This document describes the development of an electrochemical sensor for the detection of dopamine (DA) using a composite material based on carbon nanotubes (CNT), zinc oxide nanoparticles (ZnONPs), and nickel phthalocyanine (NiTsPc) immobilized on a pyrolytic graphite electrode (PGE). Characterization of the PGE/NiTsPc-ZnONPs-CNT electrode showed well-defined redox behavior of the composite materials. Differential pulse voltammetry and chronoamperometry were used to detect DA, achieving detection limits of 7.0 nM and 24 nM, respectively. Interferents like ascorbic acid, uric acid, and serotonin did not significantly affect
2. Biosensors and Bioelectronics 210 (2022) 114211
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such as Levodopa use (Rastgardani et al., 2020). In schizophrenia, for
example, DA levels tend to be higher than those found in healthy people
(Conn et al., 2020).
In the literature is possible to find reports on a large number of
studies concerning sensors designed for the detection of DA; however, a
vast majority of these sensors are not suitable for detecting DA at con
centrations of biological interest, which constitutes an issue that re
quires attention.
The DA sensors fabricated using nanomaterials, such as carbon
nanotubes (CNT), has demonstrated a satisfactory performance because
of their high electrical conductivity, biocompatibility, nontoxicity, and
low cost (Ben Aoun, 2017; Liu et al., 2017; Fayemia et al., 2018; Yusoff
et al., 2018).
Zinc oxide nanoparticles (ZnONPs) are another class of nano
materials that have been used to amplify the electrochemical response
during sensing. These nanostructures increase the electrode surface
area, favoring electrochemical reactions (Heydari et al., 2019; Cao et al.,
2020; Shaikshavali et al., 2020).
In addition to nanomaterials, phthalocyanines, which are non-toxic
macromolecules, have been used as active layers in the development
of electrochemical sensors (Pari et al., 2020; De Oliveira et al., 2021).
Among phthalocyanines, nickel tetrasulfonated phthalocyanine
(NiTsPc) demonstrates well-defined electrochemical activity and wide
application potential in the electrochemical sensing of different analytes
(Diab et al., 2019; De Lima et al., 2020).
Although a large number of studies use CNT (Arumugasamy et al.,
2020), ZnONPs (Cao et al., 2020) and/or NiTsPc (Xu et al., 2016) in the
development of electrochemical sensors, including those for the analysis
of DA, the detection limits of these sensors need to be improved so that
portable devices can be developed and used in clinical diagnosis. A
promising, yet unexplored, approach is the design of composite mate
rials with the aforementioned compounds. This strategy allows the
synergistic effect between CNT, ZnONPs, and NiTsPc, which promotes
an increase in the DA analytical signal, thereby facilitating lower
detection limits than those observed in previous studies.
This study aims to develop an electrochemical sensor for the analysis
of DA by employing a pyrolytic graphite electrode (PGE) modified using
a composite based on CNT, ZnONPs, and NiTsPc. The PGE/NiTsPc-
ZnONPs-CNT system is proposed for the rapid, selective, ultrasensi
tive, and direct detection of DA in real human serum samples.
2. Materials and methods
2.1. Materials
Single-walled carbon nanotubes (SWCNT, or simply called CNT)
(diameter: 1.2–2.0 nm), nickel tetrasulfonated phthalocyanine (NiTsPc),
serotonin (5-HT), and DA were purchased from Sigma-Aldrich. Ascorbic
acid (AA) and uric acid (AU) were purchased from Dinâmica (Brazil) and
LabTest (Brazil), respectively. All solutions were prepared using ultra
pure water from a MilliQ system, and measurements were carried out in
an acclimatized room at approximately 20 ◦
C.
The ZnONPs, with a diameter of 105 nm, were synthesized (pro
cedure described in the supplementary material), characterized and
provided by Souza et al. (2020). In order to ensure that the properties of
these nanoparticles remained stable, we proceeded with the character
ization by UV-VIS and AFM spectroscopy of the ZnONPs, and these re
sults are found in the Supplementary Material (Fig. S1 and Fig. S2).
