Label free cell sorting
Deterministic lateral displacement (DLD): a cell sorting method that makes use of intrinsic cell characteristics.
Cell sorting is an essential technique in cell biology research and in many diagnostic and therapeutic applications. Especially sorting methods that refrain from the biochemical labelling of cells are in high demand. Several microfluidic techniques provide solutions to this by making use of the intrinsic characteristics of cells like size, shape, electrical polarisability or hydrodynamic properties. Microfluidic technologies operate on the micrometer scale and require small sample volumes.
An array of pillars
One of these microfluidic label-free sorting techniques is deterministic lateral displacement (DLD). In short, this is a way to separate particles in fluids by driving them through an array of regularly placed pillars. By positioning the pillars at determined angles, particles of different sizes are forced into different streamlines and are this way separated. The pattern of the array of pillars is determining the streamlines of the particles.
Blood tests in fighting sleeping sickness
One of the projects Micronit was involved in over the past few years, was the Lapaso project, initiated by Professor Jonas Tegenfeldt of Lund University. In this project, DLD was used to detect a certain parasite in human blood that causes sleeping sickness. Sleeping sickness is a disease found in rural areas of sub-Saharan Africa. It is spread by the tsetse fly and infected patients suffer from painful symptoms. If not treated, the disease is fatal. Quick examination of the blood is of the essence. The DLD sorting method, based on particle morphology, proved to be very useful.
At Micronit GmbH, a DLD-chip was developed in silicon and glass. Both silicon and glass are known for their chemical and biological inertness. Besides, both materials can be cleaned from biological deposits, and are therefore very suitable for reusable products. The hybrid combination of silicon and glass makes a sustainable and reliable chip. To test the functionality of the chip, fluorescent microparticles were used.
Sorting by size
DLD is a process that sorts microparticles of different sizes. During the testing phase of the chip, several images were made of the DLD process. Observations show that larger particles follow a different trajectory than smaller particles. Large particles move in line with the row of pillars, thus laterally steering away from the streamline because of the diagonal placement of the pillars. Smaller particles on the other hand, do not divert from the streamline. Instead, they continue to follow the direction of the streamline and therefore change between the rows of pillars.
Remark for both pictures in the right column: Keep in mind that the image is made up of several recordings in order to show the whole trajectory. The particles were coloured red afterwards. The arrow shows the direction of the streamline.