The investigation of unique water-soluble heptamethine cyanine dye for use as NIR photosensitizer in photodynamic therapy of cancer cells

Article abstract of DOI:10.1016/j.saa.2019.117702

In this paper, a unique water-soluble heptamethine cyanine dye as NIR photosensitizer was synthesized to explore its properties associated with potential applications in photodynamic therapy (PDT). In the strategy of designing this photosensitizer, a sulfonic acid was used as a water soluble functional group and linked to the fluorophore through alkyl chains. 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl(Tempo) moiety was used as the a nitroxide spin label in obtaining biochemical reaction information in vivo due to it could greatly increase the inter-system crossing (ISC) process for triplet-state photosensitizers and low toxicity. As expected, the photosensitizers performed well in vitro photodynamic therapy. There were a remarkable absorbance band located at 692 nm and emission peaks falls at 762 nm, the quantum yield (Φ_f) was calculated to be 12.12% in pure aqueous solution using ICG as standards. The photosensitizer also has high singlet oxygen quantum yield (Φ_△) for 16.96% with NIR LED irradiation. This photosensitizer can rapidly produce singlet oxygen and exhibit high phototoxicity under NIR light irradiation. It has excellent cellular uptake ability and better cell compatibility. It was also successfully applied in Near-infrared fluorescence imaging and AO/EB staining. In a whole, the organic dye based on Heptamethine cyanine used as photosensitizer has great potential in vivo cancer treatment.

Full text of DOI:10.1016/j.saa.2019.117702

SAA-117702; No of Pages 7
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (xxxx) xxx
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The investigation of unique water-soluble heptamethine cyanine dye for
use as NIR photosensitizer in photodynamic therapy of cancer cells
∗
Xin Yang, Jin Bai, Ying Qian
School of Chemistry and Chemical Engineering, Southeast University, Nanjing, 211189, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2019
Received in revised form 17 October 2019
Accepted 24 October 2019
Available online xxxx
In this paper, a unique water-soluble heptamethine cyanine dye as NIR photosensitizer was synthesized to
explore its properties associated with potential applications in photodynamic therapy (PDT). In the strategy of
designing this photosensitizer, a sulfonic acid was used as a water soluble functional group and linked to the
fluorophore through alkyl chains. 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl(Tempo) moiety was used as
the a nitroxide spin label in obtaining biochemical reaction information in vivo due to it could greatly increase
the inter-system crossing (ISC) process for triplet-state photosensitizers and low toxicity. As expected, the pho-
tosensitizers performed well in vitro photodynamic therapy. There were a remarkable absorbance band located
at 692 nm and emission peaks falls at 762 nm, the quantum yield (Φf) was calculated to be 12.12% in pure aque-
ous solution using ICG as standards. The photosensitizer also has high singlet oxygen quantum yield (Φ△) for
16.96% with NIR LED irradiation. This photosensitizer can rapidly produce singlet oxygen and exhibit high
phototoxicity under NIR light irradiation. It has excellent cellular uptake ability and better cell compatibility. It
was also successfully applied in Near-infrared fluorescence imaging and AO/EB staining. In a whole, the organic
dye based on Heptamethine cyanine used as photosensitizer has great potential in vivo cancer treatment.
© 2019 Elsevier B.V. All rights reserved.
Keywords:
Water-soluble dye
NIR photosensitizer
Photodynamic therapy
Heptamethine cyanine
1. Introduction
photosensitizers with low dark toxicity but prominent phototoxicity
under irradiation for PDT.
