Magnetic Carbon Paste Electrode Research Articles

Electrostatically self-assembled magnetized MXene/copper ferrite nanospheres hybrids: Evaluation of molecularly imprinted electrochemical sensor for the quercetin antioxidant supplement

Quercetin, a bioflavonoid with significant biological activities, is beneficial for health. Herein, a pioneering molecularly imprinted electrochemical sensor utilizing an MXene/CuFe2O4 magnetic nanosphere hybrid was developed for the first time to detect quercetin ultra-sensitively. CuFe2O4 nanospheres (average 189 nm) were synthesized and combined with MXene sheets, then electrostatically deposited onto a magnetic carbon paste electrode. A functional monomer was then electropolymerized onto this hybrid-modified electrode to form an imprinted polymeric layer, tailored for quercetin binding. Characterizations confirmed the morphological and magnetic properties of the materials. The sensor’s response factors were optimized, achieving a low detection limit of 1.6 nM and two linear ranges (0.005–0.7 μM and 0.7–10 μM). The sensor showed excellent stability, repeatability, reproducibility, and selectivity, and was successfully used to quantify quercetin in dietary supplements.

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.

An ultra-sensitive tailor-made sensor for specific adsorption and separation of rutin based on imprinted cavities on magnetic sensing platform

Present study details the expansion of a sensing platform based on magnetic imprinted layer system for plant pigment. A scalable, simple, cost-effective and novel magnetic imprinted layer constructed of Fe3O4@polyaniline/reduce graphene oxide molecular imprinted membrane (M@PANI/rGO MIP) was manufactured on the surface of the magnetic carbon paste electrode (MCPE). The prepared M@PANI/rGO MIP was investigated with all the significant physical characteristics including composition, topography and morphology. The synthesized M@PANI/rGO MIP was displayed stability and exceptional electrochemical activity due to presenting tailor-made receptors. Upon the electrochemical investigation, a sensitive MIP sensing platform for the detection of rutin led to two linear calibration curves in the range of 0.01–1 pM and 0.00001–10 µM and an ultralow detection limit (0.356 fM). Consequently, the proposed MIP platform evidently was featured accurate detection of rutin in fruits and could be recommended for real-time analysis.

Application of magnetic nanoparticles modified with L-cysteine for pre-concentration and voltammetric detection of copper(II)

In the present study, magnetic solid-phase extraction (MSPE) was coupled with voltammetric method by using a magnetic carbon paste electrode (MCPE) to determine Cu(II) in aqueous mediums. For this purpose, L-cysteine functionalized core–shell Fe3O4@Au nanoparticles (Fe3O4@Au@L-cysteine) was used as an adsorbent during the extraction step. Following that, the magnetic adsorbent pre-concentrated with Cu(II) was collected on the surface of MCPE for electrochemical detection using differential pulse voltammetry. In the suggested assay, the extraction and determination of copper ions were carried out in a single electrochemical cell. The conditions of extraction and voltammetric determination were explored in detail. Under the optimal conditions (i.e., supporting electrolyte, phosphate buffer; sample pH, 5.0; Fe3O4@Au@L-cysteine amount, 10 mg L-1 (100 μL); agitation time, 120 s; reduction potential, −0.4 V; and reduction time, 90 s), the response currents were linear in 2.0 to 400.0 nmol L-1 Cu(II) concentration range. The limit of detection and reproducibility of the established method were calculated to be 0.4 nmol L-1 and 3.4%, respectively. The applicability of the suggested methodology was confirmed by analysis of Cu(II) in different water samples with recoveries of 96.4–103.6% (n = 3).

Electrochemical detection of Cr(III) and Cr(VI) in solution by using ZrO2 modified magnetic nanoparticles by redox probes

