ArticlePDF Available

Microwave assisted one-step green synthesis of cell-permeable multicolor photoluminescent carbon dots without surface passivation reagents

Authors:

Abstract and Figures

A facile, economic and green one-step microwave synthesis route towards photoluminescent carbon dots is proposed. The preparation requires a carbohydrate (glycerol, glycol, glucose, sucrose, etc.) and a tiny amount of an inorganic ion, and can finish in just a few minutes, no surface passivation reagent is needed. The carbon dots are biologically compatible and show favorable optical properties and have potential applications in biolabeling and bioimaging.
Content may be subject to copyright.
Microwave assisted one-step green synthesis of cell-permeable multicolor
photoluminescent carbon dots without surface passivation reagents
Xiaohui Wang,
ab
Konggang Qu,
ab
Bailu Xu,
ab
Jinsong Ren
a
and Xiaogang Qu*
a
Received 6th September 2010, Accepted 4th January 2011
DOI: 10.1039/c0jm02963g
A facile, economic and green one-step microwave synthesis route
towards photoluminescent carbon dots is proposed. The prepara-
tion requires a carbohydrate (glycerol, glycol, glucose, sucrose,
etc.) and a tiny amount of an inorganic ion, and can finish in just
a few minutes, no surface passivation reagent is needed. The
carbon dots are biologically compatible and show favorable optical
properties and have potential applications in biolabeling and
bioimaging.
Photoluminescent carbon dots have attracted growing interest in
recent years due to their great potential in biological labeling,
bioimaging, drug delivery and optoelectronic device applica-
tions.
1–8
Compared to luminescent semiconductor quantum dots,
which have known toxicity and are potentially environmentally
hazardous due to the contained heavy metals and chalcogens,
carbon based photoluminescent nanomaterials are environmen-
tally and biologically compatible.
6–9
Currently, intensive research has been concentrated on the
synthesis of these benign photoluminescent materials. Common
routes in preparing fluorescent carbon nanoparticles include the high-
energy ion beam radiation based creation of point defects in nano-
diamond particles;
1,6
the covalent modification of nanodiamond
particles with octadecylamine;
10
the oxidation of carbon nanotubes
11
or candle soot
7,12
with nitric acid; collecting nanoparticles in water
from non-sooting regions of ethylene/air laminar flames;
13
the elec-
trooxidation of carbon nanotubes
14
or graphite;
9,15,16
the laser abla-
tion of graphite;
3,4,8,17
high temperature treatment of resols tethered
on silica nanospheres;
5
the dehydration of carbohydrates by
concentrated sulfuric acid to form carbonaceous materials;
18
the
thermal oxidation of citrate acid and sodium 11-amino-undecanoate
molecular precursors at 300 Cinair;
19
the microwave pyrolysis of
glucose solution in PEG
200N
solution
20
and the laser irradiation of
a suspension of graphite powders in PEG
200N
solvent.
21
Most of these
methods require surface passivation reagents,
3–5,8,17–21
and the repor-
ted quantum yields for carbon nanoparticles without surface
passivation are relatively low (1%).
7,9,11,12
Additionally, these
methods usually involve tedious processes,
3–5,7,8,10,12,17,18
expensive
starting materials,
1,6,10,11,14
or harsh synthetic conditions,
1,5,6,13,19
which
severely limit the availability of large quantities of the luminescent
carbon nanomaterials for practical applications. Thus, the develop-
ment of simple, cost-effective and environmentally friendly method
for large scale synthesis of fluorescent carbon dots still remains
challenging. Herein, we report a facile, economic and green one-step
microwave synthesis route towards photoluminescent carbon dots.
Our preparation requires a carbohydrate (glycerol, glycol, glucose,
sucrose, etc.) and a tiny amount of an inorganic ion and can finish in
just a few minutes. A characteristic feature of this method is that no
surface passivation reagent is needed. Additionally, the photo-
luminescence intensity of the as-synthesized carbon dots do not
change at the physiological and pathological pH range of 4.5–9.5 and
show no photobleaching. Furthermore, these carbon dots enter into
cells and can be used for photoluminescence-based cell-imaging
applications.
Carbohydrates have been widely used to produce carbon mate-
rials owing to their sustainability,
18,20,22–28
but few of these materials
show strong photoluminescence.
