A mitochondria-targeted fluorescent dye naphthalimide-thioether-cyanine for NIR-activated photodynamic treatment of cancer cells

Article abstract of DOI:10.1039/d0tb02851g

In this work, an NIR-activated fluorescent dye naphthalimide-thioether-cyanine (NPSCY) was developed for the photodynamic treatment of cancer cells. In this dye, naphthalimide and cyanine were selected as the two fluorophores, which were linked by the thioether group. Under 660 nm irradiation,NPSCYcould produce¹O₂rapidly, suggesting the potential for photodynamic therapy. Cys can be considered as one of the markers of cancer cells andNPSCYcould distinguish Cys from three channels (433 nm, 475 nm, 733 nm) due to the bilateral recognition of the thioether group, which was helpful for accurately locating cancer cells. Fortunately,NPSCYcould also produce¹O₂after being reacted with the intracellular biological thiols, which also avoided the inactivation of the photosensitizer in cancer cells. The co-localization coefficient of 0.873 indicated that the cyanine group promoted the aggregation ofNPSCYin mitochondria. This photosensitizer showed low dark toxicity and high phototoxicity. Meanwhile, the half-maximal inhibitory concentration (IC₅₀) was calculated to be 3.7 μM.NPSCYcould inhibit cell migration after irradiation at 660 nm.

Full text of DOI:10.1039/d0tb02851g

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PAPER
A mitochondria-targeted fluorescent dye
naphthalimide-thioether-cyanine for
NIR-activated photodynamic treatment of
cancer cells†
Cite this: J. Mater. Chem. B, 2021,
9, 2462
Ronghua Shen,
Jin Bai
and Ying Qian
*
In this work, an NIR-activated fluorescent dye naphthalimide-thioether-cyanine (NPSCY) was developed
for the photodynamic treatment of cancer cells. In this dye, naphthalimide and cyanine were selected as
the two fluorophores, which were linked by the thioether group. Under 660 nm irradiation, NPSCY
1
could produce O2 rapidly, suggesting the potential for photodynamic therapy. Cys can be considered as
one of the markers of cancer cells and NPSCY could distinguish Cys from three channels (433 nm,
475 nm, 733 nm) due to the bilateral recognition of the thioether group, which was helpful for
1
accurately locating cancer cells. Fortunately, NPSCY could also produce O2 after being reacted with the
intracellular biological thiols, which also avoided the inactivation of the photosensitizer in cancer cells.
The co-localization coefficient of 0.873 indicated that the cyanine group promoted the aggregation of
NPSCY in mitochondria. This photosensitizer showed low dark toxicity and high phototoxicity.
Meanwhile, the half-maximal inhibitory concentration (IC50) was calculated to be 3.7 mM. NPSCY could
inhibit cell migration after irradiation at 660 nm.
Received 8th December 2020,
Accepted 14th February 2021
DOI: 10.1039/d0tb02851g
rsc.li/materials-b
reagents are mainly concentrated in the range of blue and
green light,18–20 which results in a poor therapeutic effect
1. Introduction
Cancer has become one of the most important threats to because of the assimilation and dispersal by bio-tissues and
human beings and cancer treatment has seen significant blood. NIR light can reduce the light damage and has the
developments in recent decades.1–4 Compared with traditional advantage of deep tissue penetration, which gives PDT reagents
methods, such as chemotherapy, surgery and radiotherapy,5,6 greater application prospects in biological systems.21–24
photodynamic therapy (PDT) has attracted more attention
Biological thiols are known as a biomarker of cancer cells
owing to its low toxicity and precise control.7,8 PDT mainly and are involved in a lot of physiological and pathological
involves a photosensitizer, a light source and intracellular processes.25–27 Cysteine (Cys) is one of the raw materials of
oxygen.9,10 Excited by a specific wavelength of light, the photo- glutathione (GSH) and can be synthesized from homocysteine
sensitizer transfers energy to molecular oxygen to generate (Hcy) and metabolized to hydrogen sulfide and sulfite via
cytotoxic singlet oxygen (1O2) so that the cancer cells are transaminase or dioxygenase.28–30 The normal concentration
damaged,11–13 which minimizes the side effects of PDT to the of biothiols in human cells is very important (Cys: 30–200 mM;31
greatest extent.14 The half-life (0.04 ms) and the effective Hcy: 5–12 mM;32 GSH: 1–10 mM33). Abnormal levels of biothiols
1
distance of O2 (0.02 mm) are very short,15 which means that could cause various diseases, such as liver injury, cardiovascular
cell damage is mainly limited to the site of 1O2 production. disease and Alzheimer’s disease.34–36 In recent years, a large
Therefore, PDT is considered to be a minimally invasive and number of fluorescent probes based on different sensing
safe cancer treatment method.16 Meanwhile, the effect of mechanisms or fluorophores have been synthesized for the
PDT depends on the subcellular localization in cells while detection of biothiols.37–41 It is hard to distinguish Cys, Hcy
mitochondria or lysosomes are usually considered due to their and GSH due to the structural similarity.42–44 The short emission
roles in apoptosis.17 The excitation wavelengths of most PDT wavelength and poor water solubility of current biothiols probes
also seriously limit its further application.45–48 Overall, it is
necessary to develop PDT reagents with the dual functions of
monitoring biothiols and treating cancer.
