Polyelectrolyte multilayers-modified polystyrene plate improves conventional immunoassay: full covering of the blocking reagent.

In this study, we fabricated polyelectrolyte multilayers (PEMs) on a polystyrene (PS) plate by a simple and novel alternate drop coating process (Acta Biomaterialia 2008, 4, 1255-1262), leading to the construction of a functional platform for improving conventional enzyme-linked immunosorbent assay (ELISA) systems. Poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) were used as cationic and anionic polyelectrolytes, and then positively or negatively charged surfaces were obtained on the PEMs. The PDDA/PSS PEMs on the PS plate had the following favorable characteristics. On the positive PEMs, the coverage of the blocking reagent (ovalbumin from egg white: OVA) was over 100% by electrostatic interaction between the protein and PEMs, hence, nonspecific adsorption from the secondary antibody was efficiently suppressed. Moreover, the positive PEMs showed higher sensitivity on the ELISA than the negative PEMs, including the PS plate. Regularly oscillating behavior for sensitivity (specific signal-to-noise ratio) was observed on 1-10-step assemblies. The calibration curves for antigen detection on the positive PEMs had wide range of concentration from 0.002 to 5 microg/mL, and largest change in signal as compared with the negative PEMs and the PS plate. In summary, we discovered that positive PEMs possessed excellent performance for ELISA systems, and PEMs could easily improve the immunoassay with a convenient process and diverse substrates.