Graphene-Derived GQDs for Virus Biosensing - University of Guelph, 2018

Ahmed, S. R. et al. (2018). Optoelectronic fowl adenovirus detection based on local electric field enhancement on graphene quantum dots and gold nanobundle hybrid. *Biosensors and Bioelectronics*. https://doi.org/10.1016/j.bios.2017.12.028

Biosensors and Bioelectronics · 2018

Researchers at the University of Guelph used ACS Material graphene to synthesize GQDs for an optoelectronic fowl adenovirus biosensor with 8.75 PFU/mL LOD.

About this research

Researchers at the University of Guelph used graphene nanopowder supplied by ACS Material, LLC (Pasadena, CA, USA; Lot No. GNCP0005) as the precursor to synthesize blue-emissive graphene quantum dots (GQDs) for an optoelectronic nanobiosensor that detects fowl adenovirus serotype 9 (FAdV-9) with a limit of detection of 8.75 PFU/mL in buffer. The biosensor combines antibody-functionalized gold nanobundles (Au NBs) electrodeposited on a carbon screen-printed electrode with antibody-conjugated GQDs. When the target virus is present, the two nanostructures are brought into nanoscale proximity through immunoreaction, and the resulting light–matter interaction under UV-visible illumination strongly enhances the electrochemical signal in a ferro/ferricyanide redox probe.

Fowl adenoviruses are responsible for inclusion body hepatitis, hydropericardium syndrome, respiratory disease, and tenosynovitis in poultry, causing significant economic losses worldwide. Current diagnostic options—virus isolation in embryonated eggs, electron microscopy, PCR, agar gel immunodiffusion, and ELISA—are laborious and time-consuming, often requiring 30+ minutes per assay plus skilled labor. There is therefore a clear unmet need for rapid, sensitive, and field-deployable virus detection platforms. Optoelectronic biosensors that exploit plasmonic coupling between metal nanostructures and fluorescent quantum dots are emerging as a promising answer, and biocompatible GQDs are particularly attractive because they avoid the toxicity concerns of cadmium-based quantum dots while retaining strong, stable photoluminescence.

The role of the ACS Material graphene in this work was to serve as the bulk carbon precursor for hydrothermal GQD synthesis. The authors mixed 0.5 mg/mL graphene nanopowder (20 mL) with 1 mL of 0.1 M L-(+)-ascorbic acid in deionized water and autoclaved the mixture for 1 h at 120 °C; ascorbic acid acted as both reducing agent and stabilizer. The resulting GQDs were yellow under daylight and intensely blue under UV excitation, with photoluminescence peaking at 405 nm and absorbance at 350 nm. HRTEM confirmed well-dispersed, uniform nanocrystals 2–3 nm in diameter with ordered lattice fringes of 0.24 nm corresponding to the (1120) plane of graphene. The starting bulk graphene was imaged separately and showed flake dimensions of a few hundred nanometers. The GQDs were then electrostatically conjugated with poly-l-lysine and anti-adenovirus antibodies for use as the signaling element of the biosensor.

The GQDs synthesized from the ACS Material graphene exhibited a photoluminescence quantum yield of 11.26%, calculated against Rhodamine 6G in ethanol (ΦF = 0.95), and an average fluorescence lifetime of 1.57 ns from a three-exponential fit. Au nanobundles were grown by a template-free layer-by-layer method using PLL and HAuCl4 with ascorbic acid reduction; at 0.01 M ascorbic acid, bundle-like structures formed with grain features ~700 nm long and 10 nm in diameter, providing many kinks and terraces for non-radiative-to-radiative light conversion. Cyclic voltammetry in 10 mM [Fe(CN)6]3−/4− at 50 mV/s showed a strong current enhancement upon GQD/Au NB hybrid formation. The current response scaled with FAdV concentration over 10–10,000 PFU/mL in buffer with an LOD of 8.75 PFU/mL, and over 50–10,000 PFU/mL in chicken blood with an LOD of 37.15 PFU/mL. The platform was approximately 100× more sensitive than the parallel ELISA (which detected down to ~1000 PFU/mL), produced a result in under one minute versus 30 minutes for ELISA, and showed strong selectivity against H1N1, H5N2, H9N2, H4N6, and H7N9 controls. Stored sensors retained signal for over 60 days under refrigeration.

The platform points toward rapid, low-cost point-of-care diagnostics for the poultry industry, where outbreaks of FAdV-related diseases cause major economic damage. More broadly, the GQD/plasmonic-nanostructure hybrid concept is applicable to detection of other avian and mammalian viruses, foodborne pathogens, and biomarkers in complex matrices such as whole blood. The authors highlight the appeal of replacing cadmium-based QDs with biocompatible graphene-derived QDs for sensing, imaging, and theranostic applications, and the template-free LbL Au nanostructure fabrication can be extended to other electrochemical sensor formats.

For researchers working on graphene-derived quantum dots, plasmonic biosensors, or photoluminescent carbon nanomaterials, the graphene nanopowder used in this study is available from ACS Material as part of its graphene series. The product performed as a reliable precursor for bottom-up hydrothermal synthesis of uniform, water-soluble GQDs with a competitive quantum yield, supporting biosensor development that achieved sub-10 PFU/mL viral detection and 100× sensitivity gain over ELISA.

How ACS Material products were used

• Graphene nanopowder (Lot No.: GNCP0005) (Graphene Series)  — “Graphene (Lot No.: GNCP0005) was bought from ACS Material, LLC (Pasadena, CA, USA).”

Product Performance in this Study

The ACS Material graphene nanopowder served as the precursor for autoclave-assisted bottom-up synthesis of monodispersed, water-soluble, blue-emissive graphene quantum dots (GQDs) with ~2-3 nm size, an 11.26% quantum yield, and a 1.57 ns lifetime. These GQDs were the essential signal-enhancing component of the optoelectronic nanohybrid biosensor.

Related product categories

• Graphene Series

Frequently asked questions

How are graphene quantum dots synthesized from bulk graphene powder?

Bottom-up hydrothermal synthesis is a common approach. In this study, 0.5 mg/mL graphene nanopowder was mixed with 0.1 M L-(+)-ascorbic acid in water and heated in a benchtop autoclave at 120 °C for 1 hour. Ascorbic acid functions simultaneously as a reducing agent