A simple cost-effective paper-based electrochemical device for detection of adulterated sibutramine in slimming products.

This work presents the first paper-based electrochemical device, or ePAD, for direct detection of adulterated sibutramine in slimming products. The ePAD was fabricated using a screen-printing technique for defining the hydrophilic area for sample loading and for the working, reference and counter electrodes. The ePAD gave reproducible responses comparable to both conventional rod electrodes and commercial screen-printed electrodes (SPEs). Use of paper to fabricate the ePAD device provides advantages over the conventional SPE platforms (e.g. glass, ceramics and polymers) in terms of biocompatibility, strong capillary action and environmental friendliness. To detect sibutramine, square wave voltammetry was employed after sample loading on the circular hydrophilic area. The linear range is 2.51 to 83.7 mg L-1 sibutramine, with a precision of 6 %RSD (n = 3) and an instrumental limit of detection (3SD of intercept/slope) of 2.46 mg L-1 sibutramine. Recovery of spiked samples ranged from 83 to 116%. The samples were capsules, slimming coffee powders and nutraceutical beverages. The samples were appropriately diluted to give concentrations within the linear calibration range. Filtration of undissolved solids found with the capsules and coffee powder samples was not required, demonstrating that the method is not susceptible to solid particles. The ePAD is cost-effective (

Selective Extraction, Recovery, and Sensing of Hydroquinone Mediated by a Supramolecular Pillar[5]quinone Quinhydrone Charge-Transfer Complex.

Intermolecular interactions between an electron-rich aromatic hydroquinone (HQ) with its electron deficient counterpart, benzoquinone (BQ), result in the formation of a quinhydrone charge-transfer complex. Herein, we report a novel quinhydrone-type complex between pillar[5]quinone (P[5]Q) and HQ. Characterized by a suite of spectroscopic techniques including 1H NMR, UV-visible, and FTIR together with PXRD, SEM, BET, CV, and DFT modeling studies, the stability of the complex is determined to be due to an electron-proton transfer reaction coupled with a complementary donor-acceptor interaction. The selectivity of P[5]Q toward HQ over other dihydroxybenzene isomers allows for not only the naked-eye detection of HQ but also its selective liquid-liquid extraction and recovery from aqueous media.

A paper-based device for simultaneous determination of antioxidant activity and total phenolic content in food samples.

We report the first use of a paper-based device as a simple, low-cost and rapid detection platform for simultaneous determination of antioxidant activity and total phenolic content in food samples. Two antioxidant activity assays including 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonate) radical cation (ABTS) assay and cupric reducing antioxidant capacity (CUPRAC) assay and one total phenolic content assay, Folin Ciocaltue reagent (FC) assay were simultaneously employed as a proof-of-concept. The device composed of a central sample zone connected to four pretreatment zones and consecutive detection zones to accommodate all three assays and a sample blank measurement. The analysis was achieved by dropping the samples onto the sample zone to flow to the pretreatment and detection zones containing the stored reagents for each antioxidant assay making the color change that was measured using imageJ software. Assay optimization including key reagent concentrations, reaction time, and surface modification were carried out to obtain sensitive and wide linear rage analyses. Various antioxidant standards were then evaluated to determine the analytical features of the method. The paper-based assays were successfully applied to detect antioxidant activity and total phenolic content in 10 beverage samples with similar gallic acid equivalent (GAE) values to those obtained from traditional assays at a 95% confidence interval. Moreover, the GAE values of the samples obtained from three assay analyses were well correlated to each other with relatively high Pearson's correlation coefficients. These results indicated that the assays gave accurate results and are suitable for simultaneous analysis of antioxidant activity and total phenolic content in real samples.

Paper-based DPPH Assay for Antioxidant Activity Analysis.

We report on a paper-based 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH) assay for a simple, inexpensive, low reagent and sample consumption and high throughput analysis of antioxidant activity. The paper-based device was fabricated using a lamination method to create a 5-mm in diameter circular test zone that was embedded with a DPPH reagent. The analysis was carried out in one-step by dropping an antioxidant/sample onto the test zone. After reduction by the antioxidant, the DPPH radicals become stable DPPH molecules, resulting in a change in color from deep violet to pale yellow. The violet color intensity of DPPH was inversely proportional to the antioxidant activity of the samples, and was measured using imaging software. A high precision and a low limit of detection were found in the analysis of six standard antioxidants including gallic acid, trolox, ascorbic acid, caffeic acid, vanilliic acid and quercetin. The device was then validated against the traditional spectrophotometric DPPH assay by analyzing the antioxidant activity of 7 tea samples. The results showed no significant difference for gallic acid equivalent for all 7 samples obtained from the two methods at the 95% confidence level, indicating that the developed method was reliable for antioxidant activity analysis of real samples. Finally, the paper-based DPPH device was found to be stable over 10 days when stored in a refrigerator (2 - 4°C), making it an easy-to-use device for end-users.