Observation of silver and hydrogen ion binding to self-assembled monolayers using chemically modified AFM tips

Takashi Ito, Daniel Citterio, Philippe Bühlmann, Yoshio Umezawa

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Atomic force microscopy (AFM) was used to study binding of ionic species (Ag+ and H+) to planar substrates and AFM tips chemically modified with self-assembled monolayers (SAMs) formed with terminally functionalized organosiloxanes. Adhesion forces between tips and substrates modified with methylsulfanyl-terminated SAMs and immersed into aqueous Ag+ solutions increased with an increase in the Ag+ concentration up to ≈ 10 mM Ag+ and then decreased with a further increase in the Ag+ concentration. Contact angles on the same substrates continuously decreased as the concentration of Ag+ increased. The increase in adhesion force between methylsulfanyl groups with an increase in the Ag+ concentration up to ≈ 10 mM Ag+ can be explained by simultaneous binding of Ag+ to methylsulfanyl groups on the tip and on the substrate, resulting in 1:2 complexes. The decrease in the adhesion force at very high Ag+ concentrations likely reflects the formation of 1:1 complexes in the presence of an excess of Ag+, resulting in electrostatic repulsion between tips and substrates that both bear positive charges due to Ag+ binding. On the other hand, for amino- or 2-imidazolin-1-yl-terminated SAMs, adhesion forces and contact angles similarly decreased from pH 10 to 2. This decrease in adhesion force with increasing H+ concentration seems to reflect preferential formation of 1:1 complexes, resulting in repulsion between the positively charged tip and substrate surfaces. Adhesion due to the formation of 1:2 complexes was not observed for H+, which is consistent with the low stability of such complexes in solution. These results demonstrate that adhesion forces can be used to observe sandwich-type binding of metal ions between ligands immobilized on solid substrates and chemically modified AFM tips.

Original languageEnglish
Pages (from-to)2788-2793
Number of pages6
JournalLangmuir
Volume15
Issue number8
DOIs
Publication statusPublished - 1999 Apr 13
Externally publishedYes

Fingerprint

Self assembled monolayers
hydrogen ions
Silver
Protons
Atomic force microscopy
Adhesion
silver
atomic force microscopy
adhesion
Hydrogen
Ions
Substrates
ions
Contact angle
Metal ions
bears
Electrostatics
Ligands
metal ions
electrostatics

ASJC Scopus subject areas

  • Colloid and Surface Chemistry
  • Physical and Theoretical Chemistry

Cite this

Observation of silver and hydrogen ion binding to self-assembled monolayers using chemically modified AFM tips. / Ito, Takashi; Citterio, Daniel; Bühlmann, Philippe; Umezawa, Yoshio.

In: Langmuir, Vol. 15, No. 8, 13.04.1999, p. 2788-2793.

Research output: Contribution to journalArticle

Ito, Takashi ; Citterio, Daniel ; Bühlmann, Philippe ; Umezawa, Yoshio. / Observation of silver and hydrogen ion binding to self-assembled monolayers using chemically modified AFM tips. In: Langmuir. 1999 ; Vol. 15, No. 8. pp. 2788-2793.
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