We present here the electrochemistry at a photolithographically created isolated monolayer graphene edge (GrEdge). The millimeter-long GrEdge is found to behave like a nanowire, exhibiting very high mass transport rates, characteristic of nanoelectrodes. Accordingly, the voltammetric response at such electrodes is dictated by the kinetics of heterogeneous electron transfer (HET). We observe high electron transfer rates at GrEdge electrodes, at least 14 cm/s for the outer-sphere probe ferrocenemethanol and 0.06 cm/s or higher for the innersphere probe Fe(CN) 6 3− . Upon selective modification of the edge with gold nanoparticles, the HET is found to be reversible, with the voltammetric curve showing a typical mass-transport-limited Nernstian response for both kinds of probes. Subsequently, the electrodes are evaluated as electrochemical sensors for the detection of reduced form of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). The nanoscale geometry with a unique diffusional profile of the unmodified GrEdge enables the sensing of NADH down to micromolar concentrations. Taken together, our simple strategy for the realization of graphene edge electrodes enables the availability of a versatile high-aspect one-dimensional nanoelectrode with the capability to study fast electron transfer kinetics. Moreover, such electrodes allow for facile detection of small amounts of electroactive species and hence will find applications in chemical sensing and biosensing.

Electron transfer rates at graphene are found to vary with pH, attributed to electrostatic effects at the graphene-liquid interface.

In this paper, we study the interaction of a small dye molecule, namely, methylene blue (MB) with graphene surfaces using surface plasmon resonance (SPR). We show that by utilizing all of the parameters of the SPR angular dip and exploiting the fact that MB absorbs light at the operating wavelength, it is possible to detect the binding of small molecules that would otherwise not give a significant signal. The binding of MB to unmodified graphene is found to be stronger than that for gold. By studying the interaction at modified surfaces, we demonstrate that electrostatic effects play a dominant role in the binding of MB on to graphene. Furthermore, following the binding kinetics at various concentrations allows us to estimate apparent equilibrium binding and rate constants for the interaction of MB with graphene.

We present the development of a label-free, highly sensitive fiber-optical biosensor for online detection and quantification of biomolecules. Here, the advantages of etched fiber Bragg gratings (eFBG) were used, since they induce a narrowband Bragg wavelength peak in the reflection operation mode. The gratings were fabricated point-by-point via a nonlinear absorption process of a highly focused femtosecond-pulsed laser, without the need of prior coating removal or specific fiber doping. The sensitivity of the Bragg wavelength peak to the surrounding refractive index (SRI), as needed for biochemical sensing, was realized by fiber cladding removal using hydrofluoric acid etching. For evaluation of biosensing capabilities, eFBG fibers were biofunctionalized with a single-stranded DNA aptamer specific for binding the C-reactive protein (CRP). Thus, the CRP-sensitive eFBG fiber-optical biosensor showed a very low limit of detection of 0.82 pg/L, with a dynamic range of CRP detection from approximately 0.8 pg/L to 1.2 µg/L. The biosensor showed a high specificity to CRP even in the presence of interfering substances. These results suggest that the proposed biosensor is capable for quantification of CRP from trace amounts of clinical samples. In addition, the adaption of this eFBG fiber-optical biosensor for detection of other relevant analytes can be easily realized.