Magnetic bead induced surface tension change on gas-solid-liquid interface to manipulate the reciprocating flow of droplet for rapid immunoassay of viruses

Abstract

Droplet manipulation provides tools for medical diagnostics, cell culturing, and drug screening. Among droplet manipulation techniques, magnetic manipulation can transport, mix and separate droplets, garnering broad attention for rapid immunoassay. Typically, magnetic manipulation requires ferrofluid or micron-sized magnetic particles as droplet actuators.However, ferrofluid may contaminate droplet, and magnetic particles may trap unbound molecules (e.g., viruses, antigens) within their aggregation gaps. These disadvantages decrease the accuracy of immunoassay. Here, we use a millimeter-sized magnetic bead to manipulate a droplet by inducing surface tension change on gas-solid-liquid interface. The manipulation of each droplet requires single magnetic bead that releases no solvent or contaminant, eliminating the trapping of unbound molecules in the gaps between aggregated magnetic beads. We further design a chip and its complementary miniaturized analyzer to manipulate the reciprocating flow of droplets, and develop the rapid immunoassay method to detect Sendai virus and pneumonia virus of mice within 10 min. This method can detect target viruses in serum with a sensitivity of 100% (6/6) and a specificity of 93.3% (28/30). This work demonstrates great performance in the droplet manipulation and the rapid immunoassay of viruses, with extensive prospects in medical diagnosis, cell culturing and drug screening.