# Development of a Photolithographed Ultramicroelectrode Array for Sampled Current Voltammetry: Application to Diclofenac as an Electrode-Passivating Analyte

Teodora Lupoi, Jean Schoch, Sara Bretin, Gaël Levanen, Ioana Runcan, Trung Nghia Nguyên Lê, Philippe Hapiot, Yann R. Leroux, Bogdan Feier, Cecilia Cristea, et al.

► To cite this version:

Teodora Lupoi, Jean Schoch, Sara Bretin, Gaël Levanen, Ioana Runcan, et al. Development of a Photolithographed Ultramicroelectrode Array for Sampled Current Voltammetry: Application to Diclofenac as an Electrode-Passivating Analyte. ACS Electrochemistry, 2025, 10.1021/acselec-trochem.5c00340. http://dx.doi.org/10.1021/acselec-trochem.5c00340

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# Development of a Photolithographed Ultramicroelectrode Array for Sampled Current

## Voltammetry: Application to Diclofenac as an Electrode-Passivating Analyte

Teodora Lupoi<fnref n="1" />,<fnref n="2" />, Jean Schoch<fnref n="1" />,<fnref n="3" />, Sara Bretin<fnref n="3" />, Gaël Levanen<fnref n="1" />,<fnref n="3" />, Ioana Runcan<fnref n="1" />,<fnref n="2" />, Trung Nghia Nguyen Le<fnref n="1" />, Philippe Hapiot<fnref n="1" />, Yann R. Leroux<fnref n="1" />, Bogdan Feier<fnref n="2" />, Cecilia Cristea<fnref n="2" />, Florence Razan<fnref n="3" />* and Florence Geneste<fnref n="1" />*

## ABSTRACT

Sampled-Current Voltammetry (SCV) is a particularly interesting analytical method. It represents a valuable alternative to linear sweep voltammetry (LSV) using a rotating disk electrode, which is commonly employed for evaluating the electrocatalytic activity of materials. The method involved applying a different potential to each electrode in the array, thereby renewing both the solution and the electrode surface throughout the analysis. This electrochemical analysis concept, referred to as Electrode Array for Sampled-Current Voltammetry (EASCV), was applied to the analysis of compounds that poison the electrode surface, such as phenol derivatives. Although this method provided higher sensitivity compared to LSV, a high signal-to-noise ratio resulted in similar limits of detection (LOD). In this work, we report the fabrication of arrays composed of several ultramicroelectrodes using photolithography. A life cycle assessment was conducted to quantify the environmental impacts associated with the array manufacturing. The arrays were characterized by Scanning Electron Microscopy (SEM), Scanning Electrochemical Microscopy (SECM), and cyclic voltammetry (CV). Using potassium ferrocyanide as a model compound, we demonstrated the advantages of UME arrays in reducing the signal-to-noise ratio and achieving LODs as low as 3 µM, ten times lower than those obtained with a macroelectrode, while maintaining higher sensitivities than

<footnote n="1">¹Univ Rennes, CNRS, ISCR, UMR 6226, F-35000 Rennes, France</footnote>

<footnote n="2">²“Iuliu Hatieganu” University of Medicine and Pharmacy, Faculty of Pharmacy, Department of Analytical Chemistry, 400349, Cluj-Napoca, Romania</footnote>

<footnote n="3">³Univ Rennes, ENS Rennes, CNRS, IETR - UMR 6164 F-35000 Rennes, France.</footnote>
those achieved with conventional LSV analysis. The method was also successfully applied to
the analysis of diclofenac, known to poison the electrode surface during oxidative analysis with
performance comparable to that of ferrocyanide.

Keywords: ultramicroelectrode array, electrode fouling, sampled current voltammetry, photolithography, diclofenac

INTRODUCTION

Sampled-current voltammetry (SCV) or also referred to as Sampled-transient voltammetry (STV) is an electrochemical method that is at the origin of pulsed analytical techniques such as normal pulse voltammetry (NPV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV).¹ It consists of applying a first potential at which no faradaic process occurs, followed by a second potential to oxidize or reduce a compound. The second potential is incrementally varied, resulting in a series of chronoamperograms. For each applied potential, the current is measured at a defined sampling time, allowing the construction of a current-potential sigmoid curve. The main advantage of these pulse techniques is the rapid exponential decay of the capacitive current after applying a potential, whereas the faradaic current decreases proportionally to t<sup>-1/2</sup>. SCV differs from NPV in that the solution and electrode surface are renewed between each experiment, and the sampling time can be selected differently for each potential based on the objective of the study. Although potential ramp methods such as linear sweep voltammetry (LSV) and cyclic voltammetry (CV) are efficient and widely used analytical techniques, SCV has shown particular advantages for certain applications. For example, SCV has been demonstrated to be a good alternative to steady-state voltammetry using a rotating disk electrode or an ultramicroelectrode when the electrode material is difficult to shape for these methods, such as conductive films formed on an insulator.² Furthermore, although LSV and CV have been widely used to determine the activity of electrocatalysts, for
example in water splitting, these techniques are transient, leading to an enhancement of the current density compared to electrolysis performed via chronoamperometry, mainly due to double-layer charging. Anantharaj et al. observed that the electrocatalytic activity measured with SCV was closer to that obtained in chronoamperometry experiments, allowing for a more accurate comparison of electrode materials in electrocatalysis.³ It is now commonly used to evaluate the electrocatalytic activity of materials.⁴⁻⁷ The technique has also been adapted for species that adsorb onto the electrode surface during analysis.⁸ However, using one electrode requires consistent and reproducible stirring, as well as electrochemical conditioning of the electrode before each applied potential.

We previously demonstrated the combination of SCV with an electrode array to mimic the behaviour of polarography using a dropping mercury electrode.⁹, ¹⁰ The method involves applying a different potential to each electrode in the array, resulting in SCV with the renewal of the solution and electrode surface throughout the analysis. We showed that with this concept based on Electrodes Array for Sampled-Current Voltammetry (EASCV) combined with a careful selection of the sampling time, the method could be applied to the analysis of compounds that block the electrode during their analysis.¹¹ We demonstrated with phenol, whose oxidation led to oligomer adsorption on the electrode surface, that a sampling time of 0.02 s, compatible with the response time of usual commercially available potentiostats, was sufficient to prevent the attenuation of the electrochemical signal due to electrode fouling. We also demonstrated that the method can be combined with a preconcentration step, such as the electrodeposition of Pb²⁺, leading to a sensitivity up to 300 times higher than that of LSV when a short sampling time was used.¹² However, at a short sampling time, the residual current remained high, resulting in a limit of detection for Pb²⁺ analysis comparable to that obtained with LSV.
To improve the electroanalytical method by minimizing the capacitive current, ultramicroelectrodes (UME) could be used instead of macroelectrodes. At short sampling times, the linear diffusion occurs and the current response follows Cottrell's law. However, on a UME, the capacitive current decreases more rapidly than on a macroelectrode because of the lower value of the time constant, and the double-layer charging current approaches zero within a few microseconds.¹³, ¹⁴ For longer sampling times, the diffusion is radial and the faradaic current stabilizes, becoming independent of time.¹ To achieve higher current responses, UME arrays (UMEA) were employed. A reduction in the signal-to-noise ratio can be obtained either when the UMEs operate independently or when their diffusion layers fully overlap.¹⁵

The challenge of efficiently using EASCV analysis lies in the production of UME arrays with highly reproducible surfaces. Microfabrication techniques have garnered significant interest for high-precision fabrication of gold UMEs and have been employed in various electrochemical applications.¹⁶⁻¹⁹ We previously fabricated 500 µm-diameter gold macroelectrodes using photolithography.¹¹ The contacts were successfully protected with a silicon nitride surface, enabling the array to be used in both aqueous and organic solvents.

