Peer Reviewed Journal: Graphene in Spr Imaging

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¶ … Graphene in Spr Imaging

Some sources claim that Graphene has the potential to be the new silicon due to its conductivity and flexibility. In fact, Graphene has the potential to boost the speed of the Internet and to serve as a coating that is sensitive to touch extending the lives of computers. Graphene is stronger than even a diamond and conducts electricity and energy better than any other material know to mankind.

Overlayers of Graphene on Metallic Surfaces

Overlayers of grapheme on metallic surfaces are centric to research throughout the world on the properties of the single layer graphene. This is important for two specific reasons stated as follows:

(1) The metallic substrate can be used for the preparation of graphene layers of different thicknesses; and (2) Due to the extraordinary quality the metallic substrate can be transferred onto an insulating or polymer support. (Voloshina and Dedkov, 2012, p.1)

In regards to the transferring of graphene onto an insulator or polymer support the material was used in successfully fabricating flexible touch screens. Voloshina and Dedkov (2012) in their work concluded that the ease of preparing graphene on metals and transfer onto insulating support or polymer make this a viable method for the graphene industry. (Paraphrased)

II. Graphene-Based Interfaces

Specific graphene based interfaces with metal include the following:

(1) ATOP position in which the metal atom of the top layer are surrounded by carbon atoms and are placed in the hcp and foc hollow positions of the RH (111) stack above (S) and (S-1_ Rh-layers respectively (hcp -- foc position); (Voloshina and Dedkov, 2012)

(2) FCC position in which the foc hollow site of the Rh (111) surface are surrounded by carbon atoms and are placed in the top and hcp hollow positions of the Rh (111) stack above (S) and (S-1); (Voloshina and Dedkov, 2012)

(3) HCP-position -- the hcp hollow site of the RH (111) surface is surrounded by carbon atoms and are placed in the top and fcc hollow positions of the RH (111) stack above (S) and (S-2) RH-layers respectively; (Voloshina and Dedkov, 2012) and (4) BRIDGE Position in which the Rh atom bridges the carbon atoms in (S) layer. (Voloshina and Dedkov, 2012) It is reported that the theoretical approach used most widely in the study of graphene-metal systems is that of "density functional theory" or DFT which ranges from the X method to the recently revisited random phase approximation or RPA. (Voloshina and Dedkov, 2012)

III. Graphene: Use with Silver and Gold

According to Jain et al. (2007) noble metal and most particularly gold (Au) and silver (Ag) nano particles are such that "…exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR)." (p.107) The work of Zhang, et al. (2012) states that the surface plasmon resonance (SPR) biosensor based on graphene oxide and decorated with gold nanorod (AuNR) antibody conjugates was developed and that when compared with "traditional S. PR biosensor, GO sheets were assembled on the amino-modified AU film via electrostatic interaction and then AuNR oxygen-containing functional groups, large specific surfaced area and friendly biocompatibility of GO sheets serve to benefit the immobilization of AuNR antibody conjugates." (Zhang, et al. 2012) When AuNRs are anchored to the GO surface and serve to greatly benefit the detection sensitivity. This design is reported to be applicable to a method that can be used in controls AuNR assembling on the GO sheets and extended easily to detection of other protein through preparation of corresponding AuNR antibody conjugates. (Zhang, et al., 2012, paraphrased)

