Ratiometric fluorescent sensing of Pb2+ and Hg2+ with two types of carbon dot nanohybrids synthesized from the same biomass

This work initially describes two ratiometric fluorescent nanosensors that use dual- and three-emission carbon dot (CD) nanohybrids for highly sensitive detection of sub-nanomolar Pb2+ and Hg2+, respectively. The two new types of CD hybrids are prepared via solvothermal treatment of the same extracts of bamboo leaves. This strategy is facile, cost-effective, environmentally-friendly and useful, as it avoids the post-modification of CDs or their mixing with other fluorescent probes which are typically adopted in most of CD-based ratiometric nanosensors previously reported. More importantly, the utilities of the two new nanosensors that enable built-in correction of external effects are well demonstrated by achieving detection limits as low as (similar to)0.14 and 0.22 nM (3 sigma) for Pb2+ and Hg2+, respectively. This makes them be among the most sensitive systems currently available for sensing the two analyte ions. The satisfactory recovery results of analyzing a series of real river water examples additionally validate their feasibilities for practical applications. To the best of our knowledge, this may be the first report of applying the same natural biomass as raw material to synthesize two types of multi-emission CD hybrids for ratiometric sensing. Considering their simplicity, low cost, good sensitivity and specificity, and accuracy, the developed ratiometric fluorescent nanosensors hold great potential to find wide applications in environmental monitoring, water safety, and waste management.