Reactive Blue 4 (sodium)

Reactive Blue 4 sodium is an anthraquinone dye used extensively in the textile industry. Reactive Blue 4 sodium is a single colorimetric chemosensor for sequential determination of multiple analytes with different optical responses in aqueous media^[1][2][3]. In Vitro:Reactive Blue 4 (50 μM) sodium can continuously detect copper ions (Cu²⁺), L-arginine (Arg), and L-cysteine ​​(Cys) in water (10.0 mM HEPES buffer, pH 7.0). First, the presence of Cu²⁺ causes a color change that is visible to the naked eye, and the spectrum changes according to the binding site-signaling subunit method. Subsequently, the Reactive Blue 4-Cu²⁺ complex was successfully applied to the detection of Cys and Arg through different recognition pathways^[1].
The aqueous solution of Reactive Blue 4 sodium is dark blue, and its UV-Vis spectrum demonstrates an absorption peak at 607 nm. Upon the gradual addition of Cu²⁺ ion to the Reactive Blue 4 sodium solution, a slight red shift from 607 to 619 nm and the gradual decrease in the intensity of absorbance band at 607 nm accompanying with a color change to deep sky blue was observed. Moreover, the existence of an isosbestic point at 645 nm during the titration indicated the formation of a single component^[1].
Reactive Blue 4 sodium is common textile dyes that can be adsorbed onto single-walled carbon nanotubes (SWCNTs) through electrostatic interactions, allowing the separation of residual dyes^[3].