Aptamer biosensor for label-free impedance spectroscopy detection of thrombin based on gold nanoparticles

This paper presents a simple electrochemical impedance spectroscopy (EIS) aptasensor based on an anti-thrombin-aptamer as a molecular recognition element. Improvement in sensitivity was achieved by utilizing gold nanoparticles (AuNPs), which were self-assembled on the surface of a bare electrode by using 1,6-Hexanedithiol as a medium. To quantify the amount of thrombin, changes in the interfacial electron transfer resistance (R_et) of the aptasensor were monitored using the redox couple of an [Fe(CN)₆]^3−/4− probe. The plot of (Reti−Ret₀)/Ret₀ against the logarithm of thrombin concentration is linear with over the range from 0.1 nM to 30 nM with a detection limit of 0.013 nM. Meanwhile, the packing density of aptamers was determined by cyclic voltammetric (CV) studies of redox cations (e.g., [Ru(NH₃)₆]³⁺) which were electrostatically bound to the DNA phosphate backbones. The results indicate that the total amount of aptamer probes immobilized on the gold nanoparticle surface is sixfold higher than that on the bare electrode. The aptasensor also showed good selectivity for thrombin without being affected by the presence of other proteins.     

Effect of La2CuO4 electrode area on potentiometric NOx sensor response and its implications on sensing mechanism

The intent of this work is to look at the effects of varying the La₂CuO₄ electrode area and the asymmetry between the sensing and counter electrode in a solid state potentiometric sensor with respect to NO_x sensitivity. NO₂ sensitivity was observed at 500-600 °C with a maximum sensitivity of ∼22 mV/decade [NO₂] observed at 500 °C for the sensor with a La₂CuO₄ electrode area of ∼30 mm². The relationship between NO₂ sensitivity and area is nearly parabolic at 500 °C, decreases linearly with increasing electrode area at 600 °C, and was a mixture of parabolic and linear behavior 550 °C. NO sensitivity varied non-linearly with electrode area with a minima (maximum sensitivity) of ∼−22 mV/decade [NO] at 450 °C for the sensor with a La₂CuO₄ electrode area of 16 mm². The behavior at 400 °C was similar to that of 450 °C, but with smaller sensitivities due to a saturation effect. At 500 °C, NO sensitivity decreases linearly with area.We also used electrochemical impedance spectroscopy (EIS) to investigate the electrochemical processes that are affected when the sensing electrode area is changed. Changes in impedance with exposure to NO_x were attributed to either changes in La₂CuO₄ conductivity due to gas adsorption (high frequency impedance) or electrocatalysis occurring at the electrode/electrolyte interface (total electrode impedance). NO₂ caused a decrease in high frequency impedance while NO caused an increase. In contrast, NO₂ and NO both caused a decrease in the total electrode impedance. The effect of area on both the potentiometric and impedance responses show relationships that can be explained through the mechanistic contributions included in differential electrode equilibria.     

Direct electrochemistry and electrocatalysis of hemoglobin immobilized into poly (lactic-co-glycolic acid)/room temperature ionic liquid composite film

A promising material of poly(lactic-co-glycolic acid) (PLGA) and, room temperature ionic liquid (ILs) (1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF₄) was firstly used as an immobilization matrix to entrap proteins and its bioelectrochemical properties were studied. Direct electrochemistry and electrocatalytic behaviors of hemoglobin (Hb) entrapped in the PLGA/ILs composite film on the surface of glass carbon electrode were investigated. UV-vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well-defined redox peaks of Hb was obtained at the Hb/PLGA/ILs composite film-modified GC electrode through direct electron transfer between the protein and the underlying electrode. The proposed biosensor showed good reproducibility and high sensitivity to H₂O₂ with the detection limit of 2.37 × 10⁻⁷ M (S/N = 3). In the range of 5.0 × 10⁻⁶ to 8.05 × 10⁻³ M, the catalytic reduction current of H₂O₂ was proportional to its concentration. The apparent Michaelis-Menten constant of Hb in the PLGA/ILs composite film was estimated to be 0.069 mM, showing its high affinity.     

