Scientists Separate Plasma From Blood With Working Biochip

Gravity? I don't think so.

"Powered by pre-evacuation of its PDMS substrate ...."

Pre evacuation...so you pull a vacuum and then air pressure pushes the blood through?

Air pressure is caused by gravity...so it is powered by gravity in a sense right? _{(unless you are in a pressurized spaceship of course)}

I'm just sayin...

I found this story so fascinating I had to find the original article. The word "gravity" does not occur there. The sensor is fabricated from poly(dimethylsiloxane), PDMS, which is placed in a vacuum pouch before use. When needed the pouch is opened, the blood samples are placed at one end, and the blood flows into a passive cell trap. This movement, and the further plasma movement over the sensors, is powered by suction from the PDMS vacuum. The diagram does not show that the slip is in fact covered by a clear layer, so that the channels are actually microcapillary tubes.
As to how the sensors work, I am not a chemist, but my understanding is that the sensor channels are coated with avidin, a protein from uncooked eggs, which binds irreversibly with biotin, another protein. The lab scientist has previously added biotin-antibody complexes to the sample, to bind with the antigens under investigation. These bound complexes are then picked up and concentrated by the avidin, and when the slide is peeled off the PDMS substrate, the concentrations of the complexes may be read under a fluorescence scanner.
It appears, therefore, that this system is not for determining electrolytes and glucose, but for detecting antigens as markers of various diseases. It's still a wonderful bit of engineering.