Azo dye-based on-site assay paper kit for rapid and selective naked-eye and smartphone-assisted detection of deferoxamine drug.

Ferric ion {Fe(III)} is an integral part of many structural and functional components in the body and plays critical roles in physiological and pathological processes. High Fe(III) concentrations damage many systems and organs in the body. The most common method used to prevent excessive accumulation of Fe(III) ions is chelation therapy and the most commonly used drug is deferoxamine (DFO). In this study, an azo dye-based test-paper probe was developed for the colorimetric determination of DFO. The bi-dental azo-dye, named DAZS (diazosalicylaldehyde), was synthesized with a 58 % yield as due to the coupling reaction of 4,4'-diaminobibenzyl and salicylaldehyde. The surface of cellulose-based chromatographic papers immersed in DAZS solution was coated with DAZS and peraped DAZS-coated paper (DAZS-paper) was used as a sensor kit. The structure of DAZS, DAZS-paper, and its interaction mechanism with Fe(III) and DFO were elucidated by FTIR, 1H NMR, 13C NMR, STEM, EDX, and AFM techniques. One arm of DAZS, a symmetrical molecule, interacts with the cellulose-based chromatographic paper, while the other arm remains exposed. This exposed arm interacts with the Fe(III), interrupting the intramolecular charge transfer (ICT) mechanism present in the DAZS molecule, and the color of the DAZS-paper becomes lighter. This interaction, which forms the Fe(III) sensing strategy, is disrupted in the presence of DFO. As a result of its strong chelating feature, DFO forms a chelate complex with Fe(III), enabling the separation of Fe(III) from DAZS. With the separation of the Fe(III), the ICT mechanism is activated again in the free part of DAZS, providing the coloration of DAZS-paper. Although the observed coloration is directly proportional to the concentration of DFO, color analysis was performed with a smartphone via the "colorimeter" application. By analyzing the test paper and solution medium with a smartphone, the detection limits (LOD) of DFO were found to be 95.0 nmol L-1 and 82.0 nmol L-1, respectively. In the selectivity study conducted with various Fe(III) chelating agents, DFO was determined with high selectivity. It was found that common metal cations and anions did not significantly affect the developed probe. The developed method, which was verified by a chromatographic reference method, can also be easily applied to the commercial drug Desferal and fetal bovine serum containing DFO.