Green-Mediated Synthesis of NiCo2O4 Nanostructures Using Radish White Peel Extract for the Sensitive and Selective Enzyme-Free Detection of Uric Acid

biosensors
Article
Green-Mediated Synthesis of NiCo2O4 Nanostructures Using
Radish White Peel Extract for the Sensitive and Selective
Enzyme-Free Detection of Uric Acid
Abdul Ghaffar Solangi 1 , Aneela Tahira 1 , Baradi Waryani 2 , Abdul Sattar Chang 3 , Tajnees Pirzada 1 ,
Ayman Nafady 4 , Elmuez A. Dawi 5 , Lama M. A. Saleem 6 , Mohsen Padervand 7 , Abd Al Karim Haj Ismail 5 ,
Kangle Lv 8 , Brigitte Vigolo 9 and Zafar Hussain Ibupoto 3, *
1
2
3
4
5
6
7
8
9
*
Citation: Solangi, A.G.; Tahira, A.;
Waryani, B.; Chang, A.S.; Pirzada, T.;
Nafady, A.; Dawi, E.A.; Saleem,
L.M.A.; Padervand, M.; Haj Ismail,
A.A.K.; et al. Green-Mediated
Synthesis of NiCo2 O4 Nanostructures
Using Radish White Peel Extract for
the Sensitive and Selective
Enzyme-Free Detection of Uric Acid.
Biosensors 2023, 13, 780. https://
doi.org/10.3390/bios13080780
Received: 27 June 2023
Revised: 25 July 2023
Accepted: 30 July 2023
Published: 1 August 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
Institute of Chemistry, Shah Abdul Latif University Khairpur Mirs, Khairpur Mirs 66111, Pakistan;
ghaffarchemistry786@gmail.com (A.G.S.); aneela.tahira@salu.edu.pk (A.T.); tajnees@salu.edu.pk (T.P.)
Department of Fresh Water Biology and Fisheries, University of Sindh, Jamshoro 76080, Pakistan;
baradiw@usindh.edu.pk
Institute of Chemistry, University of Sindh, Jamshoro 76080, Pakistan; asattar.chang@usindh.edu.pk
Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia;
anafady@ksu.edu.sa
Nonlinear Dynamics Research Centre (NDRC), Ajman University, Ajman P.O. Box 346, United Arab Emirates;
e.dawi@ajman.ac.ae (E.A.D.); a.hajismail@ajman.ac.ae (A.A.K.H.I.)
Biomolecular Science, Earth and Life Science, Amsterdam University, 1081 HV Amsterdam, The Netherlands;
lamysaleem@gmail.com
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh P.O. Box. 55181-83111, Iran;
padervand@maragheh.ac.ir
College of Resource and Environment, South-Central Minzu University, Wuhan 430074, China;
lvkangle@mail.scuec.edu.cn
Institut Jean Lamour, Université de Lorraine, CNRS, IJL, F-54000 Nancy, France;
brigitte.vigolo@univ-lorraine.fr
Correspondence: zaffar.ibhupoto@usindh.edu.pk
Abstract: The ability to measure uric acid (UA) non-enzymatically in human blood has been demonstrated through the use of a simple and efficient electrochemical method. A phytochemical extract
from radish white peel extract improved the electrocatalytic performance of nickel–cobalt bimetallic
oxide (NiCo2 O4 ) during a hydrothermal process through abundant surface holes of oxides, an alteration of morphology, an excellent crystal quality, and increased Co(III) and Ni(II) chemical states.
The surface structure, morphology, crystalline quality, and chemical composition were determined
using a variety of analytical techniques, including powder X-ray diffraction (XRD), scanning electron
microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization by CV revealed a linear range of
UA from 0.1 mM to 8 mM, with a detection limit of 0.005 mM and a limit of quantification (LOQ)
of 0.008 mM. A study of the sensitivity of NiCo2 O4 nanostructures modified on the surface to UA
detection with amperometry has revealed a linear range from 0.1 mM to 4 mM for detection. High
stability, repeatability, and selectivity were associated with the enhanced electrochemical performance
of non-enzymatic UA sensing. A significant contribution to the full outperforming sensing characterization can be attributed to the tailoring of surface properties of NiCo2 O4 nanostructures. EIS analysis
revealed a low charge-transfer resistance of 114,970 Ohms that offered NiCo2 O4 nanostructures prepared with 5 mL of radish white peel extract, confirming an enhanced performance of the presented
non-enzymatic UA sensor. As well as testing the practicality of the UA sensor, blood samples from
human beings were also tested for UA. Due to its high sensitivity, stability, selectivity, repeatability,
and simplicity, the developed non-enzymatic UA sensor is ideal for monitoring UA for a wide range
of concentrations in biological matrixes.
Keywords: non-enzymatic uric acid sensor; phytochemicals; radish white peel extract; biological matrix
creativecommons.org/licenses/by/
4.0/).
Biosensors 2023, 13, 780. https://doi.org/10.3390/bios13080780
https://www.mdpi.com/journal/biosensors
Biosensors 2023, 13, 780
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1. Introduction
A purine-based compound called alkaloids is used by our bodies to produce uric acid
(UA) [1,2]. UA concentrations in serum samples range between 0.13 and 0.46 mM, whereas
UA concentrations in urine samples range between 1.49 and 4.50 mM [3]. An abnormal
level of UA in the human body is associated with several chronic and life-threatening diseases, including preeclampsia, arthritis, renal dysfunction, cardiovascular disease, obesity,
high blood pressure, and kidney disease [4–7]. An increase in UA levels in blood serum
has been identified as a major cause of cardiac disease [8]. For this reason, it is essential
to measure and monitor UA in order to prevent the onset of dangerous conditions and to
reduce the risk of premature death. Several analytical methods have been developed to
measure UA as a result of this high importance, including colorimetric enzymatic tests [9].
Capillary electrophoresis method [10], surface-enhanced Raman scattering [11], liquid
chromatography [12], electrochemical method [13], fluorescence spectroscopy [14], and
chemiluminescence [15] are among the methods used. It is common for these analytical
methods to be extremely expensive, time-consuming, and complex to operate. However,
electrochemical methods are inexpensive, sensitive, and selective, thus they have been
extensively studied [16–21]. A number of electrochemical approaches have been used
to quantify UA’s high electrooxidation properties, including enzyme-based and enzymefree methods [22–26]. Due to the high costs associated with enzyme immobilization and
denatured issues with uricase enzyme during storage, non-enzymatic approaches have
become increasingly popular as alternatives to enzyme-based approaches [27]. In nonenzymatic approaches, highly electrocatalytic materials are always desirable [16,18]. To
realize non-enzymatic UA sensors quickly, it will be increasingly necessary to develop
new materials with tailored surfaces that outperform electrocatalytic properties. This task,
however, appears to be challenging because novel materials with tailored surfaces do not
possess electrocatalytic properties. For the development of highly catalytic materials for
non-enzymatic UA sensors, several challenges must be overcome, such as poor electrical
conductivity, a limited number of catalytic sites, and chemical stability concerns. Therefore, numerous electrocatalytic materials have been developed and investigated for the
development of non-enzymatic sensors [28–31]. A significant electrochemical activity of
metal oxides makes them potentially suitable for this application [32–34]. As a result of
its high electrical conductivity and favorable redox properties, a bimetallic oxide, particularly nickel–cobalt oxide (NiCo2 O4 ), has been identified as a potential candidate for
the development of non-enzymatic sensors. As NiCo2 O4 nanostructures exhibit poor
electrochemical performance due to their limited surface properties, they have been utilized in composites with other nanostructured materials, such as Fe2 O3 @ NiCo2 O4 [35],
MnO2 /NiCo2 O4 [36], Co3 O4 /NiCo2 O4 [37,38], and NiCo2 O4 @ graphene [39]. It has
been observed that composite NiCo2 O4 systems exhibit enhanced charge transfer between
electrode and analyte. Several morphologies of NiCo2 O4 have been prepared, including
nanotubes [37], nanorods [36], nanospheres [35], and nanosheets [33]. In spite of NiCo2 O4 ’s
diverse architecture, however, the material fails to perform as expected [35,36,38]. As
a result, it is imperative to identify new strategies for improving the electrochemical
performance of NiCo2 O4 in order to develop more sensitive non-enzymatic UA sensors.
Recent years have seen a great deal of interest in green chemistry due to its simplicity,
eco-friendliness, low cost, and environmental friendliness [39–42]. Several natural products
obtained from biomass wastes can be used to tailor the surface properties of nanostructured
materials, including catalytic sites and charge transfer properties [41,42]. Only a few studies
have been conducted on the synthesis of NiCo2 O4 nanostructured materials from biomass
wastes. The present study examines for the first time the effect of radish white peel extract
(Raphanus sativus) on the morphology, crystal defect, and surface properties of NiCo2 O4
that will be used for fabricating a non-enzymatic UA sensor. Radish white peel extract
contains a wide range of phytochemicals, including alkaloids, glucosinolates, phenolic
compounds, organic acids, anthocyanins, and isothiocyanates. [40,41] (Scheme 1).
Biosensors 2023, 13, x FOR PEER REVIEW
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Biosensors 2023, 13, 780
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extract contains a wide range of phytochemicals, including alkaloids, glucosinolates, phenolic compounds, organic acids, anthocyanins, and isothiocyanates. [40,41] (Scheme 1).
