The investigation of electrochemical properties for Fe3O4@Pt nanocomposites and an enhancement sensing for nitrite

Development of aptamer surface-enhanced Raman spectroscopy sensor based on Fe3O4@Pt and Au@Ag nanoparticles for the determination of acetamiprid

As a common chlorinated nicotinic pesticide with high insecticidal activity, acetamiprid has been widely used for pest control. However, the irrational use of acetamiprid will pollute the environment and thus affect human health. Therefore, it is crucial to develop a simple, highly sensitive, and rapid method for acetamiprid residue detection. In this study, the capture probe (Fe3O4@Pt-Aptamer) was connected with the signal probe (Au@DTNB@Ag CS-cDNA) to form an assembly with multiple SERS-enhanced effects. Combined with magnetic separation technology, a SERS sensor with high sensitivity and stability was constructed to detect acetamiprid residue. Based on the optimal conditions, the SERS intensity measured at 1333 cm-1 is in relation to the concentration of acetamiprid in the range 2.25 × 10-9-2.25 × 10-5 M, and the calculated limit of detection (LOD) was 2.87 × 10-10 M. There was no cross-reactivity with thiacloprid, clothianidin, nitenpyram, imidacloprid, and chlorpyrifos, indicating that this method has good sensitivity and specificity. Finally, the method was applied to the detection of acetamiprid in cucumber samples, and the average recoveries were 94.19-103.58%, with RSD < 2.32%. The sensor can be used to analyse real samples with fast detection speed, high sensitivity, and high selectivity.

Electrochemical sensor for sensitive nitrite and sulfite detection in milk based on acid-treated Fe3O4@SiO2 nanoparticles

In this work, a simple electrochemical sensing platform based on acid-treated Fe3O4@SiO2 nanoparticles was successfully prepared for nitrite and sulfite detection. Fe3O4@SiO2 nanoparticles were synthesized through the sol-gel and hydrothermal methods. Fe3O4@SiO2 presented positive charges after acid treatment, which could enhance the electrostatic attraction between Fe3O4@SiO2 and nitrite and sulfite. The Fe3O4@SiO2(acid-treated) modified magnetic glassy carbon electrode (MGCE) was applied to detect nitrite and sulfite using differential pulse voltammetry and cyclic voltammetry. Under optimized conditions, the developed electrochemical sensor presented good analytical properties for nitrite and sulfite detection with detection limits of 3.33 μmol/L and 31.57 μmol/L, respectively. The good recoveries varied from 85.18% to 111.02%, with a relative standard deviation of 0.23-4.80%. Furthermore, the Fe3O4@SiO2(acid-treated) modified MGCE showed better selectivity, reproducibility, and repeatability in nitrite and sulfite detection. Therefore, this proposed electrochemical sensor provides a new method for developing a nitrite and sulfite detection sensor.

MoS2 nanosheets supported on anodic aluminum oxide membrane: An effective interface for label-free electrochemical detection of microRNA

The interesting adsorption affinity of two-dimensional nanosheets to single stranded over double stranded nucleic acids have stimulated the exploration of these materials in biosensing. Herein, MoS₂ nanosheets decorated anodic aluminum oxide (AAO) membrane was simply prepared by suction filtration. The MoS₂/AAO hybrid membrane was initially applied to the electrochemical detection of microRNA using let-7a as the model. When let-7a was incubated with its complementary DNA, double stranded DNA-RNA formed and which displayed weak adsorption capability to the hybrid membrane. And thus the steric effect combining the electrostatic repulsion of the backbone phosphate of nucleic acids for [Fe(CN)₆]^3- transport across the hybrid membrane varied with the concentration of let-7a. In this way, a label-free electrochemical detection method for microRNA was established by monitoring the change of the redox current of [Fe(CN)₆]^3-. To further improve the detection sensitivity of the method, we proposed two separate strategies focusing on the amplification of the target-induced steric hindrance with DNA nanostructure and the magnification of the electrode sensitivity for [Fe(CN)₆]^3- by electrode modification. By using the two strategies, the hybrid membrane based-detection method exhibited broad linear range, low detection limit and good selectivity as well as reproducibility. Therefore, this study provided a proof-of-concept for the application of two-dimensional material to nucleic acids detection.

