In diagnostics, point-of-care (POC) devices play a crucial role due to their ease of use, practical application, and fast response. One major limitation in POC devices is low sensitivity. Electrokinetic techniques such as ion concentration polarization (ICP) have been utilized to address this limitation because of their ability to enrich the target analyte prior to detection. ICP is the production of ion enriched and depleted zones (IEZ/IDZ) by ion permselective transport or faradaic reactions following the application of an external electric field. The IDZ supports the formation of an extended electric field gradient due to its low ionic conductivity. Enrichment arises from focusing of a charged analyte along this electric field gradient in the presence of opposing fluid convection. ICP focusing is a reliable technique for the enrichment and mobility-based separation of charged species, such as DNA, RNA, or proteins. However, ICP focusing is negatively impacted by electroconvective vortices that result in unwanted mixing.<br/>To improve the stability of the enriched plug, we utilize an out-of-plane faradaic ion concentration polarization (fICP) technique that employs a 3D porous electrode and an adjacent packed bed of bioconjugated insulating microbeads. In this work, we exhibit the label-free detection of SARS-CoV-2 RNA at the subpicomolar concentration in this microfluidic device. When this target RNA hybridizes to bioconjugated beads, the resulting increase in negative charge on the bead surface leads to a shift in a current-voltage curve obtained between the 3D electrode and a driving electrode at the microchannel inlet. We show that this shift in conductivity serves as a non-optical sensing mechanism for detection of the hybridized SARS-CoV-2 RNA. Further, we compare the sensitivity achieved when bioconjugating the insulating beads with either neutral peptide nucleic acid (PNA) oligoprobes or charged DNA oligoprobes specific to the target RNA. The PNA probes yield greater sensitivity, which we attribute to lower initial charge on the bioconjugated beads and a higher affinity of PNA for its RNA complement. Most notably, this enrichment and sensing scheme utilizes off-the-shelf streptavidin-modified beads, making it highly versatile, while the reagent-free approach and low driving voltage render it amenable to POC implementation.

Electrokinetic preconcentration and label-free detection of SARS-CoV-2 RNA by faradaic ion concentration polarization

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.