In this study, synthesis of fluorescent polythiophene and polyurethane soft nanoparticles carrying them was carried out for bioimaging applications. Conjugated polythiophenes and polyurethane derivatives were obtained by changing their structural properties such as size, charge, and group, and were characterized by nuclear magnetic resonance, infrared spectroscopy, dynamic functional light scattering, fluorescent microscopy, methods. In the study, changing characteristics of polyurethane nanoparticle materials were investigated depending on the synthesis conditions. Synthesis of polyurethane nanoparticles was carried out by miniemulsion polymerization technique and synthesized as nanosphere to be more controllable on nanoparticle size, morphology and stability. The sizes of the polyurethane nanospheres varied in the range from 10 to 500 nm. Polyelectrolyte-polyelectrolyte complexation was investigated using cationic polythiophene-anionic polythiophene for use in bioimaging applications. Synthesized conjugated polythiophenes are divided into two groups as anionic and cationic polythiophenes. In this thesis, three kinds of cationic polythiophene synthesis are included, but poly (1,4-dimethyl-1- (3- ((4-methylthiophene-3-yl) oxy) propyl) piperazine-1-ium bromide) (PT4) was used as cationic conjugated polythiophene in the studies. Anionic polythiophene acetic acid (PTAA) was used as a counter-charged polythiophene. In addition to these studies, dual-mode imaging agents were prepared, consisting of PTAA as fluorescent agent and gadolinium metals as magnetic agent. The bioimaging studies continued under conditions imitating biological systems, and the potential of the proposed bioimaging agents was investigated.