Surface-Enhanced Raman Scattering of DNA-Nanoparticle assemblies

During the last years, soft matter colloids have gained important achievements and a large amount of results have been accomplished to the realisation of innovative and smart nanomaterials. In particular, the understanding in the mastering of DNA-nanoparticle systems, which combine the plasmonic properties of metallic nanoparticles (NPs) with the programmability and self-assembly of DNA strands – opens up a great number of applications in different branches of science, especially in nanoscience. Consequently, the importance of Surface Enhanced Raman Scattering (SERS), which associates a high sensitivity and a specific spectral signature of DNA, is significantly increasing in the detection of specific targets, thus, in the implementation of high-quality biosensors. The DNA base-pairing specificity (A-T, C-G) allows the breakthrough in “programmable bonds” between nanoparticles, serving as the basic building blocks for the creation of mesoscopic plasmonic aggregates. In our labs we provided to the realisation of DNA-NP structures by properly functionalizing metallic gold NPs with complementary and purposely programmed single-stranded DNA. To this aim, we have chosen two specific single-stranded DNA sequences, consisting of 12 base oligomers, with a thiolgroup at the end of each one which allows to covalent bond onto the metallic NP surfaces; the aforementioned sequence assures not only a harder and more reproducible bond but also a more controllable adherence. Therefore, it has been possible an ensuing study of the spectroscopic features of these binary systems through the use of SERS. We have thus characterised the SERS spectrum for both DNA sequences-which were attached on gold NPs and obtained a coherent and reproducible signal. The spectra were obtained by using a direct and label-free protocol, thus, avoiding the loss of information about the intrinsic chemical and structural properties of DNA oligonucleotides that fluorescence methods cause. In addition, we provided the realisation of DNA-nanoparticle aggregates, starting from gold nanoparticles functionalized with the two different 12-base DNA sequences and let them hybridise through the addition of a DNA ‘bridge’ which is a 24 base oligomers complementary to the two chains.