Name: thermal measurement techniques in analytical microfluidic devices
Uploaded: 2015-06-03T13:00:00.000+00:00
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Description: Watch this Scientific Journal Video about Thermal Measurement Techniques in Analytical Microfluidic Devices at JoVE.com

Apoyo financiero parcial de este trabajo fue proporcionado por la Fundación Nacional de Ciencia de Estados Unidos a través del Centro de Investigación Cooperativa Industria / Universidad de Equipos y Política ubicado en la Universidad de Wisconsin-Milwaukee (PII-0968887) y la Universidad de Marquette (PII-0968844) de agua. Damos las gracias a Glenn M. Walker, Woo-Jin Chang y Shankar Radhakrishnan útil para los debates.

1. Detección de partículas térmica (TPD) <ol><li> Prepare el dispositivo de silicio micro-fabricada con una membrana de nitruro de silicio de película delgada y el sensor de temperatura integrado por micromecanizado, utilizando la tecnología de proceso de semiconductores estándar 2. Enjuague el dispositivo fabricado con desionizada (DI). Nota: El método de fabricación para el detector de partículas térmica dispositivo de microfluidos se explica en la publicación antes 2. </li><li> Para producir polidimetilsiloxano (PDMS) sustratos con micro-canales, crear un molde de SU8 utilizando litografía estándar procesa 5. Nota: El tamaño del canal está diseñado para la dimensión de cada partícula específico. <ol><li> Hacer PDMS mezclando una proporción de 10: 1 de base (30 ml) y agente (3 ml) curar. Verter el PDMS en el molde y eliminar las burbujas exponiendo brevemente a un vacío (5-10 min). Nota: El nivel de vacío no es un valor fundamental para la desgasificación y debe continuar hasta bubb gasles son retirados totalmente de PDMS mixtos. </li><li> Colocar el molde sobre una placa caliente (~ 70 ° C) durante 2 horas para curar los PDMS. Luego pelar los PDMS con mucho cuidado a fin de no dañar el molde. Nota: El nivel de vacío no es un valor crítico. </li></ol></li><li> Con un punzón manual, perforar un agujero apretado (1 mm) para el tubo de PTFE en un extremo. Utilizar una gran punzón (2 mm) en el otro extremo para hacer los PDMS un depósito. Coloque el micro-canal perforado en la parte superior del dispositivo bajo el microscopio y alinear el RTD en el centro de la micro-canal (Figura 1A). </li><li> En la interfaz eléctrica, conecte las clavijas eléctricas en las posiciones de la almohadilla de contacto y apriete los tornillos de bloqueo. Asegúrese de que los pasadores de altura regulable (pines Pogo) se sientan en los electrodos correctos en el dispositivo. </li><li> Diluir 10 l de las perlas de PS concentradas en 100 l de agua DI en un tubo de 1,5 ml. </li><li> Para garantizar la PS cuentas permanecen flotabilidad neutra, añadir 2,7 l de glicerol (1,26g / cm 3) a agua DI para que coincida con la densidad del fluido para el poliestireno (PS) densidad talón (1,05 g / cm 3). </li><li> Conectar el tubo de PTFE al canal en un extremo y el otro extremo a una jeringa de vidrio de 1 ml. Llene la jeringa de vidrio con 0,5 ml de agua DI. Nota: Apretada hecho seleccionando el tamaño puño derecho evitará fugas en los tubos. </li><li> Coloque el agua DI llena la jeringa en la bomba de jeringa controlada por ordenador. Empuje el agua (5-20 l / min) en el canal para llenar todo el canal de líquido todo el camino hasta el depósito. </li><li> Cargar 10 l de solución de grano equilibrada al depósito e introducir la solución de talón a la micro-canal cambiando la dirección del flujo en la bomba de jeringa. </li><li> Encienda el RTD polarizando 1 mA de corriente continua a través de la fuente / metro controlado por ordenador, mientras que la medición de la resistencia de fuente / metro y clasificación de los datos medidos (Figura 2). Nota: Durante el experimento, el sensor es sesgada; Por lo tanto, la temperatura se mide continuamente hasta el final del experimento de recuento. El sensor RTD está sesgada eléctricamente mediante la aplicación de una corriente continua en el intervalo de 100 mu a 1 mA para medir continuamente la temperatura hasta el final del experimento de recuento. Es crítico para seleccionar el nivel de corriente adecuado ya que hay un equilibrio entre el nivel de ruido y de la amplitud de la señal detectada. La bomba de jeringa se utiliza para generar el flujo en micro-canal. Selección de un caudal adecuado para llevar a cabo el experimento TPD se limita a la velocidad de la medición. Esta velocidad es una función de la constante de tiempo térmica del dispositivo y la velocidad de medición eléctrica. Los resultados de la detección de partículas térmica experimento se muestran en la Figura 3. </li><li> Utilice el software de procesamiento de datos desarrollado (LabVIEW) para convertir los datos de resistencia medidos a temperatura usando la ecuación de Callendar-Van Dusen 6. </li></ol> 2. térmicaCaracterización de sustancias líquidas Utilizando un micro-calorímetro <ol><li> En este proceso, utilizar el dispositivo en el chip calorímetro (Figura 4A) 3 para medir la difusividad térmica y el calor específico de las muestras. Nota: En cada dado, hay 2 cámaras de micro-calorímetro (Figura 4B). Cada cámara tiene 2 entradas y una salida. Y cada cámara tiene un calentador y un sensor RTD integrado. </li><li> Coloque el dispositivo de micro-calorímetro en el soporte del dispositivo (Figura 4C). Alinear el dispositivo a las entradas y salidas de microfluidos con los accesorios de soporte. Coloque la capa de sellado PDMS en la parte superior del