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108 Palesa Seele
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[130] Yu L. et al. Effective determination of Zn2+, Mn2+, and Cu2+ simultaneously by using dual-emissive
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[133] Li Y, Lee JS. Insights into characterization methods and biomedical applications of nanoparticle-
protein corona. Materials Basel. 2020, 13(14). doi: 10.3390/ma13143093.
Manoj Kumar Banjare✶, Kamalakanta Behera✶, Ramesh Kumar Banjare
https://t.me/medicina_free
and Siddharth Pandey
✶
Chapter 6
Carbon dots in nanozymes
Abstract: The new artificial enzymes called nanozymes, which are built on carbon
dots (CDs), were created to address several inherent problems with natural enzymes,
such as their costing of storeroom, structural volatility, and chemical sympathy.
Owing to their high catalytic activity, biocompatibility, and ease of surface fictionalizations, CDs have attracted a lot of attention in the recent years and are now being
considered potential replacements in the biomedical,bio-sensing,detection,and
green areas. CDs nanozymes have spurred an increase in the study because of their
superior catalytic properties, biocompatibility, and environmental friendliness. Although significant advancements have bee n made, no book chapter devoted to CDs
nanozymes has yet been published. In this chapter of the book, we examine the procedures and building blocks utilized to create CDs with enzyme-like behaviour. Additionally, the crucial problems and difficulties of studying nanozymes are covered. To
offer future research possibilities, current obstacles to the thriving conversion of CDs
to possible relevance are addressed.
Keywords: Carbon dots, nanozyme, chemosensing, catalytic activity, bioimaging, properties and applications of CD nanozyme
Acknowledgement: The authors are grateful to HOD MATS School of Sciences, MATS University, Raipur,
Chhattisgarh
Authors’ contribution: The manuscript was written through the contributions of all authors. All authors
have approved the final version of the manuscript.
Note: All authors declare no competing financial interest.
✶
Corresponding authors: Manoj Kumar Banjare, MATS School of Sciences, MATS University, Pagaria
Complex, Pandri, Raipur, Chhattisgarh 492004, India, e-mails: manojbanjare7@gmail.com,
manojbanjarechem111@gmail.com
✶
Corresponding authors: Kamalakanta Behera, Department of Chemistry, University
of Allahabad, Prayagraj, Uttar Pradesh 211002, India, e-mail: kamala.iitd@gmail.com;
✶
Corresponding authors: Siddharth Pandey, Department of Chemistry, Indian Institute of Technology
Delhi, Hauz Khas, New Delhi 110016, India, e-mail: sipandey@chemistry.iitd.ac.in
Ramesh Kumar Banjare, MATS College, MATS University, Aarang, Chhattisgarh 492004, India
https://doi.org/10.1515/9783110799958-006
110 Manoj Kumar Banjare et al.
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6.1 Introduction
Proteins make up the majority of enzymes, which are potent biocatalysts, with a few
catalytic RNA molecules tossed in for good measure [1, 2]. The primary function of enzymes i s to catalyse the modification of bio-molecules, and these reactions are frequently conceded out in calm conditions. The nature of industrial catalysts depends
on the high temperature and pressure, organic solvents, and settings with severe pH
levels [3, 4]. Due to their high catalytic activity and substrate selectivity, natural enzymes have found extensive usage in the industrialized, medicinal, and biological domains [7–12]. The main work of enzymes is to catalyse the alteration of bio-molecules,
and these processes typically take place under quiet circumstances [5, 6]. Unlike typical chemical or industrial catalysts, which are frequently used in difficult circumstances including h igh temperature, high pressure, organic solvents, and environments
with intense pH stage [3, 4], their potential uses in the realms of food processing, biosensing, environmental protection, biomedicine, and other areas ar e all constrained
by these disadvantages. To get around these problems, scientists have spent a lot of
time investigating synthetic enzyme imitators [15–17]. In previous investigations, it
has been demonstrated that many compounds, including fullerenes, cyclodextrins,
polymers, dendrimers, porphyrins, metal complexes, and numerou s bio- molecules,
can act as artificial enzymes [18–24].
