Orientation and biorecognition of immunoglobulin adsorbed on spin-cast poly(3-alkylthiophenes): Impact of polymer film crystallinity.

Many of bioelectronic and biosensor applications are based on poly(3-alkylthiophenes), conducting and solution-processable polymers. The most facile approach for the fabrication of such devices relies on biofunctionalization of P3AT surfaces with antibodies through adsorption. The success of this approach depends critically on antibody orientation that affects its biorecognition. As demonstrated here both these features are controlled by the surface structure of spin-cast P3ATs. In particular, a multi-technique and multivariate study that involved Atomic Force Microscopy, Grazing Incidence X-ray Diffraction, Angle-Resolved X-ray Photoelectron Spectroscopy, Enzyme-Linked ImmunoSorbent Assay, and Time-of-Flight Secondary Ion Mass Spectrometry combined with Principal Component Analysis is conducted in order to deduce the crystalline texture of three P3AT polymers as well as its effect on orientation of adsorbed rabbit immunoglobulin (IgG) molecules. An edge-on crystalline texture is concluded for regioregular poly(3-butylthiophene) (RP3BT) and poly(3-hexylthiophene) (RP3HT), while amorphous morphology is inferred for poly(3-butylthiophene) (P3BT). In addition, end-on and head-on orientations similar for all P3ATs were concluded, based on the amount of adsorbed rabbit IgG molecules. Examination of amino acids characteristic for F(ab')2 and Fc fragments, and dominant in the external regions of adsorbed immunoglobulin molecules, points to end-on IgG alignment on RP3BT and RP3HT, but not on P3BT. Moreover, the binding of an anti-rabbit IgG antibody on the absorbed rabbit IgG is higher (up to 71%) when the biorecognition reactions are performed on regioregular rather than regiorandom P3AT surfaces. In particular, the highest biorecognition efficiency and IgG orientational order is observed for the RP3BT surfaces with the more developed crystallinity.