Little is known how CAR T cells recognize antigens. Knowledge of recognition events is needed for the rational design of safe and more selective CARs. We will devise a planar glass‐supported molecular imaging platform, which serves as a surrogate target cell for CAR T cells, to quantify synaptic receptor binding and signaling events in living CAR T cells, and resolve membrane architecture with single molecule resolution. Together with PhD6 and PhD7 we will extend this system for its use in automated microfluidics devices as a means to select individual CAR T cells based on synaptic and cytoplasmic signaling and effector functions and profile them in depth for T cell differentiation and gene transcription.