Fabrication of well-ordered silicon nanopillars embedded in a microchannel : Via metal-assisted chemical etching: A route towards an opto-mechanical biosensor

Ordered nanopillars have been used as a smart configuration to design and fabricate localized surface plasmon resonance (LSPR) sensors. Importantly, these nanostructures can be integrated within microfluidic channels as a novel opportunity to enhance the response of biosensors and also to control the fluid flow by modifying the wettability surface of the walls. In this work, we demonstrate a large-scale and low-cost nanofabrication methodology that integrates the fabrication of silicon nanopillars (SiNPs) inside a microfluidic channel. The strategy is based on placing a catalytic gold layer patterned with nanoholes inside a SU-8 microchannel, by combining nanosphere lithography, reactive ion etching, and e-beam gold deposition, to control the area, separation distance and diameter of the nanostructures. The height of the SiNPs strongly depends on a well-controlled metal-assisted silicon etching protocol. We demonstrate experimentally that the design and the cleaning of the catalytic gold mesh using ultraviolet ozone strongly affect the etching rate for the formation of large-surface-area nanopillars. Our results explain the fast fabrication of hexagonal arrays of SiNPs embedded in a microfluidic channel with varying aspect ratio from 2 to 7 and separation of 300 nm and 400 nm, respectively, which has important implications for the achievement of new optomechanical biosensors

Building of a flexible microfluidic plasmo-nanomechanical biosensor for live cell analysis

Biosensor devices can constitute an advanced tool for monitoring and study complex dynamic biological processes, as for example cellular adhesion. Cellular adhesion is a multipart process with crucial implications in physiology (i.e. immune response, tissue nature, architecture maintenance, or behaviour and expansion of tumor cells). This work focuses on offering a controlled methodology in order to fabricate a flexible plasmo-nanomechanical biosensor placed within a microfluidic channel as a new tool for future cell adhesion studies. We designed, fabricated, and optically and mechanically characterized this novel optical biosensor. As a proof-of-concept of its functionality, the biosensor was employed to observe fibroblasts adhesion in a cell culture. The device is configured by an hexagonal array of flexible rigid/soft polymeric nanopillars capped with plasmonic gold nanodisks integrated inside a microfluidic channel. The fabrication employs low-cost and large-scale replica molding techniques using two different polymers materials (EPOTECK OG142 and 310 M). By using those materials the spring constant of the polymer nanopillars (k) can be fabricated from 1.19E-02 [N/m] to 5.35E+00 [N/m] indicating different mechanical sensitivities to shear stress. Therefore, the biosensor has the feasibility to mimic soft and rigid tissues important for the description of cellular nanoscale behaviours. The biosensor exhibits a suitable bulk sensitivity of 164 nm or 206 nm/refractive index unit respectively, depending on the base material. The range of calculated forces goes from ≈1.98 nN to ≈.942 μN. This supports that the plasmo-nanomechanical biosensors could be employed as novel tool to study living cells behavior

Tailored height gradients in vertical nanowire arrays via mechanical and electronic modulation of metal-assisted chemical etching

In current top-down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask-dependent material deposition or etching techniques, is usually uniform, and on-chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect-ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-fold on-chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how high aspect-ratio nanostructure arrays with directional height gradients can be accurately tailored by: i) control of mass transport through the nanohole array, ii) mechanical properties of the perforated metal layer, and iii) conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-­-fold on-­-chip variation of nanostructure height in a spatial range of a few microns, offers a new tool for the creation of novel types of nano-­-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics

Development of integrated plasmomechanical sensors in microfluidic devices for live cell analysis

