A Quartz Crystal Microbalance Study of the Adsorption of Fluorescein‐5‐Isothiocyanate onto Gold Surfaces

Abstract

The interaction of fluorescein‐5‐isothiocyanate (F5ITC) with gold surfaces—either uncoated or pre‐coated with passivating layers of either sodium citrate (citrate), bis(p‐sulfonatophenyl)phenylphosphine dihydrate dipotassium (BSPP), Pluronic P123 (EO₂₀PO₇₀EO₂₀), or Pluronic F127 (EO₁₀₀PO₇₀EO₁₀₀)—was studied using quartz crystal microbalance (QCM) measurements in order to determine the surface coverage of F5ITC in each case. Adsorption isotherms of the polymers (P123 and F127) binding to a gold surface were also obtained. Binding of F5ITC to the gold surfaces was found to be highly dependent on the passivating layer. The surface coverage Γ_F5ITC of F5ITC on gold surfaces can be listed in decreasing order as Γ_{F5ITC, Au}>Γ_{F5ITC, citrate}>Γ_{F5ITC, P123}>Γ_{F5ITC, BSPP}>Γ_{F5ITC, F127}. Mechanisms for binding of F5ITC to the gold surfaces are also discussed.

Keywords:

• Quartz crystal microbalance
• gold
• adsorption
• fluorescein‐5‐isothiocyanate
• isotherm

Acknowledgments

We thank the Research Council of Norway (NFR) for financial support.