18,20
Glycerol (70% (v/v)) was mixed
with 7.1 mM phosphate solution (pH 7.4) and heated in a domestic
microwave oven (750 W) for 14 min. As shown in Fig. 1a, the
emission spectra of the as prepared carbon dots were broad, ranging
from 430 (blue) to 525 nm (yellow), with a dependence on the
excitation wavelengths; the carbon dots exhibited blue, yellow and
red photoluminescence under ultraviolet (330–385 nm), blue (450–
480 nm) and green (510–550 nm) light excitation (Fig. 1b). AFM
was used to observe the formed carbon dots and showed the carbon
dots have height around 2.1 0.76 nm (Fig. 1c and 1d). It should
be noted that pure glycerol solution after being treated with 20 min
microwave remained clear and no apparent photoluminescence was
observed. Since neither glycerol nor phosphate is emissive in the
visible and near-UV range, the bright and colorful photo-
luminescence emission must thereforebeattributedtotheformed
carbon dots. A typical luminescence lifetime (s) was also measured
(Figure S1, ESI†), where a value of 8.00 0.07 ns was obtained.
FT-IR spectra (Fig. 2a) were used to identify the functional groups
present on carbon dots. New bands at 1743 and 1597 cm
1
were
attributed to carboxyl groups and aromatic C]C vibrations,
a
Laboratory of Chemical Biology, Division of Biological Inorganic
Chemistry, State Key Laboratory of Rare Earth Resource Utilization,
Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun, Jilin, 130022, China. E-mail: xqu@ciac.jl.cn; Fax:
+86-431-85262656
b
Graduate School of the Chinese Academy of Sciences, Chinese Academy of
Sciences, Changchun, Jilin, 130022, China
† Electronic Supplementary Information (ESI) available: Experimental
details and supporting figures. See DOI: 10.1039/c0jm02963g/
This journal is ªThe Royal Society of Chemistry 2011 J. Mater. Chem., 2011, 21, 2445–2450 | 2445
Dynamic Article LinksC
<
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2011, 21, 2445
www.rsc.org/materials COMMUNICATION
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
/ Journal Homepage
/ Table of Contents for this issue
respectively. The presence of carboxyl groups offers various surface
modifications for potential applications in drug delivery and
biomedical imaging. The broad and intense peak centered at
3370 cm
1
, and the bands in the range of 1000–1300 cm
1
which
include the C–OH stretching and –OH bending vibrations imply the
existence of large numbers of residual hydroxyl groups. These func-
tional groups improve the hydrophilicity and stability of the carbon
dots in aqueous systems. As shown in Fig. 2b, the photoluminescence
intensity of carbon dots did not change with ion strength, indicating
that the carbon dot aqueous solution was stable. Unlike the carbon
dots reported by Liu et al.
12
and Zhao et al.,
9
the photoluminescence
intensity of the carbon dots synthesized here is pH independent at the
physiogical and pathological pH range of 4.5–9.5 (Fig. 2c). Addi-
tionally, the carbon dots show excellent photostability, as the pho-
toluminescence intensity did not change even after continuous
excitation with a 150 W Xe lamp (Fig. 2d). Moreover, the inhomo-
geneity of the photoluminescence of the carbon dots can be exploited
for optical labeling to allow the selection of different emission colors
with different excitation wavelengths.
17
All these features make
carbon dots good candidates for biological labeling, bioimaging or
other biomedical applications. Photoluminescence microscopic
observation (Figure S2, ESI†) showed that the carbon dots could
readily enter into E. coli and 293T cells and be used for biolabeling
and bioimaging.
To elucidate the factors influencing carbon dots formation, the
effect of microwave time was firstly investigated. As shown in
Figure S3a (ESI†) with the increase in microwave treatment time,
the glycerol solution turned brown and the UV-visible absorption
peak at around 260 nm of the resulting carbon dots shifted to
shorter wavelengths (4 min, 265.5 nm /14 min, 253.5 nm). AFM
analysis showed the mean height of carbon dots synthesized after
7 min and 14 min microwave treatment was 1.1 0.42 nm
(Figure S4, ESI†) and 2.1 0.76 nm (Fig. 1c and Figure 1d),
respectively. As indicated in Figure S3b (ESI†) the photo-
luminescence of the glycerol solution increased with reaction time,
but the normalized photoluminescence emission spectra could be
almost superposed and no apparent quantum confinement effect
was observed. These results indicate that the photoluminescence is
most likely to result from the dot surface, where emissive energy
trap sites are located.
5,17,20,21
In contrast to previous reported
methods,
3–5,8,17–21
no surface passivation agents and passivation steps
are incorporated in this green microwave synthesis route. Through
microwave pyrolysis, the carbohydrate is carbonized which results
in the formation of carbon dots; meanwhile, their surfaces have
oligosaccharide and aliphatic chains due to the partial dehydration
and condensation of the carbohydrate.
25,29
These functional groups
stabilize the surface energy traps and make them emissive. As
shown in Figure S5 (ESI†) in contrast to photoluminescence
intensity, which monotonically increased with microwave time, the
relative quantum yield of carbon dots firstly increased with
increasing of reaction time and then significantly decreased. This
result indicated that the carbon dots have strong photoluminescence
only when they are small enough, which is consistent with previous
studies.
