# Recent Development of Aptamer Sensors for the Quantification of Aflatoxin B1
## 2 Colorimetric, Electrochemical, and Fluorescent Aptamer Sensors to Monitor AFB1
### Electrochemical Aptamer Sensor for AFB1
The sensitivity, stability, and recognition efficiency of the probe could be improved through loading the DNA tetrahedron (containing the aptamer) onto the surface of 3 DOM MoS\({}_{2}\)-AuNPs. When AFB1 was added, the aptamer on the DNA tetrahedron bound to AFB1 and detached from the electrode surface. DNA tetrahedra can hybridize to DNA helper strands (H1), which were modified on an HRP-modified AuNPs-SiO\({}_{2}\)@Fe\({}_{3}\)O\({}_{4}\) nanospheres. A gradual increase of the current signal took place as the concentration of AFB1 increased. Under optimal conditions, the aptamer had excellent selectivity for AFB1. The current signal exhibited an excellent linear relationship with AFB1 concentration, ranging from \(1.0\times 10^{-14}\) to \(1.0\times 10^{-4}\) g\(\cdot\)L\({}^{-1}\). The detection limit for AFB1 was estimated to be \(1.0\times 10^{-14}\) g\(\cdot\)L\({}^{-1}\). In addition, the aptasensor was utilized to detect AFB1 in not only rice, but also wheat powder, and the experimental results obtained were consistent with the results obtained by the standard HPLC-MS method. [PERSON] et al. developed an electrochemical aptasensor and demonstrated that it could be applied to the detection of AFB1 (Figure 8) [25]. The probe consisted of a \(\pi\)-shape structure of aptamer-complementary strands complexes, which was used as double-layer physical barrier for the access of [Fe(CN)\({}_{6}\)]\({}^{3-4/4}\)- to the surface of a gold electrode; furthermore, Exo I was used as a signal amplifier. The sensitivity of the probe was improved by the \(\pi\)-shape structure. The \(\pi\)-shape structure was intact in the absence of AFB1, and a weak current signal was observed. When AFB1 was present, the \(\pi\)-shape structure was disassembled and, therefore, a distinctive current signal was observed in the presence of Exo I. The current signal increased with increases in the AFB1 concentration, ranging from \(7.0\times 10^{-9}\) to \(5\times 10^{-7}\) g\(\cdot\)L\({}^{-1}\). The detection limit was estimated to be \(2.0\times 10^{-9}\) g\(\cdot\)L\({}^{-1}\). The probe was successfully applied to detect AFB1 in spiked human serum, as well as in grape juice samples. Figure 6: Schematic representation of the detection of AFB1 by an electrochemical aptasensor using a telomerase- and Exo III-assisted amplification strategy. Reproduced from [23]. Copyright 2016, Elsevier. A large number of materials have been employed for electrochemical determination of AFB1, with high sensitivity as well as selectivity. For instance, [PERSON] et al. devised an electrochemical aptasensor [26], which was composed of an aptamer labeled with methylene blue (MB), serving as a signal moiety, and functional grapheme oxide (FGO), acting as a signal amplifier. The FGO was not only used as a platform for the attachment of the aptamer, but was also employed as a signal amplifier, due to its catalytic property for MB. The plot of current signal versus analyte concentration showed excellent linearity, ranging from \(5.0\times 10^{-8}\) to \(6.0\times 10^{-6}\) g\(\cdot\)L\({}^{-1}\). The detection limit of the aptasensor was found to be \(5.0\times 10^{-8}\) g\(\cdot\)L\({}^{-1}\). Significantly, the aptasensor was applied to detect the levels of AFB1 in alcoholic beverages.