Herein, modified Fe3O4 magnetic nanoparticles by ZrO2 (MNPZs) were prepared by co-precipitation method. Prepared MNPZs were characterized with XRD, SEM, EDX, TEM, FTIR and VSM techniques. In addition, a modified magnetic carbon paste electrode (CPE) by MNPZ was prepared, and its interaction with Cr(III) and Cr(VI) ions was investigated in the presence of [Fe(CN)6]3-/4- and PBQ/H2Q redox probes via CV and EIS. An electrochemical technique based on observed behavior of redox probes with accumulated each forms of chromium was developed for speciation of Cr(III) and Cr(VI) in this work. Accumulated Cr(III) on CPE/MNPZ showed electrostatic attraction toward [Fe(CN)6]3-/4- redox probe and accumulated Cr(VI) showed a blocking behavior toward PBQ/H2Q redox probe. According to different behaviors of Cr(III) and Cr(VI) at electrode interface in the presence of redox probes, a new calibration for each forms of chromium ions and an entire protocol for Cr speciation are proposed based on voltammetry and impedimetry. After optimization of affecting experimental parameters on the electrode response, linear calibration curves from 1.0 × 10-9 to 1.0 × 10-3 M with sensitivity as 3.41 μA/M and detection limit (DL) as 8.1 × 10-10 M, and from 1.0 × 10-9 to 1.0 × 10-6 M with sensitivity as 4.07 kΩ/M and DL as 6.9 × 10-11 M, were obtained for Cr(III) by using [Fe(CN)6]3-/4- as a redox probe in CV and EIS methods, respectively. Also, linear calibration curves from 5.0 × 10-9 to 1.0 × 10-4 M with sensitivity as 1.79 μA/M and DL as 5.3 × 10-10 M, and from 1.0 × 10-9 to 5.0 × 10-5 M with sensitivity as 7.05 kΩ/M and DL as 4.5 × 10-10 M, were observed for Cr(VI) when use PBQ/H2Q as redox probe in CV and EIS methods, respectively.

Experimental and theoretical study for miR-155 detection through resveratrol interaction with nucleic acids using magnetic core-shell nanoparticles.

A novel electrochemical nanobiosensor for the detection of miR-155 (as breast cancer biomarker) is introduced . Fe3O4NPs@Ag core-shell nanoparticles were synthesized and their shape and characteristics were confirmed by scanning electron microscope (SEM) imaging, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) methods. Synthesized nanoparticles were applied onto the magnetic bar carbon paste electrode and then the amine-modified anti-miR-155 (single-stranded probes) was applied on the modified electrode surface and upon hybridization with target miR-155, resveratrol (RSV) was eventuallyapplied as an electrochemical label on the double-strand oligonucleotide. Differential pulse voltammetry (DPV) of the oxidation peak of RSV was assumed as the final signal by sweeping potential from 0 to 0.6V (vs. Ag/AgCl). The fabrication process was optimized through a series of experiments and the optimized process was confirmed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Thelinear range of the fabricated nanobiosensor was 0.5fM to 1.0nM and the detection limit was 0.15fM. The nanobiosensor was able to pass reproducibility and specificity tests using different types of mismatched target sequences.Spiked real samples of human serum were used to confirm thatthe nanobiosensor enablesdetection of miR-155 without any significant interferences from other moieties and molecules. Finally, the molecular dynamics simulation of the RSV interaction with single- and double-stranded oligonucleotide was performed and confirmed the preferential binding ofRSV to double-stranded DNA; therefore, it can be used as the electrochemical label of DNA and/or miRNA hybridization-based biosensors. Graphical abstract.

New and sensitive magnetic carbon paste electrode for voltammetry determination of morphine and methadone

A novel and sensitive modified magnetic carbon paste electrode (MMCPE) is introduced. Magnetic carbon paste electrode (MCPE) was fabricated by a ring magnet that was put behind an insulin syringe packed with a mixture of graphite powder, multi-walled carbon nanotube (MWCNT), and paraffin oil. The surface of the MCPE was modified by immersing the electrode in a suspension of nanomagnetic core-shell (Fe3O4@SiO2) for 20 s, while nanomagnetic core-shells were physically adsorbed on the surface of the electrode by the magnetic force. The electrochemical behavior of morphine and methadone was studied at this new modified electrode. The efficiency of MMCPE was compared with a simple CPE and two modified CPEs prepared by mixtures of (graphite + MWCNT) and (graphite + MWCNT + nanomagnetic core-shell). The results showed that the sensitivity of MMCPE was higher than the three other CPEs. As a result, direct attachment of Fe3O4@SiO2 magnetic nanoparticles to the surface of the CPE by the magnetic force showed much higher surface area and electrode sensitivity compared to when the NPs were mixed with other compounds. Our studies showed this electrode is not selectable and can be used as a general electrode for all electro-active compounds. The electro-active surface area of MMCPE was obtained by Randles–Sevcik equation. Square wave voltammetry (SWV) was applied for determination of morphine and methadone in a linear range of 5.0 × 10–9 to 1.8 × 10–6 M and 1.0 × 10–8 to 8.0 × 10–6 M, with detection limits of 1.6 nM and 3 nM, respectively. Eventually, the proposed electrode was applied to determine morphine and methadone in urine samples.

