New lab-on-a-chip strategies for enantio-selective and non-diffusion-limited biosensing

The race for fast and small that drives nowadays society has also reached the field of biosensing. Looking for efficient and cost effective biosensors for applications including screening and treatment monitoring, biomolecular engineering, drug design and food industry; plasmonics and microfluidics technologies have synergistically grown to offer the most attractive solutions. The recent progress in nano-optics has paved the route toward the development of highly sensitive and label-free optical transducers using the localized surface plasmon resonance (LSPR). Additionally, LSPR offer high-end miniaturization and high degree of tunability of both sensors’ spatial and spectral responses. These unique properties have recently been interfaced with microfluidics towards lab-on-a-chip (LOC) functional platforms which offer reduced sample volumes and multi-tasking operations on a single chip. Combining nano-optics, microfluidics and biochemical sensing makes this PhD project highly multidisciplinary. This blend aims at pushing the limits of LSPR sensing by addressing two significant problems in the biosensing community. On one hand, we went through chiral plasmonic sensing. Chiral molecules exhibit signatures in the ultraviolet frequency region. They are typically characterized by circular dichroism (CD), which suffers of low sensitivity and the need of big sample volumes and concentrations. Plasmonic nanostructures have the potential to enhance the sensitivity of chiral detection and translate the molecular signatures to the visible spectral range. However, to date, it remains unclear which properties plasmonic sensors should exhibit to maximize this effect and apply it to reliable enantiomer discrimination. As a consequence, a collection of results of difficult interpretation and cross comparison can be found in the literature. Here, we bring further insight into this complex problem and present a chiral plasmonic sensor composed of a racemic mixture of gammadions that enables us to directly differentiate enantiomers. We also present a plasmo-fluidic sensing platform, which allows the systematic study of chiral biomolecules by enabling multiple sensing assays on a single chip. On the other hand, we addressed one of the major challenges of plasmonic sensing in microfluidics environments; the transport of the analyte to the sensor surface, which due to the laminar flow that rules in micro-channels, is limited by Brownian diffusion. Hence, dictates the total duration of the sensing assay. Here, we use the electrothermoplasmonic (ETP) effect to overcome this limit through opto-electrical fluid convective flow generation. To this end, we designed a LSPR sensing chip that integrates ETP operation into state-of-the-art microfluidics. Our results demonstrate that ETP-LSPR has improved performances over standard LSPR.La continua carrera de la miniaturización y la velocidad, que gobierna la sociedad tecnológica de hoy en día, ha alcanzado también el campo de los bio-sensores. Plasmónica y micro-fluídica, dos tecnologías complementarías, han crecido durante sinérgicamente en las últimas. Juntas son capaces de atender la exigente demanda de soluciones más efectivas y económicas en campos como el diagnóstico y tratamiento médico personalizado, la ingeniería bio-molecular, el diseño de fármacos y la industria alimentaria. El reciente progreso del campo de la nano-óptica ha forjado el camino para el desarrollo de sensores ópticos altamente sensibles y sin requerimiento de marcadores moleculares. Los sensores basados en resonancias plasmónicas superficiales localizadas (LSPR) son de gran atractivo debido a sus posibilidades de miniaturización y versatilidad en la caracterización de sus respuestas espaciales y espectrales. Estas propiedades únicas se han combinado recientemente con la micro-fluídica, dando lugar a plataformas funcionales integradas, conocidas como laboratorios en un chip (LOC). Dichas plataformas permiten reducir significativamente los volúmenes de muestra, además de realizar multiples operaciones en un solo chip. La combinación de la nano-óptica, la microfluídica y la detección bioquímica hacen de este proyecto de doctorado una tarea altamente multidisciplinar. Esta mezcla opta por llevar los límites de los sensores LSPR enfrentando dos de los problemas más notables en las últimas décadas: la detección de moléculas quirales mediante plasmónica y transporte molecular en micro-canales. Las moléculas quirales muestran respuestas ópticas en el rango ultravioleta del espectro y son comúnmente caracterizadas mediante dicroísmo circular (CD). Sin embargo, dicha respuesta óptica es minúscula y requieres grandes concentraciones y volúmenes de muestra para ser media. La plasmónica tiene el potencial de aumentar sensibilidad de los métodos actuales y además trasladar la respuesta quiral al rango visible. Aunque hasta la fecha, no se han conseguido predecir las propiedades óptimas que deben poseer los sensores para realizar dicha tarea de forma eficiente. En consecuencia, existen una variedad de trabajos publicados difíciles de interpretar y de enlazar. En este sentido hemos conseguido desarrollar un sensor compuesto por una mezcla racémica de cruces gamadas que es capaz de diferenciar entre enantiómeros de forma directa. Además, también presentamos una plataforma plasmónica y fluídica que permite el estudio sistemático de moléculas quirales mediante la realización de multiples ensayos simultáneos en un solo chip. Por otro lado, abordamos la limitación del transporte de moléculas por difusión browniana en micro-canales. Un problema que limita la velocidad en la detección de los sistemas que integran sensores plasmónicos con la microfluídica. En este frente, utilizamos el efecto electro-termo-plasmónico (ETP) para rebasar este límite a través de la generación de flujos convectivos que alteran el flujo laminar que impera en los micro-canales. Con este fin, hemos diseñado un chip que integra el estado del arte de la microfluídica con el efecto ETP. Los resultados que ofrecemos demuestran que el rendimiento de un ensayo en el nuevo sistema ETP-LSPR es superior al realizado en un LSPR estándar.Postprint (published version

