One-pot loading high-content thionine on polydopamine-functionalized mesoporous silica nanosphere for ultrasensitive electrochemical immunoassay

A thionine (TH)-doped mesoporous silica nanosphere (MSN)/polydopamine (PDA) nanocomposite was synthesized for developing a new signal transduction strategy of electrochemical immunoassay. This nanocomposite was synthesized through one-pot loading of TH and in situ formation of PDA-coating on MSN. After antibody labeling, the obtained nanoprobe was used for the signal tracing of sandwich immunoassay at a magnetic bead-assay platform. Based on the specific capture of the MSN-TH/PDA nanoprobes through sandwich immunoreaction to form a magnetic immunocomplex and the following treatment of the immunocomplex with a NaOH solution, the PDA film coated on MSN was destroyed to release TH tags from the nanoprobe. The released TH was then electrochemically measured at a carbon nanotube (CNT)-modified electrode for the signal transduction of the method. Due to the high loading of TH on the nanoprobe for tag release and effective electrochemical signal enhancement by the electrode modification of CNTs, ultrahigh sensitivity was achieved. Using human IgG as a model analyte, this method showed a wide linear range over four orders of magnitude and a low detection limit of 5.8 pg/mL. Additionally, the method has excellent specificity, satisfactory reproducibility and stability as well as acceptable reliability. Due to the simple preparation of the nanoprobe and the low cost, convenient operation of the detection strategy, this nonenzymatic immunoassay method possesses great potentials for practical applications.