New fluorescent pH sensors based on covalently linkable PET rhodamines
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AuthorAigner, Daniel; Borisov, Sergey M.; Orriach Fernández, Francisco José; Fernández Sánchez, Jorge Fernando; Saf, Robert; Klimant, Ingo
pH sensorFluorescenceRhodaminePhotoinduced electron transferCovalent dye couplingClick chemistry
Aigner, D., Borisov, S. M., Fernández, F. J. O., Sánchez, J. F. F., Saf, R., & Klimant, I. (2012). New fluorescent pH sensors based on covalently linkable PET rhodamines. Talanta, 99, 194-201. [http://dx.doi.org/10.1016/j.talanta.2012.05.039]
SponsorshipAustrian Science Fund (FWF) P 21192-N17; Spanish Government AT2009-0019
A new class of rhodamines for the application as indicator dyes in fluorescent pH sensors is presented. Their pH-sensitivity derives from photoinduced electron transfer between non-protonated amino groups and the excited chromophore which results in effective fluorescence quenching at increasing pH. The new indicator class carries a pentafluorophenyl group at the 9-position of the xanthene core where other rhodamines bear 2-carboxyphenyl substituents instead. The pentafluorophenyl group is used for covalent coupling to sensor matrices by “click” reaction with mercapto groups. Photophysical properties are similar to “classical” rhodamines carrying 2′-carboxy groups. pH sensors have been prepared with two different matrix materials, silica gel and poly(2-hydroxyethylmethacrylate). Both sensors show high luminescence brightness (absolute fluorescence quantum yield ΦF≈0.6) and high pH-sensitivity at pH 5–7 which makes them suitable for monitoring biotechnological samples. To underline practical applicability, a dually lifetime referenced sensor containing Cr(III)-doped Al2O3 as reference material is presented.