Photodynamic therapy (PDT) is a new method of treating tumor
diseases with photosensitizers and laser activation [1–4]. During pro-
cessing, the photosensitizer transfers energy to the surrounding oxygen
and produces highly active singlet oxygen. Subsequently, singlet oxygen
can react with nearby bio-macromolecules through oxidation reaction,
producing cytotoxicity and killing tumor cells [5–8]. Photosensitizers
are essential in photodynamic therapy [9,10]. The excellent photosensi-
tizers should possess low dark toxicity and highly reactive under appro-
priate irradiation. In recent years, great efforts of the researchers have
been exert to develop photosensitizers with large molar extinction
coefficient, high inter-system crossing (ISC) efficiency, and good
photostability [11]. However, most of the photosensitizer exhibits high
dark toxicity, owing to their absorbance and emission wavelength was
located in visible region rather than the NIR region [12]. There were
many advantages of the photosensitizers irradiated by near-infrared
(NIR) light [13–15], such as, working in the NIR optical window can pro-
vide a deeper irradiation depth and highly reactive [16–21]. There were
still many fluorophore has great potential to explore as photosensitizers
[22–24]. As a result, it is still a challenge for the researchers to explore
Heptamethine cyanine, one of the most common organic dyes, has
become a more promising tool for cancer imaging and targeted therapy
owing to their stability and versatility with absorption in the
near-infrared region (NIR) of the electromagnetic spectrum upon mod-
ification [25–27]. Those dyes have many advantages when used as
fluorophore. However, when those dyes were used as photosensitizers
for PDT, they have low phototoxicity owing to singlet oxygen (1O2)
quantum yields was very low, such as the singlet oxygen (1O2) quantum
yields of IR-783 and ICG are 0.007 and 0.008, respectively [28]. There-
fore, the organic fluorophores were generally modified by chemical
synthesis, usually introducing heavy atoms to increase singlet oxygen
generation efficiency [29–31]. Nthabeleng [32] et al has design and syn-
thesis a photosensitizer based on BODIPY for PDT. The structure was
introduced Br atom to increase the singlet oxygen quantum yield. How-
ever, while increasing the yield of singlet oxygen, it also produces higher
dark toxicity [33]. Jiao [34] et al has synthesis a photosensitizer based on
heptamethine aminocyanine dye for PDT, the photosensitizer shows
high singlet oxygen quantum yield for 0.2 after 40 s irradiation. As a
result, it is essential for the researcher to explore a new NIR heavy-
atom-free photosensitizers with satisfactory inter system crossing,
high singlet oxygen (1O2) yields and low dark toxicity for fast killing
the cancer cells.
∗
Corresponding author.
E-mail address: yingqian@seu.edu.cn (Y. Qian).
https://doi.org/10.1016/j.saa.2019.117702
1386-1425/© 2019 Elsevier B.V. All rights reserved.
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Keep those problems in mind, a unique organic NIR dye based on
Cell viability was calculated according to the equation [36]: cell via-
bility (%) = average value of sample OD490/average value of blank
OD490 × 100%, where, OD490 is the absorbance measured at 490 nm.
heptamethine cyanine with heavy-atom-free and water soluble func-
tional group was designed and synthesized for photodynamic therapy.
The photosensitizer was estimated has many advantages when used
for PDT, such as it can work in pure water solution, it has better biocom-
patible and high singlet oxygen (1O2) quantum yields, low dark toxicity
and so on. In the designing strategy of photosensitizer, 2,2,6,6-
Tetramethylpiperidinyloxy moiety was incorporated into a fluorophore
due to its response to the singlet oxygen (1O2) and it can increase the
inter-system crossing (ISC) process for triplet-state photosensitizers
and low toxicity. It greatly improved the PDT efficiency by NIR light
photo damage induced cell death [35]. Heptamethine cyanine was
elected as fluorophore owing their stability and versatility with absorp-
tion in the near-infrared (NIR) region, high extinction coefficient, low
biological toxicity and good biocompatibility. We anticipated that this
photosensitizer has great capacity to provide attractive results for the
treatment of tumor cells (Scheme 1).
2.1.3. Acridine orange (AO)/ethidium bromide (EB) staining assay
HepG-2 cells were seeded on a glass bottom confocal dish for 12 h
under the condition of 37 °C and 5% CO2. The dye of CyO−(20 μM)
was incubated with HepG-2 cells for 12 h under the same condition.
During the PDT process, the ice pack was placed under the glass bottom
confocal dish to eliminate the effects of elevated temperatures. Then
group A with no CyO−` was irradiated for 20 min, group B was co-
incubated with CyO− for 12 h and with no irradiation. Group C with
CyO− was irradiated for 20 min and immediately stained with AO/EB.
Group D with CyO− was irradiated for 20 min and continue to train
for 1 h. After the above treatment, the cells were washed three times
with PBS buffer. 500 μl of staining buffer was added to the glass bottom
dish, immediately after, 5 μL AO staining solution and 5 μl EB staining so-
lution were added to cell suspension mentioned above and incubate for
15 min at room temperature, protected from light.
