Colorimetric immunosensing via protein functionalized gold nanoparticle probe combined with atom transfer radical polymerization.

A novel colorimetric immunosensing strategy based on protein-modified gold nanoparticle probes combined with atom transfer radical polymerization (ATRP) technology was proposed. Gold nanoparticles (GNPs, ∼15 nm) were functionalized with antibodies through an acylamide-bond between the carboxylic group of 11-mercaptoundecanoic acid that previously self-assembled on the surface of GNPs and the amino group of the protein (here, goat anti-rabbit immunoglobulim G (anti-IgG) used as model). The surface functionalized GNPs were used for IgG capture, which introduced initiator coupled anti-IgG (Ab2*) onto the surface of GNPs through immunoreactions. Subsequently triggered polymer growth resulted in the surface graft of preformed polymer chains onto nanoparticles that altered the optical property of GNPs. A distinct color change occurred. This could be designed for IgG detection. The spectrum absorption and colorimetric detection gave a linear range of 0.5-25 ng mL(-1) with a detection limit of 0.03 ng mL(-1) for IgG. The proposed approach showed high sensitivity from both visual and absorbance measurements. In spite of the limitations of available IgG antibodies, this approach could be easily extended to the detection of other biomarkers.