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 × 10 -5 and 9 × 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 × 10 -4 down to 1.3 × 10 -4 when the concentration of the polymer in the solution increases a factor of 10, from 1.8 × 10 -4 up to 1.8 × 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.