Thermal Measurement Techniques in Analytical Microfluidic Devices

Summary

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

Abstract

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.

Introduction

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 f....

Protocol

1. Thermal Particle Detection (TPD)

1. 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.
2. To produce polydimethylsiloxane (PDMS) substrates with micro-channels, create an SU8 mold using standard lithography processes⁵.
   Note: The channel size is designed for each specific particle’s dimension.
   <....

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

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