2.2. Electrode preparation
A PGE was used for the electrochemical tests. Prior to modifying the
surface of the PGE electrode using the composite material, NiTsPc-
ZnONPs-CNT, the surface was mechanically and chemically polished
to remove possible impurities, as presented in the supplementary ma
terial (Fig. S3).
To prepare the modified PGE/NiTsPc-ZnONPs-CNT electrode,
ZnONPs and CNT were dispersed at a concentration of 1.0 mg/mL in a
0.1% agar solution, which was extracted from Gracilaria birdiae seaweed
collected from the coast of the state of Piauí, Brazil (Farias et al., 2015).
As in the case of ZnONPs, to ensure the quality of the polysaccharide
used, it was characterized by Fourier transform infrared (FTIR) spec
troscopy (Fig. S4).
NiTsPc was directly solubilized in ultrapure water at a concentration
of 1.0 mg/mL. Thereafter, 100 μL of NiTsPc, ZnONPs, and CNT were
mixed and placed in an ultrasound bath for 10 min, followed by over
night resting. Subsequently, the mixture of these materials was diluted
in the ratio 1:1 in 1.0 mg/mL agar and was allowed to interact overnight.
Before placing on the PGE, the mixture was ultrasonicated for 10 min
until a homogeneous suspension was obtained. Fig. 1 illustrates the
electrode preparation.
Fig. 1. PGE/NiTsPc-ZnONPs-CNT preparation scheme.
V.N. Carvalho da Silva et al.
3. Biosensors and Bioelectronics 210 (2022) 114211
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2.3. Electrochemical measurements
All experiments were carried out using a PGE modified with the
composite material as the working electrode; a saturated calomel elec
trode (SCE) was used as reference electrode, and a platinum plate with
an area of 2 0.0 cm2
was used as the auxiliary electrode. An Autolab
PGSTAT 128N potentiostat/galvanostat was used for all the electro
chemical tests.
2.4. Analysis of real samples
To conduct the analyses using real samples, all the standard oper
ating procedures (SOPs) for blood collection were observed. The tour
niquet procedure was followed by antisepsis with a consequent
peripheral venous puncture, preferably in the basilic or cephalic vein.
For all blood collection procedures, the person in charge was equipped
with personal protective equipment (PPE). All sharp materials were
disposed of in appropriate containers (Descarpack®), following the
norms of the National Biosafety Association (ANBio, Associação Nacional
de Biossegurança -Brazil). This study was approved by the Research
Ethics Committee of the Federal University of Piauí–UFPI (opinion
number: 1,327,105).
2.5. Surface characterization of PGE/NiTsPc-ZnONPs-CNT using AFM
The morphological analysis of the electrodes was performed using
atomic force microscopy (AFM) by employing a TT-AFM equipment
(AFM Workshop, USA). AFM analyses were performed in the intermit
tent contact mode (vibrating) (with a resolution of 512 × 512 pixels)
using TAP300-G silicon probes (Ted Pella, USA) and a resonant fre
quency of approximately 239 kHz. For the AFM analysis, the PGE was
dismantled, and the graphite pellet was carefully removed and cut to a
thickness of approximately 3.0 mm. After cutting, the PGE was modified
with the precursor solutions/dispersions of ZnONPs, CNT, and NiTsPc
and diluted when necessary. The morphology of the unmodified PGE
was also observed. The obtained images were analyzed using the pro
gram Gwyddion 2.59, from which the roughness values (average
roughness, Ra; mean square roughness, Rq; skewness, Rsk; kurtosis, Rku;
maximum height, Rz) were extracted (areas of 2.0 × 2.0 μm, n = 20).
Representative images of the amplitude (15.0 × 15.0 μm), phase (15.0
× 15.0 μm), and three-dimensional (3D) topography (4.0 × 4.0 μm) are
presented in the results and discussion section. Statistical analyses were
performed with the GraphPad Prism® 8.0.1 program, using the two-way
ANOVA and Tukey’s post hoc tests. Statistical significance was set at p <
0.05.
