Electrochemical Determination Research Articles

Selective and Sensitive MIP-Based Electrochemical Sensor for the Analytical Determination of Lanreotide

Lanreotide (LAN) is an analog of somatostatin used to treat acromegaly and neuroendocrine tumors. Considering drug toxicity and the lack of sensitive techniques in drug analysis, the development of sensitive analytical methods is of great importance. During this research, a molecular imprinted polymer (MIP) based film [P(HEMA-MAGA)@MIP/GCE] was prepared by photopolymerization technique for electrochemical determination of LAN for the first time. N-methacryloyl-L-glutamic acid (MAGA) and hydroxyethyl methacrylate (HEMA) were used as functional and basic monomers, respectively. The surface alterations were investigated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) and the chemical composition of the MIP-based sensor. Theelectrochemical characterization of the modifiedelectrodes was assessed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Using differential pulse voltammetry (DPV) in standard solution and spiked serum sample of LAN, the linear response range for LAN was obtained as 1.0x10 − 14 M – 1.0x10 − 13 M. The limit of detection (LOD) values were 1.76x10 − 15 M and 1.82x10 − 15 M in water and commercial human serum, respectively. The limit of quantitation(LOQ) values for these were 5.85x10 − 15 M and 6.07x10 − 15 M, respectively. The P(HEMA-MAGA)@MIP/GCE sensor also showed excellent recovery in pharmaceutical preparation and commercial human serum form with of 99.37 % and 99.27 %, respectively, with a good RSD value (0.51–0.73), confirming the accuracy and precision of the sensor. As a control, the non-imprinted polymer (NIP) was also prepared to serve in the same way but without the template. The selectivity experiments were conducted using somatostatin (SOM) and octreotide (OC) as potential competitors to demonstrate the selectivity of the proposed sensor against LAN molecules.

A green route for the synthesis of sponge-like Pr6O11 nanoparticles and their application for the development of chlorambucil sensor

Herein, to fabricate the sponge-like praseodymium oxide nanoparticles (SL- Pr6O11 NPs), a facile and quick sonochemical route is introduced utilizing an environmentally friendly capping agent (Vitis vinifera juice) for the first time. Investigation of the electrochemical behavior of chlorambucil (CHB) showed that the reaction at the surface of the electrode is a diffusion-controlled procedure and the value of the diffusion coefficient (D) was calculated to be 1.35 × 10-5 cm2/s. The suitable electrochemical performance of the Pr6O11 nanoparticles (NPs) enhanced the sensitivity of the sensor for the electrochemical determination of CHB. The sensor signal was linearly proportional to CHB concentration in the range of 8 nM to 220 μM with a detection limit of 1.88 nM under the optimum experimental conditions. Additionally, CHB tablets, human urine and serum samples were successfully used as real samples to detect CHB at SL-Pr6O11/SPE with good recoveries.

A green perspective for the first electrochemical detection and application of balsalazide via recycled waste core-shell carbon/CdO nanoparticles-based hybrid nanosensor

In this report, a glassy carbon electrode (GCE) modified with carbon-based core–shell structures (CSC) with CdO nanoparticles has been prepared and performed for the electrochemical detection of Balsalazide (BLZ). The electrochemical investigation of BLZ was carefully examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) on the bare GCE, and CSC-CdO/GCE. Compared to bare GCE, the proposed CSC-CdO/GCE sensor can remarkably enhance the electrocatalytic activity towards the oxidation of BLZ with an increase in the anodic peak currents. For the optimum of experimental conditions, the influence of supporting electrolyte, the pH, concentration of the nanosensor, and scan rate on the peak potentials and current were investigated on the current response of BLZ before the electrochemical determination of BLZ in commercial human serum and urine samples for GCE, and CSC-CdO/GCE. The limit of detection (LOD) for BLZ in the linear range of 8.00 × 10−9 – 8.00 × 10−5 mol/L was determined as 2.20 × 10−9 mol/L. Recovery measurements assessed the accuracy of the proposed sensor in serum and urine samples. The developed sensor indicated high sensitivity and great stability toward BLZ. Core-shell structures are frequently preferred in sensor applications due to their perfect shapes, active catalytic sites, rapid interfacial transport of pores at different length scales, and their ability to reduce or shorten diffusion action paths. CSC was used as a modification material in this study due to its superior properties and advantages. Since CSC has a high surface area during the electron transfer process, it enables more efficient charge transfer between the electrode and the electrolyte. In the study, CdO nanoparticle modification on the CSC was ensured for a synergistic effect to enhance the surface area, electroactivity, and selectivity. After morphological, physical, and chemical characterization of composite material, electrochemical experiments showed that it is extremely promising because of its wide linear concentration range, low LOD, and nearly no interference with some interfering compounds and ions.

