HIGH-FREQUENCY ELECTRIC-FIELD TRAPPING OF INDIVIDUAL HUMAN SPERMATOZOA

We present a new touch-free technique for trapping, positioning and se lecting human spermatozoa. This can be done in free solution (culture medium) by high-frequency electric fields, Ultramicroelectrodes fabric ated by photo- and electron-beam lithography on quartz and glass subst rates were used to create field cages or long field channels. If the c onductivity of the external salt solution is higher than the average v alue of sperm cell conductivity, negative polarization and negative di electrophoresis occur. As a result, the induced cell polarization lead s to forces repelling spermatozoa from the electrodes towards the fiel d minimum, Using four planar electrodes a field funnel can be formed i n which an individual spermatozoon is retarded while swimming. The sam e can be done more effectively in three-dimensional cages created by a n octopole electrode system. In these systems, rapidly swimming sperma tozoa could be trapped for several seconds but some spermatozoa stop m oving if exposed to field strengths of more than 500 V/cm at frequenci es in the MHz range. However, in stripwise and interdigitated electrod es, rapidly swimming sperm cells could be very well positioned in fron t of a break-electrode by a combination of electric field trapping and field induced laminar fluid streaming. This technique can be applied to bring individual spermatozoa to a defined position for characteriza tion followed by sampling with capillaries.