# Non-enzymatic electrochemical sensor for uric acid based on surfactant-silica-MWCNT nanohybrids functionalized with APTES

Afef Dhaffouli, Michael Holzinger, Pedro A Salazar-Carballo, Soledad

Carinelli, Houcine Barhoumi

► To cite this version:

Afef Dhaffouli, Michael Holzinger, Pedro A Salazar-Carballo, Soledad Carinelli, Houcine Barhoumi. Non-enzymatic electrochemical sensor for uric acid based on surfactant-silica-MWCNT nanohybrids functionalized with APTES. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2025, 724, pp.137520. 10.1016/j.col SURFA.2025.137520. hal-05158574

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Submitted on 11 Jul 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Non-enzymatic electrochemical sensor for uric acid based on
surfactant-silica-MWCNT nanohybrids functionalized with APTES

Afef Dhaffouli a,b, Michael Holzinger c, Pedro A. Salazar-Carballo d,*, Soledad Carinelli d,e,
Houcine Barhoumi a

a Laboratory of Interfaces and Advanced Materials, University of Monastir, Faculty of Sciences of Monastir, Monastir 5000, Tunisia

b Department of chemistry, University of Gafsa, Faculty of Sciences of Gafsa, Gafsa 2100, Tunisia

c Department of Molecular Chemistry UMR CNRS 5250, Nanobio Building Grenoble-Alpes University, CS 40700, Grenoble 38058, France

d Laboratory of Sensors, Biosensors and Advanced Materials, Institute of Materials and Nanotechnology, University of La Laguna, La Laguna, Spain

e Laboratorio de Neuroquímica y Neuroimagen, Instituto Universitarios de Neurociencia (IUNE), Instituto de Tecnologías Biom´ Spain edicas (ITB), University of La Laguna,

**Abstract:**

The CTAB@SiO₂@MWCNT-APTES composite was synthesized and used as a modifier for a glassy carbon electrode for the determination of uric acid. APTES was successfully immobilized on multi-walled carbon nanotubes (MWCNTs) through non-covalent hydrophobic interactions and formed a nanoscale network spreading from the electrode surface to facilitate direct electron transfer and access to the specific detection site for uric acid. All experimental parameters were optimized to ensure effective operation of the sensor. The combination of CTAB@SiO₂@MWCNT-APTES provided the sensor with a large surface area, excellent compatibility and stability, resulting in increased selectivity and sensitivity. Characterization by FTIR, EDX and transmission electron microscopy confirmed the integrity of the CTAB@SiO₂@MWCNT-APTES composite. This composite network efficiently separated the anodic oxidation potential of uric acid from other species with similar potentials, demonstrating its potential as a promising electrochemical sensor for selective determination. The functionality of the CTAB@SiO₂@MWCNT-APTES array was investigated for the selective detection of uric acid in real
human plasma and urine samples. The results showed acceptable recovery rates of 78% to 104%, confirming its potential as a robust platform for future sensor development.

**Keywords:** CTAB@SiO₂@MWCNT-APTES; Uric acid(UA); SiO₂@MWCNT-APTES; Electrochemical sensor.

**1.Introduction:**

Uric acid (UA) is a key nitrogenous compound found in both animals and plants. It consists of 2,6,8-trihydroxypurine, which undergoes keto-enol tautomerism and is converted into urate. Monitoring uric acid levels is crucial because elevated levels can lead to the formation of crystals in joints and connective tissues, resulting in conditions such as gout, arthritis, and rheumatic pain. Thus, maintaining appropriate uric acid levels is important for preventing these potentially debilitating conditions. Excessive deposition of uric acid and urate can also contribute to kidney failure. UA is a biomolecule found in both urine and blood and is produced by the breakdown of purine in the body's metabolic processes [1]. The standard range for uric acid in the blood is 0.12 - 0.45 mmolL⁻¹, while in the urine it is approximately 2 mmolL⁻¹ [2], this wide range necessitates highly sensitive and accurate detection methods to ensure reliable monitoring for disease diagnosis. Elevated levels of uric acid in body fluids can lead to conditions such as toxemia of pregnancy and hyperuricemia [3-4]. Several studies have suggested that abnormal serum UA levels are a risk factor for cardiovascular disease and gout, arthritis, chronic kidney [5-6]. In this context, the detection of uric acid (UA) in human body fluids is essential for disease diagnosis and necessitates monitoring with high sensitivity and accuracy. Various techniques have been employed for this purpose, including high-performance liquid chromatography with a UV detector operated at 260 nm [7], magnetic resonance imaging [8], capillary electrophoresis [9], colorimetric methods [10], and fluorescence methods [11]. However, these methods require complicated preparation, time-consuming analysis and the use of expensive reagents [12]. The development of electrochemical sensors has increased in recent years to improve their performance in terms of selectivity and sensitivity. Moreover, the electrochemical technique is widely recognized as an excellent method for determining uric acid (UA).
because of its rapid response, ease of use, specificity, affordability, and high sensitivity[13-14]. Electrochemical sensors incorporating nanomaterials with uricase and catalase activities have gained significant attention for their high sensitivity, speed, low cost, and ease of implementation, making them ideal for real-time monitoring [15-16]. These sensors have been developed for the quantitative analysis of uric acid in biological fluids [17]. For effective biomolecule sensing, electrode materials must possess electrochemical sensitivity and the capability to facilitate electron transfer reactions. Glassy carbon electrodes (GCEs) have limitations because their oxidation potential is very close to that of electroactive biomolecules, leading to poor sensitivity in unmodified GCEs [18]. To overcome this issue, modifying GCEs with conductive carbon nanomaterials is an effective strategy. Wang and colleagues found that multi-walled carbon nanotubes (MWCNTs) could increase the active surface area of the electrode, improving both biocompatibility and electron transfer rates [19]. This phenomenon has been confirmed by numerous studies on sensors modified with metallic oxides blended with MWCNTs, demonstrating the positive impact of MWCNTs on enhancing the sensing performance of these oxides for biomolecules [20-22].

