Graphene, among the many interesting predicted applications, is an excellent material for biosensing and medical purposes. Graphenea's scientific team collaborated with researchers from France's CNRS and SENSIA SL to utilize graphene as a DNA biosensor and to destroy harmful bacteria.

Image: Detection of DNA hybridization with the help of graphene.

Carbon, the only ingredient of graphene, has very low toxicity, and is thus interesting for use in human health. The peculiar response that graphene has to light turns out to also come in handy for medical applications. For example, graphene absorbs 2.3% of incident light over the entire visible part of the spectrum, which is remarkably high absorption for a single atomic layer. Graphene oxide absorbs even more, converting the incident light into heat. Heat generation by nanoparticles has earlier been used for the destruction of cancer cells, and recently even graphene oxide itself served the same purpose. However, our result is the first to consider using the same approach to target harmful bacteria, in this case exemplified by Escherichia coli (E. coli).

Like any other pathogen, E. coli, typically associated with infections of the urinary tract, reproduces quickly, posing a major threat to human health and society at large. Many bacterial infections share several dangerous characteristics such as chronic inflammation and tissue damage, which are greatly exacerbated when microorganisms grow in continuous “biofilms”. The threat of biofilm-related infections has grown in the past decades due to bacteria becoming resistant to antibiotics, a phenomenon that is closely related with the overuse and misuse of antibiotics. 

Considering the increased resistance of bacteria to antibiotics, non-biocidal strategies for getting rid of bacteria are being considered. Recent advances in nanotechnology have provided the foundation for using near-infrared (NIR) light-absorbing gold nanostructures in the treatment of bacterial infections via irradiation with focused laser pulses at suitable wavelengths. Light absorbed by the gold nanostructures can efficiently be converted into localized heat energy and used for the hyperthermic destruction of pathogens. Gold nanostructures absorb light in the NIR (700-900 nm) part of the spectrum, which safely passes through biological tissue. However, a concern with gold nanorods is the toxicity of the surfactant chemical used in their production.

An alternative material recently considered for photothermal therapy is reduced graphene oxide (rGO), which is also a good absorber of light. rGO-based nanocomposites have been proposed for cancer theranostics, however this approach has sparsely been applied to the destruction of pathogens. This is even more surprising when considering that graphene oxide is widely available on the market.

In our recent paper, published in the Journal of Materials Chemistry B, we studied the possibility to kill E. coli pathogens using reduced graphene oxide (rGO-PEG-NH2) and Au nanorods (Nrs) coated with rGO-PEG-NH2 by laser irradiation. The encapsulation of Au NRs with rGO-PEG not only decreases the toxicity of Au NRs, but also enhances the overall photothermal process and thus the temperatures which can be reached. We demonstrated 99% killing efficiency of bacteria in a water solution, at low concentrations (20-49 mg/ml). We've thus shown that graphene oxide acts as a good anti-pathogen agent, and we believe that our research is just a start of a promising new direction of using rGO as a medicine.

In a separate paper as part of the same collaboration, researchers have shown that a graphene layer on gold can act as an excellent sensor of DNA hybridization, with amazing attomolar sensitivity.

Our work, entitled “Highly Sensitive Detection of DNA Hybridization on Commercialized Graphene-Coated Surface Plasmon Resonance Interfaces” and published in the journal Analytical Chemistry, demonstrated sensitivity of detection of DNA with a concentration of a few attomoles, using a commercial (SENSIA SL) surface plasmon resonance instrument. In the work, we used our high quality CVD graphene grown on metal and transferred onto the detection chip.

Graphenea strives to continue its research excellence through intensive collaboration with the world's leading scientists, pushing the frontiers of the knowledge and applications of graphene.