N-Doped Graphene Nanoplatelets for Direct Capsaicin Detection in Chili Pepper Samples

Abstract

In this study, we have designed and fabricated a portable electrochemical sensor for direct detection of capsaicin in chili samples at the point-of-testing. The sensor, shaped like a chili pepper and highly portable, is essentially a disposable electrochemical paper-based analytical device (ePAD) modified with N-doped graphene nanoplatelets (GrNPs). The sensor consists of three components: (i) a small potentiostat device, (ii) an interface allowing connection to a smartphone for monitoring and control, and (iii) the sensor (an N-doped GrNPs/ePAD and detection chamber). The N-doped GrNPs/ePAD shows high conductivity and good electrocatalytic activity in the oxidation and reduction of capsaicin. The measurement of capsaicin was performed directly through differential pulse voltammetry once the parameters influencing capsaicin detection (i.e., pH, buffer ethanol content, N-doped GrNPs loading, accumulation potential, and accumulation time) were optimized. Linearity was obtained in the concentration range 1–100 μM, and the limit of detection was found to be 0.37 μM. Furthermore, the preparation of ten N-doped GrNPs/ePAD devices confirmed fabrication reproducibility. The sensor was successfully applied to the determination of capsaicin in chili samples, with recoveries between 89.3 ± 0.3 and 106 ± 2%, and the results showed no significant difference to those obtained by UV–vis spectrophotometry. Thus, this platform shows excellent potential for the development of portable sensors for capsaicin and future extension to different analytes.

Adsorptive Cathodic Stripping Voltammetry for Quantification of Alprazolam

“…Furthermore, the oxygen-containing functional groups information on the GCE surface before and after electrochemical pretreatment in sulfuric acid was characterized by the FT-IR technique, as shown in Figure 2 E. Before GCE electrochemical pretreatment ( Figure 2 E-a), small peaks at 2921, 2860, and 1621 cm −1 , which attribute to stretching band of -C-H and C=C in the structure of carbon material were observed [ 18 , 35 ], indicating a less functional group on the pristine GCE surface. In contrast, after GCE was electrochemically pretreated in sulfuric acid at 1.8 V ( Figure 2 E-b), stretching bands were more pronounced than pristine GCE, which can be observed in the bands of the oxygen-containing functional groups in the region of 1800 to 700 cm −1 , which can be assigned to -C=O, -C=C, -COO − , -C-O-C, and C-C stretching bands and -OH bending modes in ether, lactones, carboxyl, and phenolic structures [ 15 , 18 , 33 ]. The strong intensities of those bands after electrochemical pretreatment of GCE in sulfuric acid confirmed that the oxygen-containing functional groups were successfully functionalized on the GCE surface during electrochemical pretreatment [ 33 ].…”

“…Developed analytical methods for the detection of alprazolam include high performance liquid chromatography [ 7 ], gas chromatography [ 8 ], UV-vis spectroscopy [ 9 ], and electrochemical techniques [ 10 , 11 , 12 ]. Electrochemical techniques are simple, inexpensive, and provide fast response times and good sensitivity [ 13 , 14 , 15 , 16 , 17 ]. Adsorptive stripping voltammetry (AdSV) is an electrochemical technique that is widely used for the analysis of trace organic compounds and various elements [ 18 , 19 , 20 ].…”

Chile Pepper (Capsicum) Breeding and Improvement in the “Multi-Omics” Era

“…Recently, efforts to develop cost-effective, fast, and direct detection of capsaicinoid content from samples using different techniques, such as voltammetry and near-infrared spectroscopy, have been made ( Crapnell and Banks, 2021 ). For example, a graphene-based portable device that can be connected to a smartphone has been developed and high accuracy and collinearity between the SHU values derived from the machine and from spectroscopy were observed ( Soleh et al, 2020 ). A colorimetric approach using the Gibbs reagent has also been employed for the rapid determination of capsaicinoid content and has a high correlation with HPLC ( Ryu et al, 2017 ).…”

Selective and sensitive determination of capsaicin using polymelamine formaldehyde decorated over carbon nanotubes

“…25 Until now, various catalytic materials, including boron-doped diamond, 26 carbon-based disposable electrodes, 27,28 metal nanoparticles (Ag/Ag 2 O, CeO 2 , Ru, Sn etc. ), [29][30][31][32] mesoporous cellular foams 33 and recently, N-doped atom graphene nanoplates 34 have been explored for selective and sensitive electrochemical determination of capsaicin. However, the synthesis of these catalysts is a time consuming, complicated procedure that requires harsh conditions and high temperature, and low stability and high cost are major concerns.…”