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. 2026 Oct 6. Online ahead of print. doi: 10.1039/d6ra04782c

Poly(bromocresol green) modified screen-printed carbon electrode for selective voltametric detection of uric acid

Fentaye Fetene Alemu a, Melese Shiferaw Kebede b,✉
PMCID: PMC13639868  PMID: 42840797

Abstract

A poly(bromocresol green)-modified screen-printed carbon electrode (PBCG/SPCE) was fabricated through electropolymerization for the electrochemical determination of uric acid (UA). The modified electrode was characterized using cyclic voltammetry and Fourier transform infrared spectroscopy, confirming successful formation of the poly(bromocresol green) film on the electrode surface. Electrochemical characterization revealed an approximately 50% increase in electroactive surface area compared with the bare electrode, which contributed to improved electron-transfer kinetics and enhanced oxidation peak current for UA detection. The electrocatalytic activity of the polymer film was attributed to facilitated charge transfer and adsorption interactions between UA and the functional groups of the polymeric coating. Differential pulse voltammetry was employed for quantitative determination of UA in 0.1 M phosphate buffer solution (pH 7.0). Under optimized conditions, the sensor exhibited a linear response over the concentration range of 0.1–1000 µM with a detection limit of 0.0212 µM and a limit of quantification of 0.0638 µM. In the presence of ascorbic acid, the modified electrode showed moderate selectivity toward UA, with a selectivity coefficient of 0.23. The sensor also demonstrated good operational stability, with coefficient variations of 2.44% for peak current and 0.39% for peak potential, as well as good reproducibility and repeatability, with relative standard deviations of 2.67% and 2.91%, respectively. Finally, the developed PBCG/SPCE sensor was successfully applied to the determination of UA in human urine samples, indicating its potential utility for low-cost and sensitive clinical analysis.

A poly(bromocresol green)-modified screen-printed carbon electrode (PBCG/SPCE) was fabricated through electropolymerization for the electrochemical determination of uric acid (UA).graphic file with name d6ra04782c-ga.webp

1. Introduction

Uric acid (UA), the final product of purine metabolism, is an important biomarker found in biological fluids such as blood and urine1,2 normal UA concentrations in human serum and urine are approximately 240–520 µM and 1400–4400 µM, respectively.3,4 Abnormal UA levels are associated with several pathological conditions, including hyperuricemia, gout, renal disorders, hypertension, and cardiovascular diseases, whereas reduced UA concentrations have been linked to neurological disorders such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and optic neuritis.3,5 Therefore, accurate and reliable determination of UA in biological samples is of considerable clinical importance.6

Various analytical methods have been developed for UA determination, including capillary electrophoresis,7 high performance liquid chromatography,8 liquid chromatography-tandem mass spectrometry,9 fluorimetry,1 chemiluminescence,10 and ultraviolet-visible spectrophotometery.11 Although these techniques provide high sensitivity and accuracy, they generally require sophisticated instrumentation, extensive sample preparation, and trained personnel, limiting their routine clinical application.12,13 As UA is an electroactive compound, electrochemical sensing has emerged as an attractive alternative because it offers rapid analysis, low cost, simple operation, and compatibility with miniaturized devices.

The analytical performance of electrochemical UA sensors is largely governed by the electrode material and surface modification strategy. Among the available electrode platforms, screen-printed carbon electrodes (SPCEs) have attracted significant attention owing to their low cost, disposable nature, portability, low sample-volume requirements, and suitability for point-of-care applications.14–16 However, the bare SPCE generally exhibits limited sensitivity and poor discrimination against electroactive interferents commonly present in biological samples, such as ascorbic acid and dopamine.

Consequently, numerous surface modification strategies have been explored to improve the electrocatalytic activity and selectivity of SPCEs for UA detection.17,18 These include conducting polymers,19 biomaterials,20 photocatalytic,21 and nanomaterials,22 which have been used to overcome this problem.

Several modified SPCEs have been reported for UA determination, employing modifiers such as graphene-based nanocomposites,23 carbon nanotubes,24 metal nanoparticles,25 conductive polymers,26 and hybrid nanomaterials27 to enhance electron transfer, increase the electroactive surface area, and improve analytical performance. Electropolymerized dye films have also been extensively investigated as electrode modifiers because of their ease of fabrication, stability, and electrocatalytic properties. In particular, poly(bromocresol green) (PBG) has been widely used to modify glassy carbon electrodes and other electrode substrates for the electrochemical determination of numerous analytes. While these studies demonstrate the versatility of PBG as an electrode modifier, they also indicate that the polymer itself is not inherently selective toward UA. Therefore, the selectivity of PBG-modified electrodes depends on the overall sensor design, operating conditions, and the electrochemical discrimination achieved against coexisting interferents rather than on the modifier alone.

The novelty of this work lies in integrating NaOH pretreatment with direct electropolymerization of bromocresol green onto a disposable screen-printed carbon electrode (SPCE) to form a poly(bromocresol green) (PBG) sensing film for uric acid (UA) determination. This one-step polymer deposition on a pretreated electrode eliminates the need for additional immobilization or complex surface-modification procedures, providing a simple and reproducible fabrication strategy. The resulting PBG/SPCE exhibited satisfactory analytical performance, including a nanomolar detection limit, good selectivity, and satisfactory recovery of UA from human urine samples, with performance comparable to previously reported UA sensors.23,26–29

2. Experimental part

2.1. Materials and chemicals

Screen printed carbon electrodes 7102 conductor paste based on carbon; DuPont Ltd (UK) were kindly donated by the INTERFIBIO group at Universitat Rovira I Virgili, Spain, led by Professor Ioanis Katakis. The group has optimized printing procedure to produce a well adhered and uniform film of electrodes measuring thickness (7.5 µm).

