Analytical Letters

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Synthesis, Characterization, and Applications of

Copper Nanoparticles

Muhammad Imran Din & Rida Rehan

To cite this article: Muhammad Imran Din & Rida Rehan (2017) Synthesis, Characterization,
and Applications of Copper Nanoparticles, Analytical Letters, 50:1, 50-62, DOI:
10.1080/00032719.2016.1172081

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ANALYTICAL LETTERS
2017, VOL. 50, NO. 1, 50–62
http://dx.doi.org/10.1080/00032719.2016.1172081

NANOTECHNOLOGY

Synthesis, Characterization, and Applications of Copper

Nanoparticles
Muhammad Imran Din and Rida Rehan
Institute of Chemistry, University of the Punjab, Lahore, Pakistan

ABSTRACT ARTICLE HISTORY

Copper nanoparticles with different structural properties and effective Received 18 January 2016
biological effects may be fabricated using new green protocols. The Accepted 25 March 2016
control over particle size and in turn size-dependent properties of KEYWORDS
copper nanoparticles is expected to provide additional applications. Biotemplate; copper
Various methods for the synthesis of copper nanoparticles have been nanoparticles; green
reported including chemical methods, physical methods, biological protocol; stabilization
methods, and green synthesis. Biological methods involve the use of
plant extracts, bacteria, and fungi. Commendable work has been done
regarding the synthesis and stability of copper nanoparticles. There is
a need to summarize the behavior of copper nanoparticles in different
media under various conditions. Here, a complete list of the literature
on the synthesis of copper nanoparticles, their properties, stabilizing
agents, factors affecting the morphology, and their applications is
presented. The importance of copper nanoparticles compared to
other metal nanoparticles are due to high conductivity. Methods for
the synthesis of copper nanoparticles, including green protocols using
plants and micro-organisms compared chemical methods, have also
been reviewed.

Introduction
Nanotechnology, scientific revolution of the twenty first century, has rapidly enhanced due
to elaboration and research all over the world. Foremost involvement in the progress of this
field is the formation of matter at the nanoscale (Sivakumar et al. 2011). Particles having
minimum one dimension, of 100 nm size at most, are nanoparticles. In the case of
quantum dots, they may have no dimensions (Hudlikar et al. 2012). Completely new
and enhanced properties are demonstrated by nanoparticles. Size, dispersal, and
morphology are the chief causes for the novel and enriched properties (Singh et al.
2011). Nanoparticles offer high surface to volume ratios (Awwad, Salem, and Abdeen
2012). Nanomaterials are divided into three categories on the basis of their origin: natural,
incidental, and engineered. Besides the classification on the basis of origin, there are metal
nanoparticles, their oxides, bimetallic, and other inorganic nanoparticles.
Nanostructures are classified as zero-, one-, two-, and three-dimensional structures.
Recently, quantum dots or quantum boxes are termed as zero dimensional due to their
reduced dimensions (Reed et al. 1988; Takagahara 1993). These are also semiconductor
nanocrystals (Wu, Aiello, et al. 2010). Translational symmetry is totally absent and carriers

CONTACT Muhammad Imran Din imrandin2007@gmail.com Institute of Chemistry, University of the Punjab,
Lahore 54590, Pakistan.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lanl.
© 2017 Taylor & Francis
 ANALYTICAL LETTERS 51

(electrons, holes) are totally confined in quantum dots (Takagahara 1993). Nanostructures
in one dimension possess one dimension in the nanoscale, although their remaining
dimensions may be extended. Nanostructures in three dimensions show all dimensions
at the nanoscale; i.e., colloids, precipitates, spherical nanoparticles, fullerenes, and
dendrimers (Zheng, Fan, and Stucky 2006). These exhibit revolutionizing catalytic,
magnetic (Easom et al. 1994), mechanical, absorption, sensitivity, and bioimaging features
as well as applications in the industrial, agricultural, and medical fields (Wu, Shen, et al.
2010). Nanomaterials may also act as lubricants. They are widely used in paints and
coatings, ceramics, batteries, clays, fuel cells, etc. Metal nanoparticles are of considerable
importance due to their numerous applications in various fields.

