A selective and sensitive turn-on chemosensor for detection of Fe3+ in aqueous solution and its cell imaging in dorsal root ganglia neurons and MKN-45 cells

Abstract

A new turn-on fluorescent chemosensor (RBTM) for Fe³⁺ was designed based on Rhodamine B and a thiocarbonylimidazole moiety. The spectroscopic probe used for characterization of the synthesized system showed 300-fold fluorescence enhancement for the detection of Fe³⁺ with a 1:1 stoichiometry in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 1 mM, pH 7.30). Upon addition of Fe³⁺ in aqueous ethanol, the probe displayed a significant fluorescence enhancement and a distinct color change (colorless to pink) that can be detected by the naked eye. The binding constant between the probe and Fe³⁺ was determined to be 1.16 × 10⁴ M^-1 and the corresponding detection limit was calculated to be 0.256 µM. In addition, the energy gaps between the HOMO and LUMO in RBTM and RBTM-Fe³⁺ were calculated using DFT calculations to be 92.93 kcal/mol and 37.49 kcal/mol, respectively. The results indicate that binding of Fe³⁺ to RBTM lowered the HOMO-LUMO energy gap of the complex and stabilized the system. Fluorescence imaging experiments demonstrated that RBTM can be used as a fluorescent probe to detect Fe³⁺ in MKN-45 cells and dorsal root ganglia, thus revealing that RBTM could be used for biological applications.

Keywords: Dorsal root ganglia; Fe(III) ions; Fluorescent chemosensors; MKN-45 cells; Rhodamine B.