A non-covalent functionalization of copper tetraphenylporphyrin/chemically reduced graphene oxide nanocomposite for the selective determination of dopamine

Article abstract of DOI:10.1002/aoc.3397

A non-covalent functionalization based on a copper tetraphenylporphyrin/chemically reduced graphene oxide (Cu-TPP/CRGO) nanocomposite is demonstrated for selective determination of dopamine (DA) in pharmaceutical and biological samples. A homogeneous electron-rich environment can be created on the graphene surface by Cu-TPP due to the π-π non-covalent stacking interaction. The synthesized Cu-TPP/CRGO nanocomposite was characterized using scanning electron microscopy NMR, ultraviolet-visible and electrochemical impedance spectroscopies. The electrocatalytic activity of DA was evaluated using cyclic voltammetry and differential pulse voltammetry. The oxidation peak current (I_pa) of DA increased linearly with increasing concentration of DA in the range 2-200 μM. The detection limit was calculated as 0.76 μM with a high sensitivity of 2.46 μA μM^-1 cm^-2. The practicality of the proposed DA sensor was evaluated in DA hydrochloride injection, human urine and saliva, and showed satisfactory recovery results for the detection of DA. In addition, the Cu-TPP/CRGO nanocomposite-modified electrode showed excellent stability, repeatability and reproducibility towards the detection of DA.

Full text of DOI:10.1002/aoc.3397

Full paper
Received: 29 July 2015
Revised: 14 September 2015
Accepted: 1 October 2015
Published online in Wiley Online Library: 16 November 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3397
A non-covalent functionalization of copper
tetraphenylporphyrin/chemically reduced
graphene oxide nanocomposite for the
selective determination of dopamine
Chelladurai Karuppiah, Subramanian Sakthinathan, Shen-Ming Chen*,
Kesavan Manibalan, Sin-Ming Chen and Sheng-Tung Huang
A non-covalent functionalization based on a copper tetraphenylporphyrin/chemically reduced graphene oxide (Cu-TPP/CRGO)
nanocomposite is demonstrated for selective determination of dopamine (DA) in pharmaceutical and biological samples. A
homogeneous electron-rich environment can be created on the graphene surface by Cu-TPP due to the π–π non-covalent stacking
interaction. The synthesized Cu-TPP/CRGO nanocomposite was characterized using scanning electron microscopy NMR,
ultraviolet–visible and electrochemical impedance spectroscopies. The electrocatalytic activity of DA was evaluated using cyclic
voltammetry and differential pulse voltammetry. The oxidation peak current (I ) of DA increased linearly with increasing concen-
pa
À1
À2
tration of DA in the range 2–200 μM. The detection limit was calculated as 0.76μM with a high sensitivity of 2.46μA μM cm
.
The practicality of the proposed DA sensor was evaluated in DA hydrochloride injection, human urine and saliva, and showed
satisfactory recovery results for the detection of DA. In addition, the Cu-TPP/CRGO nanocomposite-modified electrode showed
excellent stability, repeatability and reproducibility towards the detection of DA. Copyright © 2015 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: dopamine; copper tetraphenylporphyrin; chemically reduced graphene oxide; limit of detection
Recently, carbon-based nanomaterials such as fullerenes, carbon
Introduction
nanotubes and graphene have been extensively used as suitable
[15–19]
Porphyrin is a macromolecular structural building block that con-
sists of a tetrapyrrole aromatic ring system, containing 18
delocalized π-electrons that make an electron-rich environment
on the outer sphere of porphyrin. The derivatives of porphyrin are
widely explored in various fields including biomolecule synthesis,
photosynthesis, oxygen transport, catalysis, sensors and energy
surfaces for supramolecular functionalization.
In particular,
graphene is a superior material used in current research fields and
consists of a two-dimensional honeycomb lattice structure with a
2
planar sheet of sp -bonded carbon atoms. Graphene also provides
high surface area and good thermal and electrical conductivity com-
[20]
pared with other carbon allotropes. Graphene-based hybrid ma-
terials have been explored in various applications due to their
[1–4]
storage device fabrication.
Porphyrin also provides excellent
[21–24]
binding sites for the attachment of transition metal cations due to
the strong coordination between porphyrin and metal cations.
The properties of porphyrin can be altered by the attachment or
functionalization of metal cations or functional groups on
unique physicochemical properties.
The modification of
graphene with metalloporphyrin moieties can create a homoge-
neous functional surface through non-covalent functionalization.
The preparation of such a multicomponent system can offer a stable
functional matrix due to the electrostatic interaction or π–π stacking
[5]
porphyrin. Metal–porphyrin complexes have been extensively
used in a variety of bioprocess and sensor applications owing to
the strong complexing ability and intrinsic electrocatalytic
[12]
interaction between graphene and porphyrin.
