Design of cationic conjugated polyelectrolytes for DNA concentration determination

Cationic conjugated polyelectrolytes poly1(10) and poly1(20) were designed, synthesized, and characterized with the anticipation of function in the determination of double-stranded DNA concentration [dsDNA]. Their structures contain a pi-deocalized optically active backbone composed of phenylenefluorene segments copolymerized with 2,1,3-benzothiadiazole (BT) units and charged pendant groups that allow excellent solubility in water. The subscript in poly1(x), refers to the molar percent of BT units in the chain. Addition of dsDNA to poly1(10) or poly1(20) results in a change in the color of emission from blue to green. These spectral changes can be treated to obtain the parameter 6, which can be used to generate calibration curves that indicate [dsDNA]. Analysis of photoluminescence spectra reveals that dsDNA addition gives rise to more efficient FRET from blue emitting segments to the BT sites, an increase in the BT emission quantum yield, and partial quenching of the phenylene-fluorene segments. Studies were also carried out to maximize the range of [dsDNA] determination. We find that by combining the response from two different initial concentrations of poly1(10), it is possible to generate calibration curves that respond with a difference in [dsDNA] of over 7 orders of magnitude.