The chemicals used in this study included K3[Fe(CN)6](Kira Light, India), (KNO3), NaOH (Scharlau, Spain) and HCl (Nice, India), phosphate buffer solution (PBS, 0.1 M), phosphoric acid buffer solution and acetate buffer solution, uric acid and tartaric acid (Shanghai, China); AA (India-New Delhi), bromocresol green dye (Sigma-Aldrich) and epoxy (Hawassa construction instrument supplier market). All chemicals were of analytical grade and were used as received without further purification. Double-distilled water was used for the preparation of all solutions, and all experiments were performed at room temperature.

2.2. Instrumentation and apparatus

Electrochemical measurements were performed using a BAS 50W voltammetric analyzer interfaced with a computer. A conventional three-electrode system was employed, consisting of a saturated Ag/AgCl reference electrode, a platinum wire counter electrode, and an epoxy-delimited poly(bromocresol green)-modified screen-printed carbon electrode (PBG/SPCE) as the working electrode. Other instruments and apparatus included pH meter (HANNA pH-211 Microprocessor, Germany), refrigerator (Hitachi, Germany), digital analytical balance (ADAM Model AFP-110L, England; capacity: 120 g, precision: pm ±0.0001 g) and a drying oven (Digitheat, J. P. Selecta, Germany) was used during electrode pretreatment. Surface characterization was conducted by recording Fourier-transform infrared (FTIR) spectra on a PerkinElmer FTIR spectrometer (USA) using the KBr pellet technique.

2.3. Electrode preparation & surface treatment

The screen-printed carbon electrodes were cut to the required dimensions and the sensing area was defined by applying epoxy resin to the printed region. The electrodes were then cured in an oven at 100 °C for 5 min to ensure proper adhesion of the epoxy.

Chemical pretreatment of the SPCEs was carried out by immersing the electrodes in 3 M NaOH solution for different exposure times. After treatment, the electrodes were thoroughly rinsed with double-distilled water and dried in an oven at 100 °C for 20 min. Reused electrodes were regenerated by electrochemical activation in 1 M NaOH using cyclic voltammetry over a potential range of 0.0 to 1.0 V.

2.4. Preparation of PBG/SPCE

Poly(bromocresol green)-modified screen-printed carbon electrodes (PBG/SPCEs) were prepared by electropolymerization of bromocresol green onto the pretreated SPCE surface. Electropolymerization was performed in 0.1 M NaOH containing 1 mM bromocresol green by cycling the potential between −1.0 and +1.8 V for 15 consecutive cycles at a scan rate of 100 mV s−1. After polymerization, the modified electrodes were thoroughly rinsed with double-distilled water to remove any loosely adsorbed species and were subsequently used for electrochemical determination of uric acid.

3. Results & discussion

3.1. Electrode pretreatment & characterization

Surface pretreatment procedures can have a significant impact on the heterogeneous electron-transfer kinetics of carbon-based electrodes, which frequently improve the electrochemical response of redox systems by modifying surface composition, morphology, and conductivity.30 Screen-printed carbon electrodes (SPCEs) typically exhibit limited electrochemical activity due to the presence of insulating binders and non-conductive ink components, which reduce the effective graphitic carbon content and hinder electron transfer.31 As a result, appropriate surface pretreatment is required to improve the electrochemical performance of SPCEs.

In this work, a simple chemical pretreatment procedure was employed by immersing the SPCEs in 3 M NaOH for predetermined time intervals and then rinsing with distilled water to remove any residual alkali from the electrode surface. The NaOH treatment is expected to remove loosely bound organic binders, increase surface roughness, and introduce oxygen-containing functional groups, thereby improving surface hydrophilicity and charge-transfer properties.

The effect of immersion time in NaOH solution was investigated. As shown in (Fig. 1A), the peak current increased with increasing treatment time for up to 30 min, after which it decreased. The improvement observed at moderate treatment times can be attributed to the gradual removal of insulating surface contaminants and increased exposure of conductive carbon sites. However, prolonged treatment times can result in excessive surface etching leading to poor electrochemical performance.

Fig. 1. Cyclic voltammograms of 5 mM K3[Fe(CN)6] for varying exposure times 15 minutes to 60 minutes (A) and untreated vs. treated electrodes (B) at a scan rate of 10 mV s−1.

Fig. 1

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As a result, 30 minutes was chosen as the optimal pretreatment time, achieving the best balance of surface activation and structural integrity. Compared to other reported electrode activation methods, such as saturated Na2CO3 treatment32 acidic activation at +1.20 V for 240 s, 0.5 M H2SO4,33 DMF treatment, and 10 mM H2O2 oxidation,34 the proposed NaOH pretreatment is simple, cost-effective, and environmentally friendly while still effectively improving electrode performance.

Cyclic voltammetry was used to evaluate the electrochemical performance of untreated and NaOH-treated electrodes in 5 mM K3[Fe(CN)6]3−/4− with 0.1 M KNO3 as a supporting electrolyte (Fig. 1B). 0.1 M KNO3 supporting electrolyte was to control electrode potentials, eradicate the transport of electroactive species from travelling in the electric field gradients, preserve persistent ionic strength and keep constant pH, this helped ensure that the electrode process was predominantly diffusion-controlled.35 NaOH treatment improved the electron-transfer kinetics and increased the electrochemically active surface area,36 resulting in higher peak currents and smaller peak-to-peak separation (ΔEp = 117 mV) compared with untreated electrodes (ΔEp = 400 mV).

3.2. Modification of the pretreated electrodes

Analytes with slow electron-transfer kinetics frequently exhibit weak electrochemical responses at pristine carbon electrodes because of a limited number of active surface sites and slow charge-transfer processes. To address these limitations, the electrode surface was modified with an electrocatalytically active polymer film. Prior to modification, the screen-printed carbon electrode (SPCE) was treated with 3 M NaOH to increase the density of oxygen-containing functional groups and improve surface hydrophilicity, which increased the electrochemically active surface area and facilitated subsequent polymer deposition.25,37

Poly(bromocresol green) (PBG) was then electropolymerized on the NaOH-treated SPCE using cyclic voltammetry in a solution containing 1 mM bromocresol green and 0.1 M NaOH. The potential was cycled between −1.0 and +1.8 V versus Ag/AgCl at a scan rate of 100 mV s−1. During successive potential cycles, the oxidation of bromocresol green generated reactive radical intermediates that coupled and deposited on the electrode surface, gradually forming a polymer film. The progressive changes observed in the voltammograms (Fig. 2) confirm the successful electropolymerization of bromocresol green on the SPCE surface.

