Asymmetric nozzle inlet was suggested for particles to converge into a highly confined region. The physical properties from the nano-scaled volumetric difference at nozzle inlet were investigated using computational fluid dynamics and particle motion measurement with fluorescence beads and erythrocytes. The asymmetric nozzle structure made particles converge efficiently without clogging at nozzle inlet. It could be used as a micro/nanofluidic unit for cell based assay in a microchip such as chip-based flow cytometer. (c) 2005 Elsevier B.V. All rights reserved.