In addition, the
phenyl groups on the porphyrin ring have a large number of
delocalized electrons that can uniformly distribute on the graphene
[6–10]
activity.
Specifically, metal coordinated tetraphenylporphyrin
(
TPP) has potential for use in electroanalysis such as O reduction,
2
11–13]
[
miRNA detection, aptasensor application and so on.
The ex-
cellent electron transport properties of metal coordinated TPP re-
[
14]
sult in enhanced electrocatalytic activity towards electrodes.
*
Correspondence to: Shen-Ming Chen, Electroanalysis and Bioelectrochemistry Lab,
Department of Chemical Engineering and Biotechnology, National Taipei
University of Technology, No. 1, Section 3, Chung-Hsiao East Road, Taipei 106,
Taiwan (ROC). E-mail: smchen78@ms15.hinet.net
However, the supramolecular activity or stability of TPP on bare
electrode surfaces still limits sensor applications, due to the poor
electron communication between porphyrin and electrode
[8]
surface. Therefore, various approaches or functionalization (via
covalent or non-covalent) of TPP with other stable matrices have
been used to improve the electrocatalytic properties of TPP.
Electroanalysis and Bioelectrochemistry Lab, Department of Chemical
Engineering and Biotechnology, National Taipei University of Technology, No. 1,
Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan (ROC)
Appl. Organometal. Chem. 2016, 30, 40–46
Copyright © 2015 John Wiley & Sons, Ltd.

Cu-tetraphenylporphyrin functionalized graphene for dopamine sensor
surface, which is favorable for the selective determination of various
positively charged target molecules, e.g. dopamine (DA).
and 40 ml (0.4 M) of benzaldehyde were added into 30 ml of
propionic acid and the mixture was refluxed for 45 min (Scheme 1).
The refluxed solution was cooled at room temperature and the col-
loidal suspension (TPP) was filtered through washing with metha-
nol and hot water, yielding purple crystals of TPP (20%). To
prepare Cu-TPP, 25 mg of TPP was dissolved in 20 ml of chloroform
solution, which was then refluxed for 1 h followed by the addition
of 5 ml of saturated methanolic copper acetate (0.01 M) solution
(Scheme 2). The product was further washed several times
with water to remove unreacted reagents. The as-synthesized
TPP and Cu-TPP were confirmed from NMR spectral data, as shown
DA is an important neurotransmitter in the human brain and has
been used as a significant biomarker for various kinds of diseases
such as Huntington’s disease, schizophrenia and Parkinson’s
[25]
disease. Hence, the detection of DA levels in biological samples
is essential. However, the selective detection of DA in biological
samples is quite difficult, since other biological species such as
ascorbic acid (AA) and uric acid (UA) are co-oxidized with
[26–28]
DA.
Therefore, researchers have used various protocols or
approaches with modified electrodes for selective detection of
DA, in the presence of AA and UA. For instance, the negatively
charged Nafion polymer has been predominately used on modified
electrodes for the selective detection of DA even in the presence of
[36,37]
in Figs S1 and S2.
[29,30]
higher concentrations of AA.
Moreover, the tetra-sulfonated
Preparation of Cu-TPP/CRGO nanocomposite
metal phthalocyanine macromolecule has also been used as a
selective probe for the detection of DA in the presence of AA or
Graphene oxide (GO) was prepared from graphite using a modified
[38]
[31–35]
Hummers method. CRGO was prepared following the procedure
UA.
From the above discussion it is clear that sulfonated
[39]
À1
of Li et al. To prepare Cu-TPP/CRGO, 1 mg ml GO was dispersed
in 25 ml of distilled water and stirred well. Hydrazine hydrate (0.1 ml)
was added dropwise into the GO dispersion followed by the addi-
tion of 2 ml of aqueous ammonia (28 wt%). The whole mixture was
then stirred at 95 °C for 1 h. The suspension turned black, which con-
firmed the formation of graphene sheets. The stable black-colored
CRGO was washed several times with ethanol and water, and then
dried in an oven at 60 °C overnight. The Cu-TPP/CRGO nanocompos-
ite was prepared via π–π stacking interaction by dissolving Cu-TPP in
dimethylformamide (DMF) solution and a further 0.5 ml of Cu-TPP
moieties can provide a great specificity for capture of DA. However,
TPP in combination with graphene is still limited in the electroana-
lytical field and has not been used as a selective probe for DA.
In the work presented here, we synthesized copper–TPP (Cu-TPP)-
functionalized chemically reduced graphene oxide (CRGO) via π–π
non-covalent stacking interaction to generate a homogeneous
delocalized electron-rich environment on the graphene surface.