dispositivo. </li><li> Instale los pasadores de conexión eléctrica en el soporte de dispositivo y bloquear los tornillos titular. Nota: Asegúrese de que los pasadores de Pogo de altura ajustable están alineados con las almohadillas de contacto eléctrico. </li><li> Instale la capa de interfaz de microfluidos con cierres magnéticos a la titular del dispositivo (Figura 4D). Conecte el PTFE tubos para ambas entradas y la salida. Conectar una entrada a la bomba de jeringa de la muestra cargada y cerrar el otro, como la entalpía no se mide en este caso. </li><li> Utilice un programa controlado por ordenador desarrollado para cargar la muestra en el micro-canales y cámaras. Nota: El programa utilizará flujo discontinuada para liberar la presión excesiva en la cámara suspendida de película delgada. <ol><li> Cargue la muestra 300 l en la jeringa de vidrio y colocarlo en la bomba de jeringa. Utilice velocidades de flujo muy lento (0,25 l / min) constantes para muestras de alta viscosidad (por ejemplo, glicerol y líquidos iónicos). Utilice una muestra de glicerina para las mediciones de difusividad térmica y líquidos iónicos para mediciones de calor específico. </li></ol></li><li> Mediciones <ol><li> Mediciones de difusividad térmicas <ol><li> Conectar la configuración de las mediciones como se muestra en la Figura 5A. Cargue la muestra de glicerina a la cámara de micro-calorímetro. Ejecute el programa controlado por ordenador modificado para hea<html> t penetración de la medición del tiempo. </li><li> Utilice la ecuación de penetración del calor calibrado para calcular la difusividad térmica del tiempo de penetración de calor medido 7: <img alt="Ecuación 1" src="/files/ftp_upload/52828/52828eq1.jpg" width="100" /> donde α es la difusividad térmica, L es el espesor de la cámara, p es el factor de calibración de espesor debido a la variación del proceso de fabricación, y t 0 es el tiempo de penetración de calor. </li></ol></li><li> Mediciones de calor específico <ol><li> Utilice la configuración de la medición TWA como se muestra en la Figura 5B. Utilice el mismo programa de ejemplo de carga y cargar el líquido iónico en la cámara. Ejecutar el programa de TWA para obtener la amplitud de las fluctuaciones de temperatura de corriente alterna (AC ∂ T) y el uso de la ecuación del calor específico para calcular el específico, c p, de calor para cada muestra de líquido iónico 8: 28eq2.jpg &quot;width =&quot; 117 &quot;/&gt; donde C 0 es el factor de calibración de la potencia de entrada, en P es la potencia de entrada, ω es la frecuencia de la señal de accionamiento, y m es la masa de la muestra de líquido. </li></ol></li></ol></li></ol> 3. calorimétrico detección bioquímica en base de papel de dispositivos de microfluidos <ol><li> Utilice microfabricado película delgada (40-50 nm níquel) sensor RTD. Pasos de fabricación para el sensor RTD se explican en trabajos anteriores 4. </li><li> Para en papel canal fabricación 4, use un plotter cuchillo para cortar el papel canales de microfluidos con un patrón diseñado (en forma de L). Coloque el papel en la parte superior de la base de corte, cargue el papel y la estera de corte para el plotter de cuchillo, y el uso de la receta adecuada para cortar los canales de microfluidos en papel 4. </li><li> Para el dispositivo y el canal de integración, utilice una capa de adhesivo acrílico (5 micras) para integrar el papel sobre el sensor RTD. Use un b limpialade para empujar el papel para el dispositivo y eliminar las burbujas de aire (Figura 6A). La película acrílica es una capa adhesiva para sujetar el papel sobre el sensor RTD. </li><li> Para la activación de la enzima, utilice tampón de acetato de sodio 50 mM para activar la enzima GOD. Añadir 1 mg de la enzima GOD a 1 ml de tampón de acetato de sodio para hacer la solución 1 mg / ml. Ajustar el pH de la solución a 5,1. Nota: Ajuste la cantidad de ácido acético en el tampón de acetato de sodio para mantener el pH de la solución de 5,1. </li><li> Sesgo del RTD con 1 mA de corriente DC para activar el IDT y empezar a medir la fuente de resistencia / metro continuamente mientras que la resistencia se establece después del experimento (~ 4 min). Nota: La Figura 6B muestra la configuración de la medición para el ensayo colorimétrico basado en papel. </li><li> Introducir los 2 l de la solución DIOS preparado para el centro del papel de micro-canales (sitio inmovilización) a través de la pipeta. La temperatura detectada (Figura 7A) debe empezar to disminuir. Nota: Este efecto de enfriamiento es debido a la temperatura más alta de la operación de RTD y la evaporación de la muestra juntos. </li><li> Para medir la concentración de glucosa, introducir la solución de control estándar de glucosa 9 a la entrada del canal y medir el cambio de resistencia causado por la reacción. Repita este experimento con todas las soluciones de control de glucosa diferentes (alta, normal y baja concentración) y guardar los datos de resistencia. </li><li> Utilizando el coeficiente de temperatura de resistencia (TCR) para RTD de níquel y la ecuación Callendar-Van Dusen, convertir el cambio de resistencia a la temperatura. Calcular la concentración de la glucosa en cada muestra considerando la entalpía de reacción de la glucosa y la enzima GOD (Δ H = -80 kJ / mol) y usando la ecuación de concentración 10: <img alt="Ecuación 3" src="/files/ftp_upload/52828/52828eq3.jpg" width="83" /> donde se detecta n p concentración molar, C <sub&gt; P es la capacidad de calor del sistema y Delta T se calcula la temperatura. </li></ol>