Esta Tesis doctoral se centra en el diseño, estudio y optimización de una metodología controlada para la fabricación de un sensor flexible y plasmo-mecánico integrado con microfluídica, así como en su caracterización óptica y mecánica. Estamos interesados en el uso de este sensor para estudiar las fuerzas de tracción de las células por su papel esencial en las funciones celulares (por ejemplo, adhesión, supervivencia, migración, proliferación y diferenciación) y en el desarrollo de tejidos. Hoy en día, la monitorización y cuantificación de las fuerzas de tracción son uno de los desafíos que enfrenta la biología celular. Utilizamos las ventajas de los materiales poliméricos y las técnicas de nano-fabricación para crear un nuevo prototipo de sensor flexible de bajo coste y a gran escala. El sensor está formado por un arreglo hexagonal de nanopilares de polímero con nanodiscos plasmónicos de oro en su parte superior, ubicados dentro de un canal microfluídico. La fabricación del sensor se basa en las técnicas de réplica de estructuras. El diámetro, la altura y separación de los nanopilares están diseñados para ser copiados utilizando polímeros con un módulo de Young diferente, y de esta forma controlar su flexibilidad. Los discos plasmónicos de oro son depositados sobre los nanopilares utilizando evaporación de metales. Finalmente, la construcción del sensor integrado con microfluídica se basa en una estrategia de sellado permanente. La transducción utiliza la combinación de la flexibilidad mecánica de los nanopilares de polímeros con las propiedades ópticas de los nanodiscos de oro que presentan una resonancia de plasmón superficial localizada (LSPR). Los resultados obtenidos en esta Tesis sugieren que la combinación de la flexibilidad mecánica de los nanopilares de polímero con las propiedades ópticas de los nanodiscos de oro, permiten la monitorización de los cambios del índice de refracción del medio exterior. Las propiedades mecánicas (por ejemplo, la constante elástica) pueden utilizarse para controlar la estabilidad mecánica de las estructuras de polímero y para imitar las propiedades mecánicas de tejidos blandos o duros. Se llevó a cabo un análisis preliminar de un cultivo celular sobre los nanopilares como una prueba de concepto, para conocer las ventajas y los límites del nuevo sensor diseñado y del sistema de detección óptica. Los resultados mostraron que las células vivas pudieron adherirse e interactuar con los nanodiscos plasmónicos de los nanopilares con diferente rigidez, induciendo cambios detectables en el LSPR. El trabajo en esta Tesis representa un paso significativo hacia la implementación de nuevos sensores más eficaces para ser empleados en estudios básicos de biología celular, que podrían desempeñar un papel importante en la comprensión de procesos biológicos esenciales.This doctoral Thesis focuses on the design, study, and optimization of the controlled fabrication metodology of a flexible plasmo-mechanical sensor with microfluidics, as well as its optical and mechanical characterization. We are interested in the use of this sensor to study cell traction forces for its essential role in cell functions (e.g., adhesion, survival, migration, proliferation, and differentiation) and tissue development. Nowadays, the monitoring and quantification of those traction forces are one of the challenges faced by cell biology. We take advantage of the use of polymeric materials, and low-cost and large-scale nanofabrication techniques to create the new prototype sensor. The sensor is formed by a hexagonal array of polymeric nanopillars capped with plasmonic gold nanodisks into a microfluidic channel. The main strategy for the fabrication of the sensor is based on replica molding techniques. The diameter, height, and separation of the nanopillars are designed in order to replicate the structures using polymers with different Young’s modulus, and to control their mechanical flexibility.The plasmonic gold nanodisks are deposited on top of the nanopillars by controlled metal evaporation. Finally, the building of the integrated microfluidic sensor is based on a permanent bonding strategy. The transduction is based on combining the mechanical flexibility of the nanopillars with the optical properties of the gold nanodisks that exhibit localized surface plasmon resonances (LSPR). The results suggest that the combination of the mechanical flexibility of the polymer nanopillars with the optical properties of the gold nanodisks allow the monitoring of refractive index changes in the environment. The mechanical properties (e.g., spring constant) can be used to control the mechanical stability of the polymer structures, and also to mimic the mechanical properties of soft or rigid tissues. A preliminary analysis of cell culture onto the nanopillar array was carried out as a proof-of-concept to know the advantages and the limits of the new sensor design and the optical detection system. The results showed that the living cells could adhere and interact with the Au-capped nanopillars with different rigidity, inducing detectable LSPR changes. The work in this Thesis represents a significant step towards the implementation of novel and more efficient sensors for the study of cell biology, which could play a key role in the understanding of essential biological processes

