A fabricated microfluidic paper-based analytical device (μPAD) for in situ rapid colorimetric detection of microorganisms in environmental water samples

In this study, we developed a fabricated microfluidic paper-based analytical device (PAD) for in situ rapid colorimetric detection of microorganisms in environmental water samples. We fabricated the PAD with the wax printing method at curing conditions of 100 degrees C for 7 seconds. For quick bacterial detection, we modified the catalase test with Fenton's reaction as a colorimetric biochemical reaction. This modified catalase test provided a color indicator according to the concentration of Escherichia coli (E. coli, XL-1 Blue strain). All of the image data from the detection chamber of the PAD was analyzed at the precision of 300 pixels for each color space component (i.e., hue, saturation, and value in HSV color). In addition, environmental samples were tested with our PAD, and the data were fitted in the range of colorimetric reference chart for E. coli sample testing. Twenty microliters of 50% hydrogen peroxide solution was used for a single-color detection test. Before adding the E. coli sample on the chip, the detection chambers were loaded twice with 1 mu L of ferrous sulfate (0.3 g/mL, 0.97 M) and dried. The mean values for all of the samples (n = 10) were rounded to the nearest integer. The P values (P<0.01, P<0.05) for all three of the color space components of HSV were considered to be statistically significant.