Model discrimination for the propionic acid diffusion into hydrogel beads using lifetime confocal laser scanning microscopy
Model discrimination for the propionic acid diffusion into hydrogel beads using lifetime confocal laser scanning microscopy
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DOI：
10.1016/j.ces.2008.04.005
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发表时间：
2008-07-01
影响因子：
4.7
通讯作者：
Marquardt, Wolfgang
中科院分区：
文献类型：
--
作者：
Spiess, Antje C.;Zavrel, Michael;Marquardt, Wolfgang
水凝胶越来越多地用于捕获生物催化剂，特别是用于在有机溶剂系统中使用酶。因此，有必要了解水凝胶基质对运输动力学（扩散和相转移）和反应动力学（酶的活性和稳定性）的影响。在这里，丙酸到海藻酸钙水凝胶珠的扩散进行了研究，使用结构化的方法，基于模型的实验分析（MEXA）的基础上，所有进一步的调查是一个严格的模型，丙酸到海藻酸钙水凝胶珠的扩散过程中发生的所有过程。作为竞争模型假设的Fickian和Nernst-Planck扩散定律集成。然后，进行最优实验设计以确定允许有效区分竞争对手模型候选者的那些实验。在水凝胶珠的中心观察到由丙酸扩散到水凝胶珠中引起的pH值随时间的变化。荧光pH指示剂试卤灵显示pH依赖性寿命，其通过使用共聚焦激光扫描显微镜以高时间分辨率（每1秒）进行时间相关单光子计数来测量。据我们所知，寿命共聚焦激光扫描显微镜是第一次在这项研究中的宏观大颗粒的动态pH值变化的量化。基于16个独立的实验数据集估计每个候选模型的模型参数。最后，利用似然函数对丙酸在海藻酸钙水凝胶中的扩散规律进行了评价和判别，结果表明，Fickian扩散不能准确描述丙酸在海藻酸钙水凝胶中的扩散过程.海藻酸钙水凝胶密度的影响被认为是微不足道的估计的扩散系数。(C)2008爱思唯尔有限公司保留所有权利。
Hydrogels are increasingly used for the entrapment of biocatalysts, especially for the use of enzymes in organic solvent systems. Hence, it is necessary to understand the influence of the hydrogel matrix on the transport kinetics (diffusion and phase transfer) and on the reaction kinetics (activity and stability of the enzymes). Here, the diffusion of propionic acid into Ca-alginate hydrogel beads is studied using a structured methodology, model-based experimental analysis (MEXA).The basis for all further investigations is a rigorous model of all processes occurring during the diffusion of the propionic acid into the Ca-alginate hydrogel bead. As competing model assumptions the Fickian and Nernst-Planck diffusion laws are integrated. Then, an optimal experimental design is performed to determine those experiments that allow an efficient discrimination of the rival model candidates. The change in pH-value over time resulting from the diffusion of propionic acid into the hydrogel bead is observed in the centre of the hydrogel bead. The fluorescent pH-indicator resorufin shows pH-dependent lifetimes that are measured by time-correlated single photon counting using a confocal laser scanning microscope at high temporal resolution (every 1 s). To our knowledge lifetime confocal laser scanning microscopy is used for the first time in this study for the quantification of dynamic pH-changes in macroscopically large particles. The model parameters for each candidate model are estimated based on 16 independent experimental data sets. Finally, the likelihood function is used to evaluate and discriminate the competing diffusion laws.For the diffusion of propionic acid into spherical Ca-alginate hydrogel beads, it could be shown that Fickian diffusion is not able to describe the process accurately in contrast to Nernst-Planck diffusion. The influence of the Ca-alginate hydrogel density was found to be insignificant for the estimated diffusion coefficient. (C) 2008 Elsevier Ltd. All rights reserved.