Contactless conductivity detection of bacteria in droplets using 3D printed microfluidic device

Electrochemical detection has been widely explored in microbiology grow monitoring due to its flexibility and compatibility with microfluidic systems. However, traditional methods of manufacturing microfluidic systems require specialized and costly instrumentation, as well as laborious steps such as sealing. In this way, 3D printing has become an alternative manufacturing method for analytical microdevices because it allows automated, single-stage and low-cost fabrication. In this sense, this work presents an electrochemical approach to monitor and quantify bacteria cells in microdroplets by means of contactless conductometric detection C4D system. The microdevice was manufactured using 3D printer with fused deposition modeling (FDM) technology containing integrated electrodes consisting of polylactic acid (PLA) doped with carbon nanotubes. The droplets containing E. coli were generated by pumping the bacterial sample as the dispersed phase in microchannel I, while the continuous phase (mixture of oil and 1% Span 80) was pump in microchannel II, shown in Figure 1A. Through the statistical method of Poisson it was possible to estimate bacteria quantity per drop referring to the injected bacterial density. In this way, the C4D signal intensity value was plotted against the logarithm of the number of bacteria found per drop, which can be seen in Figure 1B. A linear profile was found between the second and last four points of the curve with r2 = 0.9864, a satisfactory response to the proposed detection system showing its high potency to be used in the cell count on microfluidic devices.