Another effective technique is silanization, which involves treating functionalized surfaces with silane coupling agents, typically organosilanes. Organosilanes are commonly represented by the formula $Si(OR')_3$, where OR' is a hydrolyzable alkoxy group, and R is a functional organic group, chosen based on the matrix used [23-24]. The $(OR')_3$ group, usually trimethoxy ($OCH_3)_3$ or triethoxy ($OC_2H_5)_3$, hydrolyzes to form trisilanol, which reacts with hydroxyl groups on the nanotube surface produced during oxidation or reduction.

Recently, researchers have applied silanization to functionalize CNT surfaces Zhang, L., & Yin, Y. (2020) [25], Ma, X., Gao, Z., Wang, D., & Zhang, W. (2021) [26] and Kumar, P., Huo, P., Zhang, R., & Liu, B. (2019) [27] studied the silanization of oxidized and reduced multi-walled carbon nanotubes (MWCNTs) using 3-glycidoxypropyltrimethoxysilane and tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane. In 2022 Vast, L., Laurent, C., Peigney, A., & Rousset, A. [28] introduced new chains to
the open end caps and walls of oxidized MWCNTs through silanization with 3-mercaptopropyl trimethoxysilane. In this study, 3-aminopropyltriethoxysilane (3-APTES), a widely used aminosilane in nylon, phenolic, epoxy, and melamine resin-based composites, was employed to treat MWCNTs for improved sensor performance. Numerous researchers have reported on the fabrication and characterization of CNT-epoxy nanocomposites he fabrication and characterization of CNT-epoxy nanocomposites specifically for electrochemical sensors [29–31]. Cetyltrimethylammonium bromide (CTAB) is a cationic surfactant whose non-polar chain interacts with the hydrophobic layer around SiO₂, causing the polar groups of CTAB to face outward and stabilize the particles in an aqueous medium. Additionally, that CTAB enhances sensitivity, enabling the selective detection of uric acid (UA) even in the presence of interfering molecules [32].

In this study, we highlight the advantages of using CTAB@SiO₂@MWCNT-APTES nanoparticle-modified glassy carbon electrodes (GCE) for the electrochemical detection of uric acid. This sensor offers several benefits over traditional sensors. It provides enhanced sensitivity and selectivity, allowing for precise measurements even in the presence of interfering substances. This is a notable improvement compared to conventional sensors, which often struggle with selectivity.

The superior electrocatalytic activity of the sensor is attributed to the functionalized MWCNTs, which enable faster electron transfer rates and more efficient electrochemical reactions than less conductive materials used in other sensors. Additionally, CTAB (cetyltrimethylammonium bromide), a cationic surfactant, plays a crucial role in stabilizing the nanoparticles within the sensor matrix. CTAB's non-polar chain interacts with the hydrophobic layer around SiO₂, while its polar groups face outward, ensuring a uniform dispersion of nanoparticles. This stabilization enhances the sensor's electrocatalytic properties by improving electron transfer and minimizing interference from other molecules.

Finally, the inclusion of SiO₂ and APTES further contributes to the sensor's stability and durability, maintaining its performance across various conditions. The sensor's capability to accurately detect uric
acid in complex biological samples, such as human plasma and urine, demonstrates its versatility and broadens its application range. Moreover, the cost-effectiveness of these materials and methods makes this sensor a promising alternative to more expensive high-end sensors, offering reliable and accurate uric acid detection.