3. Results and discussion
3.1. Electrochemical characterization of PGE/NiTsPc-ZnONPs-CNT
The results presented in Fig. 2 demonstrate the electrochemical
properties of the developed PGE/NiTsPc-ZnONPs-CNT electrode, which
is used as a catalytic hybrid system for DA detection. Fig. 2A shows the
cyclic voltammograms of PGE/NiTsPc-ZnONPs-CNT in KH2PO4 0.1 mol
L− 1
(pH 3.2). Fig. 2B presents the voltammograms of PGE/NiTsPc-
ZnONPs-CNT in K3[Fe(CN)6] 0.1 mol L− 1
solubilized in KCl 0.1 mol
L− 1
. These two approaches were used to obtain a more holistic under
standing of the redox behavior in the proposed system.
When the electrochemical profile of the materials forming the
composite was evaluated individually, it was observed that the ZnONPs
did not exhibit electroactivity in KH2PO4 0.1 mol L− 1
, thus, the curve
obtained for PGE/ZnONPs in this medium was similar to the electro
chemical profile of the clean PGE (i.e., unmodified PGE) (Fig. 2A). On
the other hand, in K3[Fe(CN)6] a considerable decrease in the current
density values of the redox processes of the Fe(CN)6
− 3/− 4
pair was
observed for PGE/ZnONPs (Fig. 2B), confirming the immobilization of
this material on the electrode surface. Subsequently, the voltammetric
curve obtained for the electrode modified with CNT (PGE/CNT) showed
that, despite not being electroactive, the nanotubes acted as “activators”
of the electrode surface, increasing the capacitive current density at the
system interface.
However, when PGE was modified with NiTsPc, a characteristic
redox pair was observed during the anodic scan (Fig. 2A). A defined
process took place at +0.70 V vs. SCE (see the NiTsPc curve), which
corresponds to the macrocyclic oxidation of NiTsPc (Ni(II)TsPc6−
→ Ni
(II)TsPc4
− + e2−
). During the cathodic scan, the reduction of the above
process was observed at +0.63 V vs. SCE (Nkunu et al., 2017; Bertana
et al., 2020).
Finally, for the electrode modified with the composite (PGE/NiTsPc-
ZnONPs-CNT), the response was similar to the typical profile of the
NiTsPc in KH2PO4 0.1 mol L− 1
, with higher current values and better
definition of their electrochemical processes. Furthermore, the oxida
tion process, corresponding to the macrocycle oxidation previously
observed at +0.70 V vs. SCE, was observed at +0.77 V vs. SCE, thereby
demonstrating strong interactions with the materials present in the
composite. Potential shift were also observed for NiTsPc reduction
process (from 0.63 to 0.67V), when immobilized forming the composite.
Here, it is clearly observed that when ZnONPs and CNT are used
together, there was a considerable increase in the electroactive surface
area of the electrode, which favors the redox reactions of NiTsPc and
also of DA, as is discussed in section 3.3. This increase in active area can
be related to the roughness increased in the electrode modified with
Fig. 2. Electrochemical behavior of the successive layers used in the construction of the PGE/NiTsPc-ZnONPs-CNT electrode in A) KH2PO4 0.1 mol L− 1
and B) K3[Fe
(CN)6] 0.1 mol L− 1
solubilized in KCl 0.1 mol L− 1
. Cyclic voltammograms obtained at v = 50 mV s− 1
.
V.N. Carvalho da Silva et al.
4. Biosensors and Bioelectronics 210 (2022) 114211
4
composite material (discussed in section 3.2).
3.2. Morphology and roughness analysis of PGE/NiTsPc-ZnONPs-CNT
using AFM
AFM is a suitable technique for analyzing the surface morphology of
PGE; therefore, it was chosen to study the morphology of PGE/NiTsPc-
ZnONPs-CNT (Oliveira and Maria Oliveira-Brett, 2010; Farias et al.,
2021). Fig. 3 shows the surface of the unmodified electrode (Fig. 3A–C)
in comparison to the surface of the modified electrode with each
component of the composite separately (Fig. 3D–M) or to the
morphology of the PGE/NiTsPc-ZnONPs-CNT (Fig. 3N–P).
