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Improved adhesion of gold island films evaporated on glass

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Improved adhesion of gold island films evaporated on glass Powered By Docstoc
					  Thermal Embedding and Enhanced Stability of Gold Nanostructures on Glass

 Tanya Karakouz, Tatyana A. Bendikov, Alexander Tesler, Alexander Vaskevich, and
                                   Israel Rubinstein
 Dept. of Materials & Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel

Nanostructured noble metal (Au, Ag) films support excitation of localized surface
plasmon (SP) polaritons in the visible to NIR wavelength range. The high sensitivity of
localized surface plasmon resonance (LSPR) to the dielectric properties of the
immediate environment allows detection of analyte binding to the nanostructured films.
The simplicity of the measurements, using standard spectrophotometric equipment, has
stimulated studies of optical transducers based on LSPR spectroscopy.
Nanostructured noble metal films on transparent substrates (glass, quartz, sapphire) are
known to be unstable, hence, despite the substantial interest, to date no actual sensing
applications have been realized. The morphological instability of discontinuous metal
nanostructures on oxide substrates is a major cause of artifacts in the optical response of
LSPR based sensors. Stabilization can be achieved using adhesive promoters and/or
stabilizing overlayers, however, both methods interfere with the performance of LSPR
transducers in complicating the preparation of the recognition interface and lowering the
sensitivity.
We have recently introduced a new approach to the preparation of strongly bonded and
morphologically stable Au nanostructures on glass substrates without the use of any
adhesion promoters or coating layers. We found that annealing of nanostructured Au
films (evaporated Au islands or Au nanoparticle films) at temperatures close to or above
the glass transition temperature Tg of the glass substrate in the presence of oxygen, leads
to partial embedding of the metal nanostructures in the glass and stabilization of the
film morphology and optical properties.
Two systems were studied, i.e., Au films prepared by thermal evaporation on glass1 and
citrate-stabilized Au nanoparticles (NPs) immobilized on aminosilane-modified glass.2
The morphology of the Au features and underlying glass substrate was followed by
AFM imaging (Figure 1). Upon annealing in air the Au islands or NPs become partially
embedded in the glass and encircled by a glass rim, as seen in the AFM images of
annealed samples after Au dissolution, showing the depressions left in the glass
substrate (Figure 1).
(A)                      Annealing                      (B)
                         600°C, 10h,
                            in air

                                                                 Au dissolution
             Au dissolution            Au dissolution            in iodine tincture
              in aqua regia             in aqua regia




Figure 1. 3D AFM images of stabilized Au nanostructures. (A) Evaporated 10 nm
(nominal thickness) Au film on glass. (B) 60 nm (average diameter) citrate-stabilized
Au NPs immobilized on aminosilane-modified glass and annealed 10 h at 600 οC.
The optical response of transducers annealed at different temperatures in a common
biorecognition experiment is shown in Figure 2, demonstrating the improvement of the
system stability as the annealing temperature approaches the glass transition
temperature of the substrate (Tg = 557 °C). The superior adhesion and stability of the
optical signal is attributed to the partial embedding of the metal nanostructure in the
glass and formation of a glass rim.
      .
                                                    500 °C                       550 °C
                                                               Ethanol wash
                                        0.6                    Rabbit IgG
                                                               BSA
                                                               Anti Rabbit IgG
                                        0.5

                                        0.4
                                                                                              Specific
                                        0.3
                 Extinction (abs. u.)




                                        0.2


                                                               Ethanol wash
                                        0.6                    Rabbit IgG
                                                               BSA
                                        0.5                    Anti Mouse IgG             Nonspecific
                                        0.4

                                        0.3

                                        0.2


                                              500     600     700        500       600       700
                                                             Wavelength (nm)

Figure 2. Optical response of LSPR transducers to specific and nonspecific binding of
IgG antibodies to IgG antigen immobilized on the islands. The transducers: 10 nm Au
island films evaporated on glass substrate and annealed 10 h at 500 °C (left) and 550 °C
(right).
The morphology and optical response of thermally stabilized nanostructured Au films
(island or NPs) are also exceedingly stable toward immersion in solvents (including
PBS), drying, and thiol self-assembly. The films pass successfully the adhesive-tape
test. Nanostructured Au films stabilized by partial thermal embedding are promising as
LSPR transducers in sensing applications.

References
1. T. Karakouz, A. Tesler, T. A. Bendikov, A. Vaskevich and I. Rubinstein, Highly-Stable Localized
Plasmon Transducers Obtained by Thermal Embedding of Gold Island Films on Glass, Advanced
Materials, in press.
2. T. Karakouz, A. Vaskevich and I. Rubinstein, Thermal Embedding and Stabilization of Gold
Nanoparticles on Glass, in preparation.

				
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posted:10/25/2011
language:English
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