S
S
S
S
C
N
Pungent principal isothiocyanates
NH
Phenylethanamine
NH2
(III)
(II)
2-Pyrrolidinethione
(I)
O
HO
O
O
OH
N
H
HO
N-Methylphenylethanamine
HO
Esculetin
(V)
(IV)
4-Hydroxycinnamic acid
(VI)
HO
O
O
O
O
HO
HO
O
OH
OH
O
Caf f eic Acid
(VII)
Scopoletin
(VIII)
HO
Ferulic acid
(IX)
O
O
OH
O
OH
OH
O
Coumarinic acid
(X)
OH
HO
HO
p-hydroxybenzoic acid,
(XI)
Vanillic acid
(XII)
Scheme1.1.The
Thevarious
variousphytochemicals
phytochemicalspresent
presentininthe
theradish
radish(Raphanus
(Raphanussativus)
sativus)peel
peelextract.
extract.
Scheme
Theradish
radish
white
peel extract
possesses
major phytochemicals,
like as 4-hyThe
white
peel extract
possesses
major phytochemicals,
like as 4-hydroxycinnamic
droxycinnamic
caffeic
acid, and which
isothiocyanates,
were used
as
acid,
caffeic acid,acid,
ferulic
acid,acid,
and ferulic
isothiocyanates,
were usedwhich
as stabilizing,
capping,
and reducing
agents,
and played
a significant
role atoward
enhanced
electrochemical
stabilizing,
capping,
and reducing
agents,
and played
significant
role toward
enhanced
properties
of NiCo
electrochemical
properties
of NiCo2O4 nanostructures.
2 O4 nanostructures.
In
Inthis
thisstudy,
study,we
wehave
haveused
usedradish
radishwhite
whitepeel
peelextracts
extractsfor
forthe
thesurface
surfaceengineering
engineeringofof
NiCo
O
nanostructures
by
hydrothermal
methods.
The
volume
of
extracts
from
peels peels
was
NiCo2 2O44 nanostructures by hydrothermal methods. The volume of extracts from
examined
in order
to determine
the ideal
at which
NiCo2NiCo
O4 nanostructures
was examined
in order
to determine
the concentration
ideal concentration
at which
2O4 nanostruccould
scaled
up forup
high
production.
An extensive
linearlinear
rangerange
of UAof
tures be
could
be scaled
forperformance
high performance
production.
An extensive
detection was detected using surface-modified NiCo2 O4 nanostructures ranging from
0.1 mM to 8 mM.
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UA detection was detected using surface-modified NiCo2O4 nanostructures ranging from
0.1 mM to 8 mM.
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2. Experimental Section
2.1. Chemicals Used
2. Experimental Section
In this
cobalt
chloride hexahydrate (CoCl2·6H2O), nickel chloride hexahydrate
2.1.study,
Chemicals
Used
(NiCl2·6H2O), glucose, lactic acid, uric acid, sodium chloride, potassium chloride, ascorbic
In this study, cobalt chloride hexahydrate (CoCl2 ·6H2 O), nickel chloride hexahydrate
acid, sodium hydroxide, urea, hydrochloric acid, disodium phosphate,
and monopotas(NiCl2 ·6H2 O), glucose, lactic acid, uric acid, sodium chloride, potassium chloride, ascorbic
sium phosphate were applied without pretreatment. We obtained all analytical grade
acid, sodium hydroxide, urea, hydrochloric acid, disodium phosphate, and monopotassium
chemical reagents from Sigma Aldrich, Karachi, and Sindh Pakistan. UA detection was
phosphate were applied without pretreatment. We obtained all analytical grade chemical
performed by preparing the desired solutions in deionized water, followed by preparing
reagents from Sigma Aldrich, Karachi, and Sindh Pakistan. UA detection was performed by
a buffer solution containing 0.1 M phosphate at pH 7.0 for UA detection.
preparing the desired solutions in deionized water, followed by preparing a buffer solution
containing 0.1 M phosphate at pH 7.0 for UA detection.
2.2. Green-Mediated Synthesis of NiCo2O4 Nanostructures Using Radish White Peel Extract
A hydrothermal
method
was ofused
phytochemicalUsing
synthesis
of NiCo
4
2.2. Green-Mediated
Synthesis
NiCo2for
O4 Nanostructures
Radish White
Peel2OExtract
nanostructures.
The radish white
was purchased,
washed
with deionized
water,
and alA hydrothermal
method
was used for
phytochemical
synthesis
of NiCo
2 O4 nanoslowed totructures.
dry at room
to the growth
process.
pieceswater,
of radish
Thetemperature
radish whiteprior
was purchased,
washed
withSmall
deionized
and allowed
white were
chipped
aftertemperature
the peel hadprior
been removed.
An automatic
then
to dry
at room
to the growth
process. juicer
Small was
pieces
of used
radish white
to collectwere
juice chipped
from the after
peel. the
An peel
extract
of
the
peel
was
used
in
the
subsequent
synthesis
had been removed. An automatic juicer was then used to
of NiCo2collect
O4 nanostructures.
NiCo
2O4An
nanostructures
prepared
using
0.1 M cobaltsynthesis
juice from the
peel.
extract of the were
peel was
used in
the subsequent
chloride of
hexahydrate,
0.1 M urea, andNiCo
0.0152 O
M4 nickel
chloride hexahydrate
in 100
mL0.1
ofM cobalt
NiCo2 O4 nanostructures.
nanostructures
were prepared
using
deionizedchloride
water through
a hydrothermal
Various
amounts
of radish
white peel
hexahydrate,
0.1 M urea,process.
and 0.015
M nickel
chloride
hexahydrate
in 100 mL of
extract were
used towater
synthesize
NiCo
2O4 nanostructures.
TheVarious
pH of the
precursor
solution
deionized
through
a hydrothermal
process.
amounts
of radish
white peel
was 8.2 and
7.1, respectively.
the growth
solutions
were
sealed
with
aluminum
extract
were used to Afterward,
synthesize NiCo
O
nanostructures.
The
pH
of
the
precursor
solution
2 4
sheets and
grown
at
95
°C
for
five
hours.
Filter
paper
was
used
to
collect
the
bimetallic
was 8.2 and 7.1, respectively. Afterward, the growth solutions were sealed with aluminum
hydroxide
phase,
and
deionized
was hours.
used toFilter
washpaper
it several
times.toThe
material
sheets
and
grown
at 95 ◦water
C for five
was used
collect
the bimetallic
useddrying
to wash
times.
The material
was thenhydroxide
thermally phase,
roastedand
for deionized
five hours water
at 500 was
°C after
forit12several
h. With
the same
was
then thermally
for five were
hoursobtained
at 500 ◦ Cwithout
after drying
forradish
12 h. With
procedure,
pristine
NiCo2O4 roasted
nanostructures
adding
whitethe same
procedure,
pristineofNiCo
obtained without
adding
peel extract.
An illustration
the synthesis
of NiCo2O4were
nanostructures
as prepared
canradish
be white
2 O4 nanostructures
extract.
found in peel
Scheme
2. An illustration of the synthesis of NiCo2 O4 nanostructures as prepared can be
found in Scheme 2.
Scheme 2. Stepwise synthesis of NiCo2 O4 nanostructures using radish white peel extract during
method,
UA detection,
and real blood
analysis.
Scheme 2.hydrothermal
Stepwise synthesis
of NiCo
2O4 nanostructures
usingsample
radish white
peel extract during hydrothermal method, UA detection, and real blood sample analysis.
2.3. Physical Investigations on the Surface-Modified NiCo2 O4 Nanostructures
An assessment of the morphology of NiCo2 O4 nanostructures was carried out by
scanning electron microscopy (SEM: Auto Fine Coater: JEC-3000FC, No. JSM-IT 100, JEOL
Japan Model, Tokyo, Japan; the coating performed at 20 mA current for 60 s) using an
accelerating voltage of 10 kV. We assessed the crystal quality of radish white peel extract-
Biosensors 2023, 13, 780
5 of 21
assisted NiCo2 O4 nanostructures using powder X-ray diffraction (XRD) at 45 kV and
45 mA using CuK radiation (λ = 1.5418 Å) as an X-ray source. The localized nanoscale
structure was studied using high-resolution transmission electron microscopy (HRTEM)
at a voltage of 200 kV. Utilizing energy dispersive spectroscopy, we were able to quantify
the elemental mapping. The chemical composition of the surface was determined using
X-ray photoelectron spectroscopy (XPS) in high vacuum. As a reference binding energy, we
calibrated the XPS data using C1s at 284.6 eV and deconvolved the XPS features using a
Shirley-type background and Voigt curves.
2.4. Non-Enzymatic Sensing of UA onto Surface-Modified NiCo2 O4 Nanostructures
A variety of electrochemical methods have been used to characterize the non-enzymatic
UA sensor, including cyclic voltammetry, amperometry, electrochemical impedance spectroscopy, and linear sweeping voltammetry. The electrochemical evaluation of NiCo2 O4
nanostructures was conducted using a three-electrode setup. Three electrodes were used:
silver–silver chloride (Ag/AgCl, 3.0 M KCl) as a reference electrode, platinum sheet as
a counter electrode, and glassy carbon electrode (GCE) as a working electrode. Prior to
modification of the GCE, it was polished with an alumina paste of (0.3 µM) and silicon
paper and then cleaned with deionized water. The material ink was prepared by dispersing
10 mg of NiCo2 O4 nanostructures in 2.5 m of deionized water and 0.5 mL of Nafion (5%)
in 2.5 m of deionized water. We achieved homogeneous material ink after 15 min of an
ultrasonic bath. NiCo2 O4 nanostructures were applied to the surface of GCE using a dropcast method. A 10 mM stock solution of UA was prepared in a 0.1 M phosphate buffer
solution of pH 7.0. Prior to dissolving the phosphate buffer solution, UA was dissolved in
propanol. The selectivity of the non-enzymatic UA sensor was determined with 0.1 mM
interfering species, like urea, lactic acid, glucose, ascorbic acid, potassium ions, and sodium
ions, in the presence of the same concentration of UA. The linear range of the UA sensor
was determined by CV and chronoamperometry methods using various UA concentrations
dissolved in 0.1 M phosphate buffer solution (PBS) at pH 7.0. Using this method, it was
possible to estimate the low limit of detection of the non-enzymatic sensor [43].