Polyaniline-Supported Nickel Oxide Flower for Efficient Nitrite Electrochemical Detection in Water

A modified electrode with conducting polymer (Polyaniline) and NiO nanoflowers was prepared to detect nitrite ions in drinking water. A simple method was used to prepare the NiO nanoflower (NiOnF). Several techniques characterized the as-prepared NiOnF to determine the chemical structure and surface morphology of the NiO, such as XRD, XPS, FT-IR, and TGA. The activity of the electrode toward nitrite sensing was investigated over a wide range of pH (i.e., 2 to 10). The amperometry method was used to determine the linear detection range and limit. Accordingly, the modified electrode GC/PANI/NiOnf showed a linear range of detection at 0.1-1 µM and 1-500 µM. At the same time, the limit of detection (LOD) was 9.7 and 64 nM for low and high concentrations, respectively. Furthermore, the kinetic characteristics of nitrite, such as diffusion and transport coefficients, were investigated in various media. Moreover, the charge transfer resistance was utilized for nitrite electrooxidation in different pH values by the electrochemical impedance technique (EIS). The anti-interfering criteria of the modified surfaces were utilized in the existence of many interfering cations in water (e.g., K⁺, Na⁺, Cu²⁺, Zn²⁺, Ba²⁺, Ca²⁺, Cr²⁺, Cd²⁺, Pd²⁺). A real sample of the Nile River was spiked with nitrite to study the activity of the electrode in a real case sample (response time ~4 s). The interaction between nitrite ions and NiO{100} surface was studied using DFT calculations as a function of adsorption energy.

Fe3O4-Fused Magnetic Air Stone Prepared From Wasted Iron Slag Enhances Denitrification in a Biofilm Reactor by Increasing Electron Transfer Flow

nFe₃O₄ was prepared from waste iron slag and loaded onto air stone (named magnetic air stone or MAS in the following text). The main component of air stone is carborundum. To study the magnetic effects of MAS on denitrification, a biofilm reactor was built, and its microbial community structure and electron transfer in denitrification were analyzed. The results showed that MAS improved the performance of the reactor in both carbon and nitrogen removal compared with air stone (AS) control, and the average removal efficiencies of COD, TN, and NH₄⁺-N increased by 17.15, 16.1, and 11.58%, respectively. High-throughput sequencing revealed that magnetism of MAS had a significant effect on the diversity and richness of microorganisms in the biofilm. The MAS also reduced the inhibition of rotenone, mipalene dihydrochloride (QDH), and sodium azide on the respiratory chain in denitrification and enhanced the accumulation of nitrite, in order to provide sufficient substrate for the following denitrification process. Therefore, the denitrification process is accelerated by the MAS. The results allowed us to deduce the acceleration sites of MAS in the denitrification electron transport chain.

The existence of MAS provides a new rapid method for the denitrifying electron transport process. Even in the presence of respiratory inhibitors of denitrifying enzymes, the electron transfer acceleration provided by MAS still exists objectively. This is the mechanism through which MAS can restore the denitrification process inhibited by respiratory inhibitors to a certain extent.

Au@Carbon quantum Dots-MXene nanocomposite as an electrochemical sensor for sensitive detection of nitrite

A highly sensitive electrochemical sensor was developed through a one-pot green synthesis method for nitrite detection based on the electrochemical technique. Xylan-based carbon quantum dots (CQDs) were used as green in situ reducing agent to prepare CQDs capped gold nanoparticles (Au@CQDs). MXene of good electrical conductivity was used as the immobilized matrix to fabricate Au@CQDs-MXene nanocomposites with the advantages of good electrical conductivity and electrocatalysis. An electrochemical sensor for nitrite monitor was obtained by loading the Au@CQDs-MXene on a glassy carbon electrode. The sensor presents high sensitivity, good stability, wide linear range, and excellent selectivity due to the high catalytic activity of AuNPs and CQDs, the large specific surface area of MXene, and exceptional electrical conductivity of AuNPs and MXene. Under the optimal condition, the linear detection range of the sensor was from 1 μM to 3200 μM with a detection limit of 0.078 μM (S/N = 3), which was superior to most reported sensors using differential pulse voltammetry (DPV) method. Furthermore, this sensor was successfully applied to detect nitrite in tap water and salted vegetables with satisfactory recoveries. This modified electrocatalytic sensor shows a new pathway to fabricate nitrite detection sensor with feasibility for practical application.