The unique properties of UME arrays led us to evaluate the EASCV method on an array in which each electrode is a UME array. In this study, we report the microfabrication and characterization of a wafer containing 20 identical UME arrays with electrode diameters of 50 and 20 µm. Scanning Electrochemical Microscopy (SECM) was performed to confirm the insulating properties of the nitride layer and to validate the successful removal of this layer to expose the gold surfaces, a key step in the fabrication process. EASCV measurements were conducted on the array using a standard laboratory potentiostat. Various sampling times were assessed, and their impact on the potassium ferrocyanide response, a well-established redox probe, was compared. The results clearly demonstrate a significant improvement in the limit of detection for the UME arrays. The comparison with conventional LSV analysis highlighted the
advantage of the EASCV method in enhancing the sensitivity. The analytical technique was
then applied to a model compound, diclofenac, a widely used anti-inflammatory drug whose
detection has been extensively investigated in pharmaceutical formulations, biological fluids,
and environmental water samples.²⁰⁻²³ The detection of diclofenac by EASCV is a particularly
relevant example, as its oxidation generates phenolic by-products that contribute to electrode
fouling.²⁴

MATERIALS AND METHODS

**Reagents.** KCl, NaCl, KH₂PO₄, Na₂HPO₄, HCl, H₂SO₄, K₄[Fe(CN)₆], diclofenac sodium salt and acetone were purchased from Sigma-Aldrich. All the reagents had analytical purity and were used without further purification. All solutions were prepared in ultrapure water (12.2 MΩ, Millipore Simplicity)

**Electrochemical analyses.** Cyclic voltammetry experiments were performed in a homemade electrochemical cell (Figure 1b), using an external saturated Ag/AgCl reference electrode and a platinum wire counter electrode. Electrochemical impedance spectroscopy (EIS) measurements were conducted on an Origalys potentiostat with an impedance module in a 0.1 M KCl solution. The frequency was scanned from 1 MHz to 1 Hz at an imposed potential of 100 mV vs Ag/AgCl reference electrode, a wave amplitude of 10 mV, and a delay before integration of 0.1 s. The minimum acquisition time of the potentiostat was 10⁻⁴ s/pt.

For SECM analysis, a Model 920D Scanning Electrochemical Microscope (C.H. Instruments Austin TX) was used, equipped with an adjustable stage for the tilt angle correction. A typical three-electrode system was used in all electrochemical measurements, using a commercially available Pt UME (IJ Cambria Scientific) with a 5.89 µm radius and an RG of 10.3, an Ag/AgCl reference, and a platinum counter electrode. All measurements were conducted with an aqueous
solution of 5 mM K₄[Fe(CN)₆] and 0.1 M KCl as supporting electrolyte at room temperature.

For the analysis of the micro-electrode arrays, the surfaces were characterized by SECM in feedback mode. Positive feedback was observed on the gold electrodes, while negative feedback was observed on the insulating layer. The sample was scanned by SECM at a fixed height of 1.4 µm, positioned sufficiently high to prevent any damage to the surface. Maps were processed using the open-source Gwyddion software.²⁵ The analytical performance of the EASCV method was evaluated through the sensitivity (the slope of the calibration curve) and the limit of detection (LOD). Experimental SCV curves were fitted with sigmoid functions of the form y = A1 + (A2 - A1) / (1 + 10^(LOGx0-x)k) to determine A2, the plateau of the sigmoid corresponding to the maximum value.¹¹ The LOD was determined from St - Sb ≥ 3σ, where St is the signal given by the analyte at LOD, Sb is the average of five field blanks, and σ is the variability of five blank measurements.

**COMSOL simulations.** A 3D ultramicroelectrode array model was built using finite element modeling with COMSOL Multiphysics v6.3. The Tertiary Current Distribution module was used. The model included three domains: electrode, insulator and electrolyte. The 3D model was used to simulate CV curves as well as diffusion profiles in chronoamperometry. The electrolyte domain was modeled as a hemisphere with a radius of 500 µm, representing the actual size of a working electrode. The electrodes were modeled as slightly recessed wells with 0.6 µm depth and following a hexagonal array to optimize the spacing between the electrodes and their position relative to the wafer edges (Figure 1). The electrolyte domain was meshed using free tetrahedral elements. The mesh was finer in the regions near the electrode surface, with a minimum element size equal to the electrode radius divided by 100 to ensure convergence.
The simulations were carried out for a reversible redox reaction involving the exchange of a single electron with Butler-Volmer kinetics:

$$Ox + e^{-} \rightleftharpoons Red$$

Only reduced species were initially in solution with a bulk concentration of 1 mM. The forward and reverse reaction rate constants were given by equations 1 and 2:

$$k_f = k_0 \exp\left(\frac{-\alpha F}{RT}(E - E^\circ)\right) \qquad (1)$$

$$k_b = k_0 \exp\left(\frac{(1-\alpha)F}{RT}(E - E^\circ)\right) \qquad (2)$$

Where $k_0$ is the standard heterogeneous rate constant taken as $10^{-2}$ m s$^{-1}$, $E^\circ$ is the standard potential of the ferricyanide/ferrocyanide redox couple, set at 0.225 V, allowing the superposition of theoretical and experimental CV curves,²⁶ E is the potential applied to the electrode, $\alpha$ is the effective transfer coefficient, assumed to be 0.5, F is the Faraday constant and R is the universal gas constant. The temperature, T, was fixed at 293 K.

The simulation focuses only on diffusive transport, which is why convection and migration were neglected. Mass transport was modeled by solving Fick's second law of diffusion (equation 3):

$$\frac{\partial C}{\partial t} = D \left( \frac{\partial^2 C}{\partial x^2} + \frac{\partial^2 C}{\partial y^2} + \frac{\partial^2 C}{\partial z^2} \right) \qquad (3)$$

Where D is the diffusion coefficient, taken as $6.5 \times 10^{-10}$ m$^2$s$^{-1}$ for both Ox and Red species.²⁶

Since the electrodes are slightly recessed within the insulator, we used the expression of the steady-state current of a recessed microelectrode, as given by equation 4:²⁶

$$I = \frac{4nF_c C_0 D r}{\frac{4L}{\pi r} + 1} \qquad (4)$$
Where *n* is the number of transferred electrons, *C*₀ is the bulk concentration, *r* is the radius of the electrode, and *L* is the value of the recess height. This equation allows the calculation of an effective diffusion coefficient, which can then be incorporated into the integration of the molecular flux (further details are provided in the Supporting Information).

