Electrochemical study and voltammetric determination of sodium diethyldithiocarbamate using silver nanoparticles solid amalgam electrode

ABSTRACT We report in this work, for the first time, the voltammetric study and the development of an electroanalytical method for the determination of sodium diethyldithiocarbamate (Na-DDC) using solid amalgam electrode fabricated with silver nanoparticles. The experimental parameters were studied and the best voltammetric response was reached when using 0.02 mol L–1 Britton–Robinson buffer (pH = 5.5). Cyclic voltammograms of the substance presented two voltammetric signals: one cathodic peak at Ep = – 0.55 V and one anodic peak at Ep = – 0.49 V. The redox process of Na-DDC showed itself as an adsorption-controlled and quasi-reversible system. A mechanism for this electrochemical reaction was proposed. The analytical studies employed square-wave adsorptive stripping voltammetry (SWAdSV) and were based on the cathodic signal given by Na-DDC. Good linearity was observed in the concentration range from 2.83 × 10–7 mol L–1 to 6.89 × 10–6 mol L–1. The obtained limit of detection was 7.26 × 10–8 mol L–1. The electroanalytical approach described here was successfully employed for the determination of Na-DDC in river water at levels of concentration from 1.46 × 10–7 mol L–1 to 1.46 × 10–6 mol L–1 with good repeatability and reproducibility (RSD values of 4.2% and 5.9%, respectively). The values found during these determinations presented good concordance when compared with the expected values. According to the data presented here, the solid amalgam electrode fabricated with silver nanoparticles may be seen as an effective and green tool for the electrochemical analysis of Na-DDC and also other reducible compounds that usually require mercury-based electrode surfaces.


Introduction
Dithiocarbamates are widely used for several applications in the fields of toxicology, pharmacy, medicine, agriculture, industry, due to the fact that this class of compounds is highly reactive. Moreover, the chemical structure of the dithiocarbamates shows great efficiency on their use as chelating agents for metallic ions. Because of these features, dithiocarbamates are frequently employed on the treatment of patients who have been poisoned by metals and also as radioprotector against the damages caused by ionising radiation [1][2][3]. On the other hand, dithiocarbamates also have shown toxic effects. They may provoke chemical modulation of brain functions, lung toxicities and cause hepatotoxicity in humans [4][5][6]. Furthermore, residues of dithiocarbamates released into the environment may bring some problems for humans and ecosystems. The dithiocarbamates may form complexes with trace metals dissolved in natural waters. It inhibits their degradation and make the dithiocarbamates less soluble and more resistant in the environment. Additionally, this complexion may increase the absorption of the metals and potentialise the adverse effects of dithiocarbamates in the environment [7]. Thus, the monitoring and control of the levels of residues of dithiocarbamates in the environment is extremely important aiming to preserve human health and ensure the quality of resources such as natural waters.
Sodium diethyldithiocarbamate (Na-DDC) is largely used as chelating agent for transition metal ions, as slimicide during paper fabrication and as precursor to herbicides and vulcanisation reagents employed in rubber industry. It makes Na-DDC a possible contaminant for the environment, water and food. Therefore, the quantification of Na-DDC is an important issue due to the well-known toxic properties of the dithiocarbamate compounds [8,9]. The chemical structure of Na-DDC is shown in Figure 1.
The determination of dithiocarbamates is usually carried out through spectrophotometry [10] or gas-chromatography [11]. Spectrophotometric methods are generally based on the reaction between the carbon disulphide, which is generated during the decomposition of the dithiocarbamates, and cupric reagents or amines. This reaction produces a coloured complex that might be quantified by this technique. Meantime, these approaches have disadvantages such as high cost, low selectivity and long time required for the analyses. Moreover, significant interferences may be observed when using these methods in matrices such as water and soil due to the presence of several metallic ions [12].
In contrast, electrochemical approaches present advantages such as high reproducibility and repeatability, easiness of operation, low limits of detection, satisfactory selectivity and fast measurements. The use of voltammetric methods for the determination of electroactive molecules has attracted the attention of many researchers in the last years [13][14][15]. In this field, electroanalytical methods using the hanging mercury drop electrode (HMDE) have been extensively used for the quantification of organic molecules. The HMDE is considered the best tool for the determination of reducible compounds due to its high sensitivity and wide cathodic potential range. However, due to the known toxicity of mercury, its use as sensor in electroanalytical chemistry has decreased and novel approaches for its replacement have been developed [16][17][18].
Aiming to overcome this issue, amalgam-based electrodes have been introduced and are considered an environmental friendly option for the HMDE. This class of electrodes shows features such as wide potential window, mechanical stability and renewable surface [19][20][21]. Furthermore, amalgam electrodes require minimal amounts of mercury and may be fabricated in several shapes and sizes according to the desired requirements [22,23]. Several kinds of amalgam electrodes are reported in literature such as mercury meniscus covered [23], composite [24], polished [12], mercury film [25] and paste [26].
Although the use of voltammetric techniques for the determination of carbamates and dithiocarbamates is often reported in the literature [27][28][29][30][31], their use for the monitoring and determination of Na-DDC is not too much explored. There are few reports that describe the electrochemical behaviour of Na-DDC [32][33][34] and also its use as complexing agent aiming the voltammetric determination of metals [35,36]. However, to the best of our knowledge, there is just one work that reports the development of an electroanalytical method focused on the determination of Na-DDC in which boron-doped diamond electrode was used in protic media. The limit of detection obtained was 4 × 10 -6 mol L -1 [37].
Therefore, we present in this work, for the first time, the electrochemical study and the voltammetric determination of Na-DDC using solid amalgam electrode manufactured with silver nanoparticles. We already described previously the advantages on the use of nanoparticles for the fabrication of amalgam electrodes. They includes larger superficial areas, more electroactive sites and better sensitivities for the electrochemical sensors [38]. The parameters related to the electrochemical and electroanalytical experiments, as well as the stability of the electrode response and the selectivity of the method, were studied and optimised. Lastly, the voltammetric method developed was employed for the determination of Na-DDC in river water.