New lab-on-a-chip strategies for enantio-selective and non-diffusion-limited biosensing

The race for fast and small that drives nowadays society has also reached the field of biosensing. Looking for efficient and cost effective biosensors for applications including screening and treatment monitoring, biomolecular engineering, drug design and food industry; plasmonics and microfluidics technologies have synergistically grown to offer the most attractive solutions. The recent progress in nano-optics has paved the route toward the development of highly sensitive and label-free optical transducers using the localized surface plasmon resonance (LSPR). Additionally, LSPR offer high-end miniaturization and high degree of tunability of both sensors’ spatial and spectral responses. These unique properties have recently been interfaced with microfluidics towards lab-on-a-chip (LOC) functional platforms which offer reduced sample volumes and multi-tasking operations on a single chip. Combining nano-optics, microfluidics and biochemical sensing makes this PhD project highly multidisciplinary. This blend aims at pushing the limits of LSPR sensing by addressing two significant problems in the biosensing community. On one hand, we went through chiral plasmonic sensing. Chiral molecules exhibit signatures in the ultraviolet frequency region. They are typically characterized by circular dichroism (CD), which suffers of low sensitivity and the need of big sample volumes and concentrations. Plasmonic nanostructures have the potential to enhance the sensitivity of chiral detection and translate the molecular signatures to the visible spectral range. However, to date, it remains unclear which properties plasmonic sensors should exhibit to maximize this effect and apply it to reliable enantiomer discrimination. As a consequence, a collection of results of difficult interpretation and cross comparison can be found in the literature. Here, we bring further insight into this complex problem and present a chiral plasmonic sensor composed of a racemic mixture of gammadions that enables us to directly differentiate enantiomers. We also present a plasmo-fluidic sensing platform, which allows the systematic study of chiral biomolecules by enabling multiple sensing assays on a single chip. On the other hand, we addressed one of the major challenges of plasmonic sensing in microfluidics environments; the transport of the analyte to the sensor surface, which due to the laminar flow that rules in micro-channels, is limited by Brownian diffusion. Hence, dictates the total duration of the sensing assay. Here, we use the electrothermoplasmonic (ETP) effect to overcome this limit through opto-electrical fluid convective flow generation. To this end, we designed a LSPR sensing chip that integrates ETP operation into state-of-the-art microfluidics. Our results demonstrate that ETP-LSPR has improved performances over standard LSPR.La continua carrera de la miniaturización y la velocidad, que gobierna la sociedad tecnológica de hoy en día, ha alcanzado también el campo de los bio-sensores. Plasmónica y micro-fluídica, dos tecnologías complementarías, han crecido durante sinérgicamente en las últimas. Juntas son capaces de atender la exigente demanda de soluciones más efectivas y económicas en campos como el diagnóstico y tratamiento médico personalizado, la ingeniería bio-molecular, el diseño de fármacos y la industria alimentaria. El reciente progreso del