Microfluidic Chips Based On Polyelectrolyte Modified Nanochannel Membranes

As a new type of chemical and biological micro-analysis technology platform, micro/nanofluidic chip has a good application in chemical analysis, biological analysis, environmental monitoring, clinical diagnosis, and so forth, for its low sample consumption, low cost, rapid speed, and high integration. This paper is committed to the design and development of micro/nanofluidic chips based on environment-sensitive polyelectrolyte and the research work of this dissertation is summarized as follows:In the first part, a pH-switchable micro/nanofluidic chip with pH-sensitive poly methacrylic acid (PMAA) was fabricated. The switchable micro/nanofluidic chip was fabricated by sandwiching PMAA modified polycarbonate track-etch membrane between polydimethylsiloxane (PDMS) film and the substrate glass. Ruthenium pyridine was used as fluorescence probe to study the switchable permeability of the micro/nanofluidic chip under different pH conditions. PMAA molecules adopt relatively contracted conformation at low pHs and extended conformation at high pHs, so the chip-channel opened or closd sequently when pH was changed. The results showed that the flux of ruthenium pyridine could be reversibly controlled by changing the pH in the micro/nanofluidic chip, and this method was expected to build other nano-scale valves which may have application in flow control, controllable drug release and so on.2. Based on polyelectrolyte layer by layer self-assembly, a polyelectrolyte modified micro/nanofluidic chip with charge selectivity was fabricated in situ. The charge-selective micro/nanofluidic chip was fabricated by sandwiching polycarbonate track-etch membrane between a PDMS microfluidic chip and the substrate glass. Polystyrene sulfonate and polystyrene sulfonate (PSS/PAH) were then implanted through the chip-channel alternately, and the polyelectrolytes self-assembled layer by layer in the porous polycarbonate membrane. Rhodamine B and fluorescein sodium were used as fluorescence probes to study the charge separation capacity of this micro/nanofluidic device. The results showed that the flux of positively charged Rhodamine B was higher than that of negatively charged fluorescein sodium when the upper layer was PSS, which is negatively charged. When the upper layer was positively charged PAH, the flux of fluorescein sodium is higher than that of Rhodamine B. It is possible to carry out the separation and enrichment of biomolecules with different charges in this polyelectrolyte modified micro/nanofluidic chip.3. A novel microfluidic chip-based method for detecting red blood cell deformability was developed. Normal red blood cells (RBCs) will deform in shear flow, while the deformability of damaged RBCs decreases. Glutaraldehyde treated RBCs were chosen as a model to investigate the effect of position and flow rate on the red blood cell deformability in glass microfluidic chip. The results showed that the deformation index of red blood cells decreased as the concentration of glutaraldehyde increased, by which the cell deformability can be evaluated. The method is simple and rotator-free to apply shear stress. It has the potential to be used to detect damaged RBCs.