Optical Absorption Study of the Biotin−Avidin Interaction on Colloidal Silver and Gold Particles

Abstract

The biotin−avidin reaction is well studied and is often used as a prototypical interaction in the development of immunoassays. In this paper, this reaction is studied on the surface of colloidal silver and gold particles as a first step in the development of a sol-based assay. More specifically, silver and gold colloidal particles were biotinylated by self-assembly of a biotin disulfide molecule, and the reaction of the surface-modified colloidal particles with avidin molecules was followed using optical absorption spectroscopy. The specific interaction of avidin, a tetrameric protein, with biotin leads to cross-linking of the colloidal particles (“flocculation”) and a consequent growth of a long wavelength absorption peak. The degree of flocculation was quantified using a semiempirical flocculation parameter, and the dependence of this parameter on the extent of biotinylation of the colloidal particle surface as well as the concentration of avidin in solution was studied to determine the optimum working conditions of the sol. The silver sol required electrostatic stabilization of the biotin-capped particles through the simultaneous incorporation of a charged bifunctional molecule, 4-carboxythiophenol, in the capping monolayer while the gold sol was stable with biotin capping. Both biotinylated silver and gold sols showed a visible color change on addition of avidin. However, changes in the optical absorption spectra were more marked for the silver sol.

Engineering of poly(ethylene glycol) chain-tethered surfaces to obtain high-performance bionanoparticles

“…Gold nanoparticles (GNPs) with a size ranging from several to hundreds of nanometers show a bright pinkish color due to plasmon resonance; they have been used in stained glasses for several hundred years. A simple means of anchoring different ligand molecules onto particle surfaces allows their utilization as colloidal sensors [16][17][18]. In particular, color changes induced by the aggregation of nanometer-sized gold particles provide a basis for a simple yet highly selective method for detecting specific biological events between anchored ligand molecules and receptor molecules in the milieu.…”

Inorganic nanoparticles and the immune system: detection, selective activation and tolerance

“…It is stated that aggregation processes are concomitant with a red-shift and broadening of SPR band, due to dipole coupling between the plasmons of neighboring particles 28,29 . In fact, this aggregation can be quantified by the increase of the aggregation parameter 30 , which measures the variation of the integrated absorbance between 600 and 700 nm [30][31][32] . Figure 3 shows a set of UV-Vis spectra of citrate-stabilized Au NPs and peptide-conjugated Au NPs at various ionic strengths values taken 15 min after the addition of different amounts of sodium chloride (NaCl), where it can be seen how citratestabilized Au NPs agglomerate more and more as the amount of NaCl increases.…”

Layer-by-layer fabrication of well-packed gold nanoparticle assemblies guided by a β-sheet peptide network

“…The LbL assembly takes advantage of the same attractive forces that form complexes but in a controlled manner that produces thin, conformal films that can coat a variety of surfaces and thus are a powerful method for fabricating multilayer gold nanoparticle films. [15][16][17][18][19][20][21][22][23][24][25][26][27] In spite of these many reports, to the best of our knowledge, well-controlled gold nanoparticle assemblies guided with a polypeptide network have not yet been reported. The aim of this article is to construct homogeneously well-ordered gold nanoparticle multilayers assisted with a b-sheet peptide template.…”