DEVELOPING NANOPORE ELECTROMECHANICAL SENSORS WITH TRANSVERSE ELECTRODES FOR THE STUDY OF NANOPARTICLES/BIOMOLECULES

This study concerns development of a technology of utilizing metallic nanowires for a sensing element in nanofluidic single molecular (nanoparticle) sensors formed in plastic substrates to detect the translocation of single molecules through the nanochannel. We aimed to develop nanofluidic single molecular sensors in plastic substrates due to their scalability towards high through and low cost manufacturing for point-of-care applications. Despite significant research efforts recently on the technologies and applications of nanowires, using individual nanowires as electric sensing element in nanofluidic bioanalytic devices has not been realized yet. This dissertation work tackles several technical challenges involved in this development, which include reduction of nanowire agglomerates in the deposition of individual nanowires on a substrate, large scale alignment/assembly of metallic nanowires, placement of single nanowires on microelectrodes, characterization of electrical conductance of single nanowire, bonding of a cover plate to a substrate with patterned microelectrodes and nanowire electrodes. Overcoming the abovementioned challenges, we finally demonstrated a nanofluidic sensor with an in-plane nanowire electrode in poly(methyl methacrylate) substrates for sensing single biomolecules. In the first part of this study, we developed the processes for separation and large-scale assembly of individual NiFeCo nanowires grown using an electrodeposition process inside a porous alumina template. A method to fabricate microelectrode patterns on plastic substrates using flexible stencil masks was developed. We studied electrical and magnetic properties of new composite core-shell nanowires by measuring the electrical transport through individual nanowires. The core-shell nanowires were composed of a mechanically stable FeNiCo core and an ultrathin shell of a highly conductive Au gold (FeNiCo-Au nanowires). In the second part of this study, we simulated the effects of the nanopore geometry on the current drop signal of the translocation through a nanopore via finite element method using COMSOL. Using the above techniques, we developed for the fabrication and alignment of the microelectrodes and nanowires, we studied the optimum conditions to integrate the transverse nanoelectrode with the nanochannel on plastic substrates. The main challenge was to find the conditions to embed the micro-/nanoelectrodes into the nanochannel substrate as well as the nanochannel cover sheet

Present and Future of Surface-Enhanced Raman Scattering.

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article

Mesoporous film architectures and step gradient formation

The development of novel devices along with technological progress of our time requires miniaturization and compartmentalization, and with this nanotechnology. For example, future innovative solutions are urgently pursued for life-inspired sustainable water and energy management. Nanoscale pores and channels, as one field within nanotechnology, hold great potential in mimicking the outstanding transport phenomena of their biological paragons. Such transport properties, as observed in biological pores and channels, originate from complex architectures and are influenced by pore geometry, surface charge distribution, chemical composition, and wettability. However, desired transport properties in advanced applications require enhanced control of surface functionalization in nanoscale pores and channels along with nanoporous material architecture design. In this regard, mesoporous silica thin films represent suitable model materials for nanoporous material architecture design providing ordered nanoscale pores and nanoscale film thicknesses. In this work, mesoporous silica thin films were investigated to create mesoporous step gradient architectures with respect to pore size, surface wettability, and surface charge. This work was divided into three main sections: i) generating a material library allowing step gradient design, ii) the fabrication of mesoporous architectures, and iii) (nano)local polymer placement into such multilayer architectures. To create mesoporous architectures, a material library was built in the first place. Thereby, the ionic pore accessibility of hydrophilic mesoporous silica thin films was investigated in dependence of preparation parameters, i.e. the template removal. Hydrophobic mesoporous silica thin films with tunable surface wettability were developed using co-condensation of tetraethylorthosilicate and methylated silica precursors resulting in mesoporous (organo)silica thin films. As a side note, an enhanced chemical stability in basic environment was observed for hydrophobic thin films. To replace petro-based templating macromolecules, hydroxypropyl cellulose was successfully applied as bio-based structure directing template for the generation of mesoporous silica thin films with permselective ionic pore accessibility. Mesoporous step gradient architectures were prepared by applying the developed material library combining mesoporous layers with orthogonal properties. Examples are: the fabrication of hydrophilic pore size step gradients, and the combination of layers with different wettability. Interestingly, investigation of mesoporous wettability step gradient films with respect to the ionic pore accessibility in dependence of the hydrophobic top layer’s thickness showed an overcoming of the hydrophobic layer through electrostatic attraction of the hydrophilic bottom layer in case of the thinnest hydrophobic top layer. Regarding local polymer placement, multilayer step gradient mesoporous film formation turned out to be advantageous, too. For example, the layer-selective polymer functionalization of hydrophilic double layered mesoporous silica thin films was achieved by predisposition of a single layer, followed by selective iniferter binding. Layer-selective polymer grafting was achieved resulting in step gradients with charge density control. To further investigate the limits of polymer placement in mesoporous film architectures, plasmonic metal nanoparticles were incorporated into mesoporous silica thin films. These particles served as nanoscopic plasmonic light source and were combined with photopolymerizations. Investigation of the prepared mesoporous composite materials allowed precise placement of the nanoparticles in mesoporous silica thin films with tunable density. The concept of nanolocal polymer placement using plasmonic metal nanoparticles in combination with photopolymerization was demonstrated for two distinct polymerization approaches. Due to the sensitivity of the nanoparticle’s surface plasmons on the surrounding refractive index, such mesoporous composite materials further demonstrated application as sensing unit allowing to detect local refractive index changes, e.g. in consequence of nanolocal polymer placement

