Hematoxylin multi-wall carbon nanotubes modified glassy carbon electrode for electrocatalytic oxidation of hydrazine

A new hydrazine sensor has been fabricated by immobilizing hematoxylin at the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotube (MWCNT). The adsorbed thin films of hematoxylin on the MWCNT modified GCE show one pair of peaks with surface confined characteristics. The hematoxylin MWCNT (HMWCNT) modified GCE shows highly catalytic activity toward hydrazine electro-oxidation. The results show that the peak potential of hydrazine at HMWCNT modified GCE surface shifted by about 167 and 255 mV toward negative values compared with that at an MWCNT and activated modified GCE surface, respectively. In addition, at HMWCNT modified electrode surface remarkably improvement the sensitivity of determination of hydrazine. The kinetic parameters, such as the electron transfer coefficient, α, and the standard heterogeneous rate constant, k⁰, for oxidation of hydrazine at the HMWCNT modified GCE were determined and also is shown that the heterogeneous rate constant, k′, is strongly potential dependent. The overall number of electron involved in the catalytic oxidation of hydrazine and the number of electrons involved in the rate-determining steps are 2 and 1, respectively. The amperometric detection of hydrazine is carried out at 220 mV in 0.1 M phosphate buffer solution (pH 7) with linear response range 2.0-122.8 μM hydrazine, detection limit of 0.68 μM and sensitivity of 0.0208 μA μM⁻¹. Finally the amperometric response for hydrazine determination is reproducible, fast and extremely stable, with no loss in sensitivity over a continual 400 s operation.     

Renewable-surface sol-gel derived carbon ceramic-modified electrode fabricated by a newly synthesized polypyridil and phosphine Ru (II) complex and its application as an amperometric sensor for hydrazine

A chemically modified carbon ceramic composite electrode (CCE) containing Dichloro{(8, 9-dimethyl-dipyridio [2,3-a;2′,3′-c] phenazine-κ²-N,N′) bis(triphenylphosphine-κ-P)}ruthenium (II) complex which synthesized newly was constructed by the sol-gel technique. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltammetry. The electrocatalytic activity of CCE was investigated and showed a good effect for oxidation of hydrazine in phosphate buffer solution (PBS). A linear concentration range of 6 μM to 1.2 mM of hydrazine with an experimental detection limit of 1 μM of hydrazine was obtained. The diffusion coefficient of hydrazine and its catalytic rate constant for electrocatalytic reaction along with the apparent electron transfer rate constant (k_s) and transfer coefficient (α) were also determined.The modified carbon ceramic electrode doped with this new Ru-complex showed good reproducibility, short response time (t < 2 s), remarkable long-term stability (>3 month) and especially good surface renewability by simple mechanical polishing.The results showed that this electrode could be used as an electrochemical sensor for determination of hydrazine in real water samples used in Fars Power Plant Station, including its heat recovery steam generator (HRSG) water (at different operational condition), cooling system and clean waste water.     

Fabrication, characterization and electrochemical performance of single strand carbon fiber prepared by catalytic chemical vapor decomposition method

Preparation, fabrication and voltammetric characterizations of a single strand of carbon fiber (SSCF) electrode and their potential applications for biosensor are presented. SSCFs of diameter ca. 10 ± 2 μm and few millimeters in length are prepared by catalytic chemical vapor decomposition (CCVD) method. Voltammetry with potassium ferricyanide, α-methylferrocene methanol and hexaammineruthenium(III) chloride on SSCF electrode are used as bench marks to validate the electrode properties. Quasi-steady state voltammograms obtained were fitted into a cylindrical diffusion model. From which, the standard rate constant (k⁰) and electron transfer coefficient (α) are obtained. The use of SSCF electrode is demonstrated for the voltammetric detection of the micromolar quantity of dopamine in the presence of large excess (ca. 200 times) of ascorbic acid, without any fouling of electrode surface. The kinetics of electron transfer are investigated.     

Electrocatalytic hydrazine oxidation on quinizarine modified glassy carbon electrode

The electrocatalytic oxidation of hydrazine has been studied on glassy carbon modified by electrodeposition of quinizarine, using cyclic voltammetry and chronoamperometry techniques. It has been shown that the oxidation of hydrazine to nitrogen occurs at a potential where oxidation is not observed at the bare glassy carbon electrode. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized quinizarine were calculated as 4.44 s⁻¹ and 0.66, respectively. The heterogenous rate constant for oxidation of hydrazine at the quinizarine modified electrode surface was also determined and found to be about 4.83 × 10³ M⁻¹ s⁻¹. The diffusion coefficient of hydrazine was also estimated as 1.1 × 10⁻⁶ cm² s⁻¹ for the experimental conditions, using chronoamperometry.     