Magnetic Molecularly Imprinted Polymers: Synthesis and Applications in the Selective Extraction of Antibiotics

Recently, magnetic molecularly imprinted polymers (MMIPs) have integrated molecular imprinting technology (MIT) and magnetic separation technology and become a novel material with specific recognition and effective separation of target molecules. Based on their special function, they can be widely used to detect contaminants such as antibiotics. The antibiotic residues in the environment not only cause harm to the balance of the ecosystem but also induce bacterial resistance to specific antibiotics. Given the above consideration, it is especially important to develop sensitive and selective methods for measuring antibiotics in the complex matrix. The combination of MMIPs and conventional analytical methods provides a rapid approach to separate and determine antibiotics residues. This article gives a systematic overview of synthetic approaches of the novel MMIPs materials, briefly introduces their use in sample pretreatment prior to antibiotic detection, and provides a perspective for future research.

Magnetic nanomaterials based electrochemical (bio)sensors for food analysis

It is widely accepted that nanotechnology attracted more interest because of various values that nanomaterial applications offers in different fields. Recently, researchers have proposed nanomaterials based electrochemical sensors and biosensors as one of the potent alternatives or supplementary analytical tools to the conventional detection procedures that consumes a lot of time. Among different nanomaterials, researchers largely considered magnetic nanomaterials (MNMs) for developing and fabricating the electrochemical (bio)sensors for numerous utilizations. Among several factors, healthier and higher quality foods are the most important preferences of consumers and manufacturers. For this reason, developing new techniques for rapid, precise as well as sensitive determination of components or contaminants of foods is very important. Therefore, developing the new electrochemical (bio)sensors in food analysis is one of the key and effervescent research fields. In this review, firstly, we presented the properties and synthesis strategies of MNMs. Then, we summarized some of the recently developed MNMs-based electrochemical (bio)sensors for food analysis including detecting the antioxidants, synthetic food colorants, pesticides, heavy metal ions, antibiotics and other analytes (bisphenol A, nitrite and aflatoxins) from 2010 to 2020. Finally, the present review described advantages, challenges as well as future directions in this field.

A highly conductive thin film composite based on silver nanoparticles and malic acid for selective electrochemical sensing of trichloroacetic acid

A highly conductive thin film composite based on silver nanoparticles (AgNPs) and malic acid (MA) was deposited on glassy carbon electrode (GCE) for the selective and sensitive electrochemical sensing of trichloroacetic acid (TCA). The casting solution containing MA functionalized AgNPs was employed as a precursor for the thermal deposition of the AgNPs integrated MA thin film composite onto the GCE surface. The uniform coverage of AgNPs within the thin film composite at GCE was obtained by field emission scanning electron microscopy (FESEM). A significantly high charge transfer resistance of the modified electrode (85.7 Ω for AgNPs-MA/GCE in 2 mM [Fe(CN)₆]^3-/4- at a bias of +0.235 V as compared to bare GCE (38.01 Ω) verified the optimum coating of AgNPs-MA composite at the surface of the electrode. The AgNPs-MA composite deposited GCE revealed substantial electrocatalytic activity toward TCA reduction with significantly enhanced reduction current. The novel electrode manifested a linear square wave voltammetric (SWV) response over the concentration ranges of 0.1-2 (R² = 0.9953) and 4-100 μM (R² = 0.9969) with a limit of detection (LOD) and limit of quantification (LOQ) of 30 nM and 92.5 nM, respectively. The modified electrode exhibited an excellent long-term stability (30 days) with the retention of >95% of initial current. The selectivity of the proposed electrode for the determination of TCA was examined in the presence of dichloroacetic acid (DCA) and monochloroacetic acid (MCA) with the retention of high recovery percentages.