Biomolecular Diffusion in Nanofluidics

Imagine a small integrated biomedical analysis laboratory, connected to your home computer, which would be capable of diagnosing illnesses, a lack of vitamins, or the over-presence of substances from samples of blood, urine or saliva. This hypothetic system would be able to give a diagnosis within minutes, finally advising the user about the optimal targeted medicines to take or the right specialist to consult for fast recovery. Of course this system will not be ready in the near future, but this thesis aims to bring some new elements to this exciting project by investigating the diffusion of proteins in well-defined nanometer-sized confined areas. Understanding molecular dynamics in nanoconfinement volumes is fundamental for designing the appropriate lab-on-a-chip devices able to transport, pre-concentrate, separate and sense biomolecules. However, a multitude of phenomena occurring at the nanoscale are still to be discovered and currently, there is a lack of accurate theoretical models to predict the transport of proteins in nanofluidics. Based on measurements performed in 50 nm high 1D nanochannels, where the surface-to-volume ratio is extremely high, protein-surface interactions were initially investigated. Using electrical measurements, the adsorption and desorption kinetics of highly concentrated bovine serum albumin proteins was characterized in different scenarios. Ionic strength conditions were identified, where the electrical conductance is dominated by volume effects due to the adsorbed or bound proteins, leading to potential applications of rapid immunology on-chip. Other situations, where the protein charges were directly influencing the nanochannel conductance, were also highlighted, giving a better understanding of how the adsorbed proteins counterions modify the surface charges. Furthermore, the transport of single proteins diffusing through nanochannels was analyzed using fluorescence correlation spectroscopy. Direct measurements inside nanochannels has allowed the identification of different regimes of interacting proteins, depending on the thickness of the electrical double layer (constituted of immobile ions which equilibrate the surface charges). Taking into account the steric exclusion due to the small channel size, the reversible surface adsorption, and the exclusion-enrichment effect due to the charge of the proteins and ionic strength of the solution, novel theoretical models describing the hindered diffusion of proteins were elaborated. Conditions where the diffusion of proteins through the nanochannels were of the same magnitude as in the bulk were both predicted and experimentally verified. Finally, a novel method is presented to measure the apparent diffusion coefficients of fluorescently-labeled molecules directly inside a nanofluidic system. This technique, based on steady-state dispersion of proteins in a transversal nanoslit, demonstrates that under specific ionic conditions, the apparent diffusion coefficient of wheat germ agglutinin proteins is four orders of magnitude lower than its free diffusion value. Based on this system, the binding affinity of two different proteins was directly measured, demonstrating the potential of this method to be used as a biosensor for quantifying rapid protein complex formation. This thesis mainly deals with fundamental studies related to surface physics and physical chemistry applied to life sciences. The work points out novel, important, experimentally-verified complements to define solid theoretical models, in order to go forward with the design of complex nanofluidic systems applied to biomedical and biological applications

