pH-controlled voltammetric behaviors and detection of phytohormone 6-benzylaminopurine using MWCNT/GCE

Electro-Oxidation and Simultaneous Determination of Indole-3-Acetic Acid and Salicylic Acid on Graphene Hydrogel Modified Electrode

A selective and sensitive electrochemical sensor was developed for simultaneous detection of phytohormones indole-3-acetic acid (IAA) and salicylic acid (SA). The sensing interface was fabricated on a porous, three-dimensional networked graphene hydrogel (GH) modified glassy carbon electrode (GCE). The electrocatalytic behavior of IAA and SA on the surface of the modified electrode (GH/GCE) was investigated by cyclic voltammetry and linear sweep voltammetry. Results show that the oxidation reactions of IAA and SA occur at different potentials, which enable their simultaneous detection at the sensing interface. Under optimal conditions, the GH/GCE exhibited good selectivity and stability and its response, unaffected by various interferents, was linear in the range of 4 to 200 μM of IAA and SA. The limit of detection (S/N = 3) achieved were 1.42 μM for IAA and 2.80 μM for SA. The sensor performance was validated by measuring for IAA and SA in real vegetable samples with satisfactory results.

Developmental toxicity and alteration of gene expression in zebrafish embryo exposed to 6-benzylaminopurine

6-benzylaminopurine (6-BA) is widely used in agriculture and horticulture as plant growth regulator. Its excessive use may pose a potential risk to both environment and human health, which is causing great concern. This study was undertaken to assess the acute developmental toxicity of 6-BA to zebrafish embryos based on OECD protocols and mortality, hatching rate and malformation were investigated. Results showed that the 96 h-LC₅₀ and 96 h- EC₅₀ values were 63.29 mg/L and 41.86 mg/L, respectively. No mortality or teratogenic effects were found at concentrations lower than 10 mg/L 6-BA at concentrations higher than 50 mg/L significantly inhibited hatchability and embryo development, induced serious toxicity characterized by morphologic abnormalities (elongated pericardium, heart and yolk sac edema, spine curvature) and functional failure (slow spontaneous movement and heart rate, growth retardation, yolk sac absorption retention). Moreover, 6-BA-induced apoptosis was observed in embryos by the acridine orange staining and confirmed by the apoptotic-related genes, all of which p53 was significantly up-regulated at concentrations higher than 10 mg/L, bax at concentrations higher than 12.5 mg/L, while bcl2 was down-regulated at concentrations higher than 25 mg/L. As for genes of cardiac development, qPCR results demonstrated that nkx2.5, gata5, and amhc were significantly down-regulated at concentrations higher than 25 mg/L, vmhc and atp2a2a at concentration of 50 mg/L, in contrast, hand2 was up-regulated at concentration of 50 mg/L. Our data indicate that 6-BA induces a dose-dependent toxicity resulting in apoptosis through the involvement of p53-dependent pathways and hindering normal heart development in zebrafish embryos.

Simultaneous determination of cytokinins by high performance liquid chromatography with resonance Rayleigh scattering and mechanism discussion

A reliable, highly sensitive and highly selective method of high performance liquid chromatography associated with resonance Rayleigh scattering (HPLC-RRS) was developed to detect three cytokinins, namely, 6-benzylaminopurine (BA), kinetin (KT) and zeatin (ZT). In this work, Pd(ii) is added into the system to form ternary ion association complexes for the first time, which results in a lower limit of detection and extends the application of HPLC-RRS. The experimental conditions were optimized. In order to investigate the reaction mechanism, the ternary ion association complexes were characterized by ultraviolet-visible spectrophotometry, dynamic light scattering, scanning electron microscopy and density functional theory calculations. In a HAc-NaAc buffer solution (pH = 4.1), a ternary complex of cytokinin : Pd(ii) : EryB (1 : 1 : 2) was formed. The detection limits (S/N = 3) of BA, KT, and ZT were 0.9, 1.5 and 2.3 ng mL-1, respectively. In addition, this method was applied for the simultaneous detection of cytokinins in real samples with satisfactory results.

Electrochemical sensing of 2-methyl-4, 6-dinitrophenol by nanomagnetic core shell linked to carbon nanotube modified glassy carbon electrode

Electrochemical behavior and sensing of 2-methyl-4, 6-dinitrophenol as an herbicide has been investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). We have synthesized a cefazolin (CEF) immobilized nanomagnetic core-shell (Fe₃O₄@SiO₂-(CH₂)₃-CEF) and attached it on the modified glassy carbon electrode (GCE/MWCNT) through electrostatic adsorption (GCE/MWCNT/CEF-SiO₂@Fe₃O₄). 2-Methyl-4, 6-dinitrophenol has an oxidation peak that is related to the formation of nitrosamine from hydroxylamine species. This peak was applied for quantifying determination of 2-methyl-4, 6-dinitrophenol. The electrochemical oxidation involves two electron transfers accompanied by two protons. The electrochemical process was controlled by adsorption. The good agreement between the obtained computational studies and the experimental results has demonstrated that outer sphere electron transfer occurred on modified electrode. The new electrochemical sensor was applied to determination of 2-methyl-4, 6-dinitrophenol by SWV in the range of 1.0 × 10^-10 to 1.5 × 10^-7 M with a detection limit of 0.1 nM. The proposed sensor was applied for determination of 2-methyl-4, 6-dinitrophenol in water samples.