Chemicals and solutions
The following chemicals were used such as they were received: sodium diethyldithiocarbamate trihydrate (purity ≥ 97.0%) and silver nanopowder (particle size: < 100 nm, purity: 99%) were purchased from Sigma Aldrich (Saint Louis, MO, USA). Acros Organics (Geel, Belgium) supplied sodium sulphate, sodium hydroxide, acetic acid, boric acid and orthophosphoric acid. Potassium chloride was acquired from J.T. Baker (Phillipsburg, NJ, USA). The standard solutions of sodium diethyldithiocarbamate were prepared daily just through solubilisation of the reagent in ultrapure water. All the aqueous solutions used here were prepared using ultrapure water (18.2 MΩ.cm) provided by a Milli-Q Plus instrument (Millipore, St. Charles, MO, USA).

Fabrication of the silver solid amalgam electrode
The procedure for construction of the silver nanoparticles solid amalgam electrode (AgNP-SAE) was described elsewhere [38]. Briefly, the silver nanopowder was packed inside a glass tube (4 mm internal diameter) and posteriorly a platinum wire was inserted through the silver nanopowder to provide the electrical contact. Subsequently, the glass tube was immersed in an eppendorf tube containing liquid mercury and kept for the period of three days. This step is necessary in order to form the solid silver amalgam. Afterwards, the electrode was withdrawn from the liquid mercury and kept to rest for three days. During this stage the electrode achieves completely the state of solid amalgam. Finally, the AgNP-SAE obtained was manually polished using soft emery paper and alumina powder (0.05 and 1 µm particle sizes).
The electrode was activated through the application of the potential of -2.2 V for a period of 300 s in 0.2 mol L -1 KCl solution under continuous stirring. This activation procedure, as well as the polishing step, was repeated once per week or when some significant loss of response was observed for the electrode [39]. Quicker and most frequent activation process was carried out by the application of the potential of -2.2 V for 60 s in the electrochemical cell containing the same electrolyte such as used for the voltammetric measurements. This quicker activation procedure was performed after each series of measurements, before starting the work and after pauses longer than one hour. It is useful to remove oxides, reactants and other products that might be adsorbed on the surface of the electrode. Furthermore, it improves the electrochemical performance of solid amalgam electrodes and decreases the charge-transfer resistance [40]. Figure S1A in Supplementary Material shows one picture of the AgNP-SAE fabricated.

