FRET-based acrylic nanoparticles with dual-color photoswitchable properties in DU145 human prostate cancer cell line labeling

Article abstract of DOI:10.1016/j.polymer.2016.06.042

Dual-color photoswitchable fluorescent polymer nanoparticles have emerged as an important type of cell detectors. Here, dual-color acrylic nanoparticles containing spiropyran and azo-carbazole derivatives with remarkable photostability and photoreversibility were employed. These prominent properties were attributed to the covalent bonding between the incorporated chromophores and the polymeric matrix and provided efficient fluorescence resonance energy transfer phenomenon. The obtained nanoparticles were purified after dialysis and delivered into DU145 cancer cells. Trypan blue dye exclusion assays showed that these nanoparticles were biocompatible with no toxicity to the cells. Fluorescence microscopy images demonstrated that the prostate cancer cells containing nanoparticles exhibited excellent cell uptake with green and red fluorescence emissions after primary excitation at 410?nm and subsequent irradiation at 365?nm, respectively, depicting their dual-color characteristics.

Full text of DOI:10.1016/j.polymer.2016.06.042

Accepted Manuscript
FRET-based acrylic nanoparticles with dual-color photoswitchable properties in
DU145 human prostate cancer cell line labeling
Jaber Keyvan Rad, Ali Reza Mahdavian, Samideh Khoei, Azam Janati Esfahani
PII:
S0032-3861(16)30517-1
10.1016/j.polymer.2016.06.042
JPOL 18779
DOI:
Reference:
To appear in: Polymer
Received Date: 7 May 2016
Revised Date: 13 June 2016
Accepted Date: 16 June 2016
Please cite this article as: Rad JK, Mahdavian AR, Khoei S, Esfahani AJ, FRET-based acrylic
nanoparticles with dual-color photoswitchable properties in DU145 human prostate cancer cell line
labeling, Polymer (2016), doi: 10.1016/j.polymer.2016.06.042.
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ACCEPTED MANUSCRIPT
REVISED
FRET-based acrylic nanoparticles with dual-color photoswitchable
properties in DU145 human prostate cancer cell line labeling
Jaber Keyvan Rad1, Ali Reza Mahdavian1*, Samideh Khoei2, Azam Janati
Esfahani2
1. Polymer Science Department, Iran Polymer & Petrochemical Institute, P.O. Box:
14965/115, Tehran, Iran Tel: +9821 4478 7000, Fax: +9821 4478 7023
Email: a.mahdavian@ippi.ac.ir
2. Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Tehran,
Iran
* Corresponding author
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Abstract
Dual-color photoswitchable fluorescent polymer nanoparticles have emerged as an important type
of cell detectors. Here, dual-color acrylic nanoparticles containing spiropyran and azo-carbazole
derivatives with remarkable photostability and photoreversibility were employed. These prominent
properties were attributed to the covalent bonding between the incorporated chromophores and the
polymeric matrix and provided efficient fluorescence resonance energy transfer phenomenon. The
obtained nanoparticles were purified after dialysis and delivered into DU145 cancer cells. Trypan
blue dye exclusion assays showed that these nanoparticles were biocompatible with no toxicity to
the cells. Fluorescence microscopy images demonstrated that the prostate cancer cells containing
nanoparticles exhibited excellent cell uptake with green and red fluorescence emissions after
primary excitation at 410 nm and subsequent irradiation at 365 nm, respectively, depicting their
dual-color characteristics.
Keywords: biocompatible; cell labeling; FRET; photoswitchable; nanoparticle.
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1 Introduction
Dual-color photoswitchable fluorescent (DCPF) nanoparticles represent a new class of materials for
exploitation of fluorescent technique in biological [1–3]. These fluorescent nanoparticles, based on
fluorescence resonance energy transfer (FRET) phenomenon, have received many attentions
because of some advantages over conventional fluorescent dyes as distinguishing fake positive
signals by aberrant fluorescent biomolecules and targeted locations [4,5]. Hence, they have shown
versatile applications in optically addressable devices [2], drug delivery [6], cell labeling and
imaging [2,7,8], bioimaging and rewriteable pattering [9,10], sensing tools and optical switching
[11–13].
