Dual-ratiometric electrochemical aptasensor enabled by programmable dynamic range: Application for threshold-based detection of aflatoxin B1

Aptamer-based sensor with high-specificity typically has a fixed linear range due to the host-guest binding. To expand the dynamic range for multiple scenarios, we report here a dual-ratiometric electrochemical aptasensor that integrates two aptamer profiles with varied affinity into a single sensing interface for aflatoxin B1 (AFB1) detection. Using functional aptamer as recognition element and generator of signals, we fabricate the dual-ratiometric aptasensor with anthraquinone loaded reduced graphene oxide (AQ-rGO), methylene blue labeled hairpin DNA (MB-DNA), and ferrocene labeled linear aptamer (Fc-apt), using MB and Fc probes to work in tandem while AQ as reference. The current of Fc (IFc) is used to detect the low-concentration analyte, and that of MB (IMB) varies when the concentration of AFB1 reaches a threshold. The threshold switch for IMB could be tuned by engineering the quantity ratio of Fc-apt and MB-DNA (a ratio of 1:1 is used here). The aptasensor can rapidly achieve the positive (+)/negative (-) detection of AFB1 with a threshold concentration of 10 pg mL-1, while the quantitative detection employs the ratio of current of AQ, MB, and Fc (i.e., IAQ/IMB and IAQ/IFc) as yardsticks, offering two linear ranges of 10-106 and 10-2-5 × 104 pg mL-1, respectively. The aptasensor is successfully used to monitor the amount of AFB1 in a 7-days mildew process of peanut. Such a protocol opens a new way for the design of sensors with the programmable linear range in the advanced biological and chemical sensing.