Improved sandwich-format electrochemical immunosensor based on "smart" SiO2@polydopamine nanocarrier.

An improved sandwich-type electrochemical immunosensor based on the novel signal amplification strategy was developed. Methylene blue (MB) loaded mesoporous silica nanoparticles (MSN) with polydopamine coating (PDA) were employed as "smart" labels, while phytic acid doped polyaniline hydrogel (PANI) with high adsorption capacity was acted as substrate. In this strategy, amount of redox species (MB) encapsulated in MSN by PDA will be released under acidic condition and then absorbed stably by PANI. Meanwhile, the label tended to drop down due to the destruction of polydopamine coating and the disassociation of antibody-antigen composites. The advantages of as-prepared immunosensor are as follows: (1) Higher electron transfer efficiency was obtained because of the decrease of relative position between MB and the electrode; (2) Lower impedance was achieved due to the loss of the labels and the dissociation of antigen-antibody insulating layer; (3) Abundant MB molecules were loaded on MSN/PDA nanocarrier with large pore volume for signal amplification. Under optimum conditions, the proposed immunosensor exhibited a low detection limit of 1.25 fg mL-1 and a wide linear range from 10 fg mL-1 to 100 ng mL-1 for prostate specific antigen detection. Importantly, present method showed good stability, selectivity, and reproducibility, which possessed wide potential applications for the detection of other biomarkers.