Biomedical Engineering Reference
In-Depth Information
5.5 Experimental Results
5.5.1 Monolayers of Fluorophores on Silicon Oxide Surfaces:
Fluorescein, Quantum Dots, Lipid Films
SSFM can be used to measure the vertical position of fluorophores separated
from a silicon mirror by a transparent layer of silicon oxide. Monolayer surfaces
of fluorescein, quantum dots [7], and lipid films [6] are investigated in the
experiments below.
Fluorescein
To demonstrate detection of the axial position of a fluorescein monolayer
from the silicon mirror, a sample was prepared with a spacer layer of silicon
oxide etched to different heights, and a monolayer of fluorescein was immo-
bilized on surface via isothiocyanate-aminosilane chemistry. The surface was
then scanned in a grid pattern with fluorescence emission spectra taken every
200
m, and the spectra were processed to yield the axial position of the fluo-
rophores at each spot. Figure 5.6 displays the height data as a 3D gray-scale
image, where it is apparent that nanometer axial resolution is obtained. Note
that this is
not
the fluorescence intensity, which is relatively uniform.
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Quantum Dots
Quantum dots (QDs) are a new area of research with potential applications
in many fields. The excitation spectrum of most QDs is unusually broad.
However, the emission properties of a QD depend on its size: smaller dots emit
light with shorter wavelengths. Samples of QDs that are uniform in size have
Fig. 5.6.
Surface profile reconstructed from self-interference spectra.
