NANO
MICRO
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quinine sulfate (Fluka, USA), sulphuric acid (Merck, India), benzoquione
transform analyses were done by using Gatan Digital Micrograph
software. HORIBA Jobin Yvon FluoroMax-4 spectrofluorimeter and Perkin
Elmer LAMBDA 750 UV–vis–near-infrared (NIR) spectrophotometer
were used to record the luminescence and absorbance of the samples,
respectively. Life-Spec-II spectrofluorimeter (Edinburgh Instrument,
using 336 nm light emitting diode (LED) source and Pico Quant 375 nm
laser source) was used to record the time-resolved photoluminescence
measurements and FAST software was used to analyze the time-
resolved spectra. CIE-1931 color space of the OSRAM color calculator
was used to calculate the chromaticity of the samples. Atomic
absorption spectrophotometer (Varian AA240FS model) was used to
find the concentration of metal ions. LSM 880 confocal laser scanning
microscope (Zeiss) was used to record the single particle behavior of
the solid samples (deposited on a glass cover slip) using 355 nm laser
excitation.
(
Sigma-Aldrich), cysteine (Sigma-Aldrich), tryptophan (Sigma-Aldrich),
arginine (Sigma-Aldrich), phenyl alanine (Sigma-Aldrich), glutamic acid
Sigma-Aldrich), aspartic acid (Sigma-Aldrich), tyrosine (Sigma-Aldrich),
(
and uric acid (Sigma-Aldrich) and ethanol (Tedia) were procured and
used directly without any purification.
Synthesis of Wurtzite ZnO Qdots: ZnO Qdots were synthesized,
following a reported process,[
30,41]
with the use of ethanol as solvent.
Briefly, under vigorous stirring at 25 °C, 2.0 mL 0.5 m KOH (dissolved
in ethanol) was added dropwise to a 50.0 mL ethanolic solution of zinc
−
3
acetate having concentration of 5.0 × 10 m and the resulting mixture, of
milky white color, was kept for half an hour. Then, the resulting reaction
mixture was centrifuged with a speed of 25 000 rpm for 15 min and the
so obtained pellet was washed with ethanol (in order to remove excess
unreacted salts). The same cycle was repeated and the final pellet was
dispersed in 50.0 mL of ethanol for further experiments.
Synthesis of MSA Ligand: A reported condensation reaction between
salicyaldehyde and methylamine was followed to synthesize MSA.[
30,42,43]
In brief, 2 mmol of methylamine was added dropwise to the solution Supporting Information
of 2.0 mmol of salicylaldehyde in 20.0 mL methanol and the resulting
Supporting Information is available from the Wiley Online Library or
from the author.
mixture, of yellow color, was allowed to stir for 4 h at 25 °C. The column
chromatographic technique was used to purify the product (MSA).
Synthesis of WLE QDC: The luminescence (under spectrofluorimeter)
and chromaticity (in CIE-1931 diagram) were monitored to get optimum
amount of MSA (in ethanol) needed to generate white light from 3.0 mL
of ZnO Qdots (in ethanol: with absorbance of 0.10 at an excitation
Acknowledgements
−3
wavelength of 350 nm). The 1.0 × 10 m MSA was sequentially added
to the ethanolic dispersion of ZnO Qdots (having absorbance of 0.10
at 350 nm) at 25 °C. The optimum amount of MSA was found to be
The authors thank the Department of Electronics and Information
Technology (no. 5(9)/2012-NANO (Vol. II)) Government of India
for providing funding. Assistance from Srestha Basu, Ayan Pal,
CIF, and Department of Physics (for XRD facility under DST-FIST
programme—SR/FST/PII-020/2009), IIT Guwahati is acknowledged
here.
−6
of 9.9 × 10 m. The resulting mixture, obtained from the treatment of
−6
9
.9 × 10 m MSA to 3.0 mL ZnO Qdots, was centrifuged, with a speed
of 25000 rpm for 15 min. Then, the so obtained pellet was repeatedly
washed with ethanol and finally redispersed in same amount of
ethanol. The dispersion and corresponding solid form (obtained from
centrifugation and drying at room temperature) of the QDC were used for
further experiments.
Conflict of Interest
Cell Viability Assay: For cell viability assay, 104 human embryonic
kidney (HEK 293) cells (which were procured from National Center for
Cell Sciences, Pune, India and cultured in Dulbecco’s modified Eagle’s
medium, supplemented with 10% (v/v) fetal bovine serum, penicillin
The authors declare no conflict of interest.
−
1
−1
(
50 units mL ), and streptomycin (50 mg mL ) and maintained in
Keywords
5% CO2 humidified incubator at 37 °C) per well were seeded in a
96 well microplate and left for overnight for proper growing. Then,
complexation reactions, quantum dots, sensing, single particle, white
light
the fresh media containing varying concentrations of WLE QDC
−
1
(
1.6–33.3 µg mL ), following removal of the old medium, were added
to the cells and incubated for 24 h. Finally, the 3-(4,5-dimethylthiazol-
-yl)-2,5-diphenyltetrazolium bromide-based cell viability assay
Received: January 24, 2018
Revised: February 19, 2018
Published online:
2
was performed and the Bio-Rad 680 microplate reader was used to
monitored the absorbance at wavelength 550 nm.
Confocal Microscopic Measurements and Blinking Analysis: Confocal
imaging and single particle experiment of WLE QDC and dopamine
added WLE QDC were performed by depositing the as-prepared
dispersion (which was obtained from the treatment of 9.9 × 10−6 m MSA
to 3.0 mL ZnO Qdots with absorbance of 0.10 at 350 nm at 25 °C) of
the materials on a glass cover slip. Imaging and blinking analysis of the
samples were carried out using Zeiss LSM-880 confocal laser scanning
microscope, equipped with a 355 nm diode-pumped solid-state UV laser
[
[
1] A. L. Efros, D. J. Nesbitt, Nat. Nanotechnol. 2016, 11, 661.
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3] D. Bhatia, S. Arumugam, M. Nasilowski, H. Joshi, C. Wunder,
V. Chambon, V. Prakash, C. Grazon, B. Nadal, P. K. Maiti, Nat.
Nanotechnol. 2016, 11, 1112.
(63 mW) for excitation and Plan-Apochromat, 63x/1.40, oil-immersion
objective for imaging. The resulting fluorescence data of different
channel images and single particle experiments were collected through
the GaAsP detector and Airyscan detector, respectively. The blinking
profile and video were recorded in acquisition mode under super
[
[
4] A. L. Routzahn, P. K. Jain, Nano Lett. 2015, 15, 2504.
5] Y. F. Chen, J. Vela, H. Htoon, J. L. Casson, D. J. Werder,
D. A. Bussian, V. I. Klimov, J. A. Hollingsworth, J. Am. Chem. Soc.
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2
resolution with 64 × 64 µm frame size and by using binning time of
[
35,36]
[6] B. Omogo, F. Gao, P. Bajwa, M. Kaneko, C. D. Heyes, ACS Nano
016, 10, 4072.
2
7 ms,
with excitation power of 63 mW for a time duration of 27 s.
2
The so obtained images and data were analyzed by ZEN black software.
Instruments: Rigaku TTRAX III X-ray diffractometer and TEM (JEOL
JEM 2100F, maximum accelerating voltage 200 kV) were used to analyze
the morphology and size of the samples. TEM and inverse fast Fourier
[
7] B. Scholl, H. Y. Liu, B. R. Long, O. J. T. McCarty, T. O’Hare,
B. J. Druker, T. Q. Vu, ACS Nano 2009, 3, 1318.
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