2. Experimental section
2.1. Materials and methods
2.1.4. Confocal fluorescence microscopy
Fluorescence imaging was performed on a confocal laser scanning
microscope (FLUOVIEW FV3000. OLYMPUS). The MCF-7 cells were
seeded on a glass bottom confocal dish for 12 h and co-incubated with
CyO− for another 12 h under the condition of 37 °C and 5% CO2. The
cells were washed three times with PBS and then stained with DAPI
for 10 min. Subsequently, the cells were washed three times with PBS
to remove excess DAPI staining solution. Finally, confocal imaging was
conducted on confocal laser scanning microscope.
2.1.1. MTT assay for vitro dark cytotoxicity studies
The dark toxicity of the two dyes (CyO− and CyOH) were evaluated
by MTT assay before vitro photodynamic therapy studies using HepG-
2 cells. The hepG-2 cells were cultured using 90% DMEM medium and
10% fetal bovine serum under 5% CO2 at 37 °C until the density of cells
reached 2 × 106 cells per mL. Then the HepG-2 cells were seeded in
96-well plates and incubated at 37 °C, 5% CO2 for 24 h to allow the
cells to adhere. Then added different concentration of dyes to each
well and continue to incubate for another 24 h under the same condi-
tion. Then add new medium continue to culture the cells for 12 h before
testing. Eventually, the cells were injected with 5 mg mL−1 MTT for
4 h at the condition mentioned above. The supernatant was then
discarded, 100 mL DMSO was added to each well and oscillation was
conducted for 5 min. The absorbance of each well of the 96-well plate
was then assessed at 490 nm on a Benchmark Plus plate reader.
2.1.5. Singlet oxygen quantum yields
The singlet oxygen quantum yield was measured using methy-
lene blue (MB) as the standard in ethanol solution and examined
using 1,3-diphenylisobenzofuran (DPBF) as a 1O2 probe. At the be-
ginning, DPBF was dissolved in ethanol to adjust the concentration
to make sure the absorbance at 411 nm was about 1. The four dyes
were dissolved in ethanol, and the absorbance was adjusted so that
the absorbance at the maximum absorption peak was between 0.2
and 0.3, and the light was irradiated with monochromatic NIR light,
and the absorbance of DPBF at 411 nm was recorded every 1 s. Ac-
cording to the same method, the singlet oxygen production rate of
MB was measured, and the change of the absorbance at 411 nm
was plotted on the ordinate and the irradiation time was plotted on
the abscissa to obtain the slope. Finally, the calculation of the singlet
oxygen quantum efficiency is performed according to the following
2.1.2. MTT assay for vitro photodynamic therapy studies
The vitro photodynamic therapy studies was carried out using MTT
assay as described in the previously section. The different was after
added different concentration of dyes to each well and continue to incu-
bate for another 24 h, the fresh medium was added and irradiated by
NIR LED lamp for 30 min and cultured for 12 h. MTT array was tested
on HepG-2 cells. The dark cytotoxicity was monitored without irradia-
tion at the same time as control.
Scheme 1. The design of new NIR photosensitizer.
Please cite this article as: X. Yang, J. Bai and Y. Qian, The investigation of unique water-soluble heptamethine cyanine dye for use as NIR
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3
Scheme 2. The route of synthesis new photosensitizer.
¼Φ△ðMBÞꢀ K ye
formula: Φ
, where k is the slope between absorbance
the solvent. Then, the mixture was stirred at room for 30 min under
N2 atmosphere. The solvent was removed by rotary evaporation and pu-
rified by Column chromatography to afford the purple solid 50.0 g,
Yield: 97.8% (1H NMR (300 MHz, DMSO‑d6): δ 7.92 (s, 1 H), 7.76 (d, J
= 13.5 Hz, 2 H), 7.46 (d, J=7.5 Hz, 2 H), 7.29 (m, 4 H), 7.10 (t, J1=
7.2 Hz, J2=7.2 Hz, 2 H), 6.9 (s, 1 H), 5.94 (d, J = 12.6 Hz, 2 H), 5.71 (d,
△
K
Bꢀ FMB D
M
K
ye
d
and the irradiation time, F is the correction of dye and reference
absorbance, where F=1–10 –OD
2.2. Synthesis
J = 28.2 Hz, 1 H), 3.99 (d, J = 24.9 Hz, 4 H), 3.71 (t, J1 = 6.6 Hz, J2
=
6.9 Hz, 10 H), 2.85 (s, 1 H), 2.69 (s, 1 H), 1.72 (s, 8 H), 1.59 (s, 9 H),
1.34 (m, 12 H), 1.04 (t, J1 = 6.9 Hz, J2=6.9 Hz, 7 H) HRMS calcd for
C
The synthesis of unique NIR photosensitizer was depicted in Scheme 2.
