Biomedical Engineering Reference
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(a)
O
O
O
Tether or
cross linker
Protein or
ligand
Tether or
cross linker
+H
2
N
O
N
Protein or
ligand
H
O
NHS ester
(b)
O
O
Protein or
ligand
Tether or
cross linker
Tether or
cross linker
+HS
N
N
Protein or
ligand
S
O
Maleimide
O
EDCI
(c)
H
N
N
N
N
N
C
HO
N
Protein or
ligand
O
Protein or
ligand
O
O
O
NHS
HO
O
O
Tether or
cross linker
O
NH
2
Tether or
cross linker
Protein or
ligand
N
N
O
Protein or
ligand
O
O
FIGURE 4.4
Functionalization of surface silanols with (a) 3-aminopropyltriethoxysilane and
(b) with ethanolamine. In part (a) possible reaction outcomes are shown: (i) the desired out-
come; (ii) possible side reactions.
interact with the AFM probe and produce spurious unbinding events that might be
mistaken with actual unbinding events.
Polymerization problem can be alleviated by depositing silanes in a highly
controlled three-step process (Krasnoslobodtsev & Smirnov, 2002) or by functional-
ization of surfaces with compounds that do not polymerize in solution. Possible alter-
native to APTES include silanes with only one group that reacts with silanols (e.g.,
3-aminopropyl dimethylethoxysilane is commercially available) (Kuhner et al. 2004;
Jiang et al. 2010). In addition, silatrane compounds (Table 4.2) do not polymerize
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