Photoswitchable fluorescence labeling of cells and biomolecules has become one of the most
important techniques to study molecular processes within biological systems. Utilization of the
traditional fluorescence technologies have many restrictions practically, like autofluorescence or
intrinsic false positive signals of biological systems that can generate interferences and
consequently obscure required signals [4,5,7]. Photoswitchable polymer nanoparticles that
modulate fluorescence with external light stimulation will be a good resolution here. In fact,
reversible fluorescence modulation switches fluorophores “on” and “off” and would be exploited to
distinguish fake signals of background from original ones [2]. In many researches, the fluorescent
dye is doped or physically adsorbed into a polymeric matrix that raise potential dye leakage and dye
aggregation, and consequently produces cytotoxicity for cells and blinking in long time. These
represent additional drawbacks for their advanced biological, in-vitro and in-vivo applications
[7,14]. To address these problems, dual-color photoswitchable fluorescent nanoparticle with
covalent bonding between chromophores and polymeric matrix demonstrate several advantages
over the traditional doped ones (without any chemical linkage). These advantages will donate
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remarkably high brightness, extraordinary photostability, photoreversibility, high fatigue resistance
and biocompatibility with potential application in living cells [15].
Dual-color polymer nanoparticles based on FRET consist of both donor and acceptor moieties.
Photochromic compounds like spiropyrans are of high interest and act as acceptor chromophores
[16,17]. Spiropyran derivatives respond to incident light and involve in a photoinduced ring-
opening reaction that spiro (SP) form changes to merocyanine (MC) form with different
spectroscopic properties [18–20]. Merocyanin isomer of spiropyran can receive energy from a
fluorescent dye through fluorescence resonance energy transfer. Fluorescent molecules such as azo-
carbazole ethyl acrylate (AzoCzEA) [15], boron-dipyrromethene phenol methacrylate (BDMPA)
[9] and nitrobenzoxadizole (NBD) [14] can be used in these systems as donor moieties. To achieve
complete energy transfer, fluorescence emission of the fluorescent molecule must have a prominent
overlap with absorption band of the acceptor chromophore.
Polymer nanoparticles containing azo-derivatives have been extensively investigated due to their
changes in shape, size, alignment, porosity and polarity [21–23]. These are the consequence of cis-
trans isomerization induced by UV/Vis irradiation [24].
Zhu and coworkers [2] used photochromic spiropyran derivative and fluorescent perylene diimide
to prepare dual-fluorescent polymer nanoparticles through emulsion polymerization. Then, they
employed these photoreversible fluorescent nanoparticles as a tool for optically addressable living
cells that exhibit photoreversible red-green fluorescence in the cytosolic media. Chen et al [9]
reported the preparation of amphiphilic photoswitchable fluorescent nanoparticles using boron-
dipyrromethene (BODIPY) and spiropyran-linked methacrylate (SPMA) by RAFT polymerization.
They used chemical linkages for incorporation of the fluorescent dye to nanoparticles to improve
their previous investigations [14,25] in which the fluorescent dye was doped to the nanoparticles.
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This promoted photostability and photoswitchability for cell labeling and other biological
applications.
The current research, based on a FRET system, focuses on the utilization of dual-color
nanoparticles with covalent bond formation between all components that are excited at a single
wavelength and emit at two higher wavelengths. Hence, photoswitchable probes containing
AzoCzEA and SPEA were copolymerized with methyl methacrylate (MMA) through emulsion
polymerization with respect to our previous report in which, they were fully-characterized and their
spectral features were studied completely [15]. Here and in continuum, their photoreversibility and
non-radiation energy transfer kinetics are explained. To show the potential applications,
cytotoxicity and biocompatibility of the prepared nanoparticles are studied and in-vitro experiments
displayed their spectacular dual-color responses in DU145 prostate cancer cells by fluorescence
imaging.