3. Results and Discussion
3.1. Structural and Morphological Investigations of Radish White Peel Extract-Assisted Synthesis
of NiCo2 O4 Nanostructures
In Figure 1a, we show diffraction patterns measured by powder XRD on NiCo2 O4
nanostructures that reveal their crystal quality. Furthermore, we investigated the effects
of phytochemicals present in the white peel extract of radish on the crystal quality of
NiCo2 O4 nanostructures. The reference card number 00-020-0781 confirms that the typical
reflections of NiCo2 O4 nanostructures are well matched with the cubic phase of NiCo2 O4 .
The diffraction patterns of NiCo2 O4 nanostructures have been identified as (111), (220),
(311), (222), (400), (511), and (440), respectively, at 19.40, 31.30, 36.880, 38.590, 44.850, 59.410,
and 65.300. The morphology of NiCo2 O4 nanostructures prepared with radish peel extract
was examined by SEM. This was performed to compare them with pristine NiCo2 O4
nanostructures, as shown in Figure 1b–f. NiCo2 O4 nanostructures with a high degree of
heterogeneity exhibit a typical nanorod-like orientation as shown in Figure 1b. Figure 1c–f
illustrates that radish white peel extract altered the morphology of NiCo2 O4 nanostructures
toward short-range nanoparticles, confirming the influence of phytochemicals on surface
modification. As well as being much smaller in size, nanostructures have a size range
between 50 and 100 nm, which is characteristic of nanoparticles. Figure 1f illustrates
that radish white peel extract significantly affects the size and morphology of NiCo2 O4
nanostructures. According to Figure 1f, these phytochemicals determined the morphology
and allowed the formation of aggregated and irregularly oriented nanostructures with
unfavorable surface properties when 10 mL of radish white peel extract was used during
the growth process. A phytochemical from radish white peel extract, shown in Scheme 1,
contains oxygenated groups that provide ample coordination with nickel and cobalt metallic
Biosensors 2023, 13, 780
a size range between 50 and 100 nm, which is characteristic of nanoparticles. Figure 1f
illustrates that radish white peel extract significantly affects the size and morphology of
NiCo2O4 nanostructures. According to Figure 1f, these phytochemicals determined the
6 of 21
morphology and allowed the formation of aggregated and irregularly oriented nanostructures with unfavorable surface properties when 10 mL of radish white peel extract was
used during the growth process. A phytochemical from radish white peel extract, shown
in Scheme
groups
that in
provide
ample coordination
withnanorods
nickel
ions
during 1,
thecontains
growthoxygenated
process, which
results
morphological
changes from
cobalt metallic
ions duringNiCo
the 2growth
process, which
results
in morphological
toand
nanoparticles.
As-prepared
O4 nanostructures
were
examined
with HRTEM
changes
from
nanorods
to nanoparticles.
As-prepared
2O4 nanostructures
were eximages
and
Fourier
transform
(FFT) patterns
in order NiCo
to analyze
the deep morphological
amined and
withto
HRTEM
images
and d-spacing.
Fourier transform
patterns inthat
order
to nanoparticles
analyze the
features
calculate
atomic
Figure(FFT)
2a illustrates
the
deepassembled
morphological
features
and atonanorod-like
calculate atomic
d-spacing.
2a illustrates
that in
were
in order
to form
structure.
TheFigure
HRTEM
image shown
the nanoparticles
in order to form
a nanorod-like
structure.
The
HRTEM
Figure
2a confirmswere
the assembled
excellent crystallinity
of NiCo
O
nanostructures.
According
to
2 4
image
shown
in
Figure
2a
confirms
the
excellent
crystallinity
of
NiCo
2
O
4
nanostructures.
Figure 2b, pristine NiCo2 O4 nanostructures have a d-spacing of 0.39 nanometers. Using
Accordingmapping.
to Figure 2b,
pristine
NiCo
2O4 nanostructures have a d-spacing of 0.39 nanomeelemental
Figure
2b–d
illustrates
a uniform distribution of Ni, Co, and O.
ters.
Using
elemental
mapping.
Figure
2b–d illustrates
uniform
of Ni,
Co,
Figure 2e illustrates the EDS spectrum, which
shows Co,aNi,
and Odistribution
as the primary
elements.
and
O.
Figure
2e
illustrates
the
EDS
spectrum,
which
shows
Co,
Ni,
and
O
as
the
primary
A TEM and HRTEM examination of NiCo2 O4 nanostructures, as shown in Figure 3a,
elements.
A TEM
and with
HRTEM
of d-spacing.
NiCo2O4 nanostructures,
as revealed
shown in typical
Figwas
conducted
along
the examination
calculation of
A TEM image
ure
3a,
was
conducted
along
with
the
calculation
of
d-spacing.
A
TEM
image
revealed
nanoparticle morphologies, and HRTEM confirmed the high crystal quality of NiCo2 O4
typical nanoparticle morphologies, and HRTEM confirmed the high crystal quality of
nanostructures (Figure 3). Figure 3a shows that NiCo2 O4 nanostructures exhibit a spinel
NiCo2O4 nanostructures (Figure 3). Figure 3a shows that NiCo2O4 nanostructures exhibit
crystal structure and a cubic phase as revealed by the FFT analysis. According to Figure 3b–
a spinel crystal structure and a cubic phase as revealed by the FFT analysis. According to
d, the d-spacing value of this sample was 0.36 nm, in agreement with results published for
Figure 3b–d, the d-spacing value of this sample was 0.36 nm, in agreement with results
NiCo2 O4 nanostructures. An elemental analysis of these nanostructures utilizing 5 mL of
published for NiCo2O4 nanostructures. An elemental analysis of these nanostructures utiradish white peel extract revealed a homogeneous distribution of Co, Ni, and O elements.
lizing 5 mL of radish white peel extract revealed a homogeneous distribution of Co, Ni,
As shown in Figure 3e, the EDS spectrum indicates that the surface-modified NiCo2 O4
and O elements. As shown in Figure 3e, the EDS spectrum indicates that the surface-modnanostructures
prepared using 5 mL of radish white peel extract contain quantified amounts
ified NiCo2O4 nanostructures prepared using 5 mL of radish white peel extract contain
ofquantified
Ni, Co, and
O.
amounts of Ni, Co, and O.
Figure 1. (a) Powder XRD diffraction patterns of pristine, 5 mL, and 10 mL of radish peel extractFigure
1. NiCo
(a) Powder
XRD diffraction patterns of pristine, 5 mL, and 10 mL of radish peel extractassisted
2O4 nanostructures, (b–f) Corresponding SEM images of (b) pristine, (c,d) 5 mL, and
assisted
(b–f) Corresponding
SEM images
of (b) pristine, (c,d) 5 mL, and
respectively
(e,f) 10 NiCo
mL of2 O
radish
peel extract-assisted
NiCo2O4 nanostructures
4 nanostructures,
(e,f) 10 mL of radish peel extract-assisted NiCo2 O4 nanostructures respectively.
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images of
of pristine NiCo22O
O44 nanostructures
nanostructures and
and FFT
FFT conversion
conversion at right
Figure 2. (a) TEM/HRTEM
TEM/HRTEM images
Figure 2. (a) TEM/HRTEM
images of pristine NiCo2O4 nanostructures
and FFT conversion at right
side
with d-spacing value; (b–d) corresponding elemental mapping
mapping of (e) EDS spectra of pristine
side with
d-spacing value; (b–d) corresponding elemental mapping of (e) EDS spectra of pristine
NiCo
NiCo22O
O4 nanostructures.
nanostructures.
NiCo2O44 nanostructures.
Figure 3. (a) TEM/HRTEM images of NiCo O nanostructures prepared with 5 mL of radish white
Figure 3. (a) TEM/HRTEM images of NiCo22O44nanostructures prepared with 5 mL of radish white
Figure
3. (a)and
TEM/HRTEM
images ofvalue
NiCoon
2Oright-hand
4 nanostructures
prepared
with 5mapping
mL of radish
peel
extract
FFT
side; (b–d)
elemental
mapping
of (e)
(e)white
EDS
peel
extract
and
FFT with
with d-spacing
d-spacing
value
on
right-hand
side;
(b–d)
elemental
of
EDS
peel
extract
and
FFT
with
d-spacing
value
on
right-hand
side;
(b–d)
elemental
mapping
of
(e)
EDS
spectrum
of
NiCo
O
nanostructures
prepared
with
5
mL
of
radish
white
peel
extract.
spectrum of NiCo22O44 nanostructures prepared with 5 mL of radish white peel extract.
spectrum of NiCo2O4 nanostructures prepared with 5 mL of radish white peel extract.