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	<li>Zhang, H., Chon, C., Pan, X., Li, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+counting+particles+in+microfluidic+applications.">Methods for counting particles in microfluidic applications.</a> Microfluid Nanofluid. 7 (6), 739-749 (2009).</li><li>Vutha, A. K., Davaji, B., Lee, C. H., Walker, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microfluidic+device+for+thermal+particle+detection.">A microfluidic device for thermal particle detection.</a> Microfluid Nanofluid. 17 (5), 871-878 (2014).</li><li>Davaji, B., Bak, H. J., Chang, W. J., Lee, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Novel+On-chip+Three-dimensional+Micromachined+Calorimeter+with+Fully+Enclosed+and+Suspended+Thin-film+Chamber+for+Thermal+Characterization+of+Liquid+Samples.">A Novel On-chip Three-dimensional Micromachined Calorimeter with Fully Enclosed and Suspended Thin-film Chamber for Thermal Characterization of Liquid Samples.</a> Biomicrofluidics. 8 (3), 034101-034113 (2014).</li><li>Davaji, B., Lee, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+paper-based+calorimetric+microfluidics+platform+for+bio-chemical+sensing.">A paper-based calorimetric microfluidics platform for bio-chemical sensing.</a> Biosens. Bioelectron. 59, 120-126 (2014).</li><li>Liu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Process+research+of+high+aspect+ratio+microstructure+using+SU-8+resist.">Process research of high aspect ratio microstructure using SU-8 resist.</a> Microsystem Technologies. 10, 265-268 (2004).</li><li>Dusen, M. S. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platinum-resistance+thermometry+at+low+temperatures.">Platinum-resistance thermometry at low temperatures.</a> J. Am. Chem. Soc. 47 (2), 326-332 (1925).</li><li>Arpaci, V. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Conduction Heat Transfer. , (1966).</li><li>Garden, J. L., Chteau, E., Chaussy, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+sensitive+ac+nanocalorimeter+for+microliter-scale+liquids+or+biological+samples.">Highly sensitive ac nanocalorimeter for microliter-scale liquids or biological samples.</a> Appl. Phys. Lett. 84, 3597-3599 (2004).</li><li>Kilo, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+a+New+Blood+Glucose+Monitoring+System+with+Auto-Calibration.">Evaluation of a New Blood Glucose Monitoring System with Auto-Calibration.</a> Diabetes Technol. Ther. 7 (2), 283-294 (2005).</li><li>Scheper, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thermal Biosensors Bioactivity Bioaffinity (Advances in Biochemical Engineering/Biotechnology). , (1999).</li></ol>

