Ramsden Jeremy J, Horvath Robert
Cranfield University, Bedfordshire, UK.
J Recept Signal Transduct Res. 2009;29(3-4):211-23. doi: 10.1080/10799890903064119.
Planar optical waveguides offer an ideal substratum for cells on which to reside. The materials from which the waveguides are made--high refractive index transparent dielectrics--correspond to the coatings of medical implants (e.g., the oxides of niobium, tantalum, and titanium) or the high molecular weight polymers used for culture flasks (e.g., polystyrene). The waveguides can furthermore be modified both chemically and morphologically while retaining their full capability for generating an evanescent optical field that has its greatest strength at the interface between the solid substratum and the liquid phase with which it is invariably in contact (i.e., the culture medium bathing the cells), decaying exponentially perpendicular to the interface at a rate controllable by varying the material parameters of the waveguide. Analysis of the perturbation of the evanescent field by the presence of living cells within it enables their size, number density, shape, refractive index (linked to their constitution) and so forth to be determined, the number of parameters depending on the number of waveguide lightmodes analyzed. No labeling of any kind is necessary, and convenient measurement setups are fully compatible with maintaining the cells in their usual environment. If the temporal evolution of the perturbation is analyzed, even more information can be obtained, such as the amount of material (microexudate) secreted by the cell while residing on the surface. Separation of parallel effects simultaneously contributing to the perturbation of the evanescent field can be accomplished by analysis of coupling peak shape when a grating coupler is used to measure the propagation constants of the waveguide lightmodes.
平面光波导为细胞提供了理想的附着基质。光波导的制造材料——高折射率透明电介质——与医用植入物的涂层（如铌、钽和钛的氧化物）或用于培养瓶的高分子量聚合物（如聚苯乙烯）相对应。此外，光波导可以在化学和形态上进行修饰，同时保持其产生倏逝光场的全部能力，该倏逝光场在固体基质与始终与之接触的液相（即浸泡细胞的培养基）之间的界面处具有最大强度，并以通过改变光波导的材料参数可控制的速率垂直于界面呈指数衰减。通过分析其中活细胞的存在对倏逝场的扰动，可以确定细胞的大小、数量密度、形状、折射率（与其组成相关）等，参数的数量取决于所分析的光波导光模式的数量。无需任何形式的标记，并且方便的测量设置与将细胞维持在其通常环境中完全兼容。如果分析扰动的时间演变，则可以获得更多信息，例如细胞驻留在表面时分泌的物质（微渗出物）的量。当使用光栅耦合器测量光波导光模式的传播常数时，通过分析耦合峰形状，可以实现对同时影响倏逝场扰动的平行效应的分离。
