For use with the microfluidic device, sensor bacteria were cultured overnight in Luria Broth (LB) and resuspended
in minimal media to a culture turbidity of ca. 0.6 at 600 nm. The bacteria were mixed with the arsenite at
different concentrations just before the loading and the mixture was pipetted onto the device. Liquid flow through
the chip channels was achieved by capillary force. Bright field and fluorescence images were taken every 10
minutes during the accumulation of the cells on the filter, by means of an inverted epifluoresence microscope (Leica
DM14000 B; see also Fig.3b). The collected images were analyzed with Metaview imaging software to determine
the average grey value (AGV) fluorescence signal from the induced cells, which serves as a measure of the average
cell induction. Measurement results with chip no. 4 are shown in Fig.4 and Fig.5. As can be seen, the background
fluorescence is about equal to that of the SU-8. After 1 hour of incubation, the fluorescence starts to increase,
depending on the arsenite concentration. The detection of 50 μg/l of arsenite has been convincingly demonstrated
while10 μg/l of arsenite appears to be within reach.