Electrocatalytic reduction of hydrogen peroxide and its determination in antiseptic and soft-glass cleaning solutions at phosphotungstate-doped-glutaraldehyde-cross-linked poly-l-lysine film electrodes

The present work describes the electrocatalytic behavior of phosphotungstate-doped glutaraldehyde-cross-linked poly-l-lysine (PLL-GA-PW) film electrode towards reduction of hydrogen peroxide (H₂O₂) in acidic medium. The modified electrode was prepared by means of electrostatically trapping the phosphotungstate anion into the cationic PLL-GA coating on glassy carbon electrode. The PLL-GA-PW film electrode showed excellent electrocatalytic activity towards H₂O₂ reduction in 0.1 M H₂SO₄. Under the optimized conditions, the electrochemical sensor exhibited a linear response for H₂O₂ concentration over the range 2.5 × 10⁻⁶ to 6.85 × 10⁻³ M with a sensitivity of 1.69 μA mM⁻¹. The curvature in the calibration curve at high concentration is explained in terms of Michaelis-Menten (MM) saturation kinetics, and the kinetics parameters calculated by three different methods were compared. The PLL-GA-PW film electrode did not respond to potential interferents such as dopamine, ascorbic acid and uric acid. This unique feature of PLL-GA-PW film electrode allowed selective determination of H₂O₂. Finally, the proposed electrochemical sensor was successfully applied to determine H₂O₂ in commercially available antiseptic solution and soft-contact lenses cleaning solution and the method has been validated using independent estimation by classical potassium permanganate titration method. Major advantages of the method are simple electrode fabrication, stability and high selectivity towards hydrogen peroxide.     

A novel bienzyme glucose biosensor based on three-layer Au-Fe3O4@SiO2 magnetic nanocomposite

The magnetic core-shell Au-Fe₃O₄@SiO₂ nanocomposite was prepared by layer-by-layer assembly technique and was used to fabricate a novel bienzyme glucose biosensor. Glucose oxidase (GOD) and horseradish peroxidase (HRP) were simply mixed with Au-Fe₃O₄@SiO₂ nanocomposite and cross-linked on the ITO magnetism-electrode with nafion (Nf) and glutaraldehyde (GA). The modified electrode was designated as Nf-GOD-HRP/Au-Fe₃O₄@SiO₂/ITO. The effects of some experimental variables such as the pH of supporting electrolyte, enzyme loading, the concentration of the mediator methylene blue (MB) and the applied potential were investigated. The electrochemical behavior of the biosensor was studied using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry. Under the optimized conditions, the biosensor showed a wide dynamic range for the detection of glucose with linear ranges of 0.05-1.0 mM and 1.0-8.0 mM, and the detection limit was estimated as 0.01 mM at a signal-to-noise ratio of 3. The biosensor exhibited a rapid response, good stability and anti-interference ability. Furthermore, the biosensor was successfully applied to detect glucose in human serum samples, showing acceptable accuracy with the clinical method.     

Calculation and correlation of the Na2SO4–NaCl–H2O2–H2O system at the temperature 288.15 K using the extended Pitzer model

The extended Pitzer model has been used for calculation and correlation of the ternary NaCl–H₂O₂–H₂O, Na₂SO₄–H₂O₂–H₂O and the quaternary Na₂SO₄–NaCl–H₂O₂–H₂O systems at the temperature of 288.15 K. The necessary thermodynamic functions (binary and ternary parameters of interaction and thermodynamic solubility products) have been derived from a least-squares optimization procedure with couples activity coefficient with solubility data and the theoretical solubility isotherms has been plotted. Good agreement with experimental solubility for ternary and quaternary mixtures indicates that the model can be successfully used to predict the component solubility of the electrolyte–nonelectrolytes–water systems containing peroxide. In addition, the Pitzer interaction parameters and the thermodynamic solubility product of 4Na₂SO₄⋅2H₂O₂⋅NaCl and Na₂SO₄⋅0.5H₂O₂⋅H₂O at 288.15 K are obtained.     

