Programmable DNA Tweezer-Actuated SERS Probe for the Sensitive Detection of AFB₁

A DNA tweezer is a dynamic DNA nanomachine that can reversibly switch its state between open and closed. Here, we employed a DNA tweezer for the first time to dynamically control the distance between plasmonic silver nanoparticles (Ag NPs) for a surface enhanced Raman scattering (SERS) biosensing application. Two DNA and 4-nitrothiophenol (4-NTP) modified Ag NPs were linked to the arms of the DNA tweezer (DNA tweezer-Ag NPs probe) by complementary base pairing. Activation of the Raman intensity was achieved by the state transformation of the DNA tweezer-Ag NPs probe from open to closed. The distances between two Ag NPs in open and closed state were 8.1 ± 2.7 nm and 3.2 ± 0.8 nm, respectively. Furthermore, the two Ag NPs were spatially separated in the open state with a low Raman signal, whereas in the closed state, Raman intensity was enhanced because of the proximity of two Ag NPs. The developed biosensing system exhibited a good linear relationship when the concentration of aflatoxin B₁ (AFB₁) ranged from 1 ng/mL to 0.01 pg/mL, and the limit of detection (LOD) was 5.07 fg/mL. In addition, spike recovery and certificated real foodstuffs were used to examine the feasibility in a real situation. This protocol provides a potential candidate for SERS detection and can be used as a promising technology for biological and chemical sensors.