Label-free Cell Sorting

Cell sorting is an essential technique in cell biology research and many diagnostic and therapeutic applications. Especially sorting methods that refrain from the biochemical labeling 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. Further advantages: microfluidic technologies operate on the micrometer scale and require small sample volumes.

One of the 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.

This on-chip cell sorting technique that gives fast results without the need for further diagnostics carried out in a lab, creates opportunities for fast testing in rural areas. Micronit has been involved in the Lapaso project, in which 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 if not treated, the disease is fatal.

A quick examination of the blood is therefore of the essence. For this project, a thermoplastic polymer chip was developed that contains an array of pillars as small as 20 µm in diameter. The DLD sorting method, based on particle morphology, proved to be very useful.

To get a good impression of the DLD-process, take a look at this video, made by Stefan Holm, one of the project’s participants.

At Micronit, 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 to be reused. The hybrid combination of silicon and glass makes a sustainable and reliable chip. To test the functionality of the chip, fluorescent microparticles were used.

The goal of this project was to make a microfluidic DLD-chip that can be used for as many different applications as possible. This is a novelty, for up until now, DLD-chips were often developed for a dedicated purpose and specific devices. By choosing durable materials and making the chip suitable for general use, a multi-purpose, sustainable microfluidic DLD-chip was developed.