School of Chemistry and Chemical Engineering, Southeast University,
Nanjing 211189, China. E-mail: yingqian@seu.edu.cn; Fax: +86 25 83795857
Hence, a fluorescent dye (NPSCY) for the detection of Cys
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d0tb02851g
and PDT of cancer cells was synthesized. As shown in Scheme 1,
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Scheme 1 The specific recognition of NPSCY towards Cys and the
photodynamic therapy of cancer cells in this work.
NPSCY could selectively recognize Cys from three channels
(Cys: 733 nm, 435 nm; Hcy: 733 nm, 475 nm), which was
attributed to the double nucleophilic substitution between SH
in Cys and the thioether including naphthalimide-thioether
and cyanine-thioether. Meanwhile, cyanine promoted the 1O2
of NPSCY before and after reacting with intracellular biological
thiols under 660 nm irradiation. NPSCY was applied to detect
Cys in mitochondria and zebrafish. The low toxicity in the dark
and high phototoxicity of NPSCY towards 660 nm irradiation
demonstrated its potential for PDT of cancer cells. NPSCY could
inhibit cell migration after irradiation at 660 nm.
Scheme 2 The synthesis route and structure of NPSCY.
crude product was purified by silica gel column chromatography
to obtain compound M2. Yield: 65.7%.
Compound M2 (1.59 g, 10 mmol) and iodomethane (1.41 g,
10 mmol) were dissolved in absolute acetonitrile (30 mL).
The mixture was stirred at 80 1C for 6 h. After the reaction,
the mixture was filtered to obtain compound M3. The crude
product was used in the next step without any purification.
Yield: 72.4%.
(E)-2-Chloro-3-(hydroxymethylene)cyclohex-1-ene-1-carbaldehyde
(0.86 g, 5 mmol) and compound M3 (3.0 g, 10 mmol) were
dissolved in ethanol (30 mL). The mixture was stirred at 85 1C
for 8 h. After reaction, the ethanol was evaporated under
reduced pressure and the crude product was purified by silica gel
column chromatography to obtain compound CY. Yield: 46.1%.
1H NMR (CDCl3, ppm): d 8.35 (d, 2H, J = 14.1 Hz, QCH2),
2. Experimental section
Reagents and apparatus
All the details are shown in the ESI.†
Synthesis
Synthesis of compound NPSH. Compound NPSH was 7.39 (m, 4H, –Ar), 7.25 (t, 2H, J = 6.4Hz, –ArH), 7.19 (d, 2H,
synthesized according to
a literature report (shown in J = 7.9 Hz, –ArH), 6.23 (d, 2H, J = 14.1 Hz,QCH2), 3.77 (s, 6H,
Scheme 2).49 6-Bromo-1H,3H-benzo[de]isochromene-1,3-dione –CH3), 2.76 (t, 4H, J = 6.2 Hz, –CH2), 1.98(t, 2H, J = 6.0 Hz,
(2.77 g, 10 mmol) and butan-1-amine (2.92 g, 40 mmol) were –CH2), 1.23(s, 12H, –CH3).
dissolved in ethanol (30 mL). The mixture was stirred at 80 1C
Synthesis of compound NPSCY. Compound CY (483 mg,
for 10 h. After the reaction, the mixture was filtered to obtain 1 mmol) was dissolved in dichloromethane (20 mL). Then,
compound M1. The crude product was used in the next step compound NPSH (570 mg, 1 mmol) and triethylamine (101 mg,
without any purification. Yield: 64.5%.
1 mmol) were added and stirred at room temperature for 6 h.