2 Experimental section
2.1 Materials
2,3,3-trimethylindolenine and sodium dodecyl sulfate (SDS, 99%) were purchased from Sigma-
Aldrich. All of the solvents, 2-hydroxy-5-nitrobenzaldehyd, methyl methacrylate (MMA),
potassium persulfate (KPS) as the initiator, sodium bicarbonate as a buffer (NaHCO3), carbazole
(89%), sodium nitrite (NaNO2), potassium hydroxide (KOH), hydrochloric acid (HCl, 37%), 4-nitro
aniline, triethylamine, Triton X-100, 2-bromoethanol, acryloyl chloride (AC), sodium chloride,
potassium dihydrogen phosphate, disodium hydrogen phosphate and EDTA were supplied by
Merck Chemical Co. Trypan blue, phosphate buffer saline and formaldehyde were all purchased
from Sigma-Aldrich. Tetrahydrofuran (THF) was dried over sodium and distilled off. Other
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solvents and all reagents were used without further purification. Deionized (DI) water was used in
the polymerization recipe.
2.2 Synthesize of SPEA chromophore
1′-(2-Acryloxyethyl)-3′, 3′-dimethyl-6-nitrospiro-(2-H-1-benzopyran-2,2′-indoline) (SPEA) was
synthesized according to our previously reported procedure [18]. Typically, 1-(2-hydroxyethyl)-
2,3,3-trimethyl-3H-indolium bromide was synthesized through a substitution nucleation reaction
between 2,3,3- trimethylindolenine (1.3 g, 8 mmol) and 2-bromoethanol (1.23 g, 10 mmol) in 20
mL methyl ethyl ketone (MEK) under N2 and refluxed for 24 h. Then the mixture was cooled down
to room temperature to give pink precipitates, which were filtered off and washed with cold
acetone. In continuum, 1-(2-hydroxyethyl)-2,3,3-trimethyl-3H-indolium bromide (1.46 g, 5 mmol)
subjected to isomerization reaction with a solution of potassium hydroxide (0.46 g, 8 mmol) in
water (40 mL). Thus, (R/S)-9,9,9a-trimethyl- 2,3,9,9a-tetrahydrooxazolo [3,2-a] indole (R/S) was
extracted by diethyl ether (3×40 mL). Afterward, condensation reaction between the (R/S)-9,9,9a-
trimethyl- 2,3,9,9a-tetrahydrooxazolo[3,2-a] indole (R/S) (0.43 g, 2 mmol) and 2-hydroxy-5-
nitrobenzaldehyde (0.52 g, 3 mmol) was performed in ethanol (15 mL) to give (R/S)-2-(3′,3′-
dimethyl-6-nitro-3′H-spiro- [chromene-2,2′-indole]-1′-yl)ethanol (R/S) (SP−OH). Modification
reaction of SP−OH (2 g, 6 mmol) with acryloyl chloride (AC) (4.2 mL, 18 mmol,) was carried out
in dry THF (20 mL) as the solvent by using of triethylamine (0.8 mL, 8 mmol) at 0 °C. Then,
temperature of reaction reached to room temperature and the reaction continued for 8 h. Finally,
yellow precipitates of SPEA were filtered and washed with cold acetone.
