Fluorescence quenching of iodinated cyanine dyes gained attention in recent years in the field of Theranostics whereby cyanine dyes loaded on FDA-approved feraheme form nanoprobes with quenched fluorescence. In the present paper, we report the fluorescence quenching of three iodinated cyanine dyes (I-III) using FDA-approved nano-iron oxide as potential candidates in the field of theranostics and other applications. The dyes were synthesized by solvent-free microwave technique. The electronic absorption, fluorescence spectra and excited state lifetimes were measured. Fluorescence quenching using iron oxide nanoparticles was studied in the presence and absence of SDS micelles. Micellar media enhance dynamic quenching at the expense of static quenching pathways as revealed by Stern-Volmer plots. The binding constants between the three iodinated cyanine dyes and iron oxide nanoparticles together with the second order quenching rate constants were calculated from Stern Volmer and modified Stern Volmer relations.

Fluorescence superquenching is a well-known phenomenon obtained when nanoparticles are applied as quenchers due to the remarkably low nanoparticle concentrations capable of causing efficient fluorescence quenching.