An electrospray ion source for a mass spectrometer for generating ions of an analyte from a sample comprising the analyte dissolved in a liquid solvent comprises: an electrode receiving the sample and comprising at least a first plurality of protrusions protruding from a base, each protrusion of the at least a first plurality of protrusions having a respective tip; and a voltage source, wherein, in operation of the electrospray ion source, the sample is caused to move, in the presence of a gas or air, from the base to each protrusion tip along a respective protrusion exterior so as to form a respective stream of charged particles emitted towards an ion inlet aperture of the mass spectrometer under application of voltage applied to the electrode from the voltage source.