**UMEA manufacturing.** The analytical platform consists of an array of 20 working electrodes, a reference electrode, and a counter electrode (Figure 1).¹¹ Three types of arrays were developed, where each electrode consists of either a single macroelectrode (500 µm in diameter), 7 UMEs (50 µm each), or 19 UMEs (20 µm each). The photolithographic fabrication process of these analytical platforms was carried out in a cleanroom environment. The borosilicate substrate, 50 mm in diameter and 0.7 mm thick, was cleaned using acetone, isopropanol, ethanol (Technic France). The substrate was then subjected to air plasma treatment (Harrick® Plasma Cleaner) to remove surface impurities and improve the adhesion of the metallic layers. A layer of titanium (30 nm), followed by a layer of gold (200 nm), was deposited by thermal evaporation under high vacuum using a Plassys® ME300 system. The electrode array was defined photolithographically using S1818 positive photoresist (Shipley), applied by spin coating. The photoresist was exposed to UV light (photolithography) through a patterned mask to define the electrode array. The substrate was then immersed in a Microposit MF-319 developer solution, which dissolved the exposed regions of the photoresist. Excess metal was chemically etched using titanium and gold etchants (Transene Company). The remaining photoresist was removed by immersing the substrate in Microposit Remover 1165. A 600 nm-thick insulating layer of silicon nitride was then deposited using Plasma-Enhanced Chemical Vapor Deposition (PECVD). The thickness of the Si₃N₄ layer was measured by profilometry (KLA-Tencor® alpha-step IQ). Finally, the macro and ultramicroelectrodes were formed by selectively removing the insulating layer via Reactive Ion Etching (RIE).
**Life cycle assessment.** Life cycle assessment followed ISO 14040<sup>27</sup> and ISO 14044<sup>28</sup> standards and used the Ecoinvent 3.9.1 database. Environmental impact assessments were performed using the Brightway2 software. The functional unit for this analysis was defined as: manufacture an UME array by photolithography. This simplified functional unit, limited to the manufacturing stage, allowed for comparison with the production of other UME arrays. Environmental impacts were characterized using the recommended Product Environmental Footprint (PEF) method,<sup>29</sup> specifically EF 3.1 no LT (Table 1).

<table><caption>**Table 1.** EF 3.1 No Lt impact categories, abbreviations and units.</caption><thead><tr><th>Impact category</th><th>Abbreviation</th><th>Unit</th></tr></thead><tbody><tr><td>Climate change</td><td>GWP</td><td>kg CO<sub>2</sub> eq</td></tr><tr><td>Ozone depletion</td><td>ODP</td><td>kg CFC-11 eq</td></tr><tr><td>Human toxicity, cancer</td><td>HT</td><td>CTUh</td></tr><tr><td>Human toxicity, non-cancer</td><td>HTNC</td><td>CTUh</td></tr><tr><td>Particulate matter</td><td>PM</td><td>Disease incidences</td></tr><tr><td>Ionizing radiation, human health</td><td>IR</td><td> kBq U<sup>235</sup> eq</td></tr><tr><td>Photochemical oxidant formation, human health</td><td>POF</td><td>kg NMVOC eq</td></tr><tr><td>Acidification</td><td>TAP</td><td>mol H<sup>+</sup> eq</td></tr><tr><td>Eutrophication, terrestrial</td><td>TE</td><td>mol N eq</td></tr><tr><td>Eutrophication, freshwater</td><td>FE</td><td>kg P eq</td></tr><tr><td>Eutrophication, marine</td><td>ME</td><td>kg N eq</td></tr><tr><td>Ecotoxicity, freshwater</td><td>FET</td><td>CTUe</td></tr><tr><td>Water use</td><td>WD</td><td>m<sup>3</sup> water eq</td></tr><tr><td>Material resources: metals/minerals</td><td>MRD</td><td>kg Sb eq</td></tr><tr><td>Energy resources: non-renewable</td><td>FD</td><td>MJ</td></tr><tr><td>Land use</td><td>LU</td><td>Dimensionless</td></tr></tbody></table>

The scope of the study included raw material extraction, material fabrication, transportation to the production laboratory, and final assembly processes (i.e., cradle-to-gate study). Both the use and end-of-life phases were excluded from this assessment. The use phase was not considered because electricity consumption was associated with commercial measurement devices, which
fall outside the scope of this study. Similarly, the end-of-life phase was not considered due to a
lack of data. All materials involved in the manufacturing process were considered except for
photolithographic masks, due to unavailable data. Transportation impacts were assessed based
on the geographical location of manufacturing sites provided by material suppliers through the
"market for" processes in Ecoinvent. Packaging weight was considered negligible and thus
excluded from the assessment. Electricity consumption during manufacturing was estimated
based on the power of the machines used and their operating time. The electricity consumption
of the cleanroom was excluded from the results because the contribution from the
manufacturing process was difficult to quantify and was distributed among multiple products
being fabricated simultaneously. The LCA focused on the manufacturing phase of the arrays
and excluded impacts associated with additional sensor components such as the potentiostat
and computer required for measurement operations.

RESULTS AND DISCUSSION

**Fabrication and characterization of the electrode array.** The electrode arrays were fabricated using microfabrication techniques, as previously reported.¹¹ The novelty of this process lies in the use of a dry-etching step with SF₆ plasma to open the insulating silicon nitride layer, enabling the fabrication of a macroelectrode with a 500 µm diameter and UME arrays containing 7 and 19 gold disks with diameters of 50 and 20 µm, respectively (Figure 1).
<figure><img src="image_2.png" /><figcaption>**Figure 1.** a) Image of the gold electrode array comprising 20 working electrodes, one reference electrode, and one counter electrode. b) The assembled electrochemical cell c) Design and SEM images of a single electrode from each 20-electrode array. The light green area represents the gold surface under the Si₃N₄ insulating layer, while the black area corresponds to the etched regions with diameters of 20, 50, and 500 µm (from top to bottom). The dark green represents the glass substrate.</figcaption></figure>

As the SF₆ reactive ion etching (RIE) process was a key step in fabricating the electrode arrays, exposing silicon nitride on parts of the gold to form electrodes of uniform size while leaving the rest of the gold covered (Figure 1c, left), we aimed to verify its effectiveness. As seen in the scanning electron microscopy (SEM) images (Figure 1c, right), the process resulted in electrode arrays with identical gold surfaces and well-defined edges. To assess the quality of Si₃N₄ insulation and the definition of the gold UMEs, the three arrays were analyzed by SECM (Figure 2a). Although some heterogeneity in current response and image gradients were observed, likely due to minor sample tilting and convection artifacts during scanning, well-insulated, electroactive macroelectrode and UMEs could be clearly identified. Moreover, probe approach curves showed a positive feedback response for the gold electrodes, while an identical negative feedback was recorded for the Si₃N₄ insulating layer, whether deposited on glass or gold surfaces. These results confirm the good insulating properties of the Si₃N₄ layer.
<figure><img src="image_3.png" /><figcaption>**Figure 2.** a) SECM mapping (left) of a working electrode containing gold disks with diameters of 500, 50, and 20 µm (from top to bottom) over a scanning area of 1000 × 1000 µm² for the 500 µm array and 500 × 500 µm² for the other two. Probe approach curves (right) at different sample positions, analyzing the Si₃N₄ layer deposited on glass and gold substrates, as well as the gold electrodes. b) Cyclic voltammograms of 1 mM K₄[Fe(CN)₆] in 0.1 M KCl recorded independently on each of the 20 working electrodes of the array, with gold surfaces of 500 µm (0.1 V·s⁻¹), 50 µm, and 20 µm (0.01 V·s⁻¹) in diameter, from left to right.</figcaption></figure>