A magnetic nanocomposite prepared from electrospun CoFe2O4 nanofibers and graphene oxide as a material for highly sensitive determination of rutin

A magnetic bar carbon paste electrode (MBCPE) modified with cobalt ferrite magnetic electrospun nanofibers (NFs) and graphene oxide (GO) is described for the electrochemical determination of rutin. The NFs were prepared by electrospinning using a solution that contains poly(vinyl pyrrolidone) (PVP) and Co(II) and Fe(III) nitrates as metal sources. Carbon paste was prepared by hand mixing GO, CoFe2O4 NFs and graphite. This paste was then packed into the end of a glass tube and a very small magnetic bar was inserted into the tube to be coated with the carbon paste to provide a magnetic field. The MBCPE was used to attract the magnetic nanofibers to the electrode surface. Cyclic voltammetry and differential pulse voltammetry techniques were used to study the electrochemical behavior of rutin on the modified MBCPE at pH2.5. The electrocatalytic current, best measured at a potential ofaround 0.5V (vs. Ag/AgCl), varies with the rutin concentration in two linear ranges, viz. from0.001-0.1nM and from 1.0-100nM, with a 0.94 pM detection limit. The electrode was successfully applied to the determination of rutin in lemon, red apple, lime and orange juices. Graphical abstractSchematic representation of amodified magnetic bar carbon paste electrode for detection of rutin. To achieve the modified electrode, electrospun CoFe2O4 nanofibers, graphene oxide and a very small magnetic bar are packed into the end of a glass tube.

Comparison of two fabricated aptasensors based on modified carbon paste/oleic acid and magnetic bar carbon paste/Fe3O4@oleic acid nanoparticle electrodes for tetracycline detection

In this research, we have improved two aptasensors based on a modified carbon paste electrode (CPE) with oleic acid (OA), and a magnetic bar carbon paste electrode (MBCPE) with Fe3O4 magnetic nanoparticles and oleic acid (OA). After the immobilization process of anti-TET at the electrode surfaces, the aptasensors were named CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET respectively. In this paper, the detection of tetracycline is compared using CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET aptasensors. These modified electrodes were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), UV–vis spectroscopy, and voltammetric methods. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10−12–1.0×10−7M and 3.0×10−13M respectively by EIS method. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10−10–1.0×10−7M with a limit of detection of 2.9×10−11M using differential pulse voltammetry (DPV) technique. The MBCPE/Fe3O4NPs/OA/anti-TET aptasensor was used for determination of TET, and a liner range of 1.0×10−14–1.0×10−6M with a detection limit of 3.8×10−15M was obtained by EIS method. Also, the linear range and detection limit of 1.0×10−12–1.0×10−6M and 3.1×10−13M respectively, were obtained for MBCPE/Fe3O4NPs/OA/anti-TET aptasensor using DPV. The proposed aptasensors were applied for determination of tetracycline in some real samples such as drug, milk, honey and blood serum samples.

A novel electrochemical DNA biosensor based on a modified magnetic bar carbon paste electrode with Fe3O4NPs-reduced graphene oxide/PANHS nanocomposite

In this study, we have designed a label free DNA biosensor based on a magnetic bar carbon paste electrode (MBCPE) modified with nanomaterial of Fe3O4/reduced graphene oxide (Fe3O4NP-RGO) as a composite and 1- pyrenebutyric acid-N- hydroxysuccinimide ester (PANHS) as a linker for detection of DNA sequences. Probe (BRCA1 5382 insC mutation detection) strands were immobilized on the MBCPE/Fe3O4-RGO/PANHS electrode for the exact incubation time. The characterization of the modified electrode was studied using different techniques such as scanning electron microscopy (SEM), infrared spectroscopy (IR), vibrating sample magnetometer (VSM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry methods. Some experimental parameters such as immobilization time of probe DNA, time and temperature of hybridization process were investigated. Under the optimum conditions, the immobilization of the probe and its hybridization with the target DNA (Complementary DNA) were tested. This DNA biosensor revealed a good linear relationship between ∆Rct and logarithm of the complementary target DNA concentration ranging from 1.0×10−18molL−1 to 1.0×10−8molL−1 with a correlation coefficient of 0.9935 and a detection limit of 2.8×10−19molL−1. In addition, the mentioned biosensor was satisfactorily applied for discriminating of complementary sequences from non-complementary sequences. The constructed biosensor (MBCPE/Fe3O4-RGO/PANHS/ssDNA) with high sensitivity, selectivity, stability, reproducibility and low cost can be used for detection of BRCA1 5382 insC mutation.

