The fabrication of an Ni6MnO8 nanoflake-modified acupuncture needle electrode for highly sensitive ascorbic acid detection

Article abstract of DOI:10.1039/c9ra03850g

The current work describes the use of a steel acupuncture needle as an electrode substrate in order to construct an Ni₆MnO₈ nanoflake layer-modified microneedle sensor for highly sensitive ascorbic acid detection. For the purpose of constructing the functionalized acupuncture needle, first, a carbon film was layered on the needle surface as the seed layer. Subsequently, a straightforward hydrothermal reaction-calcination process was employed for the growth of Ni₆MnO₈ nanoflakes on the needle to function as a sensing interface. Electrochemical investigations illustrated the fact that the Ni₆MnO₈ nanoflake-altered acupuncture needle electrode manifested outstanding efficiency toward the amperometric identification of ascorbic acid. In addition, the electrode manifested elevated sensitivity of 3106 μA mM^-1 cm^-2, detection limit of 0.1 μM, and a broad linear range between 1.0 μM and 2.0 mM. As demonstrated by the results, the Ni₆MnO₈ nanoflake-modified acupuncture needle constitutes a potentially fresh platform to construct non-enzymatic ascorbic acid sensors.

Full text of DOI:10.1039/c9ra03850g

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The fabrication of an Ni MnO nanoflake-modified
6
8
acupuncture needle electrode for highly sensitive
ascorbic acid detection
Cite this: RSC Adv., 2019, 9, 26843
Hongliang Jia, Jianwei Zhao, * Lirong Qin,
Min Zhao and Gang Liu
The current work describes the use of a steel acupuncture needle as an electrode substrate in order to
construct an Ni MnO nanoflake layer-modified microneedle sensor for highly sensitive ascorbic acid
6
8
detection. For the purpose of constructing the functionalized acupuncture needle, first, a carbon film
was layered on the needle surface as the seed layer. Subsequently, a straightforward hydrothermal
reaction-calcination process was employed for the growth of Ni
6
MnO
8
nanoflakes on the needle to
MnO
function as a sensing interface. Electrochemical investigations illustrated the fact that the Ni
6
8
nanoflake-altered acupuncture needle electrode manifested outstanding efficiency toward the
amperometric identification of ascorbic acid. In addition, the electrode manifested elevated sensitivity of
Received 22nd May 2019
Accepted 9th August 2019
ꢀ1
ꢀ2
3
106 mA mM cm , detection limit of 0.1 mM, and a broad linear range between 1.0 mM and 2.0 mM. As
demonstrated by the results, the Ni MnO nanoflake-modified acupuncture needle constitutes
a potentially fresh platform to construct non-enzymatic ascorbic acid sensors.
DOI: 10.1039/c9ra03850g
6
8
rsc.li/rsc-advances
Two-dimensional (2D) nanoakes are signicantly inter-
esting due to their exclusive characteristics, which include not
Introduction
Ascorbic acid (AA), which is termed as vitamin C, refers to a kind only a large specic surface area, but also rich structural
11
of anti-oxidant that is present in a number of biological species diversity and exclusive electronic characteristics. NiO nano-
1
that take part in different kinds of crucial biological reactions.
akes are among the most appealing inorganic substances with
Moreover, AA helps promote the healthy growth of cells, aids in applications in catalysis, ion exchange, molecular adsorption,
12
calcium absorption as well as normal tissue development, and biosensing, and power conservation. Recently, the electro-
13
14
functions as a medication for scurvy, drug poisoning, liver chemical uses of NiO in detecting glucose, ascorbic acid, and
2
16
illness, allergic reactions and atherosclerosis. In this context,
the development of a straightforward and rapid methodology to applications in a variety of areas. Likewise, MnO
H
2
O
2
(ref. 15) and in gas sensing have been indicated to have
2
nanosheets
determine AA with elevated selectivity and sensitivity is are also counted among the key types of redox-active 2D nano-
3
preferred for both diagnostic and food safety applications.
