N-doped peanut membrane carbon quantum dots as a " off-on" fluorescence probe determination of hydroquinoneEI北大核心CSCD

N-doped peanut membrane carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method using peanut membrane and urea as materials. On the basis of investigating the spectral characteristics of the N-CQDs, we found that KMnO4 could cause the fluorescence signal of the N-CQDs to "turn-off" in the B-R buffer system with pH 10. 38. Once hydroquinone was added, the fluorescence signal of the N-CQDs-KMnO4 system gradually recovered and the fluorescence signal "turned on". Based on this, a new "off-on" fluorescence probe method for the detection of hydroquinone-N-CQDs-KMnO4 system was developed. Under the optimized conditions, the recovered fluorescence of N-CQDs was linearly related with the hydroquinone concentration in the range of 0. 10-200 mmol / L, the linear equation was ΔF = 1. 6819c + 153. 84 (r = 0. 9992), with the detection limit of 30 μmol / L. The method has been successfully applied to the determination of hydroquinone in simulated samples. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Use of specific peptide biomarkers for quantitative confirmation of hidden allergenic peanut proteins Ara h 2 and Ara h 3/4 for food control by liquid chromatography–tandem mass spectrometry

A liquid chromatography–electrospray-tandem mass spectrometry (LC–ESI-MS–MS) method based on the detection of biomarker peptides from allergenic proteins was devised for confirming and quantifying peanut allergens in foods. Peptides obtained from tryptic digestion of Ara h 2 and Ara h 3/4 proteins were identified and characterized by LC–MS and LC–MS–MS with a quadrupole-time of flight mass analyzer. Four peptides were chosen and investigated as biomarkers taking into account their selectivity, the absence of missed cleavages, the uniform distribution in the Ara h 2 and Ara h 3/4 protein isoforms together with their spectral features under ESI-MS–MS conditions, and good repeatability of LC retention time. Because of the different expression levels, the selection of two different allergenic proteins was proved to be useful in the identification and univocal confirmation of the presence of peanuts in foodstuffs. Using rice crispy and chocolate-based snacks as model food matrix, an LC–MS–MS method with triple quadrupole mass analyzer allowed good detection limits to be obtained for Ara h2 (5 μg protein g⁻¹ matrix) and Ara h3/4 (1 μg protein g⁻¹ matrix). Linearity of the method was established in the 10–200 μg g⁻¹ range of peanut proteins in the food matrix investigated. Method selectivity was demonstrated by analyzing tree nuts (almonds, pecan nuts, hazelnuts, walnuts) and food ingredients such as milk, soy beans, chocolate, cornflakes, and rice crispy. Figure ESI-QTOF-MS mass spectrum of Ara h3/4 triptig digest