Carbon quantum dots@metal-organic framework based catalytic nucleic acid fluorescent system for highly sensitive and selective detection of Pb2+ in aqueous solutions

Accumulation of heavy metal ions in the ecosystem has become a major concern due to their adverse impacts on animals, humans, and aquatic habitats. The development of a rapid and portable sensing system is important for the prompt detection and proper management of such pollutants. Herein, we have designed a fluorescence-based biosensor for the selective and sensitive detection of Pb2+ ions using a DNAzyme system that is active only in the presence of lead (II) ions (Pb2+). The developed nanoprobe relies on two major components: (i) boron and nitrogen carbon dots (BNCDs)-doped carboxyl functionalized-terbium metal-organic framework (COOH-Tb MOF) as a fluorescent tag and (ii) quencher-modified catalytic NH3-GR5 DNAzyme as a bioreceptor molecule. The fluorescent tag (BNCDs/MOF) exhibits dual fluorescence with emission peaks located in the regions of blue and green. In the absence of Pb2+ ions, this hybridization undergoes reduced emission intensity because of the overlap in fluorescence emission between BNCDs@Tb-MOF and quenchers. However, as the catalytic core of the DNAzyme strand is activated in the presence of Pb2+ ions, the fluorescent emission of BNCDs/Tb-MOF resumes with the cleavage of quencher-tagged substrate strand. Here, the release of a shorter oligo sequence effectively increases the intensity of the proposed novel biosensor to realize low level detection of Pb2+ (e.g., to 0.96 ppb in a wide detection range from 2 to 1000 nM). The establishment of this novel biosensing approach is expected to offer new insights into rapid, selective, and sensitive detection of major pollutants for food and environmental safety.