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In this study, CuS/Fe3O4 composite structures were prepared in a two-step process. Initially, we used a simple solvothermal method to synthesize CuS nanostructures. Hydrothermal method was employed to form CuS/Fe3O4 composites. We characterized the particles using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The particles exhibit an oxidase-like activity using the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) as oxidase substrate. The presence of chromium (VI) increases the oxidase-like activity and is dependent on the concentration. The UV/visible absorption intensity of the oxidized TMB (oxTMB) increases with the concentration of chromium (VI) which provides a route to colorimetric determination of chromium (VI). We noticed a limit of detection as small as 60 nM and a wide linear dynamic range of 0–1500 µM. We found a high selectivity of this method for chromium (VI) against potentially interference cations and anions. Its applicability for determination of chromium (VI) in real environmental samples is demonstrated using tap water. This result demonstrates the capability of the method in determination of chromium (VI) in real samples. [ABSTRACT FROM AUTHOR]

In this study, silver nanostructures decorated magnetic nanoparticles for surface-enhanced Raman scattering (SERS) measurements were prepared via photoreduction utilizing the catalytic activity of ZnO nanostructure. The ZnO/Fe3O4 composite was first prepared by dispersing pre-formed magnetic nanoparticles into alkaline zinc nitrate solutions. After annealing of the precipitates, the formed ZnO/Fe3O4 composites were successfully decorated with silver nanostructures by soaking the composites into silver nitrate/ethylene glycol solution following UV irradiations. To find the optimal condition when preparing Ag@ZnO/Fe3O4 composites for SERS measurements, factors such as the reaction conditions, photoreduction time, concentration of zinc nitrate and silver nitrate were studied. Results indicated that the photoreduction efficiency was significantly improved with the assistance of ZnO but the amount of ZnO in the composite is not critical. The concentration of silver nitrate and UV irradiation time affected the morphologies of the formed composites and optimal condition in preparation of the composites for SERS measurement was found using 20 mM of silver nitrate with an irradiation time of 90 min. Under the optimized condition, the obtained SERS intensities were highly reproducible with a SERS enhancement factor in the order of 7. Quantitative analyses showed that a linear range up to 1 µM with a detection limit lower than 0.1 µM in the detection of creatinine in aqueous solution could be obtained. Successful applying of these prepared composites to determine creatinine in urine sample was obtained. [ABSTRACT FROM AUTHOR]

The significant spectral overlap (Di)0.5 = 0.5667 which is about 75.3% overlapping of the UV/Visible absorption spectra of iron (II) and copper (II) complexes necessitates chemometric assisted methods for simultaneous analysis of these ions in the pharmaceutical mixture. These metal ions were analyzed simultaneously by UV/Visible spectrophotometric method where 8-hydroxyquinoline was used as a chromogenic reagent. The absorption spectra were recorded in the wavelength range of 350-600 nm digitized at 1 nm. Four chemometrics methods such as first derivative spectrophotometry (1D zero crossing), first derivative ratio (1D ratio), classical least squares (CLS) and principal component regression (PCR) were used to predict the concentrations of the metal ions. For the derivative spectrophotometry, measurements were made at two selected wavelengths. The calibration curves were linear in the range of 2-12 μg/ml for both ions. For classical least squares and principal component regression, the calibration model was obtained and predictions of the unknown concentrations of the ions in the synthetic mixtures and in the dosage form were done. The accuracy and the precision of these methods were determined by calculating the % recovery and the relative standard errors correspondingly. The methods were successfully applied for analyzing synthetic mixtures and commercial pharmaceutical preparation. [ABSTRACT FROM AUTHOR]

In this study, a facile one step solvo-thermal procedure has been employed in generating magnetite-silver core-shell nanocomposites (AgNPs@ Fe 3 O 4 ) with superior peroxidase-like catalytic property than bare magnetic nanoparticles (Fe 3 O 4 ). The composites were characterized using different techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and surface-enhanced infrared absorption spectroscopy (SEIRA). In the presence of hydrogen peroxide, the synthesized composites were able to oxidize the colorless o-phenylenediamine (OPD) to a yellow colour 2, 3-diaminophenazine (DAP) with a better peroxidase-like activity than Fe 3 O 4 alone. The obtained K m value of AgNPs@ Fe 3 O 4 with H 2 O 2 and OPD substrates are 28.0 mM and 2.91 mM respectively. These are substantially lower than previously reported values and indicate the strong binding affinity of the substrates towards AgNPs@ Fe 3 O 4 nanocomposites. Based on the obstruction activity of cysteine on the peroxidase-like catalytic property of the nanocomposites, a sensor was developed for detection of cystein with a limit of detection as low as 87 nM and a wider range of linearity. The sensor also exhibited excellent selectivity against potentially interfering molecules., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this study, silver nanostructures decorated magnetic nanoparticles for surface-enhanced Raman scattering (SERS) measurements were prepared via heat induced catalytic activity of ZnO nanostructures. The ZnO/Fe 3 O 4 composite was first prepared by dispersing pre-formed magnetic nanoparticles into alkaline zinc nitrate solutions. After annealing of the precipitates, the formed ZnO/Fe 3 O 4 composites were successfully decorated with silver nanostructures by dispersing the composites into silver nitrate/ethylene glycol solution at 95 °C in water bath. To find the optimal condition when preparing Ag/ZnO/Fe 3 O 4 composites for SERS measurements, factors such as reaction time and concentration of silver nitrate were studied. Results indicated that the formation of silver nanoparticles (AgNPs) on ZnO/Fe 3 O 4 was significantly improved with the assistance of ZnO. The concentration of silver nitrate and reaction time affected the morphologies and sizes of the formed composites and optimal condition in preparation of the composites for SERS measurement was found using 100 mM of silver nitrate with a reaction time of 20 min. Under optimized conditions, the obtained SERS intensities were highly reproducible. The substrates were applied for quantitative analysis of uric acid in aqueous solution and a linear response for concentrations up to 10 μM was obtained. Successful application of these prepared composites to determine uric acid in urine sample without any pretreatment of the urine sample was done., (Copyright © 2019 Elsevier B.V. All rights reserved.)