## 2. Materials and methods.

### 2.1 Materials and Reagents.

Cetyltrimethylammonium bromide (CTAB) (100 g, ≥99 %), tetraethyl orthosilicate (TEOS) (99.0%), 3-aminopropyl-triethoxysilane (APTES) (99.0%), potassium chloride (KCl), Ethanol (ETOH) (≥96 %), Sodium hydroxide (NaOH), Hydrochloric acid (HCl), potassium hexacyanoferrate (II) trihydrate ($K_4[Fe(CN)_6]·3H_2O$), potassium hexacyanoferrate(III) ($K_3[Fe(CN)_6]$), glucose(Gly), dopamine (DA), ascorbic acid (AA), salicylic acid (SA), and Uric acid (UA) were obtained from Sigma-Aldrich, France. All solutions were prepared with water (resistivity 18.2 mΩ cm). The pH phosphate buffer solution (0.1 $molL^{-1}$, pH 4.6), was prepared by dissolving 0.1 $molL^{-1}$ monosodium dihydrogen phosphate trihydrate ($NaH_2PO_4·3H_2O$) (≥99 %), and 0.1 $molL^{-1}$ disodium hydrogen phosphate dodecahydrate ($Na_2HPO_4·12H_2O$) (99,998 %) (Merck, France) in distilled water (pH 8).

This PBS served as the supporting electrolyte, with pH adjustments made by adding NaOH or HCl solutions. Various concentrations of glucose (Glu), dopamine (DA), ascorbic acid (AA), salicylic acid (SA), and uric acid (UA) were prepared in PBS using distilled water. A stock solution of UA was diluted to achieve the desired trace concentrations, with each dilution stirred until the concentration stabilized. The experiments for UA detection were conducted starting with the lowest concentration and progressing to higher concentrations.

### 2.2 Preparation of CTAB@SiO$_2$@MWCNT-APTES.

In a 50 ml bottle, 0.2 g of CTAB is added to 30 ml of ethanol and 10 ml of distilled water. The mixture is stirred for 2 hours at 40°C until the CTAB is completely dissolved and dispersed. Then 1 ml
TEOS and 0.5 ml 2 molL⁻¹ NaOH are added successively. After 1 hour of continuous stirring at the same temperature, 10 mg MWCNT is added and the solution is sonicated (40 kHz) for 1 hour until the mixture is completely homogenized. After homogenization, 1 ml of APTES is added and the mixture is stirred at 40°C for 5 hours. The resulting product is then centrifuged and washed three times with a combination of water and ethanol.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Schematic illustration of the preparation of CTAB@SiO₂@MWCNT-APTES nanoparticles.</figcaption></figure>

**2.3 Elaboration of GCE /CTAB@SiO₂@MWCNT-APTES modified electrode.**

Before modification, the glassy carbon electrode (GCE) a polishing procedure utilizing emery papers with 0.05 µm alumina powder. Following each polishing step, the electrode was sonicated in ethanol for five minutes. Subsequently, the cyclic voltammetry (CV) characteristics of the electrode were evaluated in a solution contained 5 mmolL⁻¹ Fe(CN)₆³⁻/₄⁻ and 0.1 molL⁻¹ KCl at a scan rate of 100 mV s⁻¹ until a reversible redox reaction was observed. The fabrication of the modified GCE involved several steps. Initially, 1 mg of CTAB@SiO₂@MWCNT-APTES was suspended in 1 mL of ethanol and sonicated for 30 minutes to achieve a homogeneous dispersion. Following this, 7 µL of the suspension
was applied to the polished surface of the GCE, left to dry at room temperature, and then utilized for
subsequent measurements.

## 2.4 Characterization of synthesized NPs and electrochemical characterization of CTAB@SiO₂@MWCNT-APTES modified GC electrode

The electrochemical experiments were carried out using a conventional electrochemical cell equipped with a three-electrode system. The working electrode consisted of a glassy carbon electrode modified with CTAB@SiO₂@MWCNT-APTES, while an Ag/AgCl (3 mol L⁻¹ KCl) served as reference electrode and a platinum wire (diameter 1 mm) as a counter electrode. Electrochemical measurements were performed using an Autolab PG potentiostat/galvanostat (AUT 83965) controlled by Autolab NOVA 2.1.6 software. The morphologies and microstructures of the samples were analyzed by scanning electron microscopy (SEM) using a JEOL JEM-2000 FX microscope. Transmission electron microscopy (TEM) images were taken with a JEOL 2100 microscope at 200 kV. Fourier transform infrared (FTIR) spectra were recorded with a PerkinElmer Spectrum IR version 10.7.2 spectrometer to further characterize the samples. Impedance characterization was performed in a 5 mmolL⁻¹ K₃Fe(CN)₆³⁻/₄⁻ solution with 0.1 molL⁻¹ KCl The stabilization potential was consistently maintained at +0.2 V relative to the reference electrode, and the signal amplitude was set to 10 mV across a frequency spectrum ranging from 0.1 to 10⁵ Hz.

# 3. Results and Discussion

## 3.1 Material characterization

### 3.1.1 Electron microscopy analysis of CTAB@SiO₂@MWCNT-APTES

The TEM images, shown in **Figure 2**, provide detailed insights into the surface morphology of CTAB@SiO₂@MWCNT-APTES and SiO₂ nanoparticles. The analysis reveals that SiO₂ nanoparticles are embedded with multi-walled carbon nanotubes (MWCNTs) and are covered with an amorphous layer of poly-APTES. The MWCNTs are evenly distributed across the silica spheres, while the APTES
polymers are irregularly attached around them. Crucially, the structural integrity of the MWCNTs appears
intact after functionalization (Figure 2d), indicating that the APTES treatment does not significantly alter
the nanotubes' morphology.

