Solvation Dynamics of Biological Water in a Single Live Cell under a Confocal Microscope

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• 作者：Dibyendu Kumar Sasmal ; Shirsendu Ghosh ; Atanu Kumar Das ; Kankan Bhattacharyya
• 刊名：Langmuir
• 出版年：2013
• 出版时间：February 19, 2013
• 年：2013
• 卷：29
• 期：7
• 页码：2289-2298
• 全文大小：530K
• 年卷期：v.29,no.7(February 19, 2013)
• ISSN：1520-5827

文摘

Time-resolved confocal microscopy has been applied to study the cytoplasm and nucleus region of a single live Chinese hamster ovary (CHO) cell. To select the cytoplasm and the nucleus region, two different fluorescent probes are used. A hydrophobic fluorescent dye, DCM, localizes preferentially in the cytoplasm region of a CHO cell. A DNA binding dye, DAPI, is found to be inside the nucleus of the cell. The locations of the probes are clearly seen in the image. Emission maxima of the dyes (DCM in cytoplasm and DAPI in the nucleus) are compared to those of the same dyes in different solvents. From this, it is concluded that the polarity (dielectric constant, 蔚) of the microenvironment of DCM in the cytoplasm is 15. The nucleus is found to be much more polar with 蔚 鈮?60 (as reported by DAPI). The diffusion coefficient (and hence viscosity) in the cytoplasm and the nucleus was determined using fluorescence correlation spectroscopy (FCS). The diffusion coefficient (D_t) of the dye (DCM) in the cytoplasm is 2 渭m² s^鈥? and is 150 times slower than that in bulk water (buffer). D_t of DAPI in the nucleus (15 渭m² s^鈥?) is 30 times slower than that in bulk water (buffer). The extremely slow diffusion inside the cell has been ascribed to higher viscosity and also to the binding of the probes (DCM and DAPI) to large biological macromolecules. The solvation dynamics of water in the cytoplasm (monitored by DCM) exhibits an average relaxation time 蟿_sol of 1250 卤 50 ps, which is about 1000 times slower than in bulk water (1 ps). The solvation dynamics inside the nucleus (studied using DAPI) is about 2-fold faster, 蟿_sol 鈮?775 ps. The higher polarity, faster diffusion, and faster solvation dynamics in the nucleus indicates that it is less crowded and less restricted than the cytoplasm.