Development and characterization of newly engineered chemosensor with intracellular monitoring potentialities and lowest detection of toxic elements

The widespread existence of potentially toxic heavy elements have become one of the serious environmental concerns around the globe. Thus, it is highly important to develop efficient and selective chemical sensors to detect such potentially toxic elements. Herein, we developed a rhodamine-2-amino-5-bromopyrimidine based chemosensor (RBP) for the selective detection of toxic elements using Hg²⁺ and Cr³⁺ as model elements in combination with other competitive ions such as Al³⁺, Ag⁺, Ca²⁺, Ba²⁺, Cd²⁺, Fe²⁺, Fe³⁺, Li⁺, K⁺, Mn²⁺, Mg²⁺, Cu²⁺, Na⁺, Ni²⁺, Pb²⁺and Zn²⁺. The newly developed RBP displayed good visibility, high sensitivity, excellent selectivity, high binding ability and low limit of detection in CH₃CN/HEPES buffer (1 mM 3:2 v/v, pH 7.3) as a medium. The binding constants of RBP for Hg²⁺ and Cr³⁺ were 1.09 × 10⁷ M⁻¹ and 8.3 × 10⁴ M⁻¹, respectively. As compared to earlier reported studies, the lowest detection limits (LOD), i.e., 1.6 μM for Hg²⁺ and 4.9 μM for Cr³⁺ were recorded. RBP also show reversible binding affinity with Hg²⁺ and Cr³⁺ in the presence of ethylenediaminetetraacetate (EDTA). The binding mode between metal ions and RBP were further investigated by using density functional theory (DFT) calculations, which support the experimental findings very well. More importantly, RBP can be prepared as a test paper kit to detect the concentration of Hg²⁺ and Cr³⁺ ions by changing the color of the paper visible to naked eyes and is potential for the practical infield application. In addition, the results obtained from confocal microscopy revealed that the probe is cell permeable with low cytotoxicity and can be employed as a bio-imaging reagent for intracellular recognition of Hg²⁺ and Cr³⁺ ratification in human breast cancer cells MCF-7.