campo de la nano-óptica ha forjado el camino para el desarrollo de sensores ópticos altamente sensibles y sin requerimiento de marcadores moleculares. Los sensores basados en resonancias plasmónicas superficiales localizadas (LSPR) son de gran atractivo debido a sus posibilidades de miniaturización y versatilidad en la caracterización de sus respuestas espaciales y espectrales. Estas propiedades únicas se han combinado recientemente con la micro-fluídica, dando lugar a plataformas funcionales integradas, conocidas como laboratorios en un chip (LOC). Dichas plataformas permiten reducir significativamente los volúmenes de muestra, además de realizar multiples operaciones en un solo chip. La combinación de la nano-óptica, la microfluídica y la detección bioquímica hacen de este proyecto de doctorado una tarea altamente multidisciplinar. Esta mezcla opta por llevar los límites de los sensores LSPR enfrentando dos de los problemas más notables en las últimas décadas: la detección de moléculas quirales mediante plasmónica y transporte molecular en micro-canales. Las moléculas quirales muestran respuestas ópticas en el rango ultravioleta del espectro y son comúnmente caracterizadas mediante dicroísmo circular (CD). Sin embargo, dicha respuesta óptica es minúscula y requieres grandes concentraciones y volúmenes de muestra para ser media. La plasmónica tiene el potencial de aumentar sensibilidad de los métodos actuales y además trasladar la respuesta quiral al rango visible. Aunque hasta la fecha, no se han conseguido predecir las propiedades óptimas que deben poseer los sensores para realizar dicha tarea de forma eficiente. En consecuencia, existen una variedad de trabajos publicados difíciles de interpretar y de enlazar. En este sentido hemos conseguido desarrollar un sensor compuesto por una mezcla racémica de cruces gamadas que es capaz de diferenciar entre enantiómeros de forma directa. Además, también presentamos una plataforma plasmónica y fluídica que permite el estudio sistemático de moléculas quirales mediante la realización de multiples ensayos simultáneos en un solo chip. Por otro lado, abordamos la limitación del transporte de moléculas por difusión browniana en micro-canales. Un problema que limita la velocidad en la detección de los sistemas que integran sensores plasmónicos con la microfluídica. En este frente, utilizamos el efecto electro-termo-plasmónico (ETP) para rebasar este límite a través de la generación de flujos convectivos que alteran el flujo laminar que impera en los micro-canales. Con este fin, hemos diseñado un chip que integra el estado del arte de la microfluídica con el efecto ETP. Los resultados que ofrecemos demuestran que el rendimiento de un ensayo en el nuevo sistema ETP-LSPR es superior al realizado en un LSPR estándar

Sliding and translational diffusion of molecular phases confined into nanotubes

The remaining dynamical degrees of freedom of molecular fluids confined into capillaries of nano to sub-nanometer diameter are of fundamental relevance for future developments in the field of nanofluidics. These properties cannot be simply deduced from the bulk one since the derivation of macroscopic hydrodynamics most usually breaks down in nanoporous channels and additional effects have to be considered. In the present contribution, we review some general phenomena, which are expected to occur when manipulating fluids under confinement and ultraconfinement conditions.Comment: 17 pages, 8 fig

