Engineering the surface properties of a zwitterionic polymer brush to enable simple fabrication of inkjet printed point-of-care immunoassays.

Motivated by the lack of adventitious protein adsorption on zwitterionic polymer brushes that promise low noise and hence high analytical sensitivity for surface-based immunoassays, we explored their use as a substrate for immunoassay fabrication by the inkjet printing of antibodies. We observed that a poly(sulfobetaine)methacrylate brush on glass is far too hydrophilic to enable the noncovalent immobilization of antibodies by inkjet printing. To circumvent this limitation, we developed a series of hybrid zwitterionic-cationic surface coatings with tunable surface wettability that are suitable for the inkjet printing of antibodies but also have low protein adsorption. We show that in a microarray format in which both the capture and detection antibodies are discretely printed as spots on these hybrid brushes, a point-of-care sandwich immunoassay can be carried out with an analytical sensitivity and dynamic range that is similar to or better than those of the same assay fabricated on a PEG-like brush. We also show that the hybrid polymer brushes do not bind anti-PEG antibodies that are ubiquitous in human blood, which can be a problem with immunoassays fabricated on PEG-like coatings.