The electric conductivity of bio single molecules are reported as key in the observation and detection of conformance, concentration and structural electronic properties but also for various nanoscale uses including "biosensor, biochip and scanning tunneling microscopy (STM) based DNA identification." (Zhang, et al., 2012) The work of Harana and Jha (2012) relates that surface plasmon resonance based affinity biosensor comprise of 252G chalcogenide prism, graphene-multilayer and gold as a plasmon active metal is useful for sensing over a broad wavelength range in visible and near infrared applications. According to Salihoglu, Balci, and Kocabas (2012) the electronic band structure of the two-dimensional crystal of carbon is unique in graphene. Salihoglu, Balci, and Kocabas (2012) relate a study that used 50 nm thick silver and gold films on glass substrate as the supporting surface for Plasmon-polaritons. This type of SPR sensor while having been previously proposed have not yet been applied. Proteins directly absorbed on metal surface causes denaturalization of proteins which lose their binding activity. The surface must be thin enough that detrimental effects are prevented on the properties of plasma and to allow the chemistry on the surface to enable specific citic ligands to be immobilized. There are three advantages cited for graphene funcationalized SPR sensors including that they increase the organic molecules ability to absorb because of n-n stacking, they protect the surface against oxidation and they reduce the detrimental effects against the properties of the plasma. (Salihoglu, Balci, and Kocabas, 2012) Copper coils were used in a chemical vapor deposition process to synthesize the graphene on metal surface during transfer of the printing. The copper foils were heated in a quartz chamber to 1000 degrees Celsius under a flow of hydrogen and argon gases and the samples were then anneal for 20 minutes at the same temperature so the oxide layer would be reduced. Next, methane gas was sent to the chamber at a flow rate of 15 sccm for 20 minutes and the chamber pressure kept at 5 Torr during the growth which was terminated when the flow of methane gas was stopped. The temperature in the chamber was brought to room temperature and the graphene coated copper foils were spin coated with a photoresist. After the process was complete there was approximately 2% absorption for each graphene layer. (Salihoglu, Balci, and Kocabas, 2012)

IV. SPR Imaging Biosensors with Graphene on Silver Substrate

Choi, Kim and Byun (2012) report a study that demonstrated that SPR imaging biosensors with a graphene on silver substrate is effective in achieving high sensitivity in prevention of silver oxidation and can significantly increase the sensitivity in imaging when compared to the traditional gold-film-based SPR imaging biosensor. The work of Grigorenko, Polini and Novoselov (2012) relates that graphene contains intrinsic plasmons that are both "tunable and adjustable" and that combining graphene with noble-metal nanostructures "promises a variety of exciting applications for conventional plasmonics." The work of Pillai, et al. (2006) found that surface plasmons resulted in an increase in the spectral response of thin-film cells across the entire solar spectrum. Ye, et al. (2012) reports "Light-matter coupling, such as absorption, plays a key role in optical detectors, sensors, and photovoltaics. Absorption of graphene has been experimentally observed to have a universal value _pa (2.3%) for light in the visible spectral range." (p.102) A recent study reported in the work of Szunnerits, et al. (2013) states "Graphene and graphene oxide are good supports for biomolecules because of their large surface area and rich ? conjugation structure, making them suitable dielectric top layers for SPR sensing."

Transfer of graphene onto gold and silver SPR interfaces is accomplished in several different ways. One approach is transfer of "large-area graphene grown by chemical vapor deposition (CVD) onto metal substrates" which is reported as a viable option since the result is graphene SPR interfaces where the "number of transferred graphene layers can be controlled" that is reproducible. (Szunerits, et al., 2013) A second technique is the dry-transfer technical which is reported as being much like wire bonding involving the top graphene layer being transferred onto gold or silver films that are thin resulting in "a fast and highly reproducible means of fabricating graphene-based SPR interfaces." (Szunerits, et al., 2013) This is reported to be based on "…the use of a commercial thermal release tape, which enables mechanical transfer of the surface of a 1 mm2 graphene sheet, originally grown by chemical vapor deposition (CVD), onto nickel-coated silicon substrate. The tape is released by annealing the interface at 120 "C for 2 -- 3 min and then rinsed with acetone followed by a high temperature annealing at 500 "C for 360 min to remove any remaining traces of the tape." (Szunerits, et al., 2013)

Summary and Conclusion

The use of overlayers of grapheme on metallic surfaces is the focus of study worldwide as the metallic substrates is useful for preparing grapheme layers of varying thickness and due to the special quality the metal substrate is transferrable onto insulating support of polymer support. Graphene is being studied in earnest specifically in relation to transfer of graphene onto silver and gold for use in SPR biosensor imaging. There are reported to be several graphene based interfaces that can be used with metal. Gold and silver have properties that are held as unique and tunable in optical properties due to the surface plasmon resonance (SPR) of gold and silver. This is important since light matter coupling in absorption is key… [END OF PREVIEW]

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