Sensitive Electrochemical Sensor Research Articles

Comparative electrochemical properties of polyaniline/carbon quantum dots nanocomposites modified screen-printed carbon and gold electrodes

In this study, carbon quantum dots (Cdots) synthesized from a pencil graphite precursor using a bottom-up method were incorporated into polyaniline (PANI) to form Cdots-PANI nanocomposite. Cdots, PANI and Cdots-PANI nanocomposites were characterized using the Fourier-Transform infrared spectroscopy (FT-IR), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The FT-IR spectra of graphene and Cdots show the emergence of a peak at 3500 cm−1, which was initially absent in graphene, after the formation of Cdots, among other peaks. The peak at 3500 cm−1 and the stretching vibration at 1647 cm−1 suggest the presence of –OH and C=C in the Cdots. The FT-IR spectra of PANI/Cdots and PANI show that the peaks in PANI shifted to higher wavenumbers after composite formation. Similarly, the UV–visible spectra of the PANI/Cdots composite revealed a hypsochromic shift of the characteristic PANI peaks at 320 and 600 nm to 300 and 560 nm, respectively. Electrochemical characterization of Cdots, PANI and Cdots-PANI nanocomposites was done with screen-printed carbon electrodes (SPCE) and screen-printed gold electrodes (SPAuE) modified with the nanomaterials and the nanocomposites. The electrochemical properties of the as-synthesized nanomaterials and the nanocomposite were investigated with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) in 10 mM K3[Fe(CN)6] solution using the bare screen-printed electrodes and the modified electrodes. The modified electrodes gave higher anodic peak current (Ipa) responses and lower charge transfer resistance (Rct) values in the redox probe than the bare electrodes. The SPCE-Cdots-PANI nanocomposite-modified electrode exhibited better redox potentials, faster electron transfer kinetics, larger surface area, and greater stability than the bare electrodes and the other modified electrodes. The outstanding electrochemical properties of SPCE-Cdots/PANI underscores its potentials as a sensitive electrochemical sensor for a wide range of analytes.

Facile and Sensitive Acetylene Black-Based Electrochemical Sensor for the Detection of Imatinib

A facile and sensitive electrochemical sensor for determining imatinib (IMA) was constructed by modifying a glassy carbon electrode (GCE) with a nanocarbon material, acetylene black (AB). The electrochemical behavior of IMA on the prepared GCE/AB was studied using electrochemical techniques, namely, differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy. The direct determination of IMA by the GCE/AB sensor was accomplished using DPV under optimized conditions. The method verification showed that the oxidation peak current was proportional to the concentrations of IMA in the linear ranges of 0.01–0.5 and 0.5–4 μM, with correlation coefficients of 0.9856 and 0.9946, respectively. The limit of detection of the GCE/AB sensor was 0.15 nM. Moreover, the GCE/AB sensor showed good precision and accuracy. Finally, the GCE/AB sensor was successfully applied to determine IMA in human serum samples, and the recoveries were satisfactory.

Nitrogen Defect-Rich Graphitic Carbon Nitride for Highly Sensitive Voltammetric Determination of Tryptophan.

Here, a highly sensitive electrochemical sensor for detection of tryptophan (Trp) using a nitrogen defect graphitic carbon nitride-modified glassy carbon electrode (ND-CN/GCE) was introduced. ND-CN/GCE showed a higher oxidation current for Trp than the graphitic carbon nitride-modified glassy carbon electrode (g-CN/GCE) and bare glassy carbon electrode (BGCE). The synthesized nitrogen defect-rich graphitic carbon nitride (ND-CN) was characterized using X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were used to further analyze the electrochemical properties of BGCE, g-CN/GCE, and ND-CN/GCE. The oxidation of Trp at ND-CN/GCE is a diffusion-controlled process at pH 3.0. It was calculated that the transfer coefficient, rate constant, and diffusion coefficient of Trp were 0.53, 2.24 × 103 M-1 s-1, and 8.3 × 10-3 cm2 s-1, respectively, at ND-CN/GCE. Trp was detected using square wave voltammetry, which had a linear range from 0.01 to 40 μM at pH 3.0 and a limit of detection of about 0.0034 μM (3σ/m). Analyzing the presence of Trp in a milk and multivitamin tablet sample with a percentage recovery in the range of 97.0-108% satisfactorily demonstrated the practical usability of the electrochemical sensor. The ND-CN/GCE additionally displays good repeatability and reproducibility and satisfactory selectivity.