The electrochemical characterization of the electrode arrays was first carried out using CV with 1 mM K₄[Fe(CN)₆] in 0.1 M KCl (Figure 2b). As expected, the shape of the curves exhibited
oxidation and reduction peaks for the macroelectrode, while the UME arrays displayed almost a plateau corresponding to the steady-state limiting current, due to the change in diffusion regime from linear to radial. The signal error among all 20 working electrodes, estimated from the peak or plateau currents of the voltammograms (Figure 2b), was 3.7%, 4.9%, and 1.3% for the 500, 50, and 20 µm-diameter electrode arrays, respectively, demonstrating good reproducibility of the 20 working electrodes for the three different arrays.

The limiting currents for each working electrode of the electrode arrays composed of 50 (× 7) and 20 (× 19) µm-diameter gold disks were estimated using equation 4 to be 43 nA and 44 nA, respectively. The value is consistent with the experimental results (Figure 2b) for the 50 µm array but not for the 20 µm array (approximately 25% lower). This may be due to a partial overlap of the diffusion layers of the UMEs, or to the thickness of the silicon nitride used as an insulating layer, which slows down diffusion.

To better assess the potential overlap of diffusion layers, COMSOL simulations were performed on the electrode arrays, modelling each UME as a microhole to account for the thickness of the $Si_3N_4$ insulating layer. A comparison between the simulated and experimental voltammograms (Figure 3) reveals a generally good agreement.

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>
**Figure 3.** Comparison of data simulated by COMSOL Multiphysics (red dotted lines) and experimental data (blue lines) for the array of a) 7-UME array (50 µm diameter) and b) 19-UME array (20 µm diameter) for 1 mM K₄[Fe(CN)₆] in 0.1 M KCl, scan rate 10 mV s⁻¹. The thickness of the recessed UMEs used in the simulation is 0.6 µm.

The simulation was then used to predict the overlap of the diffusion layers as a function of the UME sizes and their distance. In the absence of overlap, the sum of the voltammograms from *n* individual UMEs should match the total current measured from an array of *n* UMEs. According to the simulation (Figure 4), the reference and experimental voltammograms align for the 50 µm-diameter UME array when the spacing between UMEs is 15 times the radius. In all other cases, diffusion layer overlap was observed, leading to a decrease in current, although for arrays of 7 and 19 electrodes, with spacing ratios of 8 and 15, respectively, more than 90% of the reference signal was still achieved.
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 4.** COMSOL Multiphysics simulations showing cyclic voltammograms of 1 mM K₄[Fe(CN)₆] in 0.1 M KCl (0.01 V s⁻¹) on a) 50 and b) 20 µm-diameter electrode arrays. *d* is the distance between two electrodes and *r* is the radius of the UME. The reference (red dotted line) is the voltammograms obtained on a single UME multiplied by the number of electrodes in the array (7 and 19 for the 50 and 20 µm-diameter UME array, respectively).</figcaption></figure>

According to these results, the overlap of the diffusion layers under the experimental conditions used for the cyclic voltammetry analysis was lower than 10% for the 50 µm-diameter UME array (*d/r* = 8) but around 20% for the 20 µm-diameter array (*d/r* = 10).

Although the diffusion layers appeared to overlap in CV (Figure 4), COMSOL simulations showed that within the studied time range (≤ 90 ms), no overlap of the diffusion layers actually occurred in SCV (Figure 5). While such overlap could have improved the ratio of faradaic to residual current,¹⁵ it would also have reduced the faradaic current compared with radial
diffusion. Therefore, for this first study, a configuration without diffusion layer overlap was preferred.

<figure><img src="image_8.png" /><figcaption>**Figure 5.** Simulation of the diffusion layers of 1 mM K₄[Fe(CN)₆] in 0.1 M KCl on a) 50 µm and b) 20 µm-UME arrays (one working electrode) applying a potential of 400 mV for 120 ms.</figcaption></figure>

**Life cycle analysis (LCA).** LCA is increasingly used to quantify the environmental impacts of products. Many companies use it as part of an eco-design approach. It has even become mandatory in the building sector in France since 2020.³⁰ For this reason, an LCA was conducted to assess and take environmental considerations into account in the development of the 20 identical UME arrays. To simplify, it was exclusively focused on the manufacturing phase of the UME array. The LCA results are presented in Figure 6.
<figure><img src="image_9.png" /><figcaption>**Figure 6.** LCA results for UME arrays according to different manufacturing steps. The maximum and minimum impact values in each column are highlighted in red and green, respectively. All abbreviations are presented in Table 1.</figcaption></figure>

The analysis of manufacturing steps revealed that one of the production processes significantly contributed to the overall environmental impact. Indeed, the gold and titanium deposition steps were the most impactful across the 16 categories. On average, this step accounted for 49.7% of the total environmental impact. Then, the insulating layer deposition step accounted for an average of 28.6% across the 16 impact categories. The wafer cleaning and resin etching steps were the two least impactful stages on average across all impacts, contributing to 4.09% and 7.98%, respectively. The RIE step had generally the lowest impact across the 16 impact categories, although it represented the primary contribution to the ozone depletion category, primarily due to the use of gases such as trifluoromethane and carbon tetrafluoride, which are powerful greenhouse gases.
**Application of the electrode arrays to EASCV.** Initial experiments were conducted on the 500 µm-diameter electrode array, which served as a reference to evaluate the performance of the newly developed UME arrays. To obtain a current-potential curve using EASCV, chronoamperograms of 1 mM K₄[Fe(CN)₆] in 0.1 M KCl were recorded on the 20 electrodes. An initial potential of 0.05 V was applied to each electrode of the array, followed by pulses from 70 to 450 mV (Figure 7a). SCV analyses were carried out sequentially, with the electrode switched at each new pulse. Although the same array was reused several times after thorough washing in this first study to improve data accuracy, 20 electrodes (20 points) would have been sufficient to routinely construct the current-potential curve of an analyte.

