Abstract We examine the prospective routes for the design of synthetic/biomacromolecular/inorganic film assemblies for photothermal cell based on biomimetic approach. We demonstrate examples of channel proteins immobilized onto surfaces of silicon single crystals modified with Langmuir-Blodgett and self-assembled monolayers. These proteins can be immobilized in intact, closed-pore conformation. Their state within photosensitive monolayers can be controlled by the photoisomerization reaction triggered by UV light

Alexander Sidorenko

Maryna Ornatska

Vladimir V Tsukruk

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Progress in Organic Coatings 47 (2003) 288–291
Synthetic and bio-hybrid nanoscale layers with tailored
surface functionalities
Vladimir V. Tsukruk∗, Maryna Ornatska, Alexander Sidorenko
Department of Materials Science and Engineering, Iowa State University, 3155 Gilman Hall, Ames, IA 50011, USA
Abstract
We examine the prospective routes for the design of synthetic/biomacromolecular/inorganic film assemblies for photothermal cell based
on biomimetic approach. We demonstrate examples of channel proteins immobilized onto surfaces of silicon single crystals modified with
Langmuir–Blodgett and self-assembled monolayers. These proteins can be immobilized in intact, closed-pore conformation. Their state
within photosensitive monolayers can be controlled by the photoisomerization reaction triggered by UV light.
© 2003 Elsevier B.V. All rights reserved.
Keywords: Photosensitive monolayers; Nanoscale layer; Protein adsorption; Membrane channel proteins
1. Introduction
Biomimetics allows researchers to tap into the ingenious
designs of nature to inspire improvements on current sens-
ing technology. Often, a unique biomaterial microstructure
and specific properties are targeted in such an approach.
Recent developments in the advanced materials sciences
have given unparalleled access to biological systems at all
levels of structural organization, including nearly in vivo
conditions. This has provided an opportunity to uncover
the rules governing in situ functioning of biomolecular
structures and the routes to designs of microsensors based
on these rules. Recent studies have extensively discussed
mechanisms of heat detection in the physiological response
of such biological species as snakes and beetles[1–6]. In
both species, IR-sensitive elements are represented by a
compliant thin membrane film deflecting in respond to a
change in heat flux. The structure of these biological IR
receptors is remarkable for their ability to monitor thermal
flux with high sensitivity. Suspended membrane structure
recalls the design of a photothermal Golay cell introduced
many years ago. The working principle of this cell is based
on the detection of sub-micrometer-scale deviations of a
flexible metal membrane caused by gas expanding in a
sealed rigid cell (Fig. 1) [7,8], limits dramatically thermal
sensitivity of the Golay cell and its spatial resolution. In
a micromachined version of the Golay cell proposed very
recently, a sensitive element is composed of a solid sil-
∗ Corresponding author. Tel.:+1-515-294-6904; fax:+1-515-294-5444.
E-mail address: vladimir@iastate.edu (V.V. Tsukruk).
icon membrane of a micrometer thickness that improves
sensitivity and resolution to some extent[9].
Considering available findings on biological receptors,
several additional steps could be suggested to increase the
thermal sensitivity of existing thermal sensors. The design
of the sensing elements from compliant membrane should
provide sensibility to the structure far greater than the rigid
membrane in current Golay cell design (Fig. 2). A further im-
provement may be seen in the multilayered structure of these
membranes unlike a silicon membrane of the Golay cell. As
previously noticed in biological IR receptors, not only does
this structure provide a considerably faster response, but it
also allows a much higher probability of detection of local
temperature fluctuations. Free-suspended compliant mem-
branes can be more sensitive under stress conditions, and
thus are susceptible to consistent external disturbances.
A compliant layer with imbedded ion channel proteins can
be designed as a compliant stress-sensitive element (Fig. 3).
Indeed, on a molecular level, calcium ion channels act as
ion current modulators in response to change in membrane
tension. Similar ion channels are ubiquitous in thermal and
mechanical sensors in different live species from bacteria to
humans.
2. Results and discussion
A critical step in designing of prospective sensors
based on silicon micromachined devices and sensitive
biomacromolecule containing layers is immobilization of
very compliant membrane proteins on a solid surface with
0300-9440/$ – see front matter © 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0300-9440(03)00144-9
V.V. Tsukruk et al. / Progress in Organic Coatings 47 (2003) 288–291 289
  
Cavity gas 
Capacitance 
monitoring 
Membrane 
deflection 
Heat flux 
Fig. 1. Schematics of the photothermal Golay cell based on inorganic
material and operational principles discussed in Refs.[8,9].
preservation of their conformation[10]. Here, we discuss
our recent studies on immobilization of channel protein on
solid surfaces of silicon single crystals, which are widely
used in manufacturing of microsensors. The fabrication and
characterization procedures are discussed elsewhere (e.g.,
see[11]).
Briefly, the solid substrates were freshly cleaned atom-
ically smooth silicon wafers (Semiconductor Processing
Co.). Silicon wafers were treated for 10 min in an ultra-
sonic bath at room temperature and cleaned with a “piranha
solution” (30% concentrated hydrogen peroxide, 70% con-
centrated sulfuric acid) for 1 h. The substrates were rinsed
with Nanopure water and dried with dry nitrogen. Adsorbed
monolayers of the protein were prepared by placing a 20l
droplet of a protein solution on a bare or a modified silicon
wafer. Substrates were rinsed by water to remove excess
protein after 1 min exposure. The Langmuir–Blodgett (LB)
lipid monolayers at the air–water interface were compressed
to a condensed state (30 mN/m) and deposited onto the
Fig. 2. Schematics of a free-suspended, complaint multilayered membrane with incorporated mechanosensitive interlayer and a list of bio-inspiredelements.
 
