Supporting Information for Liquid crystal sensor for the detection of
acetylcholine using acetylcholinesterase immobilized on a nanostructured
polymeric surface
Gyeo-Re Han, and Chang-Hyun Jang*
Department of Chemistry, Gachon University, Seongnam-Si, Gyeonggi-Do 461-701, Korea
*
Corresponding author. Tel. +82-31-750-8555
E-mail address: chjang4u@gachon.ac.kr
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Experimental details
1. Cleaning of the substrates
Glass microscope slides and silicon wafers were cleaned using a piranha solution (70%
H2SO4/30% H2O2; Caution: piranha solution reacts violently with organic materials and
should be handled with extreme caution; do not store the solution in closed containers.) for 1
h at 80°C. After removal from the cleaning solution, the substrates were rinsed with copious
amounts of DI water, ethanol, and methanol and dried under a stream of gaseous N2. The
cleaned substrates were then stored overnight in an oven at 120°C.
2. Preparation of the octyltrichlorosilane (OTS)-functionalized silica substrate
The piranha-cleaned glass slides and silicon wafers were immersed into an OTS/n-heptane
solution for 30 min. The substrates were then rinsed with methylene chloride and dried under
a stream of N2. Next, the OTS-treated glass slides were tested for homeotropic alignment by
observing the orientation of 5CB sandwiched between the two OTS slides. Any slide that did
not display homeotropic alignment was discarded.
3. Deposition of the gold films
For use in combination with the liquid crystals, semi-transparent films of gold with a
thicknesses of 200 Å were deposited onto the patterned PUA substrates mounted on a rotating
planetary using an electron beam evaporator. The rotation of the substrates on the planetary
mount ensured that the gold was deposited without a preferred direction of incidence. A layer
of titanium (thickness = 80 Å) was used to promote adhesion between the PUA substrate and
the gold film. The rate of deposition of gold and titanium was 0.2 Å/s, and the pressure in the
evaporator was < 5 Torr during deposition.
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4. Atomic force microscopy (AFM)
The surface topology of the PUA substrates was characterized by AFM (NanoScope IIIa,
Veeco Metrology; Santa Barbara, CA) after fabricating the polymeric surface. The wavelength
and amplitude of the buckling patterns were determined by taking the average of the peak-topeak and peak-to-through distance, respectively, of 10 parallel waves. Images of the 11 MUAtreated surfaces after enzyme immobilization were also obtained by AFM. The samples were
imaged under ambient conditions using silicon tips with an average radius of ~ 10 nm. Images
were acquired at a scan rate of 1.0 Hz with 256 sample points per line.
5. Ellipsometry
The
ellipsometric
thicknesses
were
measured
using
an
Elli-SE(UV)-FM8
(Ellipsotechnology) at a wavelength of 380–1100 nm and an angle of incidence of 70°. All
measurements were performed using silicon wafers that were treated with the same procedure
used to prepare the enzyme immobilizations on the glass microscope slides, except for the
surface functionalization with 11-mercaptoundecanoic acid on the silicon wafers. Solutions of
3-aminopropyltriethoxysilane (APTES) and succinic anhydride (SA) were used to form
carboxylic acid-terminated SAMs on the silicon wafers. The increase in optical thickness of
the organic layer after the binding of proteins was calculated using a simple two-layer model
(organic layer/effective substrate of SiO2/Si) by assuming that the refractive index of the
organic layers was 0.
3
Figure S1.Tapping mode AFM images and cross-sectional profiles of the gold deposited
polymer substrate.
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Figure S2. Polarized light microscope images of 5CB on the AChE-immobilized surface
incubated with 1000 nM ACh solution for 2 h at 37°C: (a) before and (b) after rinsing with 15
mM NaBr. The orientational angle of the sample indicated on the left side (0° and 45°) was
defined as the angle between the direction of the anisotropic pattern and either polarizer. The
horizontal dimension of each image was 1.25 mm.
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