2.2. Microfluidic device and experimental procedures
The polydimethylsiloxane (PDMS) microfluidic device used for zebrafish
electrical response studies, under exposure to chemicals in Table 1, is
depicted with key features labelled in Fig. 1A,1B and 1C. It consisted
of three layers shown in Fig. 1C with various microchannels to enable
loading and screening of four larvae simultaneously. The top section of
the three-layer device included the main inlet and outlets from which
the fish entered and exited the device, the indirect flow inlet and
outlet to help direct the fish into the trapping regions (TRs) and the
reverse flow to aid in positioning and orienting the fish. The screening
pools were designed to provide enough space allowing complete tail
strokes without any collision with the device walls. This, in
combination with limitations associated with our microscope field of
view (FOV), restricted the number of larvae that could be tested at the
same time. The bottom layer of the device included valve channels
containing air. The middle layer consisted of a thin membrane,
approximately 200 μm thick, separating the top and bottom layers. When
the bottom valve was pressurized, the membrane deflected into the upper
layer channel to prevent the fish from swimming out of the TR. Two
anodic copper wire electrodes were attached to the outlets and a copper
wire was run through the indirect flow channel (Fig. 1A), at the middle
of the device, to function as the cathode.