**Figures 2a through 2d** further illustrate the agglomerated structure of CTAB@SiO₂@MWCNT-
APTES and prominently display the closed ends characteristic of MWCNTs, which are indicative of
MWCNTs, are visible as capped structures on the tips of the nanotubes. The high-resolution images allow
us to observe the distinct, rounded or blunt terminations of the nanotubes, distinguishing them from other
nanostructures. This feature is a key morphological trait of MWCNTs and confirms their identity in the
composite material. These images confirm the presence of MWCNTs on the silica surface and validate
the incorporation of both APTES and MWCNTs into the composite material. The observations support
the successful bonding of silane molecules to the MWCNT surfaces within the CTAB@SiO₂@MWCNT-
APTES nanocomposite. Additional TEM analysis of the composite microstructures in epoxy composites
demonstrates the covalent attachment of silane molecules to the MWCNTs, confirming effective
functionalization and integration of the components [34].
<figure><img src="image_3.png" /><figcaption>**Figure 2.** TEM image of CTAB@SiO₂@MWCNT-APTES (a,b,c,d) and SiO₂ (e).</figcaption></figure>

**3.1.3 Infrared spectrum characterization of the prepared materials:**

**Figure 3** shows the FT-IR spectra of CTAB@SiO₂@MWCNT-APTES, SiO₂@MWCNT-APTES and SiO₂. According to the results, an absorption peak at 3671 cm⁻¹ is observed which provides clues as to the presence of hydroxyl (OH) or amine (N-H) groups of APTES in the sample analysed, as well as a peak at 1363 cm⁻¹ which is attributed to the bending deformation of the hydroxyl (OH) groups found on the silanol moiety [35]. A characteristic peak at around 900 cm⁻¹ was observed, confirming the existence of silanol groups (Si-OH). This peak is attributed to the bending vibrations of the Si-OH bonds. Si-OH groups are often present on the surface of silicas or silicate compounds, where they can play a crucial role in surface interactions, such as the adsorption of molecules or the formation of hydrogen bonds. The presence of this peak indicates the presence of silicon-bonded hydroxyl groups, often associated with silanol functions formed by the hydrolysis of Si-O-Si bonds or with the presence of amorphous silica
[36]. The addition of 3-aminopropyltriethoxysilane (APTES) to multiwall carbon nanotubes (MWCNTs) leads to a functionalization of their surface, allowing the introduction of aminopropyl groups. In this reaction, APTES first hydrolyses its ethoxy groups to form silanols, which can then condense with the hydroxyl groups present on the surface of the MWCNTs, creating Si-O-C bonds between the APTES and the MWCNTs. The absorption bands observed at 2912 cm⁻¹ and 2987 cm⁻¹ in the infrared spectrum correspond to the symmetrical and asymmetrical stretching vibrations of the C-H bonds. These bands are characteristic of the methylene groups (--CH₂--) present in the carbon skeleton of APTES and indicate the presence of alkyl chains resulting from the coupling of APTES with MWCNTs [37]. The presence of these bands confirms the existence of --CH₂-- groups in the final structure, suggesting that the CTAB (cetyltrimethylammonium chloride) used to functionalize the SiO₂ and MWCNTs surfaces left methylene groups in the final CTAB@SiO₂@MWCNT-APTES complex. This validates the successful functionalization and integration of organic groups on the MWCNT surface [38]. This explanation highlights the functionalisation process and the nature of the chemical groups present in the final material, while also describing the origin of the specific bands in the infrared spectrum.

<figure><img src="image_4.png" /></figure>
**Figure 3.** FTIR spectra of CTAB@SiO₂@MWCNT-APTES, SiO₂@MWCNT-APTES and SiO₂ sample.

## 3.2 Analytical and electrochemical optimizations

### 3.2.1 Optimization of experimental variables

Firstly, we investigated the effect of the amount of deposited CTAB@SiO₂@MWCNT-APTES on the electrochemical behavior of uric acid. The results obtained indicate that the amount deposited on the electrode has an influence on the reactions of uric acid. **Figure 4a** shows that there is a relationship between the peak value of UA oxidation current and the amount of CTAB@SiO₂@MWCNT-APTES. As we have seen, the peak current gradually increased with the amount of CTAB@SiO₂@MWCNT-APTES deposited on the electrode from 3 µL to 7 µL, but when it exceeded 7 µL, it decreased slightly. When the layer deposited on the electrode was too thick, the intensity of the peak current decreased. A larger amount of CTAB@SiO₂@MWCNT-APTES in suspension resulted in a less adherent film. Therefore, 7 µL of the CTAB@SiO₂@MWCNT-APTES suspension, which gave the maximum current response, was used in the electrode.

