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Highly biocompatible amphiphilic
perylenediimide derivative for bioimaging
Jin-Kyung Park,1 Ran Hee Kim,1 Prem Prabhakaran,1 Sehoon Kim,2 and Kwang-Sup
Lee1*
1Department of Advanced Materials, Hannam University, 461-6 Jeonmin-dong, Yuseong-gu, Daejeon 305-811, South
Korea
2Department of Biomedical Science Center, Korea Institute of Science and Technology 39-1 Hawolgok-dong,
Seongbuk-gu, Seoul 136-791 South Korea
*kslee@hnu.kr
Abstract: We report the synthesis and biological studies of a fluorescence
dye with an oligoethylene glycol substituted (OEG) perylene centered dye
N,N’-(2,6-diisopropylphenyl)-1-[oligo(ethylene glycol)methyl ether]-
1,6,7,12-trichloroperylene-3,4:9,10-tetracarboxdiimide (PDI-OEG). The
activity of the dye is juxtaposed with a precursor molecule without the OEG
substitution. The OEG substitution contributes to the increased
biocompatibility of PDI-OEG. Cell viability studies lead to the survival of
more than 80% of the PDI-OEG cultured cells endorsing its
biocompatibility. Fluorescence imaging studies were carried out using
multiple cell lines. Ex-vivo studies involving nude mice were used to
establish liver and lung specific organ targeting of PDI-OEG. This
fluorophore is an excellent example of a stable and biocompatible red
emitting small molecule for bioimaging.
©2016 Optical Society of America
OCIS codes: (160.4670) Optical materials; (160.2540) Fluorescent and luminescent materials;
(170.0110) Imaging systems; (170.3880) Medical and biological imaging; (180.2520)
Fluorescence microscopy.
References and links
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Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1420
11. D. Magde, R. Wong, and P. G. Seybold, “Fluorescence quantum yields and their relation to lifetimes of
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39(2), 365–395 (2014).
1. Introduction
Peryleneiimide (PDI) derivatives have outstanding electronic and photonic properties such as
broad band absorption, high quantum efficiency as well as thermal stability [1]. They have
been extensively studied in fluorescence sensing devices [2], organic light emitting diodes
(OLED) [3], biosensors [4], as well as in vitro and in vivo bioimaging [5]. Each application in
which PDI derivatives are utilized requires specific chemical and physical properties. The
possibility of easy substitution reactions have also contributed to the interest in PDI
derivatives. The precedent PDI derivatives have substituents at bis-N-imide positions and/or
four bay regions. This prior research has drawn some plausible structure-property inferences.
The substitution of alkyl chain at N-imide position induced organic solubility and reduced
quantum yield compared to N,N'-bis(2,6-diisopropylphenyl)-1,6,7,12-tetrachloroperylene-
3,4:9,10-tetracarboxdiimide (PDI core) [6]. Further, bay substitution of electron accepting
aromatic groups induced red shift in the maximum emission wavelength, and a slight increase
in the fluorescence behavior, due to potential steric effects between the core and bay
substituents [7].
PDI derivatives are desirable as candidates of fluorescent probes for the bioimaging due to
their efficient red fluorescence activity. A challenge in using PDI dyes in bio applications is
making them water-soluble to prevent their aggregation in aqueous media whilst retaining
their exceptional fluorescent properties. Müllen and associates reported incorporation of ionic
moieties onto fluorescent PDIs while Shen and associates incorporated hyperbranched
polyglycerols around PDIs [8,9] to try to achieve the above goal. However, these
modifications were accompanied by poor solubility due to π-π stacking of PDI core as well as
diminished fluorescence signal.
In this study, we report a new fluorescence probe based on a PDI core. To induce a good
biocompatibility and high fluorescence of the PDI derivatives in human blood environment,
we replaced one chlorine in bay region of N,N'-bis(2,6-diisopropylphenyl)-1,6,7,12-
tetrachloroperylene-3,4:9,10-tetracarboxdiimide with oligomeric ethylene glycol moiety. We
have investigated optical properties in both aqueous and organic media. The cytotoxicity was
evaluated in various cancer cell lines. Following which in vivo and ex vivo fluorescence
imaging and organ specific targeting ability of the chromophore was investigated. Our studies
verily demonstrate the excellent biocompatibility, stability and fluorescence bioimaging
capability of the reported material.