Fig. 2. Successive cyclic voltammogram of 15 cycles for electropolymerization of 1 mM BCG on SPCE surface in 0.1 M NaOH at scan rate of 100 mV s−1.

Fig. 2

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The electropolymerization cycles produced a cathodic peak at −0.6 V as shown in (Fig. 2). During continuous scanning, peak current decreased, indicating the film's continued growth. The resulting PBG film improved of the electrode electrochemical performance by increasing the number of active sites for uric acid oxidation and facilitating electron transfer between the analyte and electrode surface. Furthermore, the functional groups present in the polymer matrix may have facilitated adsorption interactions with uric acid molecules, resulting in increased oxidation current and sensitivity.

3.3. Optimization of electrode conditions

Prior to the determination of uric acid, the electropolymerization conditions for the poly(bromocresol green)-modified screen-printed carbon electrode were optimized. This optimization was expected to yield an electrode with improved analytical performance. To achieve optimal analytical performance, the effects of bromocresol green monomer concentration, scan rate, and number of electropolymerization cycles were systematically investigated.

3.3.1. The effect of electro-polymerization cycles

The thickness and surface morphology of the poly(bromocresol green) (PBG) film were controlled by varying the number of electropolymerization scan cycles using cyclic voltammetry. Because electropolymerization involves the repetitive oxidation and coupling of bromocresol green monomers, increasing the number of cycles causes the polymer film on the SPCE surface to grow more gradually. As a result, the number of scan cycles is critical in determining the film thickness, homogeneity, conductivity, and electrocatalytic activity of the modified electrode.38

The effect of electropolymerization cycles on the electrochemical oxidation of 1 mM uric acid (UA) was studied using differential pulse voltammetry (DPV), as illustrated in (Fig. 3A and B). The oxidation peak current of UA increased with increasing cycle number, indicating the gradual formation of a more uniform and electroactive PBG layer. The improved response can be attributed to the increased surface coverage of the polymer film, which provided additional active sites for UA oxidation and improved electron-transfer kinetics at the electrode/electrolyte interface.

Fig. 3. DPV of 1 mM of UA in 0.1 M PBS (pH 7) at a scan rate of 10 mV s−1 (A) and influences of electropolymerization cycles of bromocresol green on the oxidation current at PBG/SPCE (B) and the effect of bromocresol green concentrations on anodic current of UA (C).

Fig. 3

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3.3.2. The effect of concentration of bromocresol green at electrode surface

The influence of bromocresol green concentration on the electrochemical behavior of the deposited poly(bromocresol green) (PBG) film was investigated over the concentration range of 0.4 mM to 1.4 mM during electropolymerization on the SPCE surface (Fig. 3C). Increasing bromocresol green concentration up to 1.0 mM improved the oxidation current owing to increased polymer coverage. Above this concentration, a decline in current was observed, most likely because a thicker polymer film impeded electron transfer and analyte diffusion. Therefore, 1.0 mM bromocresol green was selected as the optimal concentration for electrode fabrication, as it provided the best balance between active surface coverage and efficient electron-transfer kinetics.

The optimal thickness of the bromocresol green film was achieved after scanning 5 to 20 cycles. As shown in (Fig. 3A and B), the electrode was not completely electrochemically active in the cases of 5 and 10 cycle polymerization due to the insufficient modification. When the cycle count reach 15, the current were at their peak. This produced the strongest currents when the cycles reached 15. This phenomenon could be related to the PBG film's thickness. As a result, 15 cycles of electropolymerization were chosen for further study.

However, after the optimum number of electropolymerization cycles, the oxidation current decreased. This behavior is most likely due to the formation of an excessively thick polymer film, which can impede electron transport through the coating and limit UA diffusion from the bulk solution to the electrode surface. Excessive film thickness may also reduce electroactive sites accessibility of and charge transfer resistance, resulting in a lower electrochemical response. As a result, the optimal number of electropolymerization cycles is required to strike a balance between adequate surface coverage and efficient mass and electron transport.

3.4. Characterization of PBG modified SPCE

3.4.1. Cyclic voltammetry (CV) characterization of PBG/SPCE

As shown in (Fig. 5), characterization in CV was carried out by recording cyclic voltammograms in 5 mM K3[Fe(CN)6] to examine the charge transfer mechanism of the PBG-modified SPCE compared to that of unmodified SPCEs.

Fig. 5. Effects of scan rate on the CV of 5 mM K3[Fe(CN)6] (A) treated SPCE (B) PBG/SPCE at 5, 10, 15, and 20 mV s−1 with corresponding calibration curve plots.

Fig. 5

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Both the treated SPCE and PBG/SPCE exhibited well-defined anodic and cathodic redox peaks, indicating quasi-reversible electron-transfer behavior of electrode surfaces (Fig. 4). However, the PBG/SPCE showed significantly higher anodic and cathodic peak currents compared with the treated SPCE. This suggests that the electrode surface's active sites were expanded via electrochemical polymerization.

Fig. 4. 5 mM K3[Fe(CN)6] in 1 M of KNO3 treated SPCE and PBG/SPCE was used to record a cyclic voltammogram at a scan rate of 10 mV s−1.

Fig. 4

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In addition, the two electrodes exhibited a smaller peak-to-peak potential separation (ΔEp). The peak width at half-height; a more active electrode often gives narrower and more symmetric peaks. A smaller ΔEp value indicates faster electron-transfer kinetics and reduced charge-transfer resistance at the electrode/electrolyte interface. This improvement can be attributed to the conductive nature of the PBG film and the presence of functional groups within the polymer matrix that promote efficient charge transport across the electrode surface.

The enhanced electrochemical response of the PBG/SPCE also suggests that the NaOH pretreatment and subsequent electropolymerization process increased the accessibility of electroactive sites.