Instrumental setup
The electrochemical experiments were carried out in a potentiostat/galvanostat Autolab model PGSTAT 128N (Eco Chemie, Utrecht, The Netherlands) connected to a computer and managed by General Purpose Electrochemical System (GPES) 4.9 software. The electrochemical cell utilised here consisted of a three-electrode setup: the AgNP-SAE (geometric area: 0.13 cm 2 ) was used as working electrode, an Ag/AgCl electrode (filled with 3 mol L -1 KCl) was used as reference electrode and a platinum wire was employed as auxiliary electrode. Figure S1B in Supplementary Material exhibits one picture of the electrochemical cell used for the experiments.

Voltammetric experiments
The voltammetric measurements were performed in an electrochemical cell containing 10 ml of Britton-Robinson (BR) buffer. The electrolyte was prepared by the mixture of solutions of acetic acid, boric acid and phosphoric acid in order to achieve the final concentration of 0.02 mol L -1 each. The pH of this buffer solution was regulated between 4.0 and 8.0 using 0.2 mol L -1 NaOH solution. Before starting each series of measurements, the electrochemical cell was deoxygenated using pure nitrogen gas for ca. 10 minutes. All the error data presented throughout the manuscript represent standard deviations.

Sample preparation
The river water samples were collected at Anhanduí river (Campo Grande, MS, Brazil) and Dourados river (Dourados, MS, Brazil). Amounts of Na-DDC were directly solubilised in the river waters at three levels of concentration each. The spiked samples were stored at the refrigerator for 30 days before the measurements aiming to evaluate the stability of the analyte in the sample. Prior to the voltammetric analyses, the samples were diluted in 0.2 mol L -1 BR buffer (pH = 5.5) at 9:1 ratio aiming to achieve the final buffer concentration of 0.02 mol L -1 . These diluted samples were then filtered through 0.22-µm membranes. No other pretreatment step was performed. The diluted and filtered spiked samples were used in the electrochemical cell for the determinations carried out using standard addition method.

Morphological analysis
The morphology of the AgNP-SAE was investigated through scanning electron microscopy (SEM) technique. The images were recorded using a Superscan SSX-550 instrument (Shimadzu, Kyoto, Japan).

Surface structure of the AgNP-SAE
The surface of the AgNP-SAE was investigated through SEM technique and the images obtained are shown in Figure 2. The structure obtained was rough and irregular, similar to that previously reported for solid amalgam electrodes fabricated with silver nanoparticles [38]. As can be observed in Figure 2(A), the AgNP-SAE presented a very defective morphology, which may result in large electroactive areas. Furthermore, the metallic composition of the solid amalgam electrode may provide high electrical conductivity. These features might improve the electrochemical sensing of the electrode. Additionally, the SEM image presented in Figure 2(B) shows round and bright points that can be attributed to the presence of the silver nanoparticles in the electrode structure. The diameter of these nanoparticles was measured to be ca. 90 nm, which is in accordance with the size of the silver particles employed for the fabrication of the electrode.