2. Experimental
2.1 Synthesis of flurophore
N,N'-Bis(2,6-diisopropylphenyl)-1,6,7,12-tetrachloroperylene-3,4:9,10-tetracarboxdiimide
(PDI core) as a fluorophore molecule was synthesized following reported methods [10]. The
oligo(ethylene glycol)methyl ether (OEGME) of number average molecular weight 550 Da
was obtained from Sigma-Aldrich. The solution of the PDI core (1 g, 1.18 mmol) in
anhydrous tetrahydrofuran (THF) (50 mL) was stirred under N2 atmosphere. A mixture of
OEGME (0.75 mL, 1.485 mmol) and sodium hydride (35.64 mg, 1.485 mmol) in THF was
added to the above solution and stirred at 22~24 °C in a round bottom flask under N2
atmosphere for 2 days isolated from the light. The resulting reaction mixture was evaporated
under vacuum. The crude product was purified by silica gel chromatography using 4:1
volume mixture of ethyl acetate:n-hexane as an eluent. The product (PDI-OEG) is obtained in
45% yield (45 mg) as a wine colored solid. 1H-NMR (300 MHz, CDCl3, ppm) of PDI-OEG:
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1421
8.75 (s, 2H), 8.68 (d, 1H), 8.53 (d, 1H), 7.18 (m, 6H), 3.81-3.72 (m, 4H), 2.82-2.08 (br,
Ethylene glycol CH), 1.67-1.42 (br, 24H). MALDI-TOF, m/z: 1362 (100%, M+). The
uncertainty in the molecular weight of OEGMA has to be taken into account when
considering the NMR and mass spectra.
Fig. 1. Synthetic route for PDI-OEG.
2.2 Spectral measurements
1H-NMR spectrum was recorded on an Varian 300 (300 MHz, Agilent Technology,
USA).The UV-vis absorption was measured on an UV-3600 (Shimadzu, Korea) and an
Agilent 8453 (Agilent Technology, USA). Photoluminescence spectra were measured on an
F-7000 fluorescence spectrophotometer (Hitachi, Japan) and an FluoroMate FS-2
spectrophotometer (Scinco, Korea). The fluorescence quantum efficiency (ɸFL) of PDI-OEG
was measured by using Rhodamine 6G with a quantum efficiency of 0.95 in ethanol following
previous reports [11]. Phosphate buffered saline PBS (Welgene ML 008-01, in pH 7.4), fetal
bovine serum FBS (12105C) and human serum albumin (HSA) stock solution (A1653) were
purchased from Sigma Aldrich and used without further purification. For UV-vis
measurements, PBS and FBS were mixed in 1 to 1 ratio. HSA stock solution was diluted with
PBS at pH 7.4 to the concentration of 3.07 × 10−5 M.
2.3 In vitro cytotoxicity test
The cell viability of samples was estimated by 3-(4,5-dimethylthiazole-2-yl)-2,5-
diphenyltetrazolium bromide (MTT) assay. MDA-MB 231 cells (human breast
adenocarcinoma cell lines) were seeded into the 96-well plate and incubated with 150 μL cell
culture media at 37 °C with 5% CO2 for 2 days. After the incubation, the culture media was
carefully removed and the cells were washed one time with phosphate-buffered saline (PBS).
MTT solution of 0.4 mL was added to wells containing 3.6 mL of fresh cell culture media,
and 50 μL PDI solution was filled into each of the 96-well plates. Then, the cultured cells
were incubated at 37 °C with 5% CO2 for 2 hr. The formazan produced by mitochondrial
reductase of the living cells was solubilized by the addition of 150 μL of dimethyl sulfoxide
(DMSO) and shaking for 20 min. The values of the plate were measured on a micro-plate
reader at 570 nm.
