Published at : 18 Sep 2024
Volume : IJtech
Vol 15, No 5 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i5.5948
Ilmanda Zalzabhila Danistya Putri | Department of Chemistry, Faculty of Science and Technology, Universitas Airlangga, Surabaya 60115, Indonesia |
Prastika Krisma Jiwanti | Nanotechnology Engineering, Faculty of Advanced Technology and Multidiscipline, Kampus C, Universitas Airlangga, Surabaya 60115, Indonesia |
Ganden Supriyanto | Department of Chemistry, Faculty of Science and Technology, Universitas Airlangga, Surabaya 60115, Indonesia |
Ilmi Nur Indira Savitri | Department of Chemistry, Faculty of Science and Technology, Universitas Airlangga, Surabaya 60115, Indonesia |
Kiki Adi Kurnia | Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Bandung, Jalan Ganesha No 10, Bandung 40132, Indonesia |
Widiastuti Setyaningsih | Department of Food and Agricultural Product Technology, Faculty of Agricultural Technology, Gadjah Mada University, Jalan Flora, Bulak sumur, Sleman 55281 Yogyakarta, Indonesia |
Brian Yuliarto | 1. Department of Engineering Physics, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia 2. Research Center for Nanoscience and Nanotechnology (RCNN), Institut Teknologi Bandung, Jl |
Noviyan Darmawan | Department of Chemistry and Halal Science Center, IPB University, IPB Dramaga, Bogor 16880, Indonesia |
This study reports an electrochemical sensor for
detecting aspartame using square wave voltammetry (SWV) on ZnONP/BDDNP
electrode. ZnONP/BDDNP was able to oxidize aspartame at a potential of 0.34 V
in a phosphate buffer solution pH 2.0 with a current of 80.1 µA. The limit of
detection (LOD) was found to be 0.07 µM, the limit of quantitation (LOQ) was
0.25 µM and sensitivity was 1.23 µA µM-1. The relative standard deviation (RSD)
was 1.6%, less than 5% indicating that ZnONP/BDDNP has good precision. ZnONP/BDDNP
showed better results compared with the BDDNP electrode. The developed method
showed good linearity in the concentration range of 30-100 µM. This method was
successfully applied to determine aspartame in beverage samples with a recovery
range of 85-110%. This shows that ZnONP/BDDNP with the suggested method is
potentially applied in practical used.
Aspartame; Boron-doped diamond powder; Human & health; Metal oxide nanoparticles
Aspartame N-(L--aspartil-L-phenylalanine methyl ester) is one type of
artificial sweetener used by people with diabetes mellitus and obesity (Zafar, 2017; Yilmaz and Uçar,
2014). The human body will convert aspartame into aspartic acid,
phenylalanine, and methanol, which will accumulate in the blood (Saeed, 2020). Organoleptically similar to
sucrose but approximately 180-200 times sweeter than sucrose (Debras et al., 2022;
Jain Grover, and Scholar, 2015; Kirkland and Gatehouse, 2015). Excessive aspartame metabolism has a negative impact on the body if
consumed in excess. The methanol produced by aspartame is converted to formic
acid. This will cause the pH level in the blood to become acidic so our brain
will experience a lack of oxygen and cause the mitochondria of nerve cells to
be unable to carry out cellular respiration to produce ATP. Reduced energy
supply in the brain damages neuron cells, and various toxic processes can occur
(Hussein
et al., 2022; Rycerz and Jaworska-Adamu, 2013). Phenylalanine, considered a
neurotoxin, can stimulate brain neurons in high concentrations causing seizures
and other neurological defects. This is dangerous for people born with
phenylketonuria (PKU), which prevents them from metabolizing phenylalanine (Newbould et
al., 2021; Naik, Zafar, and Shrivastava, 2018). The increasing use of aspartame
in the food industry has given new impetus to developing rapid and efficient
methods for its determination.
Various methods have been used to
detect aspartame levels, some of which are high-performance liquid
chromatography (HPLC) (Barakat et al., 2022;
Shoeb et al., 2022; Berset and Ochsenbein, 2012), liquid polydimethylsiloxane
(PDMS) plasma cavity as a substrate for surface-enhanced Raman spectroscopy
(SERS) to detect aspartame added in purified water, ion chromatography (Chen et al.,
2020),
and electrophoresis (de Carvalho et al., 2014). However,
most methods require more complicated procedures, more expensive analysis time,
and more expensive instrumentation than electrochemical methods.
Electrochemical methods have many advantages, including high sensitivity, low
cost, fast analysis speed, effectiveness, efficiency, and simple
instrumentation (Munteanu and Apetrei, 2022; Rahmawati et al., 2022; Tajik
et al., 2021; Hardi and Rahman, 2020). This
research uses the voltammetric analysis method with square wave voltammetry
(SWV) measurement technique. The square wave voltammetry technique has the
advantage of high sensitivity and fast speed.
