A major challenge in biomolecular research is the investigation of biomolecular interaction at single-molecule level. Biomolecules possess heterogeneities of high physiological relevance that can only be unravelled with single-molecule tools. All current single-molecule imaging methods, however, require chemical modifications, such as fluorescent labelling or immobilization onto a surface, which might alter the biomolecule’s natural behaviour. Recently, I have developed a ground-breaking optical microscopy method – Nanofluidic Scattering Microscopy (NSM) – whose unprecedented resolution enabled me to bypass those limitations and to image individual small proteins in free motion without any label. Despite these attractive attributes, in its current form, NSM does not allow for quantitative study of interaction kinetics between individual molecules. Due to the inherently fast Brownian motion, the time that a molecule spends on average in the optically probed volume – a nanofluidic channel – is substantially shorter than the time required to record a statistically relevant number of association and dissociation events. In this project, we will develop an essential nanoscopic component – a rapid nanofluidic valve – that will enable to confine and release interacting biomolecules to and from the nanofluidic volume. The nanofluidic valves will be based on the principles of thermo-responsive polymer hydrogel in combination with nanoplasmonic heating. The integration of the nanofluidic valves with NSM will enable to track evolution of individual biomolecules at single molecule level, without the need of chemical modifications and in conditions that mimic an in-vivo state. The project will deliver a unique bioanalytical tool that will make key contributions to the fundamental understanding of biomolecular interactions, which is needed in basic research as well as in the pharmaceutical industry.