Talanta 222 (2021) 121539

Contents lists available at ScienceDirect

Talanta
journal homepage: www.elsevier.com/locate/talanta

Simultaneous determination of direct yellow 50, tryptophan, carbendazim,

and caffeine in environmental and biological fluid samples using graphite
pencil electrode modified with palladium nanoparticles
Ademar Wong a, b, **, Anderson Martin Santos b, Rafael da Fonseca Alves a,
Fernando Campanhã Vicentini c, *, Orlando Fatibello-Filho b,
Maria Del Pilar Taboada Sotomayor a
a
Department of Analytical Chemistry, Institute of Chemistry, State University of São Paulo, Araraquara, SP, Brazil
b
Department of Chemistry, Federal University of São Carlos, Rod. Washington Luís km 235, São Carlos, SP, Brazil
c
Center of Natural Sciences, Federal University of São Carlos, Rod. Lauri Simões de Barros km 12, Buri, SP, Brazil

A R T I C L E I N F O A B S T R A C T

Keywords: The present study reports the development of graphite pencil electrode modified with palladium nanoparticles
Graphite pencil electrode (PdNPs) and its application as an electrochemical sensor for the simultaneous detection of direct yellow 50,
Emerging pollutants tryptophan, carbendazim and caffeine in river water and synthetic urine samples. The combination involving the
River water and urine samples
conductive surface of the graphite pencil electrode (GPE) and the enlargement of the surface area caused by the
Modified electrode
Palladium nanoparticles
use of palladium nanoparticles (PdNPs) led to the improvement of the analytical performance of the proposed
device. The surface of the GPE-PdNPs was characterized by scanning electron microscopy (SEM) and energy
dispersive spectroscopy (EDS). The charge transfer kinetics of the electrode was evaluated based on the elec­
trochemical analysis of the potassium ferricyanide redox probe. Using square wave voltammetry (SWV), well-
defined and fully resolved anodic peaks were detected for the analytes, with peak-to-peak potential separation
not less than 200 mV. Under optimised conditions, the following linear range concentrations were obtained:
0.99–9.9 μmol L− 1 for direct yellow 50; 1.2–12 μmol L− 1 for tryptophan; 0.20–1.6 μmol L− 1 for carbendazim; and
25–190 μmol L− 1 for caffeine. The sensor showed good sensitivity, repeatability, and stability. The device was
successfully applied for the determination of analytes in urine and river water samples, where recovery rates
close to 100% were obtained. Due to its low cost and reusability by simple polishing, the sensor has strong
potential to be used as an electrochemical sensor for the determination of different analytes.

1. Introduction whole [4]. The contaminants may exhibit high toxicity even at low
concentrations, since they can accumulate in living beings, resulting in
Owing to the high population growth in recent decades, environ­ chronic or acute intoxication [3,5]. In this sense, the sensitive and
mental pollution has become a major problem worldwide, particularly precise detection of the presence of contaminants in biological and
in hugely populated cities [1,2]. Daily, contaminants from man-made natural residues has enormous importance when it comes to the pro­
manufactured products consumed worldwide are discarded into tection of human health and the environment [6]. Considering the risks
aquatic environments through untreated sewage and industrial waste­ pose by these contaminants, researchers worldwide have focused their
water [3]. These contaminants, which are referred to as emerging pol­ attention on the development and application of different analytical
lutants, are man-made chemical or natural compounds that are found in methods for monitoring a wide range of compounds in wastewater as
different environments and whose level of toxicity and/or persistence well as in other environmental samples.
can alter the metabolism of living beings, thus posing serious risks to Direct yellow 50 is a dye that belongs to the “direct dye” class. Due to
humans and other living organisms, as well as to the environment as a its ease of application and the variety of dye formulations that are

* Corresponding author.
** Corresponding author. Department of Analytical Chemistry, Institute of Chemistry, State University of São Paulo, Araraquara, SP, Brazil.
E-mail addresses: ademar.wong@hotmail.com (A. Wong), fcvicentini@ufscar.br, fercv02@yahoo.com.br (F.C. Vicentini).

https://doi.org/10.1016/j.talanta.2020.121539
Received 30 June 2020; Received in revised form 7 August 2020; Accepted 8 August 2020
Available online 18 August 2020
0039-9140/© 2020 Elsevier B.V. All rights reserved.
A. Wong et al. Talanta 222 (2021) 121539

derived from it and which are available at modest costs, this dye has researchers in the field regarding the development of efficient methods
become one of the most popular dyes employed worldwide. The direct capable of detecting and quantifying these substances with a view to
yellow 50 (DY) is widely used for the dyeing of cellulosic fibres and their mitigating the risks they pose to human health and to the environment
mixtures [7,8]. Essentially, DY are usually azo dyes with some similar­ as a whole. Several analytical methods for the determination of
ities to acid dyes [7]. emerging compounds have been reported in the literature; these include
Carbendazim (CBZ) is a fungicide, known to be widely used in spectrophotometry [33], UHPLC-QTOF-MS [34], and electrochemical
agriculture, mainly in citrus and cereal crops, applied against various methods [35]. Of the wide range of analytical methods reported in the
fungal diseases [9,10]. CBZ is classified as a possible human carcinogen literature, the use of electrochemical methods has gained enormous
[11–13], and the European Commission has placed it on the list of pri­ popularity among researchers because of their outstanding advantages.
ority endocrine-disrupting chemicals [14]. [15]. Electrochemical detection techniques have been shown to possess high
Tryptophan (TTP) is considered one of the essential amino acids sensitivity, good stability and repeatability, apart from having the
present in the human body; this amino acid is a precursor for the syn­ ability to perform detection in real-time, requiring few sample prepa­
thesis of some bioactive substances, such as serotonin (5-hydroxytryp­ rations and being relatively inexpensive to be executed [3]. Several
tamine), melatonin, quinurenic acid, 3-hydroxyquinurenin, niacin and materials can be employed in the development of electrochemical sen­
quinolinic acid [16–20]. Having knowledge of the TTP levels is vital for sors; these include ionic liquids, macrocycle compounds (cyclodextrin),
monitoring the biochemical balance in the brain, and higher levels of metal complexes (phthalocyanines and porphyrins), carbon materials
TTP have been shown to lead to common symptoms such as nausea, (graphene and nanotube), metal nanoparticles, among others. Studies
dizziness, drowsiness, hallucinations, agitation, fever and loss of appe­ reported in the literature have shown that the use of carbon materials
tite. By contrast, TTP deficiency has been shown to contribute toward combined with metallic nanoparticles for the construction of sensors
the depletion of neurotransmitters, such as serotonin (5-HT), which can produces a synergistic effect between the materials, leading to the
cause mental disorders such as anxiety, depression, insomnia, etc. generation of highly sensitive sensing platforms for the detection of
[21–24]. analytes of interest [36].
Caffeine (CF) is one of the most consumed psychoactive substances in Palladium nanoparticles (PdNPs) have been shown to possess suit­
the world [25,26]. When consumed sparingly, CF can improve one’s able properties, which include high heterogeneous catalysis and elec­
mental state, concentration, fatigue feeling and athletic performance trocatalytic activity, versatility, non-toxicity and low cost [37]. PdNPs
[27]; however, CF consumption in excess can cause problems such as have been used in combination with a wide range of supporting mate­
anxiety, headaches, nausea, and stunting, apart from increasing the risk rials, such as carbon materials (graphene and carbon nanotubes), for the
of hypertension and cardiovascular diseases [28–32]. development of electrochemical sensors with high catalytic performance
Given the underlying relevance and effects of the aforementioned [38,39].
substances, coupled with the fact that they are hugely consumed and Graphite pencil is a useful material designed for writing and is
discarded in the environment, there has been growing interest among currently used as electrode for the development of electrochemical

Fig. 1. FEG-SEM of bare GPE and its enlarged surface (a) before polishing; (b) after polishing; (c) PdNPs/GPE surface and (d) EDX spectrum of the PdNPs/GPE.

