Chemistry Reference
In-Depth Information
12
SINGLE-MOLECULE SPECTROSCOPY
OF DENDRIMER SYSTEMS
T
OM
V
OSCH
Nano-Science Center, Department of Chemistry, University of Copenhagen,
Universitetsparken 5, 2100 Copenhagen, Denmark
12.1 SINGLE-MOLECULE DETECTION AND SPECTROSCOPY
The most commonly used way to optically detect a single molecule is through
fluorescence, and hence this method is known as single-molecule fluorescence
spectroscopy (SMFS) [1-3]. SMFS is generally performed by using confocal or
wide-field fluorescence microscopy, which both have their specific advantages and
disadvantages. In addition, scanning near-field optical microscopy (SNOM or
NSOM) can also be used, which can provide a subdiffraction optical resolution
(between 10 and 100 nm) and topological information at the same time [4-7].
Drawbacks of SNOM are the less user-friendly operation and the limited depth
information (maximum up to 300 nm). Recent developments have made it possible
to also achieve subdiffraction resolution images with confocal and wide-field
microscopy [8-14]. The only other common detectable optical signal from single
molecules is surface enhanced Raman scattering but this technique requires the
presence of a metallic (commonly silver) plasmonic particle [15-17]. We will limit
ourselves here to confocal and wide-field fluorescence microscopy. In order to
detect fluorescence from a single molecule, the fluorescence intensity of the
molecule should be well above the background. This background can originate
from inelastic scattering and from impurity fluorescence in the solvents, cover
