A biotinylated anti-rat C-reactive protein (CRP) antibody was ingeniously prepared by the reaction of the unmodified antibody with a water-soluble sulfosuccinimidyl-6-(biotinamido) hexanoate. The molar biotin incorporation of the resulting modified antibody was found as 5.82. A flow-type indirect-competitive quartz crystal microbalance immunosensor system was constructed with the sensor chip immobilized with 2 mg/mL CRP as the coating antigen. When 200 mu L of the modified antibody having the concentration of 0.250 mg/mL was added with a streptavidin-coated gold nanoparticle (GNP) to the immunosensor system, the frequency shift obtained was 139.8 +/- 0.3 Hz. Compared to the frequency shift of 91.1 +/- 1.3 Hz found with the addition of the unmodified antibody only, the signal augmentation after GNP binding amounted to 53.4%, which resulted in sensitivity improvement of the current immunosensor. (C) 2010 Elsevier B.V. All rights reserved.