<figure><img src="image_10.png" /><figcaption>**Figure 7.** a) Series of chronoamperograms obtained on 20 electrodes of a 500 µm-diameter electrode array, applying on each plot a potential step of 20 mV. b) Current-potential curve obtained by sampling the current at θ = 5 ms. The sigmoid curve corresponds to the fit of all data points.¹¹</figcaption></figure>

The current increases with the applied potential in the range of 170–350 mV, and then stabilizes upon reaching the steady-state region. The resulting shape of the chronoamperograms (Figure 7a) is consistent with that of a macroelectrode exhibiting linear diffusion, and follows Cottrell's law (Figure S1, equation 5):¹

$$i_d(t) = \frac{nFAC_0\sqrt{D}}{\sqrt{\pi t}} \qquad (5)$$
where $i_d$ is the diffusion-limited current (A), $n$ is the number of electrons, $F$ is the Faraday constant, $D$ is the diffusion coefficient ($6.5 \times 10^{-6} \text{ cm}^2 \cdot \text{s}^{-1}$ for $K_4[Fe(CN)_6]$ in 0.1 M KCl $^{26}$), $C_0$ is the bulk concentration (mol cm$^{-3}$) and $A$ is the electrode surface area (cm$^2$).

When the current was sampled at a specific time point $\theta$ and plotted as a function of the applied potential, a sigmoidal curve was obtained (Figure 7b). The plateau current was proportional to the ferrocyanide concentration, as previously demonstrated.⁹,¹¹ The choice of sampling time is critical, as shorter sampling times result in a higher slope for the straight-line calibration curve (current versus analyte concentration), thereby increasing the sensitivity of the analytical method. However, short sampling time also leads to high capacitive currents $i_c$ (equation 6), leading to higher values of limit of detection (LOD).

$$i_c = \frac{E}{R_s} e^{-\frac{t}{C_{dl}R_s}} \qquad (6)$$

where $i_c$ is the capacitive current (A), $C_{dl}$ is the double-layer capacitance (F), $R_s$ is the solution resistance ($\Omega$), $E$ is the potential (V).

For an optimizing the response of the network, different values of $\theta$ were tested, ranging from 3 to 90 ms (Figure 8).

<figure><img src="image_11.png" /></figure>
**Figure 8.** Current-potential curves obtained at different sampling times in a) 0.1 M KCl (blank) b) 0.1 mM K₄[Fe(CN)₆], c) 1 mM K₄[Fe(CN)₆]

As expected, the current increased as the sampling time decreased at both 0.1 mM and 1 mM concentrations. However, the current measured for the blank at short sampling times was unexpectedly high, approximately half the value recorded at 0.1 mM K₄[Fe(CN)₆].

Assuming $\theta = RsC_{dl}$, with Rs and C<sub>dl</sub> roughly estimated at 410 Ω and 73 µF cm<sup>-2</sup>, respectively<sup>31</sup> by EIS measurements (Figure S2), θ was calculated to be 0.06 ms. According to equation 6, the resulting capacitive current reaches approximately 1 mA at 400 mV. When the sampling time is increased tenfold (0.6 ms), the capacitive current drops to 0.04 µA, and becomes negligible at 3 ms (on the order of 10<sup>-25</sup> A). Therefore, the residual current observed in the blank (Figure 8a) cannot be attributed to capacitive effects, but is more likely due to oxidation processes occurring at the gold surface that creates sort of pseudo capacitive currents.<sup>31-34</sup>

For a more accurate comparison, calibration curves were plotted for various sampling times (Figure 9).

<figure><img src="image_12.png" /></figure>

**Figure 9.** a) Example of current-intensity curves ($\theta$ = 10 ms), and b) calibration curves in K₄[Fe(CN)₆] obtained by EASCV at different sampling times (3, 5, 10, 20, 60 and 90 ms) c) Average current ($I_{avg}$) and standard deviation of 5 blank determinations, slope and LOD for each value of $\theta$.
As previously reported,¹¹, ¹² the slope of the calibration curves increased with decreasing θ. Although the standard deviation calculated from five blank determinations was higher at shorter sampling times, the average blank current (I<sub>avg</sub>) remained low compared with the faradaic one (Figure 9, Figure S3), resulting in the lowest limit of detection (LOD).

A comparison with linear sweep voltammetry (LSV) performed at 0.01 V s<sup>-1</sup> (Table 2, Figure S3) highlighted the high sensitivity of the EASCV method, with a slope 28 times higher. Interestingly, while the blank showed values of the same order of magnitude at 90 ms in EASCV and in LSV (Figure 8a), the sensitivity (slope) was five times higher and the LOD twice as low, reaching up to 3 times lower under optimal conditions (with a sampling time of 3 ms).

<table><caption>**Table 2.** Results obtained by linear sweep voltammetry analysis on the 500 µm-diameter electrode and the 50 µm and 20 µm-diameter electrode arrays.</caption><thead><tr><td>Electrode</td><td>I<sub>avg</sub> ± σ (nA)</td><td>Slope (nA/mM)</td><td>LOD (× 10<sup>-5</sup> M)</td></tr></thead><tbody><tr><td>500 µm single</td><td>1.5 ± 0.5</td><td>166</td><td>7.22</td></tr><tr><td>50 µm electrode array</td><td>0.8 ± 0.2</td><td>41</td><td>0.55</td></tr><tr><td>20 µm electrode array</td><td>0.33 ± 0.04</td><td>35</td><td>0.35</td></tr></tbody></table>

The use of UMEs as working electrodes was subsequently explored as a means to reduce the residual current. In the case of arrays composed of 50 µm and 20 µm-UMEs, the shape of the chronoamperograms recorded at each working electrode corresponds to three distinct diffusion regimes, neglecting electrode recess for simplicity.¹ At short timescales and low current levels, the diffusion layer thickness 2(Dt)<sup>1/2</sup> is small compared to the radius of the UMEs, resulting in semi-infinite linear diffusion. Under these conditions, the current follows the Cottrell's equation (equation 5). This is followed by an intermediate regime, where the diffusion layer thickness becomes comparable to the UME radius and radial diffusion becomes more dominant. Considering the time needed for the diffusion layer thickness to reach the UME radius, this transition occurs at 240 ms and 38 ms for 50 µm and 20 µm-diameter electrode arrays, respectively. It should be noted, however, that for recessed electrodes, the planar diffusion
regime would be expected to persist for a slightly longer duration. At longer times, the diffusion layer thickness significantly exceeds the UME radius, leading to steady-state conditions dominated by radial (hemispherical) diffusion. In this case, the current reaches a plateau and is described by equation 4.

To take advantage of the low time constant of UMEs ($RsC_{dl}$) in the Cottrell region and compare the results with those obtained using a 500 µm-diameter macroelectrode, the diffusion layer would need to be approximately ten times lower than the UME radius. This corresponds to sampling times of 2.4 ms and 0.38 ms for the 50 µm and 20 µm-diameter UMEs, respectively. Since we chose in this work to use a standard laboratory potentiostat, whose response did not allow operation at such short timescales, we decided to perform measurements at longer times ($\ge$ 3 ms).

Background measurements, in the absence of a redox probe, for UME arrays with diameters of 20 µm and 50 µm are shown in Figure 10.