Hybridization biosensor based on the covalent immobilization of probe DNA on chitosan-mutiwalled carbon nanotubes nanocomposite by using glutaraldehyde as an arm linker

A label-free DNA biosensor for hybridization detection of short DNA species related to the transgenic plants gene fragment of cauliflower mosaic virus (CaMV) 35S promoter was developed in this paper. The nanocomposite containing chitosan (CS) and mutiwalled carbon nanotubes (MWNTs) was first coated on a glassy carbon electrode. Then a highly reactive dialdehyde reagent of glutaraldehyde (GTD) was applied as an arm linker to covalently graft the 5′-amino modified probe DNA to the CS-MWNTs surface via the facile aldehyde-ammonia condensation reaction. The hybridization capacity of the developed biosensor was monitored with electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3−/4− as an indicating probe, and the experimental results showed that the biosensor had fast hybridization rate and low background interference. A wide dynamic detection range (1.0 × 10⁻¹³-5 × 10⁻¹⁰ M) and a low detection limit (8.5 × 10⁻¹⁴ M) were achieved for the complementary sequence. In addition, the hybridization specificity experiments showed that the sensing system can accurately discriminate complementary sequence from mismatch and noncomplementary sequences.     

Potentiometric detection of chromium (III) on the carbon fiber electrode modified by n-hexyl calix[4]resorcinarene

This study was carried out to develop the application of modified carbon fiber electrode in environmental detection, by which chromium (III) ion in water could be electrochemically detected. The modified carbon fiber electrode manifested a linear response within the range of 1.9 × 10⁻⁶–4.6 × 10⁻⁴ mol L⁻¹ (R = 0.9939) and the detection limit was 7.9 × 10⁻⁷ mol L⁻¹. The effect factors were studied to reveal the optimal conditions in the detection of chromium (III) in water, such as pH of total ionic strength adjustment buffer, the concentration of calix[4]resorcinarene, sweep cycles, and so on. The modified carbon fiber electrode, the diameter of which was about 7 μm, was characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy. Also, the proper mechanism was discussed. The identification of chromium (III) was mainly attributed to the cavity of the calix[4]resorcinarene that the chromium (III) ion could enter into the inner of calix[4]resorcinarene because of the particular structure of calix[4]resorcinarene.     

Electrical response characterization of PVA–P(AA/AMPS) IPN hydrogels in aqueous Na2SO4 solution

Interpenetrating polymer networks (IPN) hydrogels composed of poly(vinyl acohol) (PVA) and poly(acrylic acid-co-2-acrylamido-2-methyl propyl sulfonic acid) (P(AA/AMPS)) were synthesized by solution polymerization. The IPN hydrogels were characterized using Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD). The results indicated that strong hydrogen bond was formed between PVA and P(AA/AMPS), and the crystallinity of PVA in IPN hydrogels was declined significantly. The swelling/deswelling properties of IPN hydrogel in aqueous Na₂SO₄ solution were studied. When a sheet of water swollen IPN hydrogel (all the samples were swollen in deionized water) was placed in aqueous Na₂SO₄ solution, the IPN hydrogel shrunk. However, if a voltage was applied, the IPN hydrogel shrunk at high concentration of Na₂SO₄ solution, but swelled at low concentration. The results show that the critical concentration of Na₂SO₄ solution is about 0.005 mol/L. The stimuli response of the IPN hydrogel in electric field was also investigated. When water swollen samples were placed between a pair of electrodes in aqueous Na₂SO₄ solution, the IPN hydrogel showed significant bending behavior upon the application of an electric field. The bending direction of the IPN hydrogel depends on the concentration of Na₂SO₄ solution. At high concentration the IPN hydrogel bended toward anode, contrarily, at low concentration the IPN hydrogel bended toward cathode. The critical concentration of Na₂SO₄ solution is also about 0.005 mol/L. Further investigation showed that the gel component, concentration of aqueous Na₂SO₄ solution and the applied voltage influenced the bending speed of IPN hydrogel.     

