A New Injector

26.11.2013  by  Bouke Krom

We have designed a better injector - why?

Seemingly a technical detail, the use of `sheath fluid' in our cytometers is a crucial design decision. The hydraulic focusing of the particle suspension into a high speed, narrow and stable stream of particles passing the laser beam in a single file offers great advantages.  The analytical power of flow cytometry depends heavily on this most important principle: analyzing particles and cells one by one. The injection and subsequent laminar alignment of the sample into the particle free carrying fluid (sheath fluid) makes this possible even in the most difficult combination of a very wide flow cell and running highly concentrated river or coastal water samples.

Injection in sheath gives the particles identical velocity, position and orientation during their transect through the laser beam: a prerequisite to get accurate and reproducible optical properties, and to enable laser scanned profiles! Finally, it allows delayed imaging of particles after their laser scatter and fluorescence detection: targeted imaging and smart grid imaging.

Creating a reliable and practical sheath fluid system is more difficult with wider flow cells and particularly in combination with using the instrument on moving platforms.  The wide flow cell is our benchmark: it allows autonomous operation without clogging and fouling and the famous wide particle size range. We invented the recirculating sheath fluid system for practical reasons but the double stage injector was the most important invention to allow the use of this 1 mm flow cell in a sheath fluid system on moving platforms.

The first design consisted of two subsequent injection stages instead of the traditional  single step injection, folded ingeniously into a miniature package. The sample stream remained remarkably stable even when the instrument is moving around. A later improvement allowed easy alignment of the double stage system with adjustment screws while keeping it water tight.  Some practical problems remained of air bubbles getting trapped in the system sometimes causing instability and ultra-slow fluid velocities in some parts of the injector causing hard-to-remove bio fouling.

That is why we started from scratch again a year ago designing and testing a new double stage injector aiming at the same functionality but without these practical problems, and after several prototypes and production try-outs we now have a brand new double stage injector, more sturdy that the previous one, more easy to align, greatly reduced air bubble trapping and no dead water spaces any more: another in-house development that improves the reliability and autonomy of these complex instruments in harsh and remote conditions.