Strong coupling in molecular systems: a simple predictor employing routine optical measurements.

We provide a simple method that enables readily acquired experimental data to be used to predict whether or not a candidate molecular material may exhibit strong coupling. Specifically, we explore the relationship between the hybrid molecular/photonic (polaritonic) states and the bulk optical response of the molecular material. For a given material, this approach enables a prediction of the maximum extent of strong coupling (vacuum Rabi splitting), irrespective of the nature of the confined light field. We provide formulae for the upper limit of the splitting in terms of the molar absorption coefficient, the attenuation coefficient, the extinction coefficient (imaginary part of the refractive index) and the absorbance. To illustrate this approach, we provide a number of examples, and we also discuss some of the limitations of our approach.

Measuring Photonics in Photosynthesis: Combined Micro-Fourier Image Spectroscopy and Pulse Amplitude Modulated Chlorophyll Fluorimetry at the Micrometre-Scale.

Natural photonic structures are common across the biological kingdoms, serving a diversity of functionalities. The study of implications of photonic structures in plants and other phototrophic organisms is still hampered by missing methodologies for determining in situ photonic properties, particularly in the context of constantly adapting photosynthetic systems controlled by acclimation mechanisms on the cellular scale. We describe an innovative approach to determining spatial and spectral photonic properties and photosynthesis activity, employing micro-Fourier Image Spectroscopy and Pulse Amplitude Modulated Chlorophyll Fluorimetry in a combined microscope setup. Using two examples from the photosynthetic realm, the dynamic Bragg-stack-like thylakoid structures of Begonia sp. and complex 2.5 D photonic crystal slabs from the diatom Coscinodiscus granii, we demonstrate how the setup can be used for measuring self-adapting photonic-photosynthetic systems and photonic properties on single-cell scales. We suggest that the setup is well-suited for the determination of photonic-photosynthetic systems in a diversity of organisms, facilitating the cellular, temporal, spectral and angular resolution of both light distribution and combined chlorophyll fluorescence determination. As the catalogue of photonic structure from photosynthetic organisms is rich and diverse in examples, a deepened study could inspire the design of novel optical- and light-harvesting technologies.

Highly Reproducible, Bio-Based Slab Photonic Crystals Grown by Diatoms.

Slab photonic crystals (PhCs) are photonic structures used in many modern optical technologies. Fabrication of these components is costly and usually involves eco-unfriendly methods, requiring modern nanofabrication techniques and cleanroom facilities. This work describes that diatom microalgae evolved elaborate and highly reproducible slab PhCs in the girdle, a part of their silicon dioxide exoskeletons. Under natural conditions in water, the girdle of the centric diatom Coscinodiscus granii shows a well-defined optical pseudogap for modes in the near-infrared (NIR). This pseudogap shows dispersion toward the visible spectral range when light is incident at larger angles, eventually facilitating in-plane propagation for modes in the green spectral range. The optical features can be modulated with refractive index contrast. The unit cell period, a critical factor controlling the pseudogap, is highly preserved within individuals of a long-term cultivated inbred line and between at least four different C. granii cell culture strains tested in this study. Other diatoms present similar unit cell morphologies with various periods. Diatoms thereby offer a wide range of PhC structures, reproducible and equipped with well-defined properties, possibly covering the entire UV-vis-NIR spectral range. Diatoms therefore offer an alternative as cost-effective and environmentally friendly produced photonic materials.

Gold nanoparticles immobilised in a superabsorbent hydrogel matrix: facile synthesis and application for the catalytic reduction of toxic compounds.

Two methods are reported for the one-pot preparation of high concentrations of gold nanoparticles (AuNPs) embedded throughout sodium polyacrylate hydrogels; this stabilises the AuNP in even extremely high ionic strength environments, and enables them to act as effective catalysts for the hydride-reduction of nitrophenols and of dyes, with zero order kinetics.

Toward an Axial Nanoscale Ruler for Fluorescence Microscopy.

In the discussion of resolution in optical microscopy, axial precision has often come second to its lateral counterpart. However, biological systems make no special arrangements for our preferred direction of imaging. The ability to measure axial distances, that is, the heights of fluorophores relative to a plane of reference, is thus of paramount importance and has been the subject of several recent advances. A novel method is to modify the fluorescence emission based on the height of the individual fluorophore, such that its z-position is encoded somehow in the detected signal. One such approach is metal-enhanced energy transfer, recently extended to multicolor distance measurements and applied to study the topography of the nuclear membrane. Here, the fluorescence lifetime is shortened due to the proximity of the fluorophores to a thin metallic surface. Fluorescence lifetime imaging can therefore be used as an axial ruler with nanometer precision.

Hydrogen detected by the naked eye: optical hydrogen gas sensors based on core/shell plasmonic nanorod metamaterials.

Gold-core/palladium-shell metamaterials for hydrogen detection are presented. The more than 30% change in both the reflection and transmission from the metamaterial layer that is observed when the layer is exposed to 2% hydrogen mixture is clearly noticeable to the naked eye as a change in the brightness of light transmitted by the metamaterial. This sensor should make a contribution to the safety of processes involving hydrogen.