Studies On Synthesis Of Graphene-based Nanocomposite And Its Application In Biosensor

Electrochemical immunosensors, one of effective analytical technique, can rapidlydetect and quantify the target materials. The manufacturing process for electrochemicalimmunosensor reported by the literature is complicated and time-consuming, in which thebiomolecule that are prone to denature, as signal amplifiers are needed to be modified onsurface of the immunosensors. By contrast, the label-free electrochemical immunosensoris simple, which dose not requires amplifying electrical signal by coupling secondaryantibody, thus siginicantly improving their sensitivity and selectivity. Furthermore, theglassy carbon electrode (GCE) needs to be polished repeatedly before use, which lead tothe disadvantage of tedious operation and detection error. However, the advantages,including mass production, low cost, crominiaturization and portability, of immunosensorcan be realized by employing screen-printed electrodes (SPCEs) as working electrodes.Moreover, the traditional electrode materials have lower electrical conductivity, which needto be ameliorated to increase its electrochemical response.Based on the above mentioned problems, here we report a novel method tosynthesize reduced graphene oxide-silver nanopartciles (rGO-Ag NPs) composite byone-pot reaction under mild condition, in which sodium citrate were used as stabilizer,sodium citrate and hydrazine were used as binary reductant. The diameters of silvernanoparticles (Ag NPs) decorated on reduced graphene oxide (rGO) sheets was rangedfrom16.6to35.8nm, and the silver content of rGO-Ag NPs was from0.16to59.63%bycontrollably modulating the mass ratio of graphene oxide (GO) to silver nitrate. The resultsexamined by four-point probe resistivity measurement system and electrochemicalworkstation, showed that rGO-Ag NPs has a higher conductance and electrochemicalresponse compared with rGO, the conductivity of which even attained35.8S/cm at40%of solid content. The anodic peak current of CV curves for rGO-Ag NPs composite evenreached45uA at the scan rate of100mV/s.In addition, we fabricated a label-free electrochemical immunosensor by depositingrGO/Ag NPs composites on the working electrode of SPCEs, in which Ag NPs provided binding sites for antibody specific for prostate specific antigen (PSA). In addition, theelectron transport on surface of working electrodes was accelerated by modifying rGO/AgNPs composites. The obtained results showed that, the biosensor had a quick-responsefor PSA antigen and excellent selectivity, reproducibility and stability, the limit and linearrange of detection of which was0.01ng/mL and1–1000ng/mL, respectively.Finally, we synthesized a novel gene vector with magnetic property andbiodegradability. Firstly, ultrafine iron oxide nanoparticles coated with oleic acid(Fe3O4-OA) was controllably prepared via solvothermal method, the diameter of whichranged from4to8nm and the magnetic saturation intensity (Ms) of which attained27.27emu/g. Secondly, OA molecule were mostly substituted for meso-2,3-dimercaptosuccinic(DMSA) capped on Fe3O4nanoparticles, The Ms of Fe3O4-DMSA rose to35.67emu/g.Thirdly, a gene carrier, namely Fe3O4-DMSA-PEI, was obtained with superparamagnetismby grafting branched polysaccharide (PEI) to Fe3O4-DMSA by amidization reaction, thezeta potential of which was as high as52.5±1.94mV and the Ms of which was14.48emu/g. Moreover, the results at cellular level demonstrated that, EGFP plasmids can bedelivered into cells through the fabricated gene carrier in this study.