Tracking and analysing the individual diffusion of nanoscale objects such as proteins and viruses is an important methodology in life science. Here, we show a sensor that combines the efficiency of light line illumination with the advantages of fluidic confinement. Tracking of freely diffusing nano-objects inside water-filled hollow core fibers with core diameters of tens of micrometers using elastically scattered light from the core mode allows retrieving information about the Brownian motion and the size of each particle of the investigated ensemble individually using standard tracking algorithms and mean squared displacement analysis. Specifically, we successfully measure the diameter of every gold nano-sphere in an ensemble that consists of several hundreds of 40-nm particles, with an individual precision below 17% (± 8 nm). In addition, we confirm the relevance of our approach with respect to bioanalytics by analysing 70-nm λ-phages. Overall these features, together with the strongly reduced demand for memory space, principally allows us to record thousands of frames and to achieve high frame rates for high precision tracking of nano-scale objects.