Fluorescence correlation spectroscopy (FCS) is applied to demonstrate avidin-induced cross-linking in a system consisting of a helical anionic conjugated polyelectrolyte (
P1) and a biotin-tetramethylrhodamine (TMR) conjugate (
2). In a previous study, we used fluorescence spectroscopy to demonstrate that
2 binds to
P1 via intercalation of the TMR chromophore into the
P1 helix. Addition of avidin to the
P1/
2 complex induces little change in the fluorescence of the system; however, FCS reveals a remarkable increase in the diffusion time of the
P1/2 complex in the presence of avidin. This change is attributed to supramolecular polymer aggregates produced by cross-link formation between the biotin unit of intercalated
2 and avidin. Atomic force microscopy imaging provides evidence supporting the existence of these aggregates. The highly sensitive FCS method is used to develop a novel sensor for the biotin鈥揳vidin interaction, with a detection limit of <100 pM for avidin.
Keywords:
conjugated polyelectrolyte; fluorescence correlation spectroscopy; aggregation; avidin鈭抌iotin