Grassi J H, Georgiadis R M
Department of Chemistry, Boston University, Boston Massachusetts 02215.
Anal Chem. 1999 Oct 1;71(19):4392-6. doi: 10.1021/ac990125q.
Temperature-dependent measurements of surface coverage and interfacial kinetics remain relatively unexploited in thin-film sensing applications that rely on optical surface-sensitive techniques such as surface plasmon resonance spectroscopy (SPR). These techniques are inherently sensitive to the optical properties of the bulk solution in contact with the thin film; therefore, quantitative thin-film sensing requires accurate refractive index data for bulk solutions at the conditions of interest. The refractive index for bulk solutions depends strongly on temperature, solution composition, and optical excitation wavelength. In this paper, we demonstrate the use of critical angle measurements for accurate, independent determination of the refractive index of bulk solutions and present results for different experimental conditions of solution temperature, solution concentration, and excitation wavelength. We also examine the implications of incorrect accounting of the bulk solution for the case of two-color SPR sensing of ultrathin organic films. This sensing technique, which depends inherently on the contrast in the dispersion of the refractive index of the film and the bulk solution, can be over 1 order of magnitude more sensitive than single-color SPR measurements. Critical angle measurements can be implemented in conjunction with SPR measurements and will be invaluable for thin film sensing application in which the bulk refractive index varies during the experiment, for example, in temperature-dependent SPR measurements, or for applications in which the solution refractive index is not known.
在依赖诸如表面等离子体共振光谱（SPR）等光学表面敏感技术的薄膜传感应用中，与温度相关的表面覆盖率和界面动力学测量仍未得到充分利用。这些技术本质上对与薄膜接触的本体溶液的光学性质敏感；因此，定量薄膜传感需要在感兴趣的条件下获取本体溶液的准确折射率数据。本体溶液的折射率强烈依赖于温度、溶液组成和光学激发波长。在本文中，我们展示了利用临界角测量来准确、独立地测定本体溶液的折射率，并给出了不同溶液温度、溶液浓度和激发波长实验条件下的结果。我们还研究了在超薄有机膜双色SPR传感情况下，对本体溶液考虑不当的影响。这种传感技术本质上依赖于薄膜和本体溶液折射率色散的对比度，其灵敏度可比单色SPR测量高一个数量级以上。临界角测量可与SPR测量结合实施，对于在实验过程中本体折射率发生变化的薄膜传感应用（例如在与温度相关的SPR测量中），或者对于溶液折射率未知的应用来说，将具有重要价值。