Direct electrochemistry of glucose oxidase assembled on graphene and application to glucose detection

The direct electrochemistry of glucose oxidase (GOx) integrated with graphene was investigated. The voltammetric results indicated that GOx assembled on graphene retained its native structure and bioactivity, exhibited a surface-confined process, and underwent effective direct electron transfer (DET) reaction with an apparent rate constant (k_s) of 2.68 s⁻¹. This work also developed a novel approach for glucose detection based on the electrocatalytic reduction of oxygen at the GOx-graphene/GC electrode. The assembled GOx could electrocatalyze the reduction of dissolved oxygen. Upon the addition of glucose, the reduction current decreased, which could be used for glucose detection with a high sensitivity (ca. 110 ± 3 μA mM⁻¹ cm⁻²), a wide linear range (0.1-10 mM), and a low detection limit (10 ± 2 μM). The developed approach can efficiently exclude the interference of commonly coexisting electroactive species due to the use of a low detection potential (−470 mV, versus SCE). Therefore, this study has not only successfully achieved DET reaction of GOx assembled on graphene, but also established a novel approach for glucose detection and provided a general route for fabricating graphene-based biosensing platform via assembling enzymes/proteins on graphene surface.     

Colloidal silver nanoparticles modified electrode and its application to the electroanalysis of Cytochrome c

A colloidal silver nanoparticles (CSNs) chemically modified electrode was prepared and its application to the electroanalysis of Cytochrome c (Cyt. c) was studied. The CSNs were prepared by reduction of AgNO₃ with NaBH₄, and were stabilized by oleate. They could be efficiently immobilized on the surface of a silver electrode. The result showed that the CSNs could clearly enhance the electron transfer process between Cyt. c and the electrode compared with bulk silver electrode. Linear sweep voltammetric measurement of Cyt. c at the chemical modified electrode indicated that the oxidative peak current of Cyt. c was linear to its concentration ranging from 8.0 nmol L⁻¹ to 3.0 μmol L⁻¹ with the calculated detection limit was about 2.6 nmol L⁻¹. The direct electrochemistry of Cyt. c was also studied by cyclic voltammetry.     

Electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone/multi-walled carbon nanotubes immobilized on edge plane pyrolytic graphite electrode for NADH oxidation

This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoquinone. The surface charge transfer constant, k_s, and the charge transfer coefficient for the modified electrode, α, were estimated as 98.5 (±0.6) s⁻¹ and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (k_obs) of 3.1 × 10⁵ mol⁻¹ l s⁻¹. The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated.     

Preparation and electrocatalytic oxidation properties of a nickel pentacyanonitrosylferrate modified carbon composite electrode by two-step sol-gel technique: improvement of the catalytic activity

The sol-gel technique was used to construct nickel pentacyanonitrosylferrate (NiPCNF) modified composite ceramic carbon electrodes (CCEs). This involves two steps: forming a CCE containing Ni powder and then immersing the electrode into a sodium pentacyanonitrosyl-ferrate solution (electroless deposition). The cyclic voltammograms of the resulting surface modified CCE under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₅NO]^0/−1 system. The electrochemical properties and stability of the modified electrode were investigated by cyclic voltammetry. The apparent electron transfer rate constant (k_s) and transfer coefficient (α) were determined by cyclic voltammetry being about 1.1 s⁻¹ and 0.55, respectively. Sulfite has been chosen as a model to elucidate the electrocatalytic ability of NiPCNF-modified CCE prepared by one- or two-step sol-gel technique. The modified electrode showed excellent electrocatalytic activity toward the SO₃²⁻ electro oxidation in pH range 3-9 in comparison with CCE modified by homogeneous mixture of graphite powder, Ni(NO₃)₂ and Na₂[Fe(CN)₅NO] (one-step sol-gel technique). Sulfite was determined amperometrically at the surface of this modified electrode in pH 7. Under the optimized conditions the calibration curve is linear in the concentration range 2 μM to 2.0 mM. The detection limit (signal-to-noise is 3) and sensitivity are 0.5 μM and 13.5 nA/μM. The modified carbon ceramic electrode containing nickel pentacyanonitrosylferrate shows good repeatability, short response time, t (90%) <2 s, long-term stability (3 months), and it is renewed by simple mechanical polishing and its immersing in Na₂[Fe(CN)₅NO] solution. The advantages of the SO₃²⁻ amperometrically detector based on the nickel pentacyanonitrosylferrate-doped CCE is high sensitivity, inherent stability at wide pH range, excellent catalytic activity and less expense and simplicity of preparation. This sensor can be used as amperometric detector in chromatographic instruments.     