It takes five steps to complete its composition, as follows.
47H67N4O7S+2 863.44457, found: 863.44440.
2.2.1. 4-(((E)-2-((E)-2-(3,3-dimethyl-1-(4-sulfobutyl)-3H-indol-1-ium-
2-yl)vinyl)-6-((E)-2-(3,3-dimethyl-1-(4-sulfobutyl)indolin-2-ylidene)
ethylidene)cyclohex-1-en-1-yl)amino)-2,2,6,6-tetramethylpiperidin-1-
olate(CyO−)
3. Results and discussion
3.1. Design strategy of unique water soluble NIR photosensitizers with TemOH functional group
and long emission wavelength for PDT
2-((E)-2-((E)-2-chloro-3-((E)-2-(3,3-dimethyl-1-(4-sulfobutyl)
indolin-2-ylidene)ethylidene)cyclohex-1-en-1-yl)vinyl)-3,3-dimethyl-
1-(4-sulfobutyl)-3H-indol-1-ium (0.1 g, 0.14 mmol) and 4-amino-
2,2,6,6-tetramethylpiperidin-1-olate (0.071 g, 0.42 mmol) were
dissolved in anhydrous DMF(5 mL) and stirred at 75 °C for 4 h under
N2 atmosphere. The crude product was obtained through steaming off
DMF. Eventually, the crude product was purified by thin layer chro-
matograph to afford pure solid. 1H NMR (300 MHz, DMSO‑d6): δ 7.95
(s, 1 H), 7.78 (s, 1 H), 7.48 (d, J = 12.9 Hz, 2 H), 7.32 (m, 8 H), 5.96 (s,
1 H), 5.75 (s, 1 H), 4.02 (d, J=25.8 Hz, 6 H), 3.62 (m, 8 H), 2.89 (s,
3 H), 2.73 (s, 3 H), 1.93 (d, J = 13.8 Hz, 4 H), 1.72 (m, 12 H), 1.24 (s,
4 H), 1.12 (m, 12 H) HRMS calcd for C47H66N4O7S2 862.43729, found:
862.43639.
The synthetic route of photosensitizers was reported previously [37]. The unique
NIR photosensitizer was prepared via five steps as shown in Scheme 2. Heptamethine
cyanine was selected as the basic fluorescent core due to its absorbance and emission
wavelength located in near red region and it has low toxicity. Water-soluble func-
tional group was linked to fluorescent core through alkyl chain. 4-amino-2,2,6,6-
tetramethylpiperidinyloxy moiety was used as the a nitroxide spin label in obtaining
biochemical reaction information in vivo due to it could greatly increase the inter-
system crossing (ISC) process for triplet-state photosensitizers and low toxicity. It
was introduced to Heptamethine cyanine moiety through nucleophilic substitution
reaction. Eventually, new NIR photosensitizer was constructed. We anticipated that
the photosensitizer has excellent properties such as Ultra low dark toxicity and
higher singlet oxygen production efficiency, better biocompatibility.
All intermediates and target products were passed nuclear magnetic resonance spec-
troscopy and high resolution mass spectrometry (Supporting information Fig. S1-Fig. S5)
(Scheme 2).
3.2. Production of singlet oxygen of near-infrared heptamethine cyanine dye
2.2.2. 2-((E)-2-((E)-3-((E)-2-(3,3-dimethyl-1-(4-sulfobutyl)indolin-2-yl-
idene)ethylidene)-2-((1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)
amino)cyclohex-1-en-1-yl)vinyl)-3,3-dimethyl-1-(4-sulfobutyl)-3H-
indol-1-ium(CyOH)
Dye2(50 mg, 0.058 mmol) and ascorbic acid(51.05 mg, 0.29 mmol)
were added to the 50 mL round-bottomed flask using acetonitrile as
The basic fluorescence spectrum and UV-visible spectrum properties was investigated
in pure aqueous solution. As shown in Fig. 1, there were three remark absorption peak lo-
cated in 776 nm, 692 nm, 686 nm for CyCl, CyO−, CyOH, respectively, which of them were
all reached to NIR regions, it's of great value to cell imaging. The molar extinction coeffi-
cient was worked for 2.56
× × , 0.43
105 M−1 cm−1 1.42 105 M−1 cm−1
× 105 M−1 cm−1, for CyCl, CyO−, CyOH, respectively. The emission wavelength of three
Fig. 1. The fluorescence response and absorbance response of CyO-, CyOH, CyCl (10 μM) in PBS (pH= 7.4) and ethanol.