materials. They have extensive applications in biosensing due to
Different kinds of analytical methodologies including chem- their reasonable water solubility, catalytic activity and
4
5
7
17
iluminescence, uorescence, electrophoresis, liquid chro- outstanding biocompatibility. Taking into consideration the
6
8
matography, and electrochemical methodologies have been fact that Ni-based as well as Mn-based oxides manifest high
employed for the purpose of investigating the ascorbic acid electrochemical efficiencies, the corresponding mixed metal
content in drugs, foods and plants. Among these approaches, oxides would be expected to have better characteristics. In
6 8
the electrochemical methodologies have presented feasible, particular, Ni MnO shows more advantages and better appli-
straightforward and affordable identication with elevated cation prospects due to its easily available raw materials, simple
9
sensitivity. Nevertheless, enzymatic sensors suffer from preparation methods, high electroactivity and excellent
a number of potential aws, such as stereotyped shapes, stability.
instability and poor reproducibility on account of the intrinsic
Acupuncture is considered a pivotal component of Eastern
characteristics of enzymes. As a result, the development of non- medicine; it has the functions of relieving pain, warming the
enzymatic AA sensors that have excellent characteristics meridians and promoting the blood ow through the applica-
1
0
coupled with a well-designed shape is desired.
tion of an acupuncture needle into the physical body of the
patient. In addition, the stainless-steel-based needle is not only
affordable but also convenient to use and is put to common
uses in actual applications. Due to its high conductivity, small
size, and needle-like edge, the electrode, based on the
acupuncture needle, can be put to use for micro-volume
18
School of Physical Science and Technology, Southwest University, Chongqing 400715,
P. R. China. E-mail: zhaojw@swu.edu.cn; Fax: +86 23 68254608; Tel: +86 23
6
8252355
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specimens or in vivo analysis. Zhou et al. developed a nonenzy-
matic H O microsensor on the basis of an acupuncture needle
2
2
19
functionalized with MoS /Pt nanocomposites. Niu et al.
2
selected an acupuncture needle as the basic electrode to further
modify using gold nanoparticles and graphene for the sensitive
20
determination of rutin. Therefore, needle electrodes have
promising applications in constructing electrochemical sensing
platforms. In the current research work, we put forward a novel
AA sensor on the basis of a steel acupuncture needle as the
electrode substrate to construct an Ni MnO nanoake layer.
6
8
The presented sensor manifested a number of outstanding
characteristics ascribed to the synthetic impact of the mixed
metal oxides and the thin nanoake structures; furthermore,
the remarkable acupuncture needle improved the electro-
chemical response to AA to a signicant extent.
Fig. 1 (a) Fabrication process for the preparation of Ni
6
MnO
8
/C/
needle. (b) Schematic illustration of the Ni
detection of AA.
6 8
MnO nanoflakes for the
Experimental
Reagents and instrumentation
well. Subsequently, the autoclave was sealed and maintained at
a temperature of 120 C for a period of six hours. Subsequent to
Ascorbic acid, uric acid, glucose, L-tyrosine, and dopamine were
obtained from Sigma-Aldrich. Nickel nitratehexahydrate
together with manganese chloride tetrahydrate and other
chemicals of analytical grade was purchased from Chongqing
Chuandong Chemical Company. Deionized water was used
throughout the entire assay. A CHI 660E electrochemical
workstation (CH Instruments, China) was used for electro-
chemical identication using a 3-electrode system, which
comprised an altered working electrode, a Pt counter electrode,
and an Ag/AgCl reference electrode. Each and every experiment
was performed at an ambient temperature (23 ꢁ 1 ꢂC). The
characterization of the morphologies of our synthesized prod-
ucts was carried out with the help of scanning electrode
ꢂ
cooling it down to the room temperature, the acupuncture
needle was washed with ethanol and deionized water a number
of times, followed by annealing in air for a period of two hours
ꢂ
at a temperature of 450 C. In the meantime, the powder
deposited in the solution during the hydrothermal procedure
was also collected, followed by washing and annealing under
the same conditions for XRD characterization. Eventually, the
modied steel needle was encapsulated by coating with epoxy
resin directly in the middle areas, leaving the tip with about
10 mm of length for the electrochemical measurement.
microscopy (SEM, JEOL JSM 7100F) as well as the transmission Results and discussion
electron microscopy (TEM, JEM 2010); the analysis of the
Characterization of the nanoake-modied electrode
elemental composition was carried out with the help of X-ray
diffraction (XRD, TD-3500) as well as energy dispersive X-ray
spectroscopy (EDS, Aztec X-Act).
