Mussel-inspired preparation of C60 nanoparticles as photo-driven DNA cleavage reagents

Article abstract of DOI:10.1039/c8nj03970d

Designing and constructing favorable water-dispersible fullerenes and their derivatives are of huge importance for biological applications addressing DNA-cleavage and photodynamic therapy (PDT). In the present work, a mild, green and facile synthetic approach for the preparation of C₆₀ nanoparticles was developed for the first time via the combination of mussel-inspired chemistry and the Michael addition reaction. The resultant C₆₀-PDA-PEI nanoparticles were characterized by transmission electron microscopy (TEM), dynamic laser scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectra, X-ray photoelectron spectra (XPS) and thermogravimetric analysis (TGA), demonstrating that the above two-step strategy allows easy access to the preparation of highly water-dispersible fullerene derivatives. Benefiting from their unique nanostructure, the versatile C₆₀-PDA-PEI nanoparticles display a uniform hydrodynamic size of 160 nm in water and efficient ¹O₂ generation under irradiation. Furthermore, the good ability of cleaving DNA under visible light at a mass concentration of 62.5 ng μL^-1 gives them high potential as PDT agents. The universal approach described in this work is capable of introducing many other functional molecules onto PDA-modified fullerenes, thus extending the possible applications of fullerene-based species in many fields of biotechnology and pharmaceutical chemistry.

Full text of DOI:10.1039/c8nj03970d

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Mussel-inspired preparation of C60 nanoparticles
as photo-driven DNA cleavage reagents†
Cite this: New J. Chem., 2018,
42, 18102
Yihan Ma, *a Xiaoyan Zhang,a Yinjia Cheng,
Xiaosui Chen,a Yong Li*b and
a
Aiqing Zhanga
Designing and constructing favorable water-dispersible fullerenes and their derivatives are of huge
importance for biological applications addressing DNA-cleavage and photodynamic therapy (PDT). In the
present work, a mild, green and facile synthetic approach for the preparation of C60 nanoparticles was
developed for the first time via the combination of mussel-inspired chemistry and the Michael addition
reaction. The resultant C60–PDA–PEI nanoparticles were characterized by transmission electron micro-
scopy (TEM), dynamic laser scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR), Raman
spectra, X-ray photoelectron spectra (XPS) and thermogravimetric analysis (TGA), demonstrating that the
above two-step strategy allows easy access to the preparation of highly water-dispersible fullerene
derivatives. Benefiting from their unique nanostructure, the versatile C60–PDA–PEI nanoparticles display
1
a uniform hydrodynamic size of 160 nm in water and efficient O2 generation under irradiation. Further-
Received 6th August 2018,
more, the good ability of cleaving DNA under visible light at a mass concentration of 62.5 ng mLÀ1 gives
them high potential as PDT agents. The universal approach described in this work is capable of introducing
many other functional molecules onto PDA-modified fullerenes, thus extending the possible applications of
fullerene-based species in many fields of biotechnology and pharmaceutical chemistry.