In **Figure 4b**, the impact of the drying time of CTAB@SiO₂@MWCNT-APTES on differential pulse voltammetry (DPV) settings is presented over a range from 1 to 16 hours at room temperature. Notably, at a drying time of 2 hours, the response current peaks, signifying its maximum level. Beyond this 2-hour threshold, there is a discernible decline in the response current. This diminishing current can be rationalized by the requirement for a certain level of moisture for effective interaction between our sensor layer and uric acid. Excessive dryness renders the CTAB@SiO₂@MWCNT-APTES hydrophobic of the groups SiO₂-CH₂-CH₃ [39] in the surface of matrix, preventing proper filling of the pores by the analyte solutions. Consequently, the optimum time for Uric acid detection is determined to be 2 hours.

The pH of the buffer solution is a critical factor in electrochemical sensor applications, as it significantly affects the electrochemical properties of the analytes being detected. In electrochemical
sensors, the pH can influence the ionization state, stability, and reactivity of the species present, which in turn impacts the overall sensitivity and accuracy of the sensor. For this reason, we systematically study the effect of pH by testing the electrochemical performance of the modified glassy carbon electrode (GCE) with CTAB@SiO₂@MWCNT-APTES under various pH conditions. This investigation helps determine the optimal pH that provides the best sensor performance, ensuring accurate detection and quantification of the target analytes. By analyzing the response at different pH levels, we can identify the most suitable conditions for maximizing the electrochemical response, thus enhancing the sensor's efficiency and reliability [40-41].

The pH of the solution significantly influences the performance of the CTAB@SiO₂@MWCNT-APTES (Figure 4c) sensor for uric acid (UA) detection. At pH 7, UA exists predominantly as a negatively charged monobase, which optimizes its interaction with the sensor materials and results in the highest peak current. This indicates that the electrochemical reaction [42] is most efficient under these conditions. At pH values below 5, UA is mainly in its protonated, neutral form, which can reduce adsorption on the sensor and lead to a lower peak current and potentially increased fouling of the sensor surface [43]. Conversely, at pH levels above 10, UA is present as a dibasic anion, which can cause increased repulsion from the negatively charged sensor surface. This change in form results in a decrease in peak current and shifts in peak potential, often accompanied by increased fouling due to altered interactions with the anionic UA [44]. Therefore, pH 7 is identified as the optimal condition for UA detection with this sensor, as it provides the best sensitivity and reliability by ensuring effective interaction between UA and the sensor while minimizing fouling and variations in electron transfer dynamics (Figure 5).

Finally, the influence of Accumulation time on peak current intensity was investigated in a 0.1 molL⁻¹ PBS buffer solution at pH 7.0 containing 10⁻⁵ molL⁻¹ UA, with incubation times ranging from 1 to 10 minutes. Initially, an increase in current is observed between 0 and 5 minutes. This increase is due to the growing number of UA molecules adsorbed onto the electrode surface as the accumulation time
extends. The CTAB@SiO₂@MWCNT-APTES material, with its large surface area and favorable adsorption sites, facilitates this accumulation and increases the number of electroactive species available for redox reactions, resulting in a higher observed current. Nanoparticles, particularly SiO₂ and MWCNT, provide a large active surface area and facilitate electron transfer processes, contributing to the effective accumulation and subsequent electrochemical oxidation of UA molecules. The current peaks at 5 minutes, indicating the optimal accumulation time when the maximum number of UA molecules have been adsorbed and are participating in the electrochemical reaction. At this point, the electrode surface is highly active, and the electrochemical signal is at its highest. However, after 5 minutes, the current begins to decrease. This decline can be attributed to competing reactions, such as the reduction of protons, which in an aqueous buffer solution can produce hydrogen gas (H₂). This hydrogen evolution can interfere with UA detection. Additionally, the produced H₂ molecules may adsorb onto the electrode surface (Figure 5), occupying active sites that could otherwise be used for UA detection, thereby reducing the effective surface area available for UA oxidation and, consequently, decreasing the current. The saturation of the electrode surface, where all active sites are occupied, also contributes to this current drop, as further accumulation does not enhance the signal and may even lead to surface fouling. Nanoparticles play a crucial role in enhancing the sensitivity of the detection system due to their large surface area, which allows for rapid adsorption of UA molecules. The inclusion of nanoparticles such as SiO₂ and MWCNT significantly improves the sensor's sensitivity. The choice of a 5-minute accumulation time as the optimal duration balances maximizing the current response with avoiding negative effects such as hydrogen evolution and surface saturation, thereby ensuring the best possible sensitivity and reliability of the sensor. The GCE/CTAB@SiO₂@MWCNT-APTES electrode demonstrates excellent sensitivity due to its improved adsorption capabilities and effective electron transfer properties provided by the nanoparticles, with reasonable selectivity for UA [45-46].
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Influence of a) the amount of matrix deposited on the electrode, b) drying time, c) pH values of the buffer solution, and d) Accumulation time during the detection step on the voltammetric response of CGE/ electrode in 0.1 molL⁻¹ PBS buffer solution contained 10⁻⁵ molL⁻¹ of UA.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Schematic representation of the reaction between matrix and UA</figcaption></figure>

