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The interaction of fluorescent dyes with serum proteins has garnered significant interest owing to potential for non-covalent labeling and imaging applications. In this work, dimeric benzothiazole-based trimethine cyanine dyes are synthesized and their interaction with bovine serum albumin studied. The dimeric cyanine dyes mainly exist as H-dimers and H-aggregates in aqueous solution. A combination of absorbance, fluorescence, circular dichroism spectroscopy and atomic force and fluorescence microscopy indicate the formation of dye-BSA complexes. Binding of one of the dimeric dyes on BSA with a K_a of 1.49 × 10⁵ M⁻¹ results in disruption of dye self-aggregates and unfolding of the dyes into the monomeric or open conformation. Fluorescence enhancement experienced by the dimeric dyes upon interaction with BSA is superior to that registered by Thioflavin T. Surfactant SDS has been used to further tune …