The as-synthesized Cu-TPP/CRGO nanocomposite showed a high
catalytic activity towards the detection of DA, due to the high
electrical conductivity and large surface area of CRGO and the
high specificity Cu-TPP. The fabricated sensor was further used for
the detection of DA in pharmaceutical and biological samples.
À1
was added in 1 ml of CRGO suspension (0.5 mg ml in DMF) under
vigorous stirring. The solution was subjected to ultrasonic treatment
for 30 min for the complete interaction between CRGO and Cu-TPP.
The homogeneous mixture of Cu-TPP/CRGO was filtered and
washed with ethanol three times and then dried.
In order to fabricate the electrochemical biosensor, 0.2 mg of Cu-
TPP/CRGO was re-dispersed in 1 ml of DMF which was then drop-
coated (8 μl, optimized level) on an alumina-pretreated GCE surface
and dried in an air oven. The fabricated Cu-TPP/CRGO-modified
Experimental
Materials and methods
Graphite powder (<20μm), DA hydrochloride, pyrrole, benzalde-
hyde, propionic acid, copper acetate, methanol, hydrazine and all
other chemicals were purchased from Sigma Aldrich. DA hydro-
chloride injection was purchased from Aldrich for real sample anal-
ysis. All solvents and reagents were of analytical grade and used
without further purification. A solution of pH = 7, namely 0.05 M
phosphate buffer solution (PBS), was prepared using Na
2 4
HPO
and NaH PO by adjusting the pH range with 0.5M H SO or 1 M
2
4
2
4
NaOH. All other required solutions were made up using double-
distilled water for an entire experiment.
Electrochemical measurements were carried out using a CHI410a
electrochemical workstation with a three-electrode system, con-
sisting of a modified glassy carbon electrode (GCE) as working elec-
2
trode (area = 0.0793 cm ), Ag/AgCl as reference electrode and
Scheme 1. Synthesis of tetraphenylporphyrin (TPP).
platinum wire as counter electrode. The electrochemical experiments
were performed in nitrogen-saturated electrolyte solution under am-
1
bient conditions. UV–visible and H NMR spectra were recorded with
PerkinElmer and Bruker 300 MHz instruments, respectively. An
EIM6ex (ZAHNER, Kroanch, Germany) was used for electrochemical
impedance spectroscopy (EIS) studies. Scanning electron microscopy
(SEM) was carried out using a Hitachi S-3000H microscope.
Preparation of Cu-TPP complex
The porphyrin complexes, TPP and Cu-TPP, were synthesized using
[36,37]
a previously reported method.
Briefly, 23 ml (0.4 M) of pyrrole
Scheme 2. Synthesis of copper tetraphenylporphyrin (Cu-TPP).
Appl. Organometal. Chem. 2016, 30, 40–46
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

C. Karuppiah et al.
Scheme 3. Preparation of copper tetraphenylporphyrin/chemically reduced
graphene oxide (Cu-TPP/CRGO) nanocomposite.
electrode was used for the determination of DA, as shown in
Scheme 3. The prepared electrode was stored at 4 °C in a refrigerator
when not in use.
Results and discussion
Materials characterization
The surface morphology of as-prepared materials was investigated
using SEM. The SEM image in Fig. 1(A) shows crumbled structure
of a mixture of Cu-TPP and GO, which indicates un-exfoliated sheets
of GO. The inset of Fig. 1(A) shows a typical SEM image of as-
synthesized Cu-TPP macromolecule. However, the graphene sheets
are clearly exfoliated through chemical reduction of GO, the average
sheet thickness being about 58 nm (inset of Fig. 1(B)). A uniform
wrinkled structure is observed for the Cu-TPP/CRGO nanocomposite,
as shown in Fig. 1(B). The Cu-TPP molecules are well attached onto
the CRGO surface via π–π stacking interaction that manipulates
the uniform functional surface. The formation of the homogeneous
functional surface is afforded by TPP, which is an appropriate envi-
ronment for the electron transfer reaction due to the large active
surface area and good electronic and catalytic properties of both
CRGO and Cu-TPP molecules. UV–visible spectroscopy was also used
for the analysis of the interaction between Cu-TPP and CRGO.
