Rhodamine Activated Gold Nanoaggregates for Dna Detection

Surface enhanced Raman scattering (SERS) is demonstrating a lot of potentials as a sensitive precious probe for chemical and bioanalitical applications. Since long time, the vibrational spectroscopy provides highly specific chemical information about DNA, RNA, viruses and molecules that makes both FTIR and Raman spectroscopies well suited for “fingerprint” detection in biomedical analysis. However, FTIR has fundamental limitation due to water absorption, and therefore, one’s ability to be used for biological detection in native water environment is limited as well. Contrary to that, Raman scattering cross-section of water is extremely low compare to ones from biological species and molecules. The possibility of observing Raman signals, which are normally very weak, may be enhanced the order of 10–10, provides interesting applications, in particular in bioanalysis. At the last decade, the progress in high yield synthesis of non-spherical silver and gold nanoparticles with different shape has been achieved. As result, the numerous methods to produce nanorods, nanoprisms, nanodisks and nanowires have been developed. It makes possible to effectively tune the position of surface plasmon band over VS and NIR part of spectrum. Therefore, shape controlled synthesis of metal nanostructures combined with SERS has opened many new possibilities to design building blocks for future nanodevices. However, this is a serious disadvantage of some of these non-spherical nanoparticles: the bioconjungment of one’s is strictly limited due to using a toxic and hardly functionalized reagent as surfactants. On the other hand, the aggregated spherical nanoparticles have new SP resonances resulting in a variety of extended surface plasmon bands (ESPB). Moreover, the largest Raman scattering enhancements, even single molecule SERS, have been described for molecules captured between nanoparticles in nanoaggregates due to interparticle junction. Here, we report a detailed study the time dynamics of aggregation process for spherical gold nanoparticles. The specificity of this research concludes in using the Rh6G molecules both as the SERS tags and the chemical agents to initiate the aggregation of GSNP. The produced by Rh6G molecules gold nanoaggregates have linear chain-like shape that allow easily and more efficiently monitor SERS enhancement due to wavelength of laser. It is shown that the aggregation rate and molecular arrangement into nanoaggregates dependence from different concentration of Rh6G molecules relative to the gold nanoparticles and the resulting gold nanoaggregates are extremely stable. One goal of this work is to optimize the noble metal nanoparticles aggregation process to provide the feasibility of using SERS for detection of the HIV, anthrax DNA, using low-cost and portable Raman spectrometers. Typically, these spectrometers arranged with an NIR diode laser as the excitation source due to reason that NIR excitation reduces the native fluorescence background from microorganisms. One of most popular diode laser excitation wavelength is 785 nm.