Apoio financeiro parcial para este trabalho foi fornecida pela Fundação Nacional de Ciência dos EUA através do Centro de Pesquisa Cooperativa Indústria / Universidade de Equipamentos &amp; Política localizado na Universidade de Wisconsin-Milwaukee (IIP-0968887) e da Universidade de Marquette (IIP-0.968.844) de água. Agradecemos Glenn M. Walker, Woo-Jin Chang e Shankar Radhakrishnan para discussões úteis.

1. A detecção de partículas térmica (TPD) <ol><li> Prepare o dispositivo de silício micro fabricado com uma película fina membrana de nitreto de silício e sensor de temperatura integrado por micromachining, usando a tecnologia de processamento de semicondutores padrão 2. Lavar o dispositivo fabricado com deionizada (DI) de água. Nota: O processo de fabrico para o detector de partículas térmica dispositivo de microfluidos é explicado na publicação prévia 2. </li><li> Para produzir PDMS (polidimetilsiloxano) substratos com micro-canais, criar um molde SU8 utilizando litografia padrão processa 5. Nota: O tamanho do canal é projetado para a dimensão de cada partícula específico. <ol><li> Adicione PDMS por mistura de uma proporção de 10: 1 da base (30 ml) e agente (3 ml) a cura. Verter o PDMS em que o molde e remover as bolhas por exposição breve a um vácuo (5-10 min). Observação: O nível de vácuo não é um valor crítico para a desgaseificação e que deve continuar até que o gás bubbles são totalmente removido do PDMS mistos. </li><li> Coloque o molde sobre uma placa quente (~ 70 ° C) durante 2 horas para curar o PDMS. Em seguida, retire as PDMS com muito cuidado para não danificar o molde. Observação: O nível de vácuo não é um valor crítico. </li></ol></li><li> Usando um manual punch, perfurar um buraco apertado (1 mm) para o tubo de PTFE em uma extremidade. Utilizar um grande punção (2 mm) na outra extremidade para fazer o PDMS um reservatório. Inserir o micro-canal perfurado na parte superior do dispositivo sob o microscópio e alinhar o RTD no centro do micro-canal (Figura 1A). </li><li> Na interface elétrica, conecte os pinos elétricos nas posições de placa de contato e apertar os parafusos de fixação. Certifique-se os pinos com altura ajustável (Pogo pinos) sentar-se nas almofadas de eletrodo corretas no dispositivo. </li><li> Dilui-se 10 ul das esferas PS concentradas em 100 ul de água desionizada num tubo de 1,5 ml. </li><li> Para garantir o PS grânulos permanecem flutuabilidade neutra, adicionar 2,7 mL de glicerol (1,26g / cm 3) a água desionizada para coincidir com a densidade do fluido para o poliestireno (PS) a densidade do grânulo (1,05 g / cm 3). </li><li> Ligar o tubo de PTFE para o canal em uma extremidade e a outra extremidade a uma seringa de vidro de 1 ml. Encha a seringa de vidro com 0,5 ml de água DI. Nota: ajustada feita selecionando o tamanho soco direito vai evitar vazamentos em tubos. </li><li> Coloque a água Dl preenchido na seringa da bomba de seringa controlada por computador. Empurrar a água (5-20 ul / min) para dentro do canal para preencher todo o canal com o fluido por todo o caminho para o reservatório. </li><li> Carregar 10 ml de solução equilibrada grânulo para o reservatório e introduzir a solução do grânulo para o micro-canal, alterando a direcção do fluxo na bomba de seringa. </li><li> Ligue o RTD por polarização de 1 mA de corrente DC através da controlada computador de origem / metro ao medir a resistência por fonte / metro e classificando os dados medidos (Figura 2). Nota: Durante o experimento, o sensor é tendenciosa; por conseguinte, a temperatura é medida continuamente até ao final da experiência de contagem. O sensor RTD é electricamente polarizado através da aplicação de uma corrente DC na gama de 100 uA a 1 mA para medir continuamente a temperatura até ao fim da experiência de contagem. É crítico para selecionar o nível atual uma vez que existe um trade-off entre o nível de ruído e a amplitude do sinal detectado. A bomba de seringa é utilizada para gerar o fluxo em micro-canal. Seleccionar um caudal apropriado para a realização da experiência TPD é limitada à velocidade da medição. Esta velocidade é uma função da constante de velocidade e o dispositivo eléctrico de medida de tempo térmica. Os resultados da experiência de detecção térmica de partículas são mostrados na Figura 3. </li><li> Utilize o software de processamento de dados desenvolvido (LabVIEW) para converter os dados de resistência medidos a temperatura utilizando a equação de Callendar-Van Dusen 6. </li></ol> 2. térmicaCaracterização de substâncias líquidas Usando um Micro-calorímetro <ol><li> Neste processo, utilizar o dispositivo no chip calorímetro (Figura 4A) 3 para medir a difusividade térmica e calor específico das amostras. Nota: Em cada morrer, há duas câmaras micro-calorímetro (Figura 4B). Cada câmara tem duas entradas e uma saída. E cada uma das câmaras tem um aquecedor e um sensor integrado de IDT. </li><li> Colocar o dispositivo de micro-calorímetro localizado no suporte do dispositivo (Figura 4C). Alinhe o dispositivo para as entradas e saídas de microfluídicos com os acessórios titular. Coloque a camada de selagem de PDMS na parte superior do dispositivo. </li><li> Instale pinos de conexão elétrica no suporte do dispositivo