Development of an amperometric sulfite biosensor based on sulfite oxidase with cytochrome c,as electron acceptor,and a screen-printed transducer

An amperometric biosensor for sulfite has been developed. The enzyme sulfite oxidase (SOD) and electron acceptor cytochrome c are mixed into the carbon ink that is deposited onto the working electrode of a screen-printed strip. A silver–silver chloride electrode is printed alongside the working electrode and serves as reference/counter electrode. The electrochemical behaviour of the biosensor surface in plain buffer has been investigated by cyclic voltammetry. In the voltage range −0.5 to +0.5 V, a well-defined anodic peak appeared at −0.15 V and a less well-defined anodic peak at about +0.2 V. In the presence of SO₃²⁻, the cyclic voltammogram obtained with the biosensor exhibited an increase in magnitude of the more positive peak; this was considered to result from the electrocatalytic oxidation of SO₃²⁻ involving SOD and the heme (Fe²⁺/Fe³⁺) centre of cytochrome c. Amperometry in stirred solution was used to construct a hydrodynamic voltammogram for SO₃²⁻ using the biosensor; this exhibited a single wave with a plateau beginning at +0.3 V. This wave corresponds to the electrocatalytic response observed by cyclic voltammetry. The pH and concentration of buffer components have been optimised for the determination of SO₃²⁻ by amperometry in stirred solution. Using these conditions, a detection limit of 4 ppm was obtained. The stability of the biosensors was examined after storage in 0.05 M phosphate buffer pH 7.4 at 4°C; it was found that the initial response was retained for at least 45 days. The proposed biosensors were evaluated on samples of unspiked and spiked estuarine, river and tap waters. The recovery and precision data indicated that the devices could be expected to give reliable data in these waters.     

Suppression of NO and SO2 cross-sensitivity in electrochemical CO2 sensors with filter layers

Interfering effects of NO and SO₂ gases on CO₂ sensing performance of the solid state galvanic cell, Pt, O₂, CO₂, Na₂CO₃–BaCO₃ǀǀNa⁺ǀǀNa₂Ti₆O₁₃–TiO₂, O₂, Pt were investigated at 673 K and 773 K. In the interfering gases concentration ranges of 50–150 ppm NO and 5–15 ppm SO₂, exposure to NO gas guaranteed a recovery of electromotive force (EMF) from the relatively small EMF deviation. However, SO₂ gas remarkably degraded the performance of the sensor arising from the formation of sulfate on the sensing electrode. Na₂CO₃–SnO₂, Na₂CO₃–SnO₂–Cu, and Na₂CO₃–SnO₂–CuO were heat-treated and adopted as filter materials adjacent to the sensing electrode. The EMF response of the CO₂ sensors with filters was compared in terms of filter efficiency. Among them, Na₂CO₃–SnO₂–CuO filter showed the most promising characteristics in suppressing NO and SO₂ gas interference.     

Voltammetric studies of the interaction of rutin with DNA and its analytical applications on the MWNTs-COOH/Fe3O4 modified electrode

Multi-walled carbon nanotubes functionalized with a carboxylic acid group (MWNTs-COOH)/iron oxide (Fe₃O₄) modified glassy carbon electrode (MWNTs-COOH/Fe₃O₄/GCE) and DNA/MWNTs-COOH/Fe₃O₄/GCE were prepared. The electrochemical behaviors of rutin (RU) were investigated on MWNTs-COOH/Fe₃O₄/GCE by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in britton-robinson buffer solution (B-R). The interaction of RU with DNA was also explored. Dramatic decrease of peak current without obvious peak potential shift were observed in both cases of DNA in the solution and immobilized on the electrode surface. In addition, the electron transfer coefficient (α) and the rate constant (k_s) kept unchanged in the absence and presence of DNA. So interaction of DNA with RU formed a non-electroactive complex. The binding constant and binding ratio was obtained in the process. The interaction was also confirmed by UV-visible spectroscopy. The reduction peak current was linear with the concentration of RU in the range of 2.50 × 10⁻⁸ to 1.37 × 10⁻⁶ M, with a detection limit of 7.5 nM. The MWNTs-COOH/Fe₃O₄/GCE showed comparatively low detection limit, rapid response, simplicity for the determination of RU.     

