Tuning the electrophoretic separations on a surface-accessible and flexible fibre-based microfluidic devices

Electrophoresis on textile fiber substrates provides a unique surface-accessible platform for the movement, separation and concentration of charged analytes. The method employs the inherently inbuilt capillary channels existing within textile structures, which can support electroosmotic and electrophoretic transport processes upon applying an electric field. Unlike confined microchannels in classical chip-based electrofluidic devices, the capillaries formed by the roughly oriented fibers within textile substrates can impact the reproducibility of the separation process. Here, we report an approach for precise experimental conditions affecting the electrophoretic separation of two tracer solutes, fluorescein (FL) and rhodamine B (Rh-B) on textile-based substrates. A Box-Behnken response surface design methodology has been used to optimise the experimental conditions and predict the separation resolution of a solute mixture using polyester braided structures. The magnitude of the electric field, sample concentration and sample volume are of primary importance to the separation performance of the electrophoretic devices. Here, we use a statistical approach to optimise these parameters to achieve rapid and efficient separation. While a higher potential was shown to be required to separate solute mixtures of increasing concentration and sample volume, this was counteracted by a reduced separation efficiency due to joule heating, which caused electrolyte evaporation on the unenclosed textile structure at electric fields above 175 V cm^-1. Using the approach presented here, optimal experimental conditions can be predicted to limit joule heating and attain effective separation resolution without compromising the analysis time on simple and low-cost textile substrates.