A new sensitive layer based on clcinated Zn/Ti-MOF/magnetic molecularly imprinted polypyrrole: Application to preconcentration and electrochemical determination of perfluorooctane sulfonic acid by magnetic carbon paste electrode

In this research, a new approach based on magnetic electrodes has been developed for the determination of per-fluorooctane sulfonic acid (PSOF). Zinc and Titanium-based Metal-organic framework (MOF) was synthesized and used with polypyrrole as a conductive polymer for preparation of the absorbent to achieve the best performance for electrochemical application. The response of the electrode for determination of the PFOS was affected and optimized by different factors such as buffer solution, pH of the solution, amount of absorbent, extraction time of absorbent, accumulation time, as well as the Square Wave Voltammetry (SWV) instrumental parameters including voltage step, pulse amplitude, frequency and resting time. In the optimum condition, the response of the Zn/Ti/C-MOF-magnetic molecular imprinting polymer/carbon paste electrode (MOFMMIP/CPE) has increased logarithmically by increasing the concentration in the range of 0.002–165 μM by the limit of detection (LOD) of 0.7 nM. The obtained percentage of Recovery (96.00–104.14 %), Bias (–4.00 - 4.14 %) and Relative Standard Deviation (RSD) (1.89–3.74 %) for determination of the PFOS in real and spiked tap water, river water and well water samples demonstrates that the proposed method has an acceptable precision. The comparison between the gained data by the presented method and High-performance liquid chromatography (HPLC) showed that the presented method has high accuracy.

Eco-friendly synthesis of cluster-like Dy2Ce2O7 nanoparticles using orange juice and their application in electrochemical determination of isoniazid

In this study, cluster-like (CL) Dy2Ce2O7 nanoparticles were synthesized via an easy and rapid sonochemical pathway. X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) were used for the characterization of nanoparticles. The construction of an electrochemical sensor was performed to determine isoniazid (IZN) based on ionic liquid (IL) and the cluster-like nanostructure of Dy2Ce2O7 modified carbon paste electrode (CL-Dy2Ce2O7/IL/CPE). Using the fabricated sensor, cyclic voltammetry (CV) along with differential pulse voltammetry (DPV) have been utilized to examine the catalytic activity of the modified electrode toward oxidation of IZN in 0.1 M phosphate buffer solution (PBS) with pH of 7.0. The large specific surface area and electrocatalytic properties of CL-Dy2Ce2O7 as well as the good electrical conductivity of ionic liquid greatly enhanced the current signal of the IZN at the CL-Dy2Ce2O7/IL/CPE. The process at the surface of the electrode was under the diffusion control mechanism and the diffusion coefficient for IZN was 1.08 × 10−5 cm2/s. Additionally, with a low detection limit of 9.0 nM, the peak current of IZN rose linearly with concentration in the range of 0.02–340.0 μM. Our findings demonstrate that the sensitive and selective detection of IZN in pharmaceutical and biological samples can be achieved using the CL-Dy2Ce2O7/IL/CPE.

