A method of detecting a presence and/or concentration of a marker, e.g., a marker, in a liquid, e.g., a liquid, is disclosed. The method comprises: contacting the liquid with a sensor having an immobilized affinity moiety interacting with the marker and being configured to generate a detectable signal responsively to the interaction. The method further comprises washing the liquid off the sensor, and detecting the presence and/or concentration of the marker based on a detectable signal received from the sensor within a time-window beginning a predetermined time period after a beginning time of the washing.