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1422
2.4 In vitro cellular uptake studies with tumor cells
In vitro cellular imaging was carried out by three distinct cell lines namely human cervical
epithelial carcinoma (HeLa), human breast adenocarcinoma cell lines (MDA-MB 231), and
squamous cell carcinoma (SCC-7) cells. HeLa cells were cultured in Dulbecco’s modified
Eagle’s medium and MDA-MB 231 and SCC-7 cells were cultured in Rosewell Park
Memorial Institute 1640 (RPMI 1640), 10% fetal bovine serum (FBS) and 1% antibiotic-
antimycotic (AA). The cells were cultured at approximately 1 × 105 cells in 35 mm culture
plate and 2 mL of the applicable cell media was added. The culture plate was placed in
incubator at 37 °C with 5% CO2 for 48 hr. After the incubation for 48 hr, the cells were
washed with PBS and replaced with fresh media. For cell staining, 20 μL of the sample was
added to 1.98 mL of fresh cell culture media. Culture plate was returned to the incubator.
After the incubation for 2 hr with sample, the media was carefully removed and the cells
rinsed with PBS. A culture plate was added with fresh PBS and then placed for cellular
imaging under a Nuance FX multispectral imaging system (Cambridge Research &
Instrumentation Inc., USA) that was set to BP515-560 nm excitation filter.
2.5 In vivo and ex vivo studies for organ targeting with tumor cells
All animal studies were performed by the Animal Care and Use Committee of the Korea
Institute of Science and Technology and all handling of mice was performed in accordance
with institutional regulations. In vivo and ex vivo experiments were conducted by intravenous
injection of PDI-OEG labeled 5 × 106 SCC-7 cells in RPMI 1640 cell culture media in 3-
week-old-male Blab/C nude mice (Orient Bio Inc., Korea). A subcutaneous injection of 1 ×
107 SCC-7 (squamous cell carcinoma) cells suspended in RPMI1640 cell culture media in 3-
week-old male BALB/c nude mice (Orient. Korea) was used to induce xenografts on the
mice. In vivo and ex vivo images were taken with IVIS Spectrum Preclinical In Vivo Imaging
System (PerkinElmer, USA). After in vivo imaging for 1 day, ex vivo images of resected
organs were taken by IVIS Spectrum imaging system with the same condition as used for in
vivo imaging. We obtained the wavelength spectrum from fluorescence image on a Nuance
2.10.
3. Results and discussion
3.1 Optical properties
3.1.1 Optical properties in organic media
The UV-vis absorption and emission spectra of the PDI core and PDI-OEG were measured in
solvents of increasing polarity in the order of toluene, THF and DMSO. The PDI core has a
twisted structure with two halves of the perylenediimide moeities at 42° due to the repulsion
of peri-chlorine atoms in the bay regions [1]. The absorption maximum of PDI core was
observed around 520 nm, meanwhile that of PDI-OEG was bathochromically shifted to
around 550 nm. The absorption peaks of PDI core exhibited profound vibrational structure
with respect to those of PDI-OEG. It is obvious that the mono-OEGylation of a chlorine on
the bay site of PDIs results in the less twisted molecular geometry and better π-conjugation
leading to a change in the molecular structure of PDI core.
The electron donating oligo(ethylene glycol) (OEG) groups change the electronic
properties of PDI-OEG with respect to the PDI core. The emission maxima of the PDI core
barely exhibited any solvatochromic behavior between toluene and THF, however, in the
highly polar solvent of DMSO the fluorescence intensity of the PDI core was dramatically
quenched (Fig. 2(a)). This quenching is well-known phenomenon from the J-type self-
aggregations of the PDI core units through π-π stacking [2]. This feature has been a key
sticking point in its use as a fluorescent probe in in vitro and in vivo bioimaging .
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1423
Fig. 2. Optical properties of PDI derivatives depending on solvent polarity. (a) Fluorescence
spectra of PDI core in different solvents (inset is the enlarged emission in DMSO), and (b)
those of PDI-OEG in toluene (black solid line), THF (red solid line) and DMSO (blue solid
line). The concentration of each fluorophore is 7.27 × 10−7 M.