Electrochemical determination of bromide at a multiwall carbon nanotubes-chitosan modified electrode

A multiwall carbon nanotubes (MWNTs)-chitosan modified glassy carbon electrode (GCE) exhibits attractive ability for highly sensitive cathodic stripping voltammetric measurements of bromide (Br⁻). In pH 1.8 H₂SO₄ solution, a substantial increase in the stripping peak current of Br⁻ (compared to bare GCE and chitosan modified GCE) is observed using MWNTs-chitosan modified electrode. Operational parameters were optimized and the electrochemical behaviors of Br⁻ were studied by different electrochemical methods. The kinetics parameters were measured, the number of electron transfer (n) was 1 and the transfer coefficient (α) is 0.17. A wide linear calibration range (3.6 × 10⁻⁷-1.4 × 10⁻⁵ g mL⁻¹) was achieved, with a detection limit of 9.6 × 10⁻⁸ g mL⁻¹. The mechanism of electrode reaction was fully discussed.     

Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V (versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20-200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10⁻⁷ to 8.0 × 10⁻⁶ M and the detection limit was 1.0 × 10⁻⁷ M (three times the ratio of signal to noise, S/N = 3).     

Simultaneous voltammetric determination of ascorbic acid, acetaminophen and isoniazid using thionine immobilized multi-walled carbon nanotube modified carbon paste electrode

A carbon paste electrode (CPE) modified with thionine immobilized on multi-walled carbon nanotube (MWCNT), was prepared for simultaneous determination of ascorbic acid (AA) and acetaminophen (AC) in the presence of isoniazid (INZ). The electrochemical response characteristics of the modified electrode toward AA, AC and INZ were investigated by cyclic and differential pulse voltammetry (CV and DPV). The results showed an efficient catalytic role for the electro-oxidation of AA and AC, leading to a remarkable peak resolution (∼303 mV) for two compounds. On the other hand, the presence of INZ, which is considered as important drug interference for AC, does not affect the voltammetric responses of these pharmaceuticals. The mechanism of the modified electrode was analyzed by monitoring the CVs at various potential sweep rates and pHs of the buffer solutions. Under the optimum conditions, the calibration curves for AA, AC and INZ were obtained in the range of 1 × 10⁻⁶ to 1 × 10⁻⁴ M, 1 × 10⁻⁷ to 1 × 10⁻⁴ M and 1 × 10⁻⁶ to 1 × 10⁻⁴ M, respectively. The prepared modified electrode shows several advantages such as simple preparation method, high sensitivity, long-time stability, ease of preparation and regeneration of the electrode surface by simple polishing and excellent reproducibility. The proposed method was applied to determination of AA, AC and INZ in commercial drugs and in plasma samples and the obtained results were satisfactory.     

Ni(II)-quercetin complex modified multiwall carbon nanotube ionic liquid paste electrode and its electrocatalytic activity toward the oxidation of glucose

A modified electrode Ni(II)-Qu-MWCNT-IL-PE has been fabricated by electrodepositing Ni(II)-quercetin [Ni(II)-Qu] complex on the surface of multi-wall carbon nanotube ionic liquid paste electrode (MWCNT-IL-PE) in alkaline solution. The Ni(II)-Qu-MWCNT-IL-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)-Qu-MWCNT-PE. It also shows good electrocatalytic activity toward the oxidation of glucose. Kinetic parameters such as the electron transfer coefficient α, rate constant k_s of the electrode reaction and the catalytic rate constant k_cat of the catalytic reaction are determined. Moreover, the catalytic current presents linear dependence on the concentration of glucose from 5.0 μM to 2.8 mM, with a detection limit of 1.0 μM by amperometry. The modified electrode for glucose determination is of the property of simple preparation, good stability, fast response and high sensitivity.     