The presence
presence of
of green
in the
The
green organic
organic recuing,
recuing, capping,
capping, and
and stabilizing
stabilizing agents
agents in
the radish
radish
The
presence
of green
organic
recuing,
capping,
and stabilizing
agents
in the radish
white
peel
extract
have
the
capability
to
tailor
the
surface
properties
of
nanostructured
white peel extract have the capability to tailor the surface properties of nanostructured
white peel[28,42].
extractUsing
have XPS
the capability
to were
tailorable
the surface
properties
of nanostructured
materials
analysis, we
to determine
the chemical
states and
materials [28,42]. Using XPS analysis, we were able to determine the chemical states and
surface
species
ofUsing
NiCo2XPS
O4 nanostructures
both
in to
thedetermine
absence and
presence states
of radish
materials
[28,42].
analysis, we were
able
the chemical
and
surface species of NiCo2O4 nanostructures both in the absence and presence of radish
white
peel
extract,
as shown
in Figure 4. The
XPSinstudy
has demonstrated
a significant
surface
species
of NiCo
2O4 nanostructures
both
the absence
and presence
of radish
white peel extract, as shown in Figure 4. The XPS study has demonstrated a significant
role
of peel
a wide
range
greenin
organic
capping,
anddemonstrated
stabilizing agents
on the
white
extract,
asofshown
Figurereducing,
4. The XPS
study has
a significant
Biosensors 2023, 13, x FOR PEER REVIEW
8 of 21
Biosensors 2023, 13, 780
8 of 21
role of a wide range of green organic reducing, capping, and stabilizing agents on the
surface chemical composition of NiCo2O4 nanostructures. To fit the XPS binding energies
surface chemical composition of NiCo2 O4 nanostructures. To fit the XPS binding energies
of each
each element,
element, aa standard
standard carbon
carbonbinding
bindingenergy
energywas
wasused.
used. Using
Usingpristine
pristineNiCo
NiCo2O
O4
of
2 4
nanostructures
as
an
example,
Figure
4a
illustrates
the
Co
2p
spectrum,
which
indicates
nanostructures as an example, Figure 4a illustrates the Co 2p spectrum, which indicates
that there
CoCo
chemical
states.
According
to Figure
5a, the
peaks
that
there are
aretwo
twotypes
typesofof
chemical
states.
According
to Figure
5a,estimated
the estimated
3+ and 3+
2+, respecat
779.47
eV
and
780.54
eV
correspond
to
the
oxidation
states
of
Co
Co
peaks at 779.47 eV and 780.54 eV correspond to the oxidation states of Co and Co2+ ,
tively. It is illustrated
in Figure
5b how
thethe
Ni Ni
2p2p
spectrum
respectively.
It is illustrated
in Figure
5b how
spectrumcan
canbebefitted
fittedusing
using Voigt’s
Voigt’s
method.
The
fitted
data
consist
of
two
spin
orbital
doublet
peaks,
853.88
eV
and
855.60
method. The fitted data consist of two spin orbital doublet peaks, 853.88 eV and 855.60
eV,
2+ and
3+ chemical states. It should be noted that despite
2+
3+
eV,
corresponding
to
the
Ni
Ni
corresponding to the Ni and Ni chemical states. It should be noted that despite these
these limitations,
the shakeup
peaks
have
been identified,
and of
the
of Nito2p
fitted
to
limitations,
the shakeup
peaks have
been
identified,
and the data
Nidata
2p fitted
XPS
agree
XPS
agree
reasonably
well
with
the
reported
peaks
[36,44].
Furthermore,
Figure
4c
disreasonably well with the reported peaks [36,44]. Furthermore, Figure 4c displays the O 1s
plays the for
O 1s
spectrum
for
pristine NiCo2O4 nanostructures in addition to the metallic
spectrum
pristine
NiCo
2 O4 nanostructures in addition to the metallic chemical states.
chemical
states.
The material
surface
shows
threeeV,
peaks
at 529.69
eV,532.68
531.10eV,
eV,
and 532.68
The
material
surface
shows three
peaks
at 529.69
531.10
eV, and
respectively,
eV, respectively,
correspondingchemical
to metal–oxygen
chemical
oxygen ions, and
corresponding
to metal–oxygen
bonds, oxygen
ions, bonds,
and physic/chemisorbed
physic/chemisorbed
water.
Previous
studies different
[36,44] have
detectedspecies
different
water.
Previous studies
[36,44]
have detected
oxygenated
on oxygenated
the surface
−
1
species
on
the
surface
of
pristine
NiCo
2
O
4
nanostructures.
The
spectrum
of
O−1 s531.10
at 529.69
of pristine NiCo2 O4 nanostructures. The spectrum of O s at 529.69 eV and
eV
2
−
2−
eV and
531.10 eV
was
correlated
withpresent
the O on
species
on NiCo2O4 nanostructures.
was
correlated
with
the
O species
NiCopresent
A similar XPS
2 O4 nanostructures.
A similarwas
XPSconducted
analysis was
on NiCo2O4 nanostructures
prepared
in the
analysis
on conducted
NiCo2 O4 nanostructures
prepared in the
presence
of 5presmL
ence
of 5 white
mL of peel
radish
whiteaspeel
extract
as shown
in A
Figure
large
peak was
obof
radish
extract
shown
in Figure
4d–f.
large4d–f.
peakAwas
observed
in the
3+ and
3+ and Co
, at
served in of
theCo
spectrum
of Cowith
2p associated
oxidation
states,
such
as, Co
spectrum
2p associated
oxidation with
states,
such as Co
Co2+
at 779.57
eV 2+and
781.12V,
respectively.
Byrespectively.
contrast, Ni2+
Ni3+ were
at 853.96
eV and
779.57 eV
and 781.12V,
Byand
contrast,
Ni2+ observed
and Ni3+ were
observed
at 855.61
853.96 eV,
eV
respectively.
Furthermore,
three
contributions
were
observed
in
the
O1s
spectrum
at
and 855.61 eV, respectively. Furthermore, three contributions were observed in the O1s
529.67
eV, 531.16
eV, and
to the
metal–oxygen
oxygen ions
spectrum
at 529.67
eV, 533.42
531.16 eV,
eV,corresponding
and 533.42 eV,
corresponding
tobonds,
the metal–oxygen
(O
physic/chemisorbed
water on the surfacewater
of theonmaterial.
Theof
XPS
has
bonds,
oxygen
ions (O2), and physic/chemisorbed
the surface
thestudy
material.
2 ), and
revealed
green
organic reducing,
and stabilizing
agents
radish agents
white
The XPS that
study
has revealed
that greencapping,
organic reducing,
capping,
andfrom
stabilizing
peel
a relatively
high
concentration
oxygen
ions (O− ) and
Co3+ compared
fromextract
radishhave
white
peel extract
have
a relativelyofhigh
concentration
of oxygen
ions (O−)
3+
to
pristine
NiCo
O
nanostructures.
These
surface
properties
are
highly
desirable
a
and Co compared
are
2 4 to pristine NiCo2O4 nanostructures. These surface propertiesfor
catalytic
reaction
[36,44].
Furthermore,
the
green
organic
reducing,
capping,
and
stabilizing
highly desirable for a catalytic reaction [36,44]. Furthermore, the green organic reducing,
3+
agents
have
a high
abundance
of Co3+
/Co2+
and Ni2+ /Ni
positively
capping,
andinduced
stabilizing
agents
have induced
a high
abundance
of Co3+metallic
/Co2+ and
Ni2+/Ni3+
charged
in the charged
surface of
NiCo
O4 surface
nanostructures.
Consequently,
theseConsequently,
metallic ions
metallic ions
positively
ions
in 2the
of NiCo2O
4 nanostructures.
have
highhave
density
of catalytic
sites forof
the
favorable
electrocatalytic
reaction
of
theseoffered
metallica ions
offered
a high density
catalytic
sites
for the favorable
electroUA.
catalytic reaction of UA.
Figure 4. XPS-resolved Co 2p, Ni 2p, O1s spectra for pristine (a–c) and (d–f) XPS-resolved Co 2p, Ni
2p, O1s of 5 mL of radish peel extract-assisted NiCo2 O4 nanostructures.
Biosensors 2023, 13, x FOR PEER REVIEW
9 of 21
Biosensors 2023, 13, 780
9 of 21
Figure 4. XPS-resolved Co 2p, Ni 2p, O1s spectra for pristine (a–c) and (d–f) XPS-resolved Co 2p, Ni
2p, O1s of 5 mL of radish peel extract-assisted NiCo2O4 nanostructures.
Figure 5. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL and 10 mL of
Figure 5. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL and 10 mL of radish
radish white peel extract-assisted NiCo2O4 and pristine NiCo2O4-modified GCE in the presence of
white peel extract-assisted NiCo2 O4 and pristine NiCo2 O4 -modified GCE in the presence of 0.5 mM of
0.5 mM of UA in 0.1 M PBS pH 7.0. (b) Cyclic voltammograms at 50 mV/s of bare GCE and modified
UA in5 0.1
pH 7.0.
(b)2Cyclic
voltammograms
at 50inmV/s
of bare GCE
and
modified
with
mL
with
mLMofPBS
assisted
NiCo
O4 in electrolyte
and equal
the presence
of 0.5
mM
UA in 0.1
M5PBS
of
assisted
NiCo
O
in
electrolyte
and
equal
in
the
presence
of
0.5
mM
UA
in
0.1
M
PBS
pH
7.0.
2 4
pH 7.0.