In contrast to the PDI core, the emission of PDI-OEG is strongly solvent dependent and
shows positive solvatochromism. The emission maxima of PDI-OEG steadily moves to longer
wavelengths with increasing solvent polarity (594 nm in toluene, 598 nm in THF, and 619 nm
in DMSO) as shown in Fig. 2(b). This feature is responsible for the stabilization of the excited
state by the polar solvent compared to that of the ground state of PDI-OEG. It should be noted
that relatively PDI-OEG shows a higher fluorescence intensity in DMSO than PDI core alone
in DMSO. The fluorescence quantum efficiencies ɸFL for PDI-OEG was measured as 0.75 in
THF and 0.60 in DMSO. These implies that the less twisted molecular structure of PDI-OEG
compared to PDI core leads to lesser fluorescence quenching due to restricted π-π stacking.
In electronic terms the OEGylation of the PDI core induces the change in the electronic
properties, due to the electron donating nature of OEG moietiy. In the UV-vis spectra, the
absorption cut off of PDI-OEG reveals a smaller band gap than that of PDI core. Additionally
OEG chains play an active role in separating the PDI-OEG fluorophores. Further the
introduction of hydrophilic OEG chains onto hydrophobic PDI renders PDIs compatible for
bioimaging with their high quantum yields in polar and hydrophilic medium.
3.1.2 Optical properties in vitro
The UV-vis absorption and fluorescence spectra of the PDI core and the PDI-OEG were
measured in the aqueous phosphate-buffered saline (PBS) as shown in Figs. 3(a) and 3(b),
respectively. The fluorescence of the PDI core exhibited bathochromically shifted intense
emission with maximum at 669 nm. PDI-OEG was found to be non-fluorescent in PBS
accompanied with bathchromic shift compared to that in DMSO (Fig. 2(a)). The enhanced
fluorescent band of the PDI core is may be due to its partial self-aggregation to minimize
contact with a protic solvent. The fluorescence quenching of PDI-OEG in PBS is distinct from
previously observed fluorescent behavior in the polar organic solvent. Such kind of effects
may be due to micelle generation. However this possibility can be discarded because the
critical micelle concentration (CMC) required for OEG to start forming micelles were far
above the concentrations at which the optical properties were studied. We inferred that the
observed quenching of fluorescence in PDI-OEG might be due to the increased interactions
between the charged phosphate groups in buffer solution and the OEG moieties in PDI-OEG
leading to fluorescence quenching.
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1424
Fig. 3. Optical behaviors of PDI derivatives in PBS, in the FBS in PBS 50:50 buffer, and in
PBS containing HSA. (a) Fluorescence spectra of PDI core in PBS. (b) Fluorescence spectra of
PDI-OEG in FBS in PBS 50:50 buffer under at a concentration 2.02 × 10−7 M. (c) Fluorescence
spectra of PDI-OEG solution with different concentrations in PBS containing HSA. (d)
Sonication time dependent fluorescence spectra of a 2.02 × 10−7 M solution of PDI-OEG
prepared with HSA in PBS buffer. The excitation wavelength for recording the fluorescence
spectra was 510 nm.
To examine PDI core and PDI-OEG in a solution analogous to blood further studies were
carried out in a PBS solution containing 50% fetal bovine serum (FBS). The absorption and
emission spectra can be seen in Fig. 3(b). At a glance, their photoluminescent intensities in
the blood-like environment were found to counter the trend observed in PBS alone (Fig. 3(a)).
The fluorescence of PDI-OEG was far enhanced and that of PDI core was reduced. This can
be attributed to the amphiphilicity of PDI-OEG holding both the lipophilic and hydrophilic
structures in solution, consequently each part interact with the corresponding favorable
domain of proteins on FBS.