e bloquear os parafusos do suporte. Nota: Certifique-se os Pogo pinos ajustáveis ​​em altura estão alinhados com as almofadas de contato elétrico. </li><li> Instale a camada de interface microfluídico com travas magnéticas para o suporte de dispositivo (Figura 4D). Conecte o PTFE tubos para ambas as entradas e da saída. Conectar uma entrada da bomba de seringa carregadas com amostra e fechar a outra, como a entalpia não é medida, neste caso. </li><li> Utilizar um programa controlado por computador desenvolvido para carregar a amostra para o micro-canais e câmaras. Nota: O programa usará fluxo descontinuada para liberar a pressão excessiva no compartimento suspensos de película fina. <ol><li> Coloque a amostra de 300 ul para a seringa de vidro e coloque-o sobre a bomba de seringa. Use (0,25 mL / min) taxas de fluxo constantes muito lentas para amostras de alta viscosidade (por exemplo, glicerol e líquidos iônicos). Use uma amostra de glicerol para medidas de difusividade térmica e líquidos iônicos para medidas de calor específico. </li></ol></li><li> Medições <ol><li> Medidas de difusividade térmica <ol><li> Ligue a configuração medições, como mostrado na Figura 5A. Carregar a amostra de glicerol para a câmara de micro-calorímetro. Execute o programa de computador controlado modificado para hea<html> t penetração medição do tempo. </li><li> Use a equação penetração de calor calibrado para calcular difusividade térmica a partir do momento penetração de calor medido 7: <img alt="Equação 1" src="/files/ftp_upload/52828/52828eq1.jpg" width="100" /> onde α é difusividade térmica, L é a espessura da câmara, p é o factor de calibração da espessura devido à variação do processo de fabricação, e t 0 é o tempo de penetração de calor. </li></ol></li><li> Medidas de calor específico <ol><li> Utilizar a configuração de medição TWA como mostrado na Figura 5B. Utilizar o mesmo programa de carregamento de amostra e carregar o líquido iónico na câmara. Executar o programa TWA para obter a amplitude das flutuações de temperatura AC (∂ T AC) e utilizar a equação de calor específico para calcular o específico, c p, de calor para cada amostra de líquido iónico 8: &quot;Width =&quot; 117 28eq2.jpg &quot;/&gt; onde C é 0 factor de calibração de potência de entrada, P representa na potência de entrada, ω é a frequência do sinal de actuação, e m é a massa da amostra líquida. </li></ol></li></ol></li></ol> 3. Calorimétrico Detecção Biochemical em dispositivos microfluídicos baseados em papel <ol><li> Use microfabricated película fina (40-50 nm níquel) sensor RTD. Etapas de fabricação para o sensor RTD são explicados em trabalhos anteriores 4. </li><li> Para o canal de fabricação baseado em papel 4, use um plotter faca para cortar o papel canais microfluídicos com um padrão projetado (L-forma). Coloque o papel em cima da esteira de corte, coloque o papel eo tapete de corte para o plotter faca, e usar a receita adequada para cortar os canais microfluídicos de papel 4. </li><li> Por dispositivo e canais de integração, utilizar uma camada adesiva acrílica (5 uM) para integrar o papel sobre o sensor RTD. Use a b limpolade para empurrar o papel para o dispositivo e remover as bolhas de ar (Figura 6A). O filme acrílico é uma camada adesiva para segurar o papel sobre sensor RTD. </li><li> Para a activação da enzima, utilizam tampão acetato de sódio 50 mM para activar a enzima GOD. Adicionar 1 mg de enzima GOD para 1 ml de tampão de acetato de sódio para tornar a solução 1 mg / ml. Ajustar o pH da solução para 5,1. Nota: Ajustar a quantidade de ácido acético em tampão de acetato de sódio para manter o pH da solução 5,1. </li><li> Viés do IDT com 1 mA de corrente DC para ativar o IDT e começar a medir a fonte de resistência / metro continuamente enquanto a resistência se estabelece após o experimento (~ 4 min). Nota: A Figura 6B mostra a configuração de medição para o teste calorimétrico à base de papel. </li><li> Introduzir os 2 ul da solução de GOD preparado para o centro do micro-canal de papel (local imobilização) através de uma pipeta. A temperatura detectada (Figura 7A) deve começar tO diminuir. Nota: O efeito de arrefecimento é devido à temperatura mais elevada a operação de RTD e evaporação da amostra em conjunto. </li><li> Para medir a concentração de glucose, introduzir a solução de controlo de glucose padrão 9 para a entrada do canal e medir a alteração da resistência causada pela reacção. Repita essa experiência com todas as soluções de controle de glicose diferentes (alto, normal e baixas concentrações) e salvar os dados de resistência. </li><li> Utilizando o coeficiente de temperatura de resistência (TCR) por RTD níquel e equação de Callendar-Van Dusen, converter a alteração da resistência à temperatura. Calcula-se a concentração da glicose em cada amostra, considerando a entalpia de reacção da glucose e a enzima GOD (Δ H = -80 kJ / mol) e utilizando a equação de concentração 10: <img alt="Equação 3" src="/files/ftp_upload/52828/52828eq3.jpg" width="83" /> onde n p é detectada uma concentração molar, C <sub&gt; P é a capacidade de calor do sistema e AT é calculada temperatura. </li></ol>

<ol>
	<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...

