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. 2017 Dec 13;7:17484. doi: 10.1038/s41598-017-17459-y

Figure 1.

Figure 1

pH-dependent fluorescent property of FITC-PEG-lipid suspended in solution at various pH values. (a) Excitation fluorescence spectrum of FITC-PEG-lipid measured with emission at 519 nm. (b) Emission fluorescence spectra of FITC-PEG-lipid when excited at 458 nm (left) and 488 nm (right). The measurements of the spectra in (a) and (b) were performed in the buffered solutions with various pH (pH 2.0–10.0) as indicated with different colors. (c) Plot of the fluorescence ratio (Ex 488 nm/458 nm) against the pH of the buffered solutions (Black error bars). The fluorescence ratio was calculated from the integrated fluorescence intensity at 500–550 nm when excited at 458 nm and 488 nm. The dashed curve was obtained by fitting to a biphasic two-site competition ligand binding curve in non-linear regression analysis. Data of measurements in Na+-free, K+-free, and Na+, K+-free solutions at pH 6.0 are shown with colored error bars as indicated. Error bars represent SD (n = 4).