Fig. 1

Liquid-crystal (LC) and biomaterials-based metamaterials and metafluids. a An illustration of a typical LC-based metamaterial, where metallic structures are dispersed in a LC solution. LC-based metamaterials can achieve optical properties tuning by changing the alignment and orientation of LC molecules via external voltage. b The LC-infiltrated metamaterial shows a refractive index ranging from negative to zero and positive values by adjusting the permittivity of LCs. c An illustration of metafluid, where metal-dielectric metamolecules are dispersed in a fluid. Metafluid allows the dispersion of different materials or metamolecules to integrate different optical properties in order to attain exotic effective material properties. d The transmission spectrum of a metafluid containing boron-doped silicon nanocrystals and five types of Au nanorods (AuNRs) with different geometries. This metafluid possesses a transparency window at 890 nm, with a narrow window width of 0.22 eV. The transparency window is guided by the superposition of the five types of AuNRs whose transmission spectra are shown in the inset. e An illustration of a silk protein-based biomaterial metamaterial, where metal nanoparticles are doped in the silk protein structure. f The reflection spectra of the bio-compatible silk plasmonic absorber sensor (SPAS) immersed in air (refractive index n = 1), isopropyl alcohol (IPA, n = 1.37), and water (n = 1.32). Larger refractive index can result in reflection resonance redshift in SPAS, facilitating its environment sensing application. b Reprinted with permission from [52], Copyright (2007) OSA Publishing. d Reprinted with permission from [66], Copyright (2016) ACS Publications. f Reprinted with permission from [72], Copyright (2015) ACS Publications