electronic supporting information materials glycerol, glycol, glucose

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Electronic Supporting Information

Materials

Glycerol, glycol, glucose, sucrose, NaCl, Na2SO4, NaH2PO4, Na2HPO4, CaCl2,

AlCl3, CuSO4, NaOH and H2SO4 were obtained from Beijing Chemicals Inc. (Beijing,

China). All these chemicals were of analytical reagent grade and were used without

further purification.

Preparation of carbon dots

70% glycerol, 70% glycol, 20% glucose or 20%sucrose was mixed with different

concentration of inorganic salts. The solution was then put into a domestic microwave

oven (750 W) and heated for different time periods. Finally the color-changed

solutions were purified and diluted with water.

Instruments

UV-Visible absorption spectra were recorded on a Jasco V-550 spectrometer.

Fluorescence spectra were measured on a Jasco FP6500 spectrofluorometer and

appropriate blank spectrum was subtracted. FT-IR characterization was carried out on

a BRUKE Vertex 70 FTIR spectrometer (2 cm-1). Fluorescence lifetime was measured

with a Lecroy Wave Runner 6100 digital oscilloscope (1 GHz) using a 355 nm laser

(Continuum Sunlite OPO with pulse width = 4 ns) as an excitation source.

Atomic-force microscopy (AFM) measurements were performed using Nanoscope V

multimode atomic force microscope (Veeco Instruments, USA) and tapping mode

was used to acquire the images under ambient conditions.

Supplementary Material (ESI) for Journal of Materials ChemistryThis journal is (c) The Royal Society of Chemistry 2011

2

Quantum yield measurement

The quantum yield of carbon dots was calculated by comparing the integrated

fluorescence intensities (excited at 360 nm) and the absorbance values at 360 nm of

carbon dots with quantum yield standard. Quinine sulfate in 0.1 M H2SO4 (literature

quantum yield: 58%) was chose as the reference. Quantum yield can be calculated

using:

2

2( )( )R

R R

Grad nQ QGrad n

=

where Grad is the gradient obtained from the plot of the integrated fluorescence

intensity vs. absorbance and n is the refractive index The subscript R refers to the

reference fluorophore of known quantum yield. In order to minimize re-absorption

effects absorbencies in the 1 cm fluorescence cuvette were kept under 0.05 at the

excitation wavelength.

Cell Labeling Assay

The 293T cells were cultured in Iscove's modified Dulbecco's medium

supplemented with 10% fetal calf serum in culture discs at 37 °C incubator with 5%

CO2. Carbon dots were administered into the cell culture. After an incubation of 24 h,

cells were washed two times with 1×PBS BUFFER and the fluorescence images were

captured using an Olympus BX-51 optical system microscope (Tokyo, Japan) with an

Olympus EVOLT E-500 digital camera.

E. coli DH5α cells were grown in LB liquid medium at 37 oC overnight and


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subsequently washed twice with 1×PBS buffer. The cell concentration was adjusted to

optical density at 600 nm around 0.5 and carbon dots were administered to PBS cell

suspension. The mixture was kept at 37 oC, 200 rpm for 24 h. A drop of this

suspension was placed in a glass slide for imaging experiment and the images were

recorded with an Olympus BX-51 optical system microscope (Tokyo, Japan).


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4.50E-007 5.00E-007 5.50E-0070.0000

0.0005

0.0010

0.0015

0.0020

0.0025F

Τime / s

Figure S1. Photoluminescence decay curve of carbon dots in water. A single

exponential fit gives a lifetime of 8.00 ± 0.07 ns. Luminescence lifetime was

measured with a Lecroy Wave Runner 6100 digital oscilloscope (1 GHz) using a 355

nm laser (Continuum Sunlite OPO with pulse width = 4 ns) as an excitation source.


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Figure S2. Photoluminescence images of E. coli DH5α cells (upper panel) and 293T

cells (lower panel) labeled with the carbon dots. Left panel: excitation by UV light

(330-385 nm); Right panel: excitation by blue light (450-480 nm).


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200 400 600 8000.0

0.2

0.4

0.6

Abs

λ / nm

Control 4 min 7 min 14 min

control4 min 7 min 14 min

a)

400 500 600 7000

1000

2000

3000

4000

400 500 600 7000.00.20.40.60.81.0

Nor

mal

ized

F

λ / nm

λ / nm

F

14 min

7 min

4 mincontrol

b)

Figure S3. Absorption spectra (a) and photoluminescence emission spectra excited at

360 nm (b) of carbon dots synthesized by 70% glycerol in the presence of 7.1 mM

phosphate with different times of microwave pyrolysis. The samples are diluted 100

fold with water and recorded on a spectrometer or fluorescence spectrometer. Control

refers to the resulting product of 70% glycerol after 20 min microwave treatment in

the absence of phosphate. The insets show the photograph of the as prepared carbon

dots (a) and the normalized fluorescence emission spectra of carbon dots when

excited at 360 nm (b).


