Rathgeber Silke, Beauvisage Hans-Josef, Chevreau Hubert, Willenbacher Norbert, Oelschlaeger Claude
Max Planck-Institute for Polymer Research, Polymer Physics, 55128 Mainz, Germany.
Langmuir. 2009 Jun 2;25(11):6368-76. doi: 10.1021/la804170k.
We show that fluorescence correlation spectroscopy (FCS) using a commercial spectrometer can be applied to passive microrheological (MR) experiments. The method probes the local rheological properties of materials on length scales of the focus dimension of the confocal microscope. For a feasibility study, we performed measurements on a high molecular weight poly(ethylene oxide)-water solution to allow direct comparison of the results to previous studies using diffusing wave spectroscopy, quasielastic light scattering, and particle tracking methods. We were able to detect mean-square center-of-mass displacements ranging from somewhat better than [SYMBOL: SEE TEXT]2(t) approximately 100 nm2 up to above Deltar2(t) approximately 10(6) nm2. Thus, we were able to derive the bulk rheological shear moduli covering more than five decades in frequency (from omega<or=10(-1) rad/s to omega approximately 10(4) rad/s). The MR results are compared to results obtained from conventional rheological experiments on the same samples using a rotational rheometer as well as a piezo-driven squeeze flow apparatus. Good agreement between MR results probing the local rheological properties and those obtained by the conventional methods measuring the macroscopic mechanical response is found in the whole frequency range. Spatial resolution in combination with the possibility of using small tracer beads open the opportunity to probe the local, length scale-dependent rheological properties in heterogeneous samples. Small tracer concentrations and small sample sizes make FCS spectroscopy a powerful tool in particular for biological and medical applications.
我们表明，使用商用光谱仪的荧光相关光谱法（FCS）可应用于被动微流变学（MR）实验。该方法在共聚焦显微镜焦点尺寸的长度尺度上探测材料的局部流变特性。为了进行可行性研究，我们对高分子量聚环氧乙烷 - 水溶液进行了测量，以便将结果与先前使用扩散波谱、准弹性光散射和粒子追踪方法的研究进行直接比较。我们能够检测到质心位移的均方值，范围从略优于⟨r²(t)⟩约100 nm²到高于Δr²(t)约10⁶ nm²。因此，我们能够推导出在频率上跨越五个多数量级（从ω≤10⁻¹ rad/s到ω约10⁴ rad/s）的整体流变剪切模量。将微流变学结果与使用旋转流变仪以及压电驱动挤压流动装置对相同样品进行常规流变实验获得的结果进行了比较。在整个频率范围内，探测局部流变特性的微流变学结果与通过测量宏观力学响应的传统方法获得的结果之间发现了良好的一致性。空间分辨率以及使用小示踪珠的可能性为探测异质样品中局部的、与长度尺度相关的流变特性提供了机会。小示踪剂浓度和小样品尺寸使FCS光谱法成为一种强大的工具，尤其适用于生物和医学应用。
