Poly (acridine orange) film modified electrode for the determination 1-naphthol in the presence of 2-naphthol

A molecularly imprinted ratiometric fluorescent sensor for visual detection of 1-naphthol based on fluorescence-enhanced CdTeS QDs via APTES modification

CdTeS quantum dots (CdTeS QDs) were synthesized using the hydrothermal method and subsequently modified with (3-aminopropyl)triethoxysilane (APTES). This modification resulted in a significant enhancement of the fluorescence intensity, which was observed to be five times stronger than that of unmodified CdTeS QDs at 597 nm. Only after the fluorescence enhancement by APTES modification, the material showed a response to 1-naphthol (1-NP). Based on this, the molecularly imprinted polymers (MIPs) with ratiometric fluorescence were developed for the detection of 1-NP, that is, the synthetic raw material and the metabolite of the pesticide carbaryl. Under the excitation of 365 nm UV, the bright orange-red fluorescence (597 nm) of CdTeS QDs encapsulated in MIPs was quenched by 1-NP in the suspension, and 1-NP showed a gradually increasing blue emission (460 nm) with the increase of its concentration. This sensor has a good linear relationship between fluorescence intensity ratio (F460/F597) and 1-NP concentration (C1-NP) in a large concentration range (6.0-140.0 µM, LOD=0.45 µM, RSD<4.41%). It exhibits a visible fluorescence change from orange-red to blue-purple. Excellent recoveries in real samples were obtained by simulating carbaryl metabolism and demonstrated its potential in detection of 1-NP and carbaryl.

Electrochemical sensing for naphthol isomers based on the in situ growth of zeolitic imidazole framework-67 on ultrathin CoAl layered double hydroxide nanosheets by a reaction-diffusion technique

It is established that ultrathin layered double hydroxide nanosheets (LDHNS) and zeolitic imidazole frameworks (ZIF) are desirable electrochemical sensing modifiers owing to their large surface area and abundant catalytic sites. Integration of them is thus an effective solution to maximize their electrocatalytic activity. Herein, a novel reaction-diffusion framework (RDF) technique is applied for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (CoAl-LDHNS@ZIF-67). In a confined space of the agar gel matrix of RDF, the coordination reaction between organic ligands and CoAl-LDHNS without an additional Co²⁺ source achieves the controllable growth of ZIF-67 crystals through a long vertical diffusion. The prepared composite comprises both CoAl-LDHNS and ZIF-67 components with a certain ratio and provides a large surface area and amply catalytic sites, thus realizing a rapid transfer of electron and mass. The CoAl-LDHNS@ZIF-67 modified electrode is employed for the simultaneous detection of naphthol isomers by differential pulse voltammetry. Naphthol isomers display anodic reactions with a wide peak potential difference, allowing their simultaneous detection feasible. Voltammetric responses of α-naphthol and β-naphthol follow good linearity against the concentration in a wide range from 0.3 to 150 μM with limits of detection of 54 and 82 nM, respectively. The proposed sensor also demonstrates excellent selectivity, stability, reproducibility, and practicability for the simultaneous detection of naphthol isomers.

Controllable generation of ZnO/ZnCo2O4 arising from bimetal-organic frameworks for electrochemical detection of naphthol isomers

The development of a rapid and low concentration detection method for naphthol isomers is of great significance for protecting human health and environmental safety due to their high toxicity and strong corrosivity. Here, we reported a novel hollow ZnO/ZnCo₂O₄ material derived by adjusting the molar ratio of Zn/Co of bimetal-organic frameworks (BMOFs) and its application for simultaneous detection of 1-naphthol (1-NAP) and 2-naphthol (2-NAP) by electrochemical methods. The oxidation peak currents of 1-NAP and 2-NAP on a ZnO/ZnCo₂O₄ modified carbon paste electrode (ZnO/ZnCo₂O₄/CPE) depended linearly on their concentrations in the range of 0.4-50 μM and 0.06-40 μM with detection limits of 0.13 and 0.02 μM, respectively. Their electrooxidation at the ZnO/ZnCo₂O₄/CPE was a one-electron and one-proton process. These excellent performances could be driven by the high conductivity and number of active sites as well as the unique structure of ZnO/ZnCo₂O₄. The tactic may shed light on developing new electrodes for fast and efficient electrochemical detection of naphthol isomers.