3.4.1.1. Determination of effective area

A number of criteria are used to evaluate the performance of screen-printed carbon electrodes (SPCE), including the working electrode's electroactive surface area, the heterogeneous rate constant, and the redox system's peak-to-peak separation.39 As a result, determining the effective electroactive area is a critical step in assessing the impact of surface modification on electrode performance.

In this study, the enhancement in the electrochemically active region was determined by performing the SPCE characterization using cyclic voltammetry. As shown in (Fig. 5) below, a well-defined redox couple with surface-confined properties is confirmed by the redox system's peak currents being exactly proportional to the scan rate.

Based on the scan rate studies, we decided to work with slow scan rate (5, 10, 15, and 20 mV s−1)40 to get clean, symmetrical peaks with minimal background noise from capacitive current and ohmic distortion rather than faster scan rate. Faster scan rate mask surface difference and distort the peaks followed by slow electron transfer. In addition, the oxidation peak potential shifts to more positive potentials showing the kinetic limitation in the electrochemical reaction.41 This makes it is impossible to use the Randles–Sevcik relationship accurately to calculate electroactive surface area.

Moreover, the peak current and peak-to-peak potential separation both act as important indicators to reflect the charge transfer properties at the electrode surface. The observed anodic and cathodic peak current of PBG/SPCE (Ipa/Ipc = 17 µA) was larger than that of the SPCE (Ipa/Ipc = 4.4 µA), and the peak–peak potential separation of the PBG/SPCE was smaller (ΔEp = 102 mV) and for SPCE larger (ΔEp = 117 mV). Therefore, these values indicating that the electrochemical polymerization increased the active sites of the electrode surface.

In general, the electrodes' effective working area was calculated using the Randles–Sevcik relationship for the one-electron redox process of 5 mM K3[Fe(CN)6] and the slopes found for the Ipversus v1/2 graphs. The following parameters were used:Ip = (2.69 × 105)n3/2AD1/2v1/2C*Diffusion coefficient (D) = 7.60 × 10−6 cm2 s−1, number of electrons transferred (n) = 1, and concentration (C) = 5 × 10−6 mol cm−3. According to the graphs and calibration curve in (Fig. 5), the area of the electrode's electroactive portion was 3.98 × 10−2 cm2 (3.98 mm2) prior to modification (Fig. 5A) and 5.958 × 10−2 cm2 (5.958 mm2) after modification (Fig. 5B). The change obtained after modification was 1.978 × 10−2 cm2 (1.978 mm2). This change suggested that an increase in effective area changed electrodes' apparent performance improvement.

3.4.2. Fourier transform infrared (FTIR) characterization of PBG/SPCE

Fourier transform infrared (FTIR) spectroscopy was employed to identify the functional groups present on the electrode surface and to further confirm successful electropolymerization of bromocresol green on the screen-printed carbon electrode (SPCE). FTIR analysis provides important information regarding molecular structure, chemical bonding, and surface functionalization through characteristic vibrational absorption bands. The spectra were recorded using KBr pellet techniques, and the obtained results are presented in (Fig. 6A–D).

Fig. 6. Pristine SPCE (A), SPCE/NaOH (B), bromocresol green (C) and poly(bromocresol green) film (D) Fourier transform infrared spectra.

Fig. 6

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(Fig. 6A and B) show the FTIR spectra of the pristine SPCE and NaOH-treated SPCE, respectively. Compared with the untreated electrode, the NaOH-treated SPCE exhibited sharper and more distinguishable absorption bands. This behavior suggests effective surface cleaning and activation by NaOH treatment, which likely removed adsorbed impurities and introduced oxygen-containing functional groups such as hydroxyl and carboxyl species onto the carbon surface. These surface functionalities can improve hydrophilicity and facilitate subsequent electropolymerization of bromocresol green. (Fig. 6C and D) show the distinctive bands of the poly(bromocresol green) and bromocresol green monomer on SPCE, respectively. After closely examining the spectra, it was evident that the polymerized electrode had downshifted the characteristic (O–H), (–CH3), and (C–H) bands at 3450, 2997, and 2678 cm−1 respectively from the bare electrode to 3427, 2987, and 2658 cm−1. These changes unequivocally support the polymerization process brought on by the bromocresol green poly-reaction. And other characteristic bands such as (–C Created by potrace 1.16, written by Peter Selinger 2001-2019 C), (–S Created by potrace 1.16, written by Peter Selinger 2001-2019 O) and (–C–Br) 1630, 1050 and 571 cm−1 respectively from the bare electrode to 1587, 1050 and 520 cm−1 also appear to the finger print region.

Overall, the FTIR results provide strong evidence for successful electropolymerization of bromocresol green onto the SPCE surface. The spectral changes observed after polymerization are consistent with the formation of a chemically modified and functionally active polymer film capable of enhancing the electrochemical performance of the electrode. The obtained results are also in agreement with previously reported spectroscopic studies of poly(bromocresol green)-modified glassy carbon electrodes.28,29

3.5. Electrochemical oxidation of UA at the PBG/SPCE and quantitative response of PBG/SPCE for UA

DPV was utilized to determine UA using a PBG/SPC electrode to improve resolution and analytical sensitivity. The peak was seen in both treated SPCE and modified PBG/SPCE; PBG/SPCE produced a distinct peak and an increase in peak height over the SPCE electrode, as seen in (Fig. 7A) below:

Fig. 7. DPV of treated SPCE and PBG/SPCE in the presence of 1 mM UA (A) and varying UA concentrations (10, 50, 100 µM–1 mM) (B) in 0.1 M PBS pH 7 with scan rates of 10 mV s−1, pulse periods of 125 ms, and pulse amplitudes of 180 mV, respectively.

Fig. 7

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As illustrated in (Fig. 7A), UA oxidation at the treated SPCE occurred at approximately 0.40 V. The oxidation peak obtained at the unmodified electrode was broad and poorly defined, indicating sluggish electron-transfer kinetics and limited electrocatalytic activity at the pristine carbon surface. The weak and broadened response may also be attributed to surface fouling caused by adsorption of oxidation products of uric acid, which can block active sites and hinder electron transfer during the electrochemical process.

