An RNA-DNA hybridization assay chip with electrokinetically controlled oil droplet valves for sequential microfluidic operations.

A novel RNA-DNA hybridization microfluidic chip for detecting pathogens was developed. The on-chip sequential operations of reagent delivery and washing processes in the hybridization assay were performed by gravity-based pressure-driven flow controlled by a pair of electrokinetically controlled oil-droplet sequence valves (ECODSVs). Numerical method was used to simulate the fluidic processes of reagents in the complex microchannel network. Based on the parameters determined from the numerical simulations, a reasonable hybridization assay microfluidic chip was developed. The application of this on-chip assay to detect Salmonella was demonstrated. Significantly shortened assay time (25 min) and a 3-20-fold reduction in reagent/sample consumption were achieved. The detection limit was 10³ CFU/mL which is comparable to the conventional assay. With further development of automatic control and the improvement of the detection strategy, this microfluidic RNA-DNA hybridization assay technique has a potential for point-of-testing applications.