Hollow Pt Nanocage@Mesoporous SiO₂ Nanoreactors as a Nanozyme for Colorimetric Immunoassays of Viral Diagnosis

A facile and general strategy has been employed to fabricate a “nanoreactor” consisting of a hollow Pt nanocage-encapsulated mesoporous SiO2 shell. The hollow composite, which contained highly dispersed catalytic Pt nanoparticles inside the cavity enclosed by the mesoporous SiO2 shell, was considered an ideal framework structure for a nanoreactor that efficiently catalyzes substrate molecules with enhanced activity. The designed SiO2 shell can not only maintain active Pt nanoparticle resistance to harsh environments but also isolate the molecular recognition sites from the surface of Pt nanoparticles, thus retaining their catalytic activity. In addition, the certain space confinement effect aroused by the hollow structure led to a higher catalytic activity. Based on their catalytic activity, these nanoreactors have been demonstrated to function as biosensors for highly sensitive detection of measles-specific IgM antibodies in capture enzyme-linked immunosorbent assays. The detection limit of the prepared biosensor was as low as 1 ng/mL, 3 orders of magnitude lower than that of the conventional immunoassay. The specific catalytic properties of this nanoreactor could have great potential applications that include catalysis, biological labeling, and bioassays.