 
 
+ - 
+ 
+ 
- 
+ 
+ - 
- 
+ 
- 
+ 
+ - 
+ 
+ 
- 
+ 
+ - 
- 
Fig. 3. The compliant interlayer with protein/lipid/hydrogel complex.
silicon substrate on an automated LB system (Riegel and
Kirstein, GmbH) located within a laminar clean air hood.
In our research, we have studied-toxin from Staphy-
lococcus aureus as a model ion channel. Staphylococcal
-hemolysin forms a large central pore in the open state,
which can be used for the modulation of the ionic conduc-
tivity through membrane[12–14]. Atomic force microscopy
(AFM) measurements were performed using Nanoscope
IIIa, Dimension 3000 and Multimode microscopes (Digital
Instruments) according to a usual procedure adapted in our
lab [15]. Tapping mode topographic and phase images were
recoded in the air using silicon cantilevers.
As we observed with high resolution AFM imaging, a di-
rect deposition of-hemolysin on a highly hydrophilic, bare
silicon surface under ambient conditions results in the fabri-
cation of a dense monolayer or globular individual molecules
depending upon initial concentration of solution (Fig. 4). In
this state, AFM did not confirm presence of open/close-pore
structures of individual protein molecules. Contrary, pro-
tein macromolecules on a bare silicon are in collapsed,
compressed shape and structural characteristics are different
from intact conformation. On the other hand, immobilization
290 V.V. Tsukruk et al. / Progress in Organic Coatings 47 (2003) 288–291
Fig. 4. AFM images of immobilized ion channel protein, topography (left) and phase (right). Top: Collapsed-h molysin adsorbed on a bare silicon
from concentrated solution, 1m × 1m. Bottom: LB lipid monolayer with hemolysin proteins in close-pore conformation (a white round bump),
400 nm× 400 nm, and corresponding cross-section (left).
Fig. 5. Bottom: A scheme of-hemolysin immobilization in a LB monolayer from photosensitive monodendron molecules; top: 3D views of intact protein
(right) and disassembled protein after photochromic isomerization of dendritic monolayer (amphiphilic monodendron containing a benzyl-15-crown-5
polar focal point and four dodecyl tails as peripheral groups[17]); model of seven subunit of-hemolysin as obtained by structure visualization using
Raswin Molecular Graphics v2.6 software (http://www.openrasmol.org) (left).
V.V. Tsukruk et al. / Progress in Organic Coatings 47 (2003) 288–291 291
Fig. 6. AFM topographical image of open-pore-hemolysin protein im-
mobilized in a loosely packed alkylsilane self-assembled monolayer.
of these proteins onto the silicon surface mediated by a
monolayer of lipid molecules supported by a polymer gel
water-containing sub-layer resulted in their positioning pre-
dominantly in-between lipid domains (see white dots in
Fig. 4). The presence of a light depletion on top of the
molecules as labeled by markers in a cross-section inFig. 4,
indicates their closed-pore structure.
Similarly, the preservation of a closed-pore conformation
can be achieved by immobilization of-hemolysin in LB
monolayer of photochromic dendrimer molecules by adsorp-
tion from a water subphase directly in LB trough (Fig. 5).
In this monolayer deposited on a solid substrate, protein
preserves its initial conformational state. Photoisomeriza-
tion of the supporting photosensitive dendrimer molecules
within the monolayer initiated by UV illumination at 365 nm
[16] causes photochromic conversion within monolayers
that, in turn, changes the intralayer pressure and triggers
“disassembling” of the protein (Fig. 5). Clearly seen are
seven subunits grouped similarly to their initial arrangement
in an assembled protein as can be seen from comparison with
corresponding molecular model (Fig. 5). Finally, this protein
immobilized on a loosely packed alkylsilane self-assembled
monolayer, possess a clearly visible open-pore microstruc-
ture with a wide-open central pore (Fig. 6).
In conclusion, we demonstrated that channel protein with
large pore can be immobilized into organic monolayer on
a surface of a silicon wafer via self-assembly or LB depo-
sition. Conformational state (close–open pore state) of the
protein could be controlled by the nature of the supporting
monolayer and its structural organization. The incorporation
of the channel proteins in thin free-standing membranes is
another challenging step.
Acknowledgements
This work is supported by AFOSR F49620-98-1-0480 and
F496200210205 contracts. The author thanks H. Bayley for
supply of-hemolysin, and M. Stone for useful discussions.
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Synthetic and bio-hybrid nanoscale layers with tailored surface functionalities

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