Nozzle and method for flow cytometry

A method for producing a liquid flow having a particle-containing core flow surrounded by a sheath flow by introducing a particle-containing core flow liquid into an inlet opening for core flow liquid and introducing a sheath flow liquid into an inlet opening for sheath flow liquid of a nozzle, wherein the sheath flow is generated by a leading element that extends along a longitudinal axis to a larger degree along a first dimension perpendicular to the longitudinal axis up to a distance away from the inner wall of a housing than it extends in a second dimension that is perpendicular to the longitudinal axis and perpendicular to the first dimension, wherein the leading element extends from a first end, which lies in the plane of the first end of a feed tube or is offset by a distance from the first end of the feed tube, up to its second end, which is arranged at a distance from the second end of the nozzle, wherein the leading element in the nozzle extends on both sides of the feed tube for aligning the particles which are contained in the core flow, wherein the extension of the leading element in its second dimension causes different flow velocities of the sheath flow liquid, which different flow velocities lead to an alignment of the particles, and wherein the particles have the alignment also after outflow from the outlet of the nozzle.