2
A. Wong et al. Talanta 222 (2021) 121539

sensors. Graphite pencil has sp2 hybridized carbon, which allows good
adsorption, conductivity, high sensitivity in the detection of analytes
and lower background current [40,41]. Other key advantages of
graphite pencil include ease of preparation and surface modification,
low cost, and the ability to be used as a disposable material [40,41].
The present work sought to develop a quick and inexpensive elec­
trochemical method for the simultaneous determination of emerging
pollutants. For this purpose, a graphite pencil electrode (GPE) was
prepared and modified with palladium nanoparticles. The modified
electrode was then applied for the detection of analytes of interest in
synthetic urine and river water samples using the voltammetry method.

2. Materials and methods

2.1. Reagents and apparatus

All reagents used in the experiments were of analytical or HPLC

grade. The deionized water (resistivity ≥ 18 MΩ cm at 25 ◦ C) was ob­
tained from a Milli-Q Direct-0.3 purification system (Millipore). The
reagents employed in this work included the following: direct yellow 50,
Fig. 2. Nyquist plots for (■) unpolished GPE, (●) polished GPE and (▴)
tryptophan, carbendazim, caffeine, PdCl2 (purchased from Sigma-
PdNPs/GPE constructed using 0.1 mol L− 1 KCl electrolyte solution containing
Aldrich), NaOH and H2SO4 (acquired from Synth and Panreac).
1.9 × 10− 3 mol L− 1 [Fe(CN)6]3− /4− in the frequency range of 0.1 Hz–100 kHz,
The electrochemical measurements were carried out using Autolab under open circuit for each electrode. Inset: Randles equivalent circuit, where
PGSTAT 302 N potentiostat controlled by the NOVA 2.1 software and Rs is the supporting electrolyte resistance, Rct is charge-transfer resistance, CPE
equipped with a conventional electrochemical cell (10 mL volume) is constant phase element, and ZW is Warburg impedance.
containing three electrodes. The electrodes employed were as follows:
Ag/AgCl/sat.KCl used as reference electrode, platinum coil employed as
counter electrode, and graphite pencil used as a homemade working
electrode (WE).
The electrochemical impedance spectroscopy (EIS) analysis was
conducted in the frequency range of 0.1 Hz–100 kHz, amplitude of 10
mV, and under open circuit potential (OCP) using the FRA2 software.
The following was used as electrolyte solution: 0.1 mol L− 1 KCl solution
containing 1.9 × 10− 3 mol L− 1 [Fe(CN)6]3− /4− .
Morphological characterization of graphite pencil and palladium
nanoparticles was performed using images acquired from a Field Emis­
sion Gun Scanning Electron Microscope (FEG-SEM, model: FEI Magellan
400 L).
The Spectrophotometry analysis (i.e. the comparative method) was
performed using a Shimadzu UV–Vis spectrophotometer (model 2550)
with a 3.5 mL quartz cuvette quartz cells, where the absorbance was
measured for DY, TTP, CBZ and CF at room temperature.

2.2. Preparation of graphite pencil electrode modified with PdNPs

The working electrode was constructed using Pentel® Super Hi- Fig. 3. Square-wave voltammograms obtained for (a) unpolished GPE, (b)
Polymer C505 type HB mechanical graphite pencil. Initially, a delimi­ polished GPE, and (c) PdNPs/GPE from the analysis involving the use of 0.1
mol L− 1 H2SO4 in the presence of 5.0 × 10− 6 mol L− 1 DY, 7.0 × 10− 6 mol L− 1
ted part of the graphite was polished with a 2000 grit sandpaper, and a
TTP, 1.0 × 10− 6 mol L− 1 CBZ and 1.0 × 10− 4 mol L− 1 CF. SWV conditions: f =
contact area of 1.0 cm by 0.9 mm was obtained. Afterwards, the graphite
60 Hz, a = 75 mV and ΔE = 6 mV.
pencil electrode (GPE) was modified with PdNPs via the electrodeposi­
tion process using palladium chloride solution. This process involved the
mL of the sample was added in a 10 mL volumetric flask and enriched
application of − 0.2 V potential for 90 s by the amperometric method as
with DY, TTP, CBZ and CF, and the flask volume was filled up with 0.1
described previously by Hu et al. [42,43]. Graphite pencil electrode can
mol L− 1 H2SO4 acid.
be reused by simple polishing using a 2000 grit sandpaper.

2.3. Preparation of synthetic urine and river water samples 2.4. Analytical procedure

The synthetic urine sample was prepared based on the work of Laube First, the PdNPs were synthesized. Afterwards, the morphological
et al. using compounds present in real samples of 49, 10, 20, 15, 18, and and electrochemical characterizations of the electrodes were performed
18 mmol L− 1 concentrations of NaCl, CaCl2, KCl, KH2PO4, and NH4Cl, by SEM, Energy-Dispersive X-ray (EDX) and Electrochemical Impedance
respectively, and urea; all placed in a flask and filled with ultrapure Spectroscopy (EIS).
water [44]. The electrochemical behaviour of the analytes, namely, direct yellow
River water samples were collected from the Tiete River in São 50 (DY), tryptophan (TTP), carbendazim (CBZ) and caffeine (CF), was
Paulo, Brazil. The samples were subjected to conventional filtration to analysed using cyclic voltammetry (CV), followed by the optimisation of
remove the solid material; they were then stored in a 100 mL flask and the experimental conditions, including the composition and pH of the
kept in the refrigerator at 0 ◦ C. In the sample preparation procedure, 1 supporting electrolyte, and the instrumental parameters (frequency,

3
A. Wong et al. Talanta 222 (2021) 121539

Scheme 1. Proposed reaction mechanisms for the oxidation of (a) TTP, (b) CBZ and (c) CF.

applied potential and amplitude) for SWV analysis. Based on the results
obtained, analytical curves were constructed using successive additions
of DY, TTP, CBZ and CF standard solutions. The limit of detection (LOD)
was calculated based on the following equation: 3 x SD/m, where “SD”
stands for standard deviation for 10 blank solutions (n = 10) and “m” the
slope of the analytical curve. In addition, the precision and selectivity of
the proposed method was analysed based on intra-day (n = 10)
repeatability studies and the influence of potential interferents. Finally,
the simultaneous determination of DY, TTP, CBZ and CF was performed
using the proposed PdNPs/GPE sensor in river water and synthetic urine
samples. The results obtained were compared with those of the spec­
trophotometric method, where each analyte was analysed separately.

