Electrostatic desalting of micro-droplets to enable novel chemical/biosensing applications

Motivation/Background: Salt-based electrolyte plays a fundamentally important role in many chemical/biochemical processes. For example, sodium is found in extracellular fluid and controls the blood pressure. Similarly, magnesium is required for optimization of polymerase-chain reaction (PCR) which is important for genome sequencing. Further, ions have recently also found broad applications in flexible and transparent electronics. Indeed, precise control of electrolyte concentration at micro-scale is essential for many lab-on-chip technologies. In this paper, we provide a novel scheme to electrostatically control the spatial distribution of ions within a miniaturized droplet. Specifically, an applied bias helps accumulate ions near the electrode-surface, thereby depleting the bulk salt concentration of a small droplet. We demonstrate that the bulk desalting of droplet may potentially enable a broad range of novel applications, namely: improvement of detection limit of biosensor necessary for early-disease detection, modulation of pH profile for isoelectric protein separation, electrostatic denaturation of DNA for sensor reusability by modification of its melting temperature.