Fig. 2a shows an overview SEM image of the product grown on
the tip of the acupuncture needle. Evidently, the integrated and
concentrated nanoakes were distributed on the surface of the
needle. The high-magnication SEM images suggest that the
Fabrication of Ni
6
MnO
8
nanoake-modied needle electrode
21–23
product possessed ake-like morphology
(Fig. 2b and c),
Prior to synthesis, the cleaning of the stainless steel needle put with a lateral size ranging between 50 and 200 nm, and was
to use for acupuncture (diameter: 0.25 mm, length: 13 mm) was a few nanometers thick. During the hydrothermal reaction,
done with the help of sonication in ethanol and deionized water methenamine and urea were the alkali sources and generated
ꢀ
for a period of een minutes each. Subsequently, the Ni
6
MnO
8
OH to react with the metal ions. Then, they served as the
nanoake-modied needle electrode was prepared, as demon- structural guide and directed the self-assembly of the ake-like
strated in Fig. 1. Specically, the cleaned steel needle was structures. These tiny akes were interlaced, which created an
ꢀ
1
soaked in 0.03 M (mol L ) glucose solution for een hours, extremely porous 3D network on the substrate, accordingly
24
followed by annealing in argon for a period of three hours at offering an extensive specic surface area. Fig. 3 demonstrates
ꢂ
a temperature of 500 C. Without this step, that is, without the a typical TEM image of the nanoakes, and the ake-like
carbon lm as the seed layer, the Ni
the surface of the steel needle would not be well-distributed. As the respective SAED pattern (inset of Fig. 3) reveals that the
for the synthesis of the Ni MnO nanoakes, 0.58 g of nanoakes are polycrystalline. The diffraction rings in the SAED
Ni(NO ) $6H O together with 0.97 g of MnCl $4H O, 0.21 g of pattern correspond to the (222) and (400) crystal planes of the
6 8
MnO nanoakes grown on nanostructures can be observed quite clearly. Furthermore,
6
8
3
2
2
2
2
methenamine and 0.09 g of urea was dissolved in 30 mL of cubic structural Ni MnO .
6
8
deionized water with continuous stirring. In addition, the
For the purpose of analysing the elemental composition of
solution was transferred into a Teon-lined stainless autoclave, the prepared nanoakes, the EDS spectrum of the sample was
and the pre-treated stainless steel needle was placed in it as obtained, which is presented in Fig. 4a. It suggested that the
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Fig. 2 (a) Low-magnification SEM image of Ni
6
MnO
8
nanoflakes; inset: SEM image of the modified acupuncture needle. (b and c) High-
6 8
magnification SEM images of the Ni MnO nanoflakes.
nanoakes comprise Ni, Mn and O. The weak C signal origi- indicates that O, Ni and Mn are distributed within the nano-
nated from the carbon lm coated on the needle. Using addi- akes, conrming again the formation of Ni MnO .
6
8
tional quantitative analysis, the average atomic ratio of Ni : Mn
that the EDS system provided was determined to be approxi-
mately 6 : 1, and it was consistent with the value of Ni MnO .
6 8
Properties of the nanoake-modied electrode
Owing to the amount of nanoakes grown on the acupuncture The steel acupuncture needle modied with the Ni MnO8
6
needle being insufficient for XRD characterization, the powder nanoake layer can be directly applied as a sensor electrode for
deposited in the solution during the hydrothermal process was detecting AA. In addition, the electrochemical efficiency of this
also collected, followed by annealing under the same condi-
tions. SEM and EDS analyses suggested that the powder
possessed similar morphology and elemental composition to
those of the nanoakes grown on the acupuncture needle. The
XRD pattern of the powder was also obtained, and the ndings
are illustrated in Fig. 4b. The three typical characteristic peaks
ꢂ
ꢂ
ꢂ
at approximately 2q ¼ 37.4 , 43.5 , and 63.1 were attributed to
the (222), (400), and (440) diffraction modes of the face-centered
2
5,26
cubic structure of Ni
6
MnO
8
, respectively.
This result indi-
rectly veried that the nanoakes grown on the needle must be
Ni MnO . EDS in the area mapping mode was conducted to
6
8
detect the spatial distribution of specic elements. Fig. 5
Fig. 3 TEM image of the Ni
sponding SAED pattern.
