Monitoring SAW-actuated microdroplets in view of biological applications

Droplet localization is of primary importance in (Surface Acoustic Wave) SAW-actuated droplet manipulation for the blind-control of digital microfluidics in lab-on-chips (LOC). This issue is addressed by reconsidering hereafter the implementation of our already published SAW echo method. Two echo signals are now recorded: one for the droplet at its initial known position and one for the droplet at its new unknown position after displacement. Subtracting the delays of the 2 echoes leads to an accurate determination of the unknown position provided that the droplet characteristics remain identical for the 2 considered positions. No detailed analysis of the SAW scattering by the droplet is required with this new protocol. For implementing this echo-localization method, we propose a specific LOC architecture along with software monitoring, suitable for biological applications and devoted here to protein analysis by MALDI mass spectrometry.