Cup-Shaped Nanoantenna Arrays for Zeptoliter Volume Biochemistry and Plasmonic Sensing in the Visible Wavelength Range.

Although three-dimensional shaping of metallic nanostructures is an important strategy for control and manipulation of localized surface plasmon resonance (LSPR), its implementation in high-throughput, on-chip fabrication of plasmonic devices remains challenging. Here, we demonstrate nanocontact-based large-area fabrication of a novel, LSPR-active Au architecture consisting of periodic arrays of reduced-symmetry nanoantennas having sub-50 nm, out-of-plane features. Namely, by combining nanosphere and molecular self-assembly processes, we have patterned evaporated polycrystalline Au films for chemical etching of nanocups with controlled aspect ratios (outer diameter d = 100 nm and void volumes = 18 or 39 zL). The resulting nanoantennas were highly ordered, forming a hexagonal lattice structure over centimeter-sized glass substrates, and they displayed characteristic LSPR absorption in the visible/near-infrared spectral range. Theoretical simulations indicated electric field confinement and enhancement patterns located not only around the rims but also inside the nanocups. We also explored how these patterns and the overall spectral characteristics depended on the nanocup aspect ratio as well as on electric field coupling in the arrays. We have successfully tested the fabricated architecture for detection of stepwise immobilization and interactions of proteins, thus demonstrating its potential for both nanoscopic scaffolding and sensing of biomolecular assemblies.

Ultrafast laser-induced birefringence in various porosity silica glasses: from fused silica to aerogel.

We compare a femtosecond laser induced modification in silica matrices with three different degrees of porosity. In single pulse regime, the decrease of substrate density from fused silica to high-silica porous glass and to silica aerogel glass results in tenfold increase of laser affected region with the formation of a symmetric cavity surrounded by the compressed silica shell with pearl like structures. In multi-pulse regime, if the cavity produced by the first pulse is relatively large, the subsequent pulses do not cause further modifications. If not, the transition from void to the anisotropic structure with the optical axis oriented parallel to the incident polarization is observed. The maximum retardance value achieved in porous glass is twofold higher than in fused silica, and tenfold greater than in aerogel. The polarization sensitive structuring in porous glass by two pulses of ultrafast laser irradiation is demonstrated, as well as no observable stress is generated at any conditions.

Tailored surface birefringence by femtosecond laser assisted wet etching.

Surface texturing is demonstrated by the combination of wet etching and ultrafast laser nanostructuring of silica glass. Using potassium hydroxide (KOH) at room temperature as an etchant of laser modified glass, we show the polarization dependent linear increase in retardance reaching a threefold value within 25 hours. The dispersion control of birefringence by the etching procedure led to achromatic behaviour over the entire visible spectral range. The mechanism of enhanced KOH etching selectivity after femtosecond laser exposure is discussed and correlated to the formation of various laser-induced defects, such as silicon-rich oxygen deficiency and color centers.

Airy beams generated by ultrafast laser-imprinted space-variant nanostructures in glass.

We demonstrate a technique to generate accelerating Airy beams with a femtosecond laser-imprinted space variant birefringent structure in silica glass. Our approach enables the generation of dual Airy beams with polarization sensitive beam deflection. The produced beam is used for the glass scribing. After the glass-breaking process, a spontaneous self-detachment of a fiber-like structure occurs that can be exploited as an alternative way for fabricating glass cantilevers.

Belt-shaped π-systems: relating geometry to electronic structure in a six-porphyrin nanoring.

Linear π-conjugated oligomers have been widely investigated, but the behavior of the corresponding cyclic oligomers is poorly understood, despite the recent synthesis of π-conjugated macrocycles such as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an efficient template-directed synthesis of a π-conjugated butadiyne-linked cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray scattering data show that this nanoring is shape-persistent in solution, even without its template, whereas the linear porphyrin hexamer is relatively flexible. The crystal structure of the nanoring-template complex shows that most of the strain is localized in the acetylenes; the porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and fluorescence spectra indicate that the HOMO-LUMO gap of the nanoring is less than that of the linear hexamer and less than that of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is delocalized over the whole π-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red-shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully explained in terms of vibronic Herzberg-Teller (HT) intensity borrowing.