# Functionalized Carbon-Based Electrochemical Sensors for Food and Alcoholic Beverages Safety
## 3 Carbon Nanomaterial-Based Electrochemical Sensors
### CnTs  
CNTs, also known as bucky tubes, are one-dimensional tubular nanomaterials with special structures. CNTs are mainly coaxial round tubes with a single to dozens of layers composed of sp2 hybridized carbon atoms [75; 76]. In theory, CNTs can be regarded as hollow tubes rolled by graphene sheets. According to the number of rolled layers of the graphene sheets, CNTs can be subdivided into single-walled carbon nanotubes (SWCNT) formed by a hexagonal grid structure, and multi-walled carbon nanotubes (MWCNT) assembled from several to dozens of concentric cylinders with regular layer spacing [77; 78]. Because their unique structure is completely different from that of bulk carbon materials, CNTs can exhibit excellent properties, such as unique electrical, special magnetic, and strong light absorption properties. Because of their excellent electrical conductivity, large specific surface area, good biocompatibility, easily functionalization, and abundant active sites, CNTs are also an advantageous option in the design of electrochemical sensors [79; 80; 81]. In the following section, we illustrate the applications of CNTs-based materials in the development of electrochemical sensors for food and beverage safety, as summarized in Table 2.  
Wine is a complex drink mixed with hundreds of compounds, among which, phenolic compounds exist at much lower levels of concentration than other organics [82]. To evaluate the antioxidant properties of the wine samples, the gallic acid (GA, as one of the main phenolic components) oxidation process was constructed using 30% (m/m) carbon nanotube-modified electrodes [83]. The linear range of 0.5-15 uM and the detection limit of 0.3 uM were obtained in an optimized experimental condition. Finally, the proposed procedure was successfully used for estimating the determination of total polyphenols in the samples of red and white wines. Compared with traditional analytic methods, electrochemical analytic methods with CNT-modified electrodes have the advantages of high detection limit, small demand for raw materials, and strong selective identification of specific pollutants [84]. Furthermore, [PERSON] and co-workers [85] researched the oxidation peaks of phenolic antioxidants existing in red or white dry wine samples based on MWNT/GCE using differential pulse voltammetry in the phosphate buffer solution of pH 4.0. The evaluation of wine antioxidant capacity (AOC) was established by a one-step chronocoulometric method. The results demonstrated that the AOC of white wine was significantly less than that of red wine (386 \(\pm\) 112 vs. 1224 \(\pm\) 184, \(p\) < 0.0001). The presented effective measurement, AOC evaluation, made it possible for quality control at different stages in the winemaking process, which usually cannot be accurately performed due to the limitation of common analytic technology. It should be emphasized that CNT-based composite materials via introducing metal oxides and metal nanoparticles have recently shown great success in food and beverage safety testing. The possible reasons for this were that the added metal components dramatically boosted electrical conductivity, enhanced chemical signals, and promoted chemical interaction with the analyte. As shown in Figure 4a, various phenolic compounds in wine samples were determined by CV, DPV,