3. Results and discussions

3.1. Morphological characterization of PdNPs/GPE

PdNPs were electrodeposited on the GPE and were subsequently

morphologically characterized by FEG-SEM. Fig. 1 shows the SEM im­ Fig. 4. Optimisation of the concentration of H2SO4 by SWV in the presence of
4.0 × 10− 6 mol L− 1 DY, 4.0 × 10− 6 mol L− 1 TTP, 4.0 × 10− 6 mol L− 1 CBZ and
ages for bare graphite pencil electrode (a) before and (b) after polishing.
8.0 × 10− 5 mol L− 1 CF. SWV conditions: f = 60 Hz, a = 75 mV and ΔE = 6 mV.
After polishing, one can observe that the cracks in the bare graphite
pencil electrode were almost completely removed, leaving the substrate
much smoother and homogeneous. Furthermore, the SEM images of the electrodeposited on the GPE surface, the Rct value obtained for the
bare GPE surface before and after polishing exhibit a flat, uniform sur­ modified PdNPs/GPE decreased to 647 Ω (Fig. 2 (▴)); this result can be
face with a relatively lower number of exposed graphite sheets. Fig. 1(c) attributed to two factors: i) decrease of oxygen groups on the GPE, and
shows the SEM images of the PdNPs/GPE surface; here, the PdNPs can ii) higher conductivity caused by the application of PdNPs.
be found to have been successfully deposited and well distributed on the
GPE surface, with PdNPs size distribution of 250–450 nm. The EDX 3.3. Electrochemical behaviour of direct yellow 50, tryptophan,
analysis (see Fig. 1(d)) of the surface of the GPE showed the presence of carbendazim and caffeine
carbon, oxygen and palladium elements, without the presence of any
contaminants. Square Wave Voltammetry (SWV) analysis was performed in order to
determine the electrochemical behaviour of the analytes, namely, direct
3.2. Electroanalytical behaviour of PdNPs/GPE yellow 50 (DY), tryptophan (TTP), carbendazim (CBZ) and caffeine (CF).
Fig. 3 shows the voltammetric responses for unpolished GPE, polished
Through electrochemical impedance spectroscopy analysis, addi­ GPE and PdNPs/GPE used for the simultaneous determination of the
tional information can be obtained regarding the electron transfer from following analytes: 5.0 × 10− 6 mol L− 1 direct yellow 50 (DY); 7.0 ×
the modified electrode; this is because electron transfer can be influ­ 10− 6 mol L− 1 tryptophan (TTP); 1.0 × 10− 6 mol L− 1 carbendazim (CBZ);
enced by the PdNPs and the electrode surface [45]. As shown in Fig. 2 and 1.0 × 10− 4 mol L− 1 caffeine (CF); in 0.1 mol L− 1 H2SO4 (used as
(■) and (●) for unpolished and polished GPE, respectively, the highest electrolyte solution). The unpolished GPE exhibited oxidation only for
charge transfer resistance (Rct) values obtained for the unpolished and DY and TTP (see Fig. 3 inset). Both the polished GPE and PdNPs/GPE
polished GPE were 1747 Ω and 947 Ω, respectively, related to the high presented a well-defined oxidation processes for DY, TTP, CBZ and CF.
presence of oxygen groups [46]. On the other hand, when PdNPs were For comparison purposes, Scheme 1 shows the most likely oxidation

4
A. Wong et al. Talanta 222 (2021) 121539

Fig. 5. Square-wave voltammograms obtained using PdNPs/GPE in 0.1 mol L− 1 H2SO4 electrolyte solution containing (a) 5.0 × 10− 6 mol L− 1 TTP, 1.0 × 10− 6 mol
L− 1 CBZ, 1.0 × 10− 4 mol L− 1 CF and varying DY concentrations (1: 0.0 to 6: 4.5 × 10− 6 mol L− 1), (b) 5.0 × 10− 6 mol L− 1 DY, 1.0 × 10− 6 mol L− 1 CBZ, 1.0 × 10− 4
mol L− 1 CF and varying TTP concentrations (1: 0.0 to 6: 7.4 × 10− 6 mol L− 1), (c) 5.0 × 10− 6 mol L− 1 DY, 5.0 × 10− 6 mol L− 1 TTP, 1.0 × 10− 4 mol L− 1 CF and varying
CBZ concentrations (1: 0.0 to 6: 0.6 × 10− 6 mol L− 1), (d) 5.0 × 10− 6 mol L− 1 DY, 5.0 × 10− 6 mol L− 1 TTP, 5.0 × 10− 7 mol L− 1 CBZ and varying CF concentrations (1:
0.0 to 6: 1.1 × 10− 4 mol L− 1). SWV parameters: f = 60 Hz, a = 75 mV and ΔEs = 6 mV.

reaction for the electrochemical reactions involving TTP [47,48], CBZ L− 1) or different pHs (1.16, 0.89 and 0.61) through the application of the
[49,50] and CF [51,52] based on the studies reported in the literature. modified PdNPs/GPE.
To the best of our knowledge, there are no reports in the literature As shown in Fig. 4, the highest analytical signal was obtained for 0.1
regarding the redox reaction for the electrooxidation of DY. The mol L− 1 ionic strength. Thus, this ionic strength was chosen for subse­
PdNPs/GPE presented two oxidation processes for DY, which did not quent studies.
occur on the polished GPE (in this case, the two DY oxidation processes Also, the SWV parameters (frequency, step potential and amplitude)
may have overlapped). were evaluated. The best results were obtained under the following
Furthermore, the PdNPs/GPE presented a higher oxidation peak parameter conditions: f = 60 Hz, a = 75 mV and ΔEs = 6 mV.
current (anodic peak current, Ipan) for DY (465.5 μA), TTP (136.4 μA),
CBZ (313.9 μA), and CF (151.0 μA), compared to the polished GPE,
3.5. Simultaneous determination of DY, TTP, CBZ and CF
which recorded the following peak currents for the analytes: DY (256.7
μA), TTP (44.3 μA), CBZ (204.8 μA) and CF (49.1 μA). When the PdNPs/
Analytical curves for the four analytes were constructed by keeping
GPE was employed, the anodic potentials obtained for the different
the concentration of three of the analytes fixed and varying the con­
analytes were 0.634 V and 0.747 V for DY, 0.974 V for TTP, 1.120 V for
centration of the remaining analyte. First, the concentration of DY was
CBZ and 1.402 for CF. In comparison with the polished GPE, the PdNPs/
varied from 0.0 to 4.5 × 10− 6 mol L− 1 while the concentrations of TTP at
GPE exhibited an increase in analytical signal by 1.81 fold for DY, 3.08
5.0 × 10− 6 mol L− 1, CBZ at 1.0 × 10− 6 mol L− 1 and CF at 1.0 × 10− 4 mol
fold for TTP, 1.53 fold for CBZ, and 3.08 fold for CF. The polishing of the
L− 1 were kept constant. The oxidation peak current for DY increased
electrode allowed the removal of the oxide layer, leaving the surface
linearly with its concentration, as shown in Fig. 5(a), while the oxidation
more conductive. These results can be attributed to the increase in
peak current for the other analytes remained practically constant (inset:
surface area and higher conductivity caused by the modification of the
Relative Standard Deviations (RSDs)). Subsequently, the analytical plot
GPE with PdNPs (transformed into PdNPs/GPE).
for TTP was constructed from 0.0 to 7.4 × 10− 6 mol L− 1 while the
concentrations of DY at 5.0 × 10− 6 mol L− 1, CBZ at 1.0 × 10− 6 mol L− 1
3.4. Optimisation of analytical parameters and CF at 1.0 × 10− 4 mol L− 1 were kept constant. As observed previ­
ously, the Ipa for TTP also increased linearly with its concentration
The effect of ionic strength (and thus the pH) of the supporting (Fig. 5(b)) and the RSD values obtained for the fixed analytes were 5.11
electrolyte was analysed using 4.0 × 10− 6 mol L− 1 DY, 4.0 × 10− 6 mol (DY), 7.53% (CBZ) and 1.92% (CF). Afterwards, the concentration of
L− 1 TTP, 4.0 × 10− 6 mol L− 1 CBZ and 8.0 × 10− 5 mol L− 1 CF in the CBZ was varied from 0.0 to 0.6 × 10− 6 mol L− 1 and the concentrations of
presence of H2SO4 in different concentrations (0.05, 0.1 and 0.2 mol the other analytes were kept constant at 5.0 × 10− 6 mol L− 1 (DY and

5
A. Wong et al. Talanta 222 (2021) 121539

Fig. 6. (a) Square-wave voltammograms obtained

using PdNPs/GPE in 0.1 mol L− 1 H2SO4 electrolyte
solution containing DY (1–9: 0, 0.99, 2, 3, 4, 5, 6,7.6
and 9.90 μmol L− 1), TTP (10–18: 0, 1.20, 2.4, 3.7,
5.0, 6.2, 7.4, 9.8 and 12.0 μmol L− 1), CBZ (19–27: 0,
0.20, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, and 1.60 μmol L− 1),
and CF (28–36: 0, 25.0, 50, 74, 98, 120, 150, 170 and
190 μmol L− 1); (b) analytical plot obtained for DY;
(c) analytical plot obtained for TTP; (d) analytical
plot obtained for CBZ, and (e) analytical plot ob­
tained for CF. SWV parameters: f = 60 Hz, a = 75 mV
and ΔEs = 6 mV.