Direct Current Electrokinetic Particle Transport in Micro/Nano-Fluidics

Electrokinetics has been widely used to propel and manipulate particles in micro/nano-fluidics. The first part of this dissertation focuses on numerical and experimental studies of direct current (DC) electrokinetic particle transport in microfluidics, with emphasis on dielectrophoretic (DEP) effect. Especially, the electrokinetic transports of spherical particles in a converging-diverging microchannel and an L-shaped microchannel, and cylindrical algal cells in a straight microchannel have been numerically and experimentally studied. The numerical predictions are in quantitative agreement with our own and other researchers\u27 experimental results. It has been demonstrated that the DC DEP effect, neglected in existing numerical models, plays an important role in the electrokinetic particle transport and must be taken into account in the numerical modeling. The induced DEP effect could be utilized in microfluidic devices to separate, focus and trap particles in a continuous flow, and align non-spherical particles with their longest axis parallel to the applied electric field. The DEP particle-particle interaction always tends to chain and align particles parallel to the applied electric field, independent of the initial particle orientation except an unstable orientation perpendicular to the electric field imposed. The second part of this dissertation for the first time develops a continuum-based numerical model, which is capable of dynamically tracking the particle translocation through a nanopore with a full consideration of the electrical double layers (EDLs) formed adjacent to the charged particles and nanopores. The predictions on the ionic current change due to the presence of particles inside the nanopore are in qualitative agreement with molecular dynamics simulations and existing experimental results. It has been found that the initial orientation of the particle plays an important role in the particle translocation and also the ionic current through the nanopore. Furthermore, field effect control of DNA translocation through a nanopore using a gate electrode coated on the outer surface of the nanopore has been numerically demonstrated. This technique offers a more flexible and electrically compatible approach to regulate the DNA translocation through a nanopore for DNA sequencing

Manipulation of the Electrical Double Layer for Control and Sensing in a Solid State Nanopore

Nanopores have been explored with the goal of achieving non-functionalized, sub-molecular sensors, primarily with the purpose of producing fast, low-cost DNA sequencers. Because of the nanoscale volume within the nanopore structure, it is possible to isolate individual molecular and sub-molecular analytes. Nanopore DNA sequencing has remained elusive due to high noise levels and the challenge of obtaining single-nucleotide resolution. However, the complete electrical double layer within the nanopore is a key feature of fluid-nanopore interaction and has been neglected in previous studies. By exploring interactions with the electrical double layer in various nanopore systems, we characterize the material, electrical, and solution dependent properties of this structure and develop a new sensing technique. The overall goals of this project are development of a theoretically complete and useful model of the electrical double layer in a nanopore, development of a nanopore device capable of detecting and manipulating the electrical double layer, characterization of active nanofluidic control, and detection of molecular and double layer properties. By considering extensive numerical models along with experimental evaluation of the nanopore devices, we characterize the fluidic and sensor properties of the electrical double layer in a nanopore. The ability to interact with the electrochemical and structural properties of the fluid within a nanopore offers new avenues for molecular detection and manipulation. We find that the energetic balance between the nanopore surface potential and the distribution of charged species within the electrical double layer is the key relationship governing the operation of this type of device. A method of active control of the ionic conductance through the nanopore was developed, with complete gating and on-state modulation. A molecular sensing technique was developed by correlating changes to the electrochemical potential of the solution to the physical properties of molecular analytes. The theoretical and practical limits of the nanopore sensor were tested by implementing a new type of nanopore DNA sequencer. High accuracy DNA sequences were produced by combining the double layer potential and ionic current channels in parallel, along with extensive application of signal theory, digital signal processing, and machine learning techniques

Experimental and Computational Study on the Microfluidic Control of Micellar Nanocarrier Properties

Microfluidic-based synthesis is a powerful technique to prepare well-defined homogenous nanoparticles (NPs). However, the mechanisms defining NP properties, especially size evolution in a microchannel, are not fully understood. Herein, microfluidic and bulk syntheses of riboflavin (RF)-targeted poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG-RF) micelles were evaluated experimentally and computationally. Using molecular dynamics (MD), a conventional "random"model for bulk self-assembly of PLGA-PEG-RF was simulated and a conceptual "interface"mechanism was proposed for the microfluidic self-assembly at an atomic scale. The simulation results were in agreement with the observed experimental outcomes. NPs produced by microfluidics were smaller than those prepared by the bulk method. The computational approach suggested that the size-determining factor in microfluidics is the boundary of solvents in the entrance region of the microchannel, explaining the size difference between the two experimental methods. Therefore, this computational approach can be a powerful tool to gain a deeper understanding and optimize NP synthesis. © 2021 The Authors. Published by American Chemical Society