Electrocatalytic oxidation of hydrazine on magnetic bar carbon paste electrode modified with benzothiazole and iron oxide nanoparticles: Simultaneous determination of hydrazine and phenol

A magnetic bar carbon paste electrode (MBCPE) modified with Fe3O4 magnetic nanoparticles (Fe3O4NPs) and 2-(3,4-dihydroxyphenyl) benzothiazole (DPB) for the electrochemical determination of hydrazine was developed. The DPB was firstly self-assembled on the Fe3O4NPs, and the resulting Fe3O4NPs/DPB composite was then absorbed on the designed MBCPE. The MBCPE was used to attract the magnetic nanoparticles to the electrode surface. Owing to its high conductivity and large effective surface area, the novel electrode had a very large current response for the electrocatalytic oxidation of hydrazine. The modified electrode was characterized by voltammetry, scanning electron microscopy, electrochemical impedance spectroscopy, infrared spectroscopy, and UV-visible spectroscopy. Voltammetric methods were used to study the electrochemical behaviour of hydrazine on MBCPE/Fe3O4NPs/DPB in phosphate buffer solution (pH = 7.0). The MBCPE/Fe3O4NPs/DPB, acting as an electrochemical sensor, exhibited very high electrocatalytic activity for the oxidation of hydrazine. The presence of DPB was found to reduce the oxidation potential of hydrazine and increase the catalytic current. The dependence of the electrocatalytic current on the hydrazine concentration exhibited two linear ranges, 0.1–0.4 μmol/L and 0.7–12.0 μmol/L, with a detection limit of 18.0 nmol/L. Additionally, the simultaneous determination of hydrazine and phenol was investigated using the MBCPE/Fe3O4NPs/DPB electrode. Voltammetric experiments showed a linear range of 100–470 μmol/L and a detection limit of 24.3 μmol/L for phenol, and the proposed electrode was applied to the determination of hydrazine and phenol in water samples.

Self-assembled monolayer of SH-DNA strand on a magnetic bar carbon paste electrode modified with Fe3O4@Ag nanoparticles for detection of breast cancer mutation

In the present work, a simple and new electrochemical biosensor was designed based on a magnetic bar carbon paste electrode (MBCPE) modified with iron oxide and silver nanoparticles (Fe3O4@Ag) for DNA detection. MBCPE/Fe3O4@Ag composite was used for the self-assembly monolayer (SAM) of thiolated single stranded DNA (SH-DNA). The morphology of Fe3O4NPs and Fe3O4NPs@Ag was studied by scanning electron microscopy (SEM), infrared spectroscopy (IR) and UV/Vis methods. Also, electrochemical techniques were applied for characterization of the designed biosensor. The experimental conditions (the immobilization and hybridization processes) were optimized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. MBCPE/Fe3O4@Ag/ssDNA biosensor revealed a wide liner range and low detection limit (0.fM) for detection of BRCA1 5382 mutation by EIS method. Under the optimum conditions, the suggested biosensor revealed high selectivity for discriminating the complementary sequences from non-complementary sequences.

A novel 5-fluorouracile anticancer drug sensor based on ZnFe2O4 magnetic nanoparticles ionic liquids carbon paste electrode

A carbon paste electrode modified in situ with ZnFe2O4 magnetic nanoparticles (ZnFe2O4/MNPs) and 1,3-dipropylimidazolium bromide ionic liquid was developed for the determination of 5-fluorouracile (5-FU) in drug samples. The electrochemical behavior of 5-FU was investigated employing linear sweep voltammetry (LSV), square wave voltammety (SWV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). ZnFe2O4/MNPs synthesized by co-precipitation method and characterized with different methods such as energy dispersive X-ray analysis (EDAX), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). After optimization of experimental conditions employing the novel sensor at pH 7.0, the electro-oxidation peak currents for 5-FU was found to vary linearly with its concentrations in the range of 0.1–1400μM using SWV method. The ZnFe2O4/MNPs ionic liquids carbon paste electrode (ZnFe2O4/MNPs/IL/CPE) showed several advantages, such as a high sensitivity in trace analysis, good detection limits and excellent reproducibility. Furthermore, the ZnFe2O4/MNPs/IL/CPE was successfully applied for the analysis of 5-FU in pharmaceutical and urine samples.