Metal nanoparticles
Faraday recognized the existence of metal nanoparticles and Mie gave a quantitative
explanation of their color. Metal nanoparticles are used in catalysis (Wunder et al.
2010), sensing (Homola, Yee, and Gauglitz 1999; Taton, Mirkin, and Letsinger 2000),
and optoelectronics (Maier et al. 2001) due to dependence of their absorption sensitivity,
electrical, medicinal, magnetic (Sun et al. 2000), and catalytic properties based on size,
shape, and structure. Copper, zinc, gold, magnesium, silver, and titanium nanoparticles
are of particular interest because of their antibacterial properties against Bacillus subtilis
and Staphylococcus aureus, applications in medicine, dental materials, water treatment,
sunscreen lotions, and coatings (Easom et al. 1994; Homola, Yee, and Gauglitz 1999;
Sun et al. 2000; Taton, Mirkin, and Letsinger 2000; Maier et al. 2001; Zheng, Fan, and
Stucky 2006; Wu, Shen, et al. 2010; Wunder et al. 2010).
Recently, metal, metal oxides, ceramic, silicate, and polymer nanoparticles have been
synthesized and used in several applications. Their small size and high surface area have
improved their use in material science and have increased their demand. Their properties
are size dependent and also depend upon surrounding medium of nanoparticles. The
required properties may be obtained by changing the environment of nanoparticles.
Copper nanoparticles have prospective applications in optics, electronics, and medicine
and in manufacturing of lubrications, nanofluids, conductive films, and antimicrobial
agents (Glavee et al. 1993; Liz-Marzán and Lado-Tourino 1996; Yu et al. 1997; Jana,
Gearheart, and Murphy 2001; Patel et al. 2005). The preference of copper nanoparticles
compared to silver is due to the lower cost of copper than silver, the physical and chemical
stability, and ease of mixing with polymers (Mallik et al. 2001). Smaller nanoparticles offer
higher activity but may result in cluster formation causing a decrease in essential properties
(Tolaymat et al. 2010).
Much work has been done regarding the synthesis and stability of copper nanoparti-
cles. There is a need to organize data reported up to date to summarize the behavior of
copper nanoparticles in different media under various conditions. Here, a review is
presented on the methods for the synthesis of copper nanoparticles, their properties,
factors affecting the morphology, and their applications. The importance of copper
nanoparticles above the other more stable metal nanoparticles lies in its high conductive
properties. Methods for the synthesis of copper nanoparticles mainly the green synthesis
using plants and micro-organisms in comparison to chemical methods have been
discussed in this article.
52 M. I. DIN AND R. REHAN

Properties of copper nanoparticles

Metal nanoparticles possess fascinating ultraviolet–visible sensitivity, electrical, catalytic,
thermal, and antibacterial properties due to the reasons: quantum effects and large
surface-to-volume ratio (Wang 2000). A large number of atoms are present on the
surface due to smaller particle size. The surface area-to-volume ratio of particles varies
by depending on the shape and size of nanoparticles, including the ultraviolet–visible
sensitivity and conductivity. The characteristic properties including the electronic energy
levels, electron affinity, electronic transitions, magnetic properties, phase transition
temperature, melting point, and affinity to polymers, biological and organic molecules
are also modulated by the change in surface area. Quantum effects are due to the combi-
nation of quantum size and Coulomb charging effects (Volokitin et al. 1996) that impart
the charge to nanoparticles. When the Coulomb charge effect is coupled with the quantum
size, a range of fascinating properties are obtained that are not observed for the same bulk
material. Quantum effects are prominent in spherical particles and in particles with sharp
edges. Due to these effects and their size-dependent nature, nanoparticles are used in
catalysis, sensing, and imaging.

Methods for the synthesis of copper nanoparticles

Physical and chemical approaches have been used to synthesize copper nanoparticles. The
microemulsion technique is the most common chemical approach; however, it involves use
of large concentration of surfactant and is expensive (El-Nour et al. 2010). Laser ablation,
aerosol techniques, and radiolysis are common physical methods to synthesize nanoparti-
cles but the use of expensive instruments and excessive energy consumption makes these
methods less popular (Thakkar, Mhatre, and Parikh 2010). Copper nanoparticles may be
synthesized by microwave irradiation in the absence of a stabilizing agent. The formation
of nanoparticles occurs by the addition of ascorbic acid through the preparation of copper
oxide (Galletti et al. 2013).
Copper nanoparticles are readily synthesized and stabilized using high surfactant
concentrations. Usually, the micelle formation occurs where the copper ions diffuse into
the micelles. The use of strong reducing agents causes decomposition to nanoparticles.
The size and shape may be controlled using this approach to directly affect the properties.
Commonly used surfactants are polysorbate 40 and polysorbate 60 (Mandal and De 2015).
However, this method leads to by-products that are of environmental concern. In
comparison to these methods, green synthesis of the copper nanoparticles is more safe
and environmental friendly. A summarized comparison of green and chemical methods
of synthesis is presented in Table 1.

