A sensor device for quantifying luminescent targets. The device comprises a light source for exciting the targets, thus generating luminescence signals, and a detector for detecting these signals of the targets in a cell, resulting in a detected signal comprising a desired signal and a background signal. The detector has a spatial cell resolution and/or a time resolution that is so high that only a limited number of targets will be present in the cell when measuring at low concentration and/or that only a limited number of targets add to the cell in between two measurements. A change in the number of targets in the cell can be observed in the detected signal. The device comprises a processor configured to distinguish the desired and the background signal, and to combine the detected signals of the different cells and/or moments in time, to quantify the targets.