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Updated: Aug 14, 2026

Fluorescent Labeling of COS-7 Expressing SNAP-tag Fusion Proteins for Live Cell Imaging
Published on: May 17, 2010
New fluorescent labels: 4- and 7-chlorofluorescein
Feng-Yan Ge1, Xi-Long Yan, Fan-Yong Yan
1School of Pharmaceuticals and Biotechnology, Tianjin University, Tianjin, 300072, PR China.
Abstract:
A new mixture of 4- and 7-chlorofluorescein were synthesized by condensation of resorcinol with 3-chlorophthalic anhydride in the presence of methanesulfonic acid or zinc chloride. These regioisomers were successfully separated by chromatography. The photophysical properties were examined and their absorption and emission maxima at long wavelength, high fluorescence quantum yield, and narrow emission bandwidth were found, highly favorable for detecting multiple target substances in the same sample. Furthermore, 4(7)-chlorofluorescein was found to be strongly pH-dependent between 4.0 and 8.0, and could be used as pH-sensitive fluorescent probe to measure intracellular pH.
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