An electrochemical microsensor of the SARS-CoV-2 nucleocapsid protein based on a surface-imprinted acupuncture needle

A novel electrochemical microsensor was constructed on a traditional acupuncture needle (AN) and used to monitor a biomarker of the SARS-CoV-2-N protein. The reversible interaction of the borate bond between the cis-diol in this glycoprotein and the phenylboronic acid in 4-mercaptophenylboronic acid (4-MPBA) was accomplished. This interaction was applied to anchor the SARS-CoV-2-N protein onto 4-MPBA, which was covalently self-assemblied onto electrodeposited AuNPs by the S-Au bond. Meldola blue was then electropolymerized around the protein template. After the template had eluted, three-dimensional nanocavities complementary to the protein were generated within the polymeldola blue (pMB) layer. Interestingly, nanocavities could play a channel role for the electron-transfer of outer [Fe(CN)₆]^3-/4-, and the signal of the electrochemical probe could be hindered after recombination of the SARS-CoV-2-N protein, which lays a platform for the detection of this biomarker. After optimizing the influencing factors, the prepared microsensor exhibited a linear range of 0.1-1000 ng mL^-1 with a low detection limit of 0.01 ng mL^-1 (S/N = 3). In particular, the sensing ability was dramatically affected by the thickness correlative factor for the polymer matrix. A suitable thickness is effective for sensing the signals, which corresponds to the behavior of the surface-imprinted polymer. The microsensor showed comparatively high sensitivity and selectivity and practically detected the SARS-CoV-2-N protein in the serum sample, which is of scientific significance for the development of electrochemical microsensors and acupuncture.