Detection of lipopolysaccharide and lipid a employing a spermine-pyrene conjugate

An amphiphilic fluorescent spermine-pyrene conjugate (Sp-Py) is shown to interact with lipopolysaccharide (LPS) or lipid A in aqueous solution. This complexation was studied by UV/visible absorption and steady-state fluorescence spectroscopy. In the presence of LPS or lipid A, Sp-Py displayed self-aggregation, resulting in the appearance of chromophore dimer absorption and fluorescence at the expense of probe monomer features. The equivalent weight of LPS or lipid A and the binding constants for Sp-Py complexation were estimated. The change of the ratio of monomer to dimer emission with concentration of LPS or lipid A indicated that Sp-Py is a sensitive fluorescence probe for the endotoxins in aqueous media.