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2.3 Synthesize of AzoCzEA chromophore
(4-Nitrophenyl)-[3-[N-[2- (acryloyloxy)ethyl]carbazolyl]] diazene (AzoCzEA) was synthesized
according to our reported procedure [15]. At first, N-(2-hydroxyethyl) carbazole was synthesized
by nucleation substitution reaction between carbazole (3.93 g, 23.5 mmol) and 2-bromoethanol
(3.38 g, 27 mmol) in 40 mL dimethyl formamid (DMF) as the solvent in the presence of potassium
hydroxide at room temperature for 12 h. Then, the obtained mixture was poured into distilled water
and white solids were filtered, washed 3 times with water, air-dried and finally recrystallized from a
1:1 cyclohexane: toluene mixture to give white needle crystals (89% yield). To synthesize 3-[(4-
Nitrophenyl)] azo-9H-carbazole-9-ethanol (NACzEtOH), 4-nitroaniline (0.28 g, 2 mmol) was
dissolved in a solution of concentrated HCl (1 mL) in water (30 mL) at 0 °C. After dissolution,
sodium nitrite (0.16 g, 2.2 mmol) was dissolved in 1 mL water and added dropwise to above
solution while stirring for 20 min. Then 0.1 g SDS was added. Another solution containing N-(2-
hydroxyethyl) carbazole (0.64 g, 3 mmol) in DCM (30 mL) was added to the aforementioned
mixture at room temperature. After 24 h, 20 mL ethanol was added and two phases were separated.
The dispersion was heated to remove the DCM layer and the red precipitate was filtered, washed
with water and air dried. Crystallization was done in 1:1 solution of ethanol: chloroform to give red
powder (0.73 g, 92% yield). Finally, (4-nitrophenyl)-[3- [N-[2- (acryloyloxy) ethyl] carbazolyl]]
diazene (AzoCzEA) was synthesized through the reaction of NACzEtOH (0.72 g, 2 mmol) with
acryloyl chloride (0.34 mL, 2.6 mmol) in 20 mL dry THF by using of triethylamine as the catalyst.
The resulting orange solid was purified by recrystallization from a 2:1 ethanol: chloroform solution
mixture (83% yield).
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2.4 Preparation of dual-color fluorescent nanoparticles
Typically and in an emulsion polymerization recipe, an aqueous solution of SDS/Triton X-
100/NaHCO3/KPS feed (0.06 g/0.03 g/0.03 g/0.03 g) was prepared, poured into a three-necked
round bottom reactor, stirred and deaerated with nitrogen, respectively. Then the solution
temperature reached to 70°C. Afterward, polymerization was started by adding monomers i.e. 60
mg SPEA in 5 mL DI water and a solution of 4.5 mg AzoCzEA in MMA (3.2 mL) from two
separate dropping funnels simultaneously into the reactor within 20 min. The emulsion
polymerization continued at 70 °C for 180 minutes until the conversion reached to above 95%.
Finally, the resulting latex containing copolymer of AzoCzEA/SPEA/MMA was obtained and the
coagulation was less than 1 wt%. More detailed information could be found elsewhere [15]. The
nanoparticles were obtained by freeze-drying and then introduced into the dialysis bag (Mw cut-off:
12,400 Da). They were dialyzed against phosphate-buffered saline (PBS, pH=7.4, 1 L) which
replaced every 12 h in the course of over 60 h to eliminate excess surfactants, unreacted monomers
and short polymeric chains.
2.5 Delivery of DCPF Nanoparticles into DU145 living cells
Nanoparticles were delivered into DU145 cells by adding 1 mg/mL of the prepared dual-color
fluorescent nanoparticle to each cell-containing well in the culture plate. After incubating for 24
hours at 37°C in a CO2 incubator, the cells were washed with 500 µL PBS and fixed with 2%
formaldehyde. The optical imaging was carried out using an inverted fluorescence microscope
INV100-FL equipped with a CCD camera (BEL, Italia).
2.6 Cell viability assay
2×104 DU145 prostate cancer cells were seeded in 24-well plates (Nunc, Roskilde, Denmark). After
24 hours, the cells were treated with 0.1, 1, 5, 10, 15, 20 and 25 mg/mL of DCPF nanoparticles for
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24 hours. After treatment, the single cells were tested for viability using Trypan blue dye exclusion
assay. For this assay, a suspension of treated and control single cells from monolayer culture was
mixed with Trypan blue at a 9:1 ratio. The resulting mixture was examined within 3–5 minutes
under an optical microscope and blue-colored cells were considered dead. The ratio of unstained
cells to the total number of cells was reported as the viability percentage for each cell category.
