Fluorescent Detection of Heavy Metal Ions Using Benzanthrone Dye

The development of sensitive, low-cost, and biocompatible sensors for detecting toxic heavy metals remains a pressing challenge in environmental monitoring. Protein-based nanostructures present unique opportunities in this regard. Coupliang amyloid fibrils with amyloid-sensitive fluorescent dyes, which exhibit distinct spectral responses upon binding to amyloid structures and in the presence of metal ions, may lead to a promising sensing platform. In this study, the benzanthrone derivative ABM was examined as a fluorescent probe for detecting heavy metal ions in aqueous solutions and in the presence of β- β-lactoglobulin amyloid fibrils (β-lgf). In water, benzanthrone dye shows a broad emission spectrum dominated by a band at 690 nm. Binding to β- lgf produces a substantial increase in fluorescence intensity and a ~65 nm hypsochromic shift, indicating dye partitioning into the fibrillar hydrophobic environment. In aqueous solutions, ABM responds to heavy metals with characteristic spectral changes: Pb ²⁺ and Ni ²⁺ decrease the 690 nm emission band and generate a 560 nm band, while Cu ²⁺ and Zn ²⁺ cause complete quenching of the 690 nm emission with the appearance of a prominent 560 nm maximum, consistent with the formation of metal–ligand charge–transfer complexes. In the fibrillar environment, ABM displays a dominant emission at 560 nm; addition of heavy metals modulates the intensity and shape of this band in an ion-specific manner. Deconvolution of the emission spectra revealed two spectral components, whose amplitudes and shape descriptors were selectively altered by Ni ²⁺ and Cu ²⁺, while Zn ²⁺ and Pb ²⁺ had lesser effects. These findings demonstrate that ABM fluorescence reports sensitively on the strength and specificity of heavy metal interactions with amyloid fibrils, supporting its potential as an optical sensor for probing protein–metal systems.