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NIR dyes are highly sought owing to their excellent properties in chemical biology. In
Table 1
contrast with visible light, NIR light has more potential applied in biological imaging and
PDT process due to their deep tissue penetration, minimum photodamage to biological
samples, and minimum interference from background auto-fluorescence by biomolecules
in the living systems. However, NIR dyes generally sacrifice quantum yields by adopting
the loose π-conjugated structures. So the quantum yield of CyO− was evaluated using
ICG as reference. The quantum yield was calculated for 12.12% in pure aqueous solution
The detailed photophysical properties of new photosentisenzers
Dye
Λabs (nm)
Εmax (105 M-1 cm-1)
Λem (nm)
Φf
Φ△
CyO-
CyOH
CyCl
692
686
776
1.42
0.43
2.56
762
759
821
12.12%
16.96%
1.98%
1.89%
ꢀ
ꢀ
Kx nx
Þ
2
Fx
Ax
Fs
As
using the equation [38]: Φx = Φs
Þ , where Kx
¼
, Ks
¼
. F is Fluorescence
MB as a reference for singlet oxygen quantum yield measured. ICG was used as a standard
for quantum yield measure. Where Φ△ represent Singlet Oxygen quantum yield, Φf rep-
resent quantum yield.
Ks ns
area, A is absorbance, x and s represent standard and test solution. It's higher than the
reported NIR dye. The results demonstrated that the CyO− has great advantage in bio-
imaging (Table 1).
3.3. Comparison of singlet oxygen yields of three probe molecules
dyes were also located in 821 nm, 762 nm, 759 nm for CyCl, CyO−, CyOH, respectively. The
results show that the probe has a good absorption capacity for near-infrared light and has
a broad application in photodynamic therapy (see ).
The evidence confirmed that the production of reactive oxygen species (ROS) is
closely related to the excited triplet state of photosensitizers. It's estimated that the
Fig. 2. Comparison of DPBF bleaching rate at 411 nm. Near infrared LED array irradiation for different time. CyO− and CyOH were dissolved in ethanol and mixed with DPBF to a suitable
concentration.
Fig. 3. Confocal images of MCF-7 cells of DAPI- stained cells with pre-incubated with CyO− (10 μM). Scale bar = 20 μm.
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Fig. 4. Dark toxicity and phototoxicity evaluation of CyO− and CyOH on HepG-2 cells for 30 min irradiation (NIR light). MTT array was measured after incubating for 12 h with different
concentration of two dyes. Data are presented as the mean value SD (n = 6).
presence of heptamethine cyanine dye's longevity triplet excited state interacts with mo-
lecular oxygen (3O2) to form singlet oxygen (1O2), which may be useful for PDT applica-
tions. Singlet oxygen generation was examined using 1,3-diphenylisobenzofuran (DPBF)
as a 1O2 probe. As shown in Fig. 3, in presence of CyO−, the absorbance of DPBF shows a
significant drop at 411 nm under irradiation of NIR light (670 nm), confirming their ability
to generate 1O2. In contrast, CyOH and CyCl showed a small reduction in absorption at
411 nm under the same conditions even could negligible. Those results strongly confirmed
that introducing 4-amino-TEMPO into a Heptamethine cyanine dye can remarkably
enhance the ability of 1O2 generation, mainly originated from the formation of the triplet
state (T1) from Heptamethine cyanine dye. In order to quantitatively measure the singlet
oxygen production efficiency of the three dyes, the singlet oxygen efficiency measurement
was carried out. Methylene blue was used as a reference in ethanol and the singlet oxygen
quantum yields was calculated for 16.96% and 1.98%, 1.89% of CyO−, CyOH, CyCl respec-
production efficiency of this dye is significantly higher than the previously mentioned
IR-783 and ICG are 0.007 and 0.008. It has great potential applied in photodynamic
therapy (Fig. 2).
