Label‐Free Colorimetric Detection of Lead Ions with a Nanomolar Detection Limit and Tunable Dynamic Range by using Gold Nanoparticles and DNAzyme

In the presence of Pb2+, a cleaved enzyme–substrate complex releases ssDNA that adsorbs onto and stabilizes gold nanoparticles (AuNPs) against salt-induced aggregation. In the absence of Pb2+, the uncleaved complex can not stabilize the AuNPs, resulting in purple–blue AuNP aggregates (see figure). The sensor has a low detection limit of 3 nM, a high selectivity, and a tunable dynamic range.