3.2. Non-Enzymatic Uric Acid (UA) Oxidation on the Surface-Modified NiCo2 O4 Nanostructures
with Radish White Peel Extract
NiCo2 O4 nanostructures were characterized electrochemically using a three-electrode
cell configuration in order to detect UA. Figure 5a illustrates preliminary studies conducted
with cyclic voltammetry to identify the most efficient NiCo2 O4 nanostructures for the
oxidation of UA. A CV curve was measured at 50 mV/s using both pristine NiCo2 O4
nanostructures and NiCo2 O4 nanostructures, which had been surface-modified with 5 mL
and 10 mL of radish white peel extract in the absence or presence of UA. A CV curve, such as
that shown in Figure 6a, is representative of electrochemical catalytic signals obtained from
pristine and surface-modified NiCo2 O4 nanostructures placed in 0.5 mM UA in a phosphate
buffer solution at pH 7.0. When comparing NiCo2 O4 nanostructures prepared with 5 mL
of radish white peel extract with pristine and surface-modified NiCo2 O4 nanostructures
soaked in 10 mL of radish white peel extract, it is evident that the electrocatalytic properties
of these nanostructures are well described when compared to pristine and surface-modified
NiCo2 O4 nanostructures soaked in 10 mL of radish white peel extract. This is due to the
enhanced conductivity of the material and the enriched surface sites on the surface. Due
to the poor catalytic properties and the electrical conductivity of NiCo2 O4 , the CV curve
shows that the peak current is relatively low when UA is oxidized on pristine NiCo2 O4
nanostructures. However, the electrochemical performance of NiCo2 O4 nanostructures was
strongly dependent on the volume of radish white peel extract, as evidenced by the limited
electrochemical signal in Figure 5a for a sample containing 10 mL of radish white peel
extract. For the large-scale synthesis of NiCo2 O4 nanostructures that are highly desirable
for electrochemical applications, 5mL of radish white peel extract appears to provide the
best conditions. Moreover, NiCo2 O4 nanostructures prepared using 5 mL of radish white
peel extract and bare glassy carbon electrodes were tested in the presence of 0.5 mM UA
and only in the presence of a phosphate buffer solution at pH 7.0, as shown in Figure 6b.
UA is believed to cause the signal to originate primarily from NiCo2 O4 nanostructures;
however, the bare glassy carbon electrode, as shown in Figure 5b, did not demonstrate
any electrochemical signal for either the electrolyte or analyte. Based on the CV analysis,
NiCo2 O4 nanostructures synthesized with radish white peel extract were only effective for
driving UA oxidation in the phosphate buffer solution, thus full non-enzymatic UA sensor
characterization was carried out.
Biosensors 2023, 13, 780
tested in the presence of 0.5 mM UA and only in the presence of a phosphate buffer solution at pH 7.0, as shown in Figure 6b. UA is believed to cause the signal to originate primarily from NiCo2O4 nanostructures; however, the bare glassy carbon electrode, as shown
in Figure 5b, did not demonstrate any electrochemical signal for either the electrolyte or
analyte. Based on the CV analysis, NiCo2O4 nanostructures synthesized with radish 10
white
of 21
peel extract were only effective for driving UA oxidation in the phosphate buffer solution,
thus full non-enzymatic UA sensor characterization was carried out.
Figure 6. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 6. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel extract-assisted NiCo2O4-modified GCE in the presence of 0.5 mM of UA in 0.1 M PBS pH 7.0.
peel extract-assisted NiCo2 O4 -modified GCE in the presence of 0.5 mM of UA in 0.1 M PBS pH 7.0.
(b) Linear plot of peak current against square root of scan rate.
(b) Linear plot of peak current against square root of scan rate.
When UA is oxidized on NiCo2 O4 nanostructures, electrons are transferred from UA
to Co3+ and Ni3+ ions and reduced to Co2+ and Ni2+ . In addition to altering the size and
surface properties of NiCo2 O4 nanostructures, phytochemicals in radish white peel extract
enhanced the charge transfer between the electrode and analyte solution. Figure 6a shows
the electrode kinetics at various scan rates using CV analysis in a solution containing 0.5 mM
UA. It is evident from this example that increasing scan rates linearly increase peak current.
This confirms the diffusion-controlled processing of the modified GCE with NiCo2 O4 . As
shown in Figure 6b, a linear plot was obtained by plotting the peak current against the
square root of the scan rate. The purpose of this was to simplify the understanding of
electrode kinetics. NiCo2 O4 nanostructure-based electrodes have been found to have a
high scan rate in recent studies. According to CV analysis, UA oxidation is accompanied by
two electron and proton transfers [44–47]. Also, the observed regression coefficient value
(R2 —0.99) supports the analytical aspects of an enzyme-free UA sensor for precise and
accurate quantification of UA. Therefore, surface adsorption and electrochemistry were
responsible for controlling the UA oxidation reaction.
Our study examined the effect of pH on the oxidation process of NiCo2 O4 nanostructures prepared with 5 mL of radish white peel extract. As a result of the pH change of
0.5 mM of UA, CV curves for NiCo2 O4 nanostructures are illustrated in Figure 7a. We evaluated UA sensor performance at pH 7.0 based on the shape and current of the peak, which
were more apparent at this pH level. A pH study indicated that NiCo2 O4 nanostructures
are strongly regulated by the pH of the analyte solution when it comes to their activity.
Such aspects have previously been examined in a study [48]. NiCo2 O4 nanostructures
are limited in their ability to function under different pH conditions of analyte solutions.
Consequently, the catalytic sites are diminishing, the material is unstable, and the surfaces
are etched [49]. As a result of this experiment, the pH of the UA solution was varied
between 6.0, 7.0, 8.0, and 9.0. As a result, CV displayed a stable response at pH 7.0, and
all electrochemical measurements were made at this pH level. To facilitate interpretation
of CV curves, a line plot was also made of the effect of pH on the UA solution. Figure 7b
illustrates that pH 7.0 resulted in the highest peak current, which improved charge transfer
and increased the NiCo2 O4 nanostructures’ electrochemical activity. UA oxidation occurs
when two protons are lost and is suppressed by UA’s low pH of 7.0. However, at higher
pH levels, NiCo2 O4 nanostructures are likely to be etched, resulting in poor performance.
Biosensors 2023, 13, 780
6.0, 7.0, 8.0, and 9.0. As a result, CV displayed a stable response at pH 7.0, and all electrochemical measurements were made at this pH level. To facilitate interpretation of CV
curves, a line plot was also made of the effect of pH on the UA solution. Figure 7b illustrates that pH 7.0 resulted in the highest peak current, which improved charge transfer
and increased the NiCo2O4 nanostructures’ electrochemical activity. UA oxidation occurs
11 of 21
when two protons are lost and is suppressed by UA’s low pH of 7.0. However, at higher
pH levels, NiCo2O4 nanostructures are likely to be etched, resulting in poor performance.
Figure 7. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 7. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel extract-assisted NiCo2O4-modified GCE in the presence of different pH values of 0.5 mM of UA
peel extract-assisted NiCo2 O4 -modified GCE in the presence of different pH values of 0.5 mM of UA
in 0.1 M PBS. (b) Linear plot of peak current versus different pH values of 0.5 mM of UA in 0.1 M
in
0.1 M PBS. (b) Linear plot of peak current versus different pH values of 0.5 mM of UA in 0.1 M PBS.
PBS.
3.3. The Calibration Plots, Stability, Repeatability, and Selectivity Studies of a Newly Developed
Non-Enzymatic UA Sensor Based on Surface-Modified NiCo2 O4 Nanostructures
Analyses of the linear range and limit of detection of UA were conducted using
NiCo2 O4 nanostructures prepared with 5 mL of radish white peel extract. The linear range
of a non-enzymatic UA sensor was evaluated by varying electrochemical modes in order
to maintain the sensing range of each electrochemical mode. The linear range of UA was
first investigated by CV at 50 mV/s in a phosphate buffer solution at pH 7.0 at different
concentrations of UA. The linear range of UA was determined to be between 0.1 mM
and 8 mM, and the peak current for UA oxidation increased linearly with increasing UA
concentration, as shown in Figure 8a. Based on this study, it can be concluded that UA
non-enzymatic sensors have demonstrated a wide linear range to date [13,50–56] as well
as the low detection limit of 0.005 mM, indicating a high degree of applicability for the
monitoring of UA at either low or high concentrations in real samples. In addition, the
linear plot shown in Figure 8b was calculated by selecting the oxidation peak current for
each UA concentration against the UA concentration in order to determine the accuracy
and precision of a newly developed non-enzymatic UA sensor. It appears that UA sensors
have the ability to monitor a wide range of UA concentrations from practical samples based
on the linear plot of the CV results. On the basis of the methods reported in the literature, a
limit of detection (LOD) and a limit of quantification (LOQ) were estimated [56]. In this
study, the LOD and LOQ were determined to be 0.005 mM and 0.008 mM, respectively.
