Conjugated Polymers as Fluorescence-based Chemical Sensors

Reported by Jay Wackerly November 1, 2004 INTRODUCTION A chemical sensor is a molecule that interacts with another molecule giving a measurable signal in response. Chemical sensors based on conjugated polymers have received a great deal of attention due to their ability to detect analytes at low concentrations. Fluorescence quenching provides an effective means for detection because of the extreme sensitivity and simple on/off detection. When the advantages of each of these are combined, fast, simple, and accurate chemical sensors based on fluorescence quenching are obtained. Chemical sensors based on conjugated polymers detect a variety of analytes (vide infra) but they all have similar detection mechanisms. Conjugated polymers contain a chromophore requiring low energy for excitation of an electron. Because it is highly delocalized, the excited electron (exiton) can travel along the polymer until fluorescence (or quenching) occurs. Each chemical sensor contains a receptor that binds to the analyte causing a change in the fluorescence. A conjugated polymer-based chemical sensor has one receptor site for every repeat unit, and since the exiton can travel across the polymer it samples many receptor sites causing it to be more sensitive than a non-polymeric system. A fluorescence-based chemical sensor has two modes of action. The fluorescence can be quenched in the presence of the analyte producing a “turn-off” chemical sensor, (Figure 1) or its fluorescence quenching is supressed by the presence of the analyte producing a “turn-on” chemical sensor.