Christoph Florian Schaller - FU Berlin, FB MI

Christoph Schaller - STORMicroscopy 4
Figure 1.3: The size scale of
various biological structures in
comparison with the diractionlimited
resolution. [6] (left to
right) A mammalian cell, a bacterial
cell, a mitochondrion, an
inuenza virus, a ribosome, the
green uorescent protein, and a
small molecule (thymine).
1.2 Imaging and noise
Wanting to work with these distributions of photons one would like to localize single photons as precise
as possible. However it is only possible to collect photons in so called pixels and measure the current
they cause at a photoelectric cell. Here we got our rst crucial source of noise: As we collect photons
within an area, we do not know from which exact location the photon originated. This uncertainty is
called pixelation noise.
Additionally the measured current does not indicate the exact number of photons within the area
as there are eects like dark current or incoming photons generating dierent numbers of electrons.
Those inaccuracies are regarded as global inuences and therefore their impact is summarized under
the term background noise together with eects such as out-of-focus uorescence and readout errors.
Finally we do not always observe
a perfect distribution but a xed
number of localizations generated
by the distribution. The inuence
of that factor is called photon shot
noise, but becomes negligible for
large enough photon numbers.
Taking into account that pixel
sizes of about 100 nm are common,
the imaging process as depicted in
Figure 1.4 seems pretty rough. Nevertheless
the distributions remain
observable and thus we can determine
their most likely centers.
Figure 1.4: The imaging process is aggravated by dierent
sources of noise and pixelation.