Accepted 30th September 2018
DOI: 10.1039/c8nj03970d
rsc.li/njc
obtain biocompatible fullerene-based materials: (1) the intro-
duction of hydrophilic groups by chemical modification, such
Introduction
In the past few decades, the ready availability of fullerenes and as hydroxyl,15 carboxyl16 and amino17 or the conjugation of
their various derivatives has aroused considerable interest and small hydrophilic molecules (saccharides18 and peptides19) or
exploration.1–4 As a class of low-dimensional materials, fullerenes polymers20,21 via different linkers, and (2) taking advantage of a
consist of sp2 carbons, which form a highly symmetric cage with solubilizing agent to partially mask the fullerene surface, by the
different sizes. Due to their outstanding opto-electronic, chemical non-covalent encapsulation of soluble macromolecules22 or
and physiochemical properties, great research efforts have been host molecules (cyclodextrins23 and liposomes24). Commonly,
devoted to a broad range of applications.5–7 In particular, for bio- the preparation of C60 nanoparticles obtained by solvent
applications, fullerenes could be excited to their triplet state and exchange (THF25 or toluene26) needs extra washing steps to
efficiently produce reactive oxygen species (ROS) in the presence of remove the toxic byproducts. As for the host–guest complexes,
irradiation and oxygen.8 As a result, fullerenes are anticipated as previous results mentioned that the g-CDxÁC60 complex must be
promising photosensitizers to cleave DNA and further for photo- handled carefully because of its instability, which limited its
dynamic therapy (PDT).9–11 Nevertheless, the hydrophobic nature applications.27 To date, much work has focused on a class of
of fullerenes results in unfavorable solubility in polar media, polyhydroxylated fullerenes (fullerenols), disclosing that the
especially aqueous solutions, which is extremely challenging and water-solubility and toxicity effects of fullerenols are dependent
critical for biological applications. In order to get rid of this defect, on the number of hydroxyl groups present on the carbon cage
a number of methods have been developed to boost fullerene by different means.15,28 Consequently, plenty of the previous
solubility in water.12–14 In general, two strategies are adopted to methods may involve complicated reaction procedures, hazardous
ingredients or harsh reaction conditions. Therefore, it is truly
a College of Chemistry and Materials Science, South-Central University for
Nationalities, Wuhan, 430074, China. E-mail: mayihan@iccas.ac.cn
b College of Life Sciences, South-Central University for Nationalities, Wuhan,
430074, China. E-mail: liyong081@mail.scuec.edu.cn
favorable to design and develop a facile and efficient synthesis
route for highly water-dispersible fullerene derivatives, which
could be biocompatible, low-cost and eco-friendly.
Inspired by the composition of adhesive proteins in mussels,
Messersmith first proposed the fabrication of multifunctional
coatings by the self-polymerization of dopamine in a weakly
† Electronic supplementary information (ESI) available: TEM images of C60, DLS
and z potential of C60–PDA–PEI, XPS C 1s spectra and DTA curves of C60, C60–PDA
and C60–PDA–PEI. See DOI: 10.1039/c8nj03970d
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alkaline solution.29 The surface-adherent polydopamine (PDA), an can completely cleave closed supercoiled DNA to nicked DNA
emerging soft material, can be applied to the surface modification under visible light irradiation.
of almost any inorganic or organic material (noble metals, oxides,
semiconductors, ceramics and polymers) regardless of its compo-
sition, shape and size.30–33 More significantly, once the PDA thin
film is formed, it can serve as a secondary reaction platform for
Experimental
Materials and instrumentation
covalent modification with other desired compounds. Thus, mole-
cules containing amino or thiol groups, such as commercially
available small molecules, peptides and polymers, could be immo-
bilized onto PDA-modified materials through the Michael addition
reaction.31,34 Therefore, the universal adhesion capability and high
reactivity of PDA imply the broad opportunities in directly modify-
ing distinct substrates for multiple applications. Notably, consid-
erable research efforts have been devoted to PDA-modified carbon
nanomaterials.35 The Wei and Zhang groups reported a series of
work focusing on graphene oxide and carbon nanotubes fabricated
via the above two-step method to obtain enhanced dispersibility,
biocompatibility, applicability and capacity for multiple fields.36–41
Additionally, Lee et al. demonstrated that PDA-coated GQDs
(graphene quantum dots) could act as a long-term optical imaging
agent with excellent stability of photoluminescence intensity.42
In spite of this, fullerene, as a carbon-based nanomaterial, has
rarely been related to the simple mussel-inspired chemistry. It is
worthwhile introducing mussel-inspired PDA to fullerene as a
strategy for functionalization of nanoparticles and studying their
interconnection.
All of the chemicals were obtained from commercial sources
and used directly without further purification. C60 was obtained
from the Institute of Chemistry, Chinese Academy of Sciences
(Beijing, China). Tris-(hydroxymethyl) aminomethane (Tris),
polyethyleneimine (PEI, Mn
= 600), 2,2,6,6-tetramethyl-4-
piperidone (TEMP) and dopamine hydrochloride were purchased
from Aladdin Reagent Inc. (Shanghai, China). Ethylenediamine-
tetraacetic acid (EDTA) and ethidium bromide were purchased from
Sigma, and pSP72 plasmid DNA was purchased from Promega.
