The natural world exhibits numerous examples of efficient optical designs with novel hierarchical microstructures and specialized functionality after millions of years of evolution. Materials scientists have long been deriving understanding and inspiration from nature's optical ingenuity, such as vivid structural colors, light antireflection, light focusing, and chirality. Progress in engineering bioinspired optical functional materials has been exciting in the past years. In this review, the focus is on the state-of-the-art achievements of bioinspired optical materials with applications in various areas including efficient light manipulation, optical sensors, light–energy conversion, plasmonic materials with ultrahigh surface plasmon resonance (SPR) efficiency and metamaterials. The major challenges and perspectives for bioinspired designs of optical functional materials in the future are also briefly addressed.

The structural characteristics of natural species have been optimized by natural selection for millions of years. They offer specific functions much more effectively than artificial approaches. Morphology genetic materials utilize morphologies gleaned from natural selection into their hierarchical structures. The combination of natural morphologies and manually selected functional materials makes these novel materials suitable for many applications. This review focuses on the strategies by which the structures and functions of natural species can be utilized. Specific functions inherited from both the natural microstructures and coupled functional materials are highlighted with regard to various applications, including photonics, light-harvesting, surface-enhanced Raman scattering (SERS), and electrodes for supercapacitors and batteries, as well as environmentally friendly materials.

Very recently, wing scales of natural Lepidopterans (butterflies and moths) manifested themselves in providing excellent three dimensional (3D) hierarchical structures for surface-enhanced Raman scattering (SERS) detection. But the origin of the observed enormous Raman enhancement of the analytes on 3D metallic replicas of butterfly wing scales has not been clarified yet, hindering a full utilization of this huge natural wealth with more than 175 000 3D morphologies. Herein, the 3D sub-micrometer Cu structures replicated from butterfly wing scales are successfully tuned by modifying the Cu deposition time. An optimized Cu plating process (10 min in Cu deposition) yields replicas with the best conformal morphologies of original wing scales and in turn the best SERS performance. Simulation results show that the so-called “rib-structures” in Cu butterfly wing scales present naturally piled-up hotspots where electromagnetic fields are substantially amplified, giving rise to a much higher hotspot density than in plain 2D Cu structures. Such a mechanism is further verified in several Cu replicas of scales from various butterfly species. This finding paves the way to the optimal scale candidates out of ca. 175 000 Lepidopteran species as bio-templates to replicate for SERS applications, and thus helps bring affordable SERS substrates as consumables with high sensitivity, high reproducibility, and low cost to ordinary laboratories across the world.

A simple synthesis method combining a sol-gel route followed by a reduction step is developed for the fabrication of magnetophotonic crystal (MPC) materials from Morpho butterfly wings. The sol-gel route leads to hematite with a photonic crystal structure (PC-α-Fe₂O₃) being faithfully replicated from a biotemplate, and the desired magnetophotonic crystal Fe₃O₄ (MPC-Fe₃O₄) is obtained by the reduction of the PC-α-Fe₂O₃ under a H₂/Ar atmosphere. The structural replication fidelity of the process is demonstrated on both the macro- and microscale, and even down to the nanoscale, as evidenced by scanning electron microscopy, X-ray diffraction, reflectance measurements, and transmission electron microscopy. It is found that the chemical transformation of PC-α-Fe₂O₃ to MPC-Fe₃O₄ changes only the dielectric constant and does not induce structural defects that could affect the photonic-crystal properties of the composite. The photonic band gap of MPC-Fe₃O₄ can be red-shifted with an increase of the external magnetic field strength, which is further supported by theoretical calculations. The reported biomimetic technique provides an effective approach to produce magnetophotonic crystals from nature with 3D networks, which may open up an avenue for the creation of new magneto-optical devices and theoretical research in this field.

The unique structure of green leaves endows them with an extremely high light-harvesting efficiency. In this work, green leaves are applied as biotemplates to synthesize morph-TiO₂. The structural features favorable for light harvesting from the macro- to the nanoscale are replicated in morph-TiO₂ through a two-step infiltration process and the N contained in the original leaves is self-doped into the resulting samples. The absorbance intensities within the visible-light range of morph-TiO₂ derived from different leaves increase by 103–258% and the band-gap-absorption onsets at the edge of the UV and visible-light range show a red-shift of 25–100 nm compared to those in TiO₂ without the template. The photocatalytic activity of morph-TiO₂ is also improved, as proven by an electron paramagnetic resonance (EPR) study and degradation of rhodamine dye under irradiation with UV and visible light. The present work, as a new strategy, is of far-reaching significance in learning from nature, driving us to make full use of the most-abundant resources and structure-introduced functions endowed by nature, opening up possibilities for extensive study of the physical and chemical properties of morph-structured oxides and extending their potential for use in applications such as solar cells, photocatalysts, photoelectrical devices, and photoinduced sensors.

We put forward a novel and straightforward sonochemical process as a generic bottom-up assembly routeto produce ordered porous metal chalcogenide meso/nanostructures by templating of diatom frustules. We work with one of the most beautiful species of diatoms, Coscinodiscus lineatus, as a representative of diatoms with central symmetry, and with ZnS as the prototype, as it is a high refractive index material and is a typical material widely used in optics and photonics. ZnS replicas have been successfully synthesized from the interaction between the reactive surfaces of the frustules and the precursors under ultrasound. The inorganic replicas copy the morphology of the ordered porous structure and inherit its optical property, such as the existence of the photonic bandgap of the diatom frustules. It is possible to achieve tunable photonic properties in the replicas by assembly of various metal chalcogenide semiconductors of different refractive indexes. This bio-inspired discovery provides insight into the facile synthesis of elaborate meso/nanostructures from these marine microbes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)