Label-free colorimetric biosensor for sensitive detection of lead (II) ion based on aptazyme-amplified oxidase-like activity of MnO2 nanoflowers.

The significant harm inflicted on human health by minimal concentrations of lead (Pb2+) ions has rendered its detection crucial. Here, a simple label-free colorimetric biosensor was presented for detecting Pb2+ based on the enhancement of oxidase-like activity in MnO2 nanoflowers (MnO2 NFs) through the cleavage function of aptazyme strand, for the first time. The existence of Pb2+ triggered the cleavage activity of the DNAzyme strand, resulting in the fragmentation of the substrate sequence at the rA location. The catalytic performance of MnO2 nanozymes was enhanced by attaching substrate fragments to their surface, leveraging the heightened affinity of MnO2 NFs for the chromogenic substrate. This alteration resulted in a significant transformation of the biosensor medium's color. The linear concentration range for Pb2+ detection was achieved from 0.01 nmol/L to 100 μmol/L with a detection limit of 0.0024 nmol/L (2.4 pmol/L). The biosensor successfully identified Pb2+ in actual samples including shrimp extract, lipstick, and human serum. Therefore, this biosensor has promising application for monitoring Pb2+ in food products, cosmetics, and health care.