3 Result and discussion
Here, the donor and acceptor monomers based on azo-carbazole and spiropyran groups,
respectively, were employed in preparation of DCPF polymer nanoparticles and used as a labeling
agent by FRET phenomenon in the prostate cancer living cells. The chromophores were covalently
incorporated into the PMMA matrix and identified thoroughly [15]. The energy transfer between
SPEA and AzoCzEA and its kinetics, beside photoreversibility were investigated to reveal the
efficiency of FRET for these polymer nanoparticles. Then they were dialyzed to prohibit any
cytotoxicity. To approve the applicability of these nanoparticles, they were exposed to DU145
prostate cancer cells and their photoswitchable properties were examined by fluorescence imaging.
The conducted efficient copolymerization not only restricts undesirable prominent dye leakage and
dye aggregation (Figure 1), but also enhances their photostability for long time, high contrast and
brightness vastly. In addition, the consequence of these problems (arose from usual doping) is the
decrease in FRET efficiency. To have reasonable energy transfer performance, the optimized ratio
of chromophores must be kept unchanged with time. Beside essential efficient distance between
these chromophores for obtaining best spectral overlap, dye leakage and aggregation will result in
their segregation. These issues are responsible to suppress the FRET phenomenon in the doped
particles.
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To study photostability of the obtained nanoparticles, a latex dispersion was sealed and stored in
dark at room temperature. Then, the diluted dispersion was utilized for fluorescence analysis after
12 weeks. The fluorescence intensity and photoswitching efficiency of the diluted latex did not
change during these weeks, representing extensive long-term photostability and no dyes leakage for
the prepared DCPF nanoparticles. These depict the improved fatigue resistance for such a system
and this will become specifically important and compulsory for cell viability, while they are going
to be employed in biomedical applications.
Figure 1. Schematic representation of dye leakage and aggregation with duration of time
(objects are not to scale)
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UV-Vis spectrum of DCPF nanoparticles containing AzoCzEA and SPEA showed an absorption
band in 400-550 nm, which was attributed to the presence of AzoCzEA chromophores. When these
stimuli-responsive nanoparticles are exposed to UV irradiation at 365 nm, a new absorption band at
500-650 nm appears that is the result of SP to MC isomerization. Disappearance of the absorption
band at 430 nm with the exposure of nanoparticles by stimulating at 365 nm owes to the occurrence
of fluorescence resonance energy transfer from the excited state of AzoCzEA to MC isomer of
SPEA. Totally, by excitation of the above DCPF nanoparticles at 410 nm, they emit green
fluorescence light and because of FRET after UV irradiation at 365 nm, this green fluorescence
emission interchanges to red with respect to the excitation of MC isomer.
Variations in fluorescence intensity in 450-700 nm (green emission; λmax=530 nm) with irradiation
time at 365 nm have been represented in Figure 2.
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Figure 2. Time dependent fluorescence spectra of the prepared dispersion of DCPF
nanoparticles in water upon UV irradiation at 365 nm
It is evident that the fluorescence intensity decreases with the increase in irradiation time and this
returns to the increase in MC concentration at longer irradiation time at 365 nm that makes the
quenching process proceed more. The green fluorescence intensity gradually decreases until
reaches to zero after 240 s of UV irradiation at 365 nm. On the other hand, the red fluorescence
emission (λmax=620 nm) starts to appear, relating to the fluorescence emission of MC isomers.
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This is a strong evidence for observing complete fluorescence quenching process (quenching
efficiency above 98%, calculated by peak integration) in such DCPF nanoparticles as a
consequence of efficient FRET phenomenon.
