Surface enhanced resonance Raman scattering (SERRS) is an analytical technique with several advantages over
competitive techniques in terms of improved sensitivity and multiplexing. We have made great progress in the
development of SERRS as a quantitative analytical method, in particular for the detection of DNA. SERRS is an
extremely sensitive and selective technique which when applied to the detection of labelled DNA sequences allows
detection limits to be obtained which rival, and in most cases, are better than fluorescence. Here the conditions are
explored which will enable the successful detection of DNA using SERRS. The enhancing surface which is used is
crucial and in this case suspensions of nanoparticles were used as they allow quantitative behaviour to be achieved and
allow analogous systems to current fluorescence based systems to be made. The aggregation conditions required to
obtain SERRS of DNA are crucial and herein we describe the use of spermine as an aggregating agent. The nature of the
label which is used, be it fluorescent, positively or negatively charged also effects the SERRS response and these
conditions are again explored here. We have clearly demonstrated the ability to identify the components of a mixture of 5
analytes in solution by using two different excitation wavelengths and also of a 6-plex using data analysis techniques.
These conditions will allow the use of SERRS for the detection of target DNA in a meaningful diagnostic assay.
Functionalised nanoparticles have been used in a number of studies including detection of DNA at ultra low
concentrations, immuno-histochemistry and more recently as substrates for surface enhanced resonance Raman
scattering (SERRS) based imaging approaches. The advantages of using metallic nanoparticles are that they are
very bright in terms of their optical characteristics and also can be functionalised to provide a SERRS response and
hence provide a unique Raman fingerprint. Here we present the functionalisation of gold and silver nanoparticles in
such a way that the enhancement effect can be greatly increased through biological interaction and as such
effectively turn on the SERRS effect. In an advancement of this nanoparticles have been used as imaging agents for
single cells when functionalised with an appropriate antibody and can give information on the expression of specific
receptors on cell surfaces as well as sub-cellular compartmentalisation information.
Gold and silver nanoparticles functionalized with oligonucleotides can be used for the detection of specific
sequences of DNA. We show that gold nanoparticles modified with locked nucleic acid (LNA) form stronger
duplexes with a single stranded DNA target and offer better discrimination against single base pair mismatches
than analogous DNA probes. Our LNA nanoparticle probes have also been used to detect double stranded DNA
through triplex formation, whilst still maintaining selectivity for only complementary targets. Nanoparticle
conjugates embedded with suitable surface enhanced resonance Raman scattering (SERRS) labels have been
synthesized enabling simultaneous detection and identification of multiple DNA targets.
Raman spectroscopy provides a very effective method of identifying an illicit substance in situ without separation or contact other than with a laser beam. The equipment required is steadily improving and is now reliable and simple to operate. Costs are also coming down and hand held portable spectrometers are proving very effective. The main limitations on the use of the technique are that it is insensitive in terms of the number of incident photons converted into Raman scattered photons and fluorescence produced in the sample by the incident radiation interferes. Newer methods, still largely in the development phase, will increase the potential for selected applications. The use of picosecond pulsed lasers can discriminate between fluorescence and Raman scattering and this has been used in the laboratory to examine street samples of illicit drugs. Surface-enhanced Raman scattering, in which the analyte requires to be adsorbed onto a roughened metal surface, creates a sensitivity to compete with fluorescence and quenches fluorescence for molecules on a surface. This provides the ability to detect trace amounts of substances in some cases. The improving optics, detection capability and the reliability of the new methods indicate that the potential for the use of Raman spectroscopy for security purposes will increase with time.