title: Liquid-induced colour change in a beetle: the concept of a photonic cell.
abstract: The structural colour of male Hoplia coerulea beetles is notable for changing from blue to green upon contact with water. In fact, reversible changes in both colour and fluorescence are induced in this beetle by various liquids, although the mechanism has never been fully explained. Changes enacted by water are much faster than those by ethanol, in spite of ethanol's more rapid spread across the elytral surface. Moreover, the beetle's photonic structure is enclosed by a thin scale envelope preventing direct contact with the liquid. Here, we note the presence of sodium, potassium and calcium salts in the scale material that mediate the penetration of liquid through putative micropores. The result leads to the novel concept of a "photonic cell": namely, a biocompatible photonic structure that is encased by a permeable envelope which mediates liquid-induced colour changes in that photonic structure. Engineered photonic cells dispersed in culture media could revolutionize the monitoring of cell-metabolism.
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Sébastien R
authors.initials: SR
authors.lastname: Mouchet
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Eloise
authors.initials: E
authors.lastname: Van Hooijdonk
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Welch
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Louette
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Colomer
authors.affiliation: Laboratory of Inorganic Materials Chemistry (CMI), University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.|Clare Hall College, University of Cambridge, Herschel Road, Cambridge CB3 9AL, United Kingdom.
authors.forename: Bao-Lian
authors.initials: BL
authors.lastname: Su
authors.affiliation: Department of Physics, University of Namur (UNamur), Rue de Bruxelles 61, B-5000 Namur, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Deparis
mesh_terms: D000818:Animals; D001517:Coleoptera / Q000502:physiology* / Q000648:ultrastructure; D003116:Color; D005453:Fluorescence; D008297:Male; D010858:Pigmentation; D010860:Pigments, Biological / Q000737:chemistry; D014867:Water
chemical_list: D010860:Pigments, Biological; D014867:Water