Adsorption of a Carboxylated Silane on Gold: Characterization for Its Rational Use in Hybrid Glass/Gold Substrates

Abstract

Integrated sensing and biosensing microfluidic systems often require sealing between polysiloxane, glass, and gold interfaces, while maintaining functional support on the gold surface within the cell chamber (e.g., biomolecular interaction analysis). A carboxylated trimethoxysilane (TMS-EDTA) coating has been shown to facilitate the bonding of polydimethylsiloxane (PDMS) to gold and glass slides. In this work, the adsorption of TMS-EDTA onto Au is characterized in order to enable its rational use in hybrid glass/gold substrates. Surface plasmon resonance results suggest that carboxylates are available for streptavidin immobilization. Atomic force microscopy studies indicate that a uniform surface coverage with monolayer thickness is formed. Infrared spectroscopy studies confirm that the carboxyl groups are present. Moreover, there is little evidence of siloxane cross-linking. Electrochemical differential capacitance measurements reveal that the potential-dependent free energies of adsorption are ∼−20 to–30 kJ/mol (for potentials between −0.5 and 0.2 V) in the complex electrolyte solution used. Furthermore, at highly negative potentials (∼−1.1 V), TMS-EDTA desorbs from the Au surface. The fundamental knowledge obtained about TMS-EDTA adsorption on Au can be applied to construct robust PDMS-based systems with hybrid glass/gold substrates.

Measuring and Remediating Nonspecific Modifications of Gold Surfaces Using a Coupled in Situ Electrochemical Fluorescence Microscopic Methodology

“…The adsorption of this molecule onto gold has been recently investigated for use in microfluidic applications. 35 TMS-EDTA adsorption is strong enough to compete with Cl − and OH − for the gold surface, but it is less strongly adsorbed than a thiol SAM. TMS-EDTA possesses three carboxyl groups and it was used to modify a gold surface using NHS/EDC modification of the carboxyls for strepavidin immobilization in a SPR flow cell.…”

“…A carboxylated silane (TMS-EDTA) is a particularly good example of these types of species. The adsorption of this molecule onto gold has been recently investigated for use in microfluidic applications . TMS-EDTA adsorption is strong enough to compete with Cl – and OH – for the gold surface, but it is less strongly adsorbed than a thiol SAM.…”

“…TMS-EDTA adsorption is strong enough to compete with Cl – and OH – for the gold surface, but it is less strongly adsorbed than a thiol SAM. TMS-EDTA possesses three carboxyl groups and it was used to modify a gold surface using NHS/EDC modification of the carboxyls for strepavidin immobilization in a SPR flow cell . To study this interface using the coupled electrochemical-fluorescence method, the adsorbed TMS-EDTA was postfunctionalized with the AlexaFluor488 cadaverine fluorophore using NHS/EDC chemistry as was done for MUA SAM.…”

“…TMS-EDTA possesses three carboxyl groups and it was used to modify a gold surface using NHS/EDC modification of the carboxyls for strepavidin immobilization in a SPR flow cell. 35 To study this interface using the coupled electrochemical-fluorescence method, the adsorbed TMS-EDTA was postfunctionalized with the AlexaFluor488 cadaverine fluorophore using NHS/EDC chemistry as was done for MUA SAM. It is expected that some of the TMS-EDTA carboxyls exposed to solution would become fluorophore labeled.…”

“…Competition for the surface with phosphate and chloride ions, which are known to adsorb onto gold, 33,34 likely displaces these nonspecifically or weakly adsorbed TMS-EDTA molecules but not those more strongly bound. 35 Therefore, for this surface modification, soaking in buffer is more effective than a simple rinsing of the substrate evidenced by the decrease in the amount of adsorbate desorbing at small negative potentials.…”