Compound M1 (3.31 g, 10 mmol) and Na2SÁ9H2O were The mixture was evaporated under reduced pressure and the
dissolved in DMF (10 mL). The mixture was stirred at room crude product was purified by silica gel column chromatography
temperature for 2 h. After the reaction, the mixture was poured to obtain a green solid. Yield: 22.0%. 1H NMR (600 MHz, DMSO-
into deionized water (40 mL) and filtered to obtain compound d6): d 8.88 (d, 1H, J = 8.3 Hz, –ArH), 8.75 (d, 1H, J = 8.0 Hz, –ArH),
NPSH. The crude product was used in the next step without any 8.53 (d, 2H, J = 14.1 Hz, QCH2), 8.39 (d, 1H, J = 8.0Hz, –ArH),
purification. Yield: 45.8%.
7.99 (d, 1H, J = 7.9 Hz, –ArH), 7.31 (m, 3H, –ArH), 7.16 (d, 3H,
Synthesis of compound CY. Compound CY was synthesized J = 4.1 Hz, –ArH), 7.11 (d, 2H, J = 7.9 Hz, –ArH), 6.35 (d, 2H,
according to a literature report (shown in Scheme 2).50 Phenyl- J = 14.1 Hz, QCH2), 4.12 (t, 2H, J = 7.5 Hz, –CH2), 3.73
hydrazine (10.8 g, 100 mmol), 3-methylbutan-2-one (86.1 g, (s, 6H, –CH3), 2.93 (t, 4H, J = 6.1 Hz, –CH2), 2.13 (t, 2H,
100 mmol) and 3 drops of acetic acid were dissolved in ethanol J = 5.9 Hz, –CH2), 1.66 (m, 2H, –CH2), 1.61 (s, 2H, –CH2), 1.41
(30 mL). The mixture was stirred at 80 1C for 6 h. After the (m, 2H, –CH2), 1.25 (t, 12H, J = 15.5 Hz, –CH3), 0.94 (t, 3H,
reaction, the ethanol was evaporated under reduced pressure to J = 7.4Hz, –CH3). 13C NMR (150 MHz, DMSO-d6), 172.73, 163.68,
obtain a brown oil. The brown oil was dissolved in acetic acid 163.69, 147.47, 144.84, 143.95, 142.51, 140.74, 134.63, 131.22,
and the mixture was stirred at 105 1C for 1 h. After the reaction, 129.11, 128.76, 128.28, 127.20, 125.27, 123.72, 123.50, 121.85,
the acetic acid was evaporated under reduced pressure and the 119.67, 110.70, 102.61, 58.28, 48.84, 40.20, 32.52, 30.05, 29.55,
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27.45, 27.01, 20.61, 20.21, 18.30, 13.65. HRMS (ESIÀ): m/z calcd
for C48H50N3O2S+ [M]+: 732.3624, found: 732.3617.
3. Results and discussion
The design route of fluorescent dye for Cys detection and PDT
The ratiometric fluorescent signals could avoid interference from
the external environment. Therefore, as shown in Scheme 3, the
fluorophores naphthalimide and cyanine were selected as the two
fluorescent sources to form the ratiometric fluorescent responses
owing to their excellent optical properties.51,52 In addition, the
thioether group was chosen as the recognition unit, which could
provide two recognition sides including naphthalimide-thioether
and cyanine-thioether. When SH in biothiols was encountered,
nucleophilic substitution may occur at one or two recognition
sides and lead to different fluorescent signals from the naphtha-
limide and cyanine fluorophores, which could form the ratio-
metric fluorescent responses.
As a NIR fluorophore, cyanine could be a PDT photosensitizer,
which has been reported in the field of PDT.3,6,10,17 Especially,
after the reaction with the Cys and Hcy, the NH2 in the thiols
could be linked with the cyclohexenyl group in cyanine, which
could improve the stability of NPSCY and prolong the imaging
time and circulation in the bloodstream in vivo.21 Hence, NPSCY
has the potential to detect cancer-related Cys and treat cancer at
the same time.
Fig. 1 Fluorescence responses of NPSCY (10 mM) in the absence and
presence of various analytes (blank, Ala, Arg, Asn, Asp, Gln, Gly, His, Lys,
Phe, Pro, Thr, Tye, Tyr, Val, Hcy, GSH, Cys; the concentration of the
analytes is 20 mM) in DMSO/PBS buffer (5 : 5, v/v, pH = 7.4). lex = 360 nm
and 660 nm.
enhanced rapidly and the maximum enhancement was more
than 262-fold while a weak fluorescence enhancement belonging
to the naphthalimide part at 435 nm was also observed with a
maximum enhancement of less than 2-fold. Although the
fluorescence enhancement of the naphthalimide part was weak,
it was the key to distinguishing Cys over other biothiols. Owing
to the change of the double fluorescence signals of NPSCY
towards Cys, the ratiometric possibility of NPSCY was considered.
