Filtration in a microfluidic chip

Sample preparation

Sample preparation is an essential function for any Point-of-Care (PoC) diagnostic device. It enables complex analysis of virtually any sample to provide accurate results. Performing on-chip sample preparation has the advantage that the entire process is fixed and no manual steps have to be carried out. This type of workflow automation offers fast sample-to-answer solutions.

There is a wide variety of sample preparation processes that can be selected based on both the sample type and the diagnostic test. Micronit has developed several sample preparation techniques that can be incorporated into microfluidic devices. These include filtration and separation steps as well as mixing and volume metering.

On-chip filtration

In many cases, PoC assays require a filtration step. This could be a process that removes particles to prevent clotting in the microfluidic channels, but it could also be a step that is required from a diagnostic point of view. Filtration offers the opportunity to separate different components in a sample and retain the analyte of interest. At Micronit, we have modules that separate the cellular components in the blood of the plasma. This process is carried out with on-chip integrated filtration membranes in a polymer device. We can also go one step further and use filtration membranes that carry active components, like antibodies, that will bind to the analyte of interest. An on-chip labeling step could also be part of this process. This way, an immunoassay can be carried out simultaneously with the filtration step.

Cell sorting

For many assays, cell sorting is an important sample preparation step. There are more ways to sort and capture cells for further processing. At Micronit, we have knowledge of many different cell sorting techniques that could be applied, depending on the type of sample. We have experience with:

  • Acoustophoresis, a cell sorting method based on acoustic waves.
  • Dielectrophoresis, in which cell sorting is conducted using the electrical properties of the cells.
  • Pinched flow fractionation, a sorting method based on the geometry of the microfluidic channels.
  • Deterministic lateral displacement (DLD), in which an array of micro-pillars is used to separate cells based on their size and shape.

Beads-based assays

Another approach to capture your analytes of interest could involve a beads-based assay, a sample preparation method in which coated beads capture target molecules like proteins or nucleic acids. On-chip washing steps clear away the unwanted material. When capturing genetic material from cells or vesicles, an on-chip lysis step could precede this. Lysis involves destroying a cell, either by heating or via a physical or chemical process, in order to release the DNA / RNA.


Mixing is also often a necessary sample preparation step. For example, if a highly homogeneous blend of various substances is required. For this purpose, micromixers or microreactors could be incorporated on-chip. At Micronit we have experience in implementing a variety of active and passive micromixers tailored for each project’s need.

Volume metering

Volume metering is important in quantitative tests when you have to know exactly how much of a sample you are using. To achieve this, on-chip ‘containers’ can be filled on-demand, using capillary flow, burst valves, and splitter channels. In this way, precisely defined volumes of liquid can be contained on a defined location of the cartridge which will not be released until a specific trigger occurs. This type of sample preparation enables you to work with reliable volumes, which is an important step in the workflow automation that microfluidic platforms can offer.

Which are the sample preparation steps your project needs? Please, share your requirements with us.

On-chip functionalities

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