6
MnO
8
nanoflakes; inset: the corre- Fig. 4 (a) EDS spectrum and (b) XRD pattern of the Ni
nanoflakes.
6 8
MnO
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6 8
Fig. 5 (a) An SEM image of the Ni MnO nanoflakes; (b–d) the
elemental chemical maps of O, Ni, and Mn, respectively.
needle electrode was examined with cyclic voltammetry (CV) in
a 0.1 M NaOH solution over a potential range between 0.1 and
ꢀ
1
0
.6 V at the scan rate of 100 mV s . As evident from Fig. 6a, in
comparison with the result for the system with no AA, the
oxidation peak increases as 1.0 mM AA is introduced into the
solution. This result suggests that the Ni MnO nanoakes have
6 8
robust electrocatalytic activity with regard to the oxidation of
AA. Furthermore, it is possible to assign the effectively dened
redox peak in the research potential range to the electro-
chemical redox reactions of Ni(II)/Ni and Mn(IV)/Mn(II) on the
1
2,27
electrode surface.
of two hydrions and two electrons to form dehydroascorbic acid
), which shows resistance to a reversible change in an
Herein, AA oxidation involves the removal
Fig. 6 (a) CV curves of the Ni
6
MnO
8
nanoflake-modified electrode in
the absence (curve a) and presence (curve b) of AA in 0.1 M NaOH
solution. (b) Typical CVs of the modified electrode in 0.1 M NaOH
solution containing 0.5 mM AA at different scan rates (from 50 to
6 6 6
(C H O
2
8
6 8
alkaline solution. The latent catalytic activity of Ni MnO for
AA oxidation can be explained in accordance with the scheme
presented below:
ꢀ1
1/2
280 mV s ). Inset: plots of peak currents vs. n
.
+
Ni(II) + Mn(IV) + 2C
6
H
8
O
6
/ Ni + Mn(II) + 4H + 2C
H
6 6
O
6
(1)
(2)
(3)
electrode subsequent to successively adding AA into a 0.1 M
NaOH solution at a constant potential of 0.55 V. Throughout the
test, the solution was stirred at a constant pace with the help of
a magnetic stirrer to accelerate mixing. Upon injecting AA,
a fast-paced current feedback was observed and a stable value
was attained in under 5 s, which illustrated a sensitive feedback
+
ꢀ
H + OH / H
2
O
Ni / Ni(II) + 2e, Mn(II) / Mn(IV) + 2e
The kinetic and transport attributes of the response were to the modication in the AA concentration. Besides, the inset
additionally studied through cyclic voltammetry with varying in Fig. 7b indicates the linear association existing between the
scan rates. Fig. 6b shows the CVs of the modied electrode in concentration of AA and the current. In addition, an extensive
a 0.1 M NaOH solution containing 0.5 mM AA at varying scan linear response range of the electrode to the AA concentration
rates. It is quite fascinating to observe that the oxidation peak was present between 1.0 mM and 2.0 mM. Besides this, the
currents are in proportion to the square root of the scan rate linear regression equation is I (mA) ¼ 21.598 + 146.32 C (mM)
ꢀ
1
between 50 and 280 mV s , which indicates that the diffusion- with a correlation coefficient of 0.9962. The constraint of
29
controlled process occurs at the altered electrode. This result identication was approximated as 0.1 mM at a signal/noise
suggests reliable and fast electron transfer kinetics at the ratio of 3. Further determination of the sensitivity could be
ꢀ
1
ꢀ2
surface of the electrode, which is advantageous for ampero- increased to 3106 mA mM
cm . Table 1 demonstrates
metric sensing.
a comparison of the efficiency of the Ni
6
MnO nanoake-altered
8
An amperometric technique was used for the purpose of needle electrode shown herein with those of the other AA
evaluating the electrode for AA detection. Fig. 7a and b both sensors prepared using nanomaterials. It was evident that the
show the common current–time feedbacks of the needle available
electrode
material
presented
outstanding
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Fig. 8 Amperometric curve for the addition of 0.1 mM AA, oxalic acid,
glucose, uric acid, dopamine, L-cysteine, L-tyrosine and 0.1 mM AA in
1
0 mL 0.1 M NaOH solution.
acupuncture needle. At rst, the highly dense nanoakes could
provide an extensive surface region for solution percolation,
causing a rise in the electrochemically active surface sites,
10,29
accordingly giving rise to outstanding sensing efficiency.