Development of pectin-based gel electrolyte for wireless electrochemical determination of cadmium and lead using smartphone

A portable device offering effortlessness, mobility, and affordability for real-time and on-site monitoring of heavy metals is currently in great demand to maintain environmental sustainability. Herein, a platform utilizing a biopolymeric gel-based electrolyte for the on-field simultaneous determination of Cd(II) and Pb(II) is described. Pectin, a natural polymer, was exploited as a chemical delivery medium on account of its biodegradability, environmental friendliness, and rapid dissolving characteristics. The gel electrolyte was prepared by having pectin dissolved in KCl mixed with Sb(III)–Bi(III) bimetallic alloy solution, and casted onto a paper substrate. An in situ bimetallic alloy and pre-mixed bismuth nanoparticles modified screen-printed graphene electrode (Sb–Bi/BiNP/SPGE) were employed to enhance the electrochemical signals of Cd(II) and Pb(II) for the differential pulse anodic stripping voltammetry (DPASV). It was demonstrated that the platform was capable of generating sharp and well-defined current signals, achieving the low detection limits of 50.98 ng mL−1 for Cd(II) and 40.80 ng mL−1 for Pb(II). The reproducibility, as indicated by the relative standard deviation, was found to be less than 10.4 % (n = 10) for the developed gel-based device when coupled with a wireless near field communication (NFC) potentiostat. Lastly, the obtained sensor was applied for quantification of Cd and Pb in potentially contaminated groundwater samples. The recoveries obtained were satisfactorily within the acceptable range. The newly designed platform exhibited several advantages, including small sample volume (μL), low-cost, no sample preparation requirements, and being environmentally friendly. The convenience of a portable device utilizing the proposed biopolymeric gel-based electrolyte for on-field analysis makes it highly appealing for various applications.

Synthesis and application of bismuth nanoparticle-loaded longan porous carbon for simultaneous electrochemical determination of Pb(II) and cd(II) in seafoods

The discarded longan shell-derived porous carbon material (LPC) served as a scaffold for synthesizing bismuth nanoparticle-loaded longan porous carbon nanocomposite (BiNPs@LPC) via a hydrothermal method. Then BiNPs@LPC was utilized to modify screen-printed carbon electrodes (SPCE) for simultaneous detection of Pb(II) and Cd(II) by square wave anodic stripping voltammetry (SWASV). The material was thoroughly characterized by scanning electron microscopy, X-ray diffraction, Raman spectra, Brunauer-Emmett-Teller analysis, electrochemical impedance spectroscopy and cyclic voltammetry. BiNPs@LPC exhibited abundant porous structures, high surface area, and numerous active sites, which could improve significantly response sensitivity. Under optimal conditions, the peak currents of Pb(II) and Cd(II) exhibited favorable linear relationships with the concentration within a range of 0.1–150 μg L−1, with detection limits (S/N = 3) of 0.02 μg L−1 and 0.03 μg L−1, respectively. BiNPs@LPC/SPCE demonstrated remarkable selectivity, stability and repeatability. The proposed method was successfully applied for the detection of Pb(II) and Cd(II) in seafoods achieving satisfying recovery of 97.8%–108.3% and 96.7%–106.4%. These excellent test properties were coupled with convenience for batch preparation of the modified electrodes, highlighting its potential for practical applications in heavy metal detection of real samples.

Electrochemical determination of uric acid in presence of folic acid using synthesized cobalt oxide modified carbon paste electrode

Here, the synthesis of CoO nanoparticle by using co-precipitation method and characterized by XRD, SEM and EDAX techniques. The CoO nanoparticle used as modified carbon paste electrode for sensing the UA in presence of FA. The CoO/MCPE shows the excellence sensitivity towards the determination of both UA and FA. The kinetic electron transfer study of UA and FA shows with good linearity and both electrodes showed adsorption electrode process. The limit of detection (LOD) and limit of quantification (LOQ) was found to be 3.32 µM and 11.1 µM for FA and 6.09 µM and 20.3 µM for UA, respectively. The CoO/MCPE applied for the simultaneous electrochemical determination of UA and FA, the proposed method was used for real sample analysis.

First a priori Theoretical Evaluation of the Electroanalytical Cathodic Determination of Antibiotic Flavocillin

For the first time, the possibility of flavocillin electrochemical determination, assisted by vanadium (III) oxyhydroxide has been evaluated. The electrochemical determination will be given by gradual reduction of both flavonyl and penicyllyl moieties in mildly acidic medium, close to neutral. The analysis of the mathematical model, correspondent to the reaction mechanism, confirms the efficiency of cathodic electrochemical process for flavocillin electrochemical determination.