7,12,17
Fig. 1 (a) Photoluminescence emission spectra (with progressively
longer excitation wavelengths from 320 nm to 480 nm in 20 nm incre-
ments) of carbon dots (microwave pyrolysis condition: 70% glycerol,
7.1 mM phosphate, 14 min). In the inset, the emission spectral intensities
are normalized. (b) Photoluminescence photographs of carbon dots in
water under ultraviolet (330–385 nm), blue (450–480 nm) and green (510–
550 nm) light excitation; the picture was taken by an Olympus BX-51 optical system microscope (Tokyo, Japan). (c, d) AFM characterization
of the as prepared carbon dots.
2446 | J. Mater. Chem., 2011, 21, 2445–2450 This journal is ªThe Royal Society of Chemistry 2011
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
Inorganic ions have been demonstrated to effectively accelerate
the carbonization of carbohydrates.
24,30
Therefore, we subsequently
examined the role of inorganic ions in carbon dots formation. As
shown in Figure S6 (ESI†) with the increase of phosphate salt,
the absorption band at around 260 nm of the carbon dots’
bathochromic shift decreases (7.1 mM, 262 nm /35.7 mM,
254 nm). Meanwhile, as indicated in Figure S7 (ESI†) the pho-
toluminescence intensity and quantum yield of the produced
carbon dots increased with reaction time, but the photo-
luminescence emission peaks only slightly red shifted (7.1 mM,
440 nm /35.7 mM, 450 nm). By selecting quinine sulfate as the
standard, the photoluminescence quantum yield for the carbon
dots synthesized by 70% glycerol in the presence of 35.7 mM
phosphate salt with 12 min of microwave treatment was measured
and calculated to be 3.2%. The results indicate that the phosphate
salt catalyzes the carbon dots formation. Though the amount of
phosphate salt affects the formation rate and quantum yield of
carbon dots, it does not significantly affect the photoluminescence
characteristic of the carbon dots.
We also systematically investigated the effect of different valence
cations and anions on the carbon dots formation. As shown in
Fig. 3, both the formation rate and quantum yield of carbon dots
increased with the increasing valence of the cation or anion.
Compared to monovalent ions, divalent and trivalent ions show
much greater ability to catalyze carbohydrate carbonization and
carbon dot formation. The photoluminescence emission peak of the
carbon dots blue shifts with the increase in valence of the cation,
while it slightly red shifts with the increasing of valence of anions. As
expected, we found that carbon dots catalyzed by both divalent
cation and divalent anion (CuSO
4
) catalysts show very strong
fluorescence (Figure S8, ESI†) and the quantum yield was calculated
to be 9.5%, which is much higher than that of reported carbon dots
without surface passivation,
7,9,11,12
and is comparable to that of
previous reported ligand protected cardon dots.
5,17–21
It has been
known that H
+
catalyzes carbohydrate carbonization.
24,31
As shown
in Figure S9 (ESI†) H
+
can also catalyze carbohydrate to form
carbon dots, and a dose and time dependence was observed
(Figure S10, ESI†).
Fig. 2 (a) FT-IR spectra of glycerol and carbon dots. (b) Effect of salt concentration on the photoluminescence intensity at 450 nm (l
ex
¼360 nm) of
the carbon dots. (c) Effect of pH on the photoluminescence intensity at 450 nm (l
ex
¼360 nm) of carbon dots. At pH 4.5, 5.5 and 6.5, the 10 mM
phosphate buffer was used while at pH 7.5, 8.5 and 9.5, 10 mM Tris buffer was chosen. All the values are the average of triplicate measurements. (d)
The time-dependence of photoluminescence intensity at 450 nm (l
ex
¼360 nm) of carbon dots and a commercial dye 40,6-diamidino-2-phenylindole
(DAPI).
This journal is ªThe Royal Society of Chemistry 2011 J. Mater. Chem., 2011, 21, 2445–2450 | 2447
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
To investigate whether this microwave assisted photoluminescent
dots synthesis can be applicable to other systems, we also used glycol,
glucose and sucrose as the starting carbohydrate. As indicated in
Fig. 4, similar to carbon dots synthesized from the glycerol, the
carbon dots prepared from glycol, glucose or sucrose luminesce and
their emissions depended on the excitation energy. The quantum yield
for these carbon dots varied with the starting carbohydrate material
and that for carbon dots synthesized from 70% glycol in the presence
of 10 mM AlCl
3
with 14 min microwave treatment was 5.8%. In
parallel control experiments, where no inorganic ions were added, no
apparent photoluminescence was observed. Together, these results
demonstrate that this microwave assisted carbon dot synthesis
method has generality. The influence of the starting materials on the
luminescence characteristics of carbon dots was also investigated. The
results in Figure S11 (ESI†) show that photoluminescence spectrum
of carbon dots derived from glycol significantly blue shift compared
to those of carbon dots derived from glucose, glycerol and sucrose
and indicated that different starting materials resulted in the carbon
dots with different photoluminescence. Thus, it is possible to tune the
luminescence from the carbon dots by changing the starting mate-
rials.