Photoelectrocatalytic regeneration of NADH at poly(4,4′-diaminodiphenyl sulfone)/nano TiO2 composite film modified indium tin oxide electrode

Herein we report the photoelectrocatalytic regeneration of NADH at poly(4,4′-diaminodiphenyl sulfone)/nano TiO₂ (PDDS/TiO₂) composite modified indium tin oxide (ITO) electrode. The PDDS film growth was confirmed through in situ electrochemical quartz crystal microbalance (EQCM) studies. The prepared PDDS/TiO₂ composite was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) studies. SEM and AFM results confirmed that TiO₂ nanoparticles size is between 130 and 180 nm. XRD results showed that TiO₂ nanoparticles are crystalline and belong to anatase phase. Electrochemical impedance spectroscopy (EIS) and light induced EIS results substantiate a rapid electron transfer process at PDDS/TiO₂ composite surface. Cyclic voltammetry (CV) results demonstrated that composite film showed excellent response to the photoelectrocatalytic regeneration of NADH. The photoelectrocatalytic oxidation of NADH at composite film surface irradiated for 5 min (optimized irradiation time) produced a notable enhancement in anodic peak current and it was 18-fold higher than that of PDDS film and several folds higher than that of TiO₂ and bare ITO electrodes. Further, composite film showed higher sensitivity of 124.1 μA μM⁻¹ for NADH. From Square wave voltammetry (SWV) results, sensitivity of the irradiated composite film was obtained as 0.252 μA nM⁻¹ of NADH. The linear concentration range was between 23 and 39 nM NADH respectively. Further, the composite film exhibits good selectivity towards NADH and no significant interference effect was observed even when 200-fold excess of ascorbic acid (AA), dopamine (DA) and uric acid (UA) coexist in the same supporting electrolyte solution.     

Screen-printed carbon electrode for choline based on MnO2 nanoparticles and choline oxidase/polyelectrolyte layers

This paper presents the amperometric biosensor that determines choline and cholinesterase activity using a screen printed graphite electrode. In order to detect H₂O₂ we have blanket modified the electrode material with manganese dioxide nanoparticles layer. Using layer-by-layer technique on the developed hydrogen peroxide sensitive electrode surface choline oxidase was incorporated into the interpolyelectrolyte nanofilm. Its ability to serve as a detector of choline in bulk analysis and cholinesterase assay was investigated. We examined the interferences from red-ox species and heavy metals in the blood and in the environmental sample matrixes. The sensor exhibited a linear increase of the amperometric signal at the concentration of choline ranging from 1.3 × 10⁻⁷ to 1.0 × 10⁻⁴ M, with a detection limit (evaluated as 3σ) of 130 nM and a sensitivity of 103 mA M⁻¹ cm⁻² under optimized potential applied (480 mV vs. Ag/AgCl). The biosensor retained its activity for more than 10 consecutive measurements and kept 75% of initial activity for three weeks of storage at 4 °C. The R.S.D. was determined as 1.9% for a choline concentration of 10⁻⁴ M (n = 10) with a typical response time of about 10 s. The developed choline biosensor was applied for butyrylcholinesterase assay showing a detection limit of 5 pM (3σ). We used the biosensor to develop the cholinesterase inhibitor assay. Detection limit for chlorpyrifos was estimated as 50 pM.     

A facile approach to the synthesis of hydrophobic iron tetrasulfophthalocyanine (FeTSPc) nano-aggregates on multi-walled carbon nanotubes: A potential electrocatalyst for the detection of dopamine

A facile method has been utilized to synthesize a hydrophobic form of nano-scaled iron (II) tetrasulfophthalocyanine (nanoFeTSPc), integrated with functionalized multi-walled carbon nanotubes (fMWCNT-nanoFeTSPc). The nanocomposite was characterized by UV–visible spectra, EDX, FESEM, and TEM. The electrocatalytic properties of the film on a glassy carbon electrode were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and square wave voltammetry. The fMWCNT-nanoFeTSPc modified electrode demonstrated higher catalytic performance in terms of electron transport and current response compared to the other electrodes studied towards dopamine (DA) detection giving a sensitivity of 0.314 μA μM⁻¹ and a limit of detection of 9.86 × 10⁻⁸ mol L⁻¹. A selective detection was realized in elimination of ascorbic acid response on the film of fMWCNT-nanoFeTSPc. The detection limit in the presence of a high concentration of ascorbic acid was 3.5 × 10⁻⁷ mol L⁻¹.     