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Different thermal measurement techniques in microfluidic devices and their respective setup procedures are presented in this work. These thermal measurement methods such as thermal conductivity monitoring, thermal penetration time, amplitude of AC thermal fluctuations, and amplitude measurement of the generated heat are used to detect specific substances and investigate different reactions and interactions. 
The thermal time constant plays a key role in the aforementioned thermal measurement t...

Tres técnicas de medición térmicos micro-escala diferente se presentan en este artículo. Las tres configuraciones diferentes de dispositivos de microfluidos se utilizan para la detección térmica de partículas (TPD), la caracterización térmica (conductividad térmica y calor específico), y la detección colorimétrica de las reacciones químicas y las interacciones. Detección de partículas térmica Detectar y contar las partículas en dispositivos de microfluidos se utiliza ampliamente para aplicaciones medioambientales, industriales y biológicos 1. TPD es una de las aplicaciones novedosas de mediciones térmicas en dispositivos de microfluidos 2. El uso de transferencia de calor para detectar y contar las partículas basadas en el tamaño de las partículas reduce la complejidad, costo y tamaño del sistema. En otros métodos, la óptica complejos o mediciones eléctricas complejas y software avanzado de procesamiento de señales se utilizan para la detección de partículas. Chara térmicacterization de sustancias líquidas Utilizando Micro-Calorímetro Liquid caracterización térmica de la muestra es la segunda aplicación de medición térmica en dispositivos de microfluidos. Realización de calorimetría microescala reducirá el consumo de muestra y aumentar la precisión, ofreciendo mayor repetibilidad en comparación con los métodos convencionales de calorimetría, a granel. Los procedimientos para la medición de la conductividad térmica y calor específico utilizando el dispositivo de micro-calorímetro en el chip se presentan en otras partes 3. Los detalles de la técnica de tiempo de penetración de calor para la medición de la conductividad térmica y el análisis de la onda térmica (TWA) para las mediciones de calor específico en dispositivos de microfluidos se describen en la sección de protocolo. Dispositivo de microfluidos Basado en Papel calorimétrico Bio-Química Detección en Otra aplicación de medición térmica es la detección bioquímica en la microfluídica basados ​​en papel. La acción capilar en elestructura porosa de papel lleva el líquido y evita los problemas de iniciación de burbujas en microcanales. Los mecanismos de detección más comunes en los dispositivos de microfluidos en papel son técnicas ópticas o electroquímicas. Detección óptica sufre de alta complejidad y la necesidad de software avanzado procesamiento de imágenes para cuantizar la señal detectada. Detecciones electroquímicos también están limitados debido a que sólo se pueden aplicar a las reacciones que producen subproductos activos. La plataforma recientemente introducido calorimétrico basado en papel sensor bioquímico 4 toma ventaja del sistema de microfluidos basado en papel y el mecanismo de detección térmica de la etiqueta libre. Los procedimientos de detección calorimétrica de la glucosa utilizando glucosa oxidasa (GOD) enzima en una plataforma de microfluidos basado en papel se presentan en la sección de protocolo. El objetivo de este trabajo es demostrar las capacidades de las técnicas de medición térmica en dispositivos de microfluidos. El preparatio dispositivon, muestra de líquido detector de manejo y resistencia a la temperatura (RTD) de excitación del sensor y la medición se presentan en las siguientes secciones.