The FBS generally consist of peptides which are able to interact with both domains of the
fluorescent probe, PDI-OEG. Based on the examination, we expect that the hydrophilic and
hydrophobic parts of PDI-OEG to be interacting with corresponding components in the
peptides. This phenomenon was further investigated with spectroscopic examination of PDI-
OEG in PBS with the human serum albumin (HSA). Human serum albumin is a major
component in FBS. Increasing the concentration of the fluorophore PDI-OEG with respect to
the PBS/HSA media, the emission intensity gradually enhanced and their maxima slightly
shifted to a little longer wavelength (Fig. 3(c)). The fluorescence intensity of PDI-OEG in
PBS in presence of HSA increased considerably compared to PDI-OEG solution in PBS. The
enhancement of fluorescence of PDI-OEG prepared with HSA in PBS buffer with increased
time of sonication can be seen in Fig. 3(d) enhanced fluorescence is an indication of the
noncovalent interactions of the amphiphilic PDI-OEG chromophore with hydrophobic and
liphophilic domains of the HSA protein.
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1425
3.2 Cytotoxicity
Cytotoxicity of the PDI derivative was evaluated by carrying out an enzyme linked
immunosorbent assay (ELISA) test using MDA-MB 231 cell lines. MDA-MB 231 cells were
treated with PDI derivatives for different time intervals spanning 1 to 24 hours. The viability
was tested by MTT assay. The values from the assay were evaluated by a ELISA plate reader
at 570 nm. The viable percentage graphs summarizing the cell viability are obtained by
comparing MDA-MB-231 cells treated with PDI core and PDI-OEG to control sample
containing PDI core/PDI-OEG untreated MDA-MB-231 sample. The viable percentage
graphs can be seen in Fig. 4(a). Observations were made for treatment times of 1, 2, 6, 12 and
24 hours. More than 80% of MDA-MB 231 cells treated with the PDI derivatives were
maintained during the analysis time indicating low cytotoxicity. Fluorescence images of cells
treated with PDI core and PDI-OEG for 2 hours can be seen in Fig. 4(b). Cells treated with
PDI-OEG shows brighter fluorescence compared to those treated with PDI core. This can be
attributed to the greater cell penetration of the former on account of the OEG group attached
to it. The high cell viability and biocompatibility of OEG leads to better staining of cells.
Fig. 4. (a) Cell viability of MDA-MB 231 cells treated with PDI derivatives of time interval.
(b) Comparison of cellular images of HeLa cells treated with PDI core and PDI-OEG.
3.3 Cell staining
The variability of staining across various cell lines was evaluated by incubating PDI-OEG
with MDA-MB 231, HeLa and SCC-7 cells for 2 hours. The fluorescence images from these
samples can be seen in Figs. 5(a)-5(c). The cells were treated with 7.27 μM concentration of
PDI-OEG, rinsed and imaged using filter BP515 at an excitation wavelength of 560 nm. The
flurophore showed very good cell penetrability in case of all the tested cell lines. This could
be discerned from the bright red fluorescence in the images. The red fluorescence of the dye
could be seen in the cytoplasm of all the cell lines, in MDA-MB 231 and SCC-7 cell lines
fluorescence was detected in the nuclear region third image to the left in Fig. 5(a) and 5(c).
This means that PDI-OEG is capable of crossing into nuclear space in these cell lines. The
variability in the activity of PDI-OEG in the studied cell lines may be due to differences in
physiological interactions between PDI-OEG and the cell lines [12].
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Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1426
Fig. 5. Fluorescence cellular images of (a) MDA-MB 231, (b) HeLa and (c) SCC-7 tumor cells
cultured with PDI-OEG dissolved in DMSO for 2 hours.
3.4 Organ targeting
In vivo and ex vivo studies were carried out in nude mouse to assess the possibility of
delivering, and imaging using PDI-OEG. An intravenous injection of PDI-OEG stained SCC-
7 cells (5 × 106/200 μL) was used to introduce the flurophore into the sample mouse. The
results were compared with control mouse which did not undergo any treatment. After the
injecting PDI-OEG stained SCC-7 cells, the sample as well as the control mice were
monitored through in vivo imaging (Fig. 6(a)). During 1 day of recording in vivo images no
difference were observed between the sample and control.