TTP) and 1.0 × 10− 4 mol L− 1 (CF). The analytical signal for CBZ was respective plots for the simultaneous determination of DY, TTP, CBZ and
linearly proportional to its concentration (Fig. 5(c)) and the RSD values CF on the proposed PdNPs/GPE in 0.1 mol L− 1 H2SO4 solution.
obtained for the analytes were 6.75%, 2.11% and 3.26% for DY, TTP and The analytical plots were found to be linear in the concentration
CF, respectively. Next, the analytical plot for CF was constructed by ranges of 9.90 × 10− 7 to 9.90 × 10− 6 mol L− 1 for DY, 1.20 × 10− 6 to
varying the concentration of CF from 0.0 to 1.1 × 10− 4 mol L− 1 and 1.20 × 10− 5 mol L− 1 for TTP, 2.00 × 10− 7 to 1.60 × 10− 6 mol L− 1 for
keeping the concentrations of DY (at 5.0 × 10− 6 mol L− 1), TTP (at 5.0 × CBZ, and from 2.50 × 10− 5 to 1.90 × 10− 4 mol L− 1 for CF. The anodic
10− 6 mol L− 1), and CBZ (at 1.0 × 10− 6 mol L− 1) constant. As observed in peak currents were linearly proportional to the concentrations of DY,
Fig. 5(d), the analytical signal for CF was also linearly proportional to its TTP, CBZ and CF, based on the following equations:
concentration and the RSD values obtained were 17.2% (DY), 4.17%
(TTP), and 12.70% (CBZ). Ipa (μA) = − 65 + 55 CDY (mol L− 1) r = 0.9910, for DY;
Based on the results obtained in this study, one can conclude that Ipa (μA) = − 10 + 12CTTP (mol L− 1) r = 0.9935, for TTP;
each of the four analytes, namely, DY, TTP, CBZ and CF, does not Ipa (μA) = 4.0 + 173CCBZ (mol L− 1) r = 0.9925, for CBZ;
interfere in any other analyte during the square wave (SW) voltammetric Ipa (μA) = − 3.0 + 0.8CCF (mol L− 1) r = 0.9955, for CF.
detemination of each one of them.
Finally, the simultaneous determination of DY, TTP, CBZ and CF was The limits of detection (LOD) [calculated as 3 × SD/m, where SD is
carried out by SWV. Fig. 6a–e presents the SW voltammograms and the the standard deviation for the blank solutions (n = 10) and m is the slope

6
A. Wong et al. Talanta 222 (2021) 121539

Table 1
Analytical comparison of the PdNPs/GPE sensor, based on the determination of tryptophan, carbendazim and caffeine, with other studies reported in the literature.
Electrode Analyte Method Linear range (μmol L− 1) LOD (μmol L− 1) Reference
a
BDD Tryptophan and tyrosine DPV 75 - 122 (TTP) 0.5 [53]
GC-SnS/TiO2@GOb Tryptophan, paracetamol and caffeine DPV 0.013–157 (TTP) and 0.017–333 (CF) 0.008 (TTP) and 0.0044 (CF) [54]
NPG/GCEc Carbendazim and methyl paration DPV 3 - 120 (CBZ) 0.24 [55]
ZnFe2O4/SWCNTS/GCEd Carbendazim and thiabendazole DPV 0.5–100 (CBZ) 0.05 [56]
Nafion®/GCEe Caffeine and Pyridoxine DPV 63.1–600 (CF) 18.9 [57]
Poly (ARS)/GCEf Caffeine and Vanillin SWV 10 - 450 (CF) 0.8 [58]
GCE-M221-Fe3O4g Acetaminophen and Caffeine DPV 50 - 900 (CF) 23 [59]
PLCY/N-CNT/GCEh Theophylline and caffeine DPV 0.4–140 (CF) 0.2 [60]
PdNPs/GPE Tryptophan SWV 1.2–12 (TTP) 0.2 (TTP) This work
Carbendazim 0.2–1.6 (CBZ) 0.018 (CBZ)
Caffeine 25 - 190 (CF) 3.9 (CF)
a
Boron-doped diamond.
b
GCE modified with sulfide (SnS) and titanium dioxide (TiO2) on graphene oxide (GO) sheets (SnS/TiO2@GO ternary composite).
c
Glassy carbon electrode modified with r nanoporous gold.
d
ZnFe2O4 nanoparticles and carbon nanotubes on GCE.
e
Glassy carbon electrode covered with thin layer of sulfonated fluoropolymer Nafion.
f
Poly (Alizarin Red S) modified glassy carbon electrode.
g
Fe3O4 Nanoparticles Modified glassy carbon Electrode.
h
Nitrogen-doped carbon nanotubes decorated poly (L-Cysteine) on GCE.

of the analytical curve] obtained for the analytes were 4.5 × 10− 7, 2.0 ×
10− 7, 1.8 × 10− 8 and 3.9 × 10− 6 mol L− 1 for DY, TTP, CBZ and CF,
respectively. The low LODs presented by the PdNPs/GPE can be
attributed to the PdNPs nanostructure, which made the mass transfer of
DY, TTP, CBZ and CF easier.
The analytical parameters of the proposed sensor were compared
with those of other studies reported in the literature (Table 1). Based on
the comparative analysis, the results obtained for linear range of con­
centration and detection limit in the present work were comparable and
sometimes better than those from the studies reported in the literature,
with the exception of the works published by Murugan et al. and Wang
et al. It is worth noting that the proposed method is relatively cheaper
and efficiently capable of detecting four analytes simultaneously
whereas the methods reported in the literature can perform simulta­
neous detection with only two analytes and in some rare cases with three
analytes. In addition, with regard to DY dye, to the best of our knowl­
6
Fig. 7. Intra-day repeatability study using the concentration of 5.0 × 10− mol edge, no electrochemical sensor has been reported in the literature for
L− 1 DY, 2.5 × 10− 6 mol L− 1 TTP, 5.0 × 10− 7 mol L− 1 CBZ and 5.0 × 10− 5
mol
the determination of this analyte; this makes the proposed novel method
L− 1 CF in 0.1 mol L− 1 H2SO4 electrolyte solution.
highly promising.
The repeatability study of the PdNPs/GPE was conducted using