Fig. 3 shows two-dimensional topographic images (left column),
phase-contrast images (middle column), and 3D images (right column)
of the electrodes analyzed in this study. The clean PGE (Fig. 3 A and C)
presents a similar morphology to that demonstrated by Lin et al. (2009)
and Farias et al. (2015). The phase-contrast image of the same electrode
(Fig. 3 B) emphasizes the predominance of a single phase. The
phase-contrast images presented in Fig. 3 E, H, L, and O show the
electrode modification, corroborating the findings of Farias et al.
(2015).
The modification of the electrode surface induced changes in the
observed morphology. The addition of ZnONPs promoted the formation
of irregular clusters of these nanoparticles on the electrode surface
(Fig. 3 D and F). The CNT adsorbed on the electrode caused the for
mation of agglomerates characteristic of this type of material (Dionísio
et al., 2019), presenting structures similar to multiple layers of nanotube
agglomerates (Fig. 3 G and I). The topography of the electrode modified
with NiTsPc indicates that this component smoothens the electrode
surface (Fig. 3 J and M), while the modification with the composite
PGE/NiTsPc-ZnONPs-CNT promotes the formation of large irregular
agglomerates (Fig. 3N and P).
Data related to the roughness of the analyzed samples are summa
rized in Table S3 (Supplementary Material). Kachoosangi et al. (2007)
reported that the PGE has a relatively higher roughness than other
carbon electrodes, such as the glassy carbon electrode. In this study, PGE
and PGE/NiTsPc-ZnONPs-CNT showed mean roughness values of
115.89 ± 71.45 nm and 340.88 ± 146.38 nm, respectively. The increase
in roughness facilitated the oxidation of DA and an easier access to the
surface of the composite.
The observed Rz changed substantially for all the tested electrodes,
with statistically significant differences, except for PGE/NiTsPc, as
presented in Fig. 3 J-M (see Table S3). The Rsk is related to the asym
metry of the analyzed surface and does not present a significant
Fig. 3. Amplitude (15.0 × 15.0 μm), phase (15.0 × 15.0 μm), and 3D topography (4.0 × 4.0 μm) images of the modified and unmodified PGE. (A, B, and C): clean
PGE; (D, E, and F): PGE/ZnONPs; (G, H, and I): PGE/CNT; (J, L, and M): PGE/NiTsPc; (N, O, and P): PGE/NiTsPc-ZnONPs-CNT.
V.N. Carvalho da Silva et al.
5. Biosensors and Bioelectronics 210 (2022) 114211
5
difference between the analyzed samples as well as the Rku
(Méndez-Vilas et al., 2007) .
3.3. Electrochemical behavior of DA on the surface of PGE/NiTsPc-
ZnONPs-CNT
The results presented below will seek to better understand the
electrochemical behavior of DA on PGE/NiTsPc-ZnONPs-CNT surface
and how active layer composition contributes to sensor analytical
performance.
Fig. 4A shows the voltammograms obtained for modified PGE (pre
senting all the materials used in the development of the composite) in
KH2PO4 0.1 mol L− 1
in the presence of 0.42 μM DA. For the PGE
modified with CNT, a peak was observed at +0.5 V vs. SCE with a
current of 0.5 μA for DA, while for the PGE/ZnONPs electrode, the DA
peak was observed at +0.43V vs. SCE with a current of 1.7 μA. When
ZnONPs were associated with CNT, a considerable increase in current
(4.5 μA) for DA response was observed, suggesting a synergistic effect
that optimized DA oxidation. For PGE electrode modified with only
NiTsPc, DA was oxidized at +0.46 V vs. SCE with a current value of
~4.0 μA for 0.42 μM DA (Fig. 4A).
