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 language | English |
|---|---|
| Pages (from-to) | 2788-2793 |
| Number of pages | 6 |
| Journal | Langmuir |
| Volume | 15 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - 1999 Apr 13 |
| Externally published | Yes |
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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 journal › Article
}
TY - JOUR
T1 - Observation of silver and hydrogen ion binding to self-assembled monolayers using chemically modified AFM tips
AU - Ito, Takashi
AU - Citterio, Daniel
AU - Bühlmann, Philippe
AU - Umezawa, Yoshio
PY - 1999/4/13
Y1 - 1999/4/13
N2 - 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.
AB - 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.
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UR - http://www.scopus.com/inward/citedby.url?scp=0344614476&partnerID=8YFLogxK
U2 - 10.1021/la980661y
DO - 10.1021/la980661y
M3 - Article
AN - SCOPUS:0344614476
VL - 15
SP - 2788
EP - 2793
JO - Langmuir
JF - Langmuir
SN - 0743-7463
IS - 8
ER -