Graphene-Based Materials for Biosensors: A Review <s> Pristine Graphene <s> We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10(13) per square centimeter and with room-temperature mobilities of approximately 10,000 square centimeters per volt-second can be induced by applying gate voltage. <s> BIB001 </s> Graphene-Based Materials for Biosensors: A Review <s> Pristine Graphene <s> Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment. <s> BIB002 </s> Graphene-Based Materials for Biosensors: A Review <s> Pristine Graphene <s> We have achieved mobilities in excess of 200,000 cm^2/Vs at electron densities of ~2*10^11 cm^-2 by suspending single layer graphene. Suspension ~150 nm above a Si/SiO_2 gate electrode and electrical contacts to the graphene was achieved by a combination of electron beam lithography and etching. The specimens were cleaned in situ by employing current-induced heating, directly resulting in a significant improvement of electrical transport. Concomitant with large mobility enhancement, the widths of the characteristic Dirac peaks are reduced by a factor of 10 compared to traditional, non-suspended devices. This advance should allow for accessing the intrinsic transport properties of graphene. <s> BIB003 </s> Graphene-Based Materials for Biosensors: A Review <s> Pristine Graphene <s> We developed a chemical route to produce graphene nanoribbons (GNR) with width below 10 nanometers, as well as single ribbons with varying widths along their lengths or containing lattice-defined graphene junctions for potential molecular electronics. The GNRs were solution-phase–derived, stably suspended in solvents with noncovalent polymer functionalization, and exhibited ultrasmooth edges with possibly well-defined zigzag or armchair-edge structures. Electrical transport experiments showed that, unlike single-walled carbon nanotubes, all of the sub–10-nanometer GNRs produced were semiconductors and afforded graphene field effect transistors with on-off ratios of about 107 at room temperature. <s> BIB004
A monocrystalline graphitic film composed of a single one-atom-thick carbon layer can be prepared by peeling it from a small platelet of highly oriented pyrolytic graphite (HOPG) in a mechanical exfoliation approach with a Scotch tape, as seen in Figure 3a . Mechanical exfoliation is the technique by which a longitudinal or transverse stress is exerted on the surface to overcome the van der Waals binding energy of approximately 2 eV/nm 2 BIB001 . When the graphene layer is fabricated as the conducting channel in a field-effect transistor (FET) device contacted with any metal conductor such as gold or silver, the unusual electronic properties of the graphene field-effect transistor (GFET) depend on the charge transport and electron conduction in the band structure and linear behavior at low energy, so the electrons in graphene are transported ballistically analogous to the relativistic massless fermions with an effective velocity of approximately 10 6 m/s. The GFET can even be retained under ambient circumstances without any protection of the graphene. The charge carriers exhibit ultra-high mobility, found to be 200,000 cm 2 /Vs, at temperatures between 10-100 K, which can be induced by applying gate voltage, a strong ambipolar electric field effects in charge carrier concentrations at the range of 10 13 cm −2 with a long mean free path of 400 nm, high thermal conductivity, very low resistivity (less than that of silver at room temperature), low spin-orbit coupling, high mechanical strength (200 times greater than stainless steel), high elasticity, transparent (98% transmittance) and biocompatibility BIB003 BIB004 BIB002 . As a novelty of graphene, a variety of practical applications now appear possible, and graphene and new graphene-like 2D nanomaterials are used in the manufacture of innovative electronic devices. The efficiency of graphene-based sensors and biosensors are predicted to be substantially faster than that of semiconductor-based devices resulting in more efficient computers. To provide an understanding of the physics, chemistry, and engineering of graphene-based structures, and how these methods have crucial influences on their characteristic and properties, we will first discuss how graphene and related materials are prepared and synthesized. A monocrystalline graphitic film composed of a single one-atom-thick carbon layer can be prepared by peeling it from a small platelet of highly oriented pyrolytic graphite (HOPG) in a mechanical exfoliation approach with a Scotch tape, as seen in Figure 3a . Mechanical exfoliation is the technique by which a longitudinal or transverse stress is exerted on the surface to overcome the van der Waals binding energy of approximately 2 eV/nm 2 BIB001 . When the graphene layer is fabricated as the conducting channel in a field-effect transistor (FET) device contacted with any metal conductor such as gold or silver, the unusual electronic properties of the graphene field-effect transistor (GFET) depend on the charge transport and electron conduction in the band structure and linear behavior at low energy, so the electrons in graphene are transported ballistically analogous to the relativistic massless fermions with an effective velocity of approximately 10 6 m/s. The GFET can even be retained under ambient circumstances without any protection of the graphene. The charge carriers exhibit ultra-high mobility, found to be 200,000 cm 2 /Vs, at temperatures between 10-100 K, which can be induced by applying gate voltage, a strong ambipolar electric field effects in charge carrier concentrations at the range of 10 13 cm −2 with a long mean free path of 400 nm, high thermal conductivity, very low resistivity (less than that of silver at room temperature), low spin-orbit coupling, high mechanical strength (200 times greater than stainless steel), high elasticity, transparent (98% transmittance) and biocompatibility BIB003 BIB004 BIB002 . As a novelty of graphene, a variety of practical applications now appear possible, and graphene and new graphene-like 2D nanomaterials are used in the manufacture of innovative electronic devices. The efficiency of graphene-based sensors and biosensors are predicted to be substantially faster than that of semiconductor-based devices resulting in more efficient computers. However, to obtain graphene by the Scotch-tape method, the maximum dimensions of the pristine graphene that can be isolated for fundamental studies and basic research that require high quality at only 1 mm 2 . Several synthetic procedures have been established that possess scalability in their different characteristics and are more effective for matching applications.