Abstract: One aspect of the present disclosure relates to a novel sensor mechanism based on the aggregation of nanoparticles for target molecule detection and quantification. The nanoparticles that can be used include non-conducting polymers and conducting polymers such as polyaniline, polypyrrole and polythiophene derived nanofibers. Embodiments can include covalently functionalized nanoparticles with probes for target molecules, a biosensor where functionalized nanoparticles bind to one another upon presence of target to generate a visible conjugate induced aggregation, a biosensor wherein nanoparticles bind spontaneously in the presence of target molecules such as biological molecules, cells and biological markers.