Clay-chitosan-gold nanoparticle nanohybrid: Preparation and application for assembly and direct electrochemistry of myoglobin

A biocompatible nanohybrid material (clay/AuCS) based on clay, chitosan and gold nanoparticles was explored. The material could provide a favorable microenvironment for proteins to realize the direct electron transfer on glassy carbon electrodes (GCE). Myoglobin (Mb), as a model protein to investigate the nanohybrid, was immobilized between the clay/AuCS film and another clay layer. Mb in the system exhibited a pair of well-defined and quasi-reversible redox peaks at −0.160 V (vs. saturated Ag/AgCl electrode) in 0.1 M PBS (pH 7.0), corresponding to its heme Fe^III/Fe^II redox couples. UV-vis spectrum suggested that Mb retained its native conformation in the system. Basal plane spacing of clay obtained by X-ray diffraction (XRD) indicated that there was an intercalation-exfoliation-restacking process among Mb, AuCS and clay during the modified film drying. Excellent biocatalytic activity of Mb in the modified system was exemplified by the reduction of hydrogen peroxide and nitrite. The linear range of H₂O₂ determination was from 3.9 × 10⁻⁵ to 3.0 × 10⁻³ M with a detection limit of 7.5 μM based on the signal to noise ratio of 3. The kinetic parameters such as α (charge transfer coefficient), k_s (electron transfer rate constant) and K_m (Michaelis-Menten constant) were evaluated to be 0.55, 2.66 ± 0.15 s⁻¹ and 5.10 mM, respectively.     

Bilirubin oxidase bound to multi-walled carbon nanotube-modified gold

We report on direct electron transfer (DET) reactions of bilirubin oxidase at multi-walled carbon nanotube-(MWCNT) modified gold electrodes. MWCNTs are very suitable for protein immobilisation and provide surface groups that can be used for the stable fixation on electrodes. They can also effectively replace the natural substrate of BOD - bilirubin, the electron donor for oxygen reduction. The bioelectrocatalytic oxygen reduction was recorded using linear sweep voltammetry (LSV) with BOD covalently linked to the nanotubes. The start potential of the bioelectrocatalytic oxygen reduction at pH 7 and a scan rate of 10 mV/s was determined to be 485 ± 10 mV vs. Ag/AgCl, 1 M KCl (720 mV vs. SHE). Current densities up to 500 μA/cm² were detected in an air-saturated buffer at room temperature (25 ± 5 °C). Experiments with a rotating disk electrode (RDE) indicate a diffusion controlled electrode reaction. A k_s value in the range of 80-100 s⁻¹ could be estimated.The DET could also be observed directly by the redox conversion of a copper centre of BOD under anaerobic conditions. A peak pair with a formal potential of 680 ± 10 mV vs. SHE was found. The T1 site is probably addressed by the electrode as indicated by several experimental studies.     

Preparation and electrochemistry of cadmium pentacyanonitrosylferrate film modified glassy carbon electrode

A glassy carbon (GC) electrode surface was modified with a cadmium pentacyanonitrosylferrate (CdPCNF) film as a novel electrode material. The modification procedure of the GC surface includes two consecutive procedures: (i) the electrodeposition of metallic cadmium on the GC electrode surface from a CdCl₂ solution and (ii) the chemical transformation of the deposited cadmium to the CdPCNF films in 0.05 M Na₂[Fe(CN)₅NO] + 0.5 M KNO₃ solution. The modified GC electrode showed a well-defined redox couple due to [Cd^IIFe^III/II(CN)₅NO]^0/−1 system. The effects of supporting electrolytes and solution pH were studied on the electrochemical behavior of the modified electrode. The diffusion coefficients of alkali-metal cations in the film (D), the transfer coefficient (α) and the charge transfer rate constant at the modifying film | electrode interface (k_s), were calculated in the presence of various alkali-metal cations. The stability of the modified electrode was investigated under various experimental conditions.     

