Research On Functional Modification Of Nano-channel Membranes

Ion channels, which play an important role in the physiological functions of cells by modulating the penetration of nutrients and ions across cell membranes, are characteristic with small size, high selectivity, as well as stimulus responsive property. Inspired by ion channels in biological membranes, intelligent design and modification of artificial nanochannels can be realized, and the functional nanochannels can be employed to mimic the function of biological system and to devise some functional nanodevices.In this thesis, the concept of ion channels, the functional modification of artificial nanochannels were first summarized, and efforts were then focused on the incorporation of selective transport property and switchable function into artificial nanochannels with proper modification of polycarbonate membranes. The research works of this dissertation are summarized as follows:1. Nanochannel membranes with charge selectivity were prepared by alternate layer-by-layer assembly of differently charged polyelectrolytes in polycarbonate membranes. The charge properties of the porous polycarbonate membranes were determined by the charge of the outmost layer. The charge-selective transport property of the functionalized nanochannel membranes was investigated by using different charged fluorescent dyes as probe, i.e. positively charged Rhodamine B and nagetively charged fluorescein sodium. The results showed that, the diameter of the nanochannels decreased as the layers of polyelectrolytes increased , and the thickness of each polyelectrolyte was approximately 10 nm; in addition, the nanochannel's surface was negatively charged when the outermost layer was polystyrene sulfonate (PSS), the permeation rate of positively charged Rhodamine B was greater than that of nagetively charged fluorescein sodium; while in the case of polyallylamine hydrochloride (PAH), the nanochannel's surface was positively charged and the permeation rate of nagetively charged fluorescein sodium was greater than that of positively charged Rhodamine B. These charge-selective nanochannel membranes may have a potential application in the field of proteins separation.2. Temperature responsive nanochannel membranes were prepared by modifying gold nanochannel membranes with poly(N-isopropylacrylamide) (PNIPAm). The thermally switchable transport properties of the porous membranes were investigated using water-soluble dyes as probes. The results showed that the permeability was higher at 25 oC (below the LCST) than that at 37 oC (above the LCST), because at 25 oC, the nano-channel membranes were hydrophilic, however at 37 oC, the nano-channel membranes were hydrophobic. In addition, the nanochannel membranes respond to temperature reversibly, which may have a potential application in the field of micro-valves and controlled release of drugs.3. pH responsive nano-channel membranes were prepared by modifying gold nanochannel membranes with DNA-motors that tailed with hydrophobic group. The DNA-motor is a nucleic acid fragment with a specific cytosine-rich sequence, and it forms i-motif structure in acidic solution and straight-chain structure in alkaline solution. The pore diameter and wettability of the nanochannel membranes were changed as the structure transformation of the DNA in different pH solutions. The pH switchable transport property of the porous membranes was investigated by using Rubby as probe. The results showed that the permeability of the nanochannel membranes was higher at pH 4.5 than that at pH 8.5. In addition, the nanochannel membranes responded to pH reversibly, and the wettability of the porous membranes played an important role in permeability. These pH sensitive nanochannel membranes may have a potential application in the field of ion channels simulations and controlled release of drugs.4. An enzyme catalyzed fluorescent probes deposition for sensitive protein detection based on 1-D chip was developed. Target protein was sandwiched between functional beads and polyclonal antibodies, and then hybridized with HRP-secondary antibodies. Biotin-labeled tyramine was deposited around the target protein in the presence of HRP and H2O2, and the fluorescent probes were specifically captured by the biotin-labeled tyramine through biotin-streptavidin linkage, to realize a highly sensitive detection of target protein. The method was less reagent consumption, and the LOD for AFP was 0.5 pg/mL. Meeting the requirements of clinical testing, this method has a potential in the early diagnosis of liver cancer.