Development of integrated plasmomechanical sensors in microfluidic devices for live cell analysis

Esta Tesis doctoral se centra en el diseño, estudio y optimización de una metodología controlada para la fabricación de un sensor flexible y plasmo-mecánico integrado con microfluídica, así como en su caracterización óptica y mecánica. Estamos interesados en el uso de este sensor para estudiar las fuerzas de tracción de las células por su papel esencial en las funciones celulares (por ejemplo, adhesión, supervivencia, migración, proliferación y diferenciación) y en el desarrollo de tejidos. Hoy en día, la monitorización y cuantificación de las fuerzas de tracción son uno de los desafíos que enfrenta la biología celular. Utilizamos las ventajas de los materiales poliméricos y las técnicas de nano-fabricación para crear un nuevo prototipo de sensor flexible de bajo coste y a gran escala. El sensor está formado por un arreglo hexagonal de nanopilares de polímero con nanodiscos plasmónicos de oro en su parte superior, ubicados dentro de un canal microfluídico. La fabricación del sensor se basa en las técnicas de réplica de estructuras. El diámetro, la altura y separación de los nanopilares están diseñados para ser copiados utilizando polímeros con un módulo de Young diferente, y de esta forma controlar su flexibilidad. Los discos plasmónicos de oro son depositados sobre los nanopilares utilizando evaporación de metales. Finalmente, la construcción del sensor integrado con microfluídica se basa en una estrategia de sellado permanente. La transducción utiliza la combinación de la flexibilidad mecánica de los nanopilares de polímeros con las propiedades ópticas de los nanodiscos de oro que presentan una resonancia de plasmón superficial localizada (LSPR). Los resultados obtenidos en esta Tesis sugieren que la combinación de la flexibilidad mecánica de los nanopilares de polímero con las propiedades ópticas de los nanodiscos de oro, permiten la monitorización de los cambios del índice de refracción del medio exterior. Las propiedades mecánicas (por ejemplo, la constante elástica) pueden utilizarse para controlar la estabilidad mecánica de las estructuras de polímero y para imitar las propiedades mecánicas de tejidos blandos o duros. Se llevó a cabo un análisis preliminar de un cultivo celular sobre los nanopilares como una prueba de concepto, para conocer las ventajas y los límites del nuevo sensor diseñado y del sistema de detección óptica. Los resultados mostraron que las células vivas pudieron adherirse e interactuar con los nanodiscos plasmónicos de los nanopilares con diferente rigidez, induciendo cambios detectables en el LSPR. El trabajo en esta Tesis representa un paso significativo hacia la implementación de nuevos sensores más eficaces para ser empleados en estudios básicos de biología celular, que podrían desempeñar un papel importante en la comprensión de procesos biológicos esenciales.This doctoral Thesis focuses on the design, study, and optimization of the controlled fabrication metodology of a flexible plasmo-mechanical sensor with microfluidics, as well as its optical and mechanical characterization. We are interested in the use of this sensor to study cell traction forces for its essential role in cell functions (e.g., adhesion, survival, migration, proliferation, and differentiation) and tissue development. Nowadays, the monitoring and quantification of those traction forces are one of the challenges faced by cell biology. We take advantage of the use of polymeric materials, and low-cost and large-scale nanofabrication techniques to create the new prototype sensor. The sensor is formed by a hexagonal array of polymeric nanopillars capped with plasmonic gold nanodisks into a microfluidic channel. The main strategy for the fabrication of the sensor is based on replica molding techniques. The diameter, height, and separation of the nanopillars are designed in order to replicate the structures using polymers with different Young’s modulus, and to control their mechanical flexibility.The plasmonic gold nanodisks are deposited on top of the nanopillars by controlled metal evaporation. Finally, the building of the integrated microfluidic sensor is based on a permanent bonding strategy. The transduction is based on combining the mechanical flexibility of the nanopillars with the optical properties of the gold nanodisks that exhibit localized surface plasmon resonances (LSPR). The results suggest that the combination of the mechanical flexibility of the polymer nanopillars with the optical properties of the gold nanodisks allow the monitoring of refractive index changes in the environment. The mechanical properties (e.g., spring constant) can be used to control the mechanical stability of the polymer structures, and also to mimic the mechanical properties of soft or rigid tissues. A preliminary analysis of cell culture onto the nanopillar array was carried out as a proof-of-concept to know the advantages and the limits of the new sensor design and the optical detection system. The results showed that the living cells could adhere and interact with the Au-capped nanopillars with different rigidity, inducing detectable LSPR changes. The work in this Thesis represents a significant step towards the implementation of novel and more efficient sensors for the study of cell biology, which could play a key role in the understanding of essential biological processes