Fe3O4 and MnO2 assembled on halloysite nanotubes: A highly efficient solid-phase extractant for electrochemical detection of mercury(II) ions

In this study, a novel and simple magnetic electrochemical sensing protocol for the sensitive detection of Hg(II) in aqueous media was demonstrated. For this purpose, the halloysite nanotubes-iron oxide–manganese oxide nanocomposite (HNTs-Fe3O4–MnO2) was successfully synthesized for the first time. The synthesis process involves the deposition of Fe3O4 nanoparticles on the surface of HNTs using a simple chemical precipitation method, subsequent formation of wire-like MnO2 nanoparticles on the surface of HNTs-Fe3O4 composites by hydrothermal method with potassium permanganate (KMnO4) and ammonium persulfate ((NH4)2S2O8). The resulting HNTs-Fe3O4–MnO2 nanocomposite was suspended in mercury solution and then brought on the surface of a magnetic carbon paste electrode (MCPE). The amount of analyte was detected electrochemically by applying differential pulse voltammetry (DPV). The conditions of extraction and voltammetric determination were studied and optimized. The proposed method exhibited a linear relationship towards Hg(II) concentrations ranging from 0.5 to 150μgL−1. The detection limit achieved was 0.2μgL−1 (3Sb/m), which is lower than the US Environmental Protection Agency (EPA) standard (2μgL−1 for drinkable water). The proposed methodology was applied for quantification of Hg(II) in real water samples and good recoveries were obtained from 96.0 to 102.7%.

Magnetic Carbon Paste Electrode Modified with a High Performance Composite Based on Molecularly Imprinted Carbon Nanotubes for Sensitive Determination of Levofloxacin

A selective electrochemical sensor based on molecularly imprinted magnetite decorated carbon nanotubes (MCNTs@MIP) was developed for the determination of levofloxacin (Lv). The preparation of molecularly imprinted polymers was performed using Lv as template, MCNTs as support, methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linker. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the composites structures. The resulting MCNTs@MIP were suspended in Lv solution and then collected on the surface of a carbon paste electrode via a permanent magnet, situated within the carbon paste electrode and then the voltammetry signals were recorded. Under the optimized experimental conditions, a linear response was obtained in the range of 0.003–0.440 μM with a detection limit of 0.8 nM. The applicability of the method for complex matrix analysis was also evaluated and the modified electrode showed good stability and reproducibility.

Simultaneous determination of hydrazine and hydroxylamine on a magnetic bar carbon paste electrode modified with reduced graphene oxide/Fe3O4 nanoparticles and a heterogeneous mediator

We have developed a modified magnetic bar carbon paste electrode in combination with 1-[2,4-Dihydroxy-5-(phenylazo-4-sulphonic acid)phenyl]-1-phenylmethanon (DPSPP) and reduced graphene oxide/Fe3O4 nanomaterials which was named MBCPE/DPSPP/RGO/Fe3O4NPs for the determination of hydrazine and hydroxylamine. The modified electrode was characterized by various techniques such as voltammetry, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and the influence of different variables on the response of sensor was studied, too. The electrochemical behavior of hydrazine was investigated at MBCPE/DPSPP/RGO/Fe3O4NPs by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques in a phosphate buffer solution (pH 7.0). MBCPE/DPSPP/RGO/Fe3O4NPs as a novel electrochemical sensor exhibited catalytic activity toward the oxidation of hydrazine. The potential of hydrazine oxidation was shifted to more negative potentials, and its oxidation peak current increased on the modified electrode. The electrocatalytic current of hydrazine showed a good relationship in the concentration range of 120.0–600.0 nM, with a detection limit of 40.0 nM. In addition, simultaneous determination of hydrazine and hydroxylamine was studied at the proposed electrode. Voltammetric investigations showed a linear range of 10–155.0 μM with a detection limit of 3.4 μM for hydroxylamine. The proposed electrode was applied for determination of hydrazine and hydroxylamine in water samples, too.

Magnetic molecularly imprinted polymer nanoparticles based electrochemical sensor for the measurement of Gram-negative bacterial quorum signaling molecules (N-acyl-homoserine-lactones).