Figure 1(C) shows the UV–visible spectra of TPP, Cu-TPP, Cu-TPP/
CRGO and CRGO. As seen in the TPP spectrum, an absorption peak,
Soret band, appears at 417 nm due to the π–π* interaction, and also
some weaker peaks (509, 543, 586 and 643 nm) of the Q band. The
Cu-TPP spectrum shows absorption peaks of Soret and Q bands at
Figure 1. SEM images of (A) Cu-TPP/GO (inset: Cu-TPP) and (B) Cu-TPP/
CRGO (inset: CRGO). (C) UV–visible spectra of (a) TPP, (b) Cu-TPP, (c) Cu-
TPP/CRGO, (d) CRGO and (e) GO. (D) EIS spectra of (a) bare GC and (b) Cu-
TPP/GO-, (c) CRGO-, (d) Cu-TPP/CRGO-, (a’) Cu-TPP and (b’) GO-modified
3À/4À
electrodes in 0.1 M KCl containing 5 mM Fe(CN)
6
system.
To study the electrochemical properties of the prepared compos-
ite, EIS was employed using 0.1 M KCl solution containing 5 mM Fe
415 and 532, 610 nm, respectively. Also, the Cu-TPP/CRGO spectrum
3À/4À
shows a peak at 414 nm of the Soret band and at 533 nm of the Q
band. It is confirmed that Cu-TPP and CRGO have strong π–π* inter-
action between them. Thus, the insertion of metal in TPP is con-
firmed by a decrease of Soret band wavelength and a reduction in
the number of Q bands as compared to TPP. Metalation is observed
in that there is a red shift of the Soret band. The free TPP base has
two hydrogen atoms which are attached to two nitrogen atom in
the porphyrin ring that has a rectangular geometry with D2h symme-
try. So, Cu-TPP exhibits a smaller number of absorption bands than
the free TPP base. The inset of Fig. 1(C) shows the UV–visible spectra
of CRGO and GO. The GO spectrum shows an absorption band at
(CN)
6
system. As is known, EIS is a powerful tool for the analysis
of electrical properties of composite-modified electrodes. It can also
monitor the interfacial properties, chemical transformation and resis-
tance of electrodes. Figure 1(D) and its inset show the EIS curves
of bare GC and Cu-TPP/GO-, CRGO-, Cu-TPP/CRGO-, Cu-TPP- and
GO-modified electrodes. From the EIS experimental data, bare GC
and Cu-TPP- and GO-modified electrodes show large semicircles
which confirm the high resistance of the electrodes. On the other
hand, a smaller and two-phase semicircle is observed for Cu-TPP/
GO suggesting the mutual interaction between the GO and Cu-
TPP. Also, fast electron transfer is involved at CRGO due to the
high conductivity of graphene. However, the Cu-TPP/CRGO
nanocomposite-modified electrode shows a much smaller semicir-
cle than the other modified electrodes, which reveals the rapid
224 nm corresponding to the π–π* interaction and an absorption
peak of reduced GO is obtained at 282 nm based on red shift due
to the reduction of GO.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 40–46

Cu-tetraphenylporphyrin functionalized graphene for dopamine sensor
electron transfer ability of Cu-TPP/CRGO owing to the excellent
conductivity and high electron transfer capability of CRGO and
Cu-TPP, respectively.
DA, which indicates the electrocatalytic activity of Cu-TPP/CRGO-
modified GCE. The oxidation potential of DA is much lower than
the other modified electrodes: Cu-TPP, 0.305 V; bare GC, 0.327 V;
GO, 0.219 V; Cu-TPP/GO, 0.222 V; and CRGO, 0.204 V. This result re-
veals the excellent catalytic behavior of Cu-TPP/CRGO/GCE towards
DA. Also, the oxidation peak current of DA is higher than those of
the other fabricated electrodes, which indicates that the
functionalization of Cu-TPP on CRGO can promote the enhanced
oxidation signal of DA. Moreover, the peak to peak separation
Electrocatalytic behavior of DA at various modified electrodes
The electrocatalytic behavior of DA at the various modified electrodes
was studied using cyclic voltammetry (CV) in the presence of 200 μM
À1
DA in 0.05 M PBS (pH = 7) at a scan rate of 50 mV s . Figure 2(A)
shows the oxidation behavior of DA in the absence of 200 μM DA
(ΔE = 38 mV) value is lower for Cu-TPP/CRGO/GCE, whereas it is very
p
at the Cu-TPP/CRGO-modified electrode and in the presence of
high for bare GCE (282 mV), Cu-TPP/GCE (225 mV), GO/GCE (114 mV),
Cu-TPP/GO/GCE (130 mV) and CRGO/GCE (84 mV). These results con-
firm the fast electron transfer capability of the Cu-TPP/CRGO-modified
electrode. In addition, Fig. 2(B) shows the CV curves of DA oxidation
for various concentrations of DA in nitrogen-saturated 0.05 M PBS.