Electrochemical behaviour of Na-DDC
The advantages of the use of solid amalgam electrodes fabricated with silver nanoparticles in comparison with conventional silver solid amalgam electrodes were already discussed in a previous work [38]. This way, the AgNP-SAE was employed for all the experiments carried out here. Firstly, the buffer composition was evaluated in order to choose the best supporting electrolyte for the electrochemical experiments. The buffer has direct influence over analyte stability and adsorption processes [41]. Sodium sulphate solution, BR buffer, phosphate buffer and acetate buffer (all at the previously optimised pH value of 5.5) were employed as electrolytes during the cyclic voltammetry (CV) measurements involving Na-DDC. Among these solutions, BR buffer provided the best voltammetric results for Na-DDC in terms of analytical signal and peak resolution. The optimum concentration for BR buffer was determined to be 0.02 mol L -1 and this composition was used for all the electrochemical studies. Figure S2 in Supplementary Material displays some data related to this study.
The investigation of the electrochemical behaviour of Na-DDC was carried out using CV technique in the optimised electrolyte composed of 0.02 mol L -1 BR buffer solution. Figure 3(A) shows cyclic voltammograms recorded for Na-DDC using the AgNP-SAE. It can be observed that the substance presents two voltammetric signals over a welldefined profile. The cathodic peak was found at E p = -0.55 V and the anodic peak was found at E p = -0.49 V. The separation between these two voltammetric peaks (ΔE p ) was ca. 71 mV.
The influence of the scan rate on the electrochemical behaviour of Na-DDC was investigated in the range from 0.05 to 0.40 V s -1 . Both the cathodic and anodic peak currents presented linear relationship with the scan rate (υ) such as depicted in Figure 3 (B), which suggests that the redox reaction of Na-DDC over the surface of the AgNP-SAE is adsorption-controlled. The plots showed the equations I p /µA = -(0.15 ± 0.01) + (8.85 ± 0.38) × υ/V s -1 with correlation coefficient (R) of 0.994 for the anodic peak and I p /µA = -(0.39 ± 0.05) -(36.64 ± 1.11) × υ/V s -1 with R of -0.990 for the cathodic peak. Additionally, the relationship between the logarithm of the peak currents and the logarithm of the scan rate also was evaluated in order to confirm the mass transport mode of the reaction of Na-DDC over the AgNP-SAE. According to that depicted in Figure S3A in Supplementary Material, both plots presented linear dependence. The equations calculated were log (I p /µA) = (0.91 ± 0.02) + (0.97 ± 0.03) × log (υ/V s -1 ) (R value of 0.997) for the anodic peak and log (I p /µA) = (1.52 ± 0.03) + (0.89 ± 0.06) × log (υ/ V s -1 ) (R of 0.991) for the cathodic peak. The slopes of these curves (0.97 and 0.89) were very close to the theoretical value of 1.0 which is attributed for adsorption-controlled processes. It confirms that the reduction and oxidation of Na-DDC over the AgNP-SAE are mainly controlled by adsorption [42].
The effect of the scan rate on the peak potentials of Na-DDC was investigated through the plot of E p versus the logarithm of scan rate, which is presented in Figure  S3B in Supplementary Material. Both the cathodic and anodic peaks presented slight shift on the values of E p with the increase of the scan rate. The graphs provided linear relationship and the equations obtained were E p /V = -(0.484 ± 0.002) -(0.048 ± 0.001) × log (υ/V s -1 ) (R of -0.991) for the anodic peak and E p /V = -(0.589 ± 0.001) -(0.068 ± 0.002) × log (υ/V s -1 ) (R value of -0.996) for the cathodic peak. Furthermore, the ratio obtained between the anodic and cathodic peak currents (I pa /I pc ) was ca. 0.2. These data suggest that the electrochemical reaction of Na-DDC over the AgNP-SAE might be categorised as a quasi-reversible process [43,44].
According to Laviron theory [45], for non-reversible electrochemical processes in that the peak potentials depends of the scan rate, the slopes of the plots of E p versus the logarithm of scan rate are equal to -2.3RT/αηF for the cathodic peak and -2.3RT/(1 -α) ηF for the anodic peak, where R is the gas constant (8.314 J K -1 mol -1 ), T is the temperature (298 K), α is the transfer coefficient, η is the number of electrons and F is the Faraday constant (96,485 C mol -1 ) . From these relationships and assuming that α is near to 0.5 for non-reversible processes [43], the number of electrons involved in the reduction and oxidation of Na-DDC were calculated to be, respectively, ca. 1.74 and 2.35 (assumed to be 2 for both reactions).

Investigation of pH influence
The analytical studies involving Na-DDC, as well as the optimisation of the experimental parameters, were performed using square-wave adsorptive stripping voltammetry (SWAdSV) regarding the cathodic peak, since it provided higher current intensity in comparison with the anodic peak. Figure 4(A) shows one SWAdS voltammogram of Na-DDC recorded in the cathodic direction in which a well-defined voltammetric profile can be observed with one reduction peak at E p = -0.56 V.  The pH may affect the electrochemical reaction and the peak current heights during the redox processes. Thus, the investigation and optimisation of the pH of the buffer is extremely important aiming to elucidate the redox mechanism and achieve the best analytical conditions. The study of the effect of the pH in the voltammetric response of Na-DDC was carried out in the range from 4.0 to 8.0. It was observed that the variation of the pH affects directly the cathodic peak currents of Na-DDC, such as showed in Figure 4(B). The maximum voltammetric response for Na-DDC was obtained at the pH = 5.5, which was adopted as the optimum value for the experiments. Some SWAdS voltammograms of Na-DDC recorded at cathodic direction in different values of pH are presented in Figure S4 in Supplementary Material.
In parallel, the influence of the pH on the peak potentials of Na-DDC also was evaluated. According to that observed in Figure 4(B), both the anodic and cathodic peak potentials were linearly displaced to more negative values with pH increase, which indicates the participation of protons in the electrochemical reaction of Na-DDC [44,46] The slopes obtained from these curves (64 mV/pH and 55 mV/pH) suggest that the same number of protons and electrons are involved during the electrochemical oxidation and reduction of Na-DDC, since these values practically coincide with the theoretical value of 59 mV/pH derived from Nernst equation [44,47,48].
The catalytic reduction of compounds containing sulphur atoms at mercury-based electrodes is commonly related in the literature [30]. The reduction of Na-DDC may be attributed to the cleavage of the bond involving one of the sulphur atoms of the molecule after a protonation step in acid media. It generates the cathodic signal observed. Therefore, the intermediate formed on the reduction step reacts with the mercury of the electrode and provides an oxidation peak. Based on this, Figure 5 illustrates the mechanism proposed for the reduction/oxidation of Na-DDC.