Rapid and facile electrochemical detection and degradation of carbendazim in the spiked environmental trials using reduced graphene oxide/titanium dioxide-based sensor

This study aims to develop a rapid, facile, and sensitive sensor for electroanalytical carbendazim (CAR) detection. A novel and simple sensor was fabricated by incorporating a composite matrix of titanium dioxide nanoparticles (TiO2-NPs) with reduced graphene oxide (rGO) loaded carbon paste within a polytetrafluoroethylene (PTFE) tube for investigation. Characterization of the synthesized TiO2-NPs was conducted using SEM, XRD, and AFM techniques to assess their structural, morphological and functional features that could support understanding the electrocatalytic activity at the modified sensor (CPE/rGO/TiO2). Comparative analysis with the carbon paste electrode (CPE) revealed that CPE/rGO/TiO2 demonstrated sensitivity, achieving approximately a 6-fold higher detection current in CAR analysis. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and square wave voltammetry (SWV) approaches were employed for CAR's electrochemical detection and determination. The physicochemical attributes of the electrode activity were investigated under optimum experimental conditions, including electrolyte pH and accumulation time. The CPE/rGO/TiO2 exhibited a limit of detection of 7.66 nM, with a sensitivity of 1.08 µA.µM−1.cm−2 within a wide range of concentration linearity. The selectivity of CPE/rGO/TiO2 against interference metal ions with CAR was assessed. In real-time applications, the developed electrode was tested for the analysis of CAR in spiked soil and water samples, demonstrating significant detection capacity with good recovery. Moreover, the electrode exhibited stability across multiple measurements, highlighting CPE/rGO/TiO2 as a promising sensor for CAR detection.

Sulfur-functionalized graphene obtained by a non-thermal plasma process for simultaneous electrochemical determination of tert-butylhydroquinone and bisphenol A

Electrochemical sensors based on graphene have proven to be powerful tools for detecting bisphenol A (BPA) and tert-butylhydroquinone (TBHQ) individually. There are currently no reports of these analytes being detected simultaneously. By assembling graphene-based materials on gold surfaces, it is possible to improve the charge transfer of both analytes. This study utilized non-thermal plasma-assisted synthesis with a sulfur-containing precursor to functionalize graphene (S-Graph), resulting in the fabrication of an ultrasensitive electrochemical sensor that can detect both BPA and TBHQ, simultaneously. Compared with native graphene or a traditional surface of gold electrode, S-Graph/Au retained superior electrochemical activity for both analytes that showed significantly enhanced sensing performance, including a wide linear range, with a detection limit of 13 and 54 nmol L−1 for TBHQ and BPA, respectively. The enhanced long-term storage stability, as well as reproducibility showed that S-Graph is a promising strategy for promoting the application of novel graphene-based materials.

Synthesis, characterization, and electrochemical application of novel poly(Cu2P4BCl4) based glassy carbon electrodes for determination of sulfamethoxazole in pharmaceutical serum and urine samples and Cow’s milk

The synthesis of the novel complex, [Cu2P4B]Cl4·H2O (in short Cu2P4BCL4), was confirmed by UV–Vis and FT-IR data after a straightforward ion exchange reaction. The electrochemical fabrication of the Nobel Cu2P4BCl4-based GCE was done potentiodynamically by scanning the potential of the glassy carbon electrode on the buffer solution containing 1.0 mM Cu2P4BCl4. EIS and CV were employed to characterize the surface of the developed sensor. The electroactive area and charge transfer capacity of the modified electrode were improved by about 2.5-fold area and 100-fold double-layer capacitor, respectively. The electrochemical activity of the Sulfamethoxazole (SMX) on the developed electrode was improved at around 3.1-fold peak intensities. The poly(Cu2P4BCl4)/GCE showed a wide linear range of the concentration of SMX from 0.1 to 200 µM at pH 6.5. The LOD and LOQ of the developed sensor were 0.112 nM and 0.375 nM, respectively, with the associated %RSD of 0.26 % (for n = 7). The validation of the real application of the fabricated electrode for the determination of SMX was investigated by detecting the cow’s milk sample, serum, and urine samples with spike recovery in the range of 97.5–103 %. The selectivity of the developed sensor towards SMX in the presence of potential interferants revealed an excellent recovery percentage in the range of 98.66–102.7 % in the presence of 50 to 200 % of potential interferents indicating an excellent accuracy and selectivity of the sensor. The stability and reproducibility of the Nobel sensor were investigated and revealed the best means for electrochemical determination of SMX from real cow’s milk, serum, and urine samples.

