Characterization of the photoluminescence quenching of mixed water-soluble conjugated polymers for potential use as biosensor materials

The influence of oxygen and polymer concentration on the quenching of the photoluminescence (PL) from a water-soluble conjugated macromolecule, sodium poly [2-(3-thienyl)ethyloxy-4-butylsulfonate)] (PTE-BS), was investigated. The presence of oxygen in the polymer solution decreases the photoluminescence by 6.4%. The sharp changes observed in the PL when the concentration of the polymer is varied between 4 x 10(-5) and 9 x 10(-4) M result in small changes in the Stern-Volmer constant, K-SV, because the quenching is equally affected by the polymer concentration. Thus, K-SV only decreases from 2.4 x 10(-4) down to 1.3 x 10(-4) when the concentration of the polymer in the solution increases a factor of 10, from 1.8 x 10(-4) up to 1.8 x 10(-3) M. When the PL of the solution is 50% of its initial value (K-SV = 1/(quencher concentration)), a sharp change in the slope of the Stern-Volmer plots indicates the beginning of quenching saturation that occurs when most of the accessible polymer segments are quenched. Mixtures of the water-soluble polymers PTE-BS and MPS-PPV were also investigated to further understand the quenching process as well as to potentially increase sensitivity or selectivity to biological molecules. A modified version of the Stern-Volmer equation is required to describe the curvature observed in the PL plots of the polymers in the mixture. In the mixture, the increase of the K-SV of PTE-BS (the polymer with small molecular weight) is accompanied by a slight decrease of K-SV of the MPS-PPV polymer.