In situ sensing of metal ion adsorption to a thiolated surface using surface plasmon resonance spectroscopy

The kinetics of the adsorption of metal ions onto a thiolated surface and the selective and quantitative sensing of metal ions were explored using Surface plasmon resonance (SPR) spectroscopy. The target metal ion was an aqueous solution of Pt2+ and a thin-gold-film-coated glass substrate was modified with 1.6-hexanedithiol (HDT) as a selective sensing layer. SPR spectroscopy was used to examine the kinetics of metal ion adsorption by means of the chan-e in SPR angle. The selectivity of the thiolated surface for Pt2+ over other divalent metal ions Such as Cu2+ Ni2+, and Cd2+ was evident by the titre-resolved SPR measurement. SPR angle shift, Delta theta(SPR), Was found to increase logarithmically with increasing concentration of Pt2+ in the range of 1.0 x 10(-5) - 1.0 mM. The rate of Pt2+ adsorption on HDT observed at both 0.1 and 1 mM Pt2+ accelcrates Until the surface coverage reaches approximately 17%, after which the adsorption profile follows Langmuirian behavior with the Surface coverage. The experimental data indicated that heavy metal ions were adsorbed to the hydrophobic thiolated surface by a cooperative mechanism. A mixed self-assembled monolayer (SAM) composed of HDT and 11-inercaptoundecanoic acid was used to reduce the hydrophobicity of the thiol-functionalized Surface. The addition of hydrophilic groups to the surface enhanced the rate of adsorption of Pt2+ onto the surface. The findings show that the adsorption of metal ions is strongly dependent upon the hydrophilicity/hydrophobicity of the surface and that the technique represents an easy method for analyzing the adsorption of metal ions to a functionalized surface by combining SPR spectroscopy with a SAM modification. (c) 2006 Elsevier Inc. All rights reserved.