Facile preparation of a sensitive electrochemical sensor with good performance for determination of methionine

In this work, a novel voltammetric sensor for detection of methionine was designed and prepared by using carbon paste electrode (CPE) modified with ZnO hollow quasi-spheres (ZnO hollow QSs) and 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM.PF6). The results by cyclic voltammetry (CV) showed that the prepared electrode (ZnO-BMIM.PF6/CPE) effectively increased the oxidation peak current and reduced the oxidation peak potential of methionine, and had a suitable electrocatalytic activity for oxidation of methionine. Notably, the ZnO-BMIM.PF6/CPE exhibited high detection capability towards the quantification of methionine in 0.1 M PBS (pH = 7.0) over a concentration range from 0.04 µM to 330.0 µM with a limit of detection (LOD) of 0.02 μM. More importantly, the effectiveness of the ZnO-BMIM.PF6/CPE seneor was also confirmed in real sample (urine detection with acceptable recoveries (98.0-102.7%) and RSDs values ≤ 3.3%.

MoS2/Au heterojunction nanostructures for electrochemical detection of trace Hg(II) in wastewater samples

In this study, a highly sensitive electrochemical sensor was developed for the detection of mercury ions in wastewater samples. The sensor was constructed using MoS2/Au heterojunction nanostructures, which involved depositing plasmonic Au nanoparticles onto MoS2 nanosheets on screen-printed carbon electrodes. The MoS2/Au-SPCE sensor demonstrated outstanding electrochemical sensing capabilities, attributed to the emergence of a mid-gap state across the Fermi level. This state arises from the interaction between the Au 5d (Au, +1 charge state) and Mo 3d (MoS2, +4 charge state) orbitals. This performance was superior to that of single Au nanoparticles and MoS2. The sensor showed high sensitivity in detecting Hg(II) ions with a wide linear range from 0.02 ppm to 0.0004 ppb and a LOD of 0.0004 ppb. The developed sensor was effectively applied for the detection of Hg(II) ions in factory wastewater and other samples. The MoS2/Au-SPCE sensor was successfully used to detect low concentrations of 565.0 ppb and 92.0 ppb Hg(II) in the investigated samples. This study introduces a new electrochemical sensor, leveraging the MoS2/Au heterostructures, meticulously crafted for the intricate sensing of Hg(II) ions

CdS/g-C3N4/Sm-BDC MOF nanocomposite modified glassy carbon electrodes as a highly sensitive electrochemical sensor for malathion

Malathion is an organophosphate pesticide widely used in agriculture, whose elimination is highly demanded by society. This work faces this challenge by the development of a novel electrochemical sensor via modifying a glassy carbon electrode (GCE) with sustainable Sm-BDC MOFs and their corresponding novel binary and ternary composites combined with CdS and g-C3N4 for the detection of malathion. Different characterization techniques indicate the successful synthesis of desired composite materials, with notable interaction between the individual components. CdS-Sm-BDC-g-C3N4-5 wt% modified electrode exhibited higher peak current than the bare GCE, with excellent electrocatalytic ability to oxidize malathion, due to its higher conductivity, catalytic effect and synergistic effects between CdS, g-C3N4 and Sm-BDC. Under optimized condition, differential pulse voltammograms (DPV) demonstrate that the oxidation peak current was proportional to its concentration in the range of 3.0·10−8–15.0·10−8 M (R2 = 0.996), with high sensitivity (25 μAμM−1) and low detection limit (7.4·10−9 M or 7.4 μmM). In addition, the modified electrode affirms good stability and reproducibility, making it simple, cost effective with high sensitivity and selectivity. The results confirmed that making a composite is a key strategy for improving the physicochemical properties of MOFs and that modifying electrode surfaces with novel composites can enhance the detection of organophosphate pesticide.