BDDNP
can be used as an electrode material with a large specific surface area (Kondo, 2019). Compared to
conventional BDD electrodes (Prayikaputri et al., 2021; Jiwanti et al.,
2019; Tomisaki et al, 2019; Ivandini et al, 2017;), BDDNP exhibits a
low background current, and a wide potential window, which enable sensitive
electrochemical detection with a large S/B ratio (Kondo, 2019; Kondo, 2014). Due to its
excellent properties, BDD was an excellent substrate for oxide
electrodeposition (Jiwanti, 2020). On the other hand, semiconductor nanoparticles have
become a major concern for researchers because of their potential applications
in chemistry (Shetti
et al., 2019). In particular, ZnONP's unique properties, such as small size,
large surface area, higher sensitivity, and being environmentally friendly and
inexpensive, make it widely used for electrochemical sensor construction (Agarwal et al, 2019;
Chaudhary et al, 2018; Kumar et al, 2015). Moreover, no potential
oxidation peak of Zn in the aspartame potential oxidation range makes it
suitable for sensitively and selectively detecting aspartame. In this study,
the attractive properties of ZnONP and BDDNP will be developed to prepare
boron-doped diamond nanoparticle-modified ZnO nanoparticles to detect the
artificial sweetener aspartame. The ZnONP/BDDNP modification provided a larger
and wider surface area for detection. Thus, more aspartame molecules were
detected on the electrode surface and could produce highly sensitive
measurements.
2.1. Chemicals
NaH2PO4 (99%) and Na2HPO4 (99.5%) from Merck (USA), ethanol (99.9%) was purchased from Millipore Corporation (USA), ZnONP 10 nm from Sigma Aldrich (USA), aspartame (98.56%), sodium cyclamate (100.45%), acesulfame potassium (100.41%), neotame (100.49%), and saccharin (101.96%) were obtained from the National Food and Drug Agency, H2SO4 (98%) from SAP Chemical (Indonesia), Nafion (5%) were obtained from Sigma Aldrich (USA), beverage samples were obtained from local supermarkets, BDDNP (0 - 250 nm) from Somebetter (China) and ultrapure water.
2.2. Preparation and
fabrication of electrode for electrochemical sensor aspartame
GC (glassy carbon)
electrode used as a supporting electrode was first pre-treated with alumina
slurry on one side of the surface (the surface to be modified) until the
surface was shiny like glass. Subsequently, the electrode was sonicated in
1-propanol and ultrapure water for 10 minutes each. After that, the GC
electrode was optimized in 0.1 M H2SO4.
Scheme 1 Schematic drop-casting of nanoparticles onto an
electrode
2.3. Electrochemical
sensor of aspartame
In all
electrochemical measurements, 5 mL of 0.1 M PBS (pH 2.0) was added to an
electrochemical cell in which modified GC was immersed. Cells were cleaned by
ultrasonication for 5 minutes by immersing them in ultrapure water to remove
impurities that might be left in the cells. CV and SWV were performed with an
Emstat3+ Blue Palmsens potentiostat using a three-compartment cell
system with ZnONP/BDDNP/GC and BDDNP/GC as the working electrodes, Ag/AgCl as
the reference electrode, and platinum as counter electrode. Aspartame
electrochemical sensor measurements were carried out by adding 60 µM aliquot
solution of aspartame analyte into an electrochemical cell containing 0.1 M PBS
pH 2. The mixture solution was permitted to equilibrate for 5s and sweep from
-1.0 V to 1.0 V at the amplitude of 0.05 V, a frequency of 50 Hz, and a step
potential of 0.012 V in SWV mode.
3.1. Characterization of
ZnONP/BDDNP/GC
Figure 1 (a) SEM image of ZnONP/BDDNP/GC (b) EDX Mapping image
of ZnONP/BDDNP/GC
3.2. Determination of signal per background (S/B)
The results of
determining S/B from the two electrodes are shown in Table 1. Aspartame showed
anodic peak potential and peak current at 0.32 V and 195.91 µA for BDDNP/GC
electrode, while the ZnONP/BDDNP/GC electrode obtained anodic peak potential
and peak current at 0.34 V and 80.01 µA. The S/B analysis revealed that the electrode
modified with metal nanoparticles and ZnO nanoparticles had a higher S/B
compared to the electrode without nanoparticle modification. Moreover,
ZnONP/BDDNP/GC showed lower background current when compared to BDDNP/GC,
attributed to the catalytic behavior and sensitivity enhancement properties of
nanoparticles. As a result, the ZnONP/BDDNP/GC electrode is capable of
detecting low concentrations of aspartame with higher sensitivity than the
BDDNP/GC electrode.