The recovery of green fluorescence emission could be achieved by the exposure of above particles
to visible light (520 nm) upon transformation of MC to SP isomers. The complete recovery took
about 7 min after visible irradiation in such systems and corresponding fluorescence intensities
have been listed in Table 1.
Table 1. Fluorescence intensity (FI) under UV (365 nm) and visible (520 nm) irradiations at
different time for DCPF nanoparticles*
0
10 20 30 60 90 120 150 190 240 300 360 420
322 221 160 119 88 70 47 22
21 50 72 98 137 179 211 244 275 312 321
Irradiation time (s)
FI after UV irradiation
FI after Vis irradiation
-
-
-
-
-
-
-
*Fluorescence intensities were recorded in 450-700 nm
The kinetics of fluorescence intensity of AzoCzEA moiety in DCPF nanoparticles and its recovery,
according to the extracted data from Table 1 and with respect to reversible SP to MC
isomerization, could be fitted to the Equation 1 [26]:
Ln ((E∞-E0)/(E∞-Et))= kiso.t
Eq. 1
Where E0, Et and E∞ are the emission intensities (λmax=530 nm) at time 0, t and infinity,
respectively, and kiso is the rate constant of SPEA isomerization.
Time profiles of emission for DCPF nanoparticles during UV/Vis irradiation exhibit a deviation
from the first order kinetics. Figure 3a reveals that the fluorescence quenching carries out with a
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constant rate (kiso of 0.0222 s-1). Facile energy transfer illustrates the accessibility of chromophores
for immediate overlap between molecular orbitals. The duration and rate of energy transfer will
depend on either mobility of the polymeric chains or the distance between MC isomer and
AzoCzEA in DCPF nanoparticles to promote bringing them together. In other words, kiso would be
assumed as a parameter to indicate the vicinity of chromophores and mobility of polymeric matrix.
The recovery of fluorescence emission occurs in slower rate primarily with kiso of 0.0063 s-1
(Figure 3b). This process depends on the MC to SP isomerization rate entirely and is strongly
controlled by the stabilization of MC zwitterions in the medium. The dipolar or ionic interactions of
MC with the polymeric matrix (PMMA here) play important role for this issue. Consequently,
bonded MC groups to the copolymer chains in DCPF nanoparticles and establishment of ionic and
dipole-dipole interactions will reduce the mobility of polymeric chains. It has also been depicted
that π-π stacking between aromatic structures improves the stability of MC isomers and retard
isomerization rate of MC to SP [27]. This will cause in difficulty for keeping AzoCzEA away from
tightly-fixed MC isomers and accordingly, slows down the rate of fluorescence recovery. The
sudden increase in kiso (0.0319 s-1) after 300 s of visible irradiation is attributed to the significant
decrease in MC concentration in DCPF nanoparticles and inaccessibility of residual MC isomers to
AzoCzEA groups. This will result in remarkable regeneration of green fluorescence emission.
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Figure 3. Fluorescence quenching of DCPF nanoparticles by UV (365 nm) (a) and its recovery
by visible (520 nm) (b) irradiations with time
The effect of DCPF polymer nanoparticles on the viability of DU145 cells was determined by
Trypan blue dye exclusion assay and shown in Figure 4. The cells were dealt with various amounts
of DCPF nanoparticles and half maximal inhibitory concentration (IC50) for these fluorescent
nanoparticles was calculated as 22 mg/mL.
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Figure 4. DU145 cells survival after treatment with different concentrations of DCPF
nanoparticles for 24 h
This assay implies that below 22 mg/mL of the nanoparticles, they show still reasonable cell
compatibility without significant toxification. Therefore, and with respect to the biocompatibility
analysis, they could be exploited in biomedical devices without serious concern.