Table 2
Results obtained for DY, TTP, CBZ and CF analysis in natural (water) and biological (urine) samples using the SW Voltammetric and the Spectrophotometric methods.
1
Analytes Samples Added/mol L− Spectrophotometric methoda/mol L− 1
SWV methoda/mol L− 1
R (%)b RSD (%)c
6 6 6
DY River water 2.5 × 10− (2.6 ± 0.1) × 10− (2.5 ± 0.2) × 10− 100 − 3.85
6 6 6
5.0 × 10− (5.1 ± 0.1) × 10− (5.1 ± 0.3) × 10− 102 0.00
6 6 6
Synthetic urine 2.5 × 10− (2.7 ± 0.1) × 10− (2.7 ± 0.2) × 10− 108 0.00
6 6 6
5.0 × 10− (5.1 ± 0.1) × 10− (5.2 ± 0.2) × 10− 104 1.96
6 6 6
TTP River water 2.5 × 10− (2.5 ± 0.1) × 10− (2.3 ± 0.1) × 10− 92.0 − 8.00
6 6 6
5.0 × 10− (4.9 ± 0.1) × 10− (4.9 ± 0.2) × 10− 100 0.00
6 6 6
Synthetic urine 2.5 × 10− (2.6 ± 0.1) × 10− (2.4 ± 0.1) × 10− 96.0 − 7.69
6 6 6
5.0 × 10− (5.2 ± 0.1) × 10− (5.0 ± 0.3) × 10− 100 − 3.85
7 7 7
CBZ River water 2.5 × 10− (2.5 ± 0.1) × 10− (2.6 ± 0.2) × 10− 104 4.00
7 7 7
5.0 × 10− (5.1 ± 0.1) × 10− (5.1 ± 0.3) × 10− 102 0.00
7 7 7
Synthetic urine 2.5 × 10− (2.4 ± 0.1) × 10− (2.3 ± 0.2) × 10− 92.0 − 4.17
7 7 7
5.0 × 10− (4.7 ± 0.1) × 10− (4.8 ± 0.6) × 10− 96.0 2.13
6 6 6
CF River water 2.5 × 10− (2.6 ± 0.1) × 10− (2.5 ± 0.1) × 10− 100 − 3.85
6 6 6
5.0 × 10− (4.8 ± 0.1) × 10− (5.0 ± 0.1) × 10− 100 4.17
6 6 6
Synthetic urine 2.5 × 10− (2.5 ± 0.1) × 10− (2.5 ± 0.1) × 10− 100 0.00
6 6 6
5.0 × 10− (4.9 ± 0.1) × 10− (5.1 ± 0.2) × 10− 102 4.08
a
Average of 3 measured concentrations.
b
Recovery percentage, R (%) = [Founded/Added] × 100.
c
RSD = [(SWV method − Spectrophotometric method)/(Spectrophotometric method)] × 100.

7
A. Wong et al. Talanta 222 (2021) 121539

concentrations of 5.0 × 10− 6 mol L− 1 DY, 2.5 × 10− 6 mol L− 1 TTP, 5.0 × and biological (urine) samples using the Square Wave Voltammetry
10− 7 mol L− 1 CBZ, and 5.0 × 10− 5 mol L− 1 CF in 0.1 mol L− 1 H2SO4 technique. The key advantages of the proposed electrochemical sensor
electrolyte solution. As shown in Fig. 7, the RSD values obtained for are that the electrode preparation is simple and less time-consuming,
intra-day studies (n = 10) were 3.5% and 3.2% for DY, 2.1% for TTP, apart from involving a simple electrodeposition of PdNPs. In addition,
6.9% for CBZ, and 1.6% for CF. The high repeatability of the proposed the proposed sensor is cheap to produce (since the material employed -
PdNPs/GPE can be attributed to the homogeneity of the electrode sur­ graphite pencil, in the sensor fabrication is of low cost), has fast response
face and the good conductivity derived from the polishing of the elec­ and reproducibility; these advantages make the material an excellent
trode and the electrodeposition of PDNPs on the GPE. In addition, alternative for use in environmental and biological analyses. Another
reproducibility study of the PDNPS/GPE was made using five electrodes remarkable advantage is the ability to perform numerous analyses with
under the same conditions of analysis. The RSD values obtained in the same graphite bar by simple polishing of the electrode surface.
triplicate experiments were 5.5% and 4.3% for DY, 3.1% for TTP, 6.0%
for CBZ, and 2.9% for CF (data not shown). Credit author statement
In addition, the influence of possible interferents, such as ascorbic
acid, urea, NaCl, catechol, hydroquinone, Pd2+, Cd2+, uric acid, raniti­ Ademar Wong: Conceptualization, Methodology, Investigation.
dine and captopril in the ratio 1:1 and 5:1 (analyte: interferent) was Anderson Martin Santos: Methodology, Software, Investigation. Rafael
investigated. The concentrations of the analytes used in these experi­ da Fonseca Alves: Methodology, Validation. Fernando Campanhã Vice­
ments were: DY (5 μmol L− 1), TTP (5 μmol L− 1), CBZ (5 μmol L− 1) and ntini: Formal analysis, Writing - review & editing, Funding acquisition.
CF (25 μmol L− 1). Based on the voltammograms obtained, the interfer­ Orlando Fatibello-Filho: Resources, Project administration, Funding
ents were found to exert no influence on the determination of the four acquisition. Maria Del Pilar Taboada Sotomayor: Resources, Supervi­
analytes investigated. sion, Funding acquisition.

3.6. Simultaneous determination of DY, TTP, CBZ and CF in river water

and urine samples Declaration of competing interest

The application of the PdNPs/GPE in river water and synthetic urine The authors declare that they have no known competing financial
samples using the SWV technique for the simultaneous determination of interests or personal relationships that could have appeared to influence
DY, TTP, CBZ and CF was evaluated. To perform this analysis, the re­ the work reported in this paper.
covery rates were obtained in triplicate (n = 3) by adding two different
concentrations of each analyte to the water and urine samples, and the Acknowledgements
results were subsequently analysed and calculated by the interpolation
method from the respective analytical curves. The authors are grateful to Conselho Nacional de Desenvolvimento
As can be seen in Table 2, excellent recovery rates ranging from 92.0 Científico e Tecnológico – CNPq (grant numbers 150184/2019–0,
to 108% were obtained. In addition, the results obtained from the SWV 405546/2018–1 and 408430/2016–8), FAPESP (grant numbers 2014/
method were compared with those of the spectrophotometric method; 50945–4, 2019/00677–7 and 2020/01050–5) and CAPES (PROJ. AUX/
the low RSDs (− 8.00% < RSD < +4.17%) obtained show great similarity PE/PROEX Nº 0674/2018) for the financial support granted in the
between the methods. These results demonstrate that the PdNPs/GPE course of this research.
can be successfully applied for the simultaneous detection of DY, TTP,
CBZ and CF in natural and biological matrices. References
Another relevant test conducted and which deserves mentioning is
the paired t-test. This test (with a 95% confidence level) was applied to [1] P.D. Noyes, M.K. Mcelwee, H.D. Miller, B.W. Clark, L.A. Van Tiem, K.C. Walcott, K.
demonstrate the equivalence of the results obtained from the two N. Erwin, E.D. Levin, The toxicology of climate change: environmental
contaminants in a warming world, Environ. Int. 35 (2009) 971–986, https://doi.
methods under comparison. The calculated texperimental values were tDY
org/10.1016/j.envint.2009.02.006.
= 0.000, tTTP = 3.000, tCBZ = 0.522 and tCF = 1.000. As can be noted, all [2] C. Zhu, D. Liu, Y. Li, X. Shen, L. Li, Y. Liu, T. You, Ratiometric electrochemical,
the values were found to be smaller than tcritical value (3.182), indicating electrochemiluminescent, and photoelectrochemical strategies for environmental
contaminant detection, Curr. Opin. Electrochem. 17 (2019) 47–55, https://doi.
that there is no significant difference between the results when it comes
org/10.1016/j.coelec.2019.04.014.
to the quantification of DY, TTP, CBZ and CF in different samples using [3] A. Wong, A.M. Santos, M. Baccarin, É.T.G. Cavalheiro, O. Fatibello-Filho,
the two analytical methods. Thus, the results show the excellent accu­ Simultaneous determination of environmental contaminants using a graphite oxide
racy of the SW voltammetric technique, the reliability of the data ob­ – polyurethane composite electrode modified with cyclodextrin, Mater. Sci. Eng. C
99 (2019) 1415–1423, https://doi.org/10.1016/j.msec.2019.02.093.
tained and the effectiveness of the technique applied for quantifying the [4] C. Peña-Guzmán, S. Ulloa-Sánchez, K. Mora, R. Helena-Bustos, E. Lopez-Barrera,
analytes investigated in river water and urine samples. J. Alvarez, M. Rodriguez-Pinzón, Emerging pollutants in the urban water cycle in
A further point worth mentioning here is that the proposed method Latin America: a review of the current literature, J. Environ. Manag. 237 (2019)
408–423, https://doi.org/10.1016/j.jenvman.2019.02.100.
presented a great advantage over the spectrophotometric method in the [5] T. Deblonde, C. Cossu-leguille, P. Hartemann, Emerging pollutants in wastewater :
sense that the former allows simultaneous determination of the analytes, a review of the literature, Int. J. Hyg Environ. Health 214 (2015) 442–448, https://
whereas the latter only allows individual determination of the analytes. doi.org/10.1016/j.ijheh.2011.08.002.
[6] A. Vaseashta, M. Vaclavikova, S. Vaseashta, G. Gallios, P. Roy,
O. Pummakarnchana, Nanostructures in environmental pollution detection,
4. Conclusions monitoring, and remediation, Sci. Technol. Adv. Mater. 8 (2007) 47–59, https://
doi.org/10.1016/j.stam.2006.11.003.
[7] L.F.M. Ismail, H.B. Sallam, S.A. Abo Farha, A.M. Gamal, G.E.A. Mahmoud,
The present work reported the development of graphite pencil Adsorption behaviour of direct yellow 50 onto cotton fiber: equilibrium, kinetic
electrode and its modification with PdNPs. The modified electrode was and thermodynamic profile, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 131
successfully characterized by SEM, EDX, and EIS, and the data obtained (2014) 657–666, https://doi.org/10.1016/j.saa.2014.03.060.
[8] S.M. Burkinshaw, N. Kumar, Polyvinyl alcohol as an aftertreatment: Part 3 direct
showed that the PdNPs were efficiently synthesized on the GPE surface.
dyes on cotton, Dyes Pigments 85 (2010) 124–132, https://doi.org/10.1016/j.
The good electrochemical properties obtained for the proposed PdNPs/ dyepig.2009.10.014.
GPE are attributed to the increased anodic peak current and high con­ [9] N.E. McCarroll, A. Protzel, Y. Ioannou, H. Frank Stack, M.A. Jackson, M.D. Waters,
ductivity caused by the application of PdNPs on the GPE. The suitable K.L. Dearfield, A survey of EPA/OPP and open literature on selected pesticide
chemicals: III. Mutagenicity and carcinogenicity of benomyl and carbendazim,
properties of the proposed sensor enabled its application toward the Mutat. Res. Mutat. Res. 512 (2002) 1–35, https://doi.org/10.1016/S1383-5742
simultaneous determination of DY, TTP, CBZ and CF in natural (water) (02)00026-1.

