Research progress on ratiometric electrochemical sensors for the detection of mycotoxins in agricultural products

Mycotoxins have been listed as the main sources of foodborne diseases by the World Health Organization, due to their high teratogenicity, nephrotoxicity, and carcinogenicity. Electrochemical sensing technology can be used to rapidly detect the mycotoxins in agricultural products, in terms of portability, low cost, and high sensitivity. Generally, the electrochemical sensors can be selected to quantify the analytes simply by a single electrical signal susceptible to interference from some intrinsic or extrinsic factors. The ratiometric strategy with dual-signal responses has been recently applied in electroanalytical sensors, in order to deal with the unreliable trace detection from traditional single-signal sensors. The ratiometric electro-analytical sensors shared the dual signals, where the ratio of the two signals was served as a yardstick, instead of a single signal. The ratiometric strategies can be divided into the single- and dual-signal dependence on analytes. In the single-signal dependence, only one single signal was dependent on the analytes, while another signal remained unchanged. In the dual-signal dependence, both signals were dependent on the analytes, where their intensities exhibited correspondingly increasing and decreasing changes simultaneously. Theoretically, such ratiometric strategies can provide an intrinsic built-in correction to effectively reduce or eliminate the fluctuations from the intrinsic background signals, and then greatly improve the accuracy and reliability of the electrochemical sensors in complex detection conditions. This review highlighted the recent advances in ratiometric electrochemical sensors over the past three years (2018-2021). Four categories were divided as follows. 1) Direct sensors, which mainly utilize the electrode materials to directly oxidize the analyte and internal-reference substance to obtain the dual redox signals; 2) Antibody-based sensors, which use the antigen and antibody as the recognition elements to establish the dual-signal readout immunoassay; 3) DNA-based sensors, which use the DNA as the recognition element and the specific hybridization between complementary and target DNA to cause the changes in the electrical signals of the system for the ratiometric detection of targets; 4) Aptamer-based sensors, which utilize the specific binding between the aptamer and target to cause the changes in the electrical signals. This review summarized the signal generation strategies and analytical applications, particularly for the detection of mycotoxins in agricultural products. Furthermore, a systematic evaluation was performed on the recognition elements, sensing materials, real samples, and the analytical performances for the detection of mycotoxins in various sensing modes. Finally, the bottleneck and development trends were addressed for the ratiometric electrochemical sensing technology in the field of agricultural sensing, such as the development of recognition elements, the simultaneous detection of multiple mycotoxins, the on-site and real-time detection of mycotoxins in agricultural products, etc. The portable devices can be expected to realize the on-site, simultaneous, and rapid detection of various mycotoxins. This review can provide a strong reference for the mycotoxins detection techniques in agricultural products.