Fabrication of well-ordered silicon nanopillars embedded in a microchannel : Via metal-assisted chemical etching: A route towards an opto-mechanical biosensor

Ordered nanopillars have been used as a smart configuration to design and fabricate localized surface plasmon resonance (LSPR) sensors. Importantly, these nanostructures can be integrated within microfluidic channels as a novel opportunity to enhance the response of biosensors and also to control the fluid flow by modifying the wettability surface of the walls. In this work, we demonstrate a large-scale and low-cost nanofabrication methodology that integrates the fabrication of silicon nanopillars (SiNPs) inside a microfluidic channel. The strategy is based on placing a catalytic gold layer patterned with nanoholes inside a SU-8 microchannel, by combining nanosphere lithography, reactive ion etching, and e-beam gold deposition, to control the area, separation distance and diameter of the nanostructures. The height of the SiNPs strongly depends on a well-controlled metal-assisted silicon etching protocol. We demonstrate experimentally that the design and the cleaning of the catalytic gold mesh using ultraviolet ozone strongly affect the etching rate for the formation of large-surface-area nanopillars. Our results explain the fast fabrication of hexagonal arrays of SiNPs embedded in a microfluidic channel with varying aspect ratio from 2 to 7 and separation of 300 nm and 400 nm, respectively, which has important implications for the achievement of new optomechanical biosensors

Development of integrated plasmomechanical sensors in microfluidic devices for live cell analysis /

