title: Near-infrared fluorescence lifetime pH-sensitive probes.
abstract: 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 pK(a) 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 pK(a) ∼ 4.9 as determined by emission spectroscopy. In contrast, substitution at the meso-position shifted the pK(a) 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 fluorescence-lifetime 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.
authors.affiliation: Department of Radiology, Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: Mikhail Y
authors.initials: MY
authors.lastname: Berezin
authors.forename: Kevin
authors.initials: K
authors.lastname: Guo
authors.forename: Walter
authors.initials: W
authors.lastname: Akers
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Northdurft
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Culver
authors.forename: Bao
authors.initials: B
authors.lastname: Teng
authors.forename: Olga
authors.initials: O
authors.lastname: Vasalatiy
authors.forename: Kyle
authors.initials: K
authors.lastname: Barbacow
authors.forename: Amir
authors.initials: A
authors.lastname: Gandjbakhche
authors.forename: Gary L
authors.initials: GL
authors.lastname: Griffiths
authors.forename: Samuel
authors.initials: S
authors.lastname: Achilefu
mesh_terms: D000042:Absorption; D000818:Animals; D002232:Carbocyanines / Q000737:chemistry / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007259:Infrared Rays; D008297:Male; D051379:Mice; D055620:Optical Phenomena; D019047:Phantoms, Imaging; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013997:Time Factors; D041622:Tomography, Optical
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes; C501744:indotricarbocyanine