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Open AccessArticle

Magnetically-Actuated Mixing and Merging of Acid-Base Micro-Droplets on Open Surfaces: Preliminary Study

1
Queensland Micro-and Nanotechnology Centre, Griffith University, Nathan QLD 4111, Australia
2
Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Bandar Sungai Long, Kajang 43000, Selangor, Malaysia
*
Author to whom correspondence should be addressed.
Sensors 2018, 18(6), 1767; https://doi.org/10.3390/s18061767
Received: 25 April 2018 / Revised: 25 May 2018 / Accepted: 29 May 2018 / Published: 1 June 2018
(This article belongs to the Section Biosensors)
We present the mixing and merging of two reactive droplets on top of an open surface. A mobile droplet (1.0 M HCl solution + iron oxide particles) is magnetically-actuated to merge with a sessile droplet (1.0 M NaOH + phenolphthalein). The heat from the exothermic reaction is detected by a thermocouple. We vary the droplet volume (1, 5 and 10 μL), the magnet speed (1.86, 2.79, 3.72 and 4.65 mm/s) and the iron oxide concentration (0.010, 0.020 and 0.040 g/mL) to study their influences on the mixing time, peak temperature and cooling time. The sampled recording of these processes are provided as supplementary files. We observe the following trends. First, the lower volume of droplet and higher speed of magnet lead to shorter mixing time. Second, the peak temperature increases and cooling time decreases at the increasing speed of magnet. Third, the peak temperature is similar for bigger droplets, and they take longer to cool down. Finally, we also discuss the limitations of this preliminary study and propose improvements. These observations could be used to improve the sensitivity of the open chamber system in measuring the exothermic reaction of biological samples. View Full-Text
Keywords: microfluidics; micro-droplet; magnetic-actuation; micro-mixing; acid-base; exothermic reaction microfluidics; micro-droplet; magnetic-actuation; micro-mixing; acid-base; exothermic reaction
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Khaw, M.-K.; Mohd-Yasin, F.; Nguyen, N.-T. Magnetically-Actuated Mixing and Merging of Acid-Base Micro-Droplets on Open Surfaces: Preliminary Study. Sensors 2018, 18, 1767.

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