Table 1 compares the wide linear range of UA detection and the low LOD of the nonenzymatic UA sensors presented with the existing UA biosensors. Following the analysis of
the comparisons, it became evident that the proposed method can be of great interest as an
alternative method for the detection of UA in real samples, where a wide linear range and
a low limit of detection are desired. Additionally, linear sweep voltammetry (LSV) mode
was used to estimate the calibration of the newly developed non-enzymatic UA sensor,
and Figure 9a illustrates the range of UA detection obtained. Figure 9a illustrates that the
proposed UA sensor configuration is capable of detecting UA over a wide linear range from
0.1 mM to 7.0 mM and producing a significant amount of current. When UA concentration
increases in LSV measurements, there is a higher current generated, which indicates that
the newly developed UA sensor is highly sensitive. Besides the LSV measurements, we
also made a linear plot of peak current and UA concentrations (Figure 9b). The linear
fitting of LSV curves reveals that the proposed non-enzymatic UA sensor has excellent
Biosensors 2023, 13, 780
12 of 21
analytical performance, as indicated by its regression coefficient value of 0.99. Based on
full CV curves and half CV curves from LSV, the present UA sensor is capable of detecting
a wide linear range of UA with precision and accuracy. Additionally, the linear range
for another highly sensitive electrochemical mode of amperometry at 0.3 V was used to
determine the linear range of the UA sensor. Figure 10a illustrates this range for various UA
concentrations detected. UA concentrations between 0.1 and 6 mM were highly sensitive
Biosensors 2023, 13, x FOR PEER REVIEW
of 21
to the amperometric signal. Figure 10b illustrates a linear plot of the amperometric13signal
for these different concentrations of UA.
Figure 8. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 8. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel extract-assisted NiCo2O4 in the presence of various concentrations of UA in 0.1 M PBS pH 7.0.
peel extract-assisted NiCo2 O4 in the presence of various concentrations of UA in 0.1 M PBS pH 7.0.
(b) Linear plot of peak current versus successive increase in UA concentrations.
(b) Linear plot of peak current versus successive increase in UA concentrations.
Table 1. Performance comparison of the enzyme-free sensor based on NiCo2O4 nanostructures
Table 1.with
Performance
comparison
ofsativus)
the enzyme-free
sensorseveral
based on
NiCo2 O4 nanostructures
grown
5 mL radish
(Raphanus
extract versus
non-enzymatic
UA sensors grown
in the
with 5 mL radish (Raphanus sativus) extract versus several non-enzymatic UA sensors in the literature.
literature.
SensingElectrode
Electrode Material
Material
Sensing
PCN
PCN aa/MWCNT
/MWCNT b
c
B-MWCNTS
B-MWCNTS c
d
Pd/RGO
Pd/RGO d
Au/RGO dd
Au/RGO
PtNi@MoS2 e
PtNi@MoS2 e
Cysteic acid
Cysteic
Co3Oacid
4
O4
Fe2Co
O33@Au
NiCo2O4 (30%)/Nano-ZSM-5
Fe2 O3 @Au
AuNPs@GO/PPy/CFP
NiCo2 O4 (30%)/Nano-ZSM-5
MWNTs/MGF
AuNPs@GO/PPy/CFP
NiCo2O4 NPs
Linear
LinearRange
Range
(ụM)
(ụM)
0.2–20
0.2–20
62–250
62–250
6–469.5
6–469.5
8.8–53
8.8–53
0.5–600
0.5–600
1.0–19
1.0–19
500–3500
500–3500
100–10,000
0.9–1000
100–10,000
2–360
0.9–1000
300–1000
2–360
100–8000
Detection
Detection of
of Limit
Limit
(ụM)
(ụM)
0.139
0.139
0.65
0.65
1.6
1.6
1.8
1.8
0.1
0.1
0.36
0.36
100
100
0.087
0.7
0.087
1.68
0.7
0.93
1.68
0.005
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[60]
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electrode
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a
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glassy carbon electrode
Biosensors 2023, 13, 780
x FOR PEER REVIEW
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1413ofof 21
Biosensors 2023, 13, x FOR PEER REVIEW
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Figure 9. (a) Linear sweep voltammetry at a scan rate of 10 mV/s of MGCE with 5 mL of radish
Figure 9. (a) Linear sweep voltammetry at a scan rate of 10 mV/s of MGCE with 5 mL of radish
white
extract-assisted
2O4 in the
of various
concentrations
of UA
in 0.1
PBS
Figurepeel
9. (a)
Linear sweep NiCo
voltammetry
atpresence
a scan rate
of 10 mV/s
of MGCE with
5 mL
of M
radish
white peel extract-assisted NiCo2 O4 in the presence of various concentrations of UA in 0.1 M PBS pH
pH
7.0.
(b)
Linear
plot
of
peak
current
versus
successive
increase
in
UA
concentrations.
white peel extract-assisted NiCo2O4 in the presence of various concentrations of UA in 0.1 M PBS
7.0. (b) Linear plot of peak current versus successive increase in UA concentrations.
pH 7.0. (b) Linear plot of peak current versus successive increase in UA concentrations.
Figure 10. (a) Chronoamperometric response curves measured at an applied potential of 0.3 V of
MGCE
mL of radish white peel
extract-assisted
NiCo2O4 at
in an
theapplied
presencepotential
of various
concenFigure with
10. (a)5 Chronoamperometric
response
curves measured
of 0.3
V of
Figure 10. (a) Chronoamperometric response curves measured at an applied potential of 0.3 V
trations
of UA
in 0.1
PBS pH
7.0.peel
(b) Linear
plot of peak
current
successive
increaseconcenin UA
MGCE with
5 mL
ofM
radish
white
extract-assisted
NiCo
2O4 inversus
the presence
of various
of MGCE with 5 mL of radish white peel extract-assisted NiCo2 O4 in the presence of various
concentrations.
trations of UA in 0.1 M PBS pH 7.0. (b) Linear plot of peak current versus
successive increase in UA
concentrations of UA in 0.1 M PBS pH 7.0. (b) Linear plot of peak current versus successive increase
concentrations.
in UAAconcentrations.
linear fitting of the UA detection resulted in excellent performance with strong
A linear
fittingThe
of results
the UAconfirm
detection
in excellent
performance
strong
analytical
features.
theresulted
algorithm’s
promising
performancewith
for the
deA linear fitting of the UA detection resulted in excellent performance with strong
analytical
features.
results confirm
the algorithm’s
performance
fordensity
the detection
of UAs
and The
its application
in real-world
samplepromising
analysis. Due
to the high
analytical features. The results confirm the algorithm’s promising performance for the
tection
of UAs
andenhanced
its application
in real-world
sampleand
analysis.
Due to compatibility
the high density
of
catalytic
sites,
electrical
conductivity,
biomimetic
of
detection of UAs and its application in real-world sample analysis. Due to the high
of
catalytic
sites,
enhanced
electrical
conductivity,
and
biomimetic
compatibility
of
nanostructured material with the surface of GCE, UA detection on surface-modified
density of catalytic sites, enhanced electrical conductivity, and biomimetic compatibility
nanostructured
material with
withradish
the surface
GCE,
UApresented
detection outstanding
on surface-modified
NiCo
2O4 nanostructures
white of
peel
extract
linearity
of nanostructured material with the surface of GCE, UA detection on surface-modified
NiCo
2O4 nanostructures
with
radish
white
peel
extract
presented
outstanding
linearity
and
high
sensitivity.
The
SEM,
XRD,
HRTEM,
and
XPS
measurements
demonstrated
taiNiCo2 O4 nanostructures with radish white peel extract presented outstanding linearity and
and
high
sensitivity.
The
SEM,
XRD,
HRTEM,
and
XPS
measurements
demonstrated
tailored
morphology,
excellent
crystal
quality,
a
significant
amount
of
surface
vacancies,
and
high sensitivity. The SEM, XRD, HRTEM, and XPS measurements demonstrated tailored
lored
morphology,
excellent
crystal
quality,
a
significant
amount
of
surface
vacancies,
and
an
abundance
of
Co(III)
and
Ni(II)
chemical
states,
which
led
to
the
superior
performance
morphology, excellent crystal quality, a significant amount of surface vacancies, and an
an
abundance
Co(III)
and
Ni(II)
chemical
which
led
tothe
the
superior
performance
of
NiCo
2O4 nanostructures
prepared
with states,
5states,
mL of
radish
white
peel
extract.performance
In order to
abundance
of of
Co(III)
and
Ni(II)
chemical
which
led
to
superior
of
NiCo
2O
4 nanostructures
prepared
with
5
mL
of
radish
white
peel
extract.
order
evaluate
the
selectivity
of
a
UA
sensor
before
implementing
it
in
actual
sample
of NiCo2 O4 nanostructures prepared with 5 mL of radish white peel extract. In
Inanalysis,
order to
to
evaluate
a UA
sensor
before
implementing
in actual sample
we
testedthe
theselectivity
proposed of
UA
sensor
in the
presence
of possibleit interfering
speciesanalysis,
during
we tested the proposed UA sensor in the presence of possible interfering species during
Biosensors 2023, 13, 780
14 of 21
Biosensors 2023, 13, x FOR PEER REVIEW
15 of 21
evaluate the selectivity of a UA sensor before implementing it in actual sample analysis,
we tested the proposed UA sensor in the presence of possible interfering species during
detection of
of UA
UAin
inreal
realblood
bloodand
andurine
urinesamples.
samples.It It
was
determined
that
selectivity
detection
was
determined
that
thethe
selectivity
of
of the
interfering
compoundscould
couldbebemonitored
monitoredby
by preparing
preparing NiCo22O44 nanostructures
the
interfering
compounds
with radish white peel extract
extract containing
containing glucose,
glucose, ascorbic
ascorbic acid,
acid, urea,
urea, lactic
lactic acid,
acid,mannose,
mannose,
sodium ions, chloride ions, potassium ions, and calcium
calcium ions, as shown in Figure 11. CV
ofof
interfering
species
to atosolution
curves were
were measured
measuredfollowing
followingthe
thesequential
sequentialaddition
addition
interfering
species
a soluof 0.5ofmM
UA. UA.
