Monitoring an animal's brain activity during motion provides a means to interpret the brain activity in the context of movement. However, it is challenging to obtain information about the animal's movement during neural imaging in the popular model organism C. elegans due to its small size. Here, we present a microfluidic tool to immobilize only the head region of C. elegans for simultaneous recording of neuronal activity and tail movement. We combine hydrogel photopolymerization and microfluidics to realize controlled head immobilization in a semi-continuous fashion. To optimize the immobilization process, we characterize the hydrogel polymerization under different experimental conditions, including under the effect of fluid flow. We show that the Damköhler number specifically defined for our reactive transport phenomena can predict the success of such photopolymerized hydrogels used for sample immobilization. In addition to simultaneous recording of neural activity and behavior in C. elegans, we demonstrate our method's capability to temporarily reconfigure fluid flow and deliver chemical stimuli to the animal's nose to examine the animal's responses. We envision this approach to be useful for similar recordings for other small motile organisms, as well as scenarios where microfluidics and polymerization are used to control flow and rection.