The readout of Lab-on-a-Chip consumables is mostly done by automated instruments, either electrical/electrochemical, or optical. In case of an optical detection, the alignment of the consumable with the instrument plays a key role and should be addressed from the very beginning in the design and engineering phase. As an example, the typical beam diameter for optical readout in a laser-based flow cytometer is in the range of some hundred microns, while the critical detection area for many diagnostic applications is in the 10-50 microns range. How can the laser detect cells/particles in such small areas, despite the fact that process related tolerances cannot be eliminated completely?
A Ronchi Grating was implemented directly onto the consumable, which allows an active alignment by auto-focusing. Since the grating is located in a defined proximity to the detection channel, the instrument can easily detect the position of the disposable and finetune for the optical readout.