Microfluidic design: Minimizing Internal Volumes


Each component of a microfluidic system (tubing, connector, channel, etc.) has an internal volume.  This internal volume is composed of the swept volume (that is, the volume of the intended flow path) and the dead volume (volume outside or adjacent to the intended flow path).  Typically, the inclination is to keep both the dead and swept volume as small as possible.  This is especially critical when working with samples available only in very limited quantities.

How can you minimize the internal volume associated with your microfluidic set-up?

Luer with overlays showing swept volume (yellow /orange) and dead volume (blue)Luer with overlays showing swept volume (yellow /orange) and dead volume (blue)When trying to minimize the internal volume of a microfluidic system, it is only natural to think first about the volume associated with the microfluidic chip’s internal channel(s).  However, more often than not, you will find that most internal volumes are not associated with microfluidic channels, but rather with connectors and input/output tubing (as well as other elements such as valves and pumps).

For example, our standard straight-channel chip model SC-TD-300300-N, which has a relatively large microfluidic channel (300 micron wide by 300 micron deep), has an internal volume of about 6 microliters.  The same chip, equipped with two luer connectors, has a total internal volume that is ten times larger (approximately 50 microliters).  Add to this chip a small piece of tubing at the input and output and the internal volume jumps by another order of magnitude: A 1/16” [1.6mm] tube that is 30 cm long has an internal volume equal to 600 microliters!

Conclusion: If you want to minimize internal volumes, concentrate on the connectors and input/output tubing. Luers have a large internal volume (and some dead volume), and they are designed to work with relatively large diameter tubing.  Replacing Luers with Nanoport connectors will significantly reduce the internal volume associated directly with the connectors.  Furthermore, Nanoport connectors are designed to operate with small internal diameter tubes.  The type that we use (model N333) is designed for tubing that has a 1/16" (1.6 mm) OD.  This tube comes in several internal diameters.  A common ID is 0.010” (250-micron).  The internal volume associated with this tubing is only 15 microliter per foot (30 cm) length.

Note that the N333 connectors can also be used with 1/32” OD and 360-micron OD tubing, using IDEX adapter sleeve kits (provided with each Translume’s device equipped with N333).

Still too much for your application? Ask us to fabricate a multilayered chip that will eliminate most, if not all, connectors and tubing, and their associated internal volumes