Based
on Figure
11a,11a,
the interfering
species
hadhad
the the
same
concentration
tion
0.5 mM
Based
on Figure
the interfering
species
same
concentraas the
As aAs
result
of the
sequential
addition
of interfering
species
in the
presence
of
tion
asUA.
the UA.
a result
of the
sequential
addition
of interfering
species
in the
presence
UA,
UA
was
not
affected
in
terms
of
oxidation
peak
position,
drift
in
oxidation
potential,
of UA, UA was not affected in terms of oxidation peak position, drift in oxidation potenand and
peak
current,
suggesting
that
thethe
proposed
tial,
peak
current,
suggesting
that
proposedUA
UAsensor
sensorconfiguration
configuration has
has excellent
excellent
selectivity
and
is
suitable
for
the
detection
of
UA
in
biological
matrixes.
In
order
to better
better
selectivity and is suitable for the detection of UA in biological matrixes. In order to
visualize
the
variation
in
UA
peak
current
after
the
addition
of
interfering
species,
bar
visualize the variation in UA peak current after the addition of interfering species, aa bar
graph of
of the
the peak
peak current
current was
was plotted.
The change
change in
in peak
peak current
current could
could be
be seen
seen at
at less
less
graph
plotted. The
than
4%,
as
shown
in
Figure
11b.
The
excellent
selectivity
of
the
proposed
UA
sensor
can
than 4%, as shown in Figure 11b. The excellent selectivity of the proposed UA sensor can
be
attributed
to
the
surface
modification
of
NiCo
O
nanostructures
with
phytochemicals
2
4
be attributed to the surface modification of NiCo2O4 nanostructures with phytochemicals
from radish
radish white
white peel
peel extract,
extract, which
which enabled
enabled it
it to
to detect
detect specific
specific electroactive
electroactive molecules.
molecules.
from
Figure 11. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 11. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel extract-assisted NiCo2O4 in the presence of 0.5 mM UA and other competing interfering agents
peel extract-assisted NiCo2 O4 in the presence of 0.5 mM UA and other competing interfering agents in
in 0.1 M PBS pH 7.0; (b) bar graph of peak current with addition of interfering species for the illus0.1 M PBS
pHvariation
7.0; (b) bar
of peak
current with addition of interfering species for the illustration
tration
of the
ofgraph
the peak
current.
of the variation of the peak current.
We examined the repeatability of the modified UA sensor electrode by measuring 20
We examined the repeatability of the modified UA sensor electrode by measuring
CV cycles at a scan rate of 50 mV/s in 0.5 mM. It was found that the device could be reused,
20 CV cycles at a scan rate of 50 mV/s in 0.5 mM. It was found that the device could
as shown in Figure 12a. The long-term stability of UA biosensors is always a challenge,
be reused, as shown in Figure 12a. The long-term stability of UA biosensors is always a
especially for enzymatic biosensors, thus we have designed a non-enzymatic UA sensor
challenge, especially for enzymatic biosensors, thus we have designed a non-enzymatic
with potential application in real analysis. This is evident from the bar graph of peak curUA sensor with potential application in real analysis. This is evident from the bar graph of
rent after several repeatable CV cycles as shown in Figure 12b. An error of less than 5%
peak current after several repeatable CV cycles as shown in Figure 12b. An error of less
indicates the excellent analytical features of the method. A non-enzymatic UA based on
than 5% indicates the excellent analytical features of the method. A non-enzymatic UA
surface-modified
NiCo2O4 NiCo
nanostructures
can be used for long-term applications, since
based on surface-modified
2 O4 nanostructures can be used for long-term applications,
the
material
does
not
change
surface
features
under
ambient
since the material does not change surface features
under
ambientconditions.
conditions.However,
However, we
we
examined
the
stability
of
NiCo
2O4 nanostructures in 0.5 mM UA solution by measuring
examined the stability of NiCo2 O4 nanostructures in 0.5 mM UA solution by measuring the
the
amperometric
response
a period
of 1000
s. This
is depicted
in Figure
13a.
Accordamperometric
response
overover
a period
of 1000
s. This
is depicted
in Figure
13a.
According
ing
to the
response
time,
present
sensor
exhibit
current
fluctuation
for
to the
response
time,
the the
present
UA UA
sensor
did did
not not
exhibit
anyany
current
fluctuation
for the
the
selected
time.
Therefore,
it
is
suitable
for
long-term
applications.
selected time. Therefore, it is suitable for long-term applications.
Biosensors
Biosensors 2023,
2023, 13,
13, 780
x FOR PEER REVIEW
of 21
21
1615of
Biosensors 2023, 13, x FOR PEER REVIEW
16 of 21
Figure 12. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 12. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel
extract-assisted
2O4 in the presence
0.5 of
mM
inof0.1MGCE
M PBSwith
pH 57.0;
graph
of
Figure
12. (a) Cyclic NiCo
voltammograms
at a scanofrate
50 UA
mV/s
mL(b)
of bar
radish
white
peel extract-assisted NiCo2 O4 in the presence of 0.5 mM UA in 0.1 M PBS pH 7.0; (b) bar graph of
peak
current for the description
change
in the
current
with
CV
cycles.
peel extract-assisted
NiCo2O4 inofthe
presence
of peak
0.5 mM
UA in
0.1increasing
M PBS pHnumber
7.0; (b) of
bar
graph
of
peak current
thecurrent
description
of successive
change in the
peak current
with increasing number of CV cycles.
Linear
plot offor
peak
versus
increase
in UA concentrations.
peak current
for
the description
of change in the
peak current
with increasing number of CV cycles.
Linear
Linear plot
plot of
of peak
peak current
current versus
versus successive
successive increase
increase in
in UA
UA concentrations.
concentrations.
Figure 13. (a) Chronoamperometric response of MGCE with 5 mL of radish white peel extract-assisted
2O4Chronoamperometric
in 0.5 mM preparedresponse
in
0.1 M of
PBS
pH 7.0
for
of
stability
of modiFigureNiCo
13. (a)
(a)
response
of
MGCE
with
5 demonstration
mL
of radish
white
peel
extract-asFigure
13.
Chronoamperometric
MGCE
with
5the
mL
of radish
white
peel
extract-assisted
fied
electrode;
EIS
Nyquist
plots collected
for the
MGCE
with
pristine, 5 mL, and
10 mL of
sisted
NiCo
2O4(b)
in
0.5
mM
prepared
in
0.1
M
PBS
pH
7.0
for
the
demonstration
of
stability
ofradish
modiNiCo2 O4 in 0.5 mM prepared in 0.1 M PBS pH 7.0 for the demonstration of stability of modified
2O4 collected
in 0.5 mM
frequency
range5 of
100
kHz
Hz,
amwhite
peel extract-assisted
NiCo
fied electrode;
(b) EIS Nyquist
plots
forUA
theusing
MGCE
with pristine,
mL,
and
10 to
mL1 of
radish
electrode; (b) EIS Nyquist plots collected for the MGCE with pristine, 5 mL, and 10 mL of radish white
plitude
of 10
mV, and biasing
potential
of 0.6
V.UA using frequency range of 100 kHz to 1 Hz, am2O4 in 0.5
mM
white peel
extract-assisted
NiCo
peel extract-assisted NiCo2 O4 in 0.5 mM UA using frequency range of 100 kHz to 1 Hz, amplitude of
plitude of 10 mV, and biasing potential of 0.6 V.
10 mV,
andresults
biasingin
potential
ofwide
0.6 V. linear range, low limit of detection, excellent selectivity,
Our
terms of
Our and
results
in terms of confirmed
wide linearthe
range,
low limit
of detection,
excellent
stability,
repeatability
superior
performance
compared
toselectivity,
other UA
Our results in terms of wide linear range, low limit of detection, excellent selectivity,
sensors/biosensors
reported
in
the
existing
literature,
as
shown
in
Table
1.
To
support
the
stability,
and
repeatability
confirmed
the
superior
performance
compared
to
other UA
stability, and repeatability confirmed the superior performance compared to other UA
sensors/biosensors
reported
existing
literature,
as4as
shown
in Table
1.electrochemical
To
the
electrochemical
performance
ofthe
the
prepared
NiCo2O
nanostructures,
sensors/biosensors
reportedinin
the
existing
literature,
shown
in Table
1. support
To support
electrochemical
performance
of
the
prepared
NiCo
2a
O
4 nanostructures,
electrochemical
impedance
spectroscopy
(EIS)
was
performed
using
sweeping
frequency
range
of
100
the electrochemical performance of the prepared NiCo2 O4 nanostructures, electrochemical
kHz
to 1 Hz,
amplitude of
10 was
mV
and
biasingusing
potential
of 0.6 V.
The
Nyquist
plots
impedance
spectroscopy
(EIS)
was
performed
using
a sweeping
frequency
range
ofwere
100
impedance
spectroscopy
(EIS)
performed
a sweeping
frequency
range
of 100
kHz
kHz
to
1
Hz,
amplitude
of
10
mV
and
biasing
potential
of
0.6
V.
The
Nyquist
plots
were
measured
for
the
three
samples
of
NiCo
2O4 nanostructures,
including
pristine
sample
1
to 1 Hz, amplitude of 10 mV and biasing potential of 0.6 V. The Nyquist plots were measured
and
sample
2
in
0.5mM
UA,
and
the
EIS
were
fitted
with
Z-view
software
as
illusmeasured
for
the
three
samples
of
NiCo
2data
O
4 nanostructures,
including
pristine
sample
for the three samples of NiCo2 O4 nanostructures, including pristine sample 1 and sample 21
and
2 in
0.5mM
and
the
EIS
data
were fitted
withas
Z-view
as illustrated
in Figure
13b.
intercept
of
thewith
semicircle
ofsoftware
Nyquist
plots
atsoftware
high
frequency
in
0.5sample
mM
UA,
and
theThe
EISUA,
data
were
fitted
Z-view
illustrated
in Figure
13b.
trated
in
Figure
13b.