While the identification of iron oxide (Fe
2007, numerous studies on synthetic enzymes based on non-material (referred to as
“nanozymes”)havebeencarriedout[25–30]. Nanozymes, which have nanoscale dimensions of 1–100 nm and its enzyme catalytic properties, are non-materials [41, 42]. To catalyse the same bio-catalytic events as enzymes, non-materials have inherent enzymatic
catalytic capabilities [43]. The advantages of both traditional chemical catalysts and biocatalysts are successfully combined by nanozymes. The discovery of non-material having inherent catalytic abilities has received the majority of attention recently since
realizing the potential applications of non-material is an intriguing field. Nanozymes
are superior to natural enzymes in that they are more affordable, highly stable, and
long-lasting [26–28, 43] (Table 6.1). The ability of some nanozymes to catalyse synthetic
bioprocesses like bio-orthogonal catalysis is even more exciting [44–46].
Based on these unique features, nanozymes have been applied in bio-sensing
[47–49], remediation of the environment [50, 51], identification and treatment of disease
[52–54], the use of antibacterial drugs [55–58], and cyto-protection against cellular biomolecules [59–61] (Figure 6.1). Table 6.1 displays the examples of research on carbon
dots (CDs) with enzyme-mimicking properties that were produced using each method.
) NPs as peroxides mimic in year
3O4
Chapter 6 Carbon dots in nanozymes 111
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Table 6.1: Doped CDs, pristine CDs, and CD-based hybrid nanozymes with enzyme-like activities.
CDs nanozyme Substrates Carbon precursor Synthesis
methods
Doped N-, Fe-CDs H
O
and
β-Cyclodextrin Hydrothermal PeroXidase []
TMB
Se-CDs H
GQDs/Fe
O
O
HO, TMB Graphene oXide Precipitation
Selenocystine Hydrothermal SuperoXide
procedure
CDs H
Au, N-CDs KO
N, S-CDs H
CD-based hybrid
, TMB β-Cyclodextrin Chemical
O
O
H
O
Citric acid Hydrothermal PeroXidase []
, TMB Citric acid Hydrothermal PeroXidase []
, TMB CHCOONa Hydrothermal PeroXidase []
Xidation
o
nanozymes, N-CDs, and
manganese o
Xide hybrids
o
GQDs KO
Pristine CDs
CDs
Xide/ferric
H
, ABTS Citric acid,
O
Anthracite and
bituminous coal
L-glutamine, succinic
L-glutamic acid,
acid,
Chemical
Xidation
o
Pyrolysis Pero
and glycine
Cu(II)/Cu
O/N-GQDs HO, ABTS Citric acid Pyrolysis PeroXidase []
Enzyme-
References
like
activity
[]
dismutase
(SOD)
PeroXidase []
Pero
Xidase []
Supero
Xide
[]
dismutase
(SOD)
Xidase []
112 Manoj Kumar Banjare et al.
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High
catalytic
activity
Large scale
production
Properties of
Nsnozymes
Multi -
functional
Tunable
Scheme 6.1: Properties of nanozymes.
Anti-
bacterial
High
stability
Economical
Cancer
Therapy
Environ-
mental
Protection
Figure 6.1: Recent applications of CD nanozymes.
Bio-
sensing
CDs
Nano-
zymes
Cryo-
protection
Chapter 6 Carbon dots in nanozymes 113
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• TYPE I
• Active metal
centre
mimic
• TYPE III
• Nanocomposites
Figure 6.2: Types of nanozymes based on their mode of natural enzyme-mimicking behaviour.
Transition
metal
compounds
eg Fe
3O4,
MnO
CeO
2,
2
Single atom
nanozymes
Bi-metallic
alloy with
etched
channels
Metal
nonoparticles
eg. Au, Ag, Pt, Id
Carbon
nanomaterials
eg. carbon dots,
fullerenes
Hybrid of Type I
and Type II
Metallic organic
frameworks
(MOFs)
• TYPE II
• Functional
mimic
•TYPE IV
•3D structural
mimics
6.2 Varieties of CD nanozymes
Over the past few decades, numerous nanomaterials have been shown to own basic
enzyme-like activity [13, 36–40]. The ability to catalyse a specific chemical reaction is
inherent to natural enzymes, usually at a single active site. For this analysis, we have
categorized nanozymes into four groups based on how closely they mimic the activity
of normal enzymes (Figure 6.2). One technique imitates the metal catalytic active site
found in metalloenzymes by using artificial metal sites (t ype I nanozymes), that is,
metal oxides (MOx) or metal sulphides [74]. Fe
nanozymes.