Ultrafast Electrochemical Sensor Based on Electrical Potential-Assisted Hybridization for Non-Amplification Determination of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) by Differential Pulse Voltammetry (DPV)

A highly ultrafast and sensitive electrochemical sensor based on electrical potential-assisted hybridization was developed for the determination of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The electrode was modified with multi-walled carbon nanotubes (MWCNTs) and Au nanoparticles (AuNPs) for excellent electrochemical performance. The constant electric field was applied to rapidly and efficiently enrich the capture probes to the electrode surface in 60 s. Meanwhile, pyrene as the backfill reagent resulted in a significant reduction of nonspecific adsorption. The electrochemical properties of the modified electrode were investigated via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The analytical response was measured by differential pulse voltammetry (DPV). The sensor achieved the ultrafast hybridization of nucleic acids at the electrode interface within 90 s, substantially reducing the reaction time from hours to minutes. Under optimal conditions, the sensor exhibited a superior detection limit of 60 fM and showed satisfactory specificity toward single-base mismatch. Additionally, the proposed sensor realized sensitive determination of SARS-CoV-2 in throat swabs. The enzyme-free and non-amplification sensing strategy showed promising potential for application in point-of-care testing (POCT).

A highly sensitive electrochemical sensor for detecting the content of capsaicinoids based on the synergistic catalysis of rGO/PEI-CNTs/β-CD.

Rapid quantification of the content of capsaicinoids helps in classifying the degree of spiciness, standardized production, and quality control of leisure meat products. To rapidly quantify the content of capsaicinoids in soy sauce and pot-roast meat products, we developed an electrochemical sensor based on reduced graphene oxide (rGO)/polyethylene imine (PEI) - carbon nanotubes (CNTs)/β-cyclodextrin (β-CD) to detect the content of capsaicinoids in leisure meat products. Our findings showed that the electrochemical sensor presented highly sensitive performance toward capsaicinoids with a relatively wide linear range (0.01-100µmol/L), a lower limit of detection (0.01µmol/L), and an acceptable recovery rate (94.80-112.20%). The sensor performed well and was effective mainly because of the three-dimensional stacking structure and synergistic catalysis of rGO with cCNTs and also due to the improved dispersion of the composite material by β-CD. The sensor detected trace contents of capsaicinoids in leisure meat products, and thus, it might be considered for practical applications.

Sensitive electrochemical detection of benzocaine based on hollow carbon nanobowl modified electrode

Benzocaine (BZC) is a widely used anaesthetic drug coupled with multiple undesirable side effects, thus developing sensitive method for its detection is of great importance; meanwhile, hollow carbon nanospheres (HCS) have received intense interests in electroanalysis resulted from its unique merits, but the related close structures restrain the availability factor of the internal surfaces, hence suppressing their analytical performance. In this work, a novel nanomaterial with open structure, hollow carbon nanobowl (HCB) was prepared and adopted as the electrode material for fabricating a highly sensitive electrochemical sensor of BZC. The obtained results revealed the as-prepared HCB can display more superior sensing performance than conventional HCS. After optimizing various experimental conditions including the modified amount of HCB, accumulation time and the buffer pH value, the detection of BZC was performed at HCB modified electrode, and a considerably low detection limit (4.0 nM) coupled with high sensitivity (2.1527 μA μM−1) was obtained. In addition, the further experiments demonstrated that the HCB modified electrode possesses superior capability in repeatability, stability, selectivity and practical application. It’s thus expected that the as-designed HCB-based sensing platform has important application for BZC and other targets detection.

Electrochemical Sensing Based on Metal-Organic Frameworks-Derived Carbon/Molybdenum Disulfide Composites with Superstructure and Synergistic Catalysis.

