Surface-Enhanced Raman Scattering-Based Bioimaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 330

Tags (BRigHTs) offer a remarkably high SERS Ef of 1.7 × 10 11 with 785 nm excita-
tion, which is higher than any other gold-based SERS probe reported so far. More
recently, we have demonstrated core-Janus shell plasmonic nanostructures com-
prised of au and ag, which is highly Raman active, making it attractive for Raman-
based bioimaging applications [62]. Those novel SERS tags are expected to enable
high-resolution, non-invasive Raman-based molecular bioimaging. Particularly
intense Raman signal sparks from individual nanostructures with in-built EM hot
spots, in contrast to the SERS tags that rely on clusters of nanostructures to create
Raman-intense EM hot spots.

11.5 raman reporterS

apart from plasmonic engineering, rational choice of Raman reporter molecules
also plays a critical role in the brightness of the SERS probe. Recent systematic
investigations suggest that carefully chosen resonant Raman reporters can provide
up to two orders of magnitude higher SERS Ef compared to nonresonant
counterparts [63]. in this investigation, the effective differential Raman scattering
cross section ( dσ R / dΩ ) of SERS nanolabels was proposed to estimate the bright-
ness of the whole label, basing on the type of the Raman reporter and the size of
nanoparticles (see fig. 11.7). The molecular resonance of the reporters can con-
tribute to producing intense SERRS signals. SERRS typically has enhancement
several orders magnitude greater than nonresonant SERS; the maximal SERRS
intensity usually coincides with the frequency of the electronic transition
maximum rather than the plasmon maximum, emphasizing the difference between
SERRS and SERS [64-67]. an ultrasensitive niR Raman reporter cynaMLa-381
was identified in an 80-member tricarbocyanine library for SERS-based in vivo
cancer detection, showing 12-fold higher sensitivity than the standard 3,3′-dieth-
ylthiatricarbocyanine (DTTc) [68]. These reports clearly highlight the impor-
tance of rational choice of Raman reporters in improving the brightness of the
SERS probes.

11.5.1 Surface coating for Stabilization

as mentioned earlier, stability of SERS probes against desorption of Raman tags
and enzymatic degradation in physiological conditions and long circulation times
are critical for in vitro and in vivo bioimaging applications. common protection/
stabilization layers including glass (silica), lipid, and biocompatible polymers
(e.g., poly(ethylene glycol)) render stealth character to SERS probes to escape the
reticuloendothelial system and reach the target site [18, 20, 69]. figure 11.8 shows
that SERS probes stabilized by thiol-terminated polyethylene glycol, which sig-
nificantly enhances the circulation time of the SERS probes [18]. These PEgylated
SERS probes were used for in vivo tumor targeting. While there has been
significant progress in proof-of-concept SERS-based bioimaging demonstrations,
factors that determine the biodistribution, cellular uptake, and pharmacokinetics