The oxidation of 2,2′ -azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS),
o-phenylenediamine dihydrochloride, and chromogenic 3,3′,5,5′-tetramethylbenzidine
(TMB) by hydrogen peroxide (H
) peroxidases was examined by Gao et al. [25]. The
2O2
highest catalytic activity was seen for the smallest Fe
300 nm), indicating that the peroxidase-like activity was induced by the Fe
particles’ vast surface area [62–64]. According to Gao et al. [25], the ferrous and fer-
ric ions in the nanoparticles mimicked the iron-heme-binding site in HRP. CeO
nanopar ticles use their metal as a nanozyme because the metal has structural and
biological properties that are similar to those of the iron ion, particularly in terms
of protein interaction [75]. CeO
nanoparticles are multi-functional catalysts that ex-
2
hibit, in addition to peroxidase-like activity, catalase- and dismutation of O
nanoparticle were used to carrier of
3O4
nanoparticles (30, 150, and
3O4
3O4
nano-
into O
2
2
2
114 Manoj Kumar Banjare et al.
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Zn
•Carbonic
anhydrase, alcohol
dehydrogenase,
organophosphate
hydrolase
•Catalase,
Fe
Mn
Cu
peroxidase,
cytochrome oxidase
Enolase,
hexokinase
Tyrosinase, lysyl
oxidase, laccase
Co
Figure 6.3: Instances of metalloenzymes.
and H2O2. Figure 6.3 shows copper, cobalt, and manganese ions, three common
metal-heme centres found in metalloenzymes (Table 6.2) [39–73].
Contrary to type I is metal compound nanoparticles, which mimic the metal-heme
redox centre of metalloenzymes, and type II nanozymes are metal nanoparticles that
catalyse the same processes as natural enzymes [77–79]. The metals used to make these
metal nanoparticles naturally stimulate a variety of heterogeneous reactions. These
metals include, but are not limited to, gold, silver, platinum, palladium, and iridium
[83–85]. According to Rossi and colleagues, under specific circumstances unprotected
“naked” nanoparticles with a diameter of 3.6 nm in the gold nanoparticles may behave as a glucose oxidase mimic by initially catalysing glucose oxidase-like processes
in the presence of high glucose [86]. Additionally, peroxidase activity was imitated by
gold nanoparticles [87, 88].
Gao and colleagues [89] found that silver, gold, palladium, and platinum nanoparticles have peroxidase-like activities at acidic pH and catalase-like activities at basic pH.
Nie and colleagues [90] subsequently investigated the pH-switchable phenomenon
•Dipeptidase
Chapter 6 Carbon dots in nanozymes 115
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using 1–2 nm platinum nanoparticles and found that under basic conditions, catalaselike activity was evident whereas under acidic conditions, peroxidase-like activity predominated [81, 82].
Table 6.2: Examples of metallozymes.
Centre metal Enzyme
Zinc Zn Organophosphate hydrolase, alcohol
dehydrogenase, carbonic anhydrase
Iron Fe Cytochrome oxidase, peroxidase, catalase
Manganese Mn Hexokinase, enolase
Copper Cu Laccase, lysyl oxidase, tyrosinase
Cobalt Co Dipeptidase
The capacity of metal-based nanozymes to create alloys with different elemental compositions is another noteworthy quality [91, 92]. As a result, alloy compositions, which are
categorized as type III nanozymes here, can be altered to tune the enzyme-mimicking
activities [93, 96–99]. They suggested that the electronic structure of alloying was responsible for the composition-dependent activity. To further improve multi-enzymatic activities, Yin and colleagues [94] showed an additional rise in multi-enzymatic activities
using Au–Pt bimetallic nanoparticles to exhibit peroxidase, oxidase, and catalase-like activities by altering the Pt and Au molar ratio. Ir–Pd nanocubes with increased peroxidase
activity were created by covering Pd nanocubes with an atomic layer of Ir [95]. Since the
Ir–Pd(100) surface had larger adsorption energy than the Pd(100), it was predicted that
the hydrogen peroxide’s breakdown into hydroxyl radicals would be more energyefficient. Kim et al. [100] co-doped graphene oxide with nitrogen and boron to further
reduce the bandgap and improve the peroxidase-like action, resulting in considerably better catalytic performance than undoped graphene oxide. Ren et al.’s [101] use of graphene
oxide quantum dots allowed them to show both peroxidase- and catalase-like activity
[102–105].
These restrictions restrict the broad range of uses for these typical nanozymes.
