Bead-free digital immunoassays on polydopamine patterned perfluorinated surfaces

Abstract This paper reports sub-micron resolution patterning of perfluorinated surfaces and the application in bead-free digital immunoassays. We use the negative microcontact printing in conjugation with a composite stamp to fabricate polydopamine patterns with sub-micron resolution on the perfluorinated surfaces. To perform digital assays, polydopamine microspot arrays were fabricated. Using discontinuous dewetting, 106 femtoliter droplets are formed in situ on the microspots. The droplets are kept in air from evaporation for over 90 min. The polydopamine patterns on the perfluorinated surfaces are used not only as the template for microdroplet generation but also as the binding sites for various proteins without further modifications. The detection limit of the bead-free digital immunoassay for human interleukin-6 is 1.2 fM with a dynamic range from 1.2 fM to over 400 fM. The high resolution polydopamine patterned perfluorinated substrate offers a highly-sensitive and low-cost approach for digital immunoassays, showing great potential in high-throughput and digital bioassays.