Architecture of dual emissive three-dimensional nanostructure composites containing graphitic 2D sheets and iron oxide nanoparticles: detection of short single-stranded DNA sequences.

Here, we report an effect driven by repetitive heating and cooling; as a result, 2D and 1D nanomaterials are parallelly produced locally in a single reactor from the same precursors. Afterward, more repetitive heating and cooling induced the self-folding approach of a 2D nanomaterial with a 1D nanomaterial, giving them a self-assembled biconcave disk-shaped 3D nanostructure. The microscopy and spectroscopy studies reveal that the nanostructure has a diameter of nearly 200 nm and is composed of Fe, C, O and incorporated N and P. This 3D nanostructure composite shows red-shifted dual emission (430 nm and 500 nm) at two different excitations (350 nm and 450 nm), accompanied by a rare large Stokes shift (LSS), and it was employed in the detection of targeted short single-stranded DNA sequences (ssDNA). Upon the addition of target DNA, the specific binding of 3D nanostructure probes with the target triggers variations (off/on) of two signals, and by considering the decreased emission (fluorescence quenching) at 500 nm, we can detect the target ssDNA at the single-molecule level. The change of fluorescence intensity and the concentration of complementary target ssDNA sequences show a better linear relationship than a single emission-based probe, and the limit of detection (LOD) was as low as 0.47 nM.