<figure><img src="image_13.png" /><figcaption>**Figure 10.** Chronoamperograms (applied potential 400 mV vs. Ag/AgCl) describing the evolution of the blank signal and of the 0.1 mM $K_4[Fe(CN)_6]$ depending on the sampling time for a) 50 µm and b) 20 µm-diameter UME arrays. The error bars are based on five measurements.</figcaption></figure>
Due to the very short time constants (RsC<sub>dl</sub>) observed for UME arrays (0.6 µs and 0.1 µs for the 50 µm and 20 µm arrays, respectively), the capacitive current became negligible at times beyond 3 ms. The initial part of the curve corresponded to the intermediate regime and, as assumed for the 500 µm macroelectrodes, the residual current was attributed to surface phenomena occurring on the gold electrode, such as the formation of oxides.<sup>31-34</sup> Under our analytical conditions, at short sampling times, the average current was higher and the standard deviations were more significant (Figure 10), which could negatively impact the LOD value when short times were used. Current-potential curves obtained at different sampling times (Figures S5 and S6) also showed a higher I<sub>plateau</sub>/I<sub>blank</sub> ratio for longer times of 60 ms and 90 ms. This was due to an increase in residual current with potential in the intermediate regime, whereas it stabilized at longer sampling times, corresponding to steady-state conditions (Figure S7). Calibration curves established for each sampling time, along with the corresponding LOD values estimated as three times the standard deviation of five blank measurements (Figure 11),<sup>35</sup> confirmed improved performance at longer sampling times. As observed with the 500 µm-diameter macroelectrode array, the sensitivity of the analysis, given by the slope of the calibration curves, was higher at shorter sampling times. However, the mean blank current and its standard deviation were also higher under these conditions, resulting in lower LODs at longer sampling times, with the best result (3 µM) obtained at 90 ms. This outcome highlights the advantage of using the UME array, which enabled a tenfold lower LOD compared to the macroelectrode array, due to enhanced faradaic current from hemispherical diffusion.

Comparison with results obtained by LSV (Figure S8 and Table 2) showed similar LODs, whereas significantly lower LODs were obtained with the 500 µm-diameter array. This discrepancy can be attributed to the fact that currents were measured in the steady-state region rather than in the Cottrell region. Indeed, the combination of higher faradaic currents and a
lower time constant ($RsC_{dl}$) should enhance both the sensitivity and the LOD of the analytical method.

<figure><img src="image_14.png" /></figure>

<table><thead><tr><th rowspan="2">θ<br>(ms)</th><th colspan="3">50 µm UME array</th><th colspan="3">20 µm UME array</th></tr><tr><th>I<sub>avg</sub> ±σ (nA)</th><th>Slope<br>(nA/m<br>M)</th><th>LOD<br>(× 10<sup>-5</sup> M)</th><th>I<sub>avg</sub> ±σ (nA)</th><th>Slope<br>(nA/<br>mM)</th><th>LOD<br>(× 10<sup>-5</sup> M)</th></tr></thead><tbody><tr><td>3</td><td>103 ± 4</td><td>403</td><td>2.93</td><td>18 ± 1</td><td>123</td><td>2.59</td></tr><tr><td>5</td><td>61 ± 3</td><td>316</td><td>2.84</td><td>12.6 ± 0.8</td><td>105</td><td>2.30</td></tr><tr><td>10</td><td>19 ± 1</td><td>222</td><td>2.06</td><td>7.9 ± 0.5</td><td>85</td><td>1.89</td></tr><tr><td>20</td><td>13 ± 1</td><td>156</td><td>1.86</td><td>4.6 ± 0.4</td><td>70</td><td>1.75</td></tr><tr><td>60</td><td>4.7 ± 0.2</td><td>101</td><td>0.69</td><td>1.51 ± 0.08</td><td>54</td><td>0.47</td></tr><tr><td>90</td><td>4.1 ± 0.3</td><td>88</td><td>0.33</td><td>1.48 ± 0.05</td><td>51</td><td>0.30</td></tr></tbody></table>

**Figure 11.** Calibration curves in K₄[Fe(CN)₆] obtained by EASCV at different sampling times on the array with 20 working electrodes composed of a) 50 µm and b) 20 µm-diameter UME arrays c) Average current (I<sub>avg</sub>) and standard deviation of 5 blank determinations, slope and LOD for each value of θ.

However, this work demonstrates that it is possible to analyze species at low concentrations (3 × 10⁻⁶ M) by EASCV using a conventional potentiostat and arrays composed of multiple UMEs.

**Application to Diclofenac Analysis.** Given the technique advantage of being well-suited for the analysis of species that poison the electrode surface,¹¹ we applied the method to the detection of diclofenac. It has been shown that the oxidation of diclofenac leads to the formation of intermediates such as 2,6-dichloroaniline and 2-(2-hydroxyprop-2-enyl)phenol.²⁴ The oxidation of phenolic compounds is known to form oligomers on the electrode surface, resulting
in electrode fouling.¹¹ The loss of activity was observed by CV in a 0.5 mM diclofenac solution prepared in 0.1 M phosphate-buffered saline (PBS) at pH 7.4 (Figure 12a). As early as the second cycle, the electrochemical signal disappeared. To confirm electrode fouling, K₄[Fe(CN)₆] was used as a redox probe, and its electrochemical response was measured before and after diclofenac analysis on the same gold electrode. On a bare electrode, potassium ferrocyanide exhibited a reversible redox system at 0.2 V vs. Ag/AgCl (Figure 12b). After four cycles in 0.5 mM diclofenac with the same electrode, the electrochemical response of the redox probe disappeared. However, thorough cleaning of the electrode with acetone restored the redox signal. These results clearly confirmed the fouling of the gold electrode during the oxidation of diclofenac.

<figure><img src="image_15.png" /><figcaption>**Figure 12.** Cyclic voltammograms in 0.1 M PBS of a) 0.5 mM diclofenac (DCF) and b) of 1 mM K₄[Fe(CN)₆] on a 3 mm-diameter bare gold electrode (black), after diclofenac analysis (4 cycles) (blue) and acetone washing (green) (0.1 V s⁻¹) c) Cyclic voltammograms of 1 mM</figcaption></figure>
$K_4[Fe(CN)_6]$ in PBS on a bare gold UME (d = 100 µm) (**black**), and after the analysis of 0.5 mM diclofenac by LSV (**red**) and by SCV (**blue**), (10 mV s⁻¹). d) Current-potential curves obtained successively in increasing concentrations of diclofenac in PBS at a sampling time of 60 ms on a single 500 µm-diameter electrode array.

The SCV technique minimized the duration of potential application on each electrode in the array, limiting diclofenac oxidation to the 100 ms pulse period. Figure 12c compares the redox signal of the $K_4[Fe(CN)_6]$ probe on a 100 µm-diameter gold microelectrode before and after diclofenac analysis with a 100 ms potential pulse or by LSV. A clear discrepancy in the redox probe signal was observed after LSV analysis, whereas only a slight decrease was observed after the potential pulse. However, SCV analysis performed on the same electrode, even after thorough acetone cleaning between each current-potential curve, led to a gradual decrease in the electrochemical response as the diclofenac concentration increased (Figure 12d). These results highlighted the need to renew the electrode surface between each potential pulse when using SCV to minimize signal loss and to ensure good reproducibility of the results.

