Mouchet Sébastien R, Verstraete Charlotte, Mara Dimitrije, Van Cleuvenbergen Stijn, Finlayson Ewan D, Van Deun Rik, Deparis Olivier, Verbiest Thierry, Maes Bjorn, Vukusic Pete, Kolaric Branko
School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.
Department of Physics and Namur Institute of Structured Matter (NISM), University of Namur, Rue de Bruxelles 61, 5000 Namur, Belgium.
Interface Focus. 2019 Feb 6;9(1):20180052. doi: 10.1098/rsfs.2018.0052. Epub 2018 Dec 14.
Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as nonlinear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein, these techniques are applied for the first time to study of the naturally controlled fluorescence in insects. The case of the male beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's coloration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A third-harmonic generation signal is also detected, the intensity of which depends on the light polarization state. The analysis of these nonlinear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The role of form anisotropy in the photonic structure, which causes additional tailoring of the beetle's optical responses, is demonstrated by circularly polarized light and nonlinear optical measurements.
在紫外光照射下，许多动物物种通过其生物组织中嵌入的荧光团产生的荧光过程发光。然而，对活生物体的荧光研究相对较少，迄今为止仅限于线性范围。多光子激发荧光分析以及非线性光学技术为研究局部环境对荧光团激发态的影响提供了独特的可能性。在此，这些技术首次应用于研究昆虫的自然控制荧光。以雄性甲虫为例进行研究，因为覆盖甲虫鞘翅的鳞片已知具有嵌入荧光团的内部光子结构，该结构控制着甲虫的颜色和荧光发射。观察到强烈的双光子激发荧光信号，其强度在与水接触时会发生变化。还检测到了三次谐波产生信号，其强度取决于光的偏振态。对这些非线性光学和荧光响应的分析揭示了嵌入甲虫鞘翅中的荧光团分子的多激发态特性。圆偏振光和非线性光学测量证明了光子结构中形状各向异性的作用，它导致了甲虫光学响应的额外调整。
