Graphene, carbon nanotubes and silica nanoparticles are the researching focuses in the field of nanotechnology due to their remarkable physicochemical properties. As the methods for preparation and modification have been developed, the biological applications of these nanomaterials have attracted much attention. Recently, nanomaterials were widely used for biosensing, drug delivery and nanoassembly based on biomolecules. We have intensively studied the novel properties of these nanomaterials and made some progress for their biological applications. We discovered that GO-COOH and SWNTs possesses intrinsic peroxidase-like activity. Based on these findings, we designed and developed the colorimetric assay to detect glucose in blood and disease-associated single-nucleotide polymorphism. We also found multi-walled carbon nanotubes and graphene have the synergetic effect for peroxidase-like activity, which can be used for detection of copper ions and cancer cells. In addition, we have studied the interaction between SWNTs and CGC+ triplex DNA. Based on the DNA conformation change, we designed a biosensor for detection of AMP. The main results are summarized as following: 1. GO-COOH possesses intrinsic peroxidase-like activity and its catalysis is strongly dependent on pH, temperature, and H2O2 concentration, similar to horseradish peroxidase. In the presence of H2O2 and peroxidase substrate TMB, GO-COOH can produce a blue color reaction. Based on this finding, we designed and developed a simple, cheap, and highly selective and sensitive colorimetric assay to detect glucose in buffer solution or diluted blood and fruit juice samples. 2. SWNTs possess intrinsic peroxidase-like activity and can catalyze the reaction of the peroxidase substrate TMB in the presence of H2O2 to produce a color change. The catalytic effect we observed is not due to metal residues in SWNTs. As an example for potential applications, we can detect disease-associated single-nucleotide polymorphism with a direct detection limit of 1 nm by this label-free method. 3. A highly efficient approach for preparing MWNT-MSN hybrid using Cu(I) catalyzed click chemistry has been developed. Kinetic studies showed that the MWNT-MSN hybrid even possesses higher peroxidase-like activity than each individual. Using a combination of click chemistry and peroxidase-like catalytic color reaction, we developed a novel turn-on sensor for Cu2+. This sensor shows high sensitivity, high selectivity and allows simple detection of Cu2+ by the naked eye. 4. Aptamer-induced disassembly of a nano-magnetic and fluorescent silica sandwich complex was used for AMP detection. This sensor exhibits high selectivity, a low detection limit, and high photostability. Compared with using gold nanoparticles, 3000-fold greater sensitivity can be achieved. The direct AMP detection limit can be as low as 0.1 mM. 5. A folic acid conjugated graphene-hemin composite (GFH) was developed for selective, quantitative and fast colorimetric detection of cancer cell based on the color reaction catalyzed by GFH peroxidase-like activity. It can detect as low as 1000 cancer cells. Intriguingly, GF can enhance hemin catalytic activity and the composite shows synergetic effect. Furthermore, this composite has the optimal catalytic activity at pH 7.0 showing that GFH can be used under physiological conditions. 6. Duplex can be disproportioned into triplex DNA and single strand DNA in the presence of SWNTs under physiological condition. The disproportionation increases the stability of SWNTs. However, at pH 8.5, the duplex DNA will condense on the surface of SWNTs and decrease SWNTs stability. The electrostatic interaction was crucial for duplex DNA repartition
Transparent conductive film (TCF) is a key material for modern photo-electronic devices and flat panel displays. Single wall carbon nanotube (SWCNT) and graohene are nanoscale materials with excellent electric conductivity, which can be used to produce thin films with thickness of several or tens nanometers. Such films can be visually transparent and with low surface resistance, which are the essential requirements of TCFs. Furthermore, these nanoscale carbon materials are rich in resources and have excellent flexibility compared with the traditional oxide based TCFs, as a result, flexible TCFs can be produced, which may be one of available applications of SWCNT and graphene in the next decade. TCFs using SWCNTs or graphene can be fabricated by solution based processes. These processes are superior in low cost and good quality compared to the other fabrication methods. However, key points are good dispersion of SWCNTs and efficient film formation for SWCNT TCFs and efficient reduction of graphene oxide (GO) at low temperature for graphene TCFs. This work has focused on these two fields. Electrophoretic deposition (EPD) is a widely used industrial method to produce films with high uniformity from colloid solutions. We produce flexible SWCNT TCFs by combining EPD and hot-press transferring. SWCNT films can be first electrophoretically deposited on conductive stainless steel substrates and then fully transferred to transparent polymer substrates by simple hot-press transferring. A pre-dispersion-then-dilution treatment is used to uniformly disperse SWCNTs in sodium dodecyl sulfate (SDS) solution. This treatment makes the SWCNT dispersion with low electrical conductivity (48 mS) and high Zeta potential (-78.8 mV), both of which are the prerequisites for EPD. The film thickness can be well controlled by varying EPD time, which further controls the film transparency and electrical conductivity; and the hot-press during transferring makes SWCNT films partly anchored into the substrate surface. This structure enables strong interaction between SWCNT films and polymer substrates, which makes TCFs with excellent flexibility. The TCF with best performance of is 220 Ω/□ at 81% transparency can bear over 10000 repeated bending without loss of transparency and conductivity. Furthermore, this EPD-transferring method can be scalled up to a roll-to-roll process to realize the continuous fabrication of SWCNT TCFs. Producing graphene TCFs using GO as starting material is a valuable way since GO is readily water soluble. The film formation using GO solution is very simple but the key process is how to reduce insulated GO films into highly conductive graphene films. We propose the reduction of GO by hydroiodic acid (HI) based on the halogenation reaction. The GO films can be effectively reduced at a temperature no more than 100 °C; furthermore, the reduction process can further densify the film, which improves the electrical conductivity and mechanical strength of the films. TCF achieved by HI reduction has surface resistance of 1.1 kΩ/□ at 84% transparency, which is better than those reduced by the other chemical methods. The research on the reduction process of GO films reveals the substitution of hydroxyl groups by iodine and the spontaneous elimination of iodine from the reduced graphene films, which is useful for the understanding of the reduction mechanism of GO.