Uricase conjugated nanostructured NiFe2O4/rGO modified flexible screen-printed carbon electrode based interface for long-range electrochemical determination of uric acid

Uric acid (UA) is a biomarker linked with gout and kidney stones that is harmful to the human body. Thus, this study explores the detection of UA using the differential pulse voltammetry (DPV) method. Initially synthesizing a highly active Nickel ferrite/reduced graphene oxide (NiFe2O4/rGO) nanocomposite ferrite material by simple surfactant-free low-temperature hydrothermal approach. The as-synthesized material was studied using various spectroscopic and microscopic techniques. The bioelectrode was fabricated on a screen-printed carbon electrode (SPCE), and the as-prepared Uricase/NiFe2O4/rGO/SPCE demonstrated improved electrochemical oxidation peak current (Ipa). While its electrochemical biosensing performance towards various UA concentrations shows a wide linear range from 5 to 900 μM, with a lower limit of detection (21·9 μM), high sensitivity (1·05×10−4 mA/μM cm2), good selectivity (RSD < 5·7 %), excellent stability, and repeatability. In addition, the fabricated bioelectrode was also explored to quantify the amount of UA in bovine serum albumin (BSA) real spiked samples. Hence, the proposed biosensor has potential applications in point-of-care-treatment of numerous disorders related to UA metabolism.

One-step solvent thermal synthesis of 3D networked MOF composites for preparation of anultrasensitive chemosensor for hydroquinone and catechol.

Pharmaceuticals and personal care products (PPCPs) have a significant impact on the environment and human health, due to their sometimestoxic and carcinogenic characteristics. Therefore, an innovative chemosensor was constructed for ultrasensitive determinationof two typical PCCPs (hydroquinone (HQ) and catechol (CC)) in several minutes. The homemade chemosensor (UiO-67@GO/MWCNTs) consisted of MOF(UiO-67), graphene oxide (GO), and multi-walled carbon nanotubes (MWCNTs) composites; it was a networked, structurally sparse, porosity-rich, homogeneous octahedral composite, and had ultra-high electrical conductivity, which provided lots of active adsorption sites, promote charge transfer, and enrich lots of molecules to be measured in a few minutes. The prepared electrochemical sensor showed good long-term stability, applicability, reproducibility, and immunity to interference for the determination of HQ and CC, with a wide linear range of response of 5.0 ~ 940µM for both HQ and CC, and a low limit of detection with satisfactory recoveries. In addition, a new strategy of using MOF composites as the basis for electrochemical determination of organic small molecules was established, and a new platform was constructed for the quantitative determination of organic small molecules in various environmental samples.

Voltammetry determination of Cd(II) and Pb(II) at TiO2/reduced graphene oxide modified electrodes

AbstractIn this article, a TiO2/reduced graphene oxide (rGO) composite was synthesized from rGO and soluble titanium hydroxide‐peroxide complexes. The obtained materials were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption/desorption, Raman spectroscopy and energy dispersive X‐ray spectroscopy‐elementary mapping. The TiO2/rGO composite was used as an electrode modifier for developing an electrochemical sensor to simultaneous analysis of Cd(II) and Pb(II) by using differential pulse anodic stripping voltammetry (DP‐ASV). Under optimal conditions, the linear correlation between the stripping peak current and the metal ion concentration is good in the range of 5–100 ppb for both metals (R2 ≥ 0.998), and a low detection limit (3.17 ppb for Cd(II) and 2.42 ppb for Pb(II)) was obtained. The interference study revealed that some metal cations had little influence on the DP‐ASV signals of Cd(II) and Pb(II). In addition, the developed electrode exhibited satisfied reproducibility and repeatability. The TiO2/rGO‐modified electrode was tested toward the detection of Cd(II) and Pb(II) in river waters and the obtained exceptional recoveries and results were further associated with AAS results. This study indicates that the TiO2/rGO composite might be an alternative for practical applications in the electrochemical determination of heavy metal ions in aquatic solutions.

