore requires membrane
fusion between the autophagosomal vesicle and the lysosome. SNARE proteins
mediate membrane fusion events and therefore their careful regulation ensures
the proper organisation of the membrane trafficking network. The SNARE proteins
governing autophagosome clearance have been identified as syntaxin 17, SNAP29
and VAMP8 and SNARE assembly appears to be positively regulated by VPS33A.
This well established model of SNARE-mediated autophagosome clearance has not,
however, been demonstrated within the spatiotemporal framework of the cell and
little is known about how VPS33A modulates SNARE function. The research
presented in this thesis therefore aims to determine the applicability of the
proposed SNARE model within the cellular environment and to investigate the
regulatory mechanisms controlling syntaxin 17 function. To accomplish this,
carefully validated fluorescence colocalisation and time-resolved fluorescence
lifetime imaging techniques were primarily employed. The limitations of these
techniques were also considered for data interpretation and a novel prototype
SPAD array technology, designed for high-speed time-correlated single photon
counting, was trialled for widefield FLIM-FRET. FLIM-FRET revealed that VAMP8
has been incorrectly assigned as the dominant autophagosomal R-SNARE and
VPS33A studies evidence a multi-modal regulation of Stx17 that diverges from
other studied syntaxin family modulation mechanisms. A new model of SNAREmediated
autophagosome clearance is therefore proposed, where syntaxin 17
engages with SNAP29 and VAMP7 to drive membrane fusion with the
endolysosome in a manner governed by VPS33A and dependent on the
phosphorylation status of syntaxin 17