8
A. Wong et al. Talanta 222 (2021) 121539

[10] P. Mazellier, É. Leroy, B. Legube, Photochemical behavior of the fungicide [26] I.M.U. Rossetto, V.H.A. Cagnon, F.S.N. Lizarte, L.F. Tirapelli, D.P.C. Tirapelli, R.M.
carbendazim in dilute aqueous solution, J. Photochem. Photobiol. Chem. 153 S. Arantes, L.G.A. Chuffa, F.E. Martinez, M. Martinez, Ethanol and caffeine
(2002) 221–227, https://doi.org/10.1016/S1010-6030(02)00296-4. consumption modulates the expression of miRNAs in the cerebellum and plasma of
[11] W.H. Goodson III, L. Lowe, D.O. Carpenter, M. Gilbertson, A. Manaf Ali, A. Lopez UChB rats, Life Sci. 229 (2019) 180–186, https://doi.org/10.1016/j.
de Cerain Salsamendi, A. Lasfar, A. Carnero, A. Azqueta, A. Amedei, A.K. Charles, lfs.2019.05.016.
A.R. Collins, A. Ward, A.C. Salzberg, A.M. Colacci, A.-K. Olsen, A. Berg, B. [27] D.C. Mitchell, C.A. Knight, J. Hockenberry, R. Teplansky, T.J. Hartman, Beverage
J. Barclay, B.P. Zhou, C. Blanco-Aparicio, C.J. Baglole, C. Dong, C. Mondello, C.- caffeine intakes in the U.S, Food Chem. Toxicol. 63 (2014) 136–142, https://doi.
W. Hsu, C.C. Naus, C. Yedjou, C.S. Curran, D.W. Laird, D.C. Koch, D.J. Carlin, D. org/10.1016/j.fct.2013.10.042.
W. Felsher, D. Roy, D.G. Brown, E. Ratovitski, E.P. Ryan, E. Corsini, E. Rojas, E.- [28] X. Chen, Y. Liu, E.C. Jaenicke, A.N. Rabinowitz, New concerns on caffeine
Y. Moon, E. Laconi, F. Marongiu, F. Al-Mulla, F. Chiaradonna, F. Darroudi, F. consumption and the impact of potential regulations: the case of energy drinks,
L. Martin, F.J. Van Schooten, G.S. Goldberg, G. Wagemaker, G.N. Nangami, G. Food Pol. 87 (2019) 101746, https://doi.org/10.1016/j.foodpol.2019.101746.
M. Calaf, G.P. Williams, G.T. Wolf, G. Koppen, G. Brunborg, H.K. Lyerly, [29] M.-L. Nurminen, L. Niittynen, R. Korpela, H. Vapaatalo, Coffee, caffeine and blood
H. Krishnan, H. Ab Hamid, H. Yasaei, H. Sone, H. Kondoh, H.K. Salem, H.-Y. Hsu, pressure: a critical review, Eur. J. Clin. Nutr. 53 (1999) 831–839, https://doi.org/
H.H. Park, I. Koturbash, I.R. Miousse, A.I. Scovassi, J.E. Klaunig, J. Vondráček, 10.1038/sj.ejcn.1600899.
J. Raju, J. Roman, J.P. Wise Sr, J.R. Whitfield, J. Woodrick, J.A. Christopher, [30] A.E. Mesas, L.M. Leon-Muñoz, F. Rodriguez-Artalejo, E. Lopez-Garcia, The effect of
J. Ochieng, J.F. Martinez-Leal, J. Weisz, J. Kravchenko, J. Sun, K.R. Prudhomme, coffee on blood pressure and cardiovascular disease in hypertensive individuals: a
K.B. Narayanan, K.A. Cohen-Solal, K. Moorwood, L. Gonzalez, L. Soucek, L. Jian, L. systematic review and meta-analysis, Am. J. Clin. Nutr. 94 (2011) 1113–1126,
S.D. Abronzo, L.-T. Lin, L. Li, L. Gulliver, L.J. McCawley, L. Memeo, L. Vermeulen, https://doi.org/10.3945/ajcn.111.016667.
L. Leyns, L. Zhang, M. Valverde, M. Khatami, M.F. Romano, M. Chapellier, M. [31] P. Nawrot, S. Jordan, J. Eastwood, J. Rotstein, A. Hugenholtz, M. Feeley, Effects of
A. Williams, M. Wade, M.H. Manjili, M.E. Lleonart, M. Xia, M.J. Gonzalez Guzman, caffeine on human health, Food Addit. Contam. 20 (2003) 1–30, https://doi.org/
M.V. Karamouzis, M. Kirsch-Volders, M. Vaccari, N.B. Kuemmerle, N. Singh, 10.1080/0265203021000007840.
N. Cruickshanks, N. Kleinstreuer, N. van Larebeke, N. Ahmed, O. Ogunkua, P. [32] M.A. Heckman, J. Weil, E.G. De Mejia, Caffeine (1, 3, 7-trimethylxanthine) in
K. Krishnakumar, P. Vadgama, P.A. Marignani, P.M. Ghosh, P. Ostrosky-Wegman, foods: a comprehensive review on consumption, functionality, safety, and
P.A. Thompson, P. Dent, P. Heneberg, P. Darbre, P.S. Leung, P. Nangia-Makker, Q. regulatory matters, J. Food Sci. 75 (2010) R77–R87, https://doi.org/10.1111/
(Shawn) Cheng, R.B. Robey, R. Al-Temaimi, R. Roy, R. Andrade-Vieira, R.K. Sinha, j.1750-3841.2010.01561.x.
R. Mehta, R. Vento, R. Di Fiore, R. Ponce-Cusi, R. Dornetshuber-Fleiss, R. Nahta, R. [33] S. Altinöz, Ö.Ö. Dursun, Determination of nimesulide in pharmaceutical dosage
C. Castellino, R. Palorini, R.A. Hamid, S.A.S. Langie, S.E. Eltom, S.A. Brooks, forms by second order derivative UV spectrophotometry, J. Pharmaceut. Biomed.
S. Ryeom, S.S. Wise, S.N. Bay, S.A. Harris, S. Papagerakis, S. Romano, S. Pavanello, Anal. 22 (2000) 175–182, https://doi.org/10.1016/S0731-7085(99)00264-2.
S. Eriksson, S. Forte, S.C. Casey, S. Luanpitpong, T.-J. Lee, T. Otsuki, T. Chen, [34] H.A. Assress, H. Nyoni, B.B. Mamba, T.A.M. Msagati, Target quantification of azole
T. Massfelder, T. Sanderson, T. Guarnieri, T. Hultman, V. Dormoy, V. Odero- antifungals and retrospective screening of other emerging pollutants in wastewater
Marah, V. Sabbisetti, V. Maguer-Satta, W.K. Rathmell, W. Engström, W.K. Decker, effluent using UHPLC –QTOF-MS, Environ. Pollut. 253 (2019) 655–666, https://
W.H. Bisson, Y. Rojanasakul, Y. Luqmani, Z. Chen, Z. Hu, Assessing the doi.org/10.1016/j.envpol.2019.07.075.
carcinogenic potential of low-dose exposures to chemical mixtures in the [35] T.A. Saleh, G. Fadillah, O.A. Saputra, Nanoparticles as components of
environment: the challenge ahead, Carcinogenesis 36 (2015) S254–S296, doi: electrochemical sensing platforms for the detection of petroleum pollutants: a
10.1093/carcin/bgv039. review, TrAC Trends Anal. Chem. (Reference Ed.) 118 (2019) 194–206, https://
[12] G. Selmanoğlu, N. Barlas, S. Songür, E.A. Koçskaya, Carbendazim-induced doi.org/10.1016/j.trac.2019.05.045.
haematological, biochemical and histopathological changes to the liver and kidney [36] F. Lorestani, Z. Shahnavaz, P. Mn, Y. Alias, N.S.A. Manan, Sensors and Actuators B:
of male rats, Hum. Exp. Toxicol. 20 (2001) 625–630, https://doi.org/10.1191/ Chemical One-step Hydrothermal Green Synthesis of Silver Nanoparticle-Carbon
096032701718890603. Nanotube Reduced-Graphene Oxide Composite and its Application as Hydrogen
[13] X. Xu, J. Chen, B. Li, L. Tang, Carbendazim residues in vegetables in China between Peroxide Sensor, vol. 208, 2015, pp. 389–398.
2014 and 2016 and a chronic carbendazim exposure risk assessment, Food Contr. [37] Y. Sefid-sefidehkhan, K. Nekoueian, M. Amiri, M. Sillanpaa, H. Eskandari,
91 (2018) 20–25, https://doi.org/10.1016/j.foodcont.2018.03.016. Palladium nanoparticles in electrochemical sensing of trace terazosin in human