### 3.2.2 Detection of Uric acid

The performance of the glassy carbon electrode modified with CTAB@SiO₂@MWCNT-APTES was investigated over different concentrations of uric acid (UA). **Figure 6a** shows the differential pulse voltammogram of UA at different concentrations, showing an increase in the anodic current peak corresponding to higher UA concentrations. The calibration curve shown in **Figure 6b** has a peak potential (ipa) value of +0.300 V, two distinct linear regions were observed, which can be attributed to the transition in the electrochemical oxidation of uric acid. At lower concentrations (5×10⁻⁹ to 1×10⁻⁸ mol L⁻¹), the process is diffusion-controlled, while at higher concentrations (1.25×10⁻⁸ to 1×10⁻⁷ mol L⁻¹), it is surface-controlled. These regions exhibited high coefficients of determination, approximately 0.9961 and 0.9985, respectively. It should be noted that the detection limit was remarkably low, at 5×10⁻⁶ mmolL⁻¹ (S/N = 3). This value is well below the concentration recommended by the World Health Organization, which states that normal uric acid concentrations in urine may be in the order of 0.24 to
0.75 mmolL⁻¹ (millimoles per liter), or around 4 to 12 mg/dL (milligrams per deciliter). These values may vary slightly according to population and specific health conditions [47]. The limit of detection (LOD) was determined using the formula $LOD = 3Sb/m$, where Sb represents the standard deviation of the blank signal, blank signal and m denotes the slope of the calibration curve, where calculations based on the linear regression equation (Figure 6b) indicated a sensitivity of $2.7×10^7$ A·µLmol⁻¹ for the electrode. A comparison of electrode performance for UA detection, presented in Table 1, showed that the CTAB@SiO₂@MWCNT-APTES modified GCE electrode had a lower LOD compared to other electrodes, establishing it as a promising alternative sensing material for UA determination.

<figure><img src="image_7.png" /></figure>
<figure><img src="image_8.png" /><figcaption>**Figure6.** a) Differential pulse voltammograms for Uric acid on the GCE GCE/CTAB@SiO₂@MWCNT-APTES/ electrode (Drying time 2h, casting solution 7µL, accumulation time 5 min PBS solution (pH = 7 )). b) Calibration curve of UA on GCE/CTAB@SiO₂@MWCNT-APTES electrode.</figcaption></figure>

<table><caption>**Table1.** Comparison with other electrochemical sensors for the determination of Uric acid by DPV</caption><thead><tr><td>Electrochemical sensor</td><td>Linear dynamic range (molL<sup>-1</sup>)</td><td>Limit of Detection (mmolL<sup>-1</sup>)</td><td>References</td></tr></thead><tbody><tr><td>SnO<sub>2</sub>-NP/MWCNTs/CPE</td><td>3.0×10<sup>-6</sup> - 2.0×10<sup>-4</sup></td><td>1×10<sup>-3</sup></td><td>[48]</td></tr><tr><td>nano-Au/p-TA/GCE</td><td>1.6×10<sup>-5</sup> - 2.8×10<sup>-4</sup></td><td>0.8×10<sup>-3</sup></td><td>[49]</td></tr><tr><td>N-DHPB/MWCNT/PE</td><td>5.0×10<sup>-6</sup> - 4.2×10<sup>-4</sup></td><td>2×10<sup>-3</sup></td><td>[50]</td></tr><tr><td>HCNTs/GCE</td><td>6.7×10<sup>-6</sup> - 6.5×10<sup>-5</sup></td><td>1.5×10<sup>-3</sup></td><td>[51]</td></tr><tr><td>CNT@NF</td><td>4.0×10<sup>-6</sup> - 4.0×10<sup>-4</sup></td><td>1×10<sup>-3</sup></td><td>[52]</td></tr><tr><td>NgB/CPE</td><td>12.5×10<sup>-6</sup> - 7.5×10<sup>-4</sup></td><td>5×10<sup>-3</sup></td><td>[53]</td></tr><tr><td>ZIF-11/GCE</td><td>50×10<sup>-6</sup> - 540×10<sup>-6</sup></td><td>0.48×10<sup>-3</sup></td><td>[54]</td></tr><tr><td>Uricase/carbon nanotube /carboxymethylcellulose electrode</td><td>20×10<sup>-6</sup> - 5000×10<sup>-6</sup></td><td>2.8×10<sup>-3</sup></td><td>[55]</td></tr><tr><td>Methylcellulose/graphene oxide/iron oxide nanohydrogel/GCE</td><td>0.5×10<sup>-6</sup> - 140×10<sup>-6</sup></td><td>0.17×10<sup>-3</sup></td><td>[56]</td></tr><tr><td>Zinc Tetraaminophthalocyanine functionalized graphene nanosheets/GCE</td><td>0.5×10<sup>-6</sup> - 100×10<sup>-6</sup></td><td>0.15×10<sup>-3</sup></td><td>[57]</td></tr><tr><td>CeO<sub>2</sub>/CNT/GCE</td><td>1×10<sup>-8</sup> - 9×10<sup>-4</sup></td><td>2.4×10<sup>-6</sup></td><td>[58]</td></tr><tr><td>Au@NAC-MWCNTs/GCE</td><td>1×10<sup>-7</sup> - 3×10<sup>-4</sup></td><td>4×10<sup>-5</sup></td><td>[59]</td></tr><tr><td>Poly(Rhodamine B)/MWCNT/GCE</td><td>2×10<sup>-6</sup> - 1×10<sup>-4</sup></td><td>5.4×10<sup>-4</sup></td><td>[60]</td></tr><tr><td>Poly(4-(2-pyridylazo)-resorcinol)</td><td>0.01 - 50×10<sup>-6</sup></td><td>1×10<sup>-6</sup></td><td>[61]</td></tr></tbody></table>
<table><tr><td>Poly(4-aminopyridine)</td><td>0.005 - 8×10<sup>-6</sup></td><td>1×10<sup>-6</sup></td><td>[62]</td></tr><tr><td>Poly(glycine)</td><td>0.05 - 4×10<sup>-6</sup></td><td>5×10<sup>-6</sup></td><td>[63]</td></tr><tr><td>GCE/CTAB@SiO<sub>2</sub>@MWCNT-APTES</td><td>5×10<sup>-9</sup> - 1×10<sup>-8</sup><br/>1.25 × 10<sup>-8</sup> - 1×10<sup>-7</sup></td><td>5×10<sup>-6</sup></td><td>This work</td></tr></table>