<table><tbody><tr><td>Polydimethylsiloxane (PDMS)&amp;nbsp;</td><td>Dow Corning</td><td>Sylgard 184</td><td></td></tr><tr><td>PS beads - 90 &amp;#956;m</td><td>Corpuscular</td><td>100265</td><td></td></tr><tr><td>PS beads - 200 &amp;#956;m</td><td>Corpuscular</td><td>100271</td><td></td></tr><tr><td>Glycerol</td><td>SigmaAldrich</td><td>G5516</td><td></td></tr><tr><td>GOD enzyme</td><td>SigmaAldrich</td><td>G7141</td><td></td></tr><tr><td>Glucose Control Solution - Low</td><td>Bayer contour</td><td>Low Control</td><td></td></tr><tr><td>Glucose Control Solution - Normal</td><td>Bayer contour</td><td>Normal Control</td><td></td></tr><tr><td>Glucose Control Solution - High</td><td>Bayer contour</td><td>High Control</td><td></td></tr><tr><td>Chromatography filter paper</td><td>Whatman</td><td>3001-845</td><td></td></tr><tr><td>Glass</td><td>VWR&amp;nbsp;</td><td>48393-106</td><td></td></tr><tr><td>Acrylic Film</td><td>Nitto Denko</td><td>5600</td><td></td></tr><tr><td>Glass syringe (1 ml)</td><td>Hamilton</td><td>1001</td><td></td></tr><tr><td>Syringe pump</td><td>New Era</td><td>NE-500</td><td></td></tr><tr><td>knife plotter</td><td>Silhouette</td><td>portrait</td><td></td></tr><tr><td>Current Preamplifier</td><td>Stanford Research</td><td>SR-570</td><td></td></tr><tr><td>Ocilloscope</td><td>Agilent</td><td>DSO 2420A</td><td></td></tr><tr><td>Signal Generator</td><td>HP</td><td>HP3324A</td><td></td></tr><tr><td>Lock-in Amplifire</td><td>Stanford Research</td><td>SRS-830</td><td></td></tr><tr><td>Source/meter 2400</td><td>Keithley</td><td>2400</td><td></td></tr><tr><td>Source/meter 2600</td><td>Keithley</td><td>2436A</td><td></td></tr></tbody></table>

thermal measurement techniques in analytical microfluidic devices

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. Micromachining techniques allow reduction of the thermal mass of fabricated structures and introduce the possibility to perform high sensitivity thermal measurements in the micro-scale and nano-scale devices. Combining thermal measurement techniques with microfluidic devices allows performing different analytical measurements with low sample consumption and reduced measurement time by integrating the miniaturized system on a single chip. The procedures of thermal measurement techniques for particle detection, material characterization, and chemical detection are introduced in this paper.