6Â gel loading buffer was purchased from CoWin Biosciences.
Milli-Q purified water (18.2 MO) was used to prepare all of the
solutions. The hydrodynamic size distribution and zeta potential
of C60–PDA–PEI nanoparticles in water were determined on a
Zetasizer Nano ZSP instrument (DLS). Transmission electron
microscopy (TEM) images were obtained using a Tecnai G2 20
S-TWIN microscope and adding a drop of the nanoparticle ethanol
suspension onto a carbon-coated copper grid to prepare the TEM
samples. Fourier transform infrared (FT-IR) spectra were recorded
using a Thermo Nexus470 spectrometer. Raman spectra were
analysed using a LabRAM HR800 spectrometer with a 532 nm
excitation wavelength. X-ray photoelectron spectroscopy (XPS) was
performed on a VG ESCALab220i-XL spectrometer equipped with
an Al Ka X-ray source (1486.6 eV) and the binding energies were
internally calibrated by referencing to the C 1s peak of a carbon
contaminant at 284.6 eV. Thermogravimetric analysis (TGA) was
conducted on a TA instrument (Shimadzu DTG-60H) with a
heating rate of 10 1C minÀ1 under a N2 atmosphere. Electron spin
resonance (ESR) spectroscopy was performed on a Bruker ELEX-
SYSE 500 ESR spectrometer at 298 K.
In this report, we describe the facile preparation and DNA
photocleavage performance of C60–PDA–PEI nanoparticles for
the first time. C60 was first immobilized by PDA via the self-
polymerization of dopamine, then hydrophilic polymer PEI was
conjugated to the PDA-coated C60 through the Michael addition
reaction (Scheme 1). A variety of characterization techniques
was employed to verify the successful synthesis of the resultant
C
60–PDA–PEI nanoparticles. At last, the versatile C60–PDA–PEI
1
nanoparticles with efficient O2 generation in aqueous media
Preparation of C60–PDA
In brief, 100 mg of C60 was dispersed in 30 mL of Tris buffer
solution (pH = 8.5, 10 mM) with the aid of sonication for
20 minutes. Then, 200 mg of dopamine hydrochloride was
directly added into the above solution. After that, the mixture
was stirred vigorously at room temperature for 10 h and then
separated by centrifuging at 8000 rpm for 10 min. The obtained
C60–PDA was washed repeatedly with distilled water and ethanol
until the upper solution was clear and dried under vacuum at
40 1C for 12 h.
Preparation of C60–PDA–PEI
50 mg of C60–PDA and 100 mg of polyethyleneimine (PEI) were
added into 25 mL of NaOH aqueous solution (0.1 M) and
then stirred for 12 h at room temperature. The as-synthesized
C
60–PDA–PEI nanoparticles in a red-brown aqueous solution
Scheme 1 Schematic representation of the preparation of C60–PDA–PEI
via the combination of mussel-inspired chemistry and the Michael addition
reaction.
were purified by filtering through a 0.22 mm membrane filter
and dialyzed against ultrapure water with a porous cellulose
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bag (molecular weight cut-off 3500 Da) for 3 days. Finally, the
products inside the dialysis bag were collected by freeze drying.
1
Evaluation of O2 generation by ESR spectroscopy
1O2 generated under visible light irradiation was detected by
the ESR spin-trapping method. 25 mL of TEMP (30 mM) as the
spin-trapping reagent and 25 mL of C60–PDA–PEI (0.5 mg mLÀ1
)
were mixed well under aerobic conditions. Then, the above
solution was irradiated by a 50 mW cmÀ2 photoreflector at
298 K for 10 min and at once subjected to ESR measurements.
The singlet oxygen generated by irradiation was immediately
captured by 2,2,6,6-tetramethyl-4-piperidone (TEMP) to form
TEMPO, which could be detected by ESR spectroscopy with the
corresponding signal.