Since electrode poisoning occurred during analysis, EASCV appeared to be the method of choice for analyzing diclofenac. Calibration curves were obtained using EASCV for diclofenac in PBS on the three different array designs. The studied concentration range was selected to ensure both good precision of the LOD value and the occurrence of electrode fouling at high concentrations (Figure 12d). The sampling time was set to 60 ms to remain as close as possible to the radial diffusion regime, while avoiding excessively long acquisition times that could lead to electrode fouling.¹¹ The results are presented in Figure 13.
<figure><img src="image_16.png" /><figcaption>**Figure 13.** Current vs. potential curves of blank and diclofenac in PBS at a sampling time of 60 ms obtained by EASCV on electrode arrays with working electrodes of a) 500 µm diameter, and composed of c) 50 µm, d) 20 µm-diameter UME arrays, and the corresponding calibration curves (d, e, f, respectively). Error bars are based on 3 measurements.</figcaption></figure>

Since the oxidation of diclofenac occurred at a higher potential than that of K₄[Fe(CN)₆], the potential window was shifted by 450 mV. At these higher potentials, a clear positive current was observed, most likely due to surface phenomena on gold, such as the formation of gold oxides,³¹⁻³⁴ which resulted in an increased background signal. Despite this, the LODs, 0.68 × 10⁻⁵ M and 0.41 × 10⁻⁵ M for the 50 µm and 20 µm-diameter UME arrays, respectively, as determined from the calibration curves were of the same order of magnitude as those obtained for K₄[Fe(CN)₆], and ten times lower than for the 500 µm-diameter macroelectrode. Furthermore, the slopes of the calibration curves, reflecting the sensitivity of the analytical method, were even higher than those for K₄[Fe(CN)₆]. These results underscore the relevance of EASCV for the sensitive detection of passivating species such as diclofenac. As shown in Figure 13, a decrease in electrode diameter leads to slower electron transfer kinetics, a behavior that was not clearly observed in the case of ferrocyanide analysis (Figures S5 and S6). While
this was not the primary focus of the present study, it is worth mentioning that the transient
region of the curves could be exploited to extract kinetic parameters for each species and
electrode type.¹³

CONCLUSIONS

The fabrication of an array composed of 20 identical electrodes with diameters of 500 µm, and composed of 50 µm and 20 µm-diameter UME array was reported and validated through SEM and SECM analyses. The good reproducibility of each electrode or UME was confirmed by CV, resulting in a range of 1.3-4.9% error. Simulations of SCV curves using COMSOL indicated no overlap between diffusion layers of the UMEs.

EASCV analysis was initially conducted using K₄[Fe(CN)₆] as a model redox compound and a standard laboratory potentiostat. Studies with the macroelectrode array demonstrated the benefit of using short sampling times to enhance sensitivity, yielding a calibration slope 28 times higher than that obtained with LSV. This also resulted in significantly lower LOD values, estimated at 2.07 × 10⁻⁵ M. When using UME arrays as working electrodes, the best results were obtained under steady-state conditions dominated by radial diffusion, corresponding to longer sampling times (90 ms). LODs of 3 × 10⁻⁶ M were achieved with both the 50 µm and 20 µm-diameter UME arrays, comparable to those obtained via LSV, while the sensitivity was approximately twice as high.

EASCV was then applied to the detection of diclofenac, a compound known to induce electrode fouling, yielding LOD values similar to those observed for ferrocyanide. These findings emphasize the relevance of this method, which benefits from short oxidation times that help reduce electrode fouling. EASCV could serve as a sensitive analytical technique with low LOD, particularly suitable for sensors based on modified electrodes.
Although these initial experiments demonstrated the feasibility of using EASCV with a standard potentiostat, further improvements are expected with a more suitable apparatus. A potentiostat optimized for short-time measurements would enable accurate acquisition in the Cottrell region using UME arrays. This approach would minimize the residual current due to the short time constant and further reduce electrode fouling significantly.

**Funding:** This work received financial support under the EUR LUMOMAT project and the Investments for the Future program ANR-18-EURE-0012 Nanosens.

**Supporting Information:** A COMSOL simulation report exemplified with the 20 µm-diameter UME array. Figures S1 to S8, which illustrate current *versus* t⁻¹/² obtained by chronoamperometry, EIS measurements, chronoamperograms of the blank, LSV calibration curves, and current-potential curves obtained by EASCV on the arrays with working electrodes composed of 50 mm and 20 mm diameter UME arrays.

**Acknowledgments:** T.L. thanks the program "Bourses du Gouvernement Français France Excellence" for her scholarship. We thank Vmicro (Lille, France) for their help in the fabrication of the electrode arrays and their SEM characterization. We thank Origalys ElectroChem for lending us the impedance module used for surface characterization measurements.

## REFERENCES

(1) Bard, A. J.; Faulkner, L. R. *Electrochemical Methods: Fundamentals and Applications*; John Wiley & Sons, Inc., 2001.

(2) Soares, C. O.; Rodriguez, O.; Buvat, G.; Duca, M.; Garbarino, S.; Guay, D.; Denuault, G.; Tavares, A. C. Sampled current voltammetry for kinetic studies on materials unsuitable for
rotating discs or microelectrodes: Application to the oxygen reduction reaction in acidic medium. *Electrochim. Acta* **2020**, *362*, 136946.

(3) Anantharaj, S.; Kundu, S.; Noda, S. Worrisome exaggeration of activity of electrocatalysts destined for steady-state water electrolysis by polarization curves from transient techniques. *J. Electrochem. Soc.* **2022**, *169* (1), 014508.

(4) Soares, C. O.; Buvat, G.; Hernández, Y. G.; Garbarino, S.; Duca, M.; Ruediger, A.; Denuault, G.; Tavares, A. C.; Guay, D. Au (001) Thin Films: Impact of Structure and Mosaicity on the Oxygen Reduction Reaction in Alkaline Medium. *ACS Catalysis* **2022**, *12* (3), 1664–1676.

(5) Anantharaj, S.; Noda, S. Electrochemical dealloying-assisted activity enhancement: The next big thing in water electrosplitting! *Nano Energy* **2023**, *114*, 108624.

(6) Wang, C.; Liu, D.; Zhang, K.; Xu, H.; Yu, R.; Wang, X.; Du, Y. Defect and interface engineering of three-dimensional open nanocage electrocatalysts for advanced electrocatalytic oxygen evolution reaction. *ACS Appl. Mater. Interfaces* **2022**, *14* (34), 38669–38676.

(7) Zhang, W.; Wang, K.; Lin, F.; Zhang, Q.; Sun, Y.; Luo, H.; Zhang, W.; Zhou, J.; Lv, F.; Wang, D. Assembled RhRuFe Trimetallene for Water Electrolysis. *Small Methods* **2024**, *8* (12), 2400336.

