Lukács A, Garab G, Papp E
Department of Biological Physics, Eötvös University, Pázmány Péter sétány 1A, Budapest, Hungary.
Biosens Bioelectron. 2006 Feb 15;21(8):1606-12. doi: 10.1016/j.bios.2005.08.003. Epub 2005 Oct 4.
Purple membrane (bacteriorhodopsin) and plant light-harvesting complexes (LHCII) were dried on the optical waveguide sensor with varying thicknesses in a wide range (from 20 to several hundreds of nanometers) and the optical parameters were studied with optical waveguide lightmode spectroscopy. It was found that applying the approximate 4-layer mode equations for the measured effective refractive indices resulted in unacceptable results for the optical parameters: with increasing thickness the refractive index decreased monotonously from 1.5 to 1.1. Therefore an inverse waveguide numerical method was developed and used to obtain reliable results from the experiments. The inverse method yielded an approximately constant (1.53) refractive index independently of the thickness for the purple membrane and LHCII films. Light-induced changes in the optical parameters of the purple membrane and LHCII films were also studied. For purple membrane films the most significant effect is the change in refractive index and absorption. For LHCII films prolonged illumination induced irreversible structural changes, most probably of thermo-optic origin.
紫色膜（细菌视紫红质）和植物光捕获复合物（LHCII）以不同厚度（在20纳米至数百纳米的宽范围内）干燥在光波导传感器上，并采用光波导光模式光谱法研究其光学参数。结果发现，对于所测量的有效折射率应用近似的四层模式方程会导致光学参数出现不可接受的结果：随着厚度增加，折射率从1.5单调下降至1.1。因此，开发了一种反向波导数值方法，并用于从实验中获得可靠结果。该反向方法得出紫色膜和LHCII薄膜的折射率近似恒定（1.53），与厚度无关。还研究了紫色膜和LHCII薄膜光学参数的光致变化。对于紫色膜薄膜，最显著的影响是折射率和吸收的变化。对于LHCII薄膜，长时间光照会引起不可逆的结构变化，很可能源于热光效应。