Examination of DNA-cleaving activity
Fig. 1 Representative TEM images of C60–PDA (a and b) and C60–PDA–PEI
(c and d) with different magnifications.
To examine the DNA-cleaving activity of the as-prepared PDA–
PEI–C60, 2.5 mL of pSP72 plasmids (50 ng mLÀ1) was mixed with
an equal volume of different concentrations of PDA–PEI–C60
(125, 62.5, 31.25, 15.63, 7.82 and 3.91 ng mLÀ1). For the blank
control, PDA–PEI–C60 was absent, and 2.5 mL of ultrapure water
was added to bring the volume to 5 mL. After incubation for 2 h
under visible light, these mixtures were supplemented with
1 mL of 6Â gel loading buffer, and loaded into 1% (w/v) agarose
gel, prepared with 1Â TAE buffer (40 mM Tris-base, 20 mM
acetic acid and 1 mM EDTA, pH 8.0). The gel was run at 100 V
for 30 min in 1Â TAE buffer, and stained with ethidium
bromide. The resulting gel was imaged using Gene Genius.
in water was 160 nm with a single peak (Fig. S3a, ESI†). This
appropriate dimension is feasible for cell uptake. Moreover,
the above nanoparticles possess a positive value of z potential
(41.8 eV) (Fig. S3b, ESI†). Since the cytomembrane is negatively
charged, this may be beneficial for their capture by cells in vivo.
These findings further confirm the C60–PDA–PEI nanoparticles
as a candidate for promising materials with biomedical
functions.
FT-IR analysis was performed to verify the functionalization
of C60 in the reaction process. As presented in Fig. 2, distinct
peaks at 527, 576, 1187 and 1430 cmÀ1 are the characteristic
peaks of pristine C60, which could be related to the three-fold
degenerate first-order dipole active T1u modes. Other peaks
(2965, 2918 and 1453 cmÀ1) are the toluene bands and the peak
at 3450 cmÀ1 represents the hydroxyl groups of water. After
being wrapped by PDA, apart from the 1187 and 1430 cmÀ1
peaks, there were new multiple peaks observed between 1450
and 1600 cmÀ1, which could be ascribed to the stretching
vibration of polycyclic aromatic groups, and the wide band at
3426 cmÀ1 was assigned to the stretching vibration of O–H and
Results and discussion
Characterization of C60–PDA–PEI
The morphological information of the samples was observed by
TEM. Fig. S1 (ESI†) shows typical low-magnification images of
the pristine C60, in which many nanoplates are stacked together
randomly. As the diameter of a single C60 is only 0.7 nm, it is
very hard to detect and easily forms amorphous aggregates.
After modification with PDA, the as-synthesized C60–PDA
hybrids existed as cross-linked aggregates with neighbouring
ones, as displayed in Fig. 1a as well as an enlarged TEM image
in Fig. 1b, and the corresponding energy dispersive X-ray
spectroscopy (EDS) (Fig. S2a, ESI†) confirmed the existence of
C, O and N elements, which were introduced by PDA. When the
hydrophilic polymer PEI was attached to C60–PDA through the
Michael addition reaction, the well dispersed C60–PDA–PEI
existed as irregular spherical nanoparticles (Fig. 1c). Besides,
the diameter of C60–PDA–PEI is about 20–30 nm (Fig. 1d), and
the EDS characterization (Fig. S2b, ESI†) proved that the
products were also composed of C, O and N elements. These
phenomena implied that the introduction of PEI prevented the
crosslinking of neighbouring C60–PDA aggregates to a great
extent. Meanwhile, C60–PDA–PEI tended to self-assemble in
aqueous solution to form uniform nanoparticles with hydrogen
bonds, as supported by the dynamic laser scattering (DLS)
results. The hydrodynamic size of C60–PDA–PEI nanoparticles
Fig. 2 FT-IR spectra of C60, C60–PDA and C60–PDA–PEI, respectively.
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Fig. 3 Raman spectra of C60, C60–PDA and C60–PDA–PEI, respectively.
N–H of PDA, suggesting that C60–PDA was successfully
prepared.
