Ipiña Emiliano Pérez, Dawson Silvina Ponce
Departamento de Física, FCEN-UBA, and IFIBA, CONICET, Ciudad Universitaria, Pabellón I, (1428) Buenos Aires, Argentina.
Phys Rev E Stat Nonlin Soft Matter Phys. 2013 Feb;87(2):022706. doi: 10.1103/PhysRevE.87.022706. Epub 2013 Feb 13.
Diffusion is one of the main transport processes that occur inside cells determining the spatial and time distribution of relevant action molecules. In most cases these molecules not only diffuse but also interact with others as they get transported. When these interactions occur faster than diffusion the resulting transport can be characterized by "effective diffusion coefficients" that depend on both the reaction rates and the "free" diffusion coefficients. Fluorescence correlation spectroscopy (FCS) gives information on effective rather than free diffusion coefficients under this condition. In the present paper we investigate what coefficients can be drawn from FCS experiments for a wide range of values of the ratio of reaction to diffusion time scales, using different fitting functions. We find that the effective coefficients can be inferred with relatively small errors even when the condition of fast reactions does not exactly hold. Since the diffusion time scale depends on the size of the observation volume and the reaction time scale depends on concentrations, we also discuss how by changing either one or the other property one can switch between the two limits and extract more information on the system under study.
扩散是细胞内发生的主要传输过程之一，它决定了相关活性分子的空间和时间分布。在大多数情况下，这些分子不仅会扩散，而且在传输过程中还会与其他分子相互作用。当这些相互作用的发生速度快于扩散速度时，由此产生的传输可以用“有效扩散系数”来表征，该系数取决于反应速率和“自由”扩散系数。在这种情况下，荧光相关光谱法（FCS）提供的是关于有效扩散系数而非自由扩散系数的信息。在本文中，我们使用不同的拟合函数，研究了在反应时间尺度与扩散时间尺度的比值范围很广的情况下，FCS实验能够得出哪些系数。我们发现，即使快速反应的条件并不完全成立，有效系数也能以相对较小的误差推断出来。由于扩散时间尺度取决于观测体积的大小，而反应时间尺度取决于浓度，我们还讨论了如何通过改变其中一个或另一个属性，在两种极限情况之间进行切换，并提取更多关于所研究系统的信息。