In summary, we have developed a general and simple microwave
synthesis method to produce multicolor photoluminescent carbon
dots. In comparison to the previous reported synthesis methods, three
features become apparent: 1) our approach does not need surface
passivation regents; 2) the synthetic approach utilizes carbohydrate as
the starting materials and is a green method; 3) the carbon dots
synthesis is kitchen chemistry and does not involve special equipment
and harsh synthesis conditions. As the synthesized carbon dots are
biologically compatible and show favorable optical properties,
they are promising imaging agents in biomedical and imaging
applications.
Acknowledgements
This work was supported by NSFC (20831003, 90813001,
20833006, 90913007), 973 Project 2011CB936004 and Funds from
CAS.
Fig. 3 Absorption spectra (a, c) and photoluminescence emission spectra excited at 340 nm (b, d) of carbon dots synthesized from 70% glycerol in the
presence of 10 mM different valence cations (a, b) or anions (c, d) with 15 min microwave pyrolysis. The samples are diluted with water and recorded on
a spectrometer or fluorescence spectrometer. It should be noted that photoluminescence emission spectra (b, d) have been normalized to the absorbance
at 340 nm. The insets show the normalized photoluminescence emission spectra.
2448 | J. Mater. Chem., 2011, 21, 2445–2450 This journal is ªThe Royal Society of Chemistry 2011
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
Notes and references
1 C. C. Fu, H. Y. Lee, K. Chen, T. S. Lim, H. Y. Wu, P. K. Lin,
P. K. Wei, P. H. Tsao, H. C. Chang and W. Fann, Proc. Natl.
Acad. Sci. U. S. A., 2007, 104, 727–732.
2 X. Wang, L. Cao, F. Lu, M. J. Meziani, H. Li, G. Qi, B. Zhou,
B. A. Harruff, F. Kermarrec and Y.-P. Sun, Chem. Commun., 2009,
3774–3776.
3 L. Cao, X. Wang, M. J. Meziani, F. Lu, H. Wang, P. G. Luo, Y. Lin,
B. A. Harruff, L. M. Veca, D. Murray, S.-Y. Xie and Y.-P. Sun,
J. Am. Chem. Soc., 2007, 129, 11318–11319.
4 S. T. Yang, L. Cao, P. G. Luo, F. Lu, X. Wang, H. Wang,
M. J. Meziani, Y. Liu, G. Qi and Y. P. Sun, J. Am. Chem. Soc.,
2009, 131, 11308–11309.
5 R. Liu, D. Wu, S. Liu, K. Koynov, W. Knoll and Q. Li, Angew.
Chem., Int. Ed., 2009, 48, 4598–4601.
Fig. 4 Photoluminescence emission spectra of carbon dots produced from different carbohydrate sources. Microwave pyrolysis conditions: (a, b) 70%
glycol, 10 mM AlCl
3
, 14 min; (c, d) 20% glucose, 10 mM phosphate, 4 min; (e, f) 20% sucrose, 10 mM phosphate, 4 min. Insets show the UV-visible
absorption spectra of the corresponding carbon dots. Control represents the product of carbohydrate treated with the same procedure, but without the
addition of salt.
This journal is ªThe Royal Society of Chemistry 2011 J. Mater. Chem., 2011, 21, 2445–2450 | 2449
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
6 S. J. Yu, M. W. Kang, H. C. Chang, K. M. Chen and Y. C. Yu, J. Am.
Chem. Soc., 2005, 127, 17604–17605.
7 S. C. Ray, A. Saha,N. R. Jana and R. Sarkar, J. Phys. Chem. C, 2009,
113, 18546–18551.
8 S.-T. Yang, X. Wang, H. Wang, F. Lu, P. G. Luo, L. Cao,
M. J. Meziani, J.-H. Liu, Y. Liu, M. Chen, Y. Huang and
Y.-P. Sun, J. Phys. Chem. C, 2009, 113, 18110–18114.
9 Q. L. Zhao, Z. L. Zhang, B. H. Huang, J. Peng, M. Zhang and
D. W. Pang, Chem. Commun., 2008, 5116–5118.
10 V. N. Mochalin and Y. Gogotsi, J. Am. Chem. Soc., 2009, 131, 4594–4595.
11 X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker and
W. A. Scrivens, J. Am. Chem. Soc., 2004, 126, 12736–12737.
12 H. Liu, T. Ye and C. Mao, Angew. Chem., Int. Ed., 2007, 46, 6473–
6475.