Fig. 4 XPS spectra of C60, C60–PDA and C60–PDA–PEI. (a) Survey scan of
the spectral region from 0 to 1200 eV, (b) C 1s region, (c) N 1s region and
(d) O 1s region.
Furthermore, several peaks appeared in the spectrum of
C
60–PDA–PEI compared with C60 and C60–PDA. Two peaks at
2935 and 2832 cmÀ1 originated from the stretching vibration of
the C–H bond of methylene units, and the stretching vibration spectra can be seen in Fig. 4b–d. The C 1s spectrum of C60
of C–N appeared at 1128 cmÀ1. Meanwhile, the broader and contained one symmetrical peak centred at 284.9 eV (Fig. 4b
intensive peak around 3430 cmÀ1 could also be attributed to and Fig. S5a, ESI†), which can be assigned to the non-
the abundant N–H units of PEI. These observations confirmed functionalized sp2-hybridised carbons (C–C and CQC), in good
that PEI was successfully conjugated with C60–PDA.
agreement with the spherical symmetry in the electronic struc-
Raman spectroscopy has been proven to be a sensitive, local ture of the C60 molecule. Obviously, there was no nitrogen
structural probe for carbon nanomaterials and complementary signal detected for C60. However, after modification with PDA,
to IR investigation. The Raman spectra of C60, C60–PDA and novel peaks between 285.6–288.4 eV emerged and could be
C
60–PDA–PEI are displayed in Fig. 3. For the pristine C60, there further curve-fitted into two peak components with binding
are four characteristic peaks, the Ag-breathing mode at energies at about 287.5 and 286.1 eV, ascribed to the CQO and
496 cmÀ1, the Ag-pentagonal pinch mode at 1457 cmÀ1 with C–N species, respectively (Fig. S5b, ESI†). More importantly, as
two additional Hg modes at 272 cmÀ1 and 1574 cmÀ1. As for can be seen in Fig. 4c, a binding energy peak of C60–PDA of N 1s
C
60–PDA, the typical Raman vibrational frequency of C60 was at 399.9 eV can be attributed to a nitrogen-containing hetero-
nicely reproduced, evidencing that the structure of the C60 cyclic structure formed during the self-polymerization of DA,
cage remained intact after modification with PDA. Notably, indicating that PDA was successfully coated on C60 via mussel
all these bands were slightly blue-shifted, presumably due to a inspired chemistry. Furthermore, the marked increase in intensity
vibronic coupling mechanism with electron transfer between of the N 1s spectra of C60–PDA–PEI provided strong evidence that
C60 and PDA.43,44 Interestingly, in the case of the as-prepared PEI was conjugated with C60–PDA through the Michael addition
C
60–PDA–PEI, the original vibration signals of C60 disappeared reaction. The peak at 398.8 eV could be related to the amino
and two characteristic bands at 1562 and 1352 cmÀ1 appeared. groups of dopamine and PEI. In addition, the O 1s peaks
These two bands corresponded to the ordered and disordered located between 530 and 535 eV were observed in all the
carbon structures, respectively, due to the formation of amor- samples (Fig. 4d). With the modification of PDA and PEI,
phous carbon when grafted by PEI. Specifically, the peak at the O 1s peaks were significantly upshifted compared with
1562 cmÀ1 was assigned to the in-plane mode of sp2 ring pristine C60, indicating a higher electron density intensity and
vibration (G band, for graphite); while the peak at 1352 cmÀ1 consistent with the results of C 1s and N 1s. Besides, the
could be assigned as the out of plane mode (D band, for intensity of the O 1s peak in C60–PDA–PEI was a little weaker
disorder). The above observation was also consistent with our than that of C60–PDA, which was due to the relatively low
FT-IR findings, revealing that PEI was successfully attached content of O in the copolymers. Therefore, the XPS results
to C60–PDA.
further confirmed that we could effectively prepare the versatile
X-ray photoelectron spectroscopy (XPS) was further carried hybrid polymer modified C60 nanoparticles.
