Department of Chemistry, Faculty of Engineering, Istanbul University, Turkey.
Anal Chem. 2012 Sep 18;84(18):8052-9. doi: 10.1021/ac301925b. Epub 2012 Aug 27.
A sensitive colorimetric method for the detection of polyphenols (i.e., flavonoids, simple phenolic, and hydroxycinnamic acids) was proposed in this research based on the reduction of Ag(+) ions by polyphenols in the presence of citrate-stabilized silver seeds. The color of the stable suspension was controlled by varying the concentration of trisodium citrate, silver nitrate, and silver seeds. The reduction of Ag(+) to spherical silver nanoparticles (SNPs) by polyphenols in the presence of trisodium citrate and silver seeds produced a very intense surface plasmon resonance (SPR) absorption band of SNPs at 423 nm. The plasmon absorbance of SNPs allows the quantitative spectrophotometric detection of the polyphenols, and the developed method gave a linear response over a wide concentration range of standard polyphenolic compounds. In contrast to other reported NP-based antioxidant assays, it was established in this work that growth but not nucleation of SNPs gave a linear concentration-dependent response. The trolox equivalent antioxidant capacity (TEAC) values of various (hydrophilic and lipophilic) antioxidants using the developed method were comparable to those of the CUPRAC assay. Common food ingredients like oxalate, citrate, fruit acids, amino acids, and reducing sugars did not interfere with the proposed sensing method. This assay was validated through linearity, additivity, precision and recovery, demonstrating that the assay is reliable and robust. The developed method was used to screen total antioxidant capacity (TAC) of some commercial fruit juices and herbal teas without preliminary treatment, and showed a promising potential for the preparation of antioxidant inventories of a wide range of food plants.
本研究提出了一种基于银种子存在下多酚（如类黄酮、简单酚和羟基肉桂酸）还原银（+）离子的灵敏比色法。通过改变柠檬酸钠、硝酸银和银种子的浓度来控制稳定悬浮液的颜色。多酚在柠檬酸钠和银种子存在下还原银（+）为球形银纳米颗粒（SNP），在 423nm 处产生 SNP 的非常强的表面等离子体共振（SPR）吸收带。SNP 的等离子体吸收允许定量分光光度法检测多酚，并且所开发的方法在标准多酚化合物的宽浓度范围内给出了线性响应。与其他报道的基于 NP 的抗氧化剂测定法相比，本工作建立了 SNP 的生长而不是成核给出了线性浓度依赖响应。使用所开发的方法测定各种（亲水性和疏水性）抗氧化剂的 Trolox 等效抗氧化能力（TEAC）值与 CUPRAC 测定法相当。常见的食品成分，如草酸盐、柠檬酸盐、水果酸、氨基酸和还原糖，不会干扰所提出的传感方法。该测定法通过线性度、加和性、精密度和回收率进行了验证，证明该测定法可靠且稳健。该方法用于无需预处理即可筛选一些商业果汁和草药茶的总抗氧化能力（TAC），并显示出用于制备广泛的植物性食物抗氧化剂成分的有希望的潜力。