Três técnicas de medição térmica de micro-escala diferentes são apresentados neste artigo. As três configurações diferentes de dispositivos microfluidicos são utilizados para a detecção térmica de partículas (TPD), caracterização térmica (condutividade térmica e calor específico), e calorimetria de detecção de reacções químicas e interacções. Detecção de partículas térmica Detecção e contagem de partículas em dispositivos microfluídicos é amplamente utilizado para aplicações ambientais, industriais e biológicos 1. TPD é uma das novas aplicações de medições térmicas em dispositivos microfluídicos 2. Usando a transferência de calor para a detecção e contagem de partículas com base no tamanho de partícula reduz a complexidade, custo e tamanho do sistema. Em outros métodos, óptica complexos ou medições elétricas complexas e software avançado de processamento de sinal são utilizados para a detecção de partículas. Chara térmicacterization de substâncias líquidas Usando Micro-Calorimeter Líquido caracterização térmica da amostra é a segunda aplicação de medição térmica em dispositivos microfluídicos. Executando calorimetria micro-escala vai reduzir o consumo de amostra e aumentar a precisão, oferecendo maior repetibilidade, em comparação com métodos de calorimetria granel convencionais. Os procedimentos de medição de condutividade térmica e calor específico usando o dispositivo micro-calorímetro on-chip são apresentados em outros lugares 3. Os detalhes da técnica o tempo de penetração de calor para a medição da condutividade térmica e a análise de onda térmica (TWA) para medições específicas de calor em dispositivos de microfluidos são descritos na secção de protocolo. Dispositivo micro-Base de Papel Calorimétrico Bio-Chemical Detection em Outra aplicação de medição térmica é a detecção bioquímica em microfluidos baseados em papel. A acção capilar noestrutura porosa de papel transporta o líquido e evita problemas de iniciação bolha em micro-canais. Os mecanismos de detecção mais comuns em dispositivos microfluídicos baseados em papel são técnicas ópticas ou eletroquímicos. Detecção óptica sofre de alta complexidade ea necessidade de software avançado de processamento de imagem para quantificar o sinal detectado. Detecções electroquímica também é limitado dado que eles só podem ser aplicadas a reacções que produzem subprodutos activas. O sensor bioquímica plataforma calorimétrico à base de papel recentemente introduzida 4 leva vantagem de o sistema de microfluidos à base de papel e o mecanismo de detecção térmica livre de marcador. Os procedimentos de detecção de glucose através de calorimetria de enzima glucose oxidase (GOD) em uma plataforma de microfluidos à base de papel são apresentados na secção de protocolo. O objetivo deste artigo é demonstrar as capacidades de técnicas termais de medição em dispositivos microfluídicos. O dispositivo preparation, amostra de líquido detector manuseio e resistência à temperatura (RTD) de excitação do sensor e medição são apresentados nas próximas seções.

<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.

A Figura 3 mostra o gráfico do sinal térmico medido. Os sinais gerados na presença dos grânulos com imagens ópticas correspondentes mostram a detecção com sucesso das microesferas PS no micro-canal. A condutividade térmica do líquido que passa através do microcanal está a mudar devido à presença de grânulos de PS. Esta alteração na condutividade térmica do canal está a afectar a transferência de calor no micro-canal. A alteração na transferência de calor no micro-canal é detectado...

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 Medição térmicos em analíticos microfluídicos

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

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

Vídeo: 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

Sensoriamento terahertz microfluídicos usando um sensor de guia de onda de placas paralelas

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

Engenharia

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 detecção de fluorescência para as plataformas de gotículas microfluídicos

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

Bioengenharia

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.

Fibra Óptica sensores distribuídos para High-resolution Mapeamento 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.

Fabricação e teste dos termómetros fotônicos

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 medição de temperatura infravermelha para a água ao redor de uma esfera magnética pequena aquecida a indução

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.

Medições de transferência de calor convectiva instantânea Local em uma tubulação - fluxo único e duas fases

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.

Analisando falta de homogeneidade de mistura em um dispositivo micro, pela técnica Microscale Schlieren

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.

Um dispositivo micro para Quantificar Quimiotaxia bacteriana em gradientes de concentração estável

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

Biologia

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.

Procedimento litográfico macio para a produção de dispositivos microfluídicos plástico com vista-portas transparentes à luz visível e infravermelho

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 ...