**SnO<sub>2</sub>-NP**: Tin oxide nanoparticles ; **MWCNTs**: multi-walled carbon nanotubes ; **CPE**: Carbon Paste Electrode ; **nano-Au**: nanoparticles of gold ; **p-TA**: p-toluic acid ; **GCE**: Glassy Carbon Electrode ; **N-DHPB**: N-Dodecylpyridinium Bromide ; **HCNTs**: Hollow Carbon Nanotubes ; **NF**: Nanofiber ; **CTAB**: cetyltrimethylammonium bromide ; **CeO<sub>2</sub>**: Cerium dioxide ; **SiO<sub>2</sub>**: Silicon dioxide ; **APTES**: (3-Aminopropyl)triethoxysilane.

### 3.2.3 Selectivity of the Electrochemical Sensor

The essential criterion in electro-analysis is the GCE/CTAB@SiO<sub>2</sub>@MWCNT-APTES sensor's selectivity for UA over potential interfering molecules. To assess this, we conducted differential pulse voltammetry (DPV) in the presence and absence of interfering species, including dopamine (DA), ascorbic acid (AA), glucose (Glu), and salicylic acid (SA), all investigated in 0.1 molL<sup>-1</sup> PBS. Despite their coexistence in the buffer solution, these molecules, at concentrations of 10<sup>-4</sup> molL<sup>-1</sup> did not impact the oxidation current of UA. The observed changes in current were negligible (signal change < 6.0% decrease), as illustrated in **Figure 7** and **8** These findings affirm the high selectivity of the GCE/CTAB@SiO<sub>2</sub>@MWCNT-APTES sensor for UA detection, demonstrating its reliability in the presence of various interfering substances.

<figure><img src="image_9.png" /></figure>
<figure><img src="image_10.png" /><figcaption>**Figure 7.** Differential pulse voltammograms of GCE/CTAB@SiO₂@MWCNT-APTES with different UA concentrations in the presence of potential interfering ions (a) SA, (b) AA, (c) DA, and, (d) Glu.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 8.** Histogram of current peaks of UA in the presence of glucose(Glu), dopamine (DA), ascorbic acid (AA), and salicylic acid (SA), on the selectivity of the GCE/CTAB@SiO₂@MWCNT-APTES</figcaption></figure>
electrode. Data were recorded at the accumulation time of 5 min in PBS buffer solution (pH = 7) containing 1×10⁻⁴ molL⁻¹ for each of the different interferents.

### 3.2.4 Reproducibility and repeatability test

In order to evaluate the recovery of the designed electrochemical sensor, we used the same electrode to continuously determine the DPV response of 1×10⁻⁴ molL⁻¹ UA for 6 times under optimized experimental conditions, and the RSD (relative standard deviation) value was 5.97% indicating that the modified electrode had good recovery (Figure 9a, b). After use, the sensor was regenerated four times by immersing it in a 0.1 molL⁻¹ PBS solution for 20 minutes, in order to eliminate adsorbed UA on the electrode surface. It was then rinsed with water (3 times) and dried at room temperature for 1 hour. Also, to study the repeatability of GCE/CTAB@SiO₂@MWCNT-APTES five modified electrodes prepared by the same method were used to measure the concentration of UA, and the results were satisfactory. The RSD value for UA was 3.91%, indicating that the preparation method had good reproducibility (Figure 9c, d).