13 A. Bruno, C. de Lisio, P. Minutolo and A. D’Alessio, Combust.
Flame, 2007, 151, 472–481.
14 J. Zhou, C. Booker, R. Li, X. Zhou, T.-K. Sham, X. Sun and Z. Ding,
J. Am. Chem. Soc., 2007, 129, 744–745.
15 J. Lu, J. X. Yang, J. Z. Wang, A. Lim, S. Wang and K. P. Loh, ACS
Nano, 2009, 3, 2367–2375.
16 L. Zheng, Y. Chi, Y. Dong, J. Lin and B. Wang, J. Am. Chem. Soc.,
2009, 131, 4564–4565.
17 Y. P. Sun, B. Zhou, Y. Lin, W. Wang, K. A. S. Fernando, P. Pathak,
M. J. Meziani, B. A. Harruff, X. Wang, H. Wang, P. G. Luo,
H. Yang, M. E. Kose, B. Chen, L. M. Veca and S.-Y. Xie, J. Am.
Chem. Soc., 2006, 128, 7756–7757.
18 H. Peng and J. Travas-Sejdic, Chem. Mater., 2009, 21, 5563–5565.
19 A. B. Bourlinos, A. Stassinopoulos, D. Anglos, R. Zboril,
V. Georgakilas and E. P. Giannelis, Chem. Mater., 2008, 20, 4539–
4541.
20 H. Zhu, X. Wang, Y. Li, Z. Wang, F. Yang and X. Yang, Chem.
Commun., 2009, 5118–5120.
21 S. L. Hu, K. Y. Niu, J. Sun, J. Yang, N. Q. Zhao and X. W. Du,
J. Mater. Chem., 2009, 19, 484–488.
22 M. M. Titirici, A. Thomas and M. Antonietti, Adv. Funct. Mater.,
2007, 17, 1010–1018.
23 M. M. Titirici, A. Thomas, S. H. Yu, J. O. Muller and M. Antonietti,
Chem. Mater., 2007, 19, 4205–4212.
24 M.-M. Titirici, T. Arne and M. Antonietti, New J. Chem., 2007, 31,
787–789.
25 X. Sun and Y. Li, Angew. Chem., Int. Ed., 2004, 43, 597–601.
26 V. L. Budarin, J. H. Clark, J. J. E. Hardy, R. Luque, K. Milkowski,
S. J. Tavener and A. J. Wilson, Angew. Chem., Int. Ed., 2006, 45,
3782–3786.
27 R. Demir-Cakan, N. Baccile, M. Antonietti and M.-M. Titirici, Chem.
Mater., 2009, 21, 484–490.
28 Q. Wang, H. Li, L. Chen and X. Huang, Carbon, 2001, 39, 2211–
2214.
29 N. Baccile, G. Laurent, F. Babonneau, F. Fayon, M.-M. Titirici and
M. Antonietti, J. Phys. Chem. C, 2009, 113, 9644–9654.
30 S. H. Yu, X. J. Cui, L. L. Li, K. Li, B. Yu, M. Antonietti and
H. C. C
olfen, Adv. Mater., 2004, 16, 1636–1640.
31 J. P. Schuhmacher, F. J. Huntjens and D. W. van Krevelen, Fuel,
1960, 39, 223–234.
2450 | J. Mater. Chem., 2011, 21, 2445–2450 This journal is ªThe Royal Society of Chemistry 2011
Published on 18 January 2011. Downloaded by University of Colorado at Boulder on 14/03/2014 03:20:24.
View Article Online
... Another method is the Combustion Method, which employs combustion processes to produce CQDs from CQDs produced via microwave radiation typically exhibit broad absorption features that can be modified based on changes in size and surface modifications. This is advantageous for applications that require specific light absorption profiles [41]. ...
... Lastly, the Microwave Irradiation Method utilizes microwave irradiation to synthesize CQDs from carbon sources. The absorption spectra of [41] experimentally substantiated by Qu et al.'s research [51]. Through a one-step microwave synthesis approach, they successfully generated CQDs housing both categories of hybridized carbon atoms. ...
Article
Full-text available
Organic nanoparticles, especially carbon quantum dots (CQDs), have become a focal point of research due to their unique properties and extensive applications in various fields, especially in medicine. This review provides a comprehensive overview of the synthesis, structural properties, and therapeutic potential of CQDs. Synthesis methods for CQDs are categorized into top-down and bottom-up approaches, each with distinct advantages and limitations. The structural characteristics of CQDs, characterized by a core-shell configuration and functionalized surface groups, significantly influence their optical properties and biocompatibility. In therapeutic applications, CQDs show great promise in drug delivery, gene therapy, bioimaging, and cancer treatment. Their small size, low toxicity, and customizable surface chemistry facilitate targeted delivery systems that can cross biological barriers such as the blood-brain barrier. In addition, CQDs are being used in innovative cancer therapies such as photodynamic and photothermal treatments. This review highlights the evolution of CQDs research from their serendipitous discovery to their current status as versatile nanomaterials with significant implications for the advancement of healthcare technologies. By elucidating the synthesis methods, structural properties, and diverse applications of CQDs, this review aims to highlight their potential as transformative agents in therapeutic contexts.
