Abstract
A fluorescence resonance energy transfer (FRET)-based near-infrared fluorescent probe (B+) for double-checked sensitive detection of intracellular pH changes has been synthesized by binding a near-infrared rhodamine donor to a near-infrared cyanine acceptor through robust C-N bonds via a nucleophilic substitution reaction. To demonstrate the double-checked advantages of probe B+, a near-infrared probe (A) was also prepared by modification of a near-infrared rhodamine dye with ethylenediamine to produce a closed spirolactam residue. Under basic conditions, probe B+ shows only weak fluorescence from the cyanine acceptor while probe A displays nonfluorescence due to retention of the closed spirolactam form of the rhodamine moiety. Upon decrease in solution pH level, probe B+ exhibits a gradual fluorescence increase from rhodamine and cyanine constituents at 623 nm and 743 nm respectively, whereas probe A displays fluorescence increase at 623 nm on the rhodamine moiety as acidic conditions leads to the rupture of the probe spirolactam rings. Probes A and B+ have successfully been used to monitor intracellular pH alternations and possess pKa values of 5.15 and 7.80, respectively.
Highlights
Different cellular compartments regulate intracellular pH as precise control is essential for various cell functions such as vesicle trafficking, cellular metabolism, cellular signaling, cell membrane polarity, cell activation, proliferation growth, and apoptosis [1,2,3,4]
We have developed a detect intracellular pH alternations byScheme monitoring deep-red near-infrared fluorescence changes at near-infrared fluorescent probe (B ), 1, with unique and double-checked capability to accurately detect by monitoringfeature deep-red and near-infrared fluorescence changes nm intracellular and 780 nm.pH
We demonstrate that there is slight overlap between the rhodamine donor emission and cyanine acceptor absorption for energy transfer from the rhodamine donor to the cyanine acceptor presumably acceptor absorption for energy transfer from the rhodamine donor to the cyanine acceptor through the short ethylenediamino linkage [34,35]
Summary
Different cellular compartments regulate intracellular pH as precise control is essential for various cell functions such as vesicle trafficking, cellular metabolism, cellular signaling, cell membrane polarity, cell activation, proliferation growth, and apoptosis [1,2,3,4]. Lysosomes function best under acidic pH conditions between 4.5 to 5.5 to break down a variety of biomolecules while mitochondria operate under slightly alkali pH conditions around 8.0 [4,5,6]. Various diseases such as neurodegenerative disease, cancer, and Alzheimer’s disease, are associated with significant deviations from normal functional intracellular pH values [1,2,3,4]. Most of these near-infrared fluorescent probes that measure pH levels are based
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