Therefore, imaging experiments were conducted to examine the potential application of these
DCPF nanoparticles as bioimaging agents. Initial results indicated that the dual-color fluorescent
nanoparticles were directly entered into DU145 living cells (Figure 5). It is suggested that these
polymer nanoparticles are able to fuse to the prostate cancer cells membranes and internalize inside
them without noticeable toxic effects on the live cells. DU145 cells including the dual-color
nanoparticles show green fluorescence after excitation at 410 nm (Figure 5a), which is attributed to
AzoCzEA, while SPEA moieties in DCPF has no fluorescence emission under this condition. The
cellular imaging assays indicate that DCPF nanoparticles can be distinguished in the living cells
explicitly. SP to MC isomerization under UV irradiation at 365 nm will lead to the formation MC
isomer with fluorescing ability. According to the FRET phenomenon, MC can absorb energy from
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the excited state of AzoCzEA after irradiation at 410 nm. The excited MC moieties will
consequently fluoresce in red at 630 nm. Thus, the green fluorescence is quenched after irradiation
at 365 nm and the red fluorescence will be observed (Figure 5b). Figure 5c represents the bright
field image of Figure 5a. It could be observed that the green fluorescence of DCPF polymer
nanoparticles is detectable in bright field (arrows) due to the excitation at 410 nm. These smart
fluorescent probes demonstrate promising potentiality in selectively highlighting systems such as
cell labeling, cell imaging and photo-tracking with high contrast fluorescence. It would be of great
importance for having the capability to discriminate labelled cell with DCPF nanoparticles from
autofluorescence and fake signals of the background.
100 µm
100 µm
100 µm
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Figure 5. Fluorescence microscopy images of the prepared dual-color photoswitchable fluorescent
nanoparticles in DU 145 human prostate cancer cells after excitation at 410 nm (a) before and (b)
after UV irradiation at 365 nm. (c) is the bright field image of (a) (magnifications are 10X).
In this study, photoresponsive fluorescent acrylic polymer nanoparticles were employed in
phototracking and labeling of human prostate cancer cells by UV stimulus. Results of fluorimetry
analyses reveal that the prepared DCPF nanoparticles have prominent photostability and
photoreversibility that make them suitable for biomedical applications. Kinetic evaluation for the
FRET phenomenon, fluorescence quenching and its recovery under UV/Vis irradiation were
investigated extensively. The obtained results were attributed to polymer chain mobility, π-π stacking
between aromatic structure and interaction of chromophores with polymer chains. Covalent bonding
between chromophores, as a great advantage, makes excellent distribution of the chromophores in
polymer chains and preservation of FRET and also enhanced photoreversibility and fatigue resistance
in such DCPF nanoparticles. The obtained dual-color latex was purified by dialysis and a dispersion
of DCPF fluorescent nanoparticles were delivered into DU145 cancer cells. Cell viability assays
showed good biocompatibility with reasonable toxicity for DCPF nanoparticles. Results of
fluorescence microscopy images indicated excellent cell uptake and dual-color fluorescence of the
labeled prostate cancer cells. It is believed that the introduced photoswitchable fluorescent polymer
nanoparticles can be used as a promising candidate for cell labeling and tracking to remove the
probable fake background signals from original ones in precise detections.
Acknowledgment
We wish to express our gratitude to Iran Polymer and Petrochemical Institute (IPPI) for financial
support of this work (Grant# 24761172).
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For the TOC
FRET-based acrylic nanoparticles with dual-color photoswitchable properties in DU145
human prostate cancer cell line labeling
Jaber Keyvan Rad1, Ali Reza Mahdavian1*, Samideh Khoei2, Azam Janati Esfahani2
1. Polymer Science Department, Iran Polymer & Petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran
Tel: +9821 4478 7000, Fax: +9821 4478 7023, Email: a.mahdavian@ippi.ac.ir
2. Medical Physics Department, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
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Preparation of photoswitchable fluorescent polymer nanoparticles as cell detector
Dual-color acrylic nanoparticles containing spiropyran and azo-carbazole derivatives
FRET- based particles with improved photostability and photoreversibility
Reasonable cell compatibility and cell uptake to prostate cancer cells