200 μM DA at the bare GC and Cu-TPP-, GO-, Cu-TPP/GO-, CRGO-
and Cu-TPP/CRGO-modified electrodes. For Cu-TPP/CRGO/GCE, there
is no characteristic peak in the absence of 200 μM DA. Whereas a clear
quasi-reversible peak appears at 0.176 V with the addition of 200 μM
Figure 2. (A) Cyclic voltammograms for DA oxidation at (b) Cu-TPP, (c) bare
Figure 3. (A) CV response of DA oxidation at Cu-TPP/CRGO composite-
GCE, (d) GO, (e) CRGO, (f) Cu-TPP/GO and (g) Cu-TPP/CRGO in 0.05 M PBS
modified GCE in PBS (pH = 7) with 200 μM DA at scan rates of 10 to
200 mV s . Inset: calibration plot for square root of scan rate versus Ipa
À1
(pH = 7) containing 200 μM DA; (a) Cu-TPP/CRGO in the absence of 200 μM
DA. (B) Cyclic voltammograms obtained for DA oxidation at Cu-TPP/CRGO-
and Ipc. (B) CV response of DA oxidation at Cu-TPP/CRGO composite-
modified electrode in 0.05 M PBS (pH = 7) containing various
modified GCE in 200 μM DA with PBS solution of various pH (3, 5, 7, 9 and
11) at a scan rate of 50 mV s . Inset: calibration plot of Ipa versus pH.
À1
À1
concentrations of DA. Scan rate = 50 mV s
.
Appl. Organometal. Chem. 2016, 30, 40–46
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

C. Karuppiah et al.
The quasi-reversible peak currents increase significantly for a high
concentration of DA. Hence, excellent electrocatalytic activity and fast
electron transfer ability are observed at the Cu-TPP-functionalized
CRGO surface due to the π–π stacking interaction, increased surface
area and higher electron flow of the composite matrix.
Effect of scan rate and pH
Figure 3(A) shows the CV response of oxidation of 200 μM DA at the
Cu-TPP/CRGO-modified GCE in PBS (pH = 7) at various scan rates (ν)
À1
ranging from 10 to 150 mV s . It is clear that the anodic (I ) and
pa
cathodic peak current (I ) of DA increase with varying scan rates.
pc
As shown in the inset of Fig. 3(A), linear behavior is observed be-
1
/2
tween Ipa and Ipc versus the square root of scan rate (ν ), which
confirms that the electrocatalytic reaction of DA at the Cu-TPP/
CRGO composite is a diffusion-controlled electrode process.
Figure 3(B) displays the electrooxidation of DA at Cu-TPP/CRGO-
modified GCE carried out by CV in PBS of various pH (pH = 3, 5, 7,
9
and 11). With increasing pH, Ipa and Ipc also increase and corre-
spondingly decrease from lower to higher pH, respectively. The in-
set of Fig. 3(B) shows a plot of pH versus I . The highest anodic
pa
peak current is at pH = 7; therefore the neutral pH medium was se-
lected for all analytical experiments.
Electrochemical determination of DA
Figure 4(A) illustrates DA oxidation on the Cu-TPP/CRGO-modified
electrode investigated using differential pulse voltammetry (DPV) in
0.05 M PBS with various concentrations of DA (2–400 μM). Well-
defined oxidation peaks appear at a potential of 0.17 V. Cu-TPP/CRGO
does not show any characteristic peak for an absence of DA. However,
the DPV current signal increases on adding increasing concentrations
of DA in nitrogen-saturated 0.05 M PBS. As seen in Fig. 4(B), the cali-
bration plot is a well-fitted linear relation between peaks current
and concentration of DA solution. The linear concentration range of
our proposed sensor is obtained from 2 to 200 μM. The linear regres-
sion equation can be expressed as Ipa = 0.1952[DA] + 0.145 (where Ipa
Figure 4. (A) DPV response of DA oxidation at Cu-TPP/CRGO composite-
modified GCE in (a) the absence of DA and (b–m) the presence of various
concentrations of DA from 0.35 to 150.55 μM in PBS (pH = 7). (B) Linear
relationship between Ipa and [DA].
2
is in μA and [DA] in μM); R = 0.9923. The sensor shows a good detec-
tion limit of 0.76 nM (S/N= 3). The electrode sensitivity is calculated to
À1
À2
be 2.45 μAμM cm , which is much higher than that of other func-
tionalized graphene-based modified electrodes. The results are
performance compared with other materials such as polymer-,
β-cyclodextrin- and phthalocyanine-functionalized graphene. Thus,
these results demonstrate that the Cu-TPP-functionalized CRGO
[40–49]
summarized in Table 1.
