Preferential noncovalent immunoglobulin G adsorption onto hydrophobic segments of multi-functional metallic nanowires

Two-segment metallic nanowires fabricated by templated electrodeposition were functionalized with immunoglobulin G (IgG). The functionalization was selective with protein adsorption occurring preferentially on the nickel or gold segment of the wire. This selectivity was achieved by utilizing recent advances in self-assembly of organic ligands at planar electrodes. Two-component Ni–Au nanowires were functionalized to yield both a hydrophilic segment and a hydrophobic segment. Comparative studies with single segment gold and nickel nanowires were also performed. The functionalization procedures allowed the hydrophilic and hydrophobic groups to be directed to either the gold or nickel portion. The protein resistant properties of these bifunctional nanowires were studied and quantified by optical and fluorescence microscopies. A weak non-specific adsorption of IgG to hydrophilic nanowires or nanowire segments was observed. IgG bound strongly to hydrophobic nanowires or nanowire segments. Isotherms were well described by the Langmuir model from which limiting surface coverages near that expected for a monolayer ((6.0 ± 0.5) × 10−11 mol/cm2) and an equilibrium constant of K = (3 ± 2) × 106 M−1 were abstracted. Contact angle measurements on planar Au and Ni surfaces correlated well with the degree of protein adsorption to nanowires.