When all the materials were used in the composite PGE/NiTsPc-
ZnONPs-CNT, an unexpected effect during the oxidation of DA was
observed (Fig. 4A). Not only the current levels reached close to 9.0 μA
for only 0.42 μM DA, but also DA started to oxidize on the surface of
PGE/NiTsPc-ZnONPs-CNT in the region of +0.40 V vs. SCE, showing
synergistic and catalytic effects. Somehow, the interactions among the
proposed materials in composite, act to catalyze the electrochemical
response of DA to lower oxidation potentials, at each incorporation step
of composite components into the active layer to form PGE/NiTsPc-
ZnONPs-CNT. Thus, this effect favored a lower energy consumption
during the DA redox reactions.
According to Bard and Faulkner (2001), the width at half height
(W1/2) of the oxidation peak of a given species can be related to n
(number of electrons) as seen in Equation (01). Therefore, it was
determined that two electrons are involved in the DA oxidation reaction
on the PGE/NiTsPc-ZnONPs-CNT surface. These results allow us to
propose the redox mechanism shown in Fig. S5 (Supplementary
Material).
Fig. 4. A) Influence of the composite material that constitutes the active layer of the DA sensor; B) Effect of dilution on the prepared composite; C) and D) Effect of
the electrolytic pH on the DA response. All voltammograms were obtained by differential pulse voltammetry (DPV) (v = 10 mV s− 1
, amp = 25 mV) in 0.1 mol L− 1
KH2PO4 in the presence of 0.42 μM DA.
V.N. Carvalho da Silva et al.
6. Biosensors and Bioelectronics 210 (2022) 114211
6
W1/2 = 90/n mV (1)
The influence of the composite solution concentration used in elec
trode manufacture on electrochemical response also was evaluated
(Fig. 4B). For this study, PGE electrodes modified with the NiTsPc-
ZnONPs-CNT composite were prepared in proportions of 1:0, 1:1, 1:2,
and 1:3 between the composite solution and 1.0 mg/mL agar.
It is worth mentioning that the 1.0 mg/mL agar, in addition to acting
as an excellent natural dispersant for ZnONPs and CNT, also helps to
maintain the material on the electrode, with a similar function to Nafion,
which is widely used for this purpose. (Lee et al., 2020), however, agar
still has the advantages of being biocompatible, biodegradable, and
non-toxic (Farias et al., 2015).
Apparently, in the undiluted composite (1:0 dilution), Fig. 4B, the
material concentration is high enough to cause a lower electroactive
availability centers for DA oxidation, making it difficult for this neuro
transmitter to access the redox centers, which probably compete with
each other. The higher potentials observed to oxidize DA at 1:0 dilution
compared to the other dilutions support these hypotheses. At dilutions
above 1:1, there seems to be not enough composite to favor DA oxida
tion, according evidenced by the lower current levels observed. There
fore, the 1:1 dilution was selected for subsequent studies.
The effect of the electrolytic pH on the electrochemical response of
DA is shown in Fig. 4C and D. In general, the oxidation of DA on the
surface of PGE/NiTsPc-ZnONPs-CNT shows best results in an acidic
medium with a pH of 3.4. These findings corroborates with the results
obtained by Gong et al. (2020), who observed higher DA electroactivity
at a pH value close to 3.0. This is because NiTsPc, the redox mediator
present in the composite, has a better electrochemical response in acidic
media (pH 3.4) (Zampa et al., 2012).
3.4. Application of PGE/NiTsPc-ZnONPs-CNT as a DA sensor
3.4.1. DPV and chronoamperometry
The development of new analytical methodologies for the direct
quantification of DA in human serum is of significant interest, as it may
contribute to the advancement in the diagnosis and treatment’s diseases,
such as Schizophrenia, Parkinson’s and Alzheimer’s diseases. Conse
quently, we evaluated the efficiency of PGE/NiTsPc-ZnONPs-CNT for
the electrochemical detection of DA in human serum. In this regard,
calibration curves were constructed using two different electrochemical
techniques, DPV (Fig. 5 A and Fig. 5 B) and chronoamperometry (Fig. 5
C and 5 D). In both cases, different DA concentrations were correlated
with the measured current levels.
