14 Plasmonics and Super-Hydrophobicity
511
14.3 Materials and Methods
Rhodamine R6G, myoglobin, ribonuclease B, lysozyme and sodium chloride was
purchased from Sigma. De-ionized (D.I.) water (Milli-Q Direct 3, Millipore) was
used for all experiments. All chemicals, unless mentioned otherwise, were of analytical grade and were used as received. Rhodamine6G is an organic compound and
is used extensively in biotechnology applications. It is a dye which can be observed
very clearly by fluorescence microscopy. Its absorption and emission wavelength are
530 and 556 nm, respectively.
Small drops (V< 10μl, R< 1.35mm) of D.I. water containing infinitesimal amounts
of analytes were gently posted upon the surfaces and the entire process of evaporation followed over time. An automatic contact angle meter (KSV CAM 101, KSV
INSTRUMENTS LTD, Helsinki, Finland) was used at room temperature. Please
notice that the energy of adhesion Δ per unit area at the gas/water interface is
≥ 72.8mJ/m 2 at 20 ∪ C. The process enabled to concentrate very tiny amounts of
agents over micrometric areas. The evaporation processes were performed in a clean
room to reduce the presence of external contaminants and lasted approximately
30 min. The residual solute was observed using scanning electron microscope (SEM),
fluorescent microscopy and Raman spectroscopy techniques.
14.3.1 Fabrication of the Devices
Artificial super hydrophobic surfaces were fabricated. These are textures comprising
a periodic hexagonal lattice of cylindrical Si micro pillars with a certain diameter
and pitch. Nano-sized geometries appropriately positioned upon the pillars would
assure giant SERS enhancement. (100) silicon wafers (from Jocam, Milan, Italy)
were cleaned with acetone and isopropanol to remove possible contaminant and then
etched with a 4 % wet HF solution. The wafers were then rinsed with DI water and
dried with N2. Standard optical lithography techniques (Karl Suss Mask Aligner
MA 45, Suss MicroTec GA, Garching, Germany) were employed to dig regular
arrays of disks within a layer of positive resist (S1813, from Rohm and Haas) that
was spin-coated onto clean silicon wafers (Fig. 14.4a). Electroless deposition techniques were employed to grow silver nanograins within the holes (Fig. 14.4b). Upon
removal of the residual resist with acetone, a Bosch Reactive Ion Etching (MESC
Multiplex ICP, STS, Imperial Park, Newport, UK) process was utilized whereby the
final structures were obtained in the form of cylindrical pillars with an aspect ratio
greater than 2 (Fig. 14.4c). The electroless grown Ag layer served as mask during
the RIE process, while its characteristic granular structure allowed for the enhancement of the SERS signal. The substrates, as a whole, were then covered with a thin
(few nm) film of a Teflon like (C 4 F 8 ) polymer to assure hydrophobicity (Fig. 14.4d).
The masks necessary for optical lithography were fabricated using standard Electron Beam Lithography (Crestec CABL-9000C Electron beam lithography system)
methods.
511
14.3 Materials and Methods
Rhodamine R6G, myoglobin, ribonuclease B, lysozyme and sodium chloride was
purchased from Sigma. De-ionized (D.I.) water (Milli-Q Direct 3, Millipore) was
used for all experiments. All chemicals, unless mentioned otherwise, were of analytical grade and were used as received. Rhodamine6G is an organic compound and
is used extensively in biotechnology applications. It is a dye which can be observed
very clearly by fluorescence microscopy. Its absorption and emission wavelength are
530 and 556 nm, respectively.
Small drops (V< 10μl, R< 1.35mm) of D.I. water containing infinitesimal amounts
of analytes were gently posted upon the surfaces and the entire process of evaporation followed over time. An automatic contact angle meter (KSV CAM 101, KSV
INSTRUMENTS LTD, Helsinki, Finland) was used at room temperature. Please
notice that the energy of adhesion Δ per unit area at the gas/water interface is
≥ 72.8mJ/m 2 at 20 ∪ C. The process enabled to concentrate very tiny amounts of
agents over micrometric areas. The evaporation processes were performed in a clean
room to reduce the presence of external contaminants and lasted approximately
30 min. The residual solute was observed using scanning electron microscope (SEM),
fluorescent microscopy and Raman spectroscopy techniques.
14.3.1 Fabrication of the Devices
Artificial super hydrophobic surfaces were fabricated. These are textures comprising
a periodic hexagonal lattice of cylindrical Si micro pillars with a certain diameter
and pitch. Nano-sized geometries appropriately positioned upon the pillars would
assure giant SERS enhancement. (100) silicon wafers (from Jocam, Milan, Italy)
were cleaned with acetone and isopropanol to remove possible contaminant and then
etched with a 4 % wet HF solution. The wafers were then rinsed with DI water and
dried with N2. Standard optical lithography techniques (Karl Suss Mask Aligner
MA 45, Suss MicroTec GA, Garching, Germany) were employed to dig regular
arrays of disks within a layer of positive resist (S1813, from Rohm and Haas) that
was spin-coated onto clean silicon wafers (Fig. 14.4a). Electroless deposition techniques were employed to grow silver nanograins within the holes (Fig. 14.4b). Upon
removal of the residual resist with acetone, a Bosch Reactive Ion Etching (MESC
Multiplex ICP, STS, Imperial Park, Newport, UK) process was utilized whereby the
final structures were obtained in the form of cylindrical pillars with an aspect ratio
greater than 2 (Fig. 14.4c). The electroless grown Ag layer served as mask during
the RIE process, while its characteristic granular structure allowed for the enhancement of the SERS signal. The substrates, as a whole, were then covered with a thin
(few nm) film of a Teflon like (C 4 F 8 ) polymer to assure hydrophobicity (Fig. 14.4d).
The masks necessary for optical lithography were fabricated using standard Electron Beam Lithography (Crestec CABL-9000C Electron beam lithography system)
methods.