Green methods of synthesis

Plant synthesis
Plants have been used for the synthesis of metallic nanoparticles due to their availability,
cost-effectiveness, environmental friendly nature, and nonhazardous by-products. Plant
extracts such as Terminalia arjuna bark have been used for the synthesis of copper nano-
particles. The synthesized nanoparticles were of 23 nm in size (Yallappa et al. 2013).
 Table 1. Summary of green and chemical methods for the synthesis and stabilization of copper nanoparticles and the size variation in response to reducing
agents and precursor salt.
Reducing Stabilizing Size of
Precursor agent entity nanoparticles Reference
Copper nitrate Terminalia arjuna bark extract Terminalia arjuna bark extract 23 nm (Yallappa et al. 2013)
Copper/surfactant complex Hydrazine hydrate Deprotonated polyacrylic acid 40–85 nm (Kaur et al. 2014)
Sodium borohydrate 50–54 nm
Copper nitrate Ascorbic acid Starch 5–12 nm (Valodkar et al. 2012)
Copper nitrate Ligand benzildiethylenetriamine 15–20 nm Chandra, Kumar, and Tomar (2014)
Copper acetate Sodium hydroxide Ascorbic Acid 7 nm Galletti et al. (2013)
Copper nitrate 9 nm
Copper nitrate Silica matrix 2–65 nm (Yeshchenko et al. 2007)
Copper ammonia Sodium borohydride Starch 40–80 nm (Suramwar, Thakare, and Khaty 2012)
complex
Copper nitrate Hydrazine hydrate Hexadecyltrimethyl ammonium 6 nm (Feng et al. 2015)
bromide
polyethylene glycol 8 nm
Tween-80 10 nm
Copper salt Sodium borohydride Polyamidoamine (Crooks et al. 2001)
polypropylene imine dendrimers
Copper sulfate Sodium borohydride trimesyl core dendrimer 3–5 nm (Jin et al. 2008)
Copper chloride sodium borohydride PolyN-isopropylacrylamide-co-methacrylic Farooqi et al. (2013)
acid microgels
Copper chloride Hydrazine hydrate Myristic acid (Khanna et al. 2007)
Sodium formaldehyde sulfoxylate
Copper nitrate T. arjuna bark Water 23 (Yallappa et al. 2013)
Copper sulfate Magnolia leaf extract Water 37–110 (Lee et al. 2011)
Copper sulfate Curd, milk, butter, lime juice, Water 20–50 (Sastry et al. 2013)
tamarind juice, soap nut
Copper sulfate Artabotrys odoratissimus Water 109–135 (Gajera 2014)
Copper sulfate Nerium oleander Water Gopinath et al. (2014)
Copper chloride L-Ascorbic acid Water 50–60 Asim et al. (2014)
Copper sulfate Datura metel leaf extract Water 15–20 (Parikh, Zala, and Makwana 2014)
Copper sulfate L-Ascorbic acid/potato starch Water 5–40 Suresh et al. (2013)
Copper sulfate Pseudomonas stutzeri Water 8–15 (Varshney et al. 2010)
Copper sulfate Pseudomonas stutzeri/electroplating Water 4–10 (Varshney, Bhadauria, and Gaur 2012)
technique
Copper sulfate Morganella bacteria Water 15–20 (Ramanathan, Bhargava, and Bansal 2011)
Copper ammonia Starch 40–80 nm (Suramwar, Thakare, and Khaty 2012)
complex
Copper nitrate Ascorbic acid/starch 5–12 (Valodkar et al. 2012)
Copper nitrate Ascorbic acid 7 Galletti et al. (2013)

