Detection of carcinoembryonic antigen and α-fetoprotein exploiting a 3D DNA walker strategy

Carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) are known cancer biomarkers and are widely used for diagnosis in clinical research. Here, we report an Mg²⁺-based DNAzyme-mediated three-dimension (3D) DNA walker strategy and demonstrated its use for the detection of CEA and AFP. The 3D DNA walker constructed 3D tracks using hollow carbon nanospheres (HCS) as a support. In the presence of the biomarkers and the Mg²⁺ cofactor, the DNA walker actively generated multiple copies of intermediate DNA (iDNA) fragments from the substrate probe that is immobilized on the HCS support. With the use of a nicking enzyme, amplification is triggered by iDNA, resulting in the decrease of the redox signal of methylene blue (MB) and ferrocene (Fc). For the detection of CEA, the immunosensor has a limit of detection of 0.3 pg mL⁻¹ with a linear range between 1 pg mL⁻¹ and 1000 ng mL⁻¹. For AFP detection, the limit of detection is 0.5 pg mL⁻¹ with a linear range of 1 pg mL⁻¹ to 100 ng mL⁻¹. As part of this study, the employment of this strategy in serum samples is demonstrated for the detection of CEA and AFP.