Fabrication of mechanically alloyed high entropy alloys (20-Fe-20Cr-20Ni-20Mn-20Ti) modified carbon paste electrode sensor for the cyclic voltammetric determination of methyl orange

We have successfully fabricated high entropy alloys (HEA) of composition 20-Fe-20Cr-20Ni-20Mn-20Ti by ball milling method for 20 h after optimizing the milling parameters. Generally, the HEAs are very popular for their multi-elemental cocktail effect and exhibit excellent high temperature oxidation resistance, high strength, electromagnetic, wear and corrosion resistance properties. But, HEAs also exhibit significant electrocatalytic properties due to their unique morphology, composition, and structure. Therefore, we have used planetary ball milled HEA powders for the electrochemical determination of methyl orange (MO). MO is recalcitrant and very difficult to degrade and can affect the humans as well as the environment. Therefore, we must determine the presence of MO. We have investigated the effect of scan rate, modifier and analyte concentration, and the pH variation on the anodic peak current (Ipa) of MO. The calculated active syrface area of bare carbon paste electrode (BCPE) and HEA-modified carbon paste electrode (HEA-MCPE) were found to be 0.041 cm2 and 0.137 cm2 respectively. We have obtained the maximum oxidation peak current for the 8 mg HEA-MCPE at a pH of 7.2 during the electrochemical oxidation of MO. The increased Ipa in basic medium is due to structural transformation of MO from quinoid form (in acidic medium) to azo structure (in basic medium). We have also calculated the number of electrons and the protons involved in the electrochemical reaction. The calculated values of detection limit (DL) and quantification limit (QL) of 8 mg HEA-MCPE was found to be 0.114 × 10−8 M and 0.38 × 10−8 M respectively.

Cobalt(II) bis-(1,10-phenanthroline) complex electropolymerized glassy carbon electrode and its electrocatalytic sensing of diclofenac in pharmaceuticals and biological samples

Diclofenac (DCF) is a nonsteroidal anti-inflammatory drug (NSAID) that is used to treat acute and chronic inflammatory diseases. High consumption and indiscriminate use of DCF pose serious health issues, prompting the consideration of electroanalytical methods for detecting and controlling DCF levels in various samples. A sensitive and highly selective sensor was established for voltammetric determination of diclofenac (DCF) based on poly[cobalt(II) bis-(1,10-phenanthroline) complex] modified glassy carbon electrode (poly(Co(Phen)2)/GCE). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the performance of a poly(Co(Phen)2)/GCE sensor, revealing a negative oxidation potential shift and higher DCF peaks of current. CV and adsorptive stripping square wave voltammetry (AdSSWV) were used to evaluate the electrochemical behavior of DCF at poly(Co(Phen)2)/GCE. Under the optimized experimental conditions, AdSSWV current signal of DCF at poly(Co(Phen)2)/GCE provided linearity over the range of 1–250 μM with a limit of detection (LOD) and limit of quantification (LOQ) of 6.40 ×10−2 and 2.13 ×10−1, and 5.60×10−2 and 2.27×10−1 µM for Ip I and Ip II, respectively. The sensor for determining DCF was tested in pharmaceuticals, milk, serum, and urine samples, demonstrating excellent selectivity despite potential interferences like atorvastatin (ATS), chloroquine (CQ), and sulfamethoxazole (SMX). The detected DCF amounts ranged between 92.3% and 106.6%. The established sensor demonstrated excellent performance in determining DCF in real samples, with spiked recoveries exceeding 95.6%, demonstrating low LOD, high sensitivity, selectivity, repeatability, and long-term stability. These results confirm that the established method displays outstanding applicability for electrochemical determination of DCF in numerous real samples.

