The Graphene Invention: From Nobel Prize to SPR Application
Until recently, 2-D crystals (monolayers of atomic particles forming gigantic 2D molecules) were thought to be thermodynamically unstable. Conventional wisdom judged them to be of such low quality that they were unsuitable for most scientific and medical applications.
This all changed when Konstantin Novoselov and Andre Geim published their discovery of graphene (Science, 2004), which is a monolayer of carbon forming a 2-D lattice. Novoselov and Geim found that graphene is of very high quality and capable of extraordinary electrodynamic properties.
Subsequently, the “graphene gold rush” began. Surface plasmon resonance researchers have been exploring its numerous applications for biosensor chip design ever since. Graphene has led to the discovery of many new and potentially life-saving therapies.
Graphene has many advantages when applied as a monolayer atop a conventional gold SPR sensor. Compared to gold alone, graphene's large surface area affords a higher absorption of biomolecules. This makes it easier to amplify the signal and increases sensitivity. The refractive index of the graphene layer on top of the gold results in a higher refractive index.
Currently, SPR's sensitivity is only restricted by the instrument's ability to detect pixel changes by its onboard camera. SPR is capable of detecting surface plasmon polaritons (SPP) to help detect nanometer changes in thickness, density fluctuations and molecular absorption beyond what's capable of visible light's diffraction limit.
Graphene's conductivity modifies the SPPs and permits detection of changes beyond the diffraction limit, thus increasing the sensitivity of the instrument. Graphene fabrication is relatively simple and cheap; allowing scientists to customize their sensors for their particular experiments making it very friendly usable, cost efficient and dynamic.
Currently, scientists have begun fabricating and chemically altering graphene to create new materials. Graphene oxide and graphene oxide sheets have improved upon recent advances. Scientists using graphene oxide sheets (GOS)-based SPR chips compared to conventional Au-filmed-based sensors yielded a 100 fold increase in the BSA concentration detection limit. The affinity constant was 5.2 times higher than the conventional chip and the anti-BSA protein-protein concentration limit of detection was 75.75 nM.
If they increased the BSA concentration to 378.78 nM, the GOS sensor's angle shift doubled (compared to the Au-film chip). Other scientists were able to see a 25-fold decrease in non-specific binding. The graphene oxide chips' noise:signal ratio was lower than that of graphene chips.
Graphene-based chips have already been used to help scientists and clinicians to more efficiently detect changes in patient samples. The serum levels of (leukemia and kidney disease) patients were measured against a healthy control group. Patients' samples contained elevated levels of lysozyme, so clinicians now believe the enzyme can be used as a marker.
Using graphene-based chips, scientists are now able to detect the subtle changes that had previously been invisible to a conventional Au-film sensor. Crohn's disease is marked by pathogenic E. coli adhesion to epithelial cells; a diagnostic tool now available to clinicians.
Graphene-based sensors reduce the need for chemically modified antibodies for immunoassays; increasing the potential for advances in immunology.
These are just a few examples of how scientists have begun incorporating the new graphene technology into the highly sensitive and increasingly dynamic SPR platform systems like those offered by Reichert Technologies.
The discovery of graphene and the unfolding of its conductive and chemical properties make it an extremely promising avenue of SPR research and development. In 2015, Moscow Institute of Physics and Technology (MIPT) researchers submitted patents to the US Patent office for massive-scale graphene and graphene oxide SPR biosensor chips development. Graphene and graphene oxide sensor chips will soon be available for researchers here in the US.
Developers are excited about the implications for research and clinical application. Projected benefits include cost savings, reduced sample acquisition timeframes and shorter processing time. Such sensor technology advancements should benefit high throughput SPR instruments, such as the Reichert4SPR.
The high sensitivity of the Reichert4SPR, in combination with graphene or graphene oxide biosensors, may be able to provide scientists with an unprecedented ability to screen, detect and analyze data.