Simultaneous determination of steroid drugs in the ointment via magnetic solid phase extraction followed by HPLC-UV

The copper-coated iron oxide nanoparticles with core-shell were produced by deposition of a Cu shell on Fe₃O₄ NPs through reduction of Cu²⁺ ions in solution using NaBH₄. Subsequently, the organosulfur compound, bis-(2,4,4-trimethylpentyl)-dithiophosphinic acid (b-TMP-DTPA), was used to form self-assembled monolayer in order to modify sorbent's surface via covalent bonding between Cu and thiol (–SH) terminal groups. The prepared magnetic nanoparticles were characterized by using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and thermo gravimetric analysis (TGA). Then, the application of this new sorbent was investigated to extract the steroid drugs in ointment samples with the aid of ultrasound. An external magnetic field was applied to collect the magnetic nanoparticles (MNPs). The extracted analytes were desorbed using acetonitrile. The obtained extraction solution was analyzed by HPLC-UV. The main affecting factors on the extraction efficiency including pH, sonication time, amount of sorbent, salt concentration, and desorption conditions were optimized in detail. Under the optimum conditions, good linearity was obtained in the range of 2.5–250.0 µg/ L with reasonable linearity (R² > 0.99) and the limits of detection (LODs) ranged between 0.5 and 1.0 µg/L (based on S/N = 3). Repeatability (intra-day precision) based on five replicates and preconcentration factors were calculated to be 3.6%–4.7% and 87–116, respectively. Relative recoveries in ointment samples at two spiked levels of the target analytes were obtained in the range of 90.0%–103.2%. The results illustrated that the Fe₃O₄@Cu@ b-TMP-DTPA NPs have the capability of extraction of steroid drugs from ointment samples.

A new electrochemical sensor for highly sensitive and selective detection of nitrite in food samples based on sonochemical synthesized Calcium Ferrite (CaFe2O4) clusters modified screen printed carbon electrode

Herein, we report a novel, disposable electrochemical sensor for the detection of nitrite ions in food samples based on the sonochemical synthesized orthorhombic CaFe₂O₄ (CFO) clusters modified screen printed electrode. As synthesized CFO clusters were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformer infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and amperometry (i-t). Under optimal condition, the CFO modified electrode displayed a rapid current response to nitrite, a linear response range from 0.016 to 1921 µM associated with a low detection limit 6.6 nM. The suggested sensor also showed the excellent sensitivity of 3.712 μA μM^-1 cm^-2. Furthermore, a good reproducibility, long-term stability and excellent selectivity were also attained on the proposed sensor. In addition, the practical applicability of the sensor was investigated via meat samples, tap water and drinking water, and showed desirable recovery rate, representing its possibilities for practical application.

A novel strategy to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst with enhanced thermal stability

A novel strategy has been proposed to fabricate a hierarchical Ni–Al LDH platinum nanocatalyst (LDH-Pt).

Au nanoparticle modified carbon paper electrode for an electrocatalytic oxidation nitrite sensor

A AuNPs/CP electrode was fabricated by an electrodeposition technique. The highest electrocatalytic activity for nitrite oxidation was obtained with the 35 consecutive cycles modified electrode.

Highly sensitive biosensor based on the synergistic effect of Fe3O4–Co3O4 bimetallic oxides and graphene

Synergistic effect of Fe₃O₄–Co₃O₄ nanoparticles and reduced graphene oxide allows the sensitive electrochemical detection of dopamine and uric acid.

Magnetic sensing film based on Fe₃O₄@Au-GSH molecularly imprinted polymers for the electrochemical detection of estradiol