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0.0 0.4 0.8 1.2 1.6 2.00

10

20

30

40

Per

cent

age

/ %

h / nm

b)

Figure S4 AFM characterization of carbon dots synthesized by 70% glycerol in the

presence of 7.1 mM phosphate with 7 min. (a) Representative AFM image; (b) height

analysis.


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400 500 600 700

F

λ / nm

4 min 7 min 14 min

Figure S5 Photoluminescence emission spectra (λex = 360 nm) of carbon dots

normalized to the absorbance at 360 nm. Microwave synthesis conditions: 70%

glycerol, 7.1 mM phosphate, 4, 7 or 14 min.


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200 400 6000.0

0.2

0.4

0.6

0.8

1.0

λ / nm

Nor

mal

ized

Abs 7.1 mM

14.2 mM 35.7 mM

262 nm

254 nm

Figure S6. Normalized absorption spectra of carbon dots synthesized by 70%

glycerol in the presence of different amounts of phosphate salt with 12 min

microwave treatment.


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400 500 600 7000

50010001500200025003000

400 500 600 7000.00.20.40.60.81.0

Nor

mal

ized

F

λ / nm

F

λ / nm

7.1 mM14.2 mM

35.5 mM

Figure S7. Photoluminescence emission spectra (λex = 360 nm) of carbon dots

normalized to the absorbance at 360 nm. Microwave synthesis conditions: 70%

glycerol, 7.1, 14.2 or 35.5 mM phosphate, 12 min. Inset: normalized

photoluminescence emission spectra.


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200 400 600 8000

100

200

300

400

500

0.0

0.1

0.2

0.3

0.4

0.5

λ / nm

F 300 nm 320 nm 340 nm 360 nm 380 nm 400 nm 420 nm 440 nm 460 nm 480 nm 500 nm

Abs

Abs

Figure S8. UV-Visible absorption spectrum and photoluminescence emission spectra

(with progressively longer excitation wavelengths from 300 nm to 500 nm in 20 nm

increment) of carbon dots (microwave pyrolysis condition: 70% glycerol, 10 mM

CuSO4, 9 min).


12

200 400 600 8000

100

200

300

400

0.0

0.2

0.4F

λ / nm

320 nm 340 nm 360 nm 380 nm 400 nm 420 nm 440 nm460 nm480 nm 500 nm

Abs

Abs

Figure S9. UV-Visible absorption spectrum and photoluminescence emission spectra

(with progressively longer excitation wavelengths from 320 nm to 500 nm in 20 nm

increment) of carbon dots (microwave pyrolysis condition: 70% glycerol, 5 mM

H2SO4, 8 min). By selecting quinine sulfate as the standard and 360 nm as the excitation

wavelength, the photoluminescence quantum yield was measured and calculated to be 7.7%.


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200 400 600 8000.0

0.4

0.8

1.2

1.6

λ / nm

Abs 50 μM H2SO4, 5 dilution

0.5 mM H2SO4, 50 dilution 5 mM H2SO4, 500 dilution

a)

400 500 6000

400

800

1200

λ / nm

F

50 μΜ H2SO4

0.5 mM H2SO4

5 mM H2SO4

b)

150 300 450 600 7500.0

0.4

0.8

1.2

1.6

λ / nm

Abs

0 min 5 fold dilution 2 min 10 fold dilution 4 min 500 fold dilution 6 min 500 fold dilution 8 min 500 fold dilution10 min 500 fold dilution

c)

400 500 6000

40

80

120

160

200

F

λ / nm

2 min 4 min 6 min 8 min 10 min

d)

Figure S10. (a, b), Absorption spectra (a) and photoluminescence emission spectra

(Ex = 340 nm) normalized to the absorbance (b) of carbon dots synthesized by 70%

glycerol in the presence of different amounts of H2SO4 with 8 min of microwave

pyrolysis. (c, d), Absorption spectra (c) and photoluminescence emission spectra (Ex =

340 nm) normalized to the absorbance (d) of carbon dots synthesized by 70% glycerol

in the presence of 5 mM H2SO4 with different time of microwave pyrolysis.


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400 500 6000.00.20.40.60.81.0

Nor

mal

ized

F

λ / nm

Glycol Glucose Glycerol Sucrose

Figure S11. Normalized photoluminescence emission spectra (Ex = 340 nm) of

carbon dots synthesized from different carbohydrate starting materials.


electronic supporting information materials glycerol, glycol, glucose

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