La Figura 3 muestra la trama de la señal térmica medido. Las señales generadas en la presencia de las perlas con imágenes ópticas correspondientes muestran la detección exitosa de las perlas de PS de microesferas en la micro-canal. La conductividad térmica del líquido que pasa a través de la micro-canal está cambiando debido a la presencia de perlas de PS. Este cambio en la conductividad térmica del canal está afectando a la transferencia de calor en el micro-canal. El cambio en la transfere...

Watch this Scientific Journal Video about Thermal Measurement Techniques in Analytical Microfluidic Devices at JoVE.com

Thermal Measurement Techniques in Analytical Microfluidic Devices

Here, we present three protocols for thermal measurements in microfluidic devices.

Técnicas de medición Térmicas en analíticas de microfluidos Dispositivos

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. ...

thermal-measurement-techniques-in-analytical-microfluidic-devices

Universidad San Sebastian

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Engineering

9.6K vistas.  Marquette University. Here, we present three protocols for thermal measurements in microfluidic devices. 

Video: Thermal Measurement Techniques in Analytical Microfluidic Devices

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators 1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.
Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides 3, asymmetric split-ring resonators 4, and photonic band gap structures integrated into parallel-plate waveguides 5. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.
The sensor design we use here is based on a simple parallel-plate waveguide 6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE1) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove 6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index 9.
Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves 10. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.

The procedure for implementing a refractive index sensor for terahertz frequencies based on a grooved parallel-plate waveguide geometry is described here. The method yields a measurement of the refractive index of a small volume of liquid through monitoring of the shift in the resonant frequency of the waveguide structure

Terahertz microfluídicos detección utilizando un sensor de guía de ondas de placas paralelas

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic ...

Investigación

Ingeniería

Fluorescence detection methods for microfluidic droplet platforms

The development of microfluidic platforms for performing chemistry and biology has in large part been driven by a range of potential benefits that accompany system miniaturisation. Advantages include the ability to efficiently process nano- to femoto- liter volumes of sample, facile integration of functional components, an intrinsic predisposition towards large-scale multiplexing, enhanced analytical throughput, improved control and reduced instrumental footprints.1
In recent years much interest has focussed on the development of droplet-based (or segmented flow) microfluidic systems and their potential as platforms in high-throughput experimentation.2-4 Here water-in-oil emulsions are made to spontaneously form in microfluidic channels as a result of capillary instabilities between the two immiscible phases. Importantly, microdroplets of precisely defined volumes and compositions can be generated at frequencies of several kHz. Furthermore, by encapsulating reagents of interest within isolated compartments separated by a continuous immiscible phase, both sample cross-talk and dispersion (diffusion- and Taylor-based) can be eliminated, which leads to minimal cross-contamination and the ability to time analytical processes with great accuracy. Additionally, since there is no contact between the contents of the droplets and the channel walls (which are wetted by the continuous phase) absorption and loss of reagents on the channel walls is prevented.
Once droplets of this kind have been generated and processed, it is necessary to extract the required analytical information. In this respect the detection method of choice should be rapid, provide high-sensitivity and low limits of detection, be applicable to a range of molecular species, be non-destructive and be able to be integrated with microfluidic devices in a facile manner. To address this need we have developed a suite of experimental tools and protocols that enable the extraction of large amounts of photophysical information from small-volume environments, and are applicable to the analysis of a wide range of physical, chemical and biological parameters. Herein two examples of these methods are presented and applied to the detection of single cells and the mapping of mixing processes inside picoliter-volume droplets. We report the entire experimental process including microfluidic chip fabrication, the optical setup and the process of droplet generation and detection.

Droplet-based microfluidic platforms are promising candidates for high throughput experimentation since they are able to generate picoliter, self-compartmentalized vessels inexpensively at kHz rates. Through integration with fast, sensitive and high resolution fluorescence spectroscopic methods, the large amounts of information generated within these systems can be efficiently extracted, harnessed and utilized.