In contrast, the PBG/SPCE exhibited a significantly enhanced voltammetric response toward UA oxidation. A sharper and more intense oxidation peak was observed, accompanied by a slight negative shift in the oxidation potential from 0.40 V to 0.38 V. The increase in peak current indicates that the electropolymerized PBG film improved the electroactive surface area and facilitated electron transfer between UA and the electrode surface. The negative shift in oxidation potential suggests that the PBG coating exerted an electrocatalytic effect by lowering the overpotential required for UA oxidation, thereby making the oxidation process kinetically more favorable.

The quantitative response of the PBG/SPCE toward UA was further investigated by varying the concentration of uric acid, as shown in (Fig. 7B). The oxidation peak current increased progressively with increasing UA concentration under identical experimental conditions, demonstrating that the electrochemical response was strongly dependent on analyte concentration. This behavior indicates efficient electron-transfer kinetics and confirms the suitability of the modified electrode for quantitative determination of UA.

3.6. Optimization of experimental conditions involved in DPV of UA determination

The electrode's electrocatalytic activity and electrochemical reactions, such as peak current and peak potential, are dependent on experimental parameters, primarily pH and a supporting electrolyte. When DPV settings are optimized, the oxidation peak potential also changes from its original value, showing that the modified SPCE speeds up the electron transfer reaction at the electrode surface in addition to increasing peak current and changing peak shape.

3.6.1. Effect of supporting electrolyte and pH of the supporting electrolyte

To reduce solution resistance, a bulk electrolyte is utilized in the majority of voltammetric tests. To determine how the type of supporting electrolyte affected the reaction of uric acid oxidation, the impact of the supporting electrolyte on the DPV response of PBG/SPCE was examined. As illustrated in (Fig. 8A), this influence on the anodic peak current and peak potential of UA at PBG/SPCE was investigated by synthesizing various supporting electrolytes. The voltammogram revealed that 0.1 M PBS had the largest oxidation peak current compared to the others. The electrochemical processes of the analyte are significantly influenced by the pH level of the supporting electrolyte.29 This effect was examined at a scan rate of 10 mV s−1 in a solution containing 1 mM uric acid over a pH range of 4 to 7 (Fig. 8B). The anodic peak current increased with increasing pH up to pH 7, and then decreased at higher pH values beyond the optimum.23 A larger anodic response is obtained at about pH 7. Therefore, it was chosen for further electrochemical experiments.

Fig. 8. DPV of 1 mM UA with PBG/SPCE at a scan rate of 10 mV s−1, pulse amplitude of 180, and pulse period of 125 ms on various supporting electrolytes (A) and pH values (B).

Fig. 8

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The oxidation peak potential (Epa) of UA on PBG/SPCE moved negatively with a rise in pH, as (Fig. 8B) illustrates. This could be related to the analyte's and PBG's charge characteristics (two proton and two electron transfer processes). The following illustrates the potential electrochemical oxidation pathway of UA:3.6.1.

3.7. Calibration and detection limits

The concentration-peak current relationship forms the basis of the calibration curve; standard concentrations of 100 nM, 1 µM, 10 µM, 50 µM, 100 µM, 0.5 mM, and 1 mM were used to record the peak currents. For each serial concentration, the resulting calibration curve was recorded under ideal circumstances (Fig. 9). In order to produce a working or regression equation, the corresponding plot was then created by comparing the peak current to the analyte concentration. The curve revealed that Ip = 0.0906x + 1.013 (R2 = 0.999) is the linear regression equation. Peak current and analyte concentration have a linear relationship, according to this regression correlation coefficient. The high correlation coefficient indicates moderate linearity and confirms the suitability of the modified electrode for quantitative analysis of uric acid.

Fig. 9. DPV at various uric acid concentrations (100 nM–1 mM) in 0.1 M pH 7 PBS at a scan rate of 10 mV s−1, a pulse amplitude of 180 mV, a pulse period of 125 ms, and the associated calibration curve.

Fig. 9

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The linear dynamic range (LDR) corresponds to the concentration interval over which the response remains proportional to analyte concentration without significant deviation. The limit of detection (LOD) and limit of quantification (LOQ) were calculated based on the standard deviation of the blank response and the slope of the calibration curve using the equations LOD = 3σ/S and LOQ = 10σ/S, where σ is the standard deviation of the blank signal and S is the slope of the calibration plot. The moderate analytical performance can be attributed to the enhanced electroactive surface area and improved electron-transfer kinetics provided by the poly(bromocresol green) film, which facilitates efficient oxidation of uric acid even at low concentrations.

To examine the electrode's performance characteristics, such as its LOD, LDR, sensitivity, selectivity, and LOQ, it is imperative to modify the calibration of the current electrode response. Due to the use of sensitive and miniature screen-printed carbon electrodes, as indicated in (Table 1) below, the magnitude of the detection limit and the working concentration range of this study have been established, as illustrated in (Fig. 9), and the results were comparable with those of the earlier researchers.

Table 1. Comparison of the electrochemical performance of current electrode with reported previously ones.

Electrode Modifier used Method LDR (µM) LOD (µM) LOQ (µM) Ref.
GCE MWCNT/PBG DPV 2–350 0.18 — 28
GCE PBG DPV 0.5–200 0.17 — 29
CPE Poly(DPA)SiO2@Fe3O4 DPV 1.2–1.8 0.4 1.2 27
Graphite SPCE Prusian blue/poly(4-ASA)/uricase DPV 10–200 3.0 — 26
SPCE Graphene/ZrO2/GQDs DPV 20–500 1.07 3.55 23
SPCE PBG DPV 0.1–1000 0.0212 0.0638 This work
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(Table 1) makes it abundantly evident that the current electrode's electroanalytical performance is sufficiently comparable to the findings of earlier researchers and demonstrated outstanding performance.

