Badugu Ramachandram, Mao Jieying, Zhang Douguo, Descrovi Emiliano, Lakowicz Joseph R
Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, United States.
Institute of Photonics, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.
J Phys Chem C Nanomater Interfaces. 2020 Oct 15;124(41):22743-22752. doi: 10.1021/acs.jpcc.0c08246. Epub 2020 Sep 30.
Multilayer structures with two dielectrics having different optical constants and no structural features in the - plane can display photonic band gaps (PBGs) and are called one-dimensional photonic crystals (1DPCs). If the top layer thickness is carefully selected, the electromagnetic energy can be trapped at the top surface. These highly enhanced fields are called Bloch surface waves (BSWs). The BSW resonance angles are sensitive to the dielectric constant above the top dielectric layer. As a result, BSW structures have been used for surface plasmon resonance-like measurements without the use of a metal film. However, the emphasis on surface-localized BSWs has resulted in limited interest in fluorophore interactions with other optical modes of 1DPCs or Bragg gratings without the different thickness top layer. Herein, three different fluorescent probes were used to cover the short, center, and long wavelengths of the PBG. We demonstrate efficient coupling of fluorophores to both the BSW and internal modes (IMs) of a 1DPC. Coupling to the IM is expected to be low because of the micron-scale distances between the fluorophores and IM, which exists inside the Bragg gratings. At different wavelengths or observation angles, the IM-coupled emission (IMCE) can occur with the first three modes of the multilayer. This coupling is not dependent on a BSW mode. IMCE was also observed for a monolayer of fluorophore-labeled protein. IMCE enables sensitive detection of surface-bound fluorophores. Applications are anticipated in high sensitivity detection and super-resolution imaging.
具有两种光学常数不同的电介质且在平面内无结构特征的多层结构可以显示光子带隙（PBG），并被称为一维光子晶体（1DPC）。如果仔细选择顶层厚度，电磁能量可以被困在顶表面。这些高度增强的场被称为布洛赫表面波（BSW）。BSW共振角对顶层电介质层上方的介电常数敏感。因此，BSW结构已被用于类似表面等离子体共振的测量，而无需使用金属膜。然而，对表面局域化BSW的关注导致人们对荧光团与没有不同厚度顶层的1DPC或布拉格光栅的其他光学模式之间的相互作用兴趣有限。在此，使用了三种不同的荧光探针来覆盖PBG的短、中、长波长。我们展示了荧光团与1DPC的BSW和内部模式（IM）的有效耦合。由于荧光团与IM之间存在微米级距离，预计与IM的耦合会很低，IM存在于布拉格光栅内部。在不同波长或观察角度下，IM耦合发射（IMCE）可以与多层的前三种模式一起发生。这种耦合不依赖于BSW模式。对于单层荧光团标记的蛋白质也观察到了IMCE。IMCE能够灵敏地检测表面结合的荧光团。预计在高灵敏度检测和超分辨率成像方面有应用。