Second, a synergetic effect from the combination of NiO and
MnO likely augmented the catalytic efficiency of the nano-
akes, further promoting the oxidation of AA. In contrast, it is
evident from Fig. 6a that the needle electrode without the
Ni MnO nanoakes in our experiment exhibits quite a low
2
35

6
8
function for AA oxidation. Eventually, the direct development of
nanoakes onto the needle electrode enabled reasonable
22
mechanical binding as well as the electric connection of the
6 8
Fig. 7 (a) Typical current–time responses for the Ni MnO nanoflake-
modified electrode, the C-modified electrode, and the bare needle active substance to the current collector.
electrode to successive additions of 0.1 mM AA in a stirring 0.1 M
The examination of the impact of common interfering
species on the Ni MnO nanoake layer-modied microneedle
NaOH solution at an applied potential of 0.55 V vs. Ag/AgCl. (b) The
current–time responses for the Ni MnO nanoflake-modified elec-
6
8
6
8
sensor was also carried out. In accordance with Fig. 8, aer the
addition of 0.1 mM AA into a 10 mL 0.1 M NaOH solution, there
was signicant increase in the current with immense response
sensitivity. As compared with AA, upon the addition of 0.1 mM
oxalic acid, glucose, uric acid (UA), dopamine, L-cysteine and L-
tyrosine, we did not notice any apparent signal from these
materials. In this manner, a conclusion can be reached that this
trode to successive additions of different concentrations of AA; inset:
the linear relationship between the catalytic current and the
concentration of the Ni MnO nanoflakes.
6 8
electrochemical efficiency regarding its elevated sensitivity, low
detection limit, and extensive linear range. These ideal attri-
butes of the developed electrode are due to the particular
structure of the Ni MnO nanoakes modied on the
6 8
Ni MnO nanoake-modied needle electrode put forward in
6
8
Table 1 Comparison of different amperometric sensors for the determination of ascorbic acid
Sensitivity
(mA mM cm
ꢀ
1
ꢀ2
Type of electrode
GO-XDA-Mn nanocomposite
CuS@PB composites
NiO nanosheets@Tr-rGO
)
Linear range (mM)
Detection limit (mM)
Reference
2
O
3
655.74
256.91
177.83
549.3
2060
80.4
1281.9
3106
10–8000
5–3875
0.6
28
30
31
32
33
34
10
0.24
0.25
0.5
0.43
0.464
1.0
0.25–13 100
20–2410
0.43–200
2–14 000
25–10 000
1–2000
NiCoO
DGF/CuO nanoowers
Ascorbate oxidase/PEDOT-SL lm
Nanoporous Fe /Au lm
Ni MnO nanoakes/C/steel needle
2
/C
3
2
O
3
6
8
0.1
This work
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Table 2 Determination of AA in vitamin C tablets (n ¼ 3)
term stability. The Ni
needle sensor presented here has potential for the detection of
low quantities of analytes or in vivo calculations.
MnO
nanoake layer-modied micro-
6
8
Sample
Detected/mM
Added/mM
Found/mM
Recovery, %
1
2
3
201.1
382.6
516.5
200
200
200
391.5
578.6
692.1
97.6
99.3
96.5
Conflicts of interest
There are no conicts to declare.
the current research work shows reasonable selectivity to AA. As
revealed by former reports, Ni-based sensors are capable of
Acknowledgements
detecting glucose, UA, and dopamine on the basis of the The present research work received the support of the
involvement of Ni(II) as well as Ni(III) species as an electron Chongqing Research Program of Basic Research and Frontier
36–39
transfer mediator.
Herein, we think the incorporated Mn Technology (Grant No. cstc2016jcyjA0125) and the Funda-
element could inhibit the reaction of Ni(II)/Ni(III), decreasing the mental Research Funds for the Central Universities (Grant No.
oxidative ability of Ni(II). In contrast, AA, a mild reducing agent, XDJK2018B033).
can be easily oxidized than other interfering species with the
loss of two electrons to form dehydroascorbic acid, which may
be the reason for the good selectivity. More theoretical and
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