# Recent Development of Aptamer Sensors for the Quantification of Aflatoxin B1
## 2 Colorimetric, Electrochemical, and Fluorescent Aptamer Sensors to Monitor AFB1
### SERS aptamer Sensor for AFB1  
A SERS aptamer sensor with high sensitivity was devised by [PERSON] et al. for the simultaneous determination of AFB1, as well as ochratoxin [32]. As shown in Figure 13, Ag@Au core-shell (CS) nanoparticles (NPs), which were used as signal reporters, were fabricated by the embedding of 4-NTP or 4-ATP. Subsequently, Ag@4-NTP@Au NPs, as well as Ag@4-ATP@Au CS NPs, were modified with aptamer AFB1 and aptamer OTA, respectively. In the absence of the analytes, several SERS aptasensors could be captured by MNPs, which were modified with complementary strands of the aptamers, leading to the formation of SERS-active MNP-Ag@Au CS-NP core-satellite assemblies. When the analytes were present, not only AFB1, but also OTA, could bind to the aptamer, leading to the separation of Ag@Au CS-NPs from the MNPs. Consequently, the SERS signal gradually decreased with an increase in concentration of the targets. The SERS aptasensor could be used to detect double mycotoxins, including OTA and AFB1, in maize meal. A good linearity was found to exist in the plot of SERS signal versus AFB1 and OTA concentrations. The limits of detection toward AFB1 and OTA were found to be \(3.0\times 10^{-8}\) g\(\cdot\)L\({}^{-1}\) as well as \(6\times 10^{-10}\) g\(\cdot\)L\({}^{-1}\) and \(6\) pg\(\cdot\)mL\({}^{-1}\), respectively. The proposed strategy could be extended to various SERS tags for the determination of multiple targets with various lengths of aptamers. Figure 13: Schematic representation for the simultaneous determination of AFB1 and OTA by the utilization of SERS labels embedded in Ag@Au core-shell NPs. Reproduced from [32]. Copyright 2015, American Chemical Society. [PERSON] et al. developed a SERS apptasensor for the detection of AFB1, on the basis of exonuclease-aided recycling amplification (Figure 14) [33]. A hairpin was attached onto the surface of a gold film. Upon addition to AFB1, the aptamer was capable of binding to AFB1, resulting in the release of DNA which was partially complementary to the AFB1 aptamer. The released DNA could hybridize with the hairpin to form a DNA duplex. The DNA duplex could be degraded in the presence of Exo III, resulting in the presence of single-strand DNA, which was employed to capture Raman tags. Furthermore, many single-strand DNA were generated using the Exo III-aided target amplification strategy. Subsequently, many Raman probes were able to immobilize on the surface of gold film. The SERS signal was observed to be linear, ranging from \(1.0\times 10^{-12}\) to \(1.0\times 10^{-6}\) g\(\cdot\)L\({}^{-1}\), and the detection limit was as low as \(4.0\times 10^{-13}\) g\(\cdot\)L\({}^{-1}\). The rapid, simple, and low-cost strategy was applied for the detection of AFB1 in spiked peanut samples. [PERSON] et al. devised a SERS probe on the basis of gold nano-star (Au NS) core-silver nanoparticle (Ag NP) satellites for the determination of AFB1 [34]. The probe was comprised of AFB1-functionalized Ag satellites, as well as a complementary DNA-functionalized Au NS core. The intensity of SERS increased when the satellite was bound to the Au NS core. In the presence of AFB1, the AFB1 aptamer on the surface of the Ag satellites was capable of binding to the target. Subsequently, the Ag satellites moved away from the Au NS core, leading to a decrease of the SERS signal. A good linear relationship was found to exist in the range of \(1.0\times 10^{-9}\) to \(1.0\times 10^{-6}\) g\(\cdot\)L\({}^{-1}\). The detection limit of the SERS probe was found to be \(4.8\times 10^{-10}\) g\(\cdot\)L\({}^{-1}\). The SERS probe was used to detect AFB1 in food. [PERSON] et al. constructed a SERS apptasensor for the determination of AFB1 by utilizing gold nano-triangles (GNTs) and DTNB@Ag-DTNB nano-triangles (GDADNTs) acting as the SERS substrate (Figure 15) [35]. The AFB1 aptamer was modified on the surface of a magnetic bead, which served as the capture sensor.