The detection of multiple analytes by using visual colorimetric and fluorometric multimodal chemosensor based on the azo dye

In recent decades, researchers have conducted in-depth studies of the design and synthesis of colorimetric/fluorometric probes and the application of such probes to biological and practical samples. The multifunctional colorimetric and fluorescent azo benzene-based probe (4′-hydroxyl-2,4-diaminoazobenzene, MP) was designed to detect Al(3+), Fe(3+), Cu(2+) and F¯. Based on the distinct redshift of the absorption band and a significant color change (yellow → purple), MP was utilized for both naked-eyed and quantitative detection of Al(3+) and Fe(3+) after formation of the 1:1 complex. Test paper coated with MP and used in conjunction with a cell phone was used for colorimetric detection of Al(3+) and Fe(3+) ions (20 μM–2.0 mM) in water samples through naked-eye and digital image colorimetry. The “MP-Fe(3+)” coordination shift that occurs in the presence of the competitive ligand F¯ was used in the colorimetric measurement of F¯ in toothpaste. In the presence of Cu(2+) ion, the non-emissive MP has transformed into fluorescent benzotriazole product PMP (Φ = 0.53) through the bimolecular rate-limiting step, and the second-order rate constant k is calculated as 31 ± 2 M(−1) s(−1). MP exhibits a “turn-on” fluorescence response in the presence of Cu(2+) that is greater than its response in the presence of competitive species such as Fe(3+), Al(3+), Co(2+), Fe(2+), Zn(2+), Cd(2+), Mg(2+), Mn(2+), Ni(2+) and Ag(+). MP was shown to have low toxicity to living HeLa cells and to present good imaging characteristics for tracking of Cu(2+) in vivo.