<figure><img src="image_12.png" /></figure>
<figure><img src="image_13.png" /><figcaption>**Figure 10.** The assessment of the sensor's repeatability and reproducibility toward a concentration of 1×10⁻⁴ molL⁻¹ UA was conducted using a single GCE/CTAB@SiO₂@MWCNT-APTES modified electrode that had undergone regeneration through five cycles with 0.1 molL⁻¹ PBS at pH 7 (a, b). Furthermore, an exploration of five distinct GCE/CTAB@SiO₂@MWCNT-APTES modified electrodes and the same protocol was consistently applied in the preparation of these electrodes (c, d).</figcaption></figure>

### 3.3 Applications to Real Samples Analysis

The performance of the GCE/CTAB@SiO₂@MWCNT-APTES was evaluated by its application for the detection of uric acid in real urine samples. A recovery method was used to quantify uric acid in the urine samples. In this method, 1 mL of a human urine sample was filtered with a membrane and then diluted with 0.1 molL⁻¹ PBS (pH 7.0) at a ratio of 1:99. The aim of diluting the analyte is to reduce the analyte concentration to a level where the analyte becomes saturated at high analyte concentrations, which reduces detection accuracy and linearity. Diluting the sample prevents this saturation.

Urine also contains various components that can interfere with the detection of uric acid. Diluting the sample reduces the concentration of these interfering substances, which improves selectivity and accuracy. The 100-fold dilution of the urine sample is crucial for optimizing the electrochemical detection of uric acid. It prevents saturation of the electrode, reduces interfering factors and ensures that the uric
acid concentration is within the detection range of the electrode. The results obtained are consistent with this approach and confirm the accuracy of your measurements. **Table 2** shows that the sensor achieves recovery rates of 78 % to 104 %, which underlines its practical applicability in real sample analysis for uric acid determination. Subsequently, these prepared samples were subjected to DPV analysis using the GCE/CTAB@SiO₂@MWCNT-APTES modified electrode.

<table><caption>**Table 2** demonstrated satisfactory outcomes, with a recovery ranging from 78.4 to 104.4%.</caption><thead><tr><th>Sample</th><th>Added conc.<br>(molL<sup>-1</sup>)</th><th>Measured conc.<br>(molL<sup>-1</sup>)</th><th>Recovery (%)</th></tr></thead><tbody><tr><td rowspan="3">Urine</td><td>0</td><td>1.10×10<sup>-8</sup></td><td>0</td></tr><tr><td>1.09 ×10<sup>-8</sup></td><td>2.10 ×10<sup>-8</sup></td><td>91.74</td></tr><tr><td>2.5 ×10<sup>-7</sup></td><td>3.70 ×10<sup>-7</sup></td><td>104</td></tr><tr><td rowspan="3">Plasma</td><td>0</td><td>N.D*</td><td>-----</td></tr><tr><td>1.25 ×10<sup>-8</sup></td><td>1.2×10<sup>-8</sup></td><td>96</td></tr><tr><td>2.5 ×10<sup>-7</sup></td><td>2.55 ×10<sup>-7</sup></td><td>102</td></tr></tbody></table>

N.D*: non-detected

## 4. Conclusions

In this study, we synthesized CTAB@SiO₂@MWCNT-APTES nanoparticles by the sol-gel method and used them to prepare a GCE/CTAB@SiO₂@MWCNT-APTES by coating a glassy carbon electrode for the detection of uric acid. The result showed significant electrocatalytic activity, increased sensitivity and selectivity in the oxidation of uric acid at pH 7. This sensor yielded satisfactory outcomes for uric acid determination, with a Limit of Detection (LOD) about 5 ×10⁻⁶ mmolL⁻¹ under optimal conditions, spanning linearity ranges: 5×10⁻⁹ to 1×10⁻⁸ and 1.25 ×10⁻⁸ to 1×10⁻⁷ molL⁻¹. These values are lower and comparable to those reported for other modified electrodes. Finally, the practical effectiveness of the sensor was underlined by its consistently high recovery rates, which were between 78% and 104% for all samples tested. The excellent precision and dependability of this composite validate its effectiveness for the selective detection of uric acid in actual samples.
## Acknowledgements

This research was financially supported by the Department of Chemistry of Gafsa. Faculty of Sciences of Gafsa, Tunisia as part of a work-study scholarship at the Department of Molecular Chemistry DCM (BioCEN), at the University of Grenoble-Alpes. Furthermore, the authors would like to thank the PMIEL Chemistry NanoBio ICMG FR 2607 (PCN-ICMG) platform for its assistance in conducting SEM and TEM studies.

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