We have developed a novel and economical electrochemical sensor to measure Gram-negative bacterial quorum signaling molecules (AHLs) using magnetic nanoparticles and molecularly imprinted polymer (MIP) technology. Magnetic molecularly imprinted polymers (MMIPs) capable of selectively absorbing AHLs were successfully synthesized by surface polymerization. The particles were deposited onto a magnetic carbon paste electrode (MGCE) surface, and characterized by electrochemical measurements. Differential Pulse Voltammetry (DPV) was utilized to record the oxidative current signal that is characteristic of AHL. The detection limit of this assay was determined to be 8×10(-10)molL(-1) with a linear detection range of 2.5×10(-9)molL(-1) to 1.0×10(-7)molL(-1). This Fe3O4@SiO2-MIP-based electrochemical sensor is a valuable new tool that allows quantitative measurement of Gram-negative bacterial quorum signaling molecules. It has potential applications in the fields of clinical diagnosis or food analysis with real-time detection capability, high specificity, excellent reproducibility, and good stability.

Preparation of magnetic TNT-imprinted polymer nanoparticles and their accumulation onto magnetic carbon paste electrode for TNT determination

In this study, the TNT-imprinted polymer shell was created on nano-sized Fe3O4 cores in order to construct the nano-sized magnetic molecularly imprinted polymer (nano-MMIP). For this purpose, the surface of the synthesized magnetic nanoparticles was modified with methacrylic acid. The modified particles were then utilized as the core on which the TNT-imprinted polymeric shell was synthesized. The synthesized materials were then characterized by scanning electron microscopy, FT-IR and thermal gravimetric analysis (TGA). The resulting nano-MMIP particles were suspended in TNT solution and then collected on the surface of a carbon paste electrode via a permanent magnet, situated within the CP electrode. The extracted TNT was analyzed on the CP electrode by applying square wave voltammetry (SWV). It was found that the oxidative signal of TNT is much favorable for TNT detection on the resulting magnetic carbon paste electrode. The electrode with nano-MMIP showed distinctly higher signal to TNT, compared to that containing magnetic non-imprinted polymer (MNIP) nanoparticles. All parameters influencing the method performance including extraction pH, extraction time and sorbent amount were evaluated and optimized. The developed method showed a dynamic linear concentration range of 1.0–130.0nM for TNT measurement. The detection limit of the method was calculated to be 0.5nM. The method showed appropriate capability for TNT analysis in real water samples.

A dramatically enhanced electrochemiluminescence assay for CA125 based on dendrimer multiply labeled luminol on Fe3O4 nanoparticles

A novel electrochemiluminescence immunosensor for carbohydrate antigen 125 detection based on dendrimer and magnetic nanoparticles were developed in this study. In the assay, carbohydrate antigen 125 was used as a model analyte, and the detection was based on a sandwich structure formed by the first antibody, the carbohydrate antigen 125 and a second antibody labeled with luminol through poly(diethylenetriaminepentaacetic acid-ethylene glycol) ester dendrimer. The sandwich system was then modified on Fe3O4 magnetic nanoparticles and immobilized on a magnetic force-controlled carbon paste electrode with the help of a magnet to form the immunosensor. The result showed that the ECL immunosensor was ultrasensitive to carbohydrate antigen 125 detection at a concentration of 0.2–100μU/mL with a detection limit of 0.032μU/mL. The signal was enhanced dramatically than that produced by luminol labeled only, so was the sensitivity of the immunosensor, partly because much more probe molecules could be immobilized on the electrode surface. This also proved that dendrimers could be a useful material for the fabrication of ultrasensitive sensors. The proposed immunosensor was successfully applied to detect CA125 in real human plasma samples, which was compared with the result of conventional ELISA methods.

A Dopamine Sensor Based on Pre-Concentration by Magnetic Nanoparticles

Herein, Fe3O4magnetic nanoparticles (MNPs) were synthesized and characterized. Afterward, a magnetic carbon paste electrode (MCPE) was modified with MNPs via casting and drying MNPs on top of the MCPE (MCPE/MNP). Electrochemical behavior of the MCPE/MNP was studied by cyclic voltammetry in the presence of [Fe(CN)6]3−/4−as a redox probe, and surfacepKaof MNPs was evaluated as6.3±0.1. The behavior of MCPE/MNP towards dopamine (DA) and ascorbic acid (AA) has been investigated by electrochemical methods, and the obtained results showed that the MCPE/MNP has adsorption behavior towards only DA. Based on this behavior, the DA molecules were pre-concentrated on top of the MCPE/MNP and followed with stripping in DA free solution. Subsequent to experimental and instrumental optimization, a calibration curve from5.0×10-6to1.0×10-3 M DA withr2=0.999, DL =7.6×10-7 M DA, and RSD = 4.6%, was obtained in the presence of1.0×10-3 M AA. Performance of the MCPE/MNP was successfully tested in a pharmaceutical sample.