Biomedical Engineering Reference
In-Depth Information
used for SAM removal can range from ablation (with laser or an ion beam), degradation (with an
electron beam), electrochemical desorption (with the tip of a scanning tunneling microscope),
mechanical shear (with the tip of an atomic force microscope), or an oxygen plasma etch (the
latter masked with a photoresist pattern or a stencil).
2.4 Micropatterns of Proteins
Proteins can be used as the active sensor element in cell-free devices (e.g., in immunoassays)
and can play a cell-signaling role in cell-containing scafolds or surfaces. Hence, driven by bio-
technology, cell biology, and tissue engineering applications, there has been great interest in
techniques that allow for micropatterning proteins. Here, we review only the most widely used
methods, although the repertoire is much more colorful than presented here.
2.4.1 By Light
Photolithography is not really suited to directly micropattern proteins—as one would use it to
micropattern, say, a gold ilm; the solvents present in the photoresist solution and in the devel-
oper severely denature proteins because the solvents repel the water that the proteins need to
stabilize their structure (see Section 2.1). Nevertheless, before the advent of sot lithography,
photolithography was the only method available to micropattern proteins, and several tech-
nological variations on the same theme were attempted. In one highly cited scheme, photoli-
thography was used to micropattern an aminosilane SAM on a background of alkylsilane SAM
(
Figure 2.8
). Note that the irst steps were exactly as in Kleinfeld's scheme (
Figure 2.7
)—so the
same general concerns regarding the completion of silane reactions apply here. Next, the pattern
was bathed in glutaraldehyde, a cross-linker that binds to amines on both ends; one of the ends
of the cross-linker could presumably be free to bind amine groups on proteins. Alternatively,
the glutaraldehyde simply cross-linked amino groups on the aminosilane SAM. he glutaralde-
hyde pattern was exposed to luorescently-labeled horseradish peroxidase (HRP) to demonstrate
that there was more protein attached on the aminosilane areas than on the background. (It is
a
b
Glutaraldehyde
k
BHK cells
Photoresist micropattern
c
h
Alkylsilane SAM
RITC-labeled HRP
d
e
i
Aminosilane SAM
f
400 µm
g
j
FIGURE 2.8
Micropatterning.of.proteins.and.cells.via.aminosilane.and.alkylsilane.SAMs.using.pho-
tolithography..(From.Stephen.Britland,.Enrique.Perez-Arnaud,.Peter.Clark,.Brian.McGinn,.Patricia.
Connolly,.and.Geoffrey.Moores,
“Micropatterning.proteins.and.synthetic.peptides.on.solid.supports:.
A.novel.application.for.microelectronics.fabrication.technology,”.
Biotechnol. Prog.
.8,.155,.1992..
Figure.contributed.by.Stephen.Britland.)
