A Highly Sensitive Electrochemical Sensor for Capsaicinoids and Its Application in the Identification of Illegal Cooking Oil.

Capsaicinoids, mostly from chili peppers, are widely used in daily life. Capsaicinoids are considered to be markers for the identification of illegal cooking oil (ICO), which is a serious threat to public health. The identification of capsaicinoids can help reveal food-related fraud, thereby safeguarding consumers' health. Here, a novel and ultrasensitive method was established with a signal amplification strategy for the detection of capsaicinoids. AuNPs@Fe3O4 nanocomposites were functionalized with 4-aminothiophenol (4-atp). After diazotization, 4-atp on AuNPs@Fe3O4 reacted with capsaicinoids and formed capsaicinoids-azo-atp-AuNPs@Fe3O4. Ultimately, capsaicinoids-azo-atp-AuNPs@Fe3O4 was dropped onto the surface of a screen-printed carbon electrode (SPCE) and detected via the differential pulse voltammetry (DPV) method. AuNPs@Fe3O4 nanocomposites increased the specific surface area of the electrode. Moreover, the diazotization-coupling reaction enriched the analytes on the electrode surface. Liquid-liquid extraction was used for sample pretreatment. Under a pH value of 9.0 and concentration of 0.20 mol/L for the supporting electrolyte, the linearity of capsaicinoids in ICO is from 0.10 to 10.00 ng/mL, and the limit of detection (S/N = 3) is 0.05 ng/mL. This method is ultra-sensitive, reliable, and cost-effective for the detection of capsaicinoids. Herein, this method provides a promising tool for the identification of ICO.

A sensitive electrochemical method for indole based on the signal amplification strategy by gold/iron-oxide composite nanoparticles.

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.