... Of all the CQDs, N-CQDs, B-CQDs, and S-CQDs, green N-CQDs would be a good contender for numerous biological applications since they have high prolonged fluorescence as well as high water dispersibility and biocompatibility [125,126]. High contrast imaging of more than one of these MCF-7, live/dead C. elegans [100], HeLa cells [127], DU154 cells [128], cancer cells [129], zebra fish [129], human anaplastic thyroid cancer cell line [130], normal mouse fibroblast cell line [130], 3T3 cells [131], hepatic stellate cells [132], entire body of worms [124] have been reported using multicolour CQDs. Red emission of CQDs is preferred compared to [137] Recent research on MCQDs focuses on enhancing stability through surface functionalization and heteroatom doping to improve photostability and prevent aggregation. ...
Article
Full-text available
Incredible properties of quantum dots (QDs) have once again been acclaimed with this year’s (2023) Nobel prize in chemistry. On the other hand, the invention of multicolour molecular imaging of cell surface receptors for tumour diagnosis by Koyama and group has opened up a new era in diagnostics. Among them carbon quantum dots (CQDs) are interesting class of fluorescent nanomaterials, superior in terms of low toxicity, high solubility and biocompatibility along with simple and cost-effective synthesis processes unlike the traditional metal chalcogenide or perovskite quantum dots. Multi emissive fluorescence property of these carbon quantum dots are very useful in multiplex sensing. Their excellent biocompatibility and low toxicity have attracted researchers to use them extensively for biosensing and imaging of multiple analytes at a time. Core state emission from π-domains and surface state emissions of functional groups surrounding CQDs play a major role in achieving the multicolour emissions and this review discusses the various strategies used to achieve desired multi colour emissions, yet preserving their stability, non-interactive emissive states and quantum yields. Their fine tuning via variation in temperature, pH, time, and heteroatom doping has been comprehensively discussed. A thorough history compared to a list of characteristics for creating effective multicolour CQDs will point us in the proper route. This minireview also assesses the electronic band structure of these multicolour CQDs, their stability with respect to multi emissions, photoluminescence quantum yields, approaches employed for tunability of their optical band gaps, and also enhancement of carrier lifetimes, to arrive at conclusions on the reliability of these materials for multiplexing. The mechanisms namely chemical coupling, FRET, On-Off, Ab-antigen interactions involved in sensing mechanisms involving these materials are analysed in depth. Ultimately, the present obstacles and future directions for the use of these CQDs in sensing applications are discussed. Graphical Abstract
... These techniques include arc discharge, chemical oxidation, sonication, hydrothermal methods, and others ( Figure 10). 144,146,[153][154][155] Bottom-up approaches for synthesizing CQDs mean constructing the material from precursor molecules, yielding particles with consistent sizes and Figure 10 Various preparation methods can be employed to obtain CQDs, utilizing different carbon sources and synthesis procedures. The most usual division of preparation methods are top/down and bottom-up methods. ...
Article
Full-text available
Photodynamic therapy (PDT) is a non-invasive therapy that has made significant progress in treating different diseases, including cancer, by utilizing new nanotechnology products such as graphene and its derivatives. Graphene-based materials have large surface area and photothermal effects thereby making them suitable candidates for PDT or photo-active drug carriers. The remarkable photophysical properties of graphene derivates facilitate the efficient generation of reactive oxygen species (ROS) upon light irradiation, which destroys cancer cells. Surface functionalization of graphene and its materials can also enhance their biocompatibility and anticancer activity. The paper delves into the distinct roles played by graphene-based materials in PDT such as photosensitizers (PS) and drug carriers while at the same time considers how these materials could be used to circumvent cancer resistance. This will provide readers with an extensive discussion of various pathways contributing to PDT inefficiency. Consequently, this comprehensive review underscores the vital roles that graphene and its derivatives may play in emerging PDT strategies for cancer treatment and other medical purposes. With a better comprehension of the current state of research and the existing challenges, the integration of graphene-based materials in PDT holds great promise for developing targeted, effective, and personalized cancer treatments.
