In the present work, chemically synthesized graphene nanosheets were used as electrode materials and their electrochemical properties were systematically characterized. The surface morphologies of graphene nanosheets were evaluated using Raman spectroscopy and transmission electron microscopy. The results obtained were compared with that of single-walled carbon nanotubes (SWCNTs). Results indicated that the surface of graphene possesses greater sp 2 character than the SWCNTs. Using a four-point probe technique, we found the conductivity of graphene particles to be 64 mS cm -1 , which is approximately 60 times better than that of SWCNTs. Following this, different charged redox species were employed for the characterization of redox properties of the graphene thin film. Results indicated that the density of surface negative charge present on graphene surface is more than that found in SWCNTs. Furthermore, the possibility of employing graphene for the electrochemical detection of important neurotransmitters such as dopamine and serotonin was evaluated and compared with SWCNTs. In all these experiments, graphene exhibited a better sensitivity, signal-to-noise ratio, and stability than SWCNTs. In addition, graphene electrodes exhibited a superior biosensing performance than SWCNTs toward dopamine detection in the presence of common interfering agents such as ascorbic acid and serotonin. Our results demonstrate the potential of using graphene nanosheets as a new generation of biosensing materials.

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Electrochemical genosensors for the detection of the Factor V Leiden mutation from polymerase chain reaction (PCR) amplicons using the oxidation signal of colloidal gold (Au) is described. A pencil graphite electrode (PGE) modified with target DNA, when hybridized with complementary probes conjugated to Au nanoparticles, responded with the appearance of a Au oxide wave at approximately +1.20 V. Specific probes were immobilized onto the Au nanoparticles in two different modes: (a) Inosine-substituted probes were covalently attached from their amino groups at the 5' end using N-(3-dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (NHS) as a coupling agent onto a carboxylate-terminated l-cysteine self-assembled monolayer (SAM) preformed on the Au nanoparticles, and (b) probes with a hexanethiol group at their 5' phosphate end formed a SAM on Au nanoparticles. The genosensor relies on the hybridization of the probes with their complementary targets, which are covalently immobilized at the PGE surface. Au-tagged 23-mer capture probes were challenged with the synthetic 23-mer target, 131-base single-stranded DNA or denatured 256-base polymerase chain reaction (PCR) amplicon. The appearance of the Au oxidation signal shortened the assay time and simplified the detection of the Factor V Leiden mutation from PCR amplified real samples. The discrimination between the homozygous and heterozygous mutations was also established by comparing the peak currents of the Au signals. Numerous factors affecting the hybridization and nonspecific binding events were optimized. The detection limit for the PCR amplicons was found to be as low as 0.78 fmol; thus, it is suitable for point-of-care applications.

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