Fig. 6. In vivo and ex vivo real time fluorescence images using IVIS spectrum imaging system
of PDI-OEG. (a) In vivo fluorescence images of Balb/C nude mice intravenous injection of
PDI-OEG labeled SCC-7 cells (200 μl/5 × 106). (b) Ex vivo fluorescence images of major
organs obtained after in vivo images for 1 day. (c) In vivo fluorescence images of Balb/C nude
mice intravenous injection of PDI-OEG labeled SCC-7 cells (200 μl/1 × 107). (d) Ex vivo
fluorescence images of major organs obtained after in vivo images for 1 h.
The ex vivo fluorescence images of the resected major organs of the sample and the
control can be seen in Fig. 6(b). The graph in this figure compares the relative ex vivo
fluorescence of the liver from the sample and the control. The sample shows very high
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1427
fluorescence compared to the control indicating the high efficacy of PDI-OEG staining. The
in vivo and ex vivo fluorescence imaging of a mouse injected with PDI-OEG stained SCC-7
cells 1 × 107/200 μL after one hour can be seen in Figs. 6(c)-6(d). There is not much
difference between the control and the in vivo images, however the ex vivo images shows a
strong localization of red fluorescence in the lung. It is then clear from Figs. 6(b) and 6(d) that
the lung gets stained by the fluorophore ahead of the other organs. This demonstrates the
potential of PDI-OEG in preferential staining of lung.
The SSC-7 stained with PDI-OEG was introduced into the mouse by an intravenous
injection to the tail. The SSC-7 was used to achieve localization of the dye to the xenografted
tumor site on the mouse. The ex vivo studies however revealed the dye to be localizing on
liver and lung which are internal organs rather than at the subcutaneous SCC-7 xenograft
where it was expected to end up. This phenomenon might be leading to the absence of
external fluorescence during in vivo imaging. Introduction of the dye into the mouse in
solution without using SCC-7 cells as carrier resulted in high local fluorescence at the
injection site indicating the non-specificity of staining by the fluorophore. We believe the
localization and imaging on tumor can be improved by complexing the molecule with
chemical or biological entities capable of targeting specific cancer cells.
4. Conclusions
In conclusion the new fluorescence probe PDI-OEG was synthesized and characterized. They
showed a considerable difference in their fluorescence property and cellular imaging
capability compared to the PDI core. In a PBS buffer solution containing 50% HSA the PDI-
OEG exhibited enhanced fluorescence and stability. We infer that this is derived from
noncovalent interactions between its amphiphilic structure with the hydrophilic and lipophilic
parts of proteins in HSA. The cellular staining images showed clear difference between the
PDI core and the OEG containing PDI-OEG emphasizing the role of OEG group. The
fluorophore PDI-OEG showed efficient staining of MDA-MB 231, HeLa and SCC-7 cancer
cell lines. The nucleii of MDA-MB 231 and SCC-7 cell lines showed fluorescence indicating
the penetration of dye into that location. Cytotoxicity studies on MDA-MB 231 showed an
80% cell viability for up to 24 hours. Ex-vivo studies carried out on a Balb/C nude mice
showed localization of PDI-OEG specifically in the lung during the first hour, with
proliferation into other organs at longer durations after injections. Through this study we have
demonstrated the synthesis and application of a stable amphiphilic red emitting fluorescent
dye PDI-OEG and demonstrated its applications in bioimaging.
Acknowledgments
This work was supported by the Active Polymer Center for Patterned Integration (ERC R 11-
2007-050-01002-0) of the National Research Foundation of Korea and by the Hannam
University funding (Kyobi 2015).
#256995
Received 7 Jan 2016; revised 25 Mar 2016; accepted 25 Mar 2016; published 4 Apr 2016
© 2016 OSA
1 May 2016 | Vol. 6, No. 5 | DOI:10.1364/OME.6.001420 | OPTICAL MATERIALS EXPRESS 1428
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