3.8. Real sample analysis

Using the suggested procedure, human urine samples were chosen for analysis. 20 ml of each urine sample were centrifuged at 2000 rpm for twenty minutes. After filtering the supernatant, 0.1 M PBS (pH 6) was diluted ten times. Without undergoing any additional pretreatment, the solution was moved into the voltammetric cell for analysis. After diluting 1 mM UA in 100 ml of 0.1 M PBS, 10 µL and 20 µL of the mixture were added to 20 ml of urine samples in a voltammetric cell. Every answer was examined using the spiking method (Table 2). Recoveries ranging from 90.9 to 100.7% indicate satisfactory accuracy of the proposed method for uric acid determination in urine samples.

Table 2. Determination results of UA in real urine samples (n = 3).

Urine sample Amount of spiked added (µM) Expected (µM) aDetected (µM) from calibration curve (Ip) Found (µM) Recovery (%)
1 0.0 — 19.1 ± 1.1 — —
0.4997 19.5997 19.558 ± 0.5 0.458 91.65
0.999 20.099 20.1 ± 1.1 1 100.1
2 0.0 — 23.5 ± 0.3 — —
0.4997 23.997 23.9879 ± 0.1 0.4879 97.64
0.999 24.499 24.5021 ± 0.5 1.002 100.3
3 0.0 — 14.8 ± 0.2 — —
0.4997 15.2997 15.303 ± 1 0.503 100.66
0.999 15.799 15.708 ± 0.6 0.908 90.89
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a

Mean value ± standard deviation, for three repetitions' in each case and all values are multipliedby factor of ten (dilution factor).

3.9. Interference study and selectivity

Selectivity is a critical parameter for evaluating the analytical performance of an electrochemical sensor, particularly in complex biological matrices where multiple electroactive species may coexist with the target analyte. To assess the selectivity of the developed poly(bromocresol green)-modified SPCE (PBG/SPCE) toward uric acid (UA), the influence of common interfering species was investigated under identical experimental conditions.

As shown in (Fig. 10), typical bioactive compounds such as ascorbic acid (AA) and tartaric acid, (TA) produced oxidation signals at different potentials compared with UA. The clear separation of oxidation peaks indicates that the PBG-modified surface enables effective discrimination of UA based on differences in oxidation potential, thereby minimizing signal overlap and improving analytical resolution.

Fig. 10. DPV of equal conc. 1 mM of AA, UA and TA for each (A) and concentration of (1, 5 and 10) mM AA and TA for each in the presence of 1 mM UA (B) in 0.1 M phosphate buffer solution (pH 7) at the PBG modified SPCE at scan rate of 10 mV s−1, pulse amplitude of 180 mV and pulse period of 125 m s−1.

Fig. 10

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The selectivity of the PBG-modified SPCE against interfering species was determined by calculating the selectivity coefficient. The selectivity coefficient, which is the ratio of current responses of interferents to the target analyte, was found to be 0.23. An electrode demonstrates good selectivity for the analyte when the selectivity coefficient is significantly less than 1.00. Therefore, these results confirm that the PBG/SPCE sensor can selectively detect uric acid even in the presence of common interfering compounds, supporting its applicability for analysis in complex biological samples.

3.10. Repeatability, reproducibility and stability

The analytical performance of the PBG/SPCE sensor was evaluated in terms of repeatability, reproducibility, and long-term stability using differential pulse voltammetry (DPV) for the determination of 1 mM uric acid (UA) under optimized conditions.

Repeatability was assessed by performing four consecutive measurements using the same modified electrode without intermediate surface regeneration. The oxidation peak current showed minimal variation between successive runs, yielding a relative standard deviation (RSD) of 2.91%. This low RSD value indicates that the sensor provides stable and consistent electrochemical responses during repeated use, reflecting good short-term operational reliability.

Reproducibility was evaluated using independently prepared PBG/SPCE electrodes under identical fabrication conditions. The inter-electrode variation in peak current responses for UA determination resulted in an RSD of 2.67%, demonstrating good fabrication consistency and reliable electrode-to-electrode performance.

The long-term stability of the sensor was investigated by storing the modified electrodes under ambient conditions for two weeks, followed by re-evaluation of their electrochemical response. The results showed only a slight decrease in peak current, with an RSD of 2.44%, indicating that the PBG film maintains its structural integrity and electrochemical activity over time. The good stability of the sensor can be attributed to the strong adhesion of the electropolymerized PBG film onto the SPCE surface and the inherent chemical stability of the polymer layer, which helps preserve its electrocatalytic properties during storage and repeated use. Overall, the low RSD values obtained for repeatability, reproducibility, and stability confirm that the developed PBG/SPCE sensor is reliable for practical electrochemical applications.

4. Conclusions

In this study, a poly(bromocresol green)-modified screen-printed carbon electrode (PBG/SPCE) was successfully fabricated via electropolymerization of bromocresol green on a sodium hydroxide-treated carbon surface for the electrochemical determination of uric acid (UA). The NaOH pretreatment and subsequent polymer modification significantly enhanced the electrochemical properties of the electrode, leading to improved electron-transfer kinetics and increased electroactive surface area. The modified electrode was thoroughly characterized using cyclic voltammetry and Fourier transform infrared spectroscopy, provided evidence for the formation of the PBG film and its effective immobilization on the SPCE surface. Under optimized differential pulse voltammetry conditions, the sensor exhibited a wide linear dynamic range, low detection limit in the nanomolar range, and satisfactory sensitivity toward UA. The proposed sensor demonstrated acceptable selectivity in the presence of common interfering species such as ascorbic acid and tartaric acid, indicating its suitability for analysis in complex matrices. In addition, satisfactory recovery values obtained from human urine samples confirmed the practical applicability of the developed sensor for real sample analysis. Generally, the developed PBG/SPCE sensor provides a simple, low-cost, and effective electrochemical platform for the sensitive determination of uric acid in human urine samples.

