Novel On-Chip Raw Sample Preparation for Biomolecular Sensing via Teíchophoresis

Abstract

Point of care (POC) instruments are a growing class of diagnostic tools designed for use in low resource settings, such as population screening, and rapid testing in traditional healthcare settings. The current state of the art in POC diagnostics is the lateral flow assay (LFA), which is preferred due to its low cost, simple operation, and scalable manufacturing. Unfortunately, the LFA tends to exhibit poor sensitivity and selectivity. Conversely, micro total analysis systems (μTAS) are a rising class of POC diagnostic instruments which leverage a number of powerful sensitive and specific sensing techniques. μTAS platforms, however, tend to rely on bulky and expensive off-chip apparatuses for sample preparation, rendering them incompatible with the needs of the POC diagnostic market in their current form. In this work, we present a novel electrokinetic sample preparation technique, teíchophoresis (TPE), which is capable of continuous sample preparation in the form of preconcentration and electrophoretic mobility-based separations. TPE was developed as an optimization to an existing sample preparation method, isotachophoresis (ITP). In ITP, samples are concentrated and separated between a high flux zone established by a low mobility terminating electrolyte (TE) and a low flux zone established by a high mobility leading electrolyte. Alternatively, TPE replaces the low flux zone of the LE with a no flux zone generated by a physical wall. We first characterize the efficacy of TPE as a function of applied electric potential, flowrate, and TE concentration in a model dye system. We then establish that TPE is capable of performing high resolution separations of fluorescent dyes. Finally, we establish the concentrating power of TPE by performing a 60,000-fold preconcentration of Alexa 488 dye. We then aim to establish the biocompatibility of TPE. We specifically show that the electric current in TPE does not generate a significant pH gradient within the device. Furthermore, we show that both proteins and DNA exhibit the same voltage and flowrate dynamics as our model dye system. Finally, we show that TPE is compatible with fully raw biological samples by preconcentrating and sensing calcium in a tree bark extract.