Nucleobases functionalized quantum dots and gold nanoparticles bioconjugates as a fluorescence resonance energy transfer (FRET) system - Synthesis, characterization and potential applications.

Fluorescence resonance energy transfer (FRET) system based on functionalized CdTe-guanine and AuNPs-cytosine bioconjugates for the model nucleobase - guanine detection was developed. Thioglycolic acid coated cadmium telluride quantum dots (QDs) conjugated with guanine and sodium 3-mercapto-1-propanesulfonate stabilized gold nanoparticles (AuNPs) capped by cytosine were obtained and fully characterized. Successful formation of the materials was confirmed by UV-Vis, fluorescence and FTIR spectroscopies. Composition of the conjugates was also characterized with elemental analysis and XPS. By employing a guanine-cytosine interaction the bonding between these complementary nucleobases attached to the nanoparticles leads to the formation of QDs-guanine-AuNPs-cytosine assembly, with the size about 7 nm as demonstrated using atomic force microscopy. That enables an effective FRET from functionalized QDs to AuNPs since both, the required distance and the spectral characteristics of donor-acceptor pair were secured. However, it was shown that in the presence of guanine-model molecule which inhibits the interaction between conjugated QDs and AuNPs the FRET is efficiently hampered. Thus monitoring the changes in the restoring fluorescence signal allows to assay the free guanine concentration. Importantly, we have demonstrated the sensitivity and selectivity of the obtained FRET-based system towards guanine. Moreover, in order to confirm the feasibility of the proposed material for nucleobase detection in the real biological samples the developed nanoparticles were also evaluated under simulated urine conditions. The presented strategy of FRET-based conjugated system preparation might be easily used for the development of another nucleobases selective detection and thus opens many possibilities for the determination of biomolecules in the real samples.