Figure 2.

TiO₂-PNA nanoconjugates can hybridize to complementary DNA. (A) Schematic representation depicts changes in fluorescence resulting from self hybridization and melting of molecular beacons; changes in fluorescence caused by hybridization between molecular beacons and PNA-TiO₂ and self hybridization and melting of molecular beacon; changes in fluorescence when non-complementary PNA-TiO₂ and molecular beacon are mixed. Representative dissociation curves resulting from hybridization reactions containing test samples (TiO₂ = nanoparticle; PNA = PNA; PNA-TiO₂ = PNA-TiO₂ nanoconjugates) and (B) complementary molecular beacon or (C) non-complementary molecular beacon are shown. Hybridization of either PNA-TiO₂ or PNA to molecular beacons containing a complementary target results in alterations in fluorescence curves, while no such alterations are observed when a non-complementary molecular beacon is used. (D) The addition of various amounts of excess unlabeled PNA-complementary DNA oligonucleotide (r18AS), as molecular beacon competitor, to samples containing PNA-TiO₂ or PNA and complementary molecular beacons gradually returns the shape of the fluorescence curve to that obtained with samples containing molecular beacons alone. The addition of excess oligonucleotide identical to the sequence of PNA (r18S) shows a slight increase of the fluorescence (which can be expected because of additional hybridization of these DNA oligonucleotides with the beacon). In this and all other molecular beacon experiments concentrations of PNA-TiO₂ and/or PNAs were 0.66 μM, and the concentration of beacon was 0.33 μM. Concentrations of competitor in this experiment were ↑ = 0.66 μM; ↑↑ = 1.0 μM; ↑↑↑ = 1.25 μM. AFU = arbitrary fluorescent units. The results shown are representative examples from five independent experiments.