Chapter
Carbon quantum dots (CQDs) are nano-sized particles made of carbon with distinct optical, electronic, and chemical features. These particles can be produced using a range of environmentally friendly techniques, including the hydrothermal process, microwave-assistance, electrochemical methods, laser ablation, and the use of green precursors, solar energy, plant-based extracts, biomass, eco-friendly ligands, and solvents. These sustainable approaches minimize environmental harm while often resulting in CQDs with superior qualities for a wide range of uses. Their unique properties make them highly valuable in diverse sectors, including biomedical imaging, drug delivery systems, sensing technologies, photocatalytic processes, light-emitting devices, energy storage solutions, solar energy conversion, catalysis, optical labelling, and environmental surveillance. Ongoing research efforts are dedicated to finding more eco-conscious ways to manufacture CQDs.
Article
This work reports the synthesis of blue-emitting graphene quantum dots (GQDs) with an average diameter of 3.8 ± 0.5 nm from paddy straw, a sustainable biomass resource, via hydrothermal synthesis. These GQDs demonstrate excellent performance in bilirubin (BR) detection. The GQD photoluminescence (PL) intensity exhibits a proportional decrease with increasing BR concentration, indicating efficient quenching. The limit of detection for BR reaches a low value of 87.9 nM, highlighting the high sensitivity and selectivity of the GQD-based sensor. The observed quenching likely arises from a combined mechanism involving static quenching due to GQD-BR complex formation, inner filter effect (IFE), and Förster resonance energy transfer facilitated by spectral overlap.
Article
Full-text available
Fluorescent carbonnanoparticles (CNPs) were synthesized by laser irradiation of a suspension of carbon powders in organic solvent. The surface modification on the CNPs was fulfilled simultaneously with the formation of the CNPs, and tunable light emission could be generated by selecting appropriate solvents. The origin of the luminescence was attributed to carboxylate ligands on the surface of the CNPs.
Article
Full-text available
A chemical process, hydrothermal carbonization (HTC) of low value biomass, is discussed as a tool for the sequestration of atmospheric CO 2 . Via the available biomass, CO 2 can be transformed into an efficient deposited form of carbon, i.e. hardly degradable peat or carbonaceous soil. Currently, world crude oil production amounts to about 4 billion tons or 4 km 3 per year (official energy statistics of the US Government, http://www.eia.doe.gov/ipm/supply.html). Assuming a price of US-70abarrel,thiscorrespondstoavalueofUS70 a barrel, this corresponds to a value of US-1.76 trillion. As, essentially, all oil ends up— sooner or later—as CO 2 in the earth's system, the opposite side of this economy is the generation of an excess 12.5 billion tons of CO 2 per year, with the known implications on the world climate. The conventional discussion for handling this problem is to replace a minor part of the fuel and/or energy production by biomass schemes. This considers—beside direct combustion— the fermentation of carbohydrates to ethanol fuels, the cultiva-tion of oil seeds (''biodiesel''), or the generation of biogas via anaerobic digestion. 1 A very detailed analysis of the energy efficiencies, costs and biological impacts of such procedures was published by Gustavsson et al. as early as 1995. 2 For many years, sugarcane has been converted into ethanol in Brazil, replacing oil as a car fuel, which, however, turned out to be a highly inefficient process. Other countries, e.g. Sweden, try to become completely independent of oil imports through ''second generation'' biomass use, thus not only meeting their energy demand, but also significantly improving their CO 2 liberation footprint. However, in this context, it should be stated that biological fuel production schemes can only lower future increases in CO 2 emission, and cannot compensate for past and currently emitted CO 2 from fossil resources. Concerning climate change and the role of CO 2 therein, it would therefore be highly desirable to not only slow down further CO 2 emissions but also invert current development by sequestering the atmospheric CO 2 of past years of industrializa-tion. Not only is biomass a ''zero emission'' energy source, it also has the potential to generate a new chemical ''CO 2 disposal'' industry. This thought, as simple as it is, is only rarely accepted as a prerequisite for discussion. It also means that the search for new and efficient carbon deposits has to be perpetuated from a chemistry point of view. The biggest carbon converter, with the highest efficiency to bind CO 2 from the atmosphere, is certainly biomass. A rough estimate of terrestrial biomass growth amounts to 118 Â 10 9 tons per year, when calculated as dry matter. 3,4 Biomass, however, is just a short term, temporary carbon sink, as microbial decomposition liberates exactly the amount of CO 2 formerly bound in the plant material. Nevertheless, as biomass contains about 0.4 mass equivalents of carbon, removal of 8.5% of the freshly produced biomass from the active geosys-tem would indeed compensate for the complete CO 2 liberation from oil, all numbers calculated per year. To make biomass ''effective'' as a carbon sink, the carbon in it has to be fixed by ''low-tech'' operations. Coal formation is certainly one of the natural sinks that has been active in the past on the largest scale. Natural coalification of biomass takes place on a timescale of some hundred (peat) to hundred million (black coal) years. Due to its slowness, it is usually not considered in renewable energy exploitation schemes or as an active sink in CO 2 cycles. Never-theless, it is obvious that carbon fixation into coal is a lasting effort, as brown or black coal (on the contrary to peat) are obviously practically not biodegradable. The question of coa-lified carbon destabilization is, however, currently accessed in more detail. 