Fe3O4-Polyaniline Nanocomposite for Non-enzymatic Electrochemical Detection of 2,4-Dichlorophenoxyacetic Acid

Quantification of 2,4-dichlorophenoxyacetic acid in environmental samples using imprinted polyethyleneimine with enhanced selectivity as a selective adsorbent in ambient plasma mass spectrometry

Detection and quantification of various organic chemicals in the environment is critical to track their fate and control their levels. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely applied phenoxy herbicide with potential toxicity to fish and other aquatic organisms. In this study, we address the need for improved detection of 2,4-D by introducing a novel analytical method for its quantification. This method relies on the selective extraction of 2,4-D using MIPs and their subsequent direct analysis using ambient plasma mass spectrometry. During the synthesis, MIPs with various degrees of glycidol (GLY) functionalization were obtained. Experimental data showed that MIPs with no GLY functionalization displayed the highest adsorption capacity. Conversely, MIPs with 30% GLY functionalization exhibited the greatest selectivity for 2,4-D, rendering them valuable for extraction of 2,4-D even in the presence of other contaminants. Finally, the obtained MIPs were applied for quantification of 2,4-D in various water samples through direct analysis using a specially designed ambient plasma mass spectrometry setup. This approach improved the detection limits by 200-fold compared to pure solution analysis. The quantification of 2,4-D in river water samples yielded highly satisfactory recoveries, demonstrating the effective utility of the proposed analytical setup for real-life water sample analysis.

A Ratiometric Biosensor Containing Manganese Dioxide Nanosheets and Nitrogen-Doped Quantum Dots for 2,4-Dichlorophenoxyacetic Acid Monitoring

Nanomaterials are desirable for sensing applications. Therefore, MnO2 nanosheets and nitrogen-doped carbon dots (NCDs) were used to construct a ratiometric biosensor for quantification of 2,4-dichlorophenoxyacetic acid. The MnO2 nanosheets drove the oxidation of colorless o-phenylenediamine to OPDox, which exhibits fluorescence emission peaks at 556 nm. The fluorescence of OPDox was efficiently quenched and the NCDs were recovered as the ascorbic acid produced by the hydrolyzed alkaline phosphatase (ALP) substrate increased. Owing to the selective inhibition of ALP activity by 2,4-D and the inner filter effect, the fluorescence intensity of the NCDs at 430 nm was suppressed, whereas that at 556 nm was maintained. The fluorescence intensity ratio was used for quantitative detection. The linear equation was F = 0.138 + 3.863·C 2,4-D (correlation coefficient R2 = 0.9904), whereas the limits of detection (LOD) and quantification (LOQ) were 0.013 and 0.040 μg/mL. The method was successfully employed for the determination of 2,4-D in different vegetables with recoveries of 79%~105%. The fluorescent color change in the 2,4-D sensing system can also be captured by a smartphone to achieve colorimetric detection by homemade portable test kit.

Protein-Aided Synthesis of Copper-Integrated Polyaniline Nanocomposite Encapsulated with Reduced Graphene Oxide for Highly Sensitive Electrochemical Detection of Dimetridazole in Real Samples

Dimetridazole (DMZ) is a derivative of nitroimidazole and is a veterinary drug used as an antibiotic to treat bacterial or protozoal infections in poultry. The residues of DMZ cause harmful side effects in human beings. Thus, we have constructed a superior electrocatalyst for DMZ detection. A copper (Cu)-integrated poly(aniline) (PANI) electrocatalyst (PANI-Cu@BSA) was prepared by using a one-step method of biomimetic mineralization and polymerization using bovine serum albumin (BSA) as a stabilizer. Then, the synthesized PANI-Cu@BSA was encapsulated with reduced graphene oxide (rGO) using an ultrasonication method. The PANI-Cu@BSA/rGO nanocomposite had superior water dispersibility, high electrical conductivity, and nanoscale particles. Moreover, a PANI-Cu@BSA/rGO nanocomposite-modified, screen-printed carbon electrode was used for the sensitive electrochemical detection of DMZ. In phosphate buffer solution, the PANI-Cu@BSA/rGO/SPCE displayed a current intensity greater than PANI-Cu@BSA/SPCE, rGO/SPCE, and bare SPCE. This is because PANI-Cu@BSA combined with rGO increases fast electron transfer between the electrode and analyte, and this synergy results in analyte-electrode junctions with extraordinary conductivity and active surface areas. PANI-Cu@BSA/rGO/SPCE had a low detection limit, a high sensitivity, and a linear range of 1.78 nM, 5.96 μA μM-1 cm-2, and 0.79 to 2057 μM, respectively. The selective examination of DMZ was achieved with interfering molecules, and the PANI-Cu@BSA/rGO/SPCE showed excellent selectivity, stability, repeatability, and practicability.

A magnetic molecular imprinting-based fluorescence probe for sensitive and selective detection of 2,4-D herbicide

A new magnetic molecular imprinting-based turn-on fluorescence probe (Fe3 O4 NPs@SiO2 @NBD@MIPs) has been synthesized via a facile sol-gel polymerization for the detection of 2,4-dichlorophenoxyacetic acid (2,4-D). Based on the photoinduced electron transfer (PET) of nitrobenzoxadiazole (NBD), 2,4-D can be recognized by enhancement of NBD fluorescence. With the presence of Fe3 O4 in the core of the probe, this sensor can also be reused many times using magnetic aggregation methods. After the addition of various concentrations of 2,4-D, the fluorescence peak at 530 nm (excitation of 468 nm) increased linearly ranging from 0.1 to 3 μM with a detection limit of 0.023 μM. This sensing system is believed to be available for detecting 2,4-D in real samples, with high recovery rates ranging from 94% to 108% for three spike levels of 2,4-D with precisions below 5%.