[14] A.L.G. Ferreira, S. Loureiro, A.M.V.M. Soares, Toxicity prediction of binary serum and pharmaceutical preparations, Mater. Sci. Eng. C 75 (2017) 368–374,
combinations of cadmium, carbendazim and low dissolved oxygen on Daphnia https://doi.org/10.1016/j.msec.2017.02.061.
magna, Aquat. Toxicol. 89 (2008) 28–39, https://doi.org/10.1016/j. [38] A. Cipri, M. Valle, Pd Nanoparticles/Multiwalled Carbon Nanotubes Electrode
aquatox.2008.05.012. System for Voltammetric Sensing of Tyrosine, vol. 14, 2014, pp. 6692–6698,
[15] D. Wu, M. Wu, J. Yang, H. Zhang, K. Xie, C.-T. Lin, A. Yu, J. Yu, L. Fu, Delaminated https://doi.org/10.1166/jnn.2014.9370.
Ti3C2Tx (MXene) for electrochemical carbendazim sensing, Mater. Lett. 236 [39] E. Mijowska, M. Onyszko, K. Urbas, M. Aleksandrzak, X. Shi, D. Moszy, K. Penkala,
(2019) 412–415, https://doi.org/10.1016/j.matlet.2018.10.150. J. Podolski, M. El Fray, Applied Surface Science Palladium Nanoparticles Deposited
[16] Y. Li, N. Hu, D. Yang, G. Oxenkrug, Q. Yang, Regulating the Balance between the on Graphene and its Electrochemical Performance for Glucose Sensing, vol. 355,
Kynurenine and Serotonin Pathways of Tryptophan Metabolism, vol. 284, 2017, 2015, pp. 587–592, https://doi.org/10.1016/j.apsusc.2015.07.150.
pp. 948–966, https://doi.org/10.1111/febs.14026. [40] H.T. Purushothama, Y.A. Nayaka, M.M. Vinay, P. Manjunatha, R.O. Yathisha, K. V
[17] V. Karabozhikova, V. Tsakova, C. Lete, M. Marin, S. Lupu, Poly(3,4- Basavarajappa, Pencil graphite electrode as an electrochemical sensor for the
ethylenedioxythiophene)-modified electrodes for tryptophan voltammetric voltammetric determination of chlorpromazine, J. Sci. Adv. Mater. Devices. 3
sensing, J. Electroanal. Chem. 848 (2019) 113309, https://doi.org/10.1016/j. (2018) 161–166, https://doi.org/10.1016/j.jsamd.2018.03.007.
jelechem.2019.113309. [41] N. Quynh, G. Vu, H. Dang, P. Thi, H. Yen, P. Hong, P. Vu, T. Thu, Au nanodendrite
[18] S.M. O’Mahony, G. Clarke, Y.E. Borre, T.G. Dinan, J.F. Cryan, Serotonin, incorporated graphite pencil lead as a sensitive and simple electrochemical sensor
tryptophan metabolism and the brain-gut-microbiome axis, Behav. Brain Res. 277 for simultaneous detection of Pb ( II ), Cu ( II ) and Hg ( II ), J. Appl. Electrochem.
(2015) 32–48, https://doi.org/10.1016/j.bbr.2014.07.027. 49 (2019) 839–846, https://doi.org/10.1007/s10800-019-01326-x.
[19] A.R. Fiorucci, É.T.G. Cavalheiro, The use of carbon paste electrode in the direct [42] J. Hu, Z. Zhao, J. Zhang, G. Li, P. Li, W. Zhang, K. Lian, Synthesis of palladium
voltammetric determination of tryptophan in pharmaceutical formulations, nanoparticle modified reduced graphene oxide and multi-walled carbon nanotube
J. Pharmaceut. Biomed. Anal. 28 (2002) 909–915, https://doi.org/10.1016/ hybrid structures for for electrochemical applications, Appl. Surf. Sci. 396 (2016)
S0731-7085(01)00711-7. 523–529, https://doi.org/10.1016/j.apsusc.2016.10.187.
[20] V. Tsakova, G. Ilieva, D. Filjova, Role of the anionic dopant of poly(3,4- [43] G. Chang, Y. Luo, W. Lu, X. Qin, A.M. Asiri, A.O. Al-youbi, X. Sun,
ethylenedioxythiophene) for the electroanalytical performance: electrooxidation of Electrodeposition Fabrication of Pd Nanoparticles on Glassy Carbon Electrode, vol.
acetaminophen, Electrochim, Acta 179 (2015) 343–349, https://doi.org/10.1016/ 4, 2013, pp. 1–7, https://doi.org/10.3844/ajntsp.2013.1.7.
j.electacta.2015.02.062. [44] N. Laube, B. Mohr, A. Hesse, Laser-probe-based investigation of the evolution of
[21] S. Russo, I.P. Kema, F. Bosker, J. Haavik, J. Korf, Tryptophan as an evolutionarily particle size distributions of calcium oxalate particles, formed in artificial urines
conserved signal to brain serotonin: molecular evidence and psychiatric 233 (2001) 367–374.
implications, World J. Biol. Psychiatr. 10 (2009) 258–268, https://doi.org/ [45] P.A. Raymundo-Pereira, A.M. Campos, F.C. Vicentini, B.C. Janegitz, C.
10.3109/15622970701513764. D. Mendonça, L.N. Furini, N. V Boas, M.L. Calegaro, C.J.L. Constantino, S.A.
[22] S. Comai, A. Bertazzo, N. Carretti, A. Podfigurna-Stopa, S. Luisi, C.V.L. Costa, S. Machado, O.N. Oliveira, Sensitive detection of estriol hormone in creek water
Serum levels of tryptophan, 5-hydroxytryptophan and serotonin in patients using a sensor platform based on carbon black and silver nanoparticles, Talanta
affected with different forms of amenorrhea, Int. J. Tryptophan Res. 3 (2010) 174 (2017) 652–659, https://doi.org/10.1016/j.talanta.2017.06.058.
69–75. https://www.scopus.com/inward/record.uri?eid=2-s2.0-84859754240 [46] A. Ambrosi, A. Bonanni, Z. Sofer, J.S. Cross, M. Pumera, Electrochemistry at
&partnerID=40&md5=79e96a1bd039e82c564211091b4b4161. chemically modified graphenes, Chem. Eur J. 17 (2011) 10763–10770, https://doi.
[23] E. Attia, S. Wolk, T. Cooper, D. Glasofer, B.T. Walsh, Plasma tryptophan during org/10.1002/chem.201101117.
weight restoration in patients with anorexia nervosa, Biol. Psychiatr. 57 (2005) [47] F. Tadayon, Z. Sepehri, A new electrochemical sensor based on a nitrogen-doped
674–678, https://doi.org/10.1016/j.biopsych.2004.11.045. graphene/CuCo2O4 nanocomposite for simultaneous determination of dopamine,
[24] W. Prongmanee, I. Alam, P. Asanithi, Hydroxyapatite/Graphene oxide composite melatonin and tryptophan, RSC Adv. 5 (2015) 65560–65568, https://doi.org/
for electrochemical detection of L-Tryptophan, J. Taiwan Inst. Chem. Eng. 102 10.1039/C5RA12020A.
(2019) 415–423, https://doi.org/10.1016/j.jtice.2019.06.004. [48] A. Özcan, Y. Şahin, A novel approach for the selective determination of tryptophan
[25] B.B. Fredholm, J. Yang, Y. Wang, Low, but not high, dose caffeine is a readily in blood serum in the presence of tyrosine based on the electrochemical reduction
available probe for adenosine actions, Mol. Aspect. Med. 55 (2017) 20–25, https:// of oxidation product of tryptophan formed in situ on graphite electrode, Biosens.
doi.org/10.1016/j.mam.2016.11.011. Bioelectron. 31 (2012) 26–31, https://doi.org/10.1016/j.bios.2011.09.048.

