Abstract
A discrete microfluidic element with integrated thermal sensor was fabricated and demonstrated as an effective probe for process monitoring and prototyping. Elements were constructed using stereolithography and market-available glass-bodied thermistors within the modular, standardized framework of previous discrete microfluidic elements demonstrated in the literature. Flow rate-dependent response due to sensor self-heating and microchannel heating and cooling was characterized and shown to be linear in typical laboratory conditions. An acid-base neutralization reaction was performed in a continuous flow setting to demonstrate applicability in process management: the ratio of solution flow rates was varied to locate the equivalence point in a titration, closely matching expected results. This element potentially enables complex, three-dimensional microfluidic architectures with real-time temperature feedback and flow rate sensing, without application specificity or restriction to planar channel routing formats.
Highlights
Thermal sensing plays a vital role in chemical engineering systems by providing quantitative, non-specific monitoring of process reactions and conditions
Thermistors were selected to be integrated into our microfluidic platform for their fast response times, high sensitivity, generally good accuracy, and low cost compared to resistance temperature detectors or thermocouples
The thermistors used in this study have a resistance sensitivity of approximately 4.5%/ ̋ C around room temperature, a tight manufacturing tolerance of 1%, and cost less than (US) $1 when purchased in lots of 100 or more at the time of this writing. They vary approximately 3.26 and 0.25 times their nominal room temperature value at 0 and 60 ̋ C, respectively, demonstrating significant nonlinearity across a typical range of laboratory conditions. These were considered as acceptable trade-offs; a secondary objective for design of discrete microfluidic elements is to ensure they are semi-disposable and replaceable
Summary
Thermal sensing plays a vital role in chemical engineering systems by providing quantitative, non-specific monitoring of process reactions and conditions. Existing thermal probes for microfluidic systems are often either highly application specific or limited to planar manufacturing formats derivative of thin-film semiconductor processing technology. One such example is the use of liquid phase temperature-sensitive indicators that produce low-resolution visible light signals, such as fluorescent dyes [5,6,7,8,9,10]. These probes are limited in their application by the potential for unintended reactivity with processing reagents and are ill-suited for use as a general solution
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