Luminescent Probes for Sensitive Detection of pH Changes in Live Cells through Two Near-Infrared Luminescence Channels

Abstract

Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2′-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.

Reaction-free and MMP-independent fluorescent probes for long-term mitochondria visualization and tracking

“…Fluorescence microscopy has become a powerful tool for real-time visualization and tracking of biomolecules in medical and biological applications,9–18 due to its high selectivity, remarkable sensitivity, excellent spatial and temporal resolution and non-invasive operation 19–25. Current fluorescent probes for visualizing and tracking mitochondria associated dynamic changes, such as monitoring the mitophagy process, could be divided into two classes: traditional electrostatic-attraction based cationic mitochondrial probes and reaction-based MitoTracker probes (Scheme 1(1)).…”

A Near-Infrared Fluorescent Probe Based on a FRET Rhodamine Donor Linked to a Cyanine Acceptor for Sensitive Detection of Intracellular pH Alternations

“…In order to test this hypothesis, we conducted colocalization experiments by using commercial Lysosensor Green to determine the intracellular location of probe A . Intracelluar pH values were adjusted by incubating HeLa cells in different pH buffers containing 10 µM nigericine, H + ionphore, which is employed to promote equilibration between intracellular and extracellular pH values [ 7 , 9 , 29 , 41 , 42 ]. Probe A responds sensitively to intracellular pH decreases from 7.01 to 3.50 with gradual fluorescence enhancement due to acid-activated spirolactam ring opening with significantly enhanced π-conjugation, Figure 12 .…”

“…Fluorescence imaging is frequently used for real-time pH monitoring in biological systems due to its rapid response time, high sensitivity, non-destructive nature, operational simplicity, and high-speed spatial capabilities [ 4 ]. Recently, near-infrared pH fluorescent probes were developed to take advantage of near-infrared imaging unique features such as minimum photobleaching, deep tissue penetration, suppressed photodamage to cells and tissues, and low biological luminescence background [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Most of these near-infrared fluorescent probes that measure pH levels are based on fluorescence changes in a single near-infrared wavelength [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ,…”

Recent Endeavors on Molecular Imaging for Mapping Metals in Biology

“…sensor for ex vivo and in vivo assay in a WD mouse model. Impressively, the exploitation of UCL small-molecule probes and their bioimaging applications have been attracting much attention (Dong et al 2018;Yang et al 2016;Zhang et al 2017).…”