out to characterize the chemical state and composition of the
The elemental analysis of the C60 nanoparticles based on the
samples. The existence of carbon (C), nitrogen (N) and oxygen XPS spectra is listed in Table 1. The major components of
(O) elements was revealed, according to the XPS analysis pristine C60 are C (97.50%) and O (2.50%), which revealed a
depicted in Fig. 4a, with the survey scan ranging from 0 to kind of oxidization without other admixtures. In the case of
1200 eV, and the high resolution C 1s, N 1s and O 1s XPS
C60–PDA, the percentages of C and O were altered to 77.41%
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Table 1 Element contents (%) of C60, C60–PDA and C60–PDA–PEI based
on the XPS analysis
Samples
C 1s
N 1s
O 1s
C60
97.50
77.41
71.78
0
2.50
16.11
13.17
C60–PDA
C60–PDA–PEI
6.48
15.05
and 16.11%, respectively, accompanied with an extra N compo-
nent (6.48%). The existence of the new element (N) and
decrease of C content demonstrated that PDA combined with
C60 through the strong adhesion of dopamine. After modifica-
tion of C60–PDA with PEI, the elemental contents of C, N and O
in C60–PDA–PEI were 71.78%, 15.05% and 13.17%, respectively.
Compared with C60 and C60–PDA, an obvious increase in the N
content in the sample of C60–PDA–PEI was detected. These
results clearly confirmed that PEI was conjugated to C60–PDA
through the Michael addition reaction.
Fig. 6 Optical images of C60 (1), C60–PDA (2) and C60–PDA–PEI (3)
dispersed in water at room temperature at different times.
range of C60–PDA. Afterwards, two obvious endothermic
peaks appeared around 340 and 465 1C in the DTA curve of
Thermogravimetric analysis (TGA) of C60, C60–PDA and
C
60–PDA–PEI, which may be ascribed to the multiple stages of
C
60–PDA–PEI nanoparticles conducted in a nitrogen atmo-
weight loss. These results further confirmed that C60 can be
facilely modified by PDA and PEI through the combination of
mussel inspired chemistry and the Michael addition reaction.
Promoting solubility of functionalized fullerenes is primary
and crucial to extend their applications in biological fields.
The dispersibility of C60 samples in water was then assessed.
As illustrated in Fig. 6, the pristine C60 precipitated in aqueous
solution rapidly within 5 min. With regard to C60–PDA, the
water dispersibility was improved a bit, and thus it was deposited
in 2 h owing to the finite hydrophilic groups supplied by PDA.
In contrast, C60–PDA–PEI nanoparticles exhibited dramatically
enhanced dispersibility in water even for a week. Similar results
were also confirmed by centrifugation at 8000 rpm for 10 min
(Fig. S7, ESI†), implying the high stability of C60–PDA–PEI in
aqueous media. These results also demonstrated the successful
modification of C60 through mussel inspired chemistry and the
Michael addition reaction and provided the basis for further
biological applications.
sphere is presented in Fig. 5. As can be noticed, C60 was
overwhelmingly thermally stable up to 700 1C with only about
4.1% weight loss. However, the total weight loss of functiona-
lized C60 with PDA was significantly increased to 30.6% under
the same experimental conditions, manifesting that PDA was
coated on C60 via mussel inspired chemistry, thus the relative
amount of PDA grafted onto C60 was 26.5%, as calculated from
the TGA data. When C60–PDA further reacted with the hydro-
philic polymer PEI through the Michael addition reaction,
much more weight loss was detected in contrast to C60–PDA.
The weight loss of C60–PDA–PEI was increased to 59.4%.