Table 1 Signal per background of each electrode
Background |
Signal |
S/B | |
BDDNP/GC |
45.85 |
197.41 |
4.30 |
ZnONP/BDDNP/GC |
17.22 |
80.10 |
4.65 |
Figure 2 SWV curves for determining S/B of aspartame
measurement on (a) BDDNP/GC electrode (b) ZnONP/BDDNP/GC electrode
Figure 3 Current relationship curves vs root scan rate at (a)
BDDNP/GC, (b) ZnONP/BDDNP/GC electrodes
3.4. Determination of
optimum pH on the modified electrodes
The effect of pH on aspartame measurements was studied between pH 2.0 - 7.0 (Figure 4). The results of determining pH optimum at the BDDNP/GC and ZnONP/BDDNP/GC electrodes showed an increase in optimum peak current of aspartame linearly along with the decrease in pH. It is because aspartame has a carboxylic group in aspartic acid which has a pKa = 3.1. The lower the pKa, the stronger the acid and the greater its ability to donate protons to water. Due to the low pKa of the carboxylate group, aspartame's detection is optimum at an acidic pH. The range used for pH variations was measured at pH 2.0 – 7.0 because GC electrodes can be damaged at very low pH levels. Therefore, pH levels below 2.0 were not included. The results showed that pH had an influence on the high and low peak currents produced in the aspartame measurements. The optimal pH for aspartame measurement was determined at pH 2.0 because it gave a higher peak current response than other pH levels. The difference in the measured peak current value is caused by the number of aspartame molecules measured on the electrode surface. The higher the peak current value, the greater the number of analyte molecules measured on the electrode surface, and the faster the electron transfer process.
Figure 4 Effect of pH on peak current and peak potential of
aspartame using (a) BDDNP/GC, (b) ZnONP/BDDNP/GC electrodes
3.5. Linear range, limit of detection and limit of quantification
Figure 5 Voltammogram square wave voltammetry response of
30-100 M aspartame (Conditions: amplitude: 0.05 V, frequency: 50 Hz and step
potential: 0.012 V) on (a)BDDNP/GC, (b) ZnONP/BDDNP/GC
The limit of
detection (LOD) and limit of quantitation (LOQ) for ZnONP/BDDNP/GC electrodes
were calculated to be 0.07 µM and 0.25 µM, respectively, while
for BDDNP/GC electrodes, they were found to be 1.86 µM and 6.16 µM. Several
prior studies have used various methods for analyzing aspartame using modified
working electrodes and other detection methods based on the obtained limit of
detection data. As shown in Table 2, the analysis of aspartame using
ZnONP/BDDNP/GC electrodes has a lower detection limit (LOD) compared to the
other methods, indicating that ZnONP/BDDNP/GC electrodes have higher
sensitivity.
3.6. Selectivity and
reproducibility
Determination of selectivity in
aspartame measurements using ZnONP/BDDNP/GC and BDDNP/GC electrodes was carried
out using several interfering solutions that could potentially interfere with
aspartame measurements in actual samples, including sodium cyclamate,
saccharin, acesulfame-K, and neotame. Measurements were made by measuring 60 µM
of aspartame sample in 5 mL of 0.1 M PBS, then adding 60 µM of the interference
solution using the SWV method. The peak current of aspartame is known to
increase after the addition of an interfering solution. The four interfering
solutions were known to be oxidized at a potential close to the aspartame
oxidation potential. Table 3 showed that the difference in current and
potential produced by aspartame solution with interfering solution had a higher
current than the current by aspartame itself. However, the potential of the
interference solution above is close to the aspartame.
The reproducibility of ZnONP/BDDNP/GC and BDDNP/GC
electrodes was determined by measuring 60 µM of aspartame sample in 5 ml of 0.1
M PBS using the SWV method. To test the reproducibility of the proposed method,
10 replicates were performed on different days. The relative standard deviation
(RSD) values obtained were 1.60% for ZnONP/BDDNP/GC electrode and 1.96% for
BDDNP/GC electrode
When compared, ZnONP/BDDNP/GC has a smaller %RSD than
BDDNP/GC. It shows that ZnONP/BDDNP/GC is an electrode that has a better level
of precision and stability than BDDNP/GC. The %RSD obtained is less than 5%,
this indicates that the two electrodes have a fairly good level of precision
and stability. The summary of validation parameters is described in Table 4.
3.7.
Aspartame determination in real sample
ZnONP/BDDNP has been successfully prepared. It was utilized for the
electrochemical sensors of aspartame in beverage samples. SEM-EDX
characterization successfully showed the distribution of ZnONP/BDDNP
homogeneously on the surface of the GC electrode. Aspartame detection using the
SWV method was carried out with a linear calibration curve with R2 = 0.9928.
The modified electrode was used for aspartame detection in the presence of
interfering compounds such as sodium cyclamate, saccharin, acesulfame-K, and neotame.
They produced different current peaks with aspartame, thus that the possibility
of interfering with the measurements was quite small. From the results of the
method carried out, the ZnONP/BDDNP electrode has a good level of sensitivity,
good precision, good stability, and is able to detect aspartame at a good level
of µM concentration. Thus, the ZnONP/BDDNP electrode can be further developed
for real application in detecting aspartame, and potentially miniaturized as
facile use screen printed sensor.
We acknowledge the financial support from
Universitas Airlangga under Riset Kolaborasi Indonesia with contract number
155/UN3.15/LT/2021.
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