Metal-organic frameworks (MOFs)-derived nanocomposite has attracted extensive attention due to its tunable nanoscale cavities and high chemical tailorability. Herein, with the aim of developing a sensitive electrochemical sensor for p-nitrophenol, a novel MOFs-derived nanocomposite was prepared by the solvothermal method using Zr-MOFs, thiourea, and sodium molybdate as raw materials. By controlling the growth mode and reaction time, the nanohybrids displayed a superstructure composed of MOFs-derived carbon (MOFs-C) and MoS2. Scanning electron microscopy images indicated that MOFs-C/MoS2 was a flower-like porous sphere. Transmission electron microscopic images showed that the MOFs-C/MoS2 had a unique arrow target-like structure. The porous structure held great promise for the fast mass transfer into the material, while the layer-by-layer distributed carbon and MoS2 provided a great structure for the synergistic catalysis. The electrochemical oxidation of (hydroxyamino)phenol to nitrosophenol, which is an important process for the electrochemical behavior of p-nitrophenol, can be selectively catalyzed by the MOFs-C/MoS2. Therefore, the electrochemical sensor based on the MOFs-C/MoS2 material exhibited excellent analytical performance in the determination of p-nitrophenol. Using the technique of square wave voltammetry, the peak current varied quantitatively with the presence of p-nitrophenol in the wide concentration range of 0.5-500 μM. Furthermore, the electrochemical sensor exhibited good practicability in real sample analysis.

A novel strategy for realizing highly sensitive nonenzymatic detection of H2O2 based on regulating crystallinity of CoO nanosheets

This study reports a novel strategy to construct a highly sensitive electrochemical sensing method based on crystallinity regulation. Two kinds of CoO nanosheets with different crystallinity were prepared by adjusting annealing temperature. The results show that decreasing crystallinity of CoO nanosheets not only increases electrochemical surface area but also accelerates electron transport rate. This is beneficial to improve the electrocatalytic activity of CoO nanosheets for electrochemical oxidation of H2O2, and therefore makes the sensor detect H2O2 in a linear range of 0.2 µM to 11 mM, a sensitivity of 909.9 µA·mM−1·cm−2 and a low detection limit of 0.2 µM. This study provides a new perspective to regulate the electrocatalytic activity of nanomaterials for constructing highly sensitive electrochemical sensor.

Magnetic perlite based molecularly imprinted polymer on screen printed carbon electrode as a new tyramine electrochemical sensor

This paper describes the design and fabrication of a sensitive electrochemical sensor using a new magnetic pearlite-based molecularly imprinted polymer (MPt/MIP) for the voltammetric determination of tyramine (Tyr). MPt/MIP nanocomposite was synthesized by direct surface-based imprinting procedure using methacrylic acid (MAA) as monomer for MIP and also functional group for magnetic perlite (MPt). The structural properties of MPt/MIP nanocomposite were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy, vibrating sample magnetometry (VSM) and via adsorption kinetics and adsorption isotherms. The integrated analytical procedure consists of dispersion of synthesized MPt/MIPs for selective separation of target analyte from sample and their subsequent localization on the surface of a magnetic screen-printed carbon electrode (MSPCE) as a platform for determination of Tyr by differential pulse voltammetry (DPV). The experimental parameters which affect separation efficiency and electrochemical determination were optimized. The developed method provided a linear calibration range of 8.0 to 380.0 ng mL−1 (R2 = 0.998), and a detection limit of 3.8 ng mL−1. The intra-day and inter-day precision (%RSD) were in the range 3.1–4.4 %. The method was successfully applied to the determination of Tyr in real samples with recoveries ranging from 94.2 to 105.2 %.

