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.