New methods for overcoming these limitations have therefore been developed, such as
the spatial or three-dimensional structural mimicry of actual enzyme active regions
[116, 117]. The geometry of pre-existing metal-binding centres, peripheral-binding sites,
or the constrained and empty space at the heart of natural enzymes is mimicked to construct these structural imitators (type IV nanozymes) [107–111]. In this design, the transition metal nodes holding the MOFs themselves can serve as biomimetic catalysts while
the high porosity structure created by the metal organic linkers can serve as substratebinding sites. MOFs exhibit great catalytic effectiveness because of their highly specialized surface areas, exposed active sites, and tuneable pore sizes [106] [114, 115].
116 Manoj Kumar Banjare et al.
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There were both peroxidase and catalase in the Co/2Fe-MOF, a bimetallic-MOF.
Furthermore, Min and colleagues [112] demonstrated that CeO
drolase mimic by releasing a chemical link with water. Similar to MOFs that have
been successfully used as reactive oxygen species (ROS) scavengers, Prussian Blue
nanoparticles can behave as multi-enzyme catalase-like activities, peroxidase, and superoxide dismutase, among others, are mimics [113].
-MOF functions as a hy-
2
6.3 Use cases for CD-based nanozymes
Carbon-based materials are essential for the advancement of material science. Modern industrial carbon (like carbon fibres and graphite), conventional industrial carbon (like activated carbon and carbon black), and innovative carbon nanomaterials
(like graphene and carbon nanotubes) are a ll forms of carbon nanotubes. Critical
claims in several industries, such as biomedicine, catalysis, optoelectronics, and anticounterfeiting, are made possible by these features [118–125].
6.3.1 Biomedical application of CD-based nanozymes
It should come as no surprise that biomedicine is one of the most exciting and wellreported uses of CDs. Studies on the in vitro cytotoxicity of a few different cell lines show
that CDs have little to no toxicity and good biocompatibility even at large dosages [170, 195].
CDs are therefore appropriate for biomedical applications. Because they are inexpensive,
compact size, customizable surface functionalities, high photostability, and potential as a
replacement for conventional fluorescent materials in illness detection, therapy, and healthcare supplements, CDs are also a prospective alternative to these materials [128, 130–133].
The CD biomedical applications covered in this section include nano-medicine,
phototherapy, drug/gene delivery, and bio-imaging. In biological applications, CD toxicity and biocompatibility are crucial elements. Most CDs could either break down or
be eliminated directly from the organism and were generally non-toxic at low quantities (like 10 g mL
makeup, and size. Increased amounts may interfere with organ development and
cause cell damage (188). Furthermore, because ROS are produced, CDs may not be poisonous in the dark but become hazardous when exposed to light (186) [127].
−1
) (181). CD toxicit y, however, varies for their quantity, molecular
6.3.2 Biomedicine application of CD-based nanozymes
There is a significant market for affordable, durable, and efficient antimicrobials. The
above-mentioned materials can be substituted with CD-based nanozymes due to their
Chapter 6 Carbon dots in nanozymes 117
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distinct electrical, optical, thermal, and mechanical capabilities. Some CDs with nitrogen
doping were made by Zhang et al. [32] to imitate oxidase action. Such CDs can quickly
replicate the oxidation reaction and successfully stop Salmonella and Escherichia coli
(E. coli) from growing (215). However, it did have anti-microbial action [136, 138–140].
6.3.3 Bio-imaging and bio-detection of CD-based nanozymes
Biological events are immediately and painlessly observed using probes and detectors
during the bio-imaging process. Images of plant tissue, microorganisms, and cells
have been captured on numerous CDs [162].
6.3.4 Detection of O
2
Most O2sensors have, up until recently, picked up superoxide anion generated by cells.
6.3.5 Detection of H2O
2
H2O2is a significant messenger molecule as a result of different biological processes.
The high peroxidase-like activity of GQDs is the cause of this. (Table 6.3) When employed as designed, the H
abilities for H
breakdown. A hybrid FePt and graphene oxide nanozyme with a
2O2
sensor demonstrated efficient electrochemical catalytic
2O2
2.2 M [132] detection limit was also developed by Chen et al. [129] for the sensitive detection of H
Chen et al. [129] reported colorimetric detection of H
Table 6.3: Summary of the application of CD-based nanozymes in detection [126].
Detection method Sample Detection limit Linear range References
Colorimetric
detection
– Glutathione – . μM[]
– – . μM .– μM[]
– Ascorbic acid nM – nM []
– – . μM .– μM[]
– Uric acid . μM – μM[]
– Pyrophosphate . nM – [] b
[137]. Using Pt/Pd nanodendrites based on graphene oxide nanozymes,
2O2
like this.
2O2
[]
H
O
. μM – µM,
µM– mM
[]
Years
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