Journal for Biophysical Chemistry

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Open Access

Quantitative interpretation of gold nanoparticle-based bioassays designed for detection of immunocomplex formation

  • Ye Zhou1, 2,
  • Hongxing Xu1, 3,
  • Andreas B. Dahlin1,
  • Jacob Vallkil4,
  • Carl A. K. Borrebaeck4,
  • Christer Wingren4,
  • Bo Liedberg2 and
  • Fredrik Hööka1Email author

Received: 8 December 2006

Accepted: 22 January 2007


The authors present in this paper how the extended Mie theory can be used to translate not only end-point data but also temporal variations of extinction peak-position changes, δλpeak(t), into absolute mass uptake, Γ(t), upon biomacromolecule binding to localized surface plasmon resonance (SPR) active nanoparticles (NPs). The theoretical analysis is applied on a novel sensor template composed of a three-layer surface architecture based on (i) a self-assembled monolayer of HS(CH2)15COOH, (ii) a 1:1 mixture of biotinylated and pure poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), and (iii) NeutrAvidin. Assisted by independent estimations of the thickness of the three-layer architecture using quartz crystal microbalance with dissipation (QCM-D) monitoring, excellent agreement with parallel mass-uptake estimations using planar SPR is obtained. Furthermore, unspecific binding of serum to PLL-g-PEG was shown to be below the detection limit, making the surface architecture ideally suited for label-free detection of immunoreactions. To ensure that the immunocomplex formation occurred within the limited sensing depth (10 nm) of the NPs, a compact model system composed of a biotinylated human recombinant single-chain antibody fragment (2 nm) directed against cholera toxin was selected. By tracking changes in the centroid (center of mass) of the extinction peak, rather than the actual peak position, signal-to-noise levels and long-term stability upon cholera toxin detection are demonstrated to be competitive with results obtained using conventional SPR and state-of-the-art QCM-D data.