Métodos de detección de fluorescencia para las plataformas de las gotas de microfluidos

The development of microfluidic platforms for performing chemistry and biology has in large part been driven by a range of potential benefits that ...

Bioingeniería

Fiber Optic Distributed Sensors for High-resolution Temperature Field Mapping

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists chiefly of velocity and temperature readings, both ideally having high spatial and temporal resolution to facilitate rigorous code validation. While high resolution velocity data is readily obtained through optical measurement techniques such as particle image velocimetry, it has proven difficult to obtain temperature data with similar resolution. Traditional sensors such as thermocouples cannot fill this role, but the recent development of distributed sensing based on Rayleigh scattering and swept-wave interferometry offers resolution suitable for CFD code validation work. Thousands of temperature measurements can be generated along a single thin optical fiber at hundreds of Hertz. Sensors function over large temperature ranges and within opaque fluids where optical techniques are unsuitable. But this type of sensor is sensitive to strain and humidity as well as temperature and so accuracy is affected by handling, vibration, and shifts in relative humidity. Such behavior is quite unlike traditional sensors and so unconventional installation and operating procedures are necessary to ensure accurate measurements. This paper demonstrates implementation of a Rayleigh scattering-type distributed temperature sensor in a thermal mixing experiment involving two air jets at 25 and 45 &#176;C. We present criteria to guide selection of optical fiber for the sensor and describe installation setup for a jet mixing experiment. We illustrate sensor baselining, which links readings to an absolute temperature standard, and discuss practical issues such as errors due to flow-induced vibration. This material can aid those interested in temperature measurements having high data density and bandwidth for fluid dynamics experiments and similar applications. We highlight pitfalls specific to these sensors for consideration in experiment design and operation.

We demonstrate use of a fiber optic distributed sensor for mapping the temperature field of mixing air jets. The Rayleigh scattering-based sensor generates thousands of data points along a single fiber to provide exceptional spatial resolution that is unattainable with traditional sensors such as thermocouples.

De fibra óptica para sensores distribuidos de alta resolución de mapeo de temperatura Campo

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists ...

High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging techniques.
The one-time use packaging technique employs UV-based and temperature curing epoxies to connect microtubes to access holes, wire-bonding for integrated circuit connections, and silver epoxy for electrical connections. This method is based on a robust assembly technique that can support relatively high pressure close to 1 psi and does not need any support to strengthen the microfluidic architecture.
Reusable packaging techniques consist of PDMS-based microtube interconnectors and anisotropic adhesive films for electrical connections. These devices are more sensitive and fragile. Consequently, Plexiglas support is added to the microfluidic structure to improve the electrical contact when anisotropic adhesive films are used, and also to strengthen the microfluidic architecture. In addition, a micromanipulator is needed to maintain tubes while using a thin PDMS layer to connect them to the access holes. Different PDMS layer thicknesses, ranging from 0.45-3 mm, are tested to compare the best adherence versus injection rates. Applied injection rates are varied from 50-300 &#956;l/hr for 0.45-3 mm PDMS layers, respectively. These techniques are mainly applicable for low-pressure applications. However, they can be extended for high-pressure ones through plasma-oxygen process to permanently seal the PDMS to glass substrates. The main advantage of this technique, besides the fact that it is reusable, consists of keeping the device observable when the microchannel length is very short (in the range of 3 mm or lower).

In this article we describe different techniques for microfluidic rapid prototyping platforms. The proposed techniques are based on ultraviolet (UV) sensitive and temperature curing epoxies, polydimethylsiloxane (PDMS) based tubing, wire-bonding, and anisotropic adhesive films. The assembling procedures presented are developed for both one-time use devices as well as reusable microfluidic systems.