As shown in Fig. 2b, the fluorescence intensity ratio (F733/F435
)
increased rapidly in the concentration range from 0 to 20 mM and
there was a good linear relationship between the fluorescence
intensities of NPSCY in the concentration range of Cys from 2 to
12 mM. The limit of detection of NPSCY towards Cys was also
calculated to be 27.9 nM based on S/N = 3. The experimental
results demonstrated that NPSCY had high sensitivity to Cys and
had the potential to detect Cys in living cells. Moreover, the
fluorescent titration of NPSCY towards Hcy was carried out
(shown in Fig. S3, ESI†) and the limit of detection of NPSCY
towards Hcy was also calculated to be 30.1 nM. Compared with
the published works, the ratiometric fluorescent probe showed
excellent detection performance (shown in Table S1 and Scheme
S1, ESI†).
Sensitive and ratiometric responses of NPSCY towards Cys
To test our design, a selectivity experiment was carried out with
NPSCY. The NPSCY was dissolved in DMSO/PBS buffer (5 : 5, v/v,
pH = 7.4) and various amino acids were added. The mixed
solutions were placed at room temperature for 1 h and the
fluorescence spectra were obtained. As shown in Fig. 1, upon
addition of Cys, a new fluorescence peak for NPSCY occurred at
733 nm while the fluorescence of NPSCY at 435 nm was enhanced
by 1.7-fold. Meanwhile, on adding Hcy, the fluorescence of NPSCY
at 733 nm was enhanced by more than 116-fold while a new
fluorescence peak for NPSCY appeared at 475 nm. Besides, other
amino acids did not lead to obvious fluorescent change although
a weak fluorescent enhancement at 815 nm and 475 nm caused
by GSH occurred, which did not affect the selectivity of NPSCY.
Therefore, NPSCY could distinguish Cys over Hcy/GSH from three
channels, which was in line with our design.
The trend in the fluorescence intensity ratio (F733/F435) of
NPSCY towards Cys under different pH values implied that the
As shown in Fig. 2a, with increasing concentration of Cys,
the fluorescence at 733 nm belonging to the cyanine part
Fig. 2 (a) Fluorescence responses of NPSCY (10 mM) in the presence of
increasing concentrations of Cys (0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24,
30 and 40 mM) in DMSO/PBS buffer (5 : 5, v/v, pH = 7.4). (b) The linear
relationship between the fluorescence intensity ratio (F733/F435) of NPSCY
and the concentration of Cys.
Scheme 3 The design route of NPSCY.
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Fig. 4 (a) The UV-vis responses of NPSCY and DPBF towards 660 nm
irradiation in DCM. (b) The UV-Vis responses of NPSCY-SG and DPBF
towards the 660 nm irradiation in DCM. (c) The linear relationship between
UV-vis intensity of the solution NPSCY + DPBF/CY-SG + DPBF at 410 nm
and the time of 660 nm irradiation in DCM.
On the other hand, NPSCY could be reacted with the
biothiols if stained with living cells. Hence, the intracellular
concentrations of biothiols (Cys, 200 mM; Hcy, 12 mM; GSH,
Fig. 3 Proposed mechanism of NPSCY towards biothiols.
recognition performance of NPSCY was best under physiological 1 mM) were simulated under laboratory conditions. The
conditions (shown in Fig. S7, ESI†). The response time of NPSCY solution of NPSCY and biothiols was placed in the dark for
towards Cys was 50 min and the response time towards Hcy was 24 h to produce CY-SG. The UV-vis responses of CY-SG and
also calculated to be 75 min (shown in Fig. S5 and S8, ESI†).