A highly sensitive electrochemical sensor based on poly(3-aminobenzoic acid)/graphene oxide-gold nanoparticles modified screen printed carbon electrode for paraquat detection

Herein, a modified screen printed carbon electrode (SPCE) based on a composite material, graphene oxide-gold nanoparticles (GO-AuNPs), and poly(3-aminobenzoic acid)(P3ABA) for the detection of paraquat (PQ) is introduced. The modified electrode was fabricated by drop casting of the GO-AuNPs, followed by electropolymerization of 3-aminobenzoic acid to achieve SPCE/GO-AuNPs/P3ABA. The morphology and microstructural characteristics of the modified electrodes were revealed by scanning electron microscopy (SEM) for each step of modification. The composite GO-AuNPs can provide high surface area and enhance electroconductivity of the electrode. In addition, the presence of negatively charged P3ABA notably improved PQ adsorption and electron transfer rate, which stimulate redox reaction on the modified electrode, thus improving the sensitivity of PQ analysis. The SPCE/GO-AuNPs/P3ABA offered a wide linear range of PQ determination (10−9–10−4 mol/L) and low limit of detection (LOD) of 0.45 × 10−9 mol/L or 0.116 µg/L, which is far below international safety regulations. The modified electrode showed minimum interference effect with percent recovery ranging from 96.5% to 116.1% after addition of other herbicides, pesticides, metal ions, and additives. The stability of the SPCE/GO-AuNPs/P3ABA was evaluated, and the results indicated negligible changes in the detection signal over 9 weeks. Moreover, this modified electrode was successfully implemented for PQ analysis in both natural and tapped water with high accuracy.

Flow-based compact microfluidic electrochemical cell with Parafilm® channels

A planar interdigitated microelectrodes-based microfluidic electrochemical cell (P-μFEC) with channels made by Parafilm® sheets was conceptualized with the application as a sensor for detecting heavy metal ions. Herein, we first-timely proposed a new strategy for creating Parafilm® microchannels using a Plotter cutter and Hot bonding self-sealing method for solid Microfluidic devices (PPHM). For the prepared novel P-µFEC by the PPHM protocol, which operated in the laminar regime, its electrochemical performance was well-studied using the well-known electrochemical reporter potassium Ferri/Ferrocyanide (K3/K4[Fe(CN)6]). A reference electrode (RE) layer deposited at the top silica glass substrate was embedded within the device to minimize the ohmic drop (iRcell) between the working electrode (WE) and RE. The experimental and virtualized computational COMSOL results demonstrated: (i) The changes in the RE's placements had negligible influences on the P-µFEC's electrochemical performance. (ii) The laminar flow's influence on the P-µFEC's electrochemical performance was quite prominent, which was due to the changes in the mass transfer process from diffusion (stationary) to diffusion + convection (hydrodynamic). (iii) A direct virtualized demonstration of laminar flow's influences on the mass transfer process from diffusion (stationary) to diffusion + convection (hydrodynamic) was first timely validated by finite element analysis simulation using COMSOL Multiphysics. (iv) Finally, the proposed P-µFEC showed promise as a sensitive electrochemical sensor for different heavy metal ion substrate (model analytes) detection. The IUPAC detection limits for Cu2+, Pb2+, [Fe(CN)6]3- and Hg2+ is ∼318.6±3.55 μg/L, ∼191±5.4 4 μg/L, ∼113.5±9.9 μg/L, and 8.21±0.88 μg/L, respectively. Among them, the detection limit for Cu2+ and Hg2+ meets the US Environmental Protection Agency (EPA)'s water contamination level for Cu (1300 μg/L) and is close to the EPA level for Hg (2 μg/L), respectively. These findings demonstrate the potential of using the Parafilm® sheet as the microfluidic channel for a flow-based P-μFEC as a novel analytical tool.

A sensitive electrochemical sensor for chiral detection of tryptophan enantiomers by using carbon black and β‑cyclodextrin.

