Near-infrared fluorescence lifetime pH-sensitive probes

Mikhail Y. Berezin, Kevin Guo, Walter Akers, Ralph E. Northdurft, Joseph P. Culver, Bao Teng, Olga Vasalatiy, Kyle Barbacow, Amir Gandjbakhche, Gary L. Griffiths, Samuel Achilefu

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


We report what we believe to be the first near-infrared pH-sensitive fluorescence lifetime molecular probe suitable for biological applications in physiological range. Specifically, we modified a known fluorophore skeleton, hexamethylindotricarbocyanine, with a tertiary amine functionality that was electronically coupled to the fluorophore, to generate a pH-sensitive probe. The pKa of the probe depended critically on the location of the amine. Peripheral substitution at the 5-position of the indole ring resulted in a compound with pKa ∼ 4.9 as determined by emission spectroscopy. In contrast, substitution at the meso-position shifted the pKa to 5.5. The resulting compound, LS482, demonstrated steady-state and fluorescence-lifetime pH-sensitivity. This sensitivity stemmed from distinct lifetimes for protonated (∼1.16 ns in acidic DMSO) and deprotonated (∼1.4 ns in basic DMSO) components. The suitability of the fluorescent dyes for biological applications was demonstrated with a fluorescencelifetime tomography system. The ability to interrogate cellular processes and subsequently translate the findings in living organisms further augments the potential of these lifetime-based pH probes.

Original languageEnglish (US)
Pages (from-to)2063-2072
Number of pages10
JournalBiophysical journal
Issue number8
StatePublished - Apr 20 2011
Externally publishedYes

ASJC Scopus subject areas

  • Biophysics


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