The
intercept
of
the
semicircle
of
Nyquist
plots
at
high
frequency
represents
electrolyte
resistance.
The
arc
of
the
Nyquist
plots
indicates
the
charge
The intercept of the semicircle of Nyquist plots at high frequency represents electrolyte
transport
working
electrode
NiCo
2O
4 nanostructures
and
the
representsbetween
electrolyte
Theindicates
arc based
of the
Nyquist
plots
indicates
theworking
charge
resistance.
The
arc ofthe
theresistance.
Nyquist plots
the on
charge
transport
between the
transport
between
the working
onofNiCo
2O4 nanostructures
the
0.5mM
analyte
solution
[61]. Theelectrode
estimatedbased
values
charge-transfer
Rct for and
pristine
0.5mM analyte solution [61]. The estimated values of charge-transfer Rct for pristine
Biosensors 2023, 13, 780
Biosensors 2023, 13, x FOR PEER REVIEW
16 of 21
17 of 21
electrode based on NiCo2 O4 nanostructures and the 0.5 mM analyte solution [61]. The
NiCo2O4 nanostructures, sample 1, and sample 2 in the presence of analyte were as 125,100
estimated values of charge-transfer Rct for pristine NiCo2 O4 nanostructures, sample 1, and
Ohm,
Ohm,
and 181,270
Ohm,
respectively.
EIS
study Ohm,
has verified
that sample
sample114,970
2 in the
presence
of analyte
were
as 125,100 The
Ohm,
114,970
and 181,270
Ohm,
nanostructures
prepared
with
5
mL
of
radish
white
peel
extract
more
1respectively.
of NiCo2O4The
EIS study has verified that sample 1 of NiCo2 O4 nanostructures has
prepared
favorable
charge
transport
over
the
pristine
and
sample
2-based
NiCo
2O4 nanostructures;
with 5 mL of radish white peel extract has more favorable charge transport over the pristine
hence,
we observed
measurements
of samplebetter
1 toward
the quantiand sample
2-based better
NiCo2electrochemical
O4 nanostructures;
hence, we observed
electrochemical
fication
of a sensitive
UA 1signal.
measurements
of sample
toward the quantification of a sensitive UA signal.
3.4. Human Blood Sample Analytical Applications of Proposed Non-Enzymatic UA
UA Sensor-Based
SensorNiCo2NiCo
O4 Nanostructures
Based
2O4 Nanostructures
non-enzymaticUA
UAsensor
sensor
configuration
presented
in Figure
has evalbeen
The non-enzymatic
configuration
presented
in Figure
14a,b14a,b
has been
evaluated
onhuman
real human
samples.
A healthy
volunteer
and
a high
UA
patient
uated
on real
bloodblood
samples.
A healthy
volunteer
and a high
UA
patient
provided
provided
bloodwith
samples
ownThe
consent.
The
samples
were
diluted
30 0.1
times
blood
samples
their with
own their
consent.
samples
were
diluted
30 times
with
M
with
0.1
M
phosphate
buffer
solution
of
pH
7.0
and
used
directly
during
the
setup
of
phosphate buffer solution of pH 7.0 and used directly during the setup of three electrode
three
electrode
cells
for
electrochemical
quantification
of
UA.
UA
non-enzymatic
sensor
cells for electrochemical quantification of UA. UA non-enzymatic sensor performance
performance
confirms applicability
its potential applicability
andfor
reliability
for the quantification
ofbioUA
confirms
its potential
and reliability
the quantification
of UA from
from
biological
fluids,
and
even
food
products
with
high
probability,
as
shown
in
Table
2.
logical fluids, and even food products with high probability, as shown in Table 2. A perA
percent
relative
standard
deviation
RSD
(%)calculated
was calculated
from
theof
sum
of (standard
cent
relative
standard
deviation
RSD (%)
was
from the
sum
(standard
devideviation/mean
of
quantified
UA
concentration
data
using
three
repeated
experiments
for
ation/mean of quantified UA concentration data using three repeated experiments for UA
UA
detection)
×
100%.
detection) × 100%.
Figure 14. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
Figure 14. (a) Cyclic voltammograms at a scan rate of 50 mV/s of MGCE with 5 mL of radish white
peel extract assisted NiCo2O4 for the quantitation of UA form diluted human blood real samples in
peel extract assisted NiCo2 O4 for the quantitation of UA form diluted human blood real samples
0.1M PBS pH 7.0 and successive addition method; (b) Cyclic voltammograms at a scan rate of 50
in 0.1M
pHwith
7.0 and
successive
method;
Cyclic
voltammograms
at a scan rate of
2O4 for the quantitation of UA
mV/s
of PBS
MGCE
5 mL
of radish addition
white peel
extract (b)
assisted
NiCo
50
mV/s
of
MGCE
with
5
mL
of
radish
white
peel
extract
assisted
NiCo
O
for
the
of
2
4
form diluted human urine real samples in 0.1M PBS pH 7.0 and successive addition quantitation
method.
UA form diluted human urine real samples in 0.1M PBS pH 7.0 and successive addition method.
Table 2. Real sample analysis of UA from various blood samples (Blood 1 = healthy blood sample;
Blood 2 = high-level UA patient).
Sample
Blood 1
Blood 2
-
Added (mM)
0.5
1
2
2.5
1.5
Found (mM)
0.1
0.612 ± 0.002
1.123 ± 0.0023
2.084 ± 0.0017
2.621 ± 0.0013
1.00
2.533 ± 0.0022
%Recovery
101.66
101.81
99
100.77
101.2
% RSD
0.52
0.53
0.49
0.54
0.48
Biosensors 2023, 13, 780
17 of 21
Table 2. Real sample analysis of UA from various blood samples (Blood 1 = healthy blood sample;
Blood 2 = high-level UA patient).
Sample
Added (mM)
Found (mM)
%Recovery
% RSD
Blood 1
-
0.1
-
-
0.5
0.612 ± 0.002
101.66
0.52
-
1
1.123 ± 0.0023
101.81
0.53
-
2
2.084 ± 0.0017
99
0.49
-
2.5
2.621 ± 0.0013
100.77
0.54
Blood 2
-
1.00
-
-
-
1.5
2.533 ± 0.0022
101.2
0.48
-
2
3.082 ± 0.0019
102.66
0.56
-
2.5
3.514 ± 0.0024
100.28
0.50
-
3
4.063 ± 0.0018
101.5
0.53
4. Conclusions
An easy and rapid method has been developed for quantifying UA in human blood
and urine samples by using surface-modified NiCo2 O4 nanostructures. It has been combined with phytochemicals derived from radish white peel. It was determined that a
volume of 5 mL of radish white peel extract was optimal for the large-scale synthesis of
NiCo2 O4 nanostructures. The CV exhibited a linear range from 0.1 mM to 8 mM, the
LSV showed 0.1 mM to 7 mM, and the amperometric signal for the UA sensor showed
a linear range from 0.1 mM to 4 mM. We found that the LOD and LOQ of the present
non-enzymatic UA sensor were 0.005 mM and 0.008 mM, respectively. Furthermore, the
present UA sensor was evaluated in terms of its selectivity, stability, repeatability, and
sensitivity. Consequently, a wide linear range and a low limit of detection were achieved.
Several factors contribute to the sensor’s performance, including large surface vacancies,
abundant chemical states of Co(III), Ni(II), tailored surface morphology, fast charge-transfer
rate, and outstanding crystal quality. It has been demonstrated that there is a satisfactory
level of detection of UA in human blood samples (healthy and UA patients).
Author Contributions: A.G.S. performed material synthesis and partial electrochemical measurements; A.T. performed XRD analysis and measurement; B.W. performed the real sample analysis;
A.S.C. performed the partial electrochemical measurement and analyzed the obtained results; T.P.
performed the partial supervisions and preview the obtained results; A.N. performed validation of
results and proofread the paper; E.A.D. performed SEM analysis; L.M.A.S. performed EIS study;
M.P. performed HRTEM analysis; A.A.K.H.I. performed overall review of the obtained results; K.L.
performed XPS and HRTEM measurement; B.V. performed XPS analysis and proofread the structural
results; Z.H.I. performed main supervision and wrote the first draft of manuscript. All authors have
read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not Applicable.
Informed Consent Statement: Not Applicable.
Data Availability Statement: The authors declare that the data supporting the findings of this study
are available within the paper.
Acknowledgments: The authors would like to gratefully acknowledge the Higher Education Commission Pakistan for partial support under the project NRPU/8350. We also extend our sincere
appreciation to the Researchers Supporting Project Number (RSP2023R79) at King Saud University,
Riyadh, Saudi Arabia. Brigitte Vigolo would like to thank the platform “Microscopies, Microprobes
and Metallography (3 M)” (Institut Jean Lamour, IJL, Nancy, France) for access to SEM facilities and
Biosensors 2023, 13, 780
18 of 21
F. Alnjiman for his valuable help. Authors would also like to acknowledge partial funding of the
Ajman University, Grant ID: DRGS ref. 2022-IRG-HBS-5.
Conflicts of Interest: The authors declare no conflict of interest.
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