A rhodamine based fluorescent trivalent sensor (Fe3+, Al3+, Cr3+) with potential applications for live cell imaging and combinational logic circuits and memory devices

Abstract

A sensor (HL⁵) based on rhodamine 6G–en and 3-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-hydroxy-5-methyl-benzaldehyde (HL⁴) has been developed for a highly sensitive and selective CHEF based recognition of trivalent metal ions M³⁺ (M = Al, Fe and Cr) over mono- and di-valent and other biologically abundant trivalent metal ions with prominent enhancement in absorption and emission intensities. A large enhancement of fluorescence intensities for Fe³⁺ (21 fold), Al³⁺ (14 fold) and Cr³⁺ (10 fold) was observed upon addition of 1.8 equivalents of these metals into the probe in methanol/H₂O (1 : 1, v/v, pH 7.2) with the possibility of naked eye detection. The corresponding K_f values were evaluated to be 6.7 × 10⁴ M⁻¹ (Fe³⁺); 8.2 × 10⁴ M⁻¹ (Al³⁺) and 6.0 × 10⁴ M⁻¹ (Cr³⁺). The quantum yields of HL⁵ and [HL⁵–Fe³⁺] and [HL⁵–Cr³⁺] and [HL⁵–Al³⁺] complexes in methanol/H₂O (1 : 1, v/v, pH 7.2) are found to be 0.013, 0.290, 0.120, and 0.158, respectively, using rhodamine-6G as the standard. The LOD for Fe³⁺, Al³⁺ and Cr³⁺ were determined by 3σ methods with values 0.29, 0.34 and 0.31 μM, respectively. An arsenate ion snatches Al from the Al–HL⁵ complex and quenches its fluorescence via its ring closed spirolactam form. Advanced level molecular logic devices using the inputs 2 and 4 and memory devices, have been constructed. The low cytotoxicity and large enhancement in fluorescence intensity of HL⁵ upon complexation with M³⁺ metal ions make the probe suitable for bio-imaging of M³⁺ (M = Al, Fe and Cr) in living cells and native cellular iron pools.