Graphene-Based Optical Surface Plasmon Resonance

Graphene-Based Optical Surface Plasmon Resonance for Bio-Sensing Applications

Although light waves move across a surface, electrons do not move far much like when footfall fans in the stadium do "the wave." In these cases, the fans are recreating the same type of phenomenon that takes place when light is oscillated to create surface plasmon resonance. The field of plamonics has become increasingly important for researches seeking improved cancer treatments, computer processors and even plasmonics-based lasers. This paper provides a review of the relevant peer-reviewed and scholarly literature concerning surface plasmon resonance in general and graphene-based optical surface plasmon resonance for bio-sensing applications in particular. A summary of the research and important findings are presented in the paper's conclusion.

Review and Discussion

Just over a decade old, the field of plasmonics emerged in 2001 has become the focus of a growing amount of interest from scientists and engineers in recent years, as researchers continue to develop innovative tools and techniques that can create nanosized structures that are capable of guiding and shaping light-and-electron waves (Lee, 2009). According to Lee (2009) the field of plasmonics is expected to produce further innovations in miniaturized lasers, more efficacious treatments for cancer and even faster processing speeds for computers. As a result, the burgeoning field of surface plasmon resonance (SPR) technologies has attracted a growing amount of interest from researchers based on its reliability and high performance compared to existing sensing techniques (Maharana & Jha, 2012). According to Maharana and Jha (2012), ever since it was used for gas sensing purposes, surface plasmon resonance sensing methods have already been applied to a wide range of industrial settings, especially for biochemical detection purposes. In addition, a growing number of researchers are investigating other applications for SPR-based sensors (Maharana & Jha, 2012). The optical phenomenon upon which the SPR sensing principle is based is attributable to p-polarized light beams exiting charges of density oscillation when they achieve a certain resonance condition, which creates a surface plasmon wave (SPW) that propagates along the metal -- dielectric interface (Maharana & Jha, 2012).

According to Wu, Chu, Koh and Li (2010), surface plasmon resonance (SPR) biosensors are optical sensors that employ surface plasmon polariton waves in order to investigate the interactions that occur between biomolecules and the sensor surface. These researchers explain that surface plasmon polaritons are electromagnetic waves that are confined perpendicularly that are capable of propagating where the metal and dielectric, or sensing media, interface (Wu et al., 2010). Any changes in the concentration of biomolecules will generate concomitant localized changes in the refractive index near the metal surface in the sensing medium (Wu et al., 2010). In turn, the refractive index change will produce corresponding changes in the propagation constant of SPP that can likewise by measured optically by using the attenuated total reflection (ATR) method (Wu et al., 2010). In recent years, researchers have also investigated the non-reciprocal behavior that is associated with attenuated total reflection method for multi-layered dielectric and magnetic structures and determined that non-reciprocal behaviors produced by ATR have potential for semi-infinite magnetic materials (Fal & Camley, 2011).

A study by Maharana and Jha (2012) analyzed the unique optical properties of chalcogenide glass and grapheme to design a high performance affinity biosensor. According to Maharana and Jha (2012, p. 161), in those situations where graphene has been introduced, the sensitivity of the envisioned biosensor performance has been increased by 100% as a result of the superior detection provided by chacogenide glass vs. silica glass (Maharana & Jha, 2012). In addition, the sensor proposed by Maharana and Jha (2012) purportedly achieved a detection accuracy fully sixteen times as sensitive when compared to other techniques for measuring visible light. In this regard, Maharana and Jha (2012) report success in optimizing adequate values for crucial design parameters to achieve superior broad-wavelength range sensing performance.

These achievements have been possible because of the unique properties of oscillated electrons. In this regard, when electrons are oscillated, a phenomenon known as localized surface plasmon resonances (LSPRs) can occur in metallic nanoparticles when excited by electromagnetic fields (Vasic, Isic & Gajic, 2013). These are important features because according to Vasic and his associates, these resonances have frequencies that are highly sensitive to changes in dielectric environments that can be applied to achieve improved LSPR-based sensing applications.

These achievements have been made possible due to the properties of plasmons because when they are confined within subwavelength volumes on the metallic nanoparticle surface, it is possible to discern even very minute changes in subwavelength dielectric layers that are attached to the nanoparticles (Vasic et al., 2013). According to Vasic and his associates (2013), though, there are still difficulties concerning the matching of mid- and far-infrared frequencies wavelengths and the strata that is analyzed.

Because these variations in thickness are extremely difficult to measure and correct, scientists have investigated the use of various localized surface plasmon resonances techniques. In this regard, researchers have determined that it is possible to identify even nano-level imperfections in films that enable a virtually perfect end product every time. As Vasic and his associates (2013) point out, an LSPR remains weakly bounded to metallic surfaces because of its large negative permittivity of noble metals at certain frequencies which causes a weak sensitivity in the LSPR in response to the dielectric environment. As a result, a number of infrared sensors are constructed from planar metamaterials that are comprised of metallic resonators that generate hot spots that have strong electric fields confined within their subwavelength volumes (Vasic et al., 2003).

According to Vasic et al. (2013) graphene has significant potential for use in sensing applications. Likewise, the results of a study by Zhou, Lee, Nanda, Pantelides, Pennycook and Idribo (2012) support the use of surface plasmon resonance technologies using grapheme can even locally enhance the subnanometer scale at the single-point defect level. In addition, the results of the investigation by Zhou et al. (2012) indicates that doped monolayer graphene holds the potential for further refinements in existing applications for the development of atomic-scale nanoplasmonics and quantum plasmonic devices.

These innovations have been facilitated by the unique qualities of graphene for sensitive SPR imaging applications (Zhou et al., 2012). For example, the results of a study by Islam and Kouzani (2011) found that adding more layers of graphene sheets on top of gold layer (graphene biosensor) and using different coupling configuration of laser beam can improve the sensitivity of these imaging applications significantly. According to these researchers, graphene deposited on gold layers servesto increase the sensitivity of the plasmon resonance sensing, a feature that increases with the number of graphene layers that are applied (Islam & Kouzani, 2011).