ChemComm
Communication
carbon dots can efficiently enhance the intracellular drug delivery
for a sustained period of time.
In summary, we have developed fluorescent carbon dots tethered
to a quinoline based phototrigger for regulated delivery of anticancer
drugs. The fluorescence properties of Cdots have been explored for
in vitro cellular imaging application. The photoregulated drug release
ability of Qucbl-Cdots has been established by means of periodic
exposure to light and dark conditions. Furthermore, Qucbl-Cdots
were readily internalized inside the HeLa cells and showed precise
control over the drug release to kill the cancer cells upon irradiation.
Although our photoresponsive Qucbl-Cdots are effective for regulated
drug delivery, their application for in vivo studies is still restricted due
to their absorbance below 500 nm. Hence, in future we wish to design
photoresponsive Cdots which can be operated in the NIR region.
We thank Dr Roy Chaudhuri for providing the He–Ne laser for
photolysis. DST-SERB for financial support. DST-FIST for 400 MHz
NMR. S. Karthik is thankful to IIT KGP for the fellowship.
Fig. 4 (a and b) Cell viability test of (i) Cdots, (ii) chlorambucil (iii) Qucbl-Cdots in
the HeLa cell line: (a) before irradiation (b) after irradiation and values are
presented as mean Æ SD.
Furthermore, to explore the tunable emission properties of
Qucbl-Cdots, we carried out cellular imaging at two different excita-
tion wavelengths (488 nm and 569 nm), and the results are
presented in Fig. S15 (ESI†). After successful demonstration of
pronounced accumulation of Qucbl-Cdots within the nucleus of
HeLa cells, we evaluated the cytotoxicity of Qucbl-Cdots, chlorambu-
cil and Cdots in vitro using the MTT assay in the HeLa cell line.
Cytotoxicity was expressed as the percentage of cell viability relative
to the untreated control cells. The percentage of cell viability was
plotted versus the concentration. It was observed that cell viability
remains above 90% at different concentrations of Qucbl-Cdots and
Cdots, whereas an increase in cytotoxicity was observed upon
addition of increasing amounts of chlorambucil (Fig. 4a). In the
light exposure experiment, incubation of cells with different con-
centrations of Qucbl-Cdots upon irradiation for 30 min under UV
light (Z365 nm) resulted in the release of the anticancer drug
chlorambucil, thereby causing cytotoxicity in cancerous HeLa cells
as validated by the MTT toxicity data (Fig. 4b), and the cell death of
HeLa cells was further confirmed by cell cycle analysis. On the other
hand, there was no significant cell death observed when the cells
were irradiated in the presence of Cdots, indicating that the cyto-
toxicity was likely caused by the released drug, chlorambucil, upon
light irradiation. On comparison with the same concentration of
chlorambucil as that of Qucbl-Cdots, Qucbl-Cdots showed much
lower cytotoxicity compared to chlorambucil. But upon irradiation,
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c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 10471--10473 10473