As seen from the comparative study,
Cu-TPP-functionalized graphene shows an excellent electroanalytical
Table 1. Comparison of various modified electrodes for the detection of DA
À1
À2
Modified electrode
Sensitivity (μA μM cm
)
LOD (μM)
LR (μM)
4–100
Ref.
[
40]
41]
42]
43]
44]
45]
46]
47]
48]
49]
Graphene/GCE
0.0659
0.03195
—
2.64
0.25
5
[
[
[
[
[
[
[
[
[
Nitrogen-doped graphene/GCE
Chitosan–graphene/GCE
0.5–170
5–200
5–200
0.5–110
0.5–150
0.5–10
0.9–200
3–75
2
TiO /graphene/GCE
—
2
Tryp–graphene/GCE
0.5202
2.198
0.015
—
0.290
0.150
0.100
0.005
—
AuNPs–β-CD–graphene/GCE
PPyox/graphene/GCE
β-CD/graphene/GCE
Cobalt phthalocyanine–graphene/GCE
f-RGO/GCE
—
—
3
5–600
2–200
Cu-TPP/CRGO/GCE
2.46
0.76
This work
2
LOD, limit of detection; LR, linear range; GCE, glassy carbon electrode; TiO , titanium dioxide nanoparticles; Tryp, tryptophan; AuNPs, gold nanoparticles;
β-CD, β-cyclodextrin; PPyox, overoxidized polypyrrole; f-RGO, functionalized reduced graphene oxide; CRGO, chemically reduced graphene oxide;
Cu-TPP, copper tetraphenylporphyrin.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 40–46

Cu-tetraphenylporphyrin functionalized graphene for dopamine sensor
nanocomposite plays a significant role for the selective detection of
DA, because of the superior electron transfer properties as well as
the homogeneous electron-rich environment of Cu-TPP.
Also, the developed sensor was used to monitor the DA level in bio-
logical samples like human urine and saliva (Figs S3 and S4). An ap-
preciable electrochemical response is observed at the Cu-TPP/
CRGO-modified electrode. The obtained recovery results are listed
in Tables 2 and 3. The range of recovery obtained is around
Selectivity, reproducibility and repeatability of proposed
sensor
9
6.3–99.3%, indicating the good practicality of our developed sensor.
Hence, Cu-TPP/CRGO can be used as a suitable electrode material for
the detection of DA in real sample analysis.
The biological molecules UA and AA are the major interfering sub-
stances in a specific electrochemical determination of DA. This is be-
cause the oxidation potentials these interfering molecules are very
similar to that of DA. Therefore, the evaluation of interference is of
major importance for a DA sensor. DPV was used to investigate DA
Conclusions
We successfully prepared an electrochemically active Cu-TPP/CRGO
nanocomposite for the sensitive detection of DA. The prepared
nanocomposite was characterized and confirmed using NMR and
UV spectroscopies and SEM. The Cu-TPP/CRGO nanocomposite
displayed an excellent electrocatalytic activity for the oxidation
of DA at 0.176 V. The linear response range of DA was found to be
2–200 μM and the detection limit was 0.76 μM. The prepared elec-
trode material was used for the selective determination of DA with
coexisting biological species at lower potential state. Our proposed
sensor was used for practical application to detect DA in several real
samples, namely DA injection, urine and saliva. Hence, the Cu-TPP/
CRGO nanocomposite-modified electrode could be a potential elec-
trode material for the detection of DA in various biological samples
such as urine and saliva and also in blood serum for alaysis in the
near future.
(5 μM) oxidation in the presence of 100-fold higher concentration of
AA and UA. The peak current of DA is increased in the presence of
AA and UA at the Cu-TPP/CRGO-modified GCE. The results indicate
that there is no obvious peak for AA and UA due to the strong repul-
sion by the negatively charged environment of the Cu-TPP/CRGO
nanocomposite. Hence, the proposed sensor material is a useful plat-
form for the selective detection of DA in biological samples. In addi-
tion, stability studies were carried out to monitor the DA response
using DPV at Cu-TPP/CRGO with various time intervals in 5 μM DA so-
lution of pH = 7. The Cu-TPP/CRGO electrode was stored in a refriger-
ator for 15 days when not in use. After the 15 days, we measured the
sensitivity of our fabricated sensor; it loses only 4% of signal response
from its initial sensitivity, indicating a good stability of the DA sensor.
Moreover, the reproducibility of the proposed sensor was character-
ized using DPV with three different modified electrodes and used
for the detection of DA. The relative standard deviation of the three
different electrodes is found to be 2.6%. Also, a relative standard de-
viation of 3.5% is obtained for five repeat measurements of a single
fabricated electrode using 20 μM DA in a nitrogen-saturated solution
of pH = 7. The results suggest that the fabricated sensor shows good
repeatability and reproducibility.