DPBF towards 660 nm irradiation in DCM were tested. As
The reaction mechanism through which NPSCY distinguishes shown in Fig. 4b, the UV-vis intensity at 410 nm belonging to
Cys over Hcy/GSH was further speculated on. As shown in Fig. 3, DPBF decreased by about 25 percent in 180 s. The peak at
NPSCY showed as non-fluorescent. Upon the addition of Cys,
785 nm that belonged to NPSCY-SG did not show a marked
the SH in Cys showed strong nucleophilicity and double nucleo- change, implying that the chemical structure of CY-SG is stable.
philic substitution occurred on both sides of the thioether. The above experimental phenomena showed that NPSCY has
1
The NPSCY was broken down into CY–Cys and NP–Cys under the potential to be used for cancer therapy via O2.
the fierce attack of Cys. Meanwhile, after adding Hcy, the SH in
Hcy could only react with the thioether on the cyanine side and
the nucleophilic substitution broke NPSCY down into CY–Hcy
and NPSH. The different emissions of compound NP–Cys and
fluorescence imaging of NPSCY in human hepatocellular carcinoma
compound NPSH could effectively distinguish Cys and Hcy.
Detection of Cys in living cells and zebrafish
In order to expand the biological application of NPSCY, the
cells (Bel-7402) was studied. As shown in Fig. 5A, Bel-7402 cells
showed very weak fluorescence for the channels from 650 to 750 nm
Besides, the reaction mechanism of NPSCY towards GSH was
similar to that towards Hcy.
and from 430 to 470 nm after being incubated with NPSCY at 37 1C
Fortunately, HRMS analysis of NPSCY in the absence and
for 1 h. Then, Bel-7402 cells were treated with exogenous Cys for 1 h
and very strong fluorescence for the channels from 650 to 750 nm
and from 430 to 470 nm was noticed. On the other hand, the
presence of Cys verified our guess. As shown in Fig. S9a (ESI†),
the HRMS peak [NPSCY]+ = 732.3617 belonged to NPSCY.
As shown in Fig. S9b (ESI†), the HRMS peak [NP–Cys + Na]+ =
395.1791 belonged to NP–Cys and the HRMS peak [CY–Cys]+ =
fluorescence imaging of NPSCY in zebrafish was also studied.
As shown in Fig. 5B, very weak fluorescence in zebrafish was seen
from the channels from 650 to 750 nm and from 430 to 470 nm
568.2998 belonged to CY–Cys. Besides, the proposed mecha-
nism of NPSCY towards Hcy was also tested by HRMS. As shown
in Fig. S6 (ESI†), the HRMS peak [CY–Hcy]+ = 582.3151 belonged
after being treated only with NPSCY while strong fluorescence
to CY–Hcy and the HRMS peak [NPSH–H]À = 284.0752 belonged
occurred after being treated with NPSCY and exogenous Cys. The
experiment phenomenon indicated that NPSCY could detect intra-
to NPSH. The HRMS analyses of NPSCY towards Cys and Hcy
cellular exogenous Cys in living cells and zebrafish. Meanwhile, the
were all in line with our forecast of the reaction mechanism.
NPSCY with ratiometric emission could reduce the background
interference, which was favorable for deep biological applications.
Singlet oxygen generation in vitro
Cyanine is a common mitochondrial-targeted group and the
As reported in the literature, the cyanine group could produce co-localization experiment with NPSCY was worth trying.21,51
1O2 if irradiated by light.3,6 Hence, as a famous 1O2 probe,
diphenylbenzofuran (DPBF) came to mind and the UV-vis
response of the mixture of NPSCY and DPBF towards the
660 nm irradiation in DCM was tested. As shown in Fig. 4a,
upon irradiation at 660 nm, the UV-vis peak at 410 nm belonging
to the DPBF decreased rapidly and halved in 270 s, suggesting
that the 1O2 could be produced by NPSCY via the 660 nm
irradiation. Meanwhile, the peak at 805 nm belonging to NPSCY
zebrafish (B). (a1–d1) Channel from 430 to 470 nm, lem = 405 nm. (a2–d2)
remained stable, implying that the structure of NPSCY could not
Fig. 5 Fluorescence images of NPSCY (5 mM) in Bel-7402 cells (A) and
Channel from 650 to 750 nm. (a3–d3) Bright field images, lem = 640 nm.
(a4–d4) Merged images.
be destroyed by 660 nm irradiation.
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Fig. 6 Confocal fluorescence imaging of MitoRed (10 mM) and NPSCY
(5 mM) in Bel-7402 cells. (a) MitoRed (from 600 to 650n m), (b) NPSCY
(from 650 to 750 nm), (c) merged image, and (d) correlation plot of
MitoRed and NPSCY + Cys.
Fig. 8 Confocal images of AO (10 mM)/EB (10 mM) and NPSCY (5 mM) in
A549 cells. The red channel is from 570 to 670 nm and the green channel
Firstly, Bel-7402 cells were stained with MitoRed for 30 min. is from 500 to 540 nm.