53
Copper acetate 9
54 M. I. DIN AND R. REHAN

Magnolia leaf extract was used as a reducing and stabilizing agent for the synthesis of
copper nanoparticles (Lee et al. 2011). Using CuSO4 as a precursor and an aluminum-lined
reaction vessel, copper nanoparticles were reported to be prepared in the presence of curd,
milk, butter, soap nut, lime juice, and tamarind juice as capping agents in acidic solution
(Sastry et al. 2013).
Artabotrys odoratissimus (Nag Champa) has been also used as a reducing agent for the
synthesis of copper nanoparticles from CuSO4 at 95°C, which resulted in particles from 109
to 135 nm in size (Gajera 2014).The use of Nerium oleander and L-ascorbic acid as a
stabilizing and reducing agent has been reported in the literature (Asim et al. 2014;
Gopinath et al. 2014). Datura metel leaf extract was used at room temperature for the
preparation of nanoparticles (Parikh, Zala, and Makwana 2014). Potato starch has been
reported as a stabilizing agent for copper nanoparticles in the presence of L-ascorbic acid
as the antioxidant and NaOH as a catalyst (Suresh et al. 2013).

Microorganisms
The synthesis of copper nanoparticles has been reported using Pseudomonas stutzeri
bacteria that provided spherical particles (Varshney et al. 2010). The same bacteria from
wastewater have been used for the synthesis of copper nanoparticles using electroplating
that resulted in the formation of cubic nanoparticles (Varshney, Bhadauria, and Gaur 2012).
Another biological method has been reported for the synthesis of copper nanoparticles
using Morganella bacteria under aqueous physical environment to obtain polydispersed
nanoparticles (Ramanathan, Bhargava, and Bansal 2011).
Few papers have reported the preparation of copper nanoparticles using fungi. One
reported method used Aspergillus species for fungi-facilitated synthesis (Pavani et al.
2013). Penicillium vaksmanii, Penicillium aurantiogriseum, and Penicillium citrinum,
segregated from soil, have been used for the synthesis of copper nanoparticles, where
the monodispersity, pH, and concentration affected their morphology (Honary et al. 2012).

Mechanism of synthesis
Bimetallic nanoparticles as core shell structures or alloys show distinctive catalytic, optical,
and electronic properties compared to pure metallic nanoparticles. Microwave-assisted
synthesized copper–silver nanoparticles show considerable association. (Valodkar et al.
2011). The micelle formation associated with silver nanoparticles was reported to be
responsible for the stabilization of copper nanoparticles. The authors explained the mech-
anism and the role of silver nanoparticles in controlling the size of copper and possible
applications of this system as shown in Figure 1.
The mechanism of spherical nanoparticles involves micelle formation. There is an
electrostatic interaction between the head group of surfactant and the nanoparticles. The
entrapped ions are reduced under controlled conditions. In the chemical syntheses, an
electron donor–acceptor relationship is present between the nanoparticles and the reducing
agent. The magnetic dipole interactions in the micelles forms spherical nanoparticles. The
mechanism of green synthesis has not been completely reported to date; questions remain
whether micelle formation occurs or reduction and stabilization by biomolecules (Soomro
et al. 2013).
 ANALYTICAL LETTERS 55

Figure 1. Mechanism of copper nanoparticle preparation and bimetalic stabilization.

Some plant extracts have served as reducing and stabilizing agents for the synthesis of
nanoparticles. The synthesized nanoparticles are bare and not confined in a medium or
gel and their catalytic and other properties are be controlled, while micelle-stabilized
and microgel-stabilized nanoparticle properties may be controlled by the variation in
temperature and pH. Green stabilizing and reducing agents are reviewed in Table 1,
including the solvents, reducing agents, stabilizing agents, and their influence on the
nanoparticles size.

Role of polymer stabilizing agents on copper nanoparticles

Starch may serve as a stabilizing agent for aqueous bimetallic nanoparticles. The stability is
not long lasting in aqueous solution due to the tendency of copper nanoparticles to form
oxides (Valodkar et al. 2011). Chitosan offers good stabilization compared to starch owing
to its ability to form chemical bonds with metals. The use of chitosan as a stabilizing agent
increases the stability of metal nanoparticles (Muzzarelli 2011). Copper–silver nanoparti-
cles are stabilized by protonized chitosan that prevented coagulation (Zain, Stapley, and
Shama 2014). Polyacrylic acid and polymethacrylic acid are used as stabilizers for copper
nanoparticles. They form small nanoparticles whose size may be controlled by changing
the preparation conditions (Kaur et al. 2014). Musa et al. (2016) synthesized copper nano-
particles and stabilized them in cellulose. The synthesized nanoparticles were nanocrystal-
line and showed decreased stability with an increasing concentration of the precursor salt.
The role of starch for the synthesis and stability of copper nanoparticles was studied by
(Gholinejad et al. 2016). The prepared system was used due to the suitable catalytic activity.