Pt-MWCNT modified carbon electrode strip for rapid and quantitative detection of H 2 O 2 in food

A single-use screen-printed carbon electrode strip was designed and fabricated. Nano-hybrids, prepared by deposition of platinum (Pt) nanoparticles on multi-wall carbon nanotube (MWCNT), was modified on the surface of screen-printed carbon electrode for the development of a fast, sensitive and cost-effective hydrogen peroxide (H₂O₂) detection amperometric sensor strip. With Pt-MWCNT nanohybrids surface modification, current generated in response to H₂O₂ by the screen-printed carbon electrode strip was enhanced 100 fold with an applied potential of 300 mV. Quality of as-prepared electrode strip was assured by the low coefficient of variation (CV) (<5%) of currents measured at 5 s. Three linear detection ranges with sensitivity of 75.2, 120.7, and 142.8 μA mM⁻¹ cm⁻² were observed for H₂O₂ concentration in the range of 1–15 mM, 0.1–1 mM, and 10–100 μM, respectively. The lowest H₂O₂ concentration could be measured by the as-prepared strip was 10 μM. H₂O₂ levels in green tea infusion and pressed Tofu could be rapidly detected with results comparable to that measured by ferrous oxidation xylenol orange (FOX) assay and peroxidase colorimetric method.

Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles

A simple and selective colorimetric sensor thioglycolic acid capped silver nanoparticles (TGA-AgNPs) was developed for the detection of 6-benzylaminopurine (6-BAP). The synthesized TGA-AgNPs were characterized by UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopic (TEM) techniques. The TGA-AgNPs as a sensor for binding 6-BAP through hydrogen-bonding and π-π bonding that causes large conjugate clusters, resulting in a color change from yellow to reddish orange. The surface plasmon resonance (SPR) band of TGA-AgNPs at 397nm is red-shifted to 510nm, which confirms that 6-BAP induces the aggregation of TGA-AgNPs. Under the optimized conditions, a linear relationship between the absorption ratio (A510nm/A397nm) and 6-BAP concentration was found in the range of 4-26μM. The detection limit of 6-BAP was 0.2μM, which is lower than the other analytical techniques. Moreover, the proposed sensor was successfully applied for the detection of 6-BAP in environmental samples with good recoveries. The proposed assay provides a simple and cost-effective method for the analysis of 6-BAP in vegetable and water samples.

A new composite of graphene and molecularly imprinted polymer based on ionic liquids as functional monomer and cross-linker for electrochemical sensing 6-benzylaminopurine

Molecularly imprinted polymers prepared using traditional functional monomers and cross-linkers exhibit slow binding kinetics, low electrocatalytic activity and adsorption capacity. Herein, we report a new composite of ionic liquid-based graphene and molecularly imprinted polymer (IL-GR-MIP) with high electrocatalytic activity and adsorption capacity to construct an effective electrochemical sensor for 6-benzylaminopurine (6-BAP). Our objective was to enhance the efficiency of the sensor by incorporating more IL in the MIP framework. We synthesized IL-GR-MIP using ionic liquid 1-vinyl-3-butylimidazolium tetrafluoroborate (IL₁) as functional monomer, ionic liquid 1,4-butanediyl-3,3'-bis-l-vinylimidazolium dibromide (IL₂) as cross-linker, 6-BAP as template, and GR as supporter. IL-GR-MIP was characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscope. Compared with GR-MIP composites based on methacrylic acid or IL₁ as functional monomer, N, N'-methylenebisacrylamide and ethylene glycol dimethacrylate as cross-linker, the IL-GR-MIP (prepared with ionic liquids as functional monomer and cross-linker) sensor exhibited highest peak current for 6-BAP. The results indicate the ability of IL₂ as cross-linker to enhance electrocatalytic activity and adsorption capacity for 6-BAP of IL-GR-MIP. Under the optimized conditions, the peak current of IL-GR-MIP sensor was linear to 6-BAP concentration in the range of 0.5-50 μM with a detection limit of 0.2 μM (S/N = 3). The IL-GR-MIP sensor exhibited good selectivity with the anti-interference ability of 1000-fold ascorbic acid in 6-BAP determination. Furthermore, we demonstrated practical applicability of IL-GR-MIP sensor in detecting 6-BAP in real samples with satisfactory results.

Highly sensitive and stabilized sensing of 6-benzylaminopurine based on NiCo2O4 nanosuperstructures

An ultrasensitive electrochemical sensor based on NiCo₂O₄ nanosuperstructures was proposed to determine 6-benzylaminopurine contamination in food.