Easily synthesizable molecular probe for the nanomolar level detection of Cd2+in near aqueous media: Theoretical investigations and live cell imaging

The present investigation highlights a quinoline-based small molecule probe (DEQ) for the detection of Cd2+ among other metal ions in near-aqueous media. The probe DEQ and its Cd2+ complex (DEQ-Cd) have been synthesized and characterized by all possible spectroscopic methods. The weakly emissive DEQ showed its strong emission in the presence of Cd2+, which is attributed to the photoinduced electron transfer (PET) along with the chelation-enhanced fluorescence (CHEF) mechanism. The 1:1 binding mode between ligand and Cd2+ is confirmed by single crystal XRD analysis, which is further supported by Job's plot and HRMS. The detection limit of the probe to recognize Cd2+ was found to be as low as 89 nM. Furthermore, DEQ can act as a reversible fluorescence probe with the off-on-off mechanism by the alternative addition of Cd2+ and EDTA. DFT and TDDFT studies exposed the proposed mechanism after Cd2+ insertion and the obtained results for electronic spectra are in line with the experimental results. The response towards pH was quite interesting and allowed us to study its application in live cell imaging. With all the positive results, the proposed ligand DEQ can be used as a potential probe for the detection of Cd2+ in real-life applications.

Automated summary

A quinoline-based small molecule probe DEQ was developed for the detection of Cd2+ in near-aqueous media. DEQ showed strong emission in the presence of Cd2+ due to the photoinduced electron transfer and chelation-enhanced fluorescence mechanisms. The probe exhibited a reversible fluorescence response to Cd2+ and EDTA addition. With a detection limit as low as 89 nM, DEQ has the potential to be used as a probe for Cd2+ in real-life applications.