A chiral sensor for the electrochemical identification of tryptophan (Trp) isomers is described. The electrochemical sensor was prepared based on the combination of (a) carbon black (CB-COOH) as conductive material, (b) Cu2+-modified β-cyclodextrin (Cu-β-CD), and (c) β-CD-based metal-organic frameworks (β-CD-MOF) as chiral selectors. The Cu-β-CD can be self-assembled into the CB-COOH and β-CD-MOF through electrostatic interactions, which was characterized by zeta potential analysis. UV-vis spectroscopy proved that Cu-β-CD displays a higher combination for D-Trp than L-Trp, and the β-CD-MOF at the surface of the GCE has a higher affinity for L-Trp than D-Trp, which endow an easier permeation of L-Trp to the surface of the electrode, thus leading to a larger electrochemical signal of differential pulse voltammetry (DPV). The enantioselectivity for L-Trp over D-Trp (IL/ID) is 2.13, with a low detection limit for D-Trp (11.18μM) and L-Trp (5.48μM). In addition, the proposed chiral sensor can be chosen to determine the percentage of D-Trp in enantiomer mixture solutions and real sample detection with a recovery from 98.2 to 102.8% for L-Trp and 97.9 to 101.1% for D-Trp.

A highly selective and sensitive electrochemical sensor for tetracycline resistant genes detection based on the non-covalent interaction of graphene oxide and nucleobase

Antibiotic resistance genes (ARGs) are causing worldwide environmental problems, however, the traditional analytical methods and test equipment for them are time-consuming and expensive. The electrochemical sensor using the non-covalent bond between graphene oxide (GO) and single-stranded tet (ss-tet) was established for specific tetracycline resistance genes (tet, composed of ss-tet and complementary ss-tet (ss-tet') in water) detection, which preparation time was only 35 min and far less than most reported sensors based on covalent bond. As the result of the detection for tet, the developed sensor not only had the low detection limit of 50.0 pM (8.1 × 102 copies·mL−1), the short detection time within 42 min, but also had satisfactory stability, excellent reproducibility, and highly selectivity (RSD < 4.43 %). Besides, it also had acceptable accuracy comparing to the real-time quantitative polymerase chain reaction (RT-qPCR) and PCR array in tet detection. Noticeably, it also had been successfully applied to tetA detection in different water samples. In brief, the prepared non-covalent bond sensor is simple, rapid, and suitable for highly selective and sensitive detection of the ARGs in actual water.

Modified electrode decorated with silver as a novel non-enzymatic sensor for the determination of ammonium in water

Ammonium is an essential component of the nitrogen cycle, which is essential for nitrogen cycling in ecosystems. On the other hand, ammonium pollution in water poses a great threat to the ecosystem and human health. Accurate and timely determination of ammonium content is of great importance for environmental management and ensuring the safety of water supply. Here we report a highly sensitive electrochemical sensor for ammonium in water samples. The modified electrode is based on the incorporation of silver nitrate (AgNO3) into a carbon paste embedded with 1-aminoanthraquinone and supported by multi-walled carbon nanotubes, which are commercially available. A potential of 0.75 V is applied to the modified electrode, followed by activation in hydrochloric acid. The modified electrode was used for square wave voltammetry of ammonium in water in the potential range of − 0.4–0.2 V. The performance of ammonium analysis was determined in terms of square wave frequency, square wave amplitude and concentration of electrolyte solution (sodium sulphate). The calculation of the surface area according to the Randles–Sevcik equation resulted in the largest surface area for the Ag/pAAQ/MWCNTs/CPE. The modified electrode exhibited a linear range of 5–100 µM NH4+ in 0.1 M Na2SO4 with a detection limit of 0.03 µM NH4+ (3σ). In addition, the modified electrode showed high precision with an RSD value of 9.93% for 10 repeated measurements. No interfering effect was observed at twofold and tenfold additive concentrations of foreign ions. Good recoveries were obtained in the analysis of tap and mineral water after spiking with a concentration of ammonium ions.

