Sub-Picomolar Recognition of Cr3+ through Bioinspired Organic–Inorganic Ensemble Utilization

The work describes an integrated optical platform for recognition of Cr3+ at the picomolar level (0.66 pM). The condensation of a fluorene unit with l-leucine led to the development of a highly fluorescent molecular probe L which detects Cu2+ following a turn-off signaling mechanism. Further, the L-Cu2+ ensemble has been successfully utilized as a light-up signaling tool for selective turn-on sensing of Cr3+, for the first time, at the picomolar level through quencher displacement. This sensing process eventually detects selectively one paramagnetic cation through turn-on signaling by the displacement of another paramagnetic cation. We have successfully shown that the common sensitivity issues associated with displacement approaches can be overcome by suitable ligand design. The present integrated system, L-Cu2+, has been found to be sensitive enough to detect Cr3+ at the picomolar level even in real samples, including water from different sources such as tap water, river water, and drinking water.