Indole is a major metabolite of tryptophan, which plays an important role in the intestinal microecological balance and human physiological activities. The determination of indole becomes important for its researches. So, it is urgent to establish a sensitive and cost-effective method for indole detection. Herein, a sensitive electrochemical method was constructed to determine the concentration of indole using screen-printed carbon electrode (SPCE) with the signal amplification strategy by gold/iron-oxide composite nanoparticles (Au/Fe3O4). Au/Fe3O4 nanoparticles were successfully synthesized under the irradiation by high-energy electron beams. 4-aminothiophenol (4-ATP) was connected to Au/Fe3O4 via Au-S bond. And then NaNO2 reacted with 4-ATP to form the azo bond, which could form the final product of Au/Fe3O4@ATP-azo-indole by the coupling reaction. Thus, the concentration of indole was detected by the electrochemical signal produced by Au/Fe3O4@ATP-azo-indole indirectly. The detection sensitivity was greatly improved by the large specific surface area provided by Au/Fe3O4 after the modification. The linear range of indole was from 0.50 to 120.00 μg L-1 and the limit of detection (LOD) was as low as 0.10 μg L-1 (S/N = 3). Furthermore, the developed method exhibited acceptable intra-day and inter-day precisions with the coefficient of variations (CV) less than 4.9% and 8.2%, respectively. And the recoveries were from 97.2% to 105.4%. An innovative, sensitive, cost-effective method was established for indole determination in human plasma matrix in this manuscript, which provides a promising way for indole detection in conventional laboratories.

中文翻译：

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基于金/氧化铁复合纳米粒子信号放大策略的吲哚灵敏电化学方法

吲哚是色氨酸的主要代谢产物，在肠道微生态平衡和人体生理活动中起着重要作用。吲哚的测定对其研究具有重要意义。因此，迫切需要建立一种灵敏且具有成本效益的吲哚检测方法。在此，构建了一种灵敏的电化学方法，使用丝网印刷碳电极 (SPCE) 和金/氧化铁复合纳米粒子 (Au/Fe3O4) 的信号放大策略来测定吲哚的浓度。在高能电子束的照射下成功合成了Au/Fe3O4纳米颗粒。4-氨基苯硫酚 (4-ATP) 通过 Au-S 键连接到 Au/Fe3O4。然后NaNO2与4-ATP反应形成偶氮键，其可以通过偶联反应形成 Au/Fe3O4@ATP-偶氮吲哚的最终产物。因此，吲哚的浓度是通过 Au/Fe3O4@ATP-偶氮-吲哚产生的电化学信号间接检测的。改性后Au/Fe3O4提供的大比表面积大大提高了检测灵敏度。吲哚的线性范围为 0.50 至 120.00 μg L-1，检测限 (LOD) 低至 0.10 μg L-1 (S/N = 3)。此外，所开发的方法表现出可接受的日内和日间精度，变异系数 (CV) 分别小于 4.9% 和 8.2%。回收率从 97.2% 到 105.4%。在本手稿中，建立了一种创新、灵敏、具有成本效益的方法来测定人血浆基质中的吲哚，