Consequently, the mass percentage of PEI conjugated to the
surface of C60–PDA was calculated to be 32.9%. Based on the
above results, we concluded that the amino-containing polymer
PEI was indeed grafted to the surface of C60–PDA. The DTA
curves of C60, C60–PDA and C60–PDA–PEI are also presented in
Fig. S6 (ESI†). For the pristine C60, there was no specific peak
but a broad endothermic peak over the whole temperature
range could be observed, due to the high thermal-stability of
To evaluate the photosensitizing ability of C60–PDA–PEI
nanoparticles in producing singlet oxygen, the ESR spin-trapping
method was carried out under air conditions and irradiation. It is
known that pristine C60 aggregates do not generate ROS due to
C
60. In the case of C60–PDA, a distinct endothermic peak was
centred at 560 1C, well consistent with the major weight loss
3
the self-quenching of C60*.45 As shown in Fig. 7, the distinct
signals of TEMPO, a 1O2 adduct of TEMP, clearly confirmed
that C60–PDA–PEI nanoparticles well dispersed in the aqueous
solution can be excited by visible light irradiation to generate
singlet oxygen (1O2). Such efficient generation of singlet oxygen
from C60–PDA–PEI nanoparticles confirms them as a promising
phototherapeutic agent in in vitro DNA cleaving and further for
photodynamic therapy.
Due to the interaction between fullerenes and DNA: direct
electron transfer and formation of cytotoxic singlet oxygen
species, the water-soluble fullerene derivatives were expected
to show high DNA-cleaving activity. Based on the good disper-
1
sion of C60–PDA–PEI and efficient O2 generation in water, we
further evaluated its ability to cleave DNA using pSP72 plasmid
as a model. Firstly, the results of control experiments using C60
Fig. 5 TGA curves of C60, C60–PDA and C60–PDA–PEI, respectively.
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nanoparticles to achieve high dispersibility in aqueous media.
As a result, these C60–PDA–PEI nanoparticles with efficient 1O2
generation properties displayed a good ability of cleaving DNA
under visible light irradiation, endowing them with promising
application potential in photodynamic therapy. Considering
the universal adhesion of PDA and abundant second-platforms
based on C60–PDA, this achievement could not only provide a new
methodology to design and prepare multifunctional fullerene
nanoparticles, but also extend the possible applications of
fullerene-based species in many fields of pharmaceutical
chemistry and biological technology.
Fig. 7 ESR spectroscopy of TEMP (25 mL, 30 mM) adduct with 1O2
generated in C60–PDA–PEI aqueous solution (25 mL, 0.5 mg mLÀ1) under
irradiation (50 mW cmÀ2, 10 min).
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This research was supported by the National Science Founda-
tion of China (No. 51502352, 21405181 and 51703251), the
Fundamental Research Funds for the Central Universities
(CZQ 14006) and Beijing National Laboratory for Molecular
Sciences.
Fig. 8 Agarose gel electrophoresis assay for the pSP72 plasmid DNA in
the presence of C60–PDA–PEI under visible light irradiation. The concen-
tration of C60–PDA–PEI for lane 1 was 125 ng mLÀ1 and the concentration
was consecutively reduced by half from lane 2 to lane 6. DNA: blank
control without addition of C60–PDA–PEI. For all the experiments, the
DNA concentration was 25 ng mLÀ1
.
References
and C60–PDA as references are shown in Fig. S8 (ESI†). In
contrast, DNA cleavage was not observed in the presence of
hydrophobic C60 and C60–PDA. These results were consistent
with the previous reports that found that water-solubility of C60
is necessary for DNA cleavage.8,24,46 As displayed in Fig. 8, with
increased concentrations of C60–PDA–PEI and under visible
light irradiation, supercoiled DNA (Form I) was gradually
converted into nicked DNA (Form II), demonstrating the
DNA-cleaving ability of C60–PDA–PEI as a photosensitizer.
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When the concentration was increased to 62.5 ng mLÀ1
60–PDA–PEI cleaved DNA completely. Moreover, the smeared
,
C
bands of nicked DNA were also observed at relatively higher
concentrations of C60–PDA–PEI (Lane 1 to 3). In a word, the
structural conversions observed above are the results of the
DNA strand breaks, indicating that C60–PDA–PEI has a good
ability of cleaving DNA upon visible light irradiation.
Conclusions
In conclusion, we have developed a mild strategy to prepare
hybrid C60–PDA–PEI nanoparticles by the combination of 11 Y. Y. Huang, S. K. Sharma, R. Yin, T. Agrawal, L. Y. Chiang
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