9
A. Wong et al. Talanta 222 (2021) 121539

[49] P. Wei, T. Gan, K. Wu, N-methyl-2-pyrrolidone exfoliated graphene as highly [55] X. Gao, Y. Gao, C. Bian, H. Ma, H. Liu, Electroactive nanoporous gold driven
sensitive analytical platform for carbendazim, Sensor. Actuator. B Chem. 274 electrochemical sensor for the simultaneous detection of carbendazim and methyl
(2018) 551–559, https://doi.org/10.1016/j.snb.2018.07.174. parathion, Electrochim. Acta 310 (2019) 78–85, https://doi.org/10.1016/j.
[50] Y. Zhou, Y. Li, P. Han, Y. Dang, M. Zhu, Q. Li, Y. Fu, A novel low-dimensional electacta.2019.04.120.
heteroatom doped Nd2O3 nanostructure for enhanced electrochemical sensing of [56] Y. Dong, L. Yang, L. Zhang, Simultaneous electrochemical detection of
carbendazim, New J. Chem. 43 (2019) 14009–14019, https://doi.org/10.1039/ benzimidazole fungicides carbendazim and thiabendazole using a novel
C9NJ02778E. nanohybrid material-modified electrode, J. Agric. Food Chem. 65 (2017) 727–736,
[51] Y. Tadesse, A. Tadese, R.C. Saini, R. Pal, Cyclic voltammetric investigation of https://doi.org/10.1021/acs.jafc.6b04675.
caffeine at anthraquinone modified carbon paste electrode, Int. J. Electrochem. [57] A.S. Farag, K. Pravcová, L. Česlová, K. Vytřas, M. Sýs, Simultaneous determination
2013 (2013) 849327, https://doi.org/10.1155/2013/849327. of caffeine and pyridoxine in energy drinks using differential pulse voltammetry at
[52] J.A. Tassinary, P. Bianchetti, C. Rempel, P. StülS, AvaliaçãO dos efeitos do glassy carbon electrode modified with Nafion®, Electroanalysis 31 (2019)
ultrassom terapêutico sobre a cafeína e verificação da liberação em sistema de 1494–1499, https://doi.org/10.1002/elan.201800646.
difusão vertical, Quim. Nova 34 (2011) 1539–1543, https://doi.org/10.1590/ [58] H. Filik, A.A. Avan, Y. Mümin, Simultaneous electrochemical determination of
S0100-40422011000900011. caffeine and vanillin by using poly(alizarin red S) modified glassy carbon
[53] Q. Wang, A. Vasilescu, P. Subramanian, A. Vezeanu, V. Andrei, Y. Coffinier, M. Li, electrode, Food Anal. Methods. 10 (2017) 31–40, https://doi.org/10.1007/
R. Boukherroub, S. Szunerits, Simultaneous electrochemical detection of s12161-016-0545-z.
tryptophan and tyrosine using boron-doped diamond and diamond nanowire [59] A. Mulyasuryani, R.T. Tjahjanto, R. Andawiyah, Simultaneous Voltammetric
electrodes, Electrochem. Commun. 35 (2013) 84–87, https://doi.org/10.1016/j. Detection of Acetaminophen and Ca ff eine Base on Cassava Starch — Fe3O4
elecom.2013.08.010. Nanoparticles Modified Glassy Carbon Electrode, Chemosensors 7 (2019) 49,
[54] E. Murugan, K. Kumar, Fabrication of SnS/TiO2@GO composite coated glassy https://doi.org/10.3390/chemosensors7040049.
carbon electrode for concomitant determination of paracetamol, tryptophan, and [60] Y. Wang, Y. Ding, L. Li, P. Hu, Nitrogen-doped carbon nanotubes decorated poly (L-
caffeine in pharmaceutical formulations, Anal. Chem. 91 (2019) 5667–5676, Cysteine) as a novel, ultrasensitive electrochemical sensor for simultaneous
https://doi.org/10.1021/acs.analchem.8b05531. determination of theophylline and caffeine, Talanta 178 (2018) 449–457, https://
doi.org/10.1016/j.talanta.2017.08.076.

10