Q. Xu, et al.
Bioorganic & Medicinal Chemistry Letters xxx (xxxx) xxx–xxx
temperature evaluation occurred during irradiation and maximum ΔT
−
1
approached 41.2 °C at concentration of 100 μg mL
(Fig. 3A). The
temperature of pure water maintained almost unchanged after laser
irradiation, only 2.81 °C temperature evaluation was detected in pure
water. The temperature increased with the prolongation of illumination
and reached steady state after about 230 s irradiation, indicating a
balance between light energy absorbing and heat releasing. When the
−1
concentration was fixed at 25 μg mL , the temperature evaluation rate
increased with the increase of irradiation power (Fig. 3B). The above
results indicated that Cy7-PEG NPs can efficiently convert light energy
to heat. Photothermal conversion efficiency (η) is an important index
that indicated the ability of utilizing light energy. This index was cal-
3
6
culated referring to the method reported previously. Photothermal
conversion efficiency of our NPs is about 33.4% under 808 nm laser
irradiation. After reaching steady-state, thermal exchange from the
solution to environment was also monitored (Fig. 3C).
Fig. 1. Synthetic route of Cy7 and preparation of Cy7-PEG NPs.
With successful identification of excellent photothermal ability of
Cy7-PEG NPs, we then investigated their ability in killing mosquito
larvae (Aedes albopictus) through heat generation. All the previously-
reported applications of PCTAs mainly focused on cells or tissues, but
seldom on living organisms. We used mosquito larvae as living animal
here for investigation. Mosquito is a main sanitary insect pest that
transmits many deadly diseases and causes bite allergy. Mosquito larva
were firstly co-incubated with Cy7-PEG NPs for 4 h and then irradiated
with laser light of different power and the mortality was recorded at
different time intervals (Fig. 4A and B). The photothermal killing effects
on mosquito larvae increased with the increase of laser illumination
time or NPs concentration, indicating that the mortality correlated
closely with the amount of heat generation. Laser irradiation or Cy7-
PEG NPs alone did not have any influence on the larvae. These results
demonstrated that the heat production was the main factor that led to
the death of mosquito larvae. Median lethal concentrations (LC50) were
the dialysis bag was transferred to a freeze drier for freeze-drying to
afford green-yellow solid powder.
The morphology of our Cy7-PEG NPs was characterized by trans-
mission electron microscopy (TEM) (Fig. 2A). For TEM samples pre-
paration, the Cy7-PEG NPs dispersions dropped on conventional TEM
copper grids and dried in air. Cy7-PEG NPs showed spherical structures,
uniform shapes and good dispersion, indicating successful preparation
of the expected NPs. The particles size distribution of Cy7-PEG NPs was
measured by dynamic light scattering. The NPs all show a sphere-like
shape with an average size of 164.06 ± 12.5 nm (Fig. 2B). The ab-
sorption spectra of Cy7 and Cy7-PEG NPs in DMSO was presented in
Fig. 2C. The absorption maximum is at about 808 nm, which located in
the near infrared region. The Cy7 content in Cy7-PEG NPs was de-
termined using UV–Vis standard curve (Fig. 2D) providing the load rate
of 12.4% wt%.
−1
−1
−2
1
20 μg mL and 75.4 μg mL under laser power density of 6 W cm
−2
and 8 W cm , respectively.
The powder of Cy7-PEG NPs was dissolved in ethanol and analyzed
with a UV–vis spectrophotometer at 796 nm by using a standard curve
method. The linear relationship between the concentration of Cy7-PEG
NPs and absorption intensity at 796 nm in ethanol was presented in
Fig. 2D. The drug loading content (DLC) was calculated to be 5.3% by
the following equation:
We further evaluated phototoxic effects of Cy7-PEG NPs on Sf9 cells
Spodoptera frugiperda cells) (Fig. 5A). As comparison, Cy7 and Cy7-
(
PEG NPs with or without irradiation were screened using MTT assay at
−2
light intensity of 4 W cm . When treated with Cy7 alone, cell viability
−1
decreased significantly even at concentration of 5 μg mL and the LC50
−1
value was 0.62 μg mL . When Cy7 was encapsulated, its intrinsic
toxicity in the dark reduced 4-folds with LC50 approaching
DLC(wt%)
−1
2
.51 μg mL . When co-treated with Cy7-PEG NPs and laser light,
−1
the weight of Cy7 in Cy7 - PEG NPs/the weight Cy7 - PEG NPs
phototoxicity towards Sf9 cells (IC50 = 0.0048 μg mL ) enhanced
around 500-folds compared to the dark control. Sole laser illumination
had no apparent impact on cell survival. All above observations proved
that the phototoxicity of Cy7-PEG NPs to cells can be triggered by light.
The photostability of Cy7-PEG NPs was investigated by monitoring
their absorbance changes upon continuous laser irradiation at a power
−
2
37
of 4.0 W cm for different time periods. I
0
is the maximum absorbance
As PCTAs draw tremendous attention in cancer treatment, the
of Cy7-PEG NPs in the NIR region, and I is the absorbance of Cy7-PEG
NPs after different irradiation periods. As shown in Fig. 2E, no obvious
absorbance decay was observed for Cy7-PEG NPs, indicating that Cy7-
PEG NPs has good photostability.
ability of Cy7-PEG NPs in ablating HeLa (human cervical carcinoma)
and MCF-7 (human breast adenocarcinoma) cells was studied (Fig. 5B
and C). HeLa or MCF-7 cells were subjected to various concentrations of
−2
Cy7-PEG NPs and irradiated with laser light (4 W cm
for 3 min) or
The photothermal conversion ability of Cy7-PEG NPs was evaluated
in aqueous solution. Temperature changes curves was recorded under
irradiation of 300 s, various aqueous concentrations (100, 50, 25, 12.5,
kept in the dark. Without irradiation, Cy7-PEG NPs had dark toxicity to
both HeLa and MCF-7 cells, which can inhibit around 60% cell viability
−1
−1
−1
at 5 μg mL . The IC50 values are 0.43 μg mL
and 0.30 μg mL
to-
−
1
0
μg mL ) of Cy7-PEG NPs were prepared and tested. Dramatic
wards HeLa and MCF-7 cells, respectively. Upon light illumination, the
2
Xu, Qi