Detection of 2,4-dichlorophenoxyacetic acid in water sample by organosilane based silica nanocomposites

The present study aims to produce nanocomposites of silica based organosilane as sensitive and selective fluorescent sensor for the recognition of 2,4 dichlorophenoxyacetic acid (2,4-D). Hydrazone tethered triazole functionalized organosilane has been synthesized by the condensation reaction of 4-hydroxybenzaldehyde and phenyl hydrazine followed by Cu(I) catalysed cycloaddition of azide with alkyne. The prepared compound has been further grafted over silica surface and the synthesized materials were characterized by FT-IR, NMR (¹H and ¹³C), XRD, mass spectrometry and FE-SEM spectral analyses. The prepared organosilane and its HSNPs have been utilized as an effective emission probe for the selective detection of 2,4 D with good linear relationship in the range of 0-160 μM and 0-115 μM and LOD value of 46 nM and 13.5 nM respectively. In the presence of other active species, the sensor shows minimal interference while the comparison with the previously reported techniques suggests it to be more desirable for the sensitive and selective detection of 2,4 D. Further, the real sample application for detection of 2,4 D was analyzed in field water and the HSNPs based sensing system gave recovery percentage of above 98 %.

Polymer based nanocomposites: A strategic tool for detection of toxic pollutants in environmental matrices

A large fraction of population is suffering from waterborne diseases due to the contaminated drinking water. Both anthropogenic and natural sources are responsible for water contamination. Revolution in industrial and agriculture sectors along with a huge increase in human population has brought more amount of wastes like heavy metals, pesticides and antibiotics. These toxins are very harmful for human health, therefore, it is necessary to sense their presence in environment. Conventional strategies face various problems in detection and quantification of these pollutants such as expensive equipment and requirement of high maintenance with limited portability. Recently, nanostructured devices have been developed to detect environmental pollutants. Polymeric nanocomposites have been found robust, cost effective, highly efficient and accurate for sensing various environmental pollutants and this is due to their porous framework, multi-functionalities, redox properties, great conductivity, catalytic features, facile operation at room temperature and large surface area. Synergistic effects between polymeric matrix and nanomaterials are responsible for improved sensing features and environmental adaptability. This review focuses on the recent advancement in polymeric nanocomposites for sensing heavy metals, pesticides and antibiotics. The advantages, disadvantages, operating conditions and future perspectives of polymeric nanocomposites for sensing toxic pollutants have also been discussed.

Quantum dot decorated polyaniline plastic as a multifunctional nanocomposite: experimental and theoretical approach

AgO, CoO, and ZnO (ACZ) mixed metal quantum dots (QDs) were synthesized by the sol-gel process. Polyaniline (PANI) was prepared by the chemical-oxidative technique. An in situ approach was used for the synthesis of ACZ decorated PANI plastic nanocomposites (NCs). TEM, FTIR, FESEM, UV-visible, DSC, Raman, photoluminescence, and XRD techniques were used for characterizing the QDs, PANI, and ACZ decorated PANI NCs. Experimental and theoretical (DFT) studies were used to support the results. NCs were studied for their adsorption, magnetic, photocatalytic, electrical, thermal, photoluminescence, antibacterial, and anticorrosive activities. The plastic NCs of size 35 nm (observed from XRD and TEM) were found to be paramagnetic. UV-visible spectroscopy and DFT techniques were used to observe the optical band gap of NCs and show an almost equal band gap i.e., 2.75 eV. In 1.0 M H2SO4, the NCs show an 82.0% corrosion inhibition efficiency for mild steel. The adsorption power of the silica gel + NCs packed column was higher than normal silica gel column. A very small low-intensity D band in the Raman spectra confirms defect-free NCs. The photocatalytic activity was observed against methyl-red dye in visible light. The thermal stability of plastic NCs was higher than pure PANI and QDs. The NCs were investigated for bactericidal activity against Gram (positive and negative) microorganisms. The ACZ decorated PANI NCs acted as good nanomaterials for adsorption, separation, magnetic, photocatalytic, photoluminescence, antibacterial, electrical, thermal insulator, and anticorrosive agent.

Electrocatalysis of Endosulfan Based on Fe3O4: An Experimental and Computational Approach

The present work reports the electrocatalytic oxidation of the organochlorine pesticide endosulfan (EDS) using iron oxide (Fe₃O₄) nanoparticles synthesized from Callistemon viminalis leaf extracts. As a sensor for EDS, Fe₃O₄ was combined with functionalized multiwalled carbon nanotubes (f-MWCNTs) on a glassy carbon electrode (GCE). Cyclic voltammetry, electrochemical impedance spectroscopy, and the differential pulse voltammetry experiment were conducted to investigate the electrochemistry of EDS on the GCE/f-MWCNT/Fe₃O₄ sensor. Based on optimized experimental conditions, the reports of analytical parameters show a limit of detection of 3.3 μM and an effective sensitivity of 0.06464 μA/μM over a range of concentrations from 0.1 to 20 μM. With the proposed method, we were able to demonstrate recoveries between 94 and 110% for EDS determinations in vegetables. Further, a series of computational modeling studies were carried out to better understand the EDS surface adsorption phenomenon on the GCE/f-MWCNT/Fe₃O₄ sensor. The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap (-5.18 eV) computed by density functional theory (DFT) supports the layer-by-layer electrode modification strategy's charge transfer and stability. Finally, transition state modeling was able to predict and confirm the mechanism of endosulfan oxidation.