Highly sensitive and selective optosensing of quercetin based on novel complexation with yttrium ions.

A simple and fast method was developed for the determination of quercetin. The concentration of quercetin can be determined based on the fluorescence emission resulting from the coordinative interactions between quercetin and the yttrium ion (Y3+). Notably, a portable platform to quantitatively analyze quercetin was constructed. This platform incorporates our custom-built homemade reader based on a photodiode, and Arduino hardware, which accepts a paper ribbon on which Y3+ is deposited as an input. In addition, the color change of the paper ribbon was identified using a smartphone via the hue values of the photographs. The limits of detection for quercetin using spectroscopy, a smartphone, and a custom-built reader were calculated to be 27, 110, and 129 nM, respectively. The use of a custom-built device and a smartphone for detecting quercetin via fluorescence from the prepared paper ribbon reduces the time and cost of quercetin detection. This approach could be employed for on-site sensing of quercetin in real samples.

Preparing cuprous oxide nanomaterials by electrochemical method for non-enzymatic glucose biosensor.

Cuprous oxide (Cu2O) nanostructure has been synthesized using an electrochemical method with a two-electrode system. Cu foils were used as electrodes and NH2(OH) was utilized as the reducing agent. The effects of pH and applied voltages on the morphology of the product were investigated. The morphology and optical properties of Cu2O particles were characterized using scanning electron microscopy, x-ray diffraction, and diffuse reflectance spectra. The synthesized Cu2O nanostructures that formed in the vicinity of the anode at 2 V and pH = 11 showed high uniform distribution, small size, and good electrochemical sensing. These Cu2O nanoparticles were coated on an Indium tin oxide substrate and applied to detect non-enzyme glucose as excellent biosensors. The non-enzyme glucose biosensors exhibited good performance with high response, good selectivity, wide linear detection range, and a low detection limit at 0.4 µM. Synthesized Cu2O nanostructures are potential materials for a non-enzyme glucose biosensor.

Colorimetric detection of chromium(VI) using graphene oxide nanoparticles acting as a peroxidase mimetic catalyst and 8-hydroxyquinoline as an inhibitor.

A method is described for the colorimetric determination of chromate [chromium(VI)]. It is based on the use of graphene oxide (GO) nanoparticles acting as a peroxidase mimic. A blue color is generated by oxidation of 3,3,5,5-tetramethylbenzidine by H2O2 which is catalyzed by GO. This color-forming reaction is prevented in the presence of 8-hydroxyquinoline (8-HQ). However, in the presence of Cr(VI), the blue color will be formed from TMB owing to the oxidation of the inhibitor 8-HQ by Cr(VI). The color can be measured by a spectrophotometry (at 652 nm) or detected visually. Under optimal experimental conditions, response is linear in the 50 to 430 nM range of chromate concentration, and the limit of detection is 5.8 nM (at S/N = 3). The assay is highly selective and was successfully applied to the determination of Cr(VI) in spiked water samples. Graphical abstract Schematic of the colorimetric assay for Cr(VI). TMB: 3,3,5,5-tetramethylbenzidine.

Straightforward smartphone assay for quantifying tannic acid in beverages based on colour change of Eu3+/polyethyleneimine complex.

Tannic acid (TA)-a natural product-is a polyphenol derivative that occurs in certain kinds of beverages. A large amount of TA could give rise to an unpleasant flavour and could negatively affect the human body by causing stomach irritation, abdominal pain, nausea, vomiting, and even death. Thus, the need exists for a simple TA detection procedure that meets specific criteria such as on-site analysis, portability, and affordability. Herein, we present a new TA assay, which is based on the fluorescent quenching effect of an efficient fluorophore, and which comprises a smartphone-integrated homemade reader system. The fluorescent polyethyleneimine-derivatised polymer (FP), a strong emitter at 510 nm, was synthesised with the aid of a facile sonication method. In the presence of Eu3+ ions, TA quenches the fluorescence of the FP via electrostatic interaction. A smartphone was used to capture an image of the FP undergoing fluorescence for conversion to RGB values. The blue channel was chosen for further analysis because it offered the highest R2-value compared to the red and green channels. We verified these results using a commercial spectrofluorometer and calculated the limit of detection of this assay as 87 nM and 20 nM for the homemade reader and spectrofluorometer, respectively. The detection range for TA with the proposed assay is 0.16-66.66 µM. The application of the proposed method to real beverage samples for TA detection demonstrates its analytical applicability.

Key Role of Corncob Based-Hydrochar (HC) in the Enhancement of Visible Light Photocatalytic Degradation of 2,4-Dichlorophenoxyacetic Acid Using a Derivative of ZnBi-Layered Double Hydroxides.

A superior heterojunction of HC-ZnBi-LDO was synthesized in two steps, namely hydrothermal carbonization, followed by co-precipitation. The 2% HC-ZnBi-LDO heterojunction photocatalysts could degrade over 90.8% of 30 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) using 1.0 g/L of the catalyst after 135 min of visible light exposure at pH 4. The activity of 2% HC-ZnO-LDO was remarkably stable. Approximately 86.4-90.8% of 30 mg/L 2,4-D was degraded, and more than 79-86.4% of TOC was mineralized by 2% HC-ZnBi-LDO at pH 4 after 135 min of visible light exposure during four consecutive cycles. The rapid separation and migration of charge carriers at the interfaces between HC and ZnBi-LDO were achieved within 2% HC-ZnBi-LDO. Moreover, the electron acceptor characteristic of HC in 2% HC-ZnBi-LDO caused the recombination of charge carriers to decrease significantly, thus generating more reactive radicals, such as hydroxyl radicals (OH●) and superoxide radicals (O2●-). These results demonstrate that the novel 2% HC-ZnBi-LDO is a superior photocatalyst for the remediation of hazardous organic pollutants.