In consideration of the non-fluorescence of NPSCY, the Bel-7402
cells were stained with NPSCY for 1 h, and were then stained
with Cys for 1 h. As shown in Fig. 6, the fluorescence of the
channel from 650 to 750 nm of NPSCY overlapped with the
fluorescence of MitoRed well. The co-localization coefficient was
calculated to be 0.873, indicating that NPSCY could detect Cys at
the mitochondrial level.
The PDT for cancer cells using NPSCY
In order to evaluate the PDT performance of NPSCY, the
phototoxicity and dark toxicity of NPSCY were tested. As shown
in Fig. 7a, the viability of A549 cells incubated with NPSCY
(0.00, 1.25, 2.50, 3.75, 5.00 mM) was above 90%, indicating low
dark toxicity of NPSCY. Upon the 660 nm irradiation, the cell
viability decreased and the phototoxicity reached a maximum
under the irradiative condition of 60 min and 5.00 mM NPSCY,
suggesting that a high concentration and a long irradiation
time were conducive to PDT using NPSCY. The IC50 was
calculated to be 3.7 mM.
Fig. 9 Cell migration experiment on A549 cells with NPSCY.
A549 cells were damaged. The phenomenon was in line with the
phototoxicity and dark toxicity of NPSCY and showed huge
potential for PDT for cancer cells.
Acridine orange (AO)/ethidium bromide (EB) is a commercial
dual staining cell apoptosis detection kit and was adopted in our
experiment. AO could penetrate into the cell membrane and
made the cells emit green fluorescence while EB could only
penetrate damaged cells and emitted red fluorescence. The A549
cells incubated with NPSCY were irradiated for 0 or 60 min by
660 nm light. Then, the A549 cells were incubated for 6 h and
incubated with AO/EB for 1h. As shown in Fig. 8, without
irradiation, strong green fluorescence (shown in Fig. 8a) and
weak red fluorescence (shown in Fig. 8a) were noticed, suggesting
that the A549 cells grew well. Upon the 660 min irradiation, the
green fluorescence (shown in Fig. 8e) disappeared while the red
fluorescence (shown in Fig. 8f) was stronger, suggesting that the
The inhibition of cancer cell migration
Finally, the migration experiment was carried out with NPSCY.
A549 cells were incubated with NPSCY for 12 h and a straight
line was drawn. Then, A549 cells were irradiated with 660 nm
light for different times (0 and 1 h) and incubated for 0, 24 and
48 h. As shown in Fig. 9, the scratch of cells without irradiation
gradually shrank after 48 hours. The scratch width of cells
exposed to irradiation was almost unchanged within 24 h and
slightly narrowed after 48 h, which was much larger than that
without illumination. The results showed that NPSCY could
inhibit cell migration.
4. Conclusions
In summary, a new fluorescent dye, NPSCY, was designed and
synthesized for the detection of Cys and PDT of cancer cells. In
the dye, the thioether group was chosen to link naphthalimide
and cyanine. NPSCY produced 1O2 before and after being
reacted with intracellular biological thiols under 660 nm
irradiation. Furthermore, NPSCY realized the discrimination
of Cys from three channels (Cys: 733 nm, 435 nm; Hcy: 733 nm,
475 nm) based on the recognition by the thioether group.
Moreover, NPSCY was applied to detect Cys in mitochondria
and zebrafish. The low dark toxicity and high phototoxicity gave
Fig. 7 Phototoxicity evaluation of NPSCY in A549 cells with 660 nm
irradiation for 0, 30 or 60 min.
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17 J. Atchison, S. Kamila, H. Nesbitt, K. A. Logan, D. M. Nicholas,
C. Fowley, J. Davis, B. Callan, A. P. McHalea and J. F. Callan,
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us the motivation and the AO/EB staining assay of NPSCY
under the 660 nm irradiation proved the PDT of cancer cells
visually. This work provides a reference for the design of
fluorescent reagents for both real-time monitoring of Cys and
photodynamic treatment of cancer cells.
19 M. N. Z. Yurt, Y. Cakmak, G. Tekin, S. Karakurt and S. Erbas-
Cakmak, ACS Omega, 2019, 4, 12293–12299.
20 B. Yuan, H. Wang, J. F. Xu and X. Zhang, ACS Appl. Mater.
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Conflicts of interest
There are no conflicts to declare.
21 Y. H. Mai, X. F. Qu, S. L. Ding, J. J. Lv, X. M. Li, P. Y. Gao,
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (No. 62075039).
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