A simple carbon-based electrochemical/photoelectrochemical dual-mode aptasensor for the detection of aflatoxin B1

Herein , an electrochemical/photoelectrochemical (EC/PEC) dual-mode sensing platform based on carbon dots/liquid exfoliated graphene (CDs/LEG) nanocomposites was developed in this work. The CDs/LEG heterogeneous effectively exploited the excellent photoelectric activity of CDs and the high conductivity of LEG. Ferrocene-labelled aptamer (Fc-Apt) and methylene blue-labelled complementary DNA (MB-cDNA) were introduced as dual-signal probes. Upon aflatoxin B1 (AFB₁) binding, it competitively displaced MB-cDNA, restoring Fc-Apt hairpin conformation and causing MB to move away from the electrode surface while Fc approached it. This conformational change significantly increased the I_Fc to I_MB peak current ratio (I_Fc/I_MB), enhancing the EC signals; meanwhile, the aptamer complex immobilized on the electrode surface reduced the PEC signals through spatial site-blocking and light-shielding effects. The dual-mode responded synergistically to form a unique self-validation mechanism, which showed excellent linearity over the AFB₁ concentration range of 0.01-100 ng/mL, with detection limits (LOD) of 1.356 pg/mL (EC mode) and 0.087 pg/mL (PEC mode).