Metal nanoparticles based lab-on-paper for phenolic compounds evaluation with no sample pretreatment. Application to extra virgin olive oil samples

Selective extraction of maleic hydrazide in foods using magnetic molecularly imprinted polymers and colorimetric detection via smartphone

Maleic hydrazide (MH) is a plant growth regulator, herbicide, and sprout inhibitor used to improve the growth and quality of certain vegetables and fruits, unfortunately, MH has genotoxic and carcinogenic effects; thus, MH residues in food need to be analyzed. Herein, magnetic molecularly imprinted polymers (MagMIP) were synthesized by radical polymerization in just 30 min using a microwave for rapid and selective extraction of MH. The colorimetric detection of MH using the immobilized Folin Ciocalteau's reagent (FCR) on 96-well microplate via smartphone sensor exhibits useful sensitivity for MH with a limit of detection (LOD = 0.6 ppm) which is far lower than the maximum residue limits (higher than 5 ppm). The immobilized FCR was stored dry at two different storage conditions at +4 °C and room temperature without losing its performance over six months. The coupling MagMIP-extraction/clean-up and smartphone determination were tested towards food samples (i.e., potatoes, and carrots), obtaining good recovery (79-96 %), high repeatability (RSD 4.5 %; n = 10), and high selectivity for MH determination.

Rapid pretreatment-free evaluation of antioxidant capacity in extra virgin olive oil using a laser-nanodecorated electrochemical lab-on-strip

An electroanalytical lab-on-a-strip device for the direct extra-virgin olive oil (EVOO) antioxidant capacity evaluation is proposed. The lab-made device is composed of a CO₂ laser nanodecorated sensor combined with a cutter-plotter molded paper-strip designed for EVOOs sampling and extraction. Satisfactory performance towards the most representative o-diphenols of EVOOs i.e., hydroxytyrosol (HY) and oleuropein (OL) were achieved; good sensitivity (LOD_HY = 2 µM; LOD_OL = 0.6 µM), extended linear ranges (HY: 10-250 µM; OL: 2.5-50 µM) and outstanding reproducibility (RSD < 5%, n = 3) were obtained in rectified oil. The device was challenged for the extraction-free analysis of 15 different EVOO samples, with satisfactory recoveries (90-94%; RSD < 5%, n = 3) and correlation with classical photometric assays (r ≥ 0.91). The proposed device includes all analysis steps, needs 4 µL of sample, and returns reliable results in 2 min, resulting portable and usable with a smartphone.

A Three-Reagent “Green” Paper-Based Analytical Device for Solid-Phase Spectrometric and Colorimetric Determination of Dihydroquercetin

Microfluidic paper-based analytical devices (µPADs) represent one of the promising green analytical strategies for low-cost and simple determination of various analytes. The actual task is the development of such devices for quantitation of antioxidants, e.g., flavonoids. In this paper, possibilities of a novel three-reagent µPAD including silver nitrate, 4-nitrophenyldiazonium tetrafluoroborate, and iron(III) chloride as reagents are assessed with respect to the determination of dihydroquercetin. It is shown that all the three reagents produce different colorimetric responses that can be detected by a mini-spectrophotometer–monitor calibrator or by a smartphone. The method is applicable to direct measuring high contents of dihydroquercetin (the linearity range is 0.026–1 mg mL⁻¹, and the limit of detection is 7.7 µg mL⁻¹), which is favorable for many dietary supplements. The analysis of a food supplement was possible with the relative standard deviations of 9–26%, which is satisfactory for quantitative and semiquantitative determinations. It was found that plotting a calibration graph in 3D space of the three reagents’ responses allows us to distinguish dihydroquercetin from its close structural analogue, quercetin.