Fluorescent conjugated polymer dots for single molecule imaging and sensing applications

While single molecule imaging and sensing hold the promise of providing unprecedented detail about cellular processes, many advanced applications are limited by the lack of appropriate fluorescence probes. In many cases, currently available fluorescent labels are not sufficiently bright and photostable to overcome the background associated with various autofluorescence and scattering processes. This dissertation describes research efforts focused on the development of a novel class of fluorescent nanoparticles called conjugated polymers dots (CPdots) for single molecule fluorescence detection. The CPdots contain highly fluorescent pi-conjugated polymers that have been refined over the last decades as the active material in polymer light-emitting devices. Quantitative comparisons of the optical properties of the CPdots indicate their fluorescence brightness is a factor of 102-10 4 higher than conventional fluorescent dyes, and a factor of 10-10 3 higher than colloidal quantum dots. Single particle fluorescence imaging and kinetic studies indicate much higher emission rates of the CPdots as compared to quantum dots, with little or no "blinking" behavior that is often encountered for fluorescent dyes and quantum dots. In addition, efficient intra-particle energy transfer has been demonstrated in blended CPdots and dye-doped CPdots, which provides a new strategy for improving the fluorescence brightness and photostability of the CPdots, and for designing novel sensitive biosensors based on energy transfer to sensor dyes. These combined features of the CPdots and the demonstration of cellular uptake indicate that CPdots are promising probes for demanding fluorescence-based applications such as single molecule detection and tracking in live cells.