Acknowledgements
This work was supported by the National Science Council and the
Ministry of Education, Taiwan (ROC).
References
Real sample analysis
[
1] D. P. Arnold, E. I. Worthington, Y. Sakata, K. Sugiura, Chem. Commun.
1998, 21, 2331.
The practical applicability of the proposed sensor was evaluated using
DPV for the determination of DA in real DA hydrochloride injection.
[
[
2] S. Saito, A. Osuka, Angew. Chem. Int. Ed. 2011, 50, 4342.
3] L. J. Esdaile, P. Jensen, J. C. McMurtrie, D. P. Arnold, Angew. Chem. Int. Ed.
2007, 46, 2090.
[
[
4] R. X. Wang, J. J. Fan, Y. J. Fan, J. P. Zhong, L. Wang, S. G. Sun, X. C. Shen,
Nanoscale 2014, 6, 14999.
5] M. Gouterman, in The Porphyrins, Vol. III (Ed: D. Dolphin), Academic
Press, New York, 1978, pp. 1–165.
Table 2. Determination by DPV of DA in DA hydrochloride injection
using Cu-TPP/CRGO/GCE
a
Diluted DA
injection sample
Added
(μM)
Found
(μM)
Recovery
(%)
[6] M. Biesaga, K. Pyrzynska, M. Trojanowicz, Talanta 2000, 51, 209.
[
7] L. Zheng, D. Ye, L. Xiong, J. Xu, K. Tao, Z. Zou, D. Huang, X. Kang, S. Yang,
Sample 1
Sample 2
Sample 3
—
3.0
5.0
26
—
J. Xia, Anal. Chim. Acta 2013, 768, 69.
8] S. Saxena, A. L. Verma, Adv. Mater. Lett. 2014, 5, 472.
9] J. Hu, I. Pavel, D. Moigno, M. Wumaier, W. Kiefer, Z. Chen, Y. Ye, Q. Wu,
Q. Huang, S. Chen, F. Niu, Y. Gu, Spectrochim. Acta A 2003, 59, 1929.
[
[
5.5
7.4
98.2
97.4
a
[10] S. Zhang, S. Tang, J. Le, H. Dong, H. Ju, J. Electroanal. Chem. 2011, 656,
85.
Standard addition method.
2
[
11] Z. S. Wu, L. Chen, J. Liu, K. Parvez, H. Liang, J. Shu, H. Sachdev, R. Graf,
X. Feng, K. Müllen, Adv. Mater. 2014, 26, 1450.
[
[
[
12] C. D. Souza, S. Zrig, D. Wang, M. C. Pham, B. Piro, Sensors 2014, 14, 9984.
13] H. Zhang, Y. Han, Y. Guo, C. Dong, J. Mater. Chem. 2012, 22, 23900.
14] J. P. Collman, P. Denisevich, Y. Konai, M. Marrocco, C. Koval, F. C. Anson,
J. Am. Chem. Soc. 1980, 102, 6027.
Table 3. Determination by DPV of DA in human urine and saliva
samples using Cu-TPP/CRGO/GCE
a
Sample
Added (μM)
Found (μM)
Recovery (%)
[
15] R. Yamuna, S. Ramakrishnan, K. Dhara, R. Devi, N. K. Kothurkar,
E. Kirubha, P. K. Palanisamy, J. Nanopart. Res. 2013, 15, 1399.
16] W. Zhang, A. U. Shaikh, E. Y. Tsui, T. M. Swager, Chem. Mater. 2009, 21,
Human urine
—
0
2.98
0
—
99.3
—
[
3.0
3
234.
[17] I. Kruusenberg, L. Matisen, K. Tammeveski, J. Nanosci. Nanotechnol.
013, 13, 621.
18] B. Girek, W. Sliwa, J. Incl. Phenom. Macrocycl. Chem. 2015, 82, 283.
Human saliva
—
2
8
7.7
96.3
[
a
Standard addition method.
[19] K. S. Novoselov, V. I. Falko, L. Colombo, P. R. Gellert, M. G. Schwab,
K. Kim, Nature 2012, 192, 490.
Appl. Organometal. Chem. 2016, 30, 40–46
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

C. Karuppiah et al.
[
20] A. Wang, W. Yu, Z. Xiao, Y. Song, L. Long, M. P. Cifuentes,
[37] A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour,
L. Korsakoff, J. Org. Chem. 1967, 32, 476.
M. G. Humphrey, C. Zhang, Nano Res. 2015, 8, 870.
[
[
[
[
21] J. Sun, Q. Liang, Q. Han, X. Zhang, M. Ding, Talanta 2015, 132, 557.