BibliografiaEsta Tesis doctoral se centra en el diseño, estudio y optimización de una metodología controlada para la fabricación de un sensor flexible y plasmo-mecánico integrado con microfluídica, así como en su caracterización óptica y mecánica. Estamos interesados en el uso de este sensor para estudiar las fuerzas de tracción de las células por su papel esencial en las funciones celulares (por ejemplo, adhesión, supervivencia, migración, proliferación y diferenciación) y en el desarrollo de tejidos. Hoy en día, la monitorización y cuantificación de las fuerzas de tracción son uno de los desafíos que enfrenta la biología celular. Utilizamos las ventajas de los materiales poliméricos y las técnicas de nano-fabricación para crear un nuevo prototipo de sensor flexible de bajo coste y a gran escala. El sensor está formado por un arreglo hexagonal de nanopilares de polímero con nanodiscos plasmónicos de oro en su parte superior, ubicados dentro de un canal microfluídico. La fabricación del sensor se basa en las técnicas de réplica de estructuras. El diámetro, la altura y separación de los nanopilares están diseñados para ser copiados utilizando polímeros con un módulo de Young diferente, y de esta forma controlar su flexibilidad. Los discos plasmónicos de oro son depositados sobre los nanopilares utilizando evaporación de metales. Finalmente, la construcción del sensor integrado con microfluídica se basa en una estrategia de sellado permanente. La transducción utiliza la combinación de la flexibilidad mecánica de los nanopilares de polímeros con las propiedades ópticas de los nanodiscos de oro que presentan una resonancia de plasmón superficial localizada (LSPR). Los resultados obtenidos en esta Tesis sugieren que la combinación de la flexibilidad mecánica de los nanopilares de polímero con las propiedades ópticas de los nanodiscos de oro, permiten la monitorización de los cambios del índice de refracción del medio exterior. Las propiedades mecánicas (por ejemplo, la constante elástica) pueden utilizarse para controlar la estabilidad mecánica de las estructuras de polímero y para imitar las propiedades mecánicas de tejidos blandos o duros. Se llevó a cabo un análisis preliminar de un cultivo celular sobre los nanopilares como una prueba de concepto, para conocer las ventajas y los límites del nuevo sensor diseñado y del sistema de detección óptica. Los resultados mostraron que las células vivas pudieron adherirse e interactuar con los nanodiscos plasmónicos de los nanopilares con diferente rigidez, induciendo cambios detectables en el LSPR. El trabajo en esta Tesis representa un paso significativo hacia la implementación de nuevos sensores más eficaces para ser empleados en estudios básicos de biología celular, que podrían desempeñar un papel importante en la comprensión de procesos biológicos esenciales.This doctoral Thesis focuses on the design, study, and optimization of the controlled fabrication metodology of a flexible plasmo-mechanical sensor with microfluidics, as well as its optical and mechanical characterization. We are interested in the use of this sensor to study cell traction forces for its essential role in cell functions (e.g., adhesion, survival, migration, proliferation, and differentiation) and tissue development. Nowadays, the monitoring and quantification of those traction forces are one of the challenges faced by cell biology. We take advantage of the use of polymeric materials, and low-cost and large-scale nanofabrication techniques to create the new prototype sensor. The sensor is formed by a hexagonal array of polymeric nanopillars capped with plasmonic gold nanodisks into a microfluidic channel. The main strategy for the fabrication of the sensor is based on replica molding techniques. The diameter, height, and separation of the nanopillars are designed in order to replicate the structures using polymers with different Young's modulus, and to control their mechanical flexibility.The plasmonic gold nanodisks are deposited on top of the nanopillars by controlled metal evaporation. Finally, the building of the integrated microfluidic sensor is based on a permanent bonding strategy. The transduction is based on combining the mechanical flexibility of the nanopillars with the optical properties of the gold nanodisks that exhibit localized surface plasmon resonances (LSPR). The results suggest that the combination of the mechanical flexibility of the polymer nanopillars with the optical properties of the gold nanodisks allow the monitoring of refractive index changes in the environment. The mechanical properties (e.g., spring constant) can be used to control the mechanical stability of the polymer structures, and also to mimic the mechanical properties of soft or rigid tissues. A preliminary analysis of cell culture onto the nanopillar array was carried out as a proof-of-concept to know the advantages and the limits of the new sensor design and the optical detection system. The results showed that the living cells could adhere and interact with the Au-capped nanopillars with different rigidity, inducing detectable LSPR changes. The work in this Thesis represents a significant step towards the implementation of novel and more efficient sensors for the study of cell biology, which could play a key role in the understanding of essential biological processes

Tailored height gradients in vertical nanowire arrays via mechanical and electronic modulation of metal-assisted chemical etching

In current top-down nanofabrication methodologies the design freedom is generally constrained to the two lateral dimensions, and is only limited by the resolution of the employed nanolithographic technique. However, nanostructure height, which relies on certain mask-dependent material deposition or etching techniques, is usually uniform, and on-chip variation of this parameter is difficult and generally limited to very simple patterns. Herein, a novel nanofabrication methodology is presented, which enables the generation of high aspect-ratio nanostructure arrays with height gradients in arbitrary directions by a single and fast etching process. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how nanostructure arrays with directional height gradients can be accurately tailored by: (i) the control of the mass transport through the nanohole array, (ii) the mechanical properties of the perforated metal layer, and (iii) the conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-fold on-chip variation of nanostructure height in a spatial range of a few micrometers, offers a new tool for the creation of novel types of nano-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics. Based on metal-assisted chemical etching using a catalytic gold layer perforated with nanoholes, it is demonstrated how high aspect-ratio nanostructure arrays with directional height gradients can be accurately tailored by: i) control of mass transport through the nanohole array, ii) mechanical properties of the perforated metal layer, and iii) conductive coupling to the surrounding gold film to accelerate the local electrochemical etching process. The proposed technique, enabling 20-­-fold on-­-chip variation of nanostructure height in a spatial range of a few microns, offers a new tool for the creation of novel types of nano-­-assemblies and metamaterials with interesting technological applications in fields such as nanophotonics, nanophononics, microfluidics or biomechanics