From the differential pulse voltammograms (Fig. 5A), an analytical
curve with a linear range between 0.0 and 15.0 μM (Fig. 5B) was ob
tained. The analytical sensitivity of the system was estimated to be 10
μA/μM DA. The limits of detection (LD - Equation (02)) and quantifi
cation (LQ- Equation (03)) for DA, using DPV, were estimated to be
0.007 μM (or 7.0 nM) and 0.024 μM (or 24.0 nM), respectively. It is
important to highlight that, after DA analysis, it can be disassociated
from electrode by washing with ultrapure water (Fig. S6), i.e., don’t
occur the DA’s adsorption electroactive residues on electrode surface.
This means that the same modified electrode can be reused for succes
sive DA analysis, as observed in other works (Savk et al., 2019; Ko et al.,
2021).
Fig. 5. A) Differential pulse voltammograms (v = 10 mV s− 1
, amp = 25 mV) obtained for different DA concentrations and B) their respective analytical curve. C)
Chronoamperograms obtained for different DA concentrations at +0.4 V vs. SCE and D) their respective analytical curve. All measurements were performed in
KH2PO4 0.1 mol L− 1
, with pH = 3.4.
V.N. Carvalho da Silva et al.
7. Biosensors and Bioelectronics 210 (2022) 114211
7
LD = 3.0 SD/S (2)
LQ = 10 SD/S (3)
SD = Standard white deviation response.
S = Slope of the analytical plot.
Chronoamperometry was performed at +0.4 V (optimized potential)
to obtain a linear range current vs. DA concentration between 0.0 and
7.0 μM. The detection and quantification limits for DA, using this
technique, were estimated to be 0.31 μM and 1.04 μM, respectively.
Analytical sensitivity was 0.16 μA/μM DA. Table S2 presents a com
parison between the obtained LD values in this study to those found in
the literature.
DPV is a sensitive technique because it enables the elimination of the
excess capacitive current from the system through the application of
potential in the form of a ladder with current readings before and after
the steps of applied potentials (Aravindan and Sangaranarayanan, 2017;
Selvolini et al., 2019), which favors the lowest LD and LQ observed using
this technique. However, chronoamperometry works with fixed poten
tial and constant current readings, which favors less complexity when
considering the design of portable devices.
3.4.2. Influence of main DA interferers and the validation of the method
The electrochemical analysis of DA may be unfeasible or limited by
the presence of possible interference in the study matrix. The examples
of common interferers in human serum are AA, AU, and other neuro
transmitters, such as 5H-T. These interferers are highlighted because
they possess oxidation potentials very close to DA, or they promote
interference in the DA oxidation process in biological samples, which
result in response overlap, thereby making the electrochemical detec
tion of DA difficult (Zhou et al., 2013; Gong et al., 2020; Xu et al., 2021).
To evaluate the influence of AA, AU, and 5-HT on the electro
chemical response of DA to the proposed PGE/NiTsPc-ZnONPs-CNT
electrode, 42 μM of each of these interferers were added to the elec
trolyte solution of KH2PO4 0.1 mol L− 1
containing 21 μM DA (Fig. 6A).
For comparison, the electrochemical profiles of the electrode were also
evaluated in electrolytic mediums without DA or with only 21 μM DA.
In the presence of AA, AU, and 5-HT, the DA analytical signal
remained constant with variations in current at less than 3%. Despite
being electroactive on the surface of the developed electrode, the
response from 5-HT did not overlap with the DA response. 5-HT still
presented a pair of oxidation peaks at +0.1 and + 0.27 V, thereby
enabling the simultaneous analysis of both neurotransmitters. This
Fig. 6. A) DPVs obtained for DA in the presence of its main interferents. B) shows the influence of UA, 5-HT e AA in the variation of DA signal obtained during DPV.
Voltammograms obtained in 0.1 mol L− 1
KH2PO4, pH 3.4 (v = 10 mV s− 1
, Amp = 25 mV).
V.N. Carvalho da Silva et al.
8. Biosensors and Bioelectronics 210 (2022) 114211
8
hypothesis should be investigated further in future.
