Enzyme immobilization plays an essential
role in solving the problems
of the inherently fragile nature of enzymes. Although prominent stability
and reuse of enzymes can be achieved by enzyme immobilization, their
bioactivity and catalytic efficiency will be adversely affected. Herein,
PdCu hydrogel nanozymes with a hierarchically porous structure were
used to immobilize horseradish peroxidase (HRP) to obtain PdCu@HRP.
In addition to the improvement of stability and reusability, PdCu@HRP
displayed synergistically enhanced activities than native HRP and
PdCu hydrogels. Not only the specific interactions between PdCu hydrogel
nanozymes and enzymes but also the enrichment of substrates around
enzymes by electrostatic adsorption of hydrogels was proposed to expound
the enhanced catalytic activity. Accordingly, by taking advantage
of the excellent catalytic performance of the PdCu@HRP and the glucose
oxidase encapsulated in zeolitic imidazolate framework-8, colorimetric
biosensing of the carcinoembryonic antigen via catalytic cascade reactions
for achieving signal amplification was performed. The obtained biosensor
enhanced the detection sensitivity by approximately 6.1-fold as compared
to the conventional HRP-based enzyme-linked immunosorbent assay, demonstrating
the promising potential in clinical diagnosis.