Electrochemical detection of 4(5)-methylimidazole in aqueous solutions

4(5)-methylimidazole (4-MeI) is a potential carcinogen widely used in food colours. EU regulations specify a maximum allowable concentration of 200 ppm for 4-MeI in caramel colours. This study reports an electrochemical determination technique for 4-MeI in caramel colours for the first time. The effect of pH and interference from air were studied to optimize the detection conditions on a glassy carbon electrode in aqueous alkaline solutions using square wave voltammetry (SWV) technique. The concentration of 4-MeI was quantitatively measured down to 10 μM (∼0.8 ppm). Traditional methods such as HPLC, GC, spectrometry and immunoassays involve either expensive instrumentation and reagents or time consuming preparation and detection processes. This study demonstrates the possibility of rapid and simple electrochemical determination of (4-MeI) in food colours with minimum workup using a portable potentiostat.

Novel Ce(OH)CO3/carbon nanotubes hybrid material towards a highly sensitive electrochemical dopamine determination in real urine samples

Cerium hydroxycarbonate and multiwalled carbon nanotubes (Ce(OH)CO3/CNT), drop-casted onto a glassy carbon (GC) electrode and electrochemically treated (tCe(OH)CO3/CNT) has been obtained as a new hybrid material. tCe(OH)CO3/CNT was characterized through SEM, FT-IR, UV–Vis, and electrochemical techniques such as cyclic voltammetry (CV) with different redox couples as Fe2+/3+, Fe(CN)63-/4− or Ru(NH3)62+/3+and electrochemical impedance spectroscopy (EIS) measurements with Fe(CN)63-/4−. The charge transfer resistance (RCT) value of tCe(OH)CO3/CNT was up to two orders of magnitude lower than the RCT of bare GC electrodes and these results were confirmed by the effective heterogeneous electron transfer rate constant values (k°eff, 2.4 10−3 vs 7.0 10−4, respectively). The calibration curve of DA exhibits a linear response within the range of 0.1 and 70 μmol L−1 with a correlation coefficient (R2) of 0.987 (n = 3) and a limit of detection of 0.003 μmol L−1. Inorganic and organic interferents do not alter significatively the selectivity. The electrochemical treatment of Ce(OH)CO3 and CNT generates a modified electrode which successfully combines the selectivity of Ce towards catechol with the high conductivity of CNT presenting an ideal performance for the electrochemical DA determination in 5 real urine samples (1.94 μmol L−1 in a 1:20 dilution) using differential pulse voltammetry (DPV) with an RSD < 6.1 %.

Comparison of ultrasonic vs mechanochemistry methods for fabrication of mixed-ligand Zn-based MOFs for electrochemical determination of luteolin

Looking for green synthesis methods is the main direction of MOFs research in the green chemical industry to meet large-scale preparation of modified materials suitable for highly active electrodes. In this study, 1,3,5-benzenetricarboxylic acid (1,3,5-H3BTC) and 4,4’-bipyridine (4,4’-Bpy) were used as ligands. The micro-nano structure mixed-ligand Zn-MOFs compounds, [Zn(bpy)(Hbtc)(H2O)]n·3nH2O prepared by ultrasonic and mechanochemical method were marked as Zn-MOF-U and Zn-MOF-M, respectively. The construction of the as-prepared mixed-ligand Zn-MOFs modified carbon paste electrodes (Zn-MOF/CPE) for luteolin (LUT) detection are then studied. Different preparation methods lead to differences in micro-structure, in which lath-shaped Zn-MOF-U has higher electrochemical sensing luteolin activity than bulk-shaped Zn-MOF-M. The current signal of Zn-MOF-U/CPE was linear with the concentration of LUT in the range between 0.005−1.0 and 1.0−10 μM with a sensitivity of 9.70 and 15.6 μA·mM−1·cm−2, respectively, with the limit of detection (LOD) of 3 nM. This study provides a green routes for the simple large-scale synthesis of mixed-ligands MOFs materials and the sensitive sensing detection of small biomolecules.