5 Sufficient condensation of the carbon scaffold is, in any case, mandatory for the purposes of carbon fixation. It is therefore the purpose of this contribution to discuss the feasibility of turning coal formation into an active element of carbon sequestration schemes, simply by accelerating the under-lying coalification processes by chemical means. The natural process of peat or coal formation is presumably not biological but chemical in its nature. 6 As ''coaling'' is a rather elemental experiment, coals and tars have been made and used by mankind since the Stone Age, and one can find trials to imitate carbon formation from carbohydrates with faster chemical processes in the modern scientific literature. In this context, it is an exciting observation of soil research that the Indians of the Amazon basin used locally generated charcoal for the improve-ment of soil quality for hundreds of years (i.e. improving the water and ion binding of ''rich black'' soil) and that this carbon fraction was not easily decomposed. 7,8 Besides ''charcoal formation,'' which is performed with high quality, dry biomass only, hydrothermal carbonization (HTC)
Article
Hydrothermal carbonization is a convenient way to convert biomass at rather moderate conditions into carbonaceous nanostructures, here, mesoporous network structures. A structural view on the micro- and nanoscale reveals interesting features defining the usefulness and application possibilities of the resulting carbonaceous materials as supports and for sorption purposes. Whereas weakly connected plant tissues result in good yields of carbon nanoparticles with very small sizes where the porosity is mainly interstitial, "hard" plant tissue is structurally transformed into a carbon replica with a rather well-defined, bicontinuous mesopore structure.
Article
Fluorescent carbon nanoparticles (CNPs) 2−6 nm in size with a quantum yield of about 3% were synthesized via nitric acid oxidation of carbon soot, and this approach can be used for milligram-scale synthesis of these water-soluble particles. These CNPs are nanocrystalline with a predominantly graphitic structure and show green fluorescence under UV exposure. Nitric acid oxidation induces nitrogen and oxygen incorporation into soot particles, which afforded water solubility and a light-emitting property; the isolation of small particles from a mixture of different sized particles improved the fluorescence quantum yield. These CNPs show encouraging cell-imaging applications. They enter into cells without any further functionalization, and the fluorescence property of these particles can be used for fluorescence-based cell imaging applications.
Article
The present study concerns the one-step aqueous route production of carbonaceous materials loaded with carboxylic groups using hydrothermal carbonization of glucose in the presence of acrylic acid. This method provides a “green” solvent and surfactant free access to hydrophilic functionalized carbons with very good water dispersivity. The resulting materials were characterized using various methods including, FT-IR, Zeta Potential, N2 adsorption, Raman Spectroscopy, SEM, TGA, and 13C solid-state NMR. Among other possible applications of these types of materials, here, we discuss their use as adsorbents for heavy metals removal from aqueous solutions
Article
A study was conducted for synthesis of supported carbon dots by thermal oxidation of an ion-exchanged NaY zeolite. The study used chemical synthesis and photoluminescence properties of supported carbogenic dots. The study found that spherical carbogenic nanoparticles grafted onto the external surfaces of the zeolite. The study reported that these hybrids has the properties of zeolites with the photoluminescence of the supported carbon dots. The study confirmed that precursor to the carbon dots can be obtained by protanating amine groups of sodium 11-amino-undecanoate with citric acid. The study proved that thermal oxidation of the citrate salt at 300 °C in air produces a modified carbogenic nanoparticels with nominal composition. The study also found that nanoparticles shows a high concentration of carbosylate groups with sodium.
Article
Hierarchical carbon materials with functional groups residing at the surface are prepared for the first time by using nanostructured silica materials as templates in combination with hydrothermal carbonization at mild temperatures (180 °C). Different carbon morphologies (e.g., macroporous casts, hollow spheres, carbon nanoparticles, and mesoporous microspheres) can be obtained by simply altering the polarity of the silica surface. The surface functionality and hydrophilicity of the resulting materials are assessed by Fourier transform IR spectroscopy, X-ray photoelectron analysis, and water porosimetry. Raman spectroscopy and X-ray diffraction measurements show that the materials are of the carbon-black type, similar to charcoal.
Article
The bulk processing of novel metal/carbon nanohybrids was described under hydrothermal conditions using saccharides as the precursor. Various carboneous nanoarchitectures, such as nanocables, hollow tubes, and hollow spheres were readily produced. The realization of carbonization under mild hydrothermal conditions were expected to provide a unique approach for the future bulk synthesis and functionalization of various carbon-related nanomaterials of technical importance. A low-magnification transmission electron microscopy (TEM) image shows that the predominant morphology of the product obtained after treatment at 160°C for 12 h.