A novel magnetic molecularly imprinted sensing film (MMISF) was fabricated for the determination of estradiol (E2) based on magnetic glassy carbon electrode (MGCE) and magnetic molecularly imprinted polymers (MMIPs). The MMIPs were synthesized by in situ polymerization of glutathione (GSH)-functionalized gold (Au)-coated Fe3O4 (Fe3O4@Au-GSH) nanocomposites and aniline. The MMISF was constructed with MMIPs via a kind of "soft modification" where MMIPs were assembled and immobilized on the surface of MGCE or removed from it by freely installing a magnet into MGCE or not. The E2-MMIPs were obtained by MMIPs recognizing E2 from sample, and the electrochemical detection was carried out after forming the "soft modification" sensing film by putting MGCE into the E2-MMIPs suspension liquid. Afterwards, the "soft modification" MMISF was peeled off from the electrode by removing the magnet from MGCE. The interface of the electrode could be quickly refreshed through simple treatment for the next detection. The structures and morphologies of Fe3O4@Au-GSH, MMIPs and MMISF were investigated by Fourier transform infrared spectrometer, ultraviolet and visible spectrophotometer, scanning electron microscope and atomic force microscope. In addition, the MMISF was successfully used for detecting E2 in milk powder with good sensitivity, selectivity, reproducibility and efficiency. The linear range of the MMISF for E2 was 0.025-10.0μmolL(-1) with the limit of detection of 2.76nmolL(-1) (S/N= 3).

Synthesis and characterization of Pt magnetic nanocatalysts with a TiO2 or CeO2 layer

The Pt magnetic nanocatalysts with a TiO₂ or CeO₂ layer have been fabricated successfully.

Synthesis and characterization of ferric tannate as a novel porous adsorptive-catalyst for nitrogen removal from wastewater

Ferric tannate was synthesized herein using tannic acid and ferric chloride at neutral pH, showing a unique capacity for adsorption-catalyzed conversion of NH₄⁺-N and NO₂⁻-N to N₂.

Simultaneous electrochemical detection of dopamine and ascorbic acid using an iron oxide/reduced graphene oxide modified glassy carbon electrode

The fabrication of an electrochemical sensor based on an iron oxide/graphene modified glassy carbon electrode (Fe₃O₄/rGO/GCE) and its simultaneous detection of dopamine (DA) and ascorbic acid (AA) is described here. The Fe₃O₄/rGO nanocomposite was synthesized via a simple, one step in-situ wet chemical method and characterized by different techniques. The presence of Fe₃O₄ nanoparticles on the surface of rGO sheets was confirmed by FESEM and TEM images. The electrochemical behavior of Fe₃O₄/rGO/GCE towards electrocatalytic oxidation of DA was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analysis. The electrochemical studies revealed that the Fe₃O₄/rGO/GCE dramatically increased the current response against the DA, due to the synergistic effect emerged between Fe₃O₄ and rGO. This implies that Fe₃O₄/rGO/GCE could exhibit excellent electrocatalytic activity and remarkable electron transfer kinetics towards the oxidation of DA. Moreover, the modified sensor electrode portrayed sensitivity and selectivity for simultaneous determination of AA and DA. The observed DPVs response linearly depends on AA and DA concentration in the range of 1–9 mM and 0.5–100 μM, with correlation coefficients of 0.995 and 0.996, respectively. The detection limit of (S/N = 3) was found to be 0.42 and 0.12 μM for AA and DA, respectively.

A nanocomposite/crude extract enzyme-based xanthine biosensor

A novel amperometric biosensor for xanthine was developed based on covalent immobilization of crude xanthine oxidase (XOD) extracted from bovine milk onto a hybrid nanocomposite film via glutaraldehyde. Toward the preparation of the film, a stable colloids solution of core-shell Fe3O4/polyaniline nanoparticles (PANI/Fe3O4 NPs) was dispersed in solution containing chitosan (CHT) and H2PtCl6 and electrodeposited over the surface of a carbon paste electrode (CPE) in one step. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used for characterization of the electrode surface. The developed biosensor (XOD/CHT/Pt NPs/PANI/Fe3O4/CPE) was employed for determination of xanthine based on amperometric detection of hydrogen peroxide (H2O2) reduction at -0.35V (vs. Ag/AgCl). The biosensor exhibited a fast response time to xanthine within 8s and a linear working concentration range from 0.2 to 36.0μM (R(2)=0.997) with a detection limit of 0.1μM (signal/noise [S/N]=3). The sensitivity of the biosensor was 13.58μAμM(-1)cm(-2). The apparent Michaelis-Menten (Km) value for xanthine was found to be 4.7μM. The fabricated biosensor was successfully applied for measurement of fish and chicken meat freshness, which was in agreement with the standard method at the 95% confidence level.