The present invention provides a composition for detecting and/or characterizing a multiple-charged biomolecule comprising a charged d or d metal complex, wherein the metal complex electrostatically binds to the multiple-charged biomolecule to induce aggregation and self-assembly of the metal complex through metalmetal interactions, pp interactions, or a combination of both interactions. The present invention further provides assay methods and kits for label-free optical detection and/or characterization of biomolecules carrying multiple charges, e.g., single-stranded nucleic acids, polyaspartate, polyglutamate, using a composition comprising a charged d or d metal complex.published_or_final_versio