Optimisation of the SWAdSV parameters
The experimental parameters regarding the voltammetric method were evaluated and optimised aiming to achieve the maximum electrochemical response for the reduction of Na-DDC over the surface of the AgNP-SAE. The parameters investigated were the accumulation potential (E acc ), accumulation time (t acc ), frequency of the pulses (f), amplitude of the pulses (a) and scan increment (ΔE s ).
The influence of the accumulation potential on the cathodic peak currents of Na-DDC was evaluated in the range from -0.10 to -0.45 V. It can be observed in Figure S5A in Supplementary Material that the peak current depends on the accumulation potential and the maximum voltammetric response was obtained when values of E acc near to -0.4 V were used. Thus, this was defined as the optimum value for this parameter. The accumulation time was investigated from 20 to 120 s and the complete saturation of the electrode surface for the concentration range evaluated (ca. 5 × 10 -6 mol L -1 ) was achieved with t acc = 60 s, such as presented in Figure S5B in Supplementary Material.
The effect of the frequency was investigated from 10 Hz to 90 Hz. Figure S6A in Supplementary Material presents the plot of peak current versus the square root of frequency, where a non-linear behaviour was observed. It is typical for quasi-reversible reactions [49]. The value of 40 Hz was adopted as optimum since it afforded satisfactory intensity on the analytical signal and good peak resolution.
The relationship between the cathodic peak current and the scan increment was studied in the range from 1 to 16 mV. The best response in terms of current intensity and peak resolution was observed when the value of 3 mV was used. Higher values of ΔE s led to peak broadening and loss of resolution. The plot of I p versus ΔE s is displayed in Figure S6B in Supplementary Material.
The pulse amplitude was investigated from 10 to 70 mV. The peak currents increased with the increase of a such as showed in Figure S6C in Supplementary Material. When values of a higher than 60 mV were used, a displacement to more negative values of the half-peak potentials (E p/2 ) was observed. This behaviour suggests loss of sensitivity of the method [49]. The value of 55 mV was defined as optimum since it provided good signal/noise ratio.

Repeatability and reproducibility studies
The stability of the voltammetric response of Na-DDC over the surface of the AgNP-SAE was investigated. Twenty consecutive voltammograms were recorded in the optimised buffer solution containing 2.23 × 10 -6 mol L -1 Na-DDC using the same electrode. The relative standard deviation (RSD) obtained for this series of measurements was ca. 4.2%. The reproducibility was evaluated through recording voltammograms in the same solution using three different silver nanoparticles solid amalgam electrodes. For this series of measurements the RSD calculated was ca. 5.9%. These data suggests satisfactory stability of the electrode and no passivation effects.

