The ability to control the position of a mesoscopic object with nanometric precision is important for the rapid progress of nanoscience. One of the most promising tools to achieve such control is optical tweezers, which trap objects near the focus of a laser beam. However, the drawbacks of conventional tweezers include a trapping volume that is diffraction-limited and significant brownian motion of trapped nanoobjects. Here, we report the first experimental realization of three-dimensional nanometric optical tweezers that are based on nanostructured substrates. Using electromagnetically coupled pairs of gold nanodots in a standard optical tweezers set-up, we create an array of subwavelength plasmonic optical traps that offer a significant increase in trapping efficiency. The nanodot optical near-fields reduce the trapping volume beyond the diffraction limit and quench brownian motion of the trapped nanoparticles by almost an order of magnitude as compared to conventional tweezers operating under the same trapping conditions. Our tweezers achieve nanoscale control of entities at significantly smaller laser powers and open new avenues for nanomanipulation of fragile biological objects.

Coloration mediates the relationship between an organism and its environment in important ways, including social signaling, antipredator defenses, parasitic exploitation, thermoregulation, and protection from ultraviolet light, microbes, and abrasion. Methodological breakthroughs are accelerating knowledge of the processes underlying both the production of animal coloration and its perception, experiments are advancing understanding of mechanism and function, and measurements of color collected noninvasively and at a global scale are opening windows to evolutionary dynamics more generally. Here we provide a roadmap of these advances and identify hitherto unrecognized challenges for this multi- and interdisciplinary field.

Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet.

Dielectric multilayer reflectors that are non-polarizing are an important class of optical device and have numerous applications within optical fibres [1], dielectric waveguides [2] and LEDs [3]. Here we report analyses of a biological non-polarizing optical mechanism found in the broadband guanine-cytoplasm “silver” multilayer reflectors of three species of fish. Present in the fish stratum argenteum are two populations of birefringent guanine crystal, each with their optic axes either parallel to the long axis of the crystal or perpendicular to the plane of the crystal. This arrangement neutralizes the polarization of reflection due the different interfacial Brewster’s angles of each population. The fish reflective mechanism is distinct from existing non-polarizing mirror designs [4, 5, 6, 7] with the important feature that there is no refractive index contrast between the low index layers in the reflector and the external environment. It is a mechanism that could be readily manufactured and exploited in synthetic optical devices.

Summary Some vertebrate species have evolved means of extending their visual sensitivity beyond the range of human vision. One mechanism of enhancing sensitivity to long-wavelength light is to replace the 11-cis retinal chromophore in photopigments with 11-cis 3,4-didehydroretinal. Despite over a century of research on this topic, the enzymatic basis of this perceptual switch remains unknown. Here, we show that a cytochrome P450 family member, Cyp27c1, mediates this switch by converting vitamin A1 (the precursor of 11-cis retinal) into vitamin A2 (the precursor of 11-cis 3,4-didehydroretinal). Knockout of cyp27c1 in zebrafish abrogates production of vitamin A2, eliminating the animal's ability to red-shift its photoreceptor spectral sensitivity, and reducing its ability to see and respond to near-infrared light. Thus, the expression of a single enzyme mediates dynamic spectral tuning of the entire visual system by controlling the balance of vitamin A1 and A2 in the eye.

In our investigations of a family of achiral bent-core bis-(phenyl)oxadiazole derivatives, we observed some unusual properties of the nematic phase. These include evidence of segregation into domains of opposite handedness and the formation of clusters, nematic phase biaxiality, and a strongly kinetically governed phase behaviour, which leads to the display of unique filament structures at the onset of new order. We suggest that the combination of a deviant calamitic molecular shape with a considerable transverse dipole leads to an unusual strength and combination of molecular interactions, and as a consequence these nematic materials need to be considered as fluctuating and dynamically changing, multi-hierarchical fluids.

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Gaze stabilization is an almost ubiquitous animal behaviour, one that is required to see the world clearly and without blur. Stomatopods, however, only fix their eyes on scenes or objects of interest occasionally. Almost uniquely among animals they explore their visual environment with a series pitch, yaw and torsional (roll) rotations of their eyes, where each eye may also move largely independently of the other. In this work, we demonstrate that the torsional rotations are used to actively enhance their ability to see the polarization of light. Both Gonodactylus smithii and Odontodactylus scyllarus rotate their eyes to align particular photoreceptors relative to the angle of polarization of a linearly polarized visual stimulus, thereby maximizing the polarization contrast between an object of interest and its background. This is the first documented example of any animal displaying dynamic polarization vision, in which the polarization information is actively maximized through rotational eye movements.