Novel immunoassay for Toxoplasma gondii-specific immunoglobulin G using a silica nanoparticle-based biomolecular immobilization method

A direct and highly sensitive piezoelectric immunoassay for Toxoplasma gondii-specific IgG (Tg-IgG) in infected rabbit serum (IRS) has been proposed on the basis of a new biomolecular immobilization strategy incorporating silica nanoparticles/matrix and a plasma-polymerized film (PPF) of n-butyl amine. SiO2 nanoparticles prepared by using a water-in-oil microemulsion route were chemically activated and then used to conjugate T. gondii antigens (TgAg) onto the PPFdeposited crystal. Compared to the commonly applied methods, i.e. the glutaraldehyde (GLU) cross-linking procedure, this strategy could allow for antigens immobilized with higher loading amount and better retained immunoactivity, as demonstrated by the immunofluorescence measurements. Moreover, a mild reduction agent 2-mercaptoethanol (2-ME) which can deactivate T. gondii-specific IgM in the analytical samples was utilized to achieve the direct determination of Tg-IgG. Some applications including an optimized assay medium, a blocking reagent and a versatile regenerating solution may facilitate a sensitivity amplified, non-specific adsorption-minimized and renewable sensing system. A dynamic dilution range of ~ 1:5000 to 1:70 and detection limit of 1:5350 dilution were observed. Results obtained by evaluating IRS samples indicate that the detection sensitivity of the developed immunoassay is comparable to that of the ELISA method and superior to that of the dot-immunogold test.