DNA Electrochemical Sensing Based On Graphene Composite Interfaces

In the scope of nanomaterials fields, the nanocomposite interfaces based on graphene, ionic liquids (IL), gold nanoparticles, polymer, and metal oxides were synthesized and applied in electrochemical biosensing. The resulted novel DNA electrochemical biosensors show good performances and exhibit potential application in bioanalysis. The main points of this dissertation are addressed as follows:(1) Electrochemical activities of typically electrochemical targets at three kinds of modified carbon electrodes, i.e. carbon ionic liquid electrode (CILE), graphene/carbon paste electrode (CPE), and ionic liquid-functionalized graphene (IL-graphene)/CPE, were compared. The redox processes of the targets at IL-graphene/CPE were faster than those at CILE and graphene/CPE. Single base mutation of sequence-specific DNA could be discriminated by IL-graphene/CPE.(2) A direct electrochemical DNA sensor was constructed based on gold nanoparticles/graphene film. A precursor graphene film was fabricated on the glassy carbon electrode (GCE) using both electrochemically reduced graphene oxide (ERGNO) and chemically reduced graphene oxide (CRGNO). Electrochemical approach was green and fast, and would not result in contamination of the reduced material compared with chemical reduction, and at highly negative potential could reduce the oxygen functionalities of graphene oxide more efficiently than chemical reduction. ERGNO exhibited better electrochemical and electrocatalytic performances than CRGNO. The gold nanoparticles (AuNPs) were electrodeposited on the ERGNO/GCE to amplify the electrochemical signals. The electrochemical responses of DNA bases were investigated at AuNPs/ERGNO/GCE, which showed more favorable electron transfer kinetics than at ERGNO/GCE, demonstrating the significantly synergistic electrocatalytic effect of ERGNO and AuNPs. The synthetic sequence-specific DNA was successfully detected. (3) A novel DNA electrochemical biosensor was described for the detection of specific gene sequences. ERGNO was prepared on polyaniline (PAN) nanofibers modified GCE. Compared with the electrochemical reduction of graphene oxide directly on bare GCE, more positive reduction potential for graphene oxide was observed with the PAN membrane existing. The formed ERGNO/PAN nanocomposites were applied to bind single-stranded DNA (ssDNA) probe via the non-covalent assembly. After the hybridization of ssDNA probe with complementary DNA, the response of surface-bound [Ru(NH3)6]3+changed obviously, which could been adopted to recognize the DNA hybridization. This biosensor could be used to detect the sequence-specific DNA of cauliflower mosaic virus (CaMV35S) gene.(4) An electrochemical platform was employed for rapid detection of protein, where Fe2O3was fabricated on graphene surface using electrochemical deposition. The negatively charged lysozyme-binding aptamer (LBA) was immobilized on the positively charged Fe2O3via electrostatic interaction. Electrochemical impedance spectroscopy was adopted for the indicator-free detection of lysozyme. The LBA on the outermost layer would catch lysozyme in solution by physical affinity, which induced an increase of impedimetric signals. The results showed that the indicator-free impedimetric aptasensing strategy had good sensitivity and selectivity.(5) Graphene was obtained by the nontoxic reductant L-histidine, and demonstrated as a dual-analyte biosensing platform that functioned as electrochemical logic gate. Thrombin and lysozyme were used as inputs to activate the change of aptamer configuration. The electrochemical signals of redox cation [Ru(NH3)e]3+bound to the aptamer were read out as outputs in the presence of the appropriate inputs. The fabricated logic aptasensor could determine whether both specific targets were present through the built-in NAND logic gate.(6) The electrochemical co-deposition of Al3+/graphene composites directly from an aqueous mixture containing graphene oxide (GNO) and Al3+was presented. The obtained Al3+/graphene composites with good electrochemical activity were regarded as the appropriate immobilization platform for double-stranded DNA (dsDNA). The nontoxic redox probe xanthurenic acid (XA) was successfully applied to recognize ssDNA and dsDNA. The scission of dsDNA caused by GNO combining with some metal ions could be detected by monitoring the electrochemical signals of XA.