Graphite oxide film-modified electrode as an electrochemical sensor for acetaminophen

The graphite oxide (GO) was prepared via the chemical oxidation of natural graphite powder, and then used to modify the surface of glassy carbon electrode (GCE). The electrochemical behavior of acetaminophen was examined. In 0.01 mol L⁻¹ HCl, an irreversible oxidation peak is observed for acetaminophen, and the peak current remarkably increases at the GO film-modified GCE. The influences of supporting electrolyte, amount of GO suspension, accumulation potential and time were studied on the oxidation peak current of acetaminophen. As a result, a new electrochemical method was developed for the detection of acetaminophen. The linear range is from 25 μg L⁻¹ to 4 mg L⁻¹, and the limit of detection is 6 μg L⁻¹ based on three signal-noise ratio. Finally, it was successfully used to detect acetaminophen in tablets.     

Nanolayer treatment to realize suitable configuration for electrochemical allopurinol sensor based on molecular imprinting recognition sites on multiwall carbon nanotube surface

In this work, nanolayer MIP (molecularly imprinted polymer) is used to achieve suitable conformation for catalyzing AP (allopurinol) redox reaction. Also, a sensitive electrochemical sensor was fabricated for AP based on MIP immobilized on multiwall carbon nanotube (MWCNT) surface. Thin film of MIP immobilized on MWCNT surface (MIPCNT) with specific recognition sites for AP was cast on glassy carbon electrode (GCE). The morphology and features of the film were characterized by field emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometric measurements (I–t) in detail. The near equilibrium time to adsorb AP on the surface of electrode is about 9 min. The modified electrode was used to detect the concentration of AP with a linear range and detection limit (S/N = 3) of 0.01–1.0 μM and 6.88 nM, respectively. The MIPCNT film displayed an excellent selectivity toward AP. Finally, the modified electrode was successfully applied to determine AP in the human serum sample and two brand tablets.     

Locked nucleic acids biosensor for detection of BCR/ABL fusion gene using benzoate binuclear copper (II) complex as hybridization indicator

Benzoate binuclear copper (II) complex, [Cu₂(C₇H₅O₂)₄(C₂H₆O)₂] (abbreviated as CuR₂) was prepared and its interaction with double-stranded salmon sperm DNA (dsDNA) in pH 7.4 phosphate buffer solution was studied by electrochemical experiments at the Au electrode (AuE). It was revealed that CuR₂ presented an excellent electrochemical activity on AuE and could bind with dsDNA by intercalation mode. The CuR₂ was further utilized as a new indicator in the fabrication of an electrochemical DNA biosensor for detection of BCR/ABL fusion gene. The biosensor based on nanogold (NG) modified AuE was developed by using thiolated-hairpin locked nucleic acids (LNA) as the capture probe for hybridization with BCR/ABL fusion gene. The results indicated this new method has excellent specificity for single-base mismatch and complementary after hybridization. The constructed electrochemical DNA biosensor achieved a detection limit of 1.0 × 10⁻¹⁰ M for complementary target DNA with a good stability.     

Sensitive amperometric determination of chemical oxygen demand using Ti/Sb-SnO2/PbO2 composite electrode

A novel Ti/Sb-SnO₂/PbO₂ composite electrode was fabricated for COD determination. The new electrode configuration improved the sensitivity of the amperometric method apparently. Effects of common experimental parameters, such as applied potential, pH and concentration of the electrolyte on its analytical performance were investigated. A linear range of 0.5-200 mg L⁻¹ COD and a detection limit (a signal-to-noise ratio of 3) of 0.3 mg L⁻¹ were achieved under optimized conditions. The experiments for detecting COD in model samples and real samples were carried out to evaluate the electrode's performance. The obtained results were in good agreement with those determined by the standard dichromate method, with a relative error less than 12%.     

Graphene-polyaniline composite film modified electrode for voltammetric determination of 4-aminophenol

An electrochemical sensor based on graphene-polyaniline (GR-PANI) nanocomposite for voltammetric determination of 4-aminophenol (4-AP) is presented. The electrochemical behavior of 4-AP at the GR-PANI composite film modified glassy carbon electrode (GCE) was investigated by cyclic voltammetry. 4-AP exhibits enhanced voltammetric response at GR-PANI modified GCE. This electrochemical sensor shows a favorable analytical performance for 4-AP detection with a detection limit of 6.5 × 10⁻⁸ M and high sensitivity of 604.2 μA mM⁻¹. Moreover, 4-AP and paracetamol can be detected simultaneously without interference of each other in a large dynamic range.