Fabrication of a Free‐Standing MWCNT Electrode by Electric Field Force for an Ultra‐Sensitive MicroRNA‐21 Nano‐Genosensor

Abnormal expression of microRNA-21 (miR-21) is considered to be closely associated with the pathogenesis of colorectal cancer. However, great challenges do exist for the development of ultra-sensitive biosensors to detect the abnormal expression of miR-21 due to the low concentration in serum (fm level) at the early stage of colorectal cancer. Therefore, electric field force is used to rotate and rearrange random multi-walled carbon nanotubes (MWCNTs) at the microscale to improve the active sites of the electrode in this study. The free-standing MWCNTs are densely and high-orderly embedded into the bare electrode along the direction of the electric field. Compared to the bare electrode, the peak-current response of the free-standing MWCNT electrode improves by 150 times in cyclic voltammetric measurement. A nano-genosensor based on the free-standing MWCNT electrode is developed for measuring miR-21. The nano-genosensor for miR-21 shows an ultra-high sensitivity of 48.24 µA µm-1 , a wide linear range from 0.01 × 10-15 to 100 × 10-12 m, and a low detection limit of 1.2 × 10-18 m. The present nano-genosensor shows superior performance for miR-21 in human serum samples and demonstrates a potential application for the diagnosis of early stage colorectal cancer.