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Here we show that uracil and sodium form a three-dimensional metal-mediated nucleic acid network; it is grown in atomic/molecular layer-by-layer manner using the atomic/molecular layer deposition (ALD/MLD) thin-film technique. The long-range ordered Na-uracil crystalline structure is evidenced as sharp Bragg reflections. Based on density functional theory (DFT) calculations, a tetrameric-like crystal structure is proposed. Na-uracil thin films are fluorescent with a lifetime three orders of magnitude higher than commonly seen for nucleic acid molecules. Our method provides a new approach to designing 3D nucleic acid-metal nanostructures.

Surface plasmon waves have been widely utilized to enhance the light-matter interaction near the surface of the structures for a broad range of sensing methods, including surface plasmon spectroscopy, [1][2][3][4] plasmon-controlled fl uorescence [ 5,6 ] and surface-enhanced Raman scattering (SERS). [7][8][9] In particular, SERS has been demonstrated as one of the most important and promising approaches for various applications [10][11][12][13][14] (e.g., high-sensitivity bio-sensing down to a single-molecule level [ 7,15 ] ), because of its effective identifi cation of chemical bonds. Numerous nanostructures have been investigated to effectively improve the electromagnetic enhancement, a predominant mechanism contributing to the total enhancement in light-matter interaction. [ 16,17 ] Among these nanostructures, periodic metal nanostructures fabricated by e-beam lithography (EBL) or focused ion beam (FIB) patterning, [18][19][20] have been widely utilized to investigate the light-matter interaction mechanism, especially coupling effects such as nearfi eld dipole and long-range interactions, because of the merit of adjustable nanostructure dimensions in these methods. In addition, a few disordered nanostructures (e.g., gold nanoparticle dimers and trimers, [ 7,21,22 ] silver (Ag) nanowires, [23][24][25][26] Ag nanoparticles decorated nanotrees [ 27 ] or nanorods [ 28 ] ) fabricated by various methods (e.g., chemical reduction process, [ 29,30 ] Langmuir-Blodgett technique, [ 23,24 ] self-assembled synthesis [31][32][33] ) have attracted considerable attention. In contrast to the periodic nanostructures, disordered aggregates of metal nanostructures also can result in extremely high fi eld enhancement, which is typically observed on the so-called "hot spot" sites. [ 34 ] Indeed, these periodic and disordered nanostructures have been extensively investigated, addressing their potential for various applications. [ 35,36 ] However, the aforementioned fabrication methods have their drawbacks. For example, the nanofabrication methods such as EBL [ 18,19 ] and FIB [ 20 ] require expensive equipments and are typically time-consuming for large-scale applications. The chemical methods (e.g., chemical reduction process, [ 29,30 ] Langmuir-Blodgett technique [ 23,24 ] ) usually are inapplicable due to the challenges of repeatability control in these fabrication processes for applications, where high fi eld enhancement is required. Therefore, novel fabrication methods for simple, cost-effective, large-area nanostructure devices with high enhancement factors (e.g., >10 9 ) [ 37 ] are thus of great importance for various practical applications (e.g., SERS, [ 38 ] plasmon-enhanced fl uorescence [ 39 ] ).Black silicon (BS) is a nano-roughened silicon (Si) surface, which can be produced by a wide variety of dry and wet etching techniques. Initially discovered as an unwanted side-effect of dry etching, it has gathered a lot of attention lately due to the low-cost and simple process to achieve nanostructures on a large scale. The na...

To develop biomimetic dye-polymers for photonics, two different types of Zn chlorin-poly(4-vinylpyridine) (P4VP) assemblies were prepared by varying Zn pyro-pheophorbide a methylester (ZnPPME) and Zn 3 1-OHpyro-pheophorbide a methylester (Zn-3 1-OH-PPME) doping levels. 1 H NMR spectroscopy and diffusion ordered NMR spectroscopy (DOSY) studies revealed that a coordinative interaction between Zn chlorin and P4VP was predominant in solution (d 5-nitrobenzene). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) characterization of bulk samples of polystyrene-block-poly(4vinylpyridine) (PS-b-P4VP) doped with variable amounts of Zn chlorin showed that the pigment doping transformed the native cylindrical block copolymer nanostructures to lamellar morphologies. The result indicates that the pyridine moiety-Zn chlorin coordination is stronger than the aggregation tendency between the pigment molecules even in the solid state. UV-Vis absorption spectroscopy studies of a Zn chlorin-P4VP thin film showed characteristic monomeric chlorin spectra, while steady-state fluorescence spectroscopy displayed quenching of fluorescence and time-resolved studies indicated shortening of fluorescence lifetimes with an increasing chlorin doping level. Notably, time-resolved fluorescence spectroscopy revealed that the lifetime decay changed from monoexponential to biexponential above 0.5 wt% (ca. 0.001 equiv.) loadings. The Förster analysis implies that excitonic chlorin-chlorin interactions are observed in the thin films when the distance between the pigment molecules is approximately 50Å. The Zn chlorin-P4VP solid films emit strongly up to 1 wt% (ca. 0.002 equiv.) doping level above which the chlorin-chlorin interactions start to linearly dominate with an increase of doping level, while with 10 wt% (ca. 0.02 equiv.) loading less than 10% of fluorescence remains. Doping levels up to 300 wt% (0.5 equiv.) can be used in absorbing materials without the formation of chlorin aggregates. These defined optical response regions pave the way for photonic materials based on biopigment assemblies.

Atomic/molecular layer deposition (ALD/MLD) offers unique possibilities in the fabrication of inorganic-organic thin films with novel functionalities. Especially, incorporating nucleobases in the thin-film structures could open new avenues in the development of bio-electronic and photonic devices. Here we report an intense blue and widely excitation-dependent fluorescence in the visible region for ALD/MLD fabricated sodium-uracil thin films, where the crystalline network is formed from hydrogen-bonded uracil molecules linked via Na atoms. The excitation-dependent fluorescence is caused by the red-edge excitation shift (REES) effect taking place in the red-edge of the absorption spectrum, where the spectral relaxation occurs in continuous manner as demonstrated by the time-resolved measurements.