Microfluidic Control of Complex Emulsions for Chemical Sensing

In this study, CNFCPEG, an innovative compound, plays a major role in stabilizing complex emulsions without the need for external surfactants. CNFCPEG also exhibits two fluorescence colors (blue and green) depending on its aggregation state. When CNFCPEG aggregates in an organic phase, a blue color is observed, while the green excimer is observed when CNFCPEG self-assembles at the fluorinated oil/water interface (F/W). By evaluating fluorescence emissions, the distinction between H/F/W and F/H/W emulsions becomes clear and easily distinguishable.

Heptane-FC 770-CNFCPEG complex emulsion in DI water presents the H/F/W morphology. Addition of iodine to the DI water reduces the hydrophilicity of CNFCPEG’s PEG group, leading to an instantaneous morphology shift from H/F/W to Janus to F/H/W complex emulsion. This morphological shift, combined with the fluorescent color change, makes it possible to to detect the presence of iodine in water. 

Complex droplets as iodine real-time sensing platform

To enhance the precision and accuracy of data acquisition in real-time flow sensing, the researchers designed a Multiple-well Flow PDMS Chip (MWFC) that allows for parallel tracking of multiple droplets (figure 6). This innovative chip facilitates the monitoring of droplet behavior, morphological changes, and interactions within complex droplets.

Iodine was injected into the MWFC, inducing a decrease in the hydrophobic nature of the CNFCPEG and initiating an instantaneous morphological change in the stabilized complex droplets (figure 7b, figure 8). The droplets transitioned from H/F/W to Janus more quickly with increasing iodine concentration. Slower flow rates corresponded to longer transition times, providing quantitative insights into analytes (figure 7c).