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. 2020 Aug 20;10(51):30825-30831.
doi: 10.1039/d0ra04935b. eCollection 2020 Aug 17.

A deep-red fluorescent molecular rotor based on donor-two-acceptor modular system for imaging mitochondrial viscosity

Xiaoxi Yin  1   2 , Yiping Cai  1   2 , Songtao Cai  1   2 , Xiaojie Jiao  1   2 , Chang Liu  1   2 , Song He  1   2 , Xianshun Zeng  1   2
Affiliations

A deep-red fluorescent molecular rotor based on donor-two-acceptor modular system for imaging mitochondrial viscosity

Xiaoxi Yin et al. RSC Adv. .

Abstract

A new donor-two-acceptor modular fluorescence rotor DpCy7 involving a phenolate donor unit and two benzothiazolium acceptor moieties was designed and synthesized. The DpCy7 underwent an internal charge transfer to form a Cy7-like longer conjugated system fluorochrome at a physiological pH. The probe exhibited a strong turn-on (8.5-fold) deep-red emission with a larger Stokes shift in glycerol aqueous solutions with restriction of rotation. Both the fluorescence intensity and fluorescence lifetime displayed the linear relationship of viscosity changes in the logarithmic plots. Furthermore, the HeLa cell imaging experiments of DpCy7 indicated that the rotor could be used to monitor the mitochondrial viscosity in living cells. This new type of deep-red fluorescence rotor provides a potential platform for determining viscosity at subcellular levels.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. The synthesis route of the protonated DpCy7.
Scheme 2
Scheme 2. Proposed structure conversions of DpCy7 under different pH conditions (red arrow is the rotatory unit).
Fig. 1
Fig. 1. UV absorption spectra of the dye DpCy7 (10 μM) in aqueous solution with different pHs.
Fig. 2
Fig. 2. Fluorescence spectra of DpCy7 (5 μM) in various freshly prepared solvents. The solvents included: DMSO, tetrahydrofuran, dichloromethane, methanol, H2O, acetonitrile and glycerol.
Fig. 3
Fig. 3. The DFT optimised frontier orbital pictures of DpCy7@H+ and DpCy7.
Fig. 4
Fig. 4. Fluorescence spectra of DpCy7 (5 μM) in different ratios of glycerol–water solutions. Inset: the linear relationship between log (I688) and log (viscosity) in the glycerol–water solutions.
Fig. 5
Fig. 5. Fluorescence lifetime of the DpCy7 (5 μM) probe with changes of viscosity of the solution (10–60% glycerol) at 670 nm.
Fig. 6
Fig. 6. Confocal microscopy images of HeLa cells. (a) Incubation with 1 μM DpCy7 for 30 min; (b) bright field microscopy; (c) overlay of (a) and (b); (d) incubation with 1 μM DpCy7 and 10 μM monensin for 30 min. (e) Bright field microscopy; (f) overlay of (d) and (e); (g) incubation with 1 μM DpCy7 and 10 μM nystatin for 30 min; (h) bright field microscopy; (i) overlay of (g) and (h); λex = 559 nm, λem = 600–700 nm; scale bar = 30 μm.
Fig. 7
Fig. 7. Co-localization experiments involving the DpCy7 probe (0.1 μM) and MitoTracker Green in HeLa cells incubated with 1 μM monensin at 37 °C for 30 min. (a) Confocal image from MitoTracker Green (200 nM) on green channel; (b) confocal image from 0.1 μM probe DpCy7 on red channel; (c) merged image of (a) and (b); (d) the intensity profile of ROI lines; (e) fluorescence intensity dot plot of MitoTracker Green channel and DpCy7 channel. Scale bar = 10 μm.
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