Optogenetic manipulation of freely moving C. elegans in an elastomeric environment mimicking and force-measuring chip
This paper presents integration of optogenetic illumination of C. elegans neural circuits and muscular force measurement in a structured microfluidic chip mimicking the C. elegans soil habitat. The integrated system deploys two optical pathways in an inverted microscope. One is for bright-field illumination to extract the worm body contour for real-time closed-loop tracking, the other is for optogenetic illumination to project structured light patterns with specific wavelength onto the worm body segments of interest. The behaviors of a freely moving worm in the chip under optogenetic manipulation can be recorded for off-line analysis which mainly collects the contact force between the worm body muscle and its surrounding environment. This enabling platform allows stimulating or inhibiting worm neurons and simultaneously measuring its thrust force, which offers a new insight into the correlation between neurons and locomotion behaviors of the nematode. Using wild-type C. elegans, we demonstrated the capability and potential of the system, and found no significant difference in thrust forces of wild-type worm under optogenetic illumination or not.