Ethical statement

All experiments involving human urine samples were conducted in accordance with relevant laws and institutional guidelines and were approved by the Department of Chemistry, College of Natural and Computational Sciences, Debre Tabor University. Informed consent was obtained from all human subjects.

Author contributions

Fentaye Fetene Alemu: conceptualization, data analysis, writing – original draft, resources, investigation, methodology, reviewing and editing. Melese Shiferaw Kebede: reviewing, supervision, reviewing and editing, and data curation.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The all the data supporting this study are included within this article.

References

  1. Stark K. et al., Common polymorphisms influencing serum uric acid levels contribute to susceptibility to gout, but not to coronary artery disease. PLoS One. 2009;4(11):e7729. doi: 10.1371/journal.pone.0007729. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Lee S. J. Oh B. K. Sung K. C. Uric acid and cardiometabolic diseases. Clin. Hypertens. 2020;26:13. doi: 10.1186/s40885-020-00146-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Alipour E. et al., Determination of uric acid in biological samples on the pretreated pencil graphite electrode. Anal. Methods. 2012;4(8):2288–2295. doi: 10.1039/C2AY25463H. [DOI] [Google Scholar]
  4. Saito Y. et al., Uric acid and cardiovascular disease: A clinical review. J. Cardiol. 2021;78(1):51–57. doi: 10.1016/j.jjcc.2020.12.013. [DOI] [PubMed] [Google Scholar]
  5. Nishizawa H. Maeda N. Shimomura I. Impact of hyperuricemia on chronic kidney disease and atherosclerotic cardiovascular disease. Hypertens. Res. 2022;45(4):635–640. doi: 10.1038/s41440-021-00840-w. [DOI] [PubMed] [Google Scholar]
  6. Johnson R. J. et al., Is there a pathogenetic role for uric acid in hypertension and cardiovascular and renal disease? Hypertension. 2003;41(6):1183–1190. doi: 10.1161/01.HYP.0000069700.62727.C5. [DOI] [PubMed] [Google Scholar]
  7. Zhao S. et al., Determination of uric acid in human urine and serum by capillary electrophoresis with chemiluminescence detection. Anal. Biochem. 2008;378(2):127–131. doi: 10.1016/j.ab.2008.04.014. [DOI] [PubMed] [Google Scholar]
  8. Perelló J. Sanchis P. Grases F. Determination of uric acid in urine, saliva and calcium oxalate renal calculi by high-performance liquid chromatography/mass spectrometry. J. Chromatogr. B. 2005;824(1–2):175–180. doi: 10.1016/j.jchromb.2005.07.024. [DOI] [PubMed] [Google Scholar]
  9. Sakurai T. Irii T. Iwadate K. Simultaneous quantification of urea, uric acid, and creatinine in human urine by liquid chromatography/mass spectrometry. J. Leg. Med. 2022;55:102011. doi: 10.1016/j.legalmed.2021.102011. [DOI] [PubMed] [Google Scholar]
  10. Chen Z. Zu Y. Selective detection of uric acid in the presence of ascorbic acid based on electrochemiluminescence quenching. J. Electroanal. Chem. 2008;612(1):151–155. doi: 10.1016/j.jelechem.2007.09.018. [DOI] [Google Scholar]
  11. Norazmi N. and et al., Uric acid detection using uv-vis spectrometer, in IOP Conference Series: Materials Science and Engineering, IOP Publishing, 2017 [Google Scholar]
  12. Aafria S. et al., Electrochemical biosensing of uric acid: A review. Microchem. J. 2022;182:1–14. doi: 10.1016/j.microc.2022.107945. [DOI] [Google Scholar]
  13. Bahadir E. B. Sezginturk M. K. Applications of commercial biosensors in clinical, food, environmental, and biothreat/biowarfare analyses. Anal. Biochem. 2015;478:107–120. doi: 10.1016/j.ab.2015.03.011. [DOI] [PubMed] [Google Scholar]
  14. Zhao G. Wang H. Liu G. Recent advances in chemically modified electrodes, microfabricated devices and injection systems for the electrochemical detection of heavy metals: A review. Int. J. Electrochem. Sci. 2017;12(9):8622–8641. doi: 10.20964/2017.09.39. [DOI] [Google Scholar]
  15. Taleat Z. Khoshroo A. Mazloum-Ardakani M. Screen-printed electrodes for biosensing: a review (2008–2013) Microchim. Acta. 2014;181(9–10):865–891. doi: 10.1007/s00604-014-1181-1. [DOI] [Google Scholar]
  16. Kubo I. Fujita K. Nihei K. Molecular design of multifunctional antibacterial agents against methicillin resistant Staphylococcus aureus (MRSA) Bioorg. Med. Chem. 2003;11(19):4255–4262. doi: 10.1016/S0968-0896(03)00433-4. [DOI] [PubMed] [Google Scholar]
  17. Reshetilov A., Zyrina N. and Zheleznaya L., Portable Biosensing of Food Toxicants and Environmental Pollutants, Taylor and Francis,, London: 2013, pp. 243–258 [Google Scholar]
  18. Wang J. Electrochemical biosensors: towards point-of-care cancer diagnostics. Biosens. Bioelectron. 2006;21(10):1887–1892. doi: 10.1016/j.bios.2005.10.027. [DOI] [PubMed] [Google Scholar]
  19. Revin S. B. John S. A. Highly sensitive determination of uric acid in the presence of major interferents using a conducting polymer film modified electrode. Bioelectrochemistry. 2012;88:22–29. doi: 10.1016/j.bioelechem.2012.05.005. [DOI] [PubMed] [Google Scholar]
  20. Kaviyarasu K. et al., Photocatalytic performance and antimicrobial activities of HAp-TiO2 nanocomposite thin films by sol-gel method. Surf. Interfaces. 2017;6:247–255. doi: 10.1016/j.surfin.2016.10.002. [DOI] [Google Scholar]
  21. Maria Magdalane C. et al., hydrogenation by UV–illuminated CeO2/CdO multilayered nanoplatelet arrays: Investigation of antifungal and antimicrobial activities. J. Photochem. Photobiol., B. 2017;169:110–123. doi: 10.1016/j.jphotobiol.2017.03.008. [DOI] [PubMed] [Google Scholar]