Effect of preparation conditions on nanoparticles

Free surface electrons of uncapped nanoparticles are highly reactive which makes and may
promote aggregation. The stability, functionality, and applications are significant for the
incorporation of nanoparticles with biological molecules (Valodkar et al. 2012).
The morphology of nanoparticles is highly affected by the precursor salt. Fibrous nano-
particles increase in size whether the salt is copper acetate, copper chloride, or copper
56 M. I. DIN AND R. REHAN

sulfate in the presence of NaOH. The shape and size are both affected when ascorbic acid is
used as a reducing agent. Rod-shaped nanoparticles vary in size and shape to triangular or
tetrahedron and spherical shaped for copper acetate, copper chloride, and copper sulfate,
respectively (Shankar and Rhim 2014).
Chandra characterized the effect of solvent on the size of copper nanoparticles. They
explored ethanol as the optimum solvent for the synthesis of copper nanoparticles.
Dimethyl sulfoxide, acetonitrile, cyclohexane, water, and methanol offer polydispersity
and lower stabilization. Here, it is noteworthy that water is the least suitable solvent for
the copper nanoparticles as their size distribution is the highest (Chandra, Kumar, and
Tomar 2014).
The optimization of reducing agent’s concentration has also been reported in the litera-
ture. The reducing agent affects the size of copper nanoparticle as high concentrations may
decrease the size while maintaining the concentration of the precursor. The reducing agent
should be at least five times more concentrated compared to the precursor (Chandra,
Kumar, and Tomar 2014). The nucleation rate is also related to the concentration of the
reducing agent. Soomro et al. (2013)reported that increasing concentration of reducing
agent causes reduced monodispersity and the number of nanoparticles is increased. The
effect of reducing agent concentration is summarized in Figure 2.
The stabilizing agent or the surfactant also affects the size of nanoparticles. The micelle
formation stabilizes the nanoparticles and makes the system monodispersive and stable in
air (Soomro et al. 2013). Copper nanoparticles prepared by microwave irradiation are
influenced by the irradiation time; a linear relationship was observed between particle size
and time (Yallappa et al. 2013)
The pH is the most important factor that affects the size of nanoparticles. Acidic
solution supports smaller nanoparticles; i.e., as the pH of reaction mixture is increased,
the size of nanoparticles also increases. A marked increase in size appears above pH 5.
Copper nanoparticles are not present at higher pH, rather copper nanoparticle oxides
are formed due to excess hydroxide. Further increases in pH produce copper hydroxide

Figure 2. Influence of the concentration of reducing agent upon the size and dispersity of copper
nanoparticles.
 ANALYTICAL LETTERS 57

without nanoparticle formation (Soomro et al. 2013). However, some papers have reported
the formation of copper nanoparticles at pH values from 9 to 11. As the pH is increased,
the concentration of hydroxide increases leading to the formation of copper hydroxide.
This explains the formation of copper nanoparticles in basic solution.

Characterization
Copper nanoparticles have been characterized by ultraviolet–visible absorption spec-
troscopy, X-ray diffraction (Sasaki et al. 2016), scanning electron microscopy (Chan
et al. 2007; Khanna et al. 2007; Park et al. 2007; Lee et al. 2008), transmission electron
microscopy (Hambrock et al. 2002; Zhu, Zhang, and Yin 2004; Yeshchenko et al. 2007;
Yoon et al. 2007; Ruparelia et al. 2008), atomic force microscopy (Male et al. 2004; Chan
et al. 2007), and infrared spectroscopy.
Ultraviolet–visible spectroscopy is used because the absorption peak positions are
dependent upon particle size and shape (Chen and Sommers 2001). Copper nanoparticles
usually absorb from 280 to 360 nm. Ascorbic acid, a common reducing agent, provides
a shoulder peak from 240 to 280 nm (Shankar and Rhim 2014). Particles prepared by
microwave irradiation are usually spherical and show surface plasmon resonance at
535 nm (Yallappa et al. 2013). The nanoparticles are characterized by the absorption spec-
troscopy with a peak 580 nm. Infrared spectroscopy is used to characterize biomolecules
interacting with the copper nanoparticles (Shankar and Rhim 2014). Most commonly,
ethers, alcohols, and carbon–hydrogen bonds are responsible for the interaction of nano-
particles with biomolecules (Valodkar et al. 2012).

