Partial financial support for this work was provided by the U.S. National Science Foundation through the Industry/University Cooperative Research Center on Water Equipment &#38; Policy located at the University of Wisconsin-Milwaukee (IIP-0968887) and Marquette University (IIP-0968844). We thank Glenn M. Walker, Woo-Jin Chang and Shankar Radhakrishnan for helpful discussions.

1. Thermal Particle Detection (TPD)
<ol>
	<li>Prepare the micro-fabricated silicon device with a thin-film silicon nitride membrane and integrated temperature sensor by micromachining, using standard semiconductor processing technology2. Rinse the fabricated device with deionized (DI) water. 
	Note: The fabrication method for thermal particle detector microfluidic device is explained in prior publication2.</li>
	<li>To produce polydimethylsiloxane (PDMS) substrates with micro-channels, create...

<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>

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...

Three different micro-scale thermal measurement techniques are presented in this article. The three different configurations of microfluidic devices are used for thermal particle detection (TPD), thermal characterization (thermal conductivity and specific heat), and calorimetric detection of chemical reactions and interactions.
Thermal Particle Detection
Detecting and counting particles in microfluidic devices is widely used for environmental, industrial, and biological applications1. TPD is one of the novel applications of thermal measurements in microfluidic devices2. Using heat transfer for detecting and counting particles based on the particle size reduces the complexity, cost, and size of the system. In other methods, complex optics or complex electrical measurements and advanced signal processing software are used for detecting particles.
Thermal Characterization of Liquid Substances Using Micro-Calorimeter
Liquid sample thermal characterization is the second application of thermal measurement in microfluidic devices. Performing micro-scale calorimetry will reduce the sample consumption and increase the precision by offering higher repeatability compared to conventional, bulk calorimetry methods. The procedures for thermal conductivity and specific heat measurement using the on-chip micro-calorimeter device are presented elsewhere3. The details of the heat penetration time technique for thermal conductivity measurement and the thermal wave analysis (TWA) for specific heat measurements in microfluidic devices are described in the protocol section.
Calorimetric Bio-Chemical Detection in Paper-Based Microfluidic Device
Another application of thermal measurement is biochemical detection in paper-based microfluidics. The capillary action in the porous structure of paper carries the liquid and avoids bubble initiation problems in micro-channels. The most common detection mechanisms in paper-based microfluidic devices are optical or electrochemical techniques. Optical detection suffers from high complexity and the necessity of advanced image processing software to quantize the detected signal. Electrochemical detections are also limited because they can only be applied to reactions that produce active byproducts. The recently introduced calorimetric paper-based biochemical sensor platform4 takes advantage of the paper-based microfluidic system and the label-free thermal detection mechanism. The procedures of calorimetric detection of glucose using glucose oxidase (GOD) enzyme in a paper-based microfluidic platform are presented in the protocol section.
The goal of this paper is to demonstrate the capabilities of thermal measurement techniques in microfluidic devices. The device preparation, liquid sample handling and resistance temperature detector (RTD) sensor excitation and measurement are presented in the next sections.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Polydimethylsiloxane (PDMS)&#160;</td>
			<td>Dow Corning</td>
			<td>Sylgard 184</td>
			<td></td>
		</tr>
		<tr>
			<td>PS beads - 90 um&#160;</td>
			<td>Corpuscular</td>
			<td>100265</td>
			<td></td>
		</tr>
		<tr>
			<td>PS beads - 200 um&#160;</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&#160;</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.

Figure 3 shows the plot of the measured thermal signal. The generated signals in the presence of the beads with corresponding optical images show the successful detection of the microsphere PS beads in the micro-channel. The thermal conductivity of the liquid passing through the micro-channel is changing due to the presence of PS beads. This change in the thermal conductivity of the channel is affecting the heat transfer in the micro-channel. The change in the heat transfer in the micro-channel is detect...

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Thermal Measurement Techniques in Analytical Microfluidic Devices

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

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

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9.5K vistas.  Marquette University. Here, we present three protocols for thermal measurements in microfluidic devices. 