3 Surface-enhanced Raman Scattering ...
45
ing NIR lasers in this area. It could reduce fluorescence and background spectra of
biological matrix [130].
Another example of sensing biomolecules are SERS experiments with bacterial
spores. Indirect SERS detection of some bacterial spores is based on tracking down
its biomarkers—molecules which are released from the spores while absent from
vegetative cells. In case of bacterial genus of Bacillus, dipicolinic acid (dPA) serves
as a biomarker for its spores. Sensitive dPA sensor is interesting from medical point
of view, as one member of the genus, Bacillus anthracis, causes an acute disease:
anthrax. AgFoN substrate turned out to be applicable in this problem as well [131].
obtained limit of detection for Bacillus subtilis spores (~ 2600 spores per 0,2 μl)
was well below anthrax infectious dose of ~ 10000 spores per 0,2 μl. Similar experiment was carried out using Au-nanoparticles-based substrate [132].
various fields of biosensing make use of so called nanotags: nanoparticles providing Raman enhancement for molecules adsorbed on them. having labelled a
biomolecule of interest with such a nanotag, one may be able to detect it indirectly:
SERS spectrum of a molecular dye adsorbed on a tag indicates presence of the
studied analyte.
Adenosine triphosphate (AtP) biosensor based on such nanolabels was demonstrated by Li et al. [133]. Nanotag consisted of malachite green isothiocyanate
(mgItC) molecules attached to gold nanostars which were additionally covered
with a layer of silica to prevent the reporter from detachment. It was functionalized
with a single-stranded dNA creating the signalling probe, while the capture probe:
complementary dNA strand was immobilized on a gold substrate. under normal
conditions, aptamer with the nanotag attached and the complementary strand create a duplex dNA, thus immobilizing the tag on the gold surface. however, dNA
dissociates in the presence of AtP which leads to decrease in the SERS signal from
the nanotag. Such a device determines not only absence or presence of AtP but also
its concentration.
dNA hybridization is also exploited in detecting dNA itself (Fig. 3.8). dye
molecule might be adsorbed on a SERS inactive substrate; collecting its SERS
spectrum becomes possible in the presence of a target strand after its hybridization
with a capture strand on the surface and a dNA-probe functionalized with a silver
nanoparticle [134].
on the other hand, reporter molecule can be adsorbed on a metal nanoparticle
bound to the probe dNA strand; it is only after hybridization of the probe strand
with an appropriate target strand on the sample surface when collecting the SERS
spectrum of the dye is feasible [135]. detected dNA strand might be also labeled
directly with a reporter molecule whose SERRS is collected, thanks to creating
a duplex dNA with a complementary strand on a SERS-active surface [136]. By
modifying different strands with different dyes, multiplexed dNA detection was
also obtained [137].
SERS nanotags are widely used in immunoassays [138–140]. In this case,
nanoparticles are functionalized not only with a reporter molecule but also with
an antibody which introduces selectivity for a certain antigen. Antigen binds to the
capture antibody immobilized on the surface and then to the antibody on the nano-
45
ing NIR lasers in this area. It could reduce fluorescence and background spectra of
biological matrix [130].
Another example of sensing biomolecules are SERS experiments with bacterial
spores. Indirect SERS detection of some bacterial spores is based on tracking down
its biomarkers—molecules which are released from the spores while absent from
vegetative cells. In case of bacterial genus of Bacillus, dipicolinic acid (dPA) serves
as a biomarker for its spores. Sensitive dPA sensor is interesting from medical point
of view, as one member of the genus, Bacillus anthracis, causes an acute disease:
anthrax. AgFoN substrate turned out to be applicable in this problem as well [131].
obtained limit of detection for Bacillus subtilis spores (~ 2600 spores per 0,2 μl)
was well below anthrax infectious dose of ~ 10000 spores per 0,2 μl. Similar experiment was carried out using Au-nanoparticles-based substrate [132].
various fields of biosensing make use of so called nanotags: nanoparticles providing Raman enhancement for molecules adsorbed on them. having labelled a
biomolecule of interest with such a nanotag, one may be able to detect it indirectly:
SERS spectrum of a molecular dye adsorbed on a tag indicates presence of the
studied analyte.
Adenosine triphosphate (AtP) biosensor based on such nanolabels was demonstrated by Li et al. [133]. Nanotag consisted of malachite green isothiocyanate
(mgItC) molecules attached to gold nanostars which were additionally covered
with a layer of silica to prevent the reporter from detachment. It was functionalized
with a single-stranded dNA creating the signalling probe, while the capture probe:
complementary dNA strand was immobilized on a gold substrate. under normal
conditions, aptamer with the nanotag attached and the complementary strand create a duplex dNA, thus immobilizing the tag on the gold surface. however, dNA
dissociates in the presence of AtP which leads to decrease in the SERS signal from
the nanotag. Such a device determines not only absence or presence of AtP but also
its concentration.
dNA hybridization is also exploited in detecting dNA itself (Fig. 3.8). dye
molecule might be adsorbed on a SERS inactive substrate; collecting its SERS
spectrum becomes possible in the presence of a target strand after its hybridization
with a capture strand on the surface and a dNA-probe functionalized with a silver
nanoparticle [134].
on the other hand, reporter molecule can be adsorbed on a metal nanoparticle
bound to the probe dNA strand; it is only after hybridization of the probe strand
with an appropriate target strand on the sample surface when collecting the SERS
spectrum of the dye is feasible [135]. detected dNA strand might be also labeled
directly with a reporter molecule whose SERRS is collected, thanks to creating
a duplex dNA with a complementary strand on a SERS-active surface [136]. By
modifying different strands with different dyes, multiplexed dNA detection was
also obtained [137].
SERS nanotags are widely used in immunoassays [138–140]. In this case,
nanoparticles are functionalized not only with a reporter molecule but also with
an antibody which introduces selectivity for a certain antigen. Antigen binds to the
capture antibody immobilized on the surface and then to the antibody on the nano-