SUPPORTING INFORMATION
Biogenic synthesis of Fluorescent Carbon Dots at ambient temperature
using Azadirachta indica (Neem) gum
Chinmay Phadke$§, Ashmi Mewada$§, Roopa Dharmatti§, Mukeshchand Thakur§, Sunil
Pandey§, Madhuri Sharon§€*
§ N. S. N. Research Centre for Nanotechnology & Bio-Nanotechnology, Ambernath, MS,
India
€ Monad Nanotech Pvt Ltd, A-702 Bhavani Towers, Powai, Mumbai, Ms, India
$ Authors have equal contribution
*Author for correspondence: sharonmadhuri@gmail.com
Phone: +91 9552599207
___________________________________________________________________________
Stability studies of Azadirachta indica (Neem) gum carbon dots:
In order to be used as drug carrier or for any other biological applications, it’s mandatory for
CDs to be stable under different circumstances. Stability of CDs was checked at different
temperature, pH and in different solvents.
1.
Temperature
CDs solution was subjected to different temperatures and changes in the optical spectra were
measured by UV-Vis spectrophotometer (Perkin Elmer, Lambda 25, USA) at regular
intervals.
At the different temperatures (4ºC, RT, 37 ºC, 60 ºC and 100 ºC) there was negligible shift
(Fig. S1) observed up to 72 hrs indicating exceptional stability making them best candidates
for many applications including biological applications.
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Figure S1. Stability studies of CDs at 4ºC, 37 ºC, 60 ºC, 100 ºC and RT
2.
pHStability of 10 ml aqueous CDs solution was checked at both acidic and basic pH. At
pH 2, 4, 6 and 8 there was blue shift in the peak (216 to 200 nm) (Fig. S2), which
might be because of protonation of NH groups and deprotonation of COOH groups
present on the surface of CDs. However blue shift at basic pH 10 and 12 was
relatively less (216 nm to 202 nm) may be due to only deprotonation of NH groups.
Overall CDs were found to be stable in terms of intensity at all pH conditions.
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Figure S2. Stability studies of CDs at various pH
3.
Solvent stability:
Methanol as a solvent shows average stability of C-dots as depicted from the Figure
S3. There is a minor blue shift of 2 nm (216 nm to 214 nm) probably due the
stabilisation of C-dot surface with addition of hydroxyl groups. On the contrary
DMSO and Chloroform show a red shift of 4 nm (216 nm to 220 nm) and 10 nm (216
nm to 226 nm) respectively over increasing period of time in the UV-Vis spectra
along with drastic decrease in the intensity (Fig. S3). This could be because of the
dampening of the inherent functional groups on the surface of C-dots by interacting
with the functional groups of the solvent like –Cl.
Interaction with HCl shows a considerable blue shift of 5-6 nm (absorption maxima
210 nm-209 nm) as seen in with a moderate decrease in intensity which remains
constant over time. The blue shift and stabilisation could be because of the
protonation and deprotonation of amine and carboxylic functional groups respectively
as observed and confirmed in the pH stability test for C-dots. C-dots show exceptional
stability with acetone with minor blue shift and negligible fluctuation in the intensity
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as observed in the (Fig. S3). Thus, Acetone, Methanol and HCl and be considered as
the most suitable solvents for application of C-dots in drug delivery or bio-imaging.
Figure S3. Solvent stability studies of CDs
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