22] C. K. Chua, M. Pumera, Chem. Soc. Rev. 2014, 43, 291.
23] T. H. Tsai, S. C. Chiou, S. M. Chen, Int. J. Electrochem. Sci. 2011, 6, 3333.
24] A. Barras, M. R. Das, R. R. Devarapalli, M. V. Shelkec, S. Cordier,
S. Szunerits, R. Boukherroub, Appl. Catal. B 2013, 130, 270.
[38] W. S. Hummers, R. E. Offeman, J. Am. Chem. Soc. 1958, 80, 1339.
[39] D. Li, M. B. Muller, S. Gilje, R. B. Kaner, G. G. Wallace, Nat. Nanotechnol.
2008, 3, 101.
[40] Y. R. Kim, S. Bong, Y. J. Kang, Y. Yang, R. K. Mahajan, J. S. Kim, H. Kim,
Biosens. Bioelectron. 2010, 25, 2366.
[
[
[
[
25] T. Qiana, C. Yua, X. Zhoua, S. Wua, J. Shen, Sens. Actuators B 2014, 193,
[41] Z. H. Sheng, X. Q. Zheng, J. Y. Xu, W. J. Bao, F. B. Wang, X. H. Xia, Biosens.
Bioelectron. 2012, 34, 125.
[42] Y. Wang, Y. Li, L. Tang, J. Lu, J. Li, Electrochem. Commun. 2009, 11, 889.
[43] Y. Fan, H. T. Lu, J. H. Liu, C. P. Yang, Q. S. Jing, Y. X. Zhang, X. K. Yang,
K. J. Huang, Colloids Surf. B 2011, 83, 78.
7
59.
26] K. S. Prasad, G. Muthuraman, J. M. Zen, Electrochem. Commun. 2008, 10,
59.
5
27] H. R. Zare, N. Rajabzadeh, N. Nasirizadeh, M. M. Ardakani, J. Electroanal.
Chem. 2006, 589, 60.
28] H. R. Zhu, W. Wu, H. Zhang, L. Z. Fan, S. H. Yang, Electroanalysis 2009, 21,
[44] Q. Lian, Z. He, Q. He, A. Luo, K. Yan, D. Zhang, X. Lu, X. Zhou, Anal. Chim.
Acta 2014, 823, 32.
2
660.
[45] X. Tian, C. Cheng, H. Yuan, J. Du, D. Xiao, S. Xie, M. M. Choi, Talanta
2012, 93, 79.
[
[
29] S. Ku, S. Palanisamy, S. M. Chen, J. Colloid Interface Sci. 2013, 411, 182.
30] P. Y. Chen, R. Vittal, P. C. Nien, K. C. Ho, Biosens. Bioelectron. 2009, 24,
[46] Z. Zhuang, J. Li, R. Xu, D. Xiao, Int. J. Electrochem. Sci. 2011, 6, 2149.
[47] L. Tan, K. G. Zhou, Y. H. Zhang, H. X. Wang, X. D. Wang, Y. F. Guo,
H. L. Zhang, Electrochem. Commun. 2010, 12, 557.
[48] J. Yan, D. Mu, Y. Gao, J. Tan, A. Lu, D. Ma, J. Natural Gas Chem. 2012, 21,
265.
3
504.
31] W. Zhu, W. Zhang, S. Li, H. Ma, W. Chen, H. Pang, Sens. Actuators B 2013,
81, 773.
32] J. Han, X. Xu, X. Rao, M. Wei, D. G. Evans, X. Duan, J. Mater. Chem. 2011,
1, 2126.
[
[
[
[
[
[
1
2
[49] H. Wang, F. Ren, R. Yue, C. Wang, C. Zhai, Y. Du, Colloids Surf. A 2014,
448, 181.
33] M. F. Zampa, I. M. S. de Araújo, J. R. dos Santos, Jr., V. Zucolotto,
J. R. S. A. de Leite, C. Eiras, Int. J. Anal. Chem. 2012, 2012, 850969.
34] L. N. Furini, E. Feitosa, P. Alessio, M. H. Shimabukuro, A. Riul, Jr.,
C. J. L. Constantino, Mater. Sci. Eng. C 2013, 33, 2937.
35] C. Karuppiah, R. Devasenathipathy, S. M. Chen, D. Arulraj, S. Palanisamy,
V. Mani, V. S. Vasantha, Electroanalysis 2015, 27, 485.
Supporting information
36] X. Gong, T. Milic, C. Xu, J. D. Batteas, C. M. Drain, J. Am. Chem. Soc. 2002,
Additional supporting information may be found in the online ver-
124, 14290.
sion of this article at the publisher’s web site.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2016, 30, 40–46