The Preparation Of Fluorescent Graphene Oxide And Its Applications On Biosensors

Graphene oxide (GO) nanosheets, which are derived from graphite flakes by oxidation and exfoliation, bear lots of oxygen-containing groups, such as epoxy group, hydroxyl group, and carboxylic group. Due to the conjugated sp2structure on the surface of the nanosheets, many fluorophors can adsorb onto the GO nanosheet, and their fluorescence can be quenched because of the dipole-dipole coupling interactions. Therefore, GO nanosheets are usually used as the fluorescence quencher in optical sensors, and seldom as the fluorescence donor. In this dissertation, we used alkylamines to modified GO for reduction the non-radiactive recombination of electron-hole pairs which is induced by the oxygen-containing groups. After the modification, we acquired the highly efficient photoluminescent graphene oxide. Then, we found that silver nanoparticles can quench the fluorescence of the prepared GO, and we designed a visual test paper for the versatile detections of biological species. At last, different valent iron ions exhibit distinct influence on the fluorescence of the prepared GO. According to the fact, we designed a molecular logic gates to discriminate the different valent iron ions in living cells by imaging. The main parts of these results are summarized briefly as follows:1. We have prepared a bright blue photoluminescent GO with a highly fluorescent efficiency by surface alkylamine functionalization under mild conditions. The fluorescence quantum yields of the alklyamine-functionalized GO can reach13%, which are remarkably enhanced up to six hundreds times compared with the original GO. This provides a material basis for the constructions of chemo/biosensors. Meanwhile, the fluorescent GO can be prepared by many other alkylamines through this method, which provides not only a feasibility for the post-functionalization, but also a possibility to tune the surface properties of the modified GO from hydrophilic to hydrophobic by changing the molecular structures of the used amines. These will greatly expand the applications of GO in many fields.2. The reported graphene oxide nanosheets emit a highly stable fluorescence in soluble and dry states, and can adsorb various functionalized silver nanoparticles by the nonspecific interactions at surface. These make the ultrathin nanosheets be an excellent chemosensory material for the direct usage in solution detection and the easy fabrication of sensors on microporous membrane. Very few silver nanoparticles can quench the fluorescence of graphene oxide by resonance energy transfer, and then are disassociated from the nanosheets by the analytes through the specific interactions, in which the fluorescence on provides an ultrasensitive biological detection. In particular, the ink of graphene oxide can easily be printed into the highly uniform "word" or "image" for the fabrication of test paper. The portable sensors for the visual detections of peptide, protein and DNA are rapid, simple, efficient and inexpensive. If the library of silver nanoparticles with various recognition elements is available, a nearly universal bioassay will be achieved.3. The fluorescence of photoluminescent graphene oxide is quenched by Fe3+through the electron transfer mechanism, but not by other metal ions including Fe2+because of their weak electron withdrawing ability. However, Fe2+ions exhibit significant quenching of the fluorescence in the presence of H2O2attributed to the dual quenching by the resultant Fe3+and hydroxyl radical. According to these results, we have designed a three-input combinational logic gate to discriminate different valent iron ions. Moreover, the proposed logic gate is also used for the identification the existence of Fe3+, Fe2+, and the mixture of them in living cells by fluorescence imaging. These provide a potential application of logic gates in the imaging of different valent metal ions in living cells and further extension in the disease diagnosis.