A water-dispersible, ferrocene-tagged peptide nanowire for amplified electrochemical immunosensing.

A ferrocence (Fc)-tagged peptide comprising the phenylalanine-phenylalanine (Phe-Phe) sequence was synthesized and allowed to self-assemble into uniform nanowires with a diameter of ca. 100 nm and lengths in the range of 5-10 µm. The Fc-tagged peptide nanowire (Fc-PNW) become well dispersed in aqueous solution when coated with poly(diallyldimethylammonium chloride) (PDDA). Gold nanoparticles (AuNPs) and antibody molecules can then be adsorbed onto the Fc-PNW surface. The resultant antibody modified Fc-PNW was explored as a detection probe for sensitive electrochemical immunosensing in a sandwich assay wherein the capture antibody was attached onto a graphene/gold nanoparticle (AuNPs-GN) composite film. The as prepared electrochemical immunosensor possesses a low detection limit (5 fg/mL) for human IgG and a wide linear range encompassing four orders of magnitude (from 10 fg/mL to 100 pg/mL). Such a low detection limit stems from the significant signal amplification by the large number of Fc moieties on the PNW (for a 5-µm-long Fc-PNW, the number of Fc moieties is 5×10⁵). The electrochemical immunosensor is also highly selective and the sensor was demonstrated to be amenable to real sample analysis.