Fig. 6B compares the effects of AA, AU, and 5-HT on the DA current
levels. The voltammograms obtained during these tests are presented in
the supplementary material (Figs. S7, S8, and S9, respectively). In
general, none of the interferers caused significant interference in the DA
electrochemical response, with variations in current levels of less than
5%, indicating that the sensor is very specific and selective for DA. These
results motivated us to evaluate the use of PGE/NiTsPc-ZnONPs-CNT for
the direct detection of DA in human serum, and the results are presented
in Table 1.
In Fig. S10 of the supplementary material, it is possible to observe a
calibration curve obtained directly from diluted human serum (real
sample), confirming the possibility of using PGE/NiTsPc-ZnONPs-CNT
to detect DA in this complex analysis matrix. From the calibration
curve shown in Fig. S10, the following equation was determined: DA (in
μM) = i μA - 0.0756/0.5963 (R = 0.998). It can be used to quantify DA in
human serum. In addition, DA recovery was also tested by the analytical
standard recovery method (Table 01).
Data presented in Table 1 indicate that the direct detection of DA
levels close to 0.05 μM in human serum was possible using the proposed
electrode (voltammograms of this analysis are shown in Fig. S11). For
the three other concentrations tested, the analytical recovery levels were
close to 100%, with low relative deviations. Therefore, it can be stated
that PGE/NiTsPc-ZnONPs-CNT is an excellent candidate for direct DA
analysis in human serum.
4. Conclusions
This study demonstrated the synthesis of a new composite material,
on the surface of a PGE, that could act as a catalytic hybrid system for DA
detection. Moreover, the newly developed electrode allowed the direct
detection of DA in human serum without the need for sample pre-
treatment. The PGE/NiTsPc-ZnONPs-CNT presented a DA detection
limit of 7.0 nM. Furthermore, the prepared sensor demonstrated a very
high selectivity in the presence of main interferents, such as AA, AU, and
5-HT. The interferents induced minimal variations in the DA signal.
Although more detailed studies are needed, PGE/NiTsPc-ZnONPs-CNT is
a promising candidate for future clinical diagnostic applications.
CRediT authorship contribution statement
Valécia Natália Carvalho da Silva: Conceptualization, Data cura
tion, Investigation, Methodology, Writing – original draft, Writing –
review & editing. Emanuel Airton de O. Farias: Conceptualization,
Data curation, Investigation, Methodology, Writing – original draft,
Supervision, Writing – review & editing. Alyne R. Araújo: Data cura
tion, Investigation. Francisco Elezier Xavier Magalhães: Conceptual
ization, Data curation, Investigation. Jacks Renan Neves Fernandes:
Conceptualization, Data curation, Investigation. Jéssica Maria Teles
Souza: Conceptualization, Data curation, Investigation. Carla Eiras:
Conceptualization, Data curation, Investigation, Supervision, Visuali
zation, Funding acquisition. Durcilene Alves da Silva: Investigation,
Supervision. Victor Hugo do Vale Bastos: Conceptualization, Data
curation, Investigation. Silmar Silva Teixeira: Conceptualization, Data
curation, Investigation, Funding acquisition, Methodology, Project
administration, Resources, Supervision, Visualization.
Declaration of competing interest
The authors declare that they have no known conflict interests or
personal relationships that could have appeared to influence the work
reported in this paper.
Acknowledgment
The authors are grateful to the Coordination for the Improvement of
Higher Education Personnel (CAPES), National Council for Scientific
and Technological Development (CNPq) for the financial support
received through the process 431275/2018–1 (Call MCTIC/CNPq No.
28/2018-Universal/Range B–Carla Eiras) and Research Productivity
Grant (process 311802/2017–6 (Call CNPq No. 12/2017–Carla Eiras)
and process 305133/2019–5 (Call CNPq No. 06/2019–Silmar Silva
Teixeira)).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.bios.2022.114211.
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Table 1
Direct determination of DA in human serum.
Added (μmol L− 1
) Found (μmol L− 1
) Recovery (%) RSD (%)
0.0 0.05* – 5.13
2.0 2.08 104.00 4.11
4.0 4.07 101.75 3.25
6.0 6.05 100.83 4.16
V.N. Carvalho da Silva et al.