INKJET PRINTED PAPER SURFACE ENHANCED RAMAN SPECTROSCOPY DEVICES FOR TRACE CHEMICAL ANALYSIS

The needs of an ever growing human population are fueling demands for better and cheaper sensors for the early detection of harmful chemicals, pathogens and diseases markers from a variety of sources such as food, water, bodily fluids and contaminated surfaces. To address this, recent innovations utilize Microelectromechanical Systems (MEMS) technology to integrate multiple laboratory functions onto millimeter-sized chips to form Micro Total Analysis Systems (µTAS) or Lab-on-chip (LOC) devices. While sophisticated and powerful, the use of these devices for chemical and biological sensing is limited by complicated fabrication processes, high cost and robustness of the sensors. In this work we have developed a simple and inexpensive but exceptionally sensitive portable chemical and biological sensing platform through the innovative use of paper combined with Surface Enhanced Raman spectroscopy (SERS). Paper is functionalized with plasmonic nanostructures to transform it into a SERS substrate, while the natural properties of paper are leveraged for sample collection, cleanup, and analyte concentration in user-friendly formats such as wipes, dipsticks, and filters. The use of simple deposition methods such as inkjet printing for sensor fabrication combined with paper as the construction material means that sensors can be made at a very low cost. Additionally, the ability to be printed on demand eliminates issues with sensor shelf-life, while the absence of mechanical components makes these paper sensors much more robust than conventional sensors. In this work, practical applications of paper SERS sensors for the detection of food contaminants, narcotics, pesticides and other chemicals at trace levels are presented. Paper SERS sensors, by virtue of their low cost, simplicity of fabrication, high sensitivity and ease of use, promises to make chemical and biological sensing more accessible to the common user

A hybrid piezoelectric and electrostatic energy harvester for scavenging arterial pulsations

Implantable and wearable biomedical devices suffer from a limited lifespan of on-board batteries which results in a requirement to change the battery or the device itself causing additional physical discomfort. In order to overcome this, various energy harvesters have been developed. The human body possesses several types of energy available for scavenging through appropriately designed energy harvesting devices, while cardiovascular system in particular represents a constant reliable source of mechanical energy from vibration. Most conventional energy harvesters exploit only a single phenomenon, such piezo- or triboelectricity, thus producing reduced power density. As an improvement, hybridisation of energy harvesters intends to negate this drawback by simultaneously scavenging energy by multiple harvesters. In the present work, the reverse electrowetting on dielectric (REWOD) phenomenon is combined with the piezoelectric effect in a proof-of-concept hybrid harvester for scavenging biomechanical energy from arterial or other type pulsations. A mathematical model of the harvester was developed, and a computational investigation using CFD, and fluid-structure interaction simulations were carried out using the COMSOL Multiphysics software. The effect of the materials of piezoelectric film and geometrical features of the harvester on parameters such as the displacement, the frequency of pulsations and the energy produced were studied. An experimental setup that could imitate the displacements caused from arterial pulsations was designed and the produced electrical energy characteristics were analysed. A comparison between experimental and computational data was carried out and demonstrated a good agreement. Dependencies between geometrical parameters and electrical output were obtained, recommendation on piezoelectric materials and design solutions were provided

Light harvesting in low dimensional systems: application of driven Brownian ratchets in supported lipid bilayers for the creation of light harvesting mimics

Supported lipid bilayers are a well known model system for the cell membrane. They allow for the investigation of the membrane in a controlled environment. The solid supported bilayer is accessible through the surface it is formed on and allows for different experimental techniques to be applied. This thesis presents work on free diffusion in the membrane and electrophoretically driven transport concentration of charged membrane components. In addition to that, novel supports for the support of membrane proteins have been investigated and surface enhanced Raman spectroscopy is presented as a label-free method for the detection of membrane components. Brownian ratchets have been used for applications such as molecular sorting with and without the use of lipid bilayers. So far the work has mainly been focussed on their use without a thorough investigation of their properties and the parameters influencing their efficiency. Here, the size and time parameters are varied in experiment and calculation and their role in the ratcheting process is discussed. The efficiency of the ratchets can be significantly reduced when the parameters are chosen in an optimal manner. The use of electrophoresis in lipid bilayers for the concentration and separation of membrane components has focussed on using two electrodes in simple patterns such as squares or lines. This is expanded here on more complex patterns which also allow for the retention of charged material in trapping regions. The pattern was then used to demonstrate the ability to determine binding coefficients in the trapping regions even for membrane components with a low initial concentration or low fluorescence quantum yield. More complex electrode systems using four patterned electrodes are also presented which allow for the application of electric fields in two dimensions where the strength and orientation of the field can be chosen almost arbitrarily. Polymer supports have the ability to support lipid bilayers with membrane proteins which exhibit significant extramembranous domains. Two novel supports are investigated here and different lipid bilayer formation routes are explored. To allow for label free detection of lipids, peptides or proteins within the membrane, surface enhanced Raman spectroscopy is used. The ability of this method to distinguish between different lipids and to detect peptides within the membrane is shown, as well