Biology Reference
In-Depth Information
developments in the ield of nanophotonics and speciically nanoplasmonics
are triggering a renewed interest in the NSOM community. This is because
optical antennas in combination with plasmonics promise super-resolution
at the nanometre scale accompanied by a great degree of electric ield
enhancement and thus brighter local illumination sources.
The main idea of optical antennas is to localize and enhance the optical
radiation to a nanometric region, similar to electromagnetic antennas, which
convert propagating radiation into a conined zone. In the biological context,
gold nanoparticles attached to glass tips have been exploited as nano-
antennas
channels on erythrocyte plasma
membranes at 50 nm optical resolution.
34
Unfortunately, the method relies
on far-ield illumination to excite the antenna, therefore adding a signiicant
background contribution to the antenna response and requiring modulation
techniques to reduce the background.
33
and used to image single Ca
2+
A different excitation scheme that
suppresses background illumination was irst proposed by Frey
35
et al.
68
and
more recently reined by Taminiau
In these tip-on-aperture antennas,
the local illumination properties of aperture-type NSOM are used to drive
the antenna to resonance. Using this coniguration, single-molecule detection
with 30 nm resolution and virtually no background has been recently
demonstrated.
et al.
69
Although nanoscale imaging of biological samples should be
one of the most promising applications of this approach,
70
its use in intact
cell membranes in physiological conditions has not been explored until very
recently.
Our group has recently demonstrated the potential of optical antennas
for nanobioimaging of individual receptors and nanodomains on intact cells
of the immune system.
69
The probe-based monopole optical antennas were
fabricated by carving of the antenna on the tip apex of conventional NSOM
probes at the glass-metal interface using (Ga+)-FIB milling.
71
The geometry,
i.e., length, width and radius, of the curvature of the antennas can be carefully
controlled during FIB to maximize their response in liquid conditions. In
our case, the dimensions of the fabricated antennas varied from 50 to 60 nm
in width, ~20 nm of radius of curvature and lengths between 90 and 135
antenna conditions to image individual antibodies in liquid conditions with
an unprecedented resolution of 26 ± 4 nm and virtually no surrounding
background. On intact cell membranes in physiological conditions, the
obtained resolution is currently 30 ± 6 nm. Importantly, the method allowed
us to distinguish individual proteins from nanodomains and to quantify the
degree of clustering by directly measuring physical size and intensity of
71
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