Determination of the linear range and limit of detection
The dependence of the analytical signal on the concentration of Na-DDC was evaluated through the construction of an analytical curve. Figure 6 exhibits SWAdS voltammograms of Na-DDC recorded in different concentrations and the plot of I p versus the concentration. Linear relationship was obtained in the range from 2.83 × 10 -7 mol L -1 to 6.89 × 10 -6 mol L -1 . The calibration curve provided the equation I p /µA = (0.935 ± 0.146) -(6.03 ± 0.16) × [Na-DDC]/10 -6 mol L -1 with R of -0.993 (for n = 3), which indicates good correlation between the data. The values for the limits of detection (LOD) and quantification (LOQ) were determined through the relationships 3SD a /b and 10SD a /b, respectively, where SD a is the standard deviation of the intercept of the calibration curve and b is the slope of the same curve [50]. Using this method, the LOD and LOQ values were calculated to be 7.26 × 10 -8 mol L -1 and 2.42 × 10 -7 mol L -1 , respectively.
The performance of the AgNP-SAE regarding the electrochemical determination of Na-DDC was compared with previously published reports. To the best of our knowledge, there is only one single work in literature that also describes the voltammetric determination of Na-DDC [37]. In comparison with this unique work, the AgNP-SAE used here provided significative higher sensitivity (6.03 µA/µM versus 0.01 µA/µM) and lower LOD (7.26 × 10 -8 mol L -1 versus 4 × 10 -6 mol L -1 ). Moreover, the use of the AgNP-SAE allowed the determination of Na-DDC through its electrochemical reduction, which was firstly demonstrated here. No other reports regarding the electrochemical detection of Na-DDC could be found for comparison.

Determination of Na-DDC in river water
Due to the high solubility of Na-DDC in water (ca. 100 g/L) [51], the feasibility of the developed method was investigated through the quantification of Na-DDC in river water samples. Preliminary analysis carried out did not show contamination at detectable levels. This way, the samples were spiked with known amounts of Na-DDC standard in order to allow the analysis. The quantitative assays were performed in triplicate using standard addition method, aiming to evaluate the precision of the measurements and avoid matrix effects. The river water samples were spiked with Na-DDC in three different levels of concentration and the results achieved during the analyses are depicted in Table 1. The recovery values obtained presented satisfactory concordance with the spiking values. It indicates good accuracy and makes the method here developed an interesting option for the quantification of Na-DDC in environmental samples.

Selectivity study
The possible interference of species that may be present in natural waters was investigated in order to evaluate the selectivity of the voltammetric method developed. For this purpose, the determination of Na-DDC was carried out in the presence of some possible interferers. Inorganic ions (K + , Na + , NH 4 + , Ca 2+ , Mg 2+ , Fe 2+ , Cu 2+ , OH -, F -, Cl -, SO 4 -2 and PO 4 -2 ), commonly used pesticides (molinate, terbutryn, atrazine, trifluralin, linuron and endosulfan) and carbamate/dithiocarbamate compounds (thiram, thiodicarb, ziram, methiocarb and carbaryl) were individually added to the river water sample and Na-DDC was quantified in their presence. The ratios between Na-DDC/interfering were 1:1 and 1:100. From all the interferers evaluated, thiodicarb was the unique substance that presented one voltammetric signal at same peak potential of Na-DDC and did not allow the analysis. The presence of the other selected compounds brought on variations of ca. 7.2% on the results of the analyses in comparison with the expected value. These data suggest that Na-DDC can be determined with satisfactory selectivity even in the presence of these substances, with exception of thiodicarb, without meaningful levels of interference. Table S1 in Supplementary Material exhibits the results achieved on the determinations of Na-DDC carried out in the presence of the selected substances.

Conclusions
The electrochemical behaviour of sodium diethyldithiocarbamate was investigated here, for the first time, using solid amalgam electrode fabricated with silver nanoparticles. This electrode was also employed for the development of a voltammetric method aiming the electroanalytical determination of the substance. The electrochemical reaction of Na-DDC over the amalgam electrode was defined as quasi-reversible and an electrochemical mechanism for this process was proposed. The quantitative studies were carried out using square-wave adsorptive stripping voltammetry in the cathodic direction, since the cathodic peak presented higher intensity when compared to the anodic peak. The experimental and instrumental parameters were investigated and optimised in order to obtain the maximum voltammetric response of Na-DDC.
The analytical performance of the method developed was satisfactory since it provided good sensitivity, reproducibility and accuracy when employed for the determination of Na-DDC in river water samples. Furthermore, the method also presented good selectivity since that with exception of thiodicarb, no interferences of the species added to the sample were observed.
The AgNP-SAE used here presents itself as a very interesting alternative to the HDME for the voltammetric analysis of reducible compounds. It agrees with the concept of green chemistry, since the use of this electrode decreases the environmental contamination once there is no mercury discard throughout the voltammetric measurements. Moreover, the surface of the AgNP-SAE may be easily renewed only through electrochemical treatment, which easily provides a new, clean and reproducible surface. Based on this and according to the data reported here, the AgNP-SAE may be pointed as a promising tool for the detection of target reducible analytes.