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

Fabricación y pruebas de termómetros fotónicos

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Química

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This technique utilizes wavelengths of 1150 and 1412 nm, at which the absorption coefficient of water is dependent on temperature. Water or a non-turbid aqueous gel containing a 2.0-mm- or 0.5-mm-diameter magnetic sphere is irradiated with 1150 nm or 1412 nm incident light, as selected using a narrow bandpass filter; additionally, two-dimensional absorbance images, which are the transverse projections of the absorption coefficient, are acquired via a near-infrared camera. When the three-dimensional distributions of temperature can be assumed to be spherically symmetric, they are estimated by applying inverse Abel transforms to the absorbance profiles. The temperatures were observed to consistently change according to time and the induction heating power.

A technique utilizing wavelengths of 1150 and 1412 nm to measure the temperature of water surrounding an induction-heated small magnetic sphere is presented.

Técnica de medición de temperatura infrarroja para el agua que rodea una esfera magnética pequeño calentado por inducción

A technique to measure the temperature of water and non-turbid aqueous media surrounding an induction-heated small magnetic sphere is presented. This ...

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

Mediciones de transferencia de calor convectivo instantánea Local en una pipa - flujo bifásico y solo

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index1-3. The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a two-dimensional projection of the disturbed light produced by three-dimensional inhomogeneity.
To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator4. For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process.

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

Analizando Mezcla falta de homogeneidad en un dispositivo de microfluidos por Microscale Schlieren Técnica

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

A Microfluidic Device for Quantifying Bacterial Chemotaxis in Stable Concentration Gradients

Chemotaxis allows bacteria to approach sources of attractant chemicals or to avoid sources of repellent chemicals. Bacteria constantly monitor the concentration of specific chemoeffectors by comparing the current concentration to the concentration detected a few seconds earlier. This comparison determines the net direction of movement. Although multiple, competing gradients often coexist in nature, conventional approaches for investigating bacterial chemotaxis are suboptimal for quantifying migration in response to concentration gradients of attractants and repellents. Here, we describe the development of a microfluidic chemotaxis model for presenting precise and stable concentration gradients of chemoeffectors to bacteria and quantitatively investigating their response to the applied gradient. The device is versatile in that concentration gradients of any desired absolute concentration and gradient strength can be easily generated by diffusive mixing. The device is demonstrated using the response of Escherichia coli RP437 to gradients of amino acids and nickel ions.

This protocol describes the development of a microfluidic device for investigating bacterial chemotaxis in stable concentration gradients of chemoeffectors.

Un dispositivo de microfluidos para la cuantificación de la quimiotaxis bacteriana en gradientes de concentración estable

Chemotaxis allows bacteria to approach sources of attractant chemicals or to avoid sources of repellent chemicals. Bacteria constantly monitor the ...

Biología

Soft Lithographic Procedure for Producing Plastic Microfluidic Devices with View-ports Transparent to Visible and Infrared Light

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable microfluidic devices. Here, a protocol for the fabrication of plastic microfluidic devices is demonstrated, where soft lithographic techniques are used to embed transparent Calcium Fluoride (CaF2) view-ports in connection with observation chamber(s). The method is based on a replica casting approach, where a polydimethylsiloxane (PDMS) mold is produced through standard lithographic procedures and then used as the template to produce a plastic device. The plastic device features ultraviolet/visible/infrared (UV/Vis/IR) -transparent windows made of CaF2 to allow for direct observation with visible and IR light. The advantages of the proposed method include: a reduced need for accessing a clean room micro-fabrication facility, multiple view-ports, an easy and versatile connection to an external pumping system through the plastic body, flexibility of the design, e.g., open/closed channels configuration, and the possibility to add sophisticated features such as nanoporous membranes.

A protocol for the fabrication of plastic microfluidic devices with transparent view-ports for visible and infrared light imaging is described.

Procedimiento suave litográfica para la producción de dispositivos microfluídicos plástico con puertos de vista transparentes a luz Visible e infrarroja

Infrared (IR) spectro-microscopy of living biological samples is hampered by the absorption of water in the mid-IR range and by the lack of suitable ...