Applications of copper nanoparticles

A major threat to human health is water contamination by microbes so the number
disinfectant procedures have increased because some microbes are resistant to older anti-
microbial agents. Copper nanoparticles have been used as a disinfectant for wastewater
(Ruparelia et al. 2008). Copper nanoparticles stabilized on carbon, polymers, sepiolite,
and polyurethane foam provide effective antibacterial activity. Copper nanoparticles pro-
vide high affinity for surface active groups of bacteria and have been used for B. subtilis
(Ruparelia et al. 2008). Nanoparticles are also widely used as catalysts due to large
surface-to-volume ratio, constantly renewable surface, and changes in microelectrode
potential values. Stable copper nanoparticles offer suitable catalytic properties. The
mechanism of catalysis by copper nanoparticles is shown in Figure 3. Stabilized copper
nanoparticles are also suitable for dye reduction due to the number density of particles that
generally increases with the precursor concentration; the particle shape and organization,
as discrete spherical particles have highest catalyst activity as compared to honeycomb-
packed hexagonal nanoparticles; the composition of the nanoparticles as either the pure
copper or the oxides; and the size of nanoparticles, as the smaller the particle size, the
greater the catalytic activity.
Another requirement to ensure the optimum catalytic activity is increased reactant–
catalyst interaction. Copper oxide nanoparticles have lower activity as compared to pure
copper nanoparticles, but the activity is also affected by preparation conditions. The higher
activity of small nanoparticles may be explained on the basis of electropotentials; i.e., small
58 M. I. DIN AND R. REHAN

Figure 3. Mechanism of the catalysis of copper nanoparticles upon the reduction of nitroaromatics.

nanoparticles have large negative electropotentials (Mandal and De 2015). Polymer-

stabilized copper nanoparticles are the suitable catalysts for the reduction of nitrobenzene
(Kaur et al. 2014).
The effects of copper nanoparticles on fluorescent materials have also been reported.
Copper nanoparticles may cause fluorescence quenching, dye aggregation, dye deaggrega-
tion, and fluorescence enhancement. This property may be used for biosensing and
biolabeling(Mandal and De 2015). Copper-based drugs are widely used to destabilize
tumors and cancer cells. Copper nanoparticles may serve as screening agents for hemoglo-
binopathies, such as b-thalassemia, since the clusters precipitate with a human hemoglobin
mutant. High antithrombic activity and imaging applications of copper nanoparticles have
been explored. These materials have also been used for conducting applications (Hokita
et al. 2015).

Summary and outlook

Copper nanoparticles are among the most important and useful metal nanoparticles. They
are widely used as catalysts for various processes including catalytic reduction. In this
review, green methods have been summarized for the synthesis of copper nanoparticles
as their production and stabilization is difficult due to the formation of oxides. Green
sources for nanoparticles are preferable as these serve as the reducing and the stabilizing
moieties. The prepared nanoparticles show various plasmonic peaks depending on the
conditions. The reported applications demonstrate more applications than silver nano-
particles. However, copper nanoparticles are toxic, while silver is a noble metal.
All conditions for copper nanoparticle preparation have yet to be optimized, such as the
influence of pH. Some reports involve the synthesis at high pH, although greater formation
 ANALYTICAL LETTERS 59

of copper oxide or hydroxide is expected under these conditions. Hence, the behavior of
copper nanoparticles should be characterized across a wide range of pH values. Various
techniques have been used to characterize the mechanism of green synthesis. Polymeric
stabilized systems have less explored for copper nanoparticles, so this area requires
attention. Considerable characterization of the cytotoxicity of the copper nanoparticles
has been performed, but their use as electrodes and electronic applications may be inves-
tigated further. These environmental friendly nanoparticles are anticipated to enhance the
conductivity of various electrodes.

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