A newly emerging field in bioanalytics based on biomolecular binding detected label-free at single metal nanoparticles is introduced. Thereby particles which show the effect of localized surface plasmon resonance (LSPR) are used as plasmonic transducers. They change their spectroscopic properties (a band in the UV-VIS range) upon binding of molecules. This effect is even observable at the single nanoparticle level using micro spectroscopy and presents the base for a new field of single particle bioanalytics with the promise of highly parallel and miniaturized sensor arrays. The paper describes this approach and shows first result from our work regarding the detection of DNA binding at single nanoparticle sensors.