Chemically modified electrochemical sensors for the detection of β-blockers: an overview of electrode modifiers

β-blockers are a significant class of medications generally used to treat cardiovascular related diseases, but toxicity from overdoses can lead to serious side effects. In addition to this, they may also be used as doping agents by athletes due to their sedative effects. Therefore, it is crucial for their detection. Traditional detection methods include chromatography, spectroscopy, etc., but these techniques are tedious and labor-intensive, and the instruments are cumbersome. Electrochemical methods have become an important alternative to traditional methods because of their high selectivity, high sensitivity, minimal expense, and portability. For the purpose of enhancing the performance of electrochemical methods, this article focuses on three types of electrode modification materials: molecularly imprinted polymers (MIPs), carbon nanomaterials, and metal nanoparticles. MIPs are an important class of selective adsorption materials, which can adsorb a certain type of β-blockers through hydrophobic interaction, π-π interaction, hydrogen bonding, etc., thereby improving the selectivity and sensitivity of electrochemical sensors. Carbon nanomaterials and metal nanoparticles have strong electroconductivity and enormous specific surface area, which can promote the electron transfer rate on the working electrode surface and improve the sensitivity of the sensor. In addition, they also have some unique properties respectively. Furthermore, the trend of electrochemical detection of β-blockers and the prospect of future development are suggested.

Cobalt-based metal-organic framework-functionalized graphene oxide modified electrode as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work reports the profit of using a MOF compound for developing a sensitive electrochemical sensor to free chlorine detection in an aqueous solution. Co-MOF and FGO composites were synthesized and combined with the carbon paste (CP) to prepare an efficient electrochemical sensor with high sensing ability. The fabricated Co-MOF and FGO composites were characterized by SEM, EDX, FT-IR, and XRD techniques. Meanwhile, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to assess the electrochemical performance of the Co-MOF-FGO/CP modified electrode. Under the optimized condition, the amperometric detection showed that the reduction current of free chlorine increased linearly with a coefficient determination of 0.995 during its wide concentration range of 0.1–700 ppm. Also the detection limit (LOD) (S/N = 3) was 0.01 ppm. The selectivity of the sensor was tested with possible interferences, and satisfactory results were obtained. The proposed sensor was successfully used to determine the free chlorine in tap water and swimming pool water real samples. The results suggested that this proposed sensor could pave the way for developing the electrochemical sensor of free chlorine in aqueous media with MOFs.

Three-dimensional dual-network magnetic conductive hydrogel for the highly sensitive electrochemical detection of ponceau 4R in foods

Synthetic pigment Ponceau 4 R is a commonly used additive in the process of various foods. Due to its potential toxicity to humans, realizing high sensitivity and rapid detection of Ponceau 4 R is extremely important. In this study, we synthesized a novel dual-network magnetic conductive hydrogel (MCHG) via a simple one-pot low temperature stirring method. In MCHG, cationic guar gum (CGG) and β-cyclodextrin (β-CD) formed a primary three-dimensional network cross-linked by N, N-methylene bisacrylamide. A second network was formed in MCHG by CGG, β-CD and magnetite@carboxylate-terminated carbon nanotubes (Fe3O4@COOH-MWCNTs) through hydrogen bonding and electrostatic interactions. Fe3O4@COOH-MWCNTs enhanced cross-linking in the MCHG hydrogel, whilst also boosting the equilibrium adsorption capacity of Ponceau 4 R (61.8 mg g−1), electrical conductivity and electrocatalytic performance. Application of MCHG to a glassy carbon electrode (GCE) created a highly sensitive electrochemical sensor for the detection of Ponceau 4 R. Under optimized testing conditions, the sensor offered a very wide linear range (0.01–200.0 μM) and a low limit of detection (1.8 nM) for Ponceau 4 R. When the sensor was applied to the detection of Ponceau 4 R in spiked honey and liqueur samples, excellent recoveries were achieved (88.2%–107.0%). Furthermore, analyses of commercial biscuit and candy samples using the MCHG/GCE sensor and a national standard ultraviolet spectrophotometry method afforded identical results. Results demonstrate that multifunctional hydrogels show great promise as signal amplification agents in electrochemical detection of target compounds in foods.