Sensors that leverage the influence of a biorecognition event on charge transport, such as field-effect transistors and nanoporous membranes, are among the most sensitive because they translate localized binding into a change in a system-scale property. However, fabrication and custom functionalization of these sensors is not trivial, and their integration with protocols that pre-enrich target species and facilitate their transport to the biorecognition site is an active area of research. In this presentation, we demonstrate that ion concentration polarization (ICP) in the presence of fluid flow drives focusing and efficient capture of target nucleic acids within a bed of oligoprobe-conjugated beads embedded in a microfluidic channel. A key finding is that ion conduction along the surface of the bioconjugated beads is the dominant contributor to current through this channel segment under an applied voltage bias. Therefore, hybridization of a target nucleic acid (a polyanion) to the bead surface leads to a shift in the slope of the current-voltage curve. This approach is versatile in that a target nucleic acid can be detected electrically, in the absence of a label. The resulting approach allows for a plug-and-play nucleic acid sensor using off-the-shelf bioconjugated beads and simple electronics, making it advantageous for point-of-care testing. Finally, we share preliminary results for enrichment and sensing of other classes of analytes including viral RNA and antibodies.

a) Schematic illustration of the microfluidic device with metal interconnects at the inlet and outlet, to which voltage <i>V</i><sub>1</sub> and <i>V</i><sub>3 </sub>are applied versus a three-dimensional electrode comprising conductive beads (<i>V</i><sub>2</sub>). DNA is electrokinetically enriched within the bed of oligoprobe-modified beads. b) Plot of the shift in current observed following 30 min enrichment of target DNA from initial concentrations of 1 pM, 10 pM, 1 nM, and 100 nM. c) Plot of the shift in current observed at 1.0, 3.0, and 5.0 V as a function of enrichment time. The enrichment factor (EF) is approximately 50-, 100-, and 300-fold at 10, 30, and 60 min of enrichment.

a) Schematic illustration of the microfluidic device with metal interconnects at the inlet and outlet, to which voltage V₁ and V₃are applied versus a three-dimensional electrode comprising conductive beads (V₂). DNA is electrokinetically enriched within the bed of oligoprobe-modified beads. b) Plot of the shift in current observed following 30 min enrichment of target DNA from initial concentrations of 1 pM, 10 pM, 1 nM, and 100 nM. c) Plot of the shift in current observed at 1.0, 3.0, and 5.0 V as a function of enrichment time. The enrichment factor (EF) is approximately 50-, 100-, and 300-fold at 10, 30, and 60 min of enrichment.

Dr. Kira L. Rahn

Appearances