Electrochemical behavior of folic acid at calixarene based chemically modified electrodes and its determination by adsorptive stripping voltammetry

Voltammetric behavior of folic acid at plain carbon paste electrode and electrode modified with calixarenes has been studied. Two peaks for irreversible oxidation were observed. Out of the three calixarenes chosen for modification of the electrodes, p-tert-butyl-calix[6]arene modified electrode (CME-6) was found to have better sensitivity for folic acid. Chronocoulometric and differential pulse voltammetric studies reveal that folic acid can assemble at CME-6 to form a monolayer whose electron transfer rate is 0.00273 s⁻¹ with 2-electron/2-proton transfer for the peak at +0.71 V against SCE. An adsorption equilibrium constant of 5 × 10³ l/mol for maximum surface coverage of 2.89 × 10⁻¹⁰ mol/cm² was obtained. The current is found to be rectilinear with concentration by differential pulse voltammetry. However, linearity in the lower range of concentration 8.79 × 10⁻¹² M to 1.93 × 10⁻⁹ M with correlation coefficient of 0.9920 was achieved by adsorptive stripping voltammetry. The limit of detection obtained was found to be 1.24 × 10⁻¹² M. This method was used for the determination of folic acid in a variety of samples, viz. serum, asparagus, spinach, oranges and multivitamin preparations.     

Simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid by methylene blue adsorbed on a phosphorylated zirconia-silica composite electrode

This paper describes the preparation, characterization and application of a composite electrode based on methylene blue adsorption to phosphorylated zirconia-silica mixed oxide particles prepared by a sol-gel process. This electrode electrocatalytically oxidizes ascorbic acid (AA), dopamine (DA) and uric acid (UA), allowing their simultaneous voltammetric detection. Well-defined and -separated oxidation peaks were observed by differential pulse voltammetry in a 0.35 mol l⁻¹ Tris-HCl buffer solution (pH 7.4) containing 0.5 mol l⁻¹ KCl. The anodic peak currents observed at −74, 94 and 181 mV increased with increasing concentrations of AA, DA and UA, respectively. Linear calibration plots were obtained over the range of 100-1600 μmol l⁻¹ for ascorbic acid, 6-100 μmol l⁻¹ for dopamine and 22-350 μmol l⁻¹ for uric acid with detection limits of 8.3 ± 0.1, 1.7 ± 0.1 and 3.7 ± 0.2 μmol l⁻¹, respectively. DA and UA concentrations could also be determined under conditions of excess AA (1 mmol l⁻¹).     

Flow injection amperometric determination of pyridoxine at a Prussian blue nanoparticle-modified carbon ceramic electrode

This work describes the electrocatalytic properties of a carbon composite electrode (CCE) modified with Prussian blue (PB) nanoparticles (NPs) for the electrocatalytic oxidation of pyridoxine (PN). The morphology of the PBNP-modified CCE was characterized by scanning electron microscopy (SEM). The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry. The rate-limiting step of the charge transfer reaction was found to be a one-electron abstraction. The value of α, k, and D were calculated as 0.66, 6.7 × 10⁴ M⁻¹ s⁻¹, and 1.88 × 10⁻⁵ cm² s⁻¹, respectively. The modified electrode showed electrocatalytic activity toward the oxidation of PN and was used as an amperometric sensor. The sensor exhibited good linear response for PN over the concentration ranges 5-69 and 1-80 μM with detection limits of 0.51 and 0.87 μM, and sensitivities of 0.97 and 0.673 A M⁻¹ cm⁻² in batch and flow conditions, respectively. Some important advantages such as simple preparation, fast response, good stability, and reproducibility of the sensor for the amperometric determination of PN were achieved.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

Potentiometric stripping analysis of bismuth based on carbon paste electrode modified with cryptand [2.2.1] and multiwalled carbon nanotubes

An electrochemical method based on potentiometric stripping analysis (PSA) employing a cryptand [2.2.1] (CRY) and carbon nanotube (CNT) modified paste electrode (CRY-CNT-PE) has been proposed for the subnanomolar determination of bismuth. The characterization of the electrode surface has been carried out by means of scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry (CC). It was observed that by employing CRY-CNT-PE, a 9-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (s/V) was proportional to the Bi(III) concentration in the range of 5.55 × 10⁻⁸ to 9.79 × 10⁻¹¹ M (r = 0.9990) with the detection limit (S/N = 3) of 3.17 × 10⁻¹¹ M. The practical analytical utilities of the modified electrode were demonstrated by the determination of bismuth in pharmaceutical formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as a simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. Moreover, the results obtained for bismuth analysis in commercial and real samples using CRY-CNT-PE and those obtained by atomic absorption spectroscopy (AAS) are in agreement at the 95% confidence level.