Electrochemical sensing platform for naphthol isomers based on in situ growth of ZIF-8 on reduced graphene oxide by a reaction-diffusion technique

Enhancing the dispersibility and conductivity is an effective solution to develop the application zeolitic imidazole frameworks (ZIF) in the electrochemical field. This work thus employs a novel reaction-diffusion framework (RDF) technique for the in situ growth of ZIF-8 crystals on graphene oxide (GO@ZIF-8) matrixes. In detail, the outer electrolyte of 2-methyl imidazole naturally diffuses into the inner agar gel matrix containing Zn²⁺ cations and GO nanosheets. The long reaction-diffusion makes the growth of ZIF-8 crystals controllable in a vertical gradient. After thermal treatment, the title product of ZIF-8 in situ grown on reduced graphene oxide (rGO@ZIF-8) is obtained and thus exhibits good dispersibility, high conductivity, large surface area, and more catalytic sites. The glassy carbon electrode (GCE) was modified by casting the rGO@ZIF-8 suspension. The obtained rGO@ZIF-8/GCE displays excellent catalytic activity toward naphthol (NAP) isomers. Under the optimal conditions, the amperometric currents of 1-NAP and 2-NAP demonstrate the good linear relationship in wide ranges of 0.05-12 μM and 0.02-15 μM, respectively. Their limits of detection are as low as 15 and 17 nM, respectively. The fabricated modified electrode exhibits excellent selectivity, stability, and reproducibility. The sensor is also utilized to detect NAP molecules in real water samples and indicates good accuracy and reliability.

Electroanalytical Analysis of Guaifenesin on Poly(Acridine Orange) Modified Glassy Carbon Electrode and its Determination in Pharmaceuticals and Serum Samples

BACKGROUND

Electroanalytical methods are very functional to detect drugs in pharmaceuticals (tablets, syrups, suppositories, creams, and ointments) and biological samples.

OBJECTIVE

This study is aimed to make selective, sensitive, simple, fast, and low cost electrochemical analysis of expectorant drug guaifenesin in pharmaceuticals and serum samples.

METHODS

Differential pulse adsorptive stripping voltammetric method for determination of guaifenesin on a poly(acridine orange) modified glassy carbon electrode has been developed. Glassy carbon electrode was modified with electropolymerization of the acridine orange monomer for the sensitive determination of guaifenesin. Guaifenesin provided highly reproducible and welldefined irreversible oxidation peaks at +1.125 V and +1.128 V (vs. Ag/AgCl) in the selected supporting electrolyte and human serum samples, respectively.

RESULTS

Under optimized conditions, linear response of peak current on the concentration of guaifenesin has been obtained in the ranges of 2.00×10-7 to 1.00×10-4 M in Britton Robinson buffer solution at pH 7.0 and 4.00×10-7 to 1.00×10-4 M in serum samples. The precision of the method was detected by intraday and inter-day repeatability studies in the supporting electrolyte and serum samples media.

CONCLUSION

The analytical applicability of the proposed method exhibited satisfying determination results for guaifenesin from pharmaceutical dosage forms (syrup) and human serum samples without any pre-separation procedures.

Ordered Mesoporous NiCo2O4 Nanospheres as a Novel Electrocatalyst Platform for 1-Naphthol and 2-Naphthol Individual Sensing Application

The novel ordered mesoporous NiCo₂O₄ (meso-NiCo₂O₄) nanospheres were synthesized by the nanocasting strategy followed by a calcination process for 2-naphthol (2-NAP) and 1-naphthol (1-NAP) individual sensing application. The as-obtained meso-NiCo₂O₄ material possesses mesoporous structure in spinel crystalline type with a larger specific surface area than other structures. The meso-NiCo₂O₄-modified carbon paste electrode exhibited excellent electrocatalytic performance for NAP detection by amperometry measurement. The fabricated sensor of 2-NAP and 1-NAP has a wide linear detection range (0.02-300 and 0.02-20 μM) with high sensitivity (1.822 and 1.510 μA μM^-1 cm^-2) and low limit of detection (0.007 and 0.007 μM), respectively. In addition, the NAP sensors possess excellent reproducibility, stability, and selectivity.

Selective electrochemical recognition of the α-naphthol isomer and in situ immobilization of naphthoquinones for tunable electrocatalysis

Fits like a glove: Separationless and selective electrochemical oxidation of the α-naphthol (α-NAP) isomer yields naphthoquinone species on the surface of multiwalled carbon nanotubes, which can further catalyze the electro-oxidation of NADH and hydrazine at different potentials. The β-NAP isomer failed to show any such electro-oxidation.