Influence of structural colour on the photoprotective mechanism in the gametophyte phase of the red alga Chondrus crispus.

Marine life is populated by a huge diversity of organisms with an incredible range of colour. While structural colour mechanisms and functions are usually well studied in marine animal species, there is a huge knowledge gap regarding the marine macroalgae (red, green and brown seaweeds) that have structural coloration and the biological significance of this phenomenon in these photosynthetic organisms. Here we show that structural colour in the gametophyte life history phase of the red alga Chondrus crispus plays an important role as a photoprotective mechanism in synergy with the other pigments present. In particular, we have demonstrated that blue structural coloration attenuates the more energetic light while simultaneously favouring green and red light harvesting through the external antennae (phycobilisomes) which possess an intensity-dependent photoprotection mechanism. These insights into the relationship between structural colour and photosynthetic light management further our understanding of the mechanisms involved.

Inkjet Printed Photonic Cellulose Nanocrystal Patterns.

Naturally-sourced cellulose nanocrystals (CNCs) are elongated, birefringent nanoparticles that can undergo cholesteric self-assembly in water to produce vibrant, structurally colored films. As such, they are an ideal candidate for use as sustainable and cost-effective inks in the printing of scalable photonic coatings and bespoke patterns. However, the small volume and large surface area of a sessile CNC drop typically leads to rapid evaporation, resulting in microfilms with a coffee-stain-like morphology and very weak coloration. Here, it is demonstrated that inkjet printing of CNC drops directly through an immiscible oil layer can immediately inhibit water loss, resulting in reduced internal mass flows and greater time for cholesteric self-assembly. The color of each microfilm is determined by the initial composition of the drop, which can be tuned on-demand by exploiting the overprinting and coalescence of multiple smaller drops of different inks. This enables the production of multicolored patterns with complex optical behaviors, such as angle-dependent color and polarization-selective reflection. Finally, the array can be made responsive to stimuli (e.g., UV light, polar solvent) by the inclusion of a degradable additive. This suite of functional properties promotes inkjet-printed photonic CNC arrays for smart colorimetric labeling or optical anticounterfeiting applications.