Brain Function: Novel Technologies Driving Novel Understanding - Bioinspired Approaches for Human-Centric Technologies - page 321

Fig. 10.15 3D hollow nanocylinders fabricated as arrays for advanced neural interfacing and
spectroscopy applications (De Angelis et al. 2013 )
light, with light stimulation performed at power levels below the threshold of
damage.
An example of an optical transducer is Raman spectroscopy cell-based bio-
sensors. Raman signals are inelastic scattering events of the incoming photons with
vibrating molecules of the bio-system. Consequently, the spectrum of scattered
Raman signals at different wavelengths represents a comprehensive map of the
biochemical environment of the system. Each molecular species found in cells, like
proteins, DNA, and lipids, has characteristic Raman peaks that can be used to
measure the presence and quantity of this species. Moreover, by acquiring Raman
spectra in time, it is possible to measure the dynamics of various molecular species
by tracking the positions and intensities of peaks as a function of time. The
sensitivity of Raman spectroscopy can be greatly improved by exploiting
nanostructures as functional interfaces to the biological analyte. These improve-
ments are due to the “field enhancement” generated by surface plasmons on the
nanostructure surface that is excited with light. Surface plasmons are coherent
oscillations of electrons generated by photon excitation at the interface between a
dielectric medium and a metal. If the metal surface has spatial extensions in the
nanometer range, the surface plasmon frequency has a resonance when excited with
light in the visible and near-infrared range. Biosensing techniques such as surface-
enhanced Raman spectroscopy (SERS) exploit these phenomena. SERS is a Raman
spectroscopy technique in which the Raman signals of biomolecules are enor-
mously enhanced by the presence of metallic nanostructures on the sensor's