The cellular uptake property of CyO− was measured in MCF-7 cells using confocal im-
aging. As shown in Fig. 3, the CyO− could get into MCF-7 cells and showed a strong red
fluorescence under NIR light excitation. The clear red channel illustrate that the CyO−
can easily uptake by MCF-7 cells and it has great ability to penetrate cell with good cell
compatibility (Fig. 3).
3.4. Cell study for dark toxicity and photo toxicity
To evaluated the photodynamic therapy effect of CyOH and CyO−, dark toxicity and
phototoxicity was carried out by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetra-
zole) assay in the dark and the light irradiation, respectively. As shown in Fig. 4, negligible
or small change in cell viability with both low and high concentration of dye is observed
KðdyeÞ FðMBÞ
tively according to the equation: Φδ ¼ ΦδðMBÞ ꢀ
ꢀ
. The singlet oxygen
KðMBÞ FðdyeÞ
Fig. 5. Confocal imaging after AO/EB staining in PDT process. HepG-2 Cells were incubated with CyO− (20 μM) for 12 h prior to AO/EB staining. Then the HepG-2 cells were irradiated for
20 min under the NIR light Group A: The cells were irradiated for 20 min with no CyO− pre-incubated. Group B: The cells were pre-incubated with CyO− for 12 h but with no irradiation.
Group C: The cells were pre-incubated with CyO− for 12 h and irradiated for 20 min and immediately stained with AO/EB. Group D: The cells were pre-incubated with CyO− for 12 h and
irradiated for 20 min and continue incubated for 1 h before stained with AO/EB. Scale bar = 20 μm.
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3.5. AO/EB staining
In order to evaluate the feasibility of photosensitizers in visual mode, confocal imaging
was performed on confocal microscope in HepG-2 cells. Acridine orange (AO) can pene-
trate into cells of the cell membrane and embed the nuclear DNA to make it emit bright
green fluorescence. Ethidium bromide (EB) can only penetrate the damaged cells of the
cell membrane, embed nuclear DNA, and emit orange-red fluorescence. There were four
groups of cells that have been treated differently. As shown in Fig. 5, group A was irradi-
ated 20 min with no CyO− pre-incubated with cells, the cells only showed green fluores-
cence of AO, while the red fluorescence of EB did not appeared. The result demonstrates
that phototoxicity was not caused by irradiation with a 670 nm light source. The cells
used in group B were pre-incubated with the CyO− for 12 h while with no irradiation of
near-infrared light. As mentioned above, the cells in this group also showed only green
fluorescence, indicating that the CyO− entering the cells did not induce cell death. At
the same concentration and under the same light conditions, the apoptotic cells stained
with AO/EB were significantly more stained than the direct staining after 1 h of incubation.
All results show that the photosensitizer can be well applied in photodynamic therapy
process with low dark toxicity and high phototoxicity.
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4. Conclusion
In summary, we have designed and synthesized a unique water
soluble Heptamethine cyanine dye for use as a NIR sensitizer for
photodynamic therapy. Heptamethine cyanine was selected as the
basic fluorescent core due to its NIR emission wavelength and low
toxicity. Water-soluble functional group was linked to fluorescent
core through multiple methylene flexible chains. 4-amino-2,2,6,6-
tetramethylpiperidinyloxy acted as singlet oxygen generating group.
Eventually, new NIR photosensitizer was constructed. There were a re-
markable absorbance band located 692 nm and emission peaks falls at
762 nm, the quantum yield was calculated for 12.12% in pure aqueous so-
lution using ICG as standards. It has great potential in bio-imaging. The
photosensitizer showed excellent properties in PDT process. Singlet
oxygen production efficiency of this photosensitizer is 16.98%, which is
significantly higher than the previously reported literature. It also shows
ultra-low dark toxicity and high phototoxicity in HepG-2 cells. Negligible
or small change in cell viability with both low and high concentration of
dye is observed without light irradiation. However, significant cell death
is observed for CyO− at the concentration of 30 μM when the dye CyO−
was irradiated with NIR light. The CyO− also has great ability to penetrate
cells with good cell compatibility. In a word, the photosensitizer can be
well applied in photodynamic therapy process with low dark toxicity
and high phototoxicity.
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Declaration of competing interest
There are no conflicts to declare.
Acknowledgements
We thank the financial support from the Fundamental Research
Funds for the National Natural Science Foundation of China (No.
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