# Recent Development of Aptamer Sensors for the Quantification of Aflatoxin B1
## 2 Colorimetric, Electrochemical, and Fluorescent Aptamer Sensors to Monitor AFB1
### Fluorescent Aptamer Sensor for AFB1  
Recently, we have developed a simple, rapid, and label-free method for the quantification of AFB1, by utilizing TPE-Z, graphene, and aptamers. Graphene oxide (GO) with high water resolvability served as a quencher and was employed to quench TPE-Z fluorescence (see Figure 9A) [27]. Additionally, GO could adsorb positively-charged TPE-Z molecules and aptamers by electrostatic and \(\pi\)-\(\pi\) interactions. Figure 8: Scheme illustration of the fabrication process of an aptasensor and detection mechanism for the detection of AFB1. Reproduced from [25]. Copyright 2017, Elsevier. Figure 7: Schematic representation of the detection mechanism of the AFB1 aptasensor based on DNA tetrahedrons and horseradish peroxidase-modified Fe\({}_{3}\)O\({}_{4}\). Reproduced from [24]. Copyright 2018, American Chemical Society. As TPE-Z was positively charged, it had great dispersibility in aqueous media. Therefore, negligible fluorescence was observed, due to the dispersibility. In addition, graphene oxide could also quench the fluorescence of TPE-Z, minimizing the fluorescent background. Upon addition of AFB1, the aptamer bound to AFB1, rather than interacting with the graphene, resulting in the detachment of the aptamer and TPE-Z from the GO. As the positively charged TPE-Z could bind to the negatively charged aptamer through electrostatic interaction, the TPE-Z fluorescence was enhanced, due to the activation of an RIM process (Figure 9B). The approach simply mixed TPE-Z, GO, and the AFB1 aptamer for quantification of the analyte. The limit of detection for AFB1 was found to be \(2.5\times 10^{-7}\) g\(\cdot\)L\({}^{-1}\), and a high selectivity toward AFB1 was shown (Figure 9C). This probe monitored AFB1 in actual samples, including corn, milk, and rice, with good selectivity. Figure 9: (**A**) Scheme representation of the label-free aptasensor for AFB1 determination in food samples. (**B**) Fluorescence spectra of the proposed probe for AFB1 with various concentrations. (**C**) Selectivity of the proposed probe toward AFB1. Reproduced from [27]. Copyright 2019, Elsevier. [PERSON] et al. fabricated a fluorescent light-up probe for the ultra-sensitive determination of AFB1. Carbon dots were prepared and an AFB1 aptamer was decorated onto gold nanoparticles (see Figure 10A) [28]. As the carbon dots were positively charged and the AFB1 aptamer-decorated gold nanoparticles were negatively charged, the carbon dots tended to assemble onto the gold nanoparticles through electrostatic interactions, forming a nanocomposite. As the gold nanoparticles were an excellent quencher, they could be used to quench the fluorescence of the carbon dots. When AFB1 was present, AFB1 bound to the aptamer on the gold nanoparticle, causing the carbon dots to be released. As shown in Figure 10B, a gradual increase of fluorescence intensity was observed as the concentration of the target increased. Furthermore, on account of the good selectivity of the aptamer toward AFB1, the probe, thus, had the advantage of high selectivity (Figure 10C). The probe displayed a good linear relationship from \(5.0\times 10^{-9}\) to \(2.0\times 10^{-6}\) g\(\cdot\)L\({}^{-1}\). The detection limit of the probe was \(5.0\times 10^{-9}\) g\(\cdot\)L\({}^{-1}\). An enzyme-free, amplified, and ultra-fast aptasentor capable of one-test-tube homogeneous determination of aflatoxin B1 (AFB1) has been developed by [PERSON] et al. (see Figure 11) [29]. As the aptasensor was designed with a dual-terminal proximity structure, one molecule was capable of switching up to two fluorophores. As a consequence, the signal was amplified without using enzymes. Additionally, the signal-noise ratio and sensitivity toward AFB1 were improved by taking advantage of the above strategy. The aptasensor could be applied for rapidly testing for the presence of AFB1, concluding within 1 min. On account of the universality and simplicity of the aptasensor, it demonstrated great potential for AFB1 determination in food safety.