(8) Rodríguez, O.; Denuault, G. The electron transfer kinetics of adsorbed species derived by sampled current voltammetry. *J. Electroanal. Chem.* **2021**, *882*, 115021.

(9) Mignard, L.; Denoual, M.; Lavastre, O.; Floner, D.; Geneste, F. Sampled voltammetry on an electrode array for the renewal of the electrode surface and the analytical solution during the analysis. *J. Electroanal. Chem.* **2013**, *689*, 83–87. DOI: 10.1016/j.jelechem.2012.10.015 From American Chemical Society. All Rights Reserved. CAPLUS.
(10) Lavastre, O.; Floner, D.; Geneste, F. Electrochemical method and device for voltammetric analysis. FR FR2884318, 2006.

(11) Mazerie, I.; Didier, P.; Razan, F.; Hapiot, P.; Coulon, N.; Girard, A.; de Sagazan, O.; Floner, D.; Geneste, F. A General Approach Based on Sampled-Current Voltammetry for Minimizing Electrode Fouling in Electroanalytical Detection. *ChemElectroChem* **2018**, *5* (1), 144–152.

(12) Mazerie, I.; Geneste, F. Coupling of anodic stripping voltammetry with sampled-current voltammetry on an electrode array: Application to lead detection. *Sensors* **2020**, *20* (5), 1327.

(13) Perry, S. C.; Al Shandoudi, L., M; Denuault, G. Sampled-Current Voltammetry at Microdisk Electrodes: Kinetic Information from Pseudo Steady State Voltammograms. *Anal. Chem.* **2014**, *86*, 9917–9923.

(14) Heinze, J. Ultramicroelectrodes in electrochemistry. *Angew. Chem., Int. Ed. Engl.* **1993**, *32* (9), 1268–1288.

(15) Stulík, K.; Amatore, C.; Holub, K.; Marecek, V.; Kutner, W. Microelectrodes. Definitions, characterization, and applications (Technical report). *Pure Appl. Chem.* **2000**, *72* (8), 1483–1492.

(16) Moazzenzade, T.; Walstra, T.; Yang, X.; Huskens, J.; Lemay, S. G. Ring ultramicroelectrodes for current-blockade particle-impact electrochemistry. *Anal. Chem.* **2022**, *94* (28), 10168–10174.

(17) Flaman, G. T.; Boyle, N. D.; Vermelle, C.; Morhart, T. A.; Ramaswami, B.; Read, S.; Rosendahl, S. M.; Wells, G.; Newman, L. P.; Atkinson, N. Chemical Imaging of Mass Transport Near the No-Slip Interface of a Microfluidic Device using Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy. *Anal. Chem.* **2023**, *95* (11), 4940–4949.
(18) Qi, J.; Wang, W.; Li, Y.; Sun, Y.; Wu, Z.; Bao, K.; Wang, L.; Ye, R.; Ding, M.; He, Q. On-chip investigation of electrocatalytic oxygen reduction reaction of 2D materials. *Small* **2022**, *18* (47), 2204010.

(19) Ayres, L. B.; Pimentel, G. J.; Costa, J. N.; Piazzetta, M. H.; Gobbi, A. L.; Shimizu, F. M.; Garcia, C. D.; Lima, R. S. Ultradense Array of On-Chip Sensors for High-Throughput Electrochemical Analyses. *ACS sensors* **2024**, *9* (8), 4089–4097.

(20) Boumya, W.; Taoufik, N.; Achak, M.; Bessbousse, H.; Elhalil, A.; Barka, N. Electrochemical sensors and biosensors for the determination of diclofenac in pharmaceutical, biological and water samples. *Talanta Open* **2021**, *3*, 100026.

(21) Kassahun, G. S.; Griveau, S.; Bedioui, F.; Slim, C. Input of electroanalytical methods for the determination of diclofenac: A review of recent trends and developments. *ChemElectroChem* **2022**, *9* (2), e202100734.

(22) Gomes, N. O.; Calegaro, M. L.; Mattoso, L. H. C.; Oliveira Jr, O. N.; Machado, S. A.; Raymundo-Pereira, P. A. Carbon spherical shells functionalized with nitrogen as sustainable electrochemical materials for rapid detection of diclofenac in saliva, urine, water, and tablets. *ACS Appl. Nano Mater. 2024*, *7* (23), 27520–27530.

(23) Aidli, W.; Comis, S.; Falciola, L.; Pifferi, V. Benzoquinone-modified vertically aligned mesoporous silica for ratiometric electrochemical detection of diclofenac. *Talanta* **2025**, 288, 127711.

(24) Cid-Cerón, M.; Guzmán-Hernández, D.; Ramírez-Silva, M.; Galano, A.; Romero-Romo, M.; Palomar-Pardavé, M. New insights on the kinetics and mechanism of the electrochemical oxidation of diclofenac in neutral aqueous medium. *Electrochim. Acta* **2016**, *199*, 92–98.

(25) Nečas, D.; Klapetek, P. Gwyddion: an open-source software for SPM data analysis. *Open Physics* **2012**, *10* (1), 181–188.
(26) Godino, N.; Borrise, X.; Munoz, F. X.; Del Campo, F. J.; Compton, R. G. Mass transport to nanoelectrode arrays and limitations of the diffusion domain approach: theory and experiment. *J. Phys. Chem. C.* **2009**, *113* (25), 11119–11125.

(27) ISO 14044 : Environmental management—life cycle assessment—requirements and guidelines, 2009.

(28) ISO 14040 : Environmental management—life cycle assessment—principles and framework, 2009.

(29) Zampori, L.; Pant, R. *Suggestions for updating the Organisation Environmental Footprint (OEF) method*, EUR 29681 EN. Publications Office of the European Union, Luxembourg; ISBN 978-92-76-00651-0. https://doi.org/10.2760/577225.JRC115960, 2019.

(30) Bourru, L. RE2020 : Calculer l'impact carbone d'un bâtiment | Cerema. https://www.cerema.fr/fr/actualites/re2020-calculer-impact-carbone-batiment (accessed 2025-04-23).

(31) Piela, B.; Wrona, P. K. Capacitance of the gold electrode in 0.5 M H2SO4 solution: ac impedance studies. *J. Electroanal. Chem.* **1995**, *388* (1-2), 69–79.

(32) Juodkazis, K.; Juodkazyt, J.; Jasulaitien, V.; Lukinskas, A.; Šebeka, B. XPS studies on the gold oxide surface layer formation. *Electrochem. Commun.* **2000**, *2* (7), 503–507.

(33) Laitinen, H.; Chao, M. The anodic surface oxidation of gold. *J. Electrochem. Soc.* **1961**, *108* (8), 726.

(34) Gong, J. Structure and surface chemistry of gold-based model catalysts. *Chem. Rev.* **2012**, *112* (5), 2987–3054.

(35) MacDougall, D.; Crummett, W. B. Guidelines for data acquisition and data quality evaluation in environmental chemistry. *Anal. Chem.* **1980**, *52* (14), 2242–2249.
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<figure><img src="image_17.png" /></figure>