  22. Kasinathan K. et al., Photodegradation of organic pollutants RhB dye using UV simulated sunlight on ceria based TiO2 nanomaterials for antibacterial applications. Sci. Rep. 2016;6:38064. doi: 10.1038/srep38064. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Zhou Q. Chang D. Pan H. Determination of uric acid in clinical samples using screen-printed carbon electrode assemblies modified with graphene/ZrO2/GQDs polymeric film. Results Chem. 2025:102527. doi: 10.1016/j.rechem.2025.102527. [DOI] [Google Scholar]
  24. Sihombing Y. A. et al., Enhanced uric acid detection using functionalized multi-walled carbon nanotube/AgNi nanocomposites: A comparative study on screen-printed carbon electrode (SPCE) and fabric-based biosensors. Sens. Actuators Rep. 2024;8:1–12. [Google Scholar]
  25. Ma K. et al., Electrochemical Sensor Nanoarchitectonics for Sensitive Detection of Uric Acid in Human Whole Blood Based on Screen-Printed Carbon Electrode Equipped with Vertically-Ordered Mesoporous Silica-Nanochannel Film. Nanomaterials. 2022;12(7):3. doi: 10.3390/nano12071157. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. da Cruz F. S. et al., Electrochemical detection of uric acid using graphite screen-printed electrodes modified with Prussian blue/poly (4-aminosalicylic acid)/Uricase. J. Electroanal. Chem. 2017;806:172–179. doi: 10.1016/j.jelechem.2017.10.070. [DOI] [Google Scholar]
  27. Reddy Y. V. M. et al., Electrochemical sensor for detection of uric acid in the presence of ascorbic acid and dopamine using the poly (DPA)/SiO2@ Fe3O4 modified carbon paste electrode. J. Electroanal. Chem. 2018;820:168–175. doi: 10.1016/j.jelechem.2018.04.059. [DOI] [Google Scholar]
  28. Hou J.-Y. Ai S.-Y. Electrochemical determination of reduced glutathione at multiwalled carbon nanotubes/poly (bromocresol green) modified glassy carbon electrode. Biosensors. 2011;20:21. [Google Scholar]
  29. Ouyang X. et al., Simultaneous determination of uric acid, dopamine and ascorbic acid based on poly (bromocresol green) modified glassy carbon electrode. J. Electroanal. Chem. 2015;748:1–7. doi: 10.1016/j.jelechem.2015.04.026. [DOI] [Google Scholar]
  30. Jia X. Dong S. Wang E. Engineering the bioelectrochemical interface using functional nanomaterials and microchip technique toward sensitive and portable electrochemical biosensors. Biosens. Bioelectron. 2016;76:80–90. doi: 10.1016/j.bios.2015.05.037. [DOI] [PubMed] [Google Scholar]
  31. Washe A. P. et al., Facile and versatile approaches to enhancing electrochemical performance of screen printed electrodes. Electrochim. Acta. 2013;91:166–172. doi: 10.1016/j.electacta.2012.12.110. [DOI] [Google Scholar]
  32. Dossi C. et al., Exploiting chemistry to improve performance of screen-printed, bismuth film electrodes (SP-BiFE) Biosensors. 2016;6(3):38. doi: 10.3390/bios6030038. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Tudorache M. Bala C. Biosensors based on screen-printing technology, and their applications in environmental and food analysis. Anal. Bioanal. Chem. 2007;388(3):565–578. doi: 10.1007/s00216-007-1293-0. [DOI] [PubMed] [Google Scholar]
  34. González-Sánchez M. I. et al., Highly activated screen-printed carbon electrodes by electrochemical treatment with hydrogen peroxide. Electrochem. Commun. 2018;91:36–40. doi: 10.1016/j.elecom.2018.05.002. [DOI] [Google Scholar]
  35. Beshahwored S. Cyclic voltammetric (CV) evaluation of electro chemical behaviors of K3 [Fe (CN) 6] and uric acid. Int. J. Nat. Sci. Res. 2020;8(2):52–59. [Google Scholar]
  36. Paimard G. Ghasali E. Baeza M. Screen-Printed Electrodes: Fabrication, Modification, and Biosensing Applications. Chemosensors. 2023;11(2):6. doi: 10.3390/chemosensors11020113. [DOI] [Google Scholar]
  37. Ouyang X. et al., Simultaneous determination of uric acid, dopamine and ascorbic acid based on poly(bromocresol green) modified glassy carbon electrode. J. Electroanal. Chem. 2015;748:1–7. doi: 10.1016/j.jelechem.2015.04.026. [DOI] [Google Scholar]
  38. Kodakat K. Girish Kumar K. Fabrication and comprehensive comparison of the performance of chemically modified GCE and SPCE for the simultaneous determination of uric acid and vanillylmandelic acid. Microchem. J. 2024;197:2. doi: 10.1016/j.microc.2023.109767. [DOI] [Google Scholar]
  39. Sekli-Belaidi F. Temple-Boyer P. Gros P. Voltammetric microsensor using PEDOT-modified gold electrode for the simultaneous assay of ascorbic and uric acids. J. Electroanal. Chem. 2010;647(2):159–168. doi: 10.1016/j.jelechem.2010.06.007. [DOI] [Google Scholar]
  40. Metto M. et al., Voltammetric determination of uric acid in clinical serum samples using DMF modified screen printed carbon electrodes. Int. J. Electrochem. 2019;2019(1):6318515. doi: 10.1155/2019/6318515. [DOI] [Google Scholar]
  41. Shahamirifard S. A. et al., A simple ultrasensitive electrochemical sensor for simultaneous determination of gallic acid and uric acid in human urine and fruit juices based on zirconia-choline chloride-gold nanoparticles-modified carbon paste electrode. Biosens. Bioelectron. 2018;114:30–36. doi: 10.1016/j.bios.2018.05.009. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The all the data supporting this study are included within this article.

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