Department of Analytical Chemistry and Food Technology, Faculty of Chemical Science and Technology, University of Castilla-La Mancha, 13071, Ciudad Real, Spain; Regional Institute for Applied Chemistry Research (IRICA), 13071, Ciudad Real, Spain; National Hydrogen and Fuel Cell Technology Testing Centre (CNH2), Prolongación Fernando El Santo S/N, 1500 Puertollano, Ciudad Real, Spain.
Department of Analytical Chemistry and Food Technology, Faculty of Chemical Science and Technology, University of Castilla-La Mancha, 13071, Ciudad Real, Spain; Regional Institute for Applied Chemistry Research (IRICA), 13071, Ciudad Real, Spain.
Anal Chim Acta. 2022 Oct 16;1230:340406. doi: 10.1016/j.aca.2022.340406. Epub 2022 Sep 20.
A selective and sensitive fluorescent nanoprobe (sulfur and nitrogen co-doped graphene quantum dots, S,N-GQDs) was designed for both detection and discrimination between free and quercetin-loaded nanoemulsion in food samples of diverse nature. Quercetin nanoemulsions (Q-NEs) were synthesized by a phase inversion temperature (PIT) procedure, while S,N-GQDs were synthesized using a bottom-up methodology by means of simple hydrothermal treatment of citric acid and cysteamine. Both synthetized nanomaterials (analyte and fluorescent probe), were carefully characterized through advanced spectroscopic and high-resolution microscopic techniques. It was observed that fluorescence intensity of S,N-GQDs could be markedly and distinctively quenched by the addition of both quercetin forms through inner filter effect (IFE) mechanisms, exhibiting static quenching events for free quercetin and Q-NEs but with a characteristic 13 nm red-shift spectra in presence of Q-NEs. Linear dynamic ranges between 0.05 and 10 mg L and 0.025-70 mg L, with detection limits of 17 and 8 μg L were revealed for free and nanoquercetin, respectively. After nanostructural and physic-chemical optimization, the discrimination strategy was metrologically validated and applied to nutraceutical supplements containing nanoencapsulated quercetin and on diverse free quercetin products such as onion peels and dietary supplements. Accuracy and reliability were proved by means of a statistical comparison with the results obtained by a μHPLC-DAD method (paired Student's t-test at 95% confidence level). The method provides the exciting prospect of analyzing new designed nanoencapsulated bioactives without altering their native nanostructure, as well as being able to accomplish the challenge to distinguish between both forms of quercetin.
设计了一种选择性和灵敏性的荧光纳米探针（硫氮共掺杂石墨烯量子点，S，N-GQDs），用于检测和区分不同性质的食品样品中的游离和槲皮素负载纳米乳液。通过相转变温度（PIT）程序合成了槲皮素纳米乳液（Q-NEs），而 S，N-GQDs 则通过柠檬酸和半胱氨酸的简单水热处理，采用自上而下的方法合成。两种合成的纳米材料（分析物和荧光探针）均通过先进的光谱和高分辨率显微镜技术进行了仔细的表征。观察到，通过内滤效应（IFE）机制，S，N-GQDs 的荧光强度可以明显且明显地被两种槲皮素形式的加入所猝灭，表现出游离槲皮素和 Q-NEs 的静态猝灭事件，但在存在 Q-NEs 时，光谱有一个特征的 13nm 红移。分别对游离和纳米槲皮素的线性动态范围为 0.05-10mg/L 和 0.025-70mg/L，检测限为 17 和 8μg/L。经过纳米结构和物理化学优化后，对该区分策略进行了计量验证，并应用于含有纳米封装槲皮素的营养补充剂和不同的游离槲皮素产品，如洋葱皮和膳食补充剂。通过与μHPLC-DAD 方法（95%置信水平下的配对学生 t 检验）的结果进行统计比较，证明了该方法的准确性和可靠性。该方法提供了分析新设计的纳米封装生物活性物质的令人兴奋的前景，而不会改变其天然纳米结构，并且能够应对区分两种形式的槲皮素的挑战。
