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Ratiometric Near-Infrared Fluorescent Probes Based on Hemicyanine Dyes Bearing Dithioacetal and Formal Residues for pH Detection in Mitochondria.

ABSTRACT: Ratiometric near-infrared fluorescent probes (AH⁺ and BH⁺) have been prepared for pH determination in mitochondria by attaching dithioacetal and formal residues onto a hemicyanine dye. The reactive formyl group on probe BH⁺ allows for retention inside mitochondria as it can react with a protein primary amine residue to form an imine under slightly basic pH 8.0. Probes AH⁺ and BH⁺ display ratiometric fluorescent responses to pH changes through the protonation and deprotonaton of a hydroxy group in hemicyanine dyes with experimentally determined pKa values of 6.85 and 6.49, respectively. Calculated pK_a values from a variety of theoretical methods indicated that the SMD_BONDI method of accounting for solvent and van der Waals radii plus including a water molecule located near the site of protonation produced the closest overall agreement with the experimental values at 7.33 and 6.14 for AH⁺ and BH⁺ respectively.

SUBMITTER: Yan Y

PROVIDER: S-EPMC8038704 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In this paper, we present three ratiometric near-infrared fluorescent probes (A-C) for accurate, ratiometric detection of intracellular pH changes in live cells. Probe A consists of a tetraphenylethene (TPE) donor and near-infrared hemicyanine acceptor in a through-bond energy transfer (TBET) strategy, while probes B and C are composed of TPE and hemicyanine moieties through single and double sp2 carbon-carbon bond connections in a π-conjugation modulation strategy. The specific targeting of the probes to lysosomes in live cells was achieved by introducing morpholine residues to the hemicyanine moieties to form closed spirolactam ring structures. Probe A shows aggregation-induced emission (AIE) property at neutral or basic pH, while probes B and C lack AIE properties. At basic or neutral pH, the probes only show fluorescence of TPE moieties with closed spirolactam forms of hemicyanine moieties, and effectively avoid blind fluorescence imaging spots, an issue which typical intensity-based pH fluorescent probes encounter. Three probes show ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with TPE fluorescence decreases and hemicyanine fluorescence increases, because acidic pH makes the spirolactam rings open to enhance π-conjugation of hemicyanine moieties. However, probe A shows much more sensitive ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with remarkable ratio increase of TPE fluorescence to hemicyanine fluorescence up to 238-fold than probes B and C because of its high efficiency of energy transfer from TPE donor to the hemicyanine acceptor in the TBET strategy. The probe offers dual Stokes shifts with a large pseudo-Stokes shift of 361 nm and well-defined dual emissions, and allows for colocalization of the imaging readouts of visible and near-infrared fluorescence channels to achieve more precisely double-checked ratiometric fluorescence imaging. These platforms could be employed to develop a variety of novel ratiometric fluorescent probes for accurate detection of different analytes in applications of chemical and biological sensing, imaging, and diagnostics by introducing appropriate sensing ligands to hemicyanine moieties to form on-off spirolactam switches.

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Ratiometric Near-Infrared Fluorescent Probes Based on Hemicyanine Dyes Bearing Dithioacetal and Formal Residues for pH Detection in Mitochondria.

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