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Optimized resistor pattern

Part of the PhD thesis of Bertrand SELVA

This part is related to the controle of temperature within a microfluidic cavity using heating resistor that have been shape optimized.
Generating a constant temperature gradient within a microfluidic cavity 

We demonstrate the possibility of generating high-temperature gradients with a linear temperature profile when heating is provided in situ. Thanks to improved optimization algorithms, the shape of resistors, which constitute the heating source, is optimized by applying the genetic algorithm NSGA-II (acronym for the non-dominated sorting genetic algorithm) (Deb et al 2002 IEEE Trans. Evol. Comput. 6 2). Experimental validation of the linear temperature profile within the cavity is carried out using a thermally sensitive fluorophore, called Rhodamine B (Ross et al 2001 Anal. Chem. 73 4117–23, Erickson et al 2003 Lab Chip 3 141–9). The high level of agreement obtained between experimental and numerical results serves to validate the accuracy of this method for generating highly controlled temperature profiles. In the field of actuation, such a device is of potential interest since it allows for controlling bubbles or droplets moving by means of thermocapillary effects (Baroud et al 2007 Phys. Rev. E 75 046302). Digital microfluidics is a critical area in the field of microfluidics (Dreyfus et al 2003 Phys. Rev. Lett. 90 14) as well as in the so-called lab-on-a-chip technology. Through an example, the large application potential of such a technique is demonstrated, which entails handling a single bubble driven along a cavity using simple and tunable embedded resistors.

Integration of a uniform and rapid heating source into microfluidic systems

in collaboration with Pascaline Mary

The purpose of this study has been to demonstrate the possibilities of uniform heating of a cavity, with great accuracy, by means of an integrated resistor built with the same dimensions as the cavity, i.e., with a high level of integration. For application purposes, a compact resistor allows increasing the number of cavities in which temperature can be independently controlled on the same substrate, which can prove critical for high-throughput screening applications. Potential applications lie in the field of biology or chemistry. In order to achieve the desired result, an optimization procedure was performed on the shape of the resistor. The heater size reduction enables a high level of integration with a reduced heating source surface area. Resistor shape has been optimized to reduce the influence of boundary effects, using improvements introduced in genetic algorithms. An experimental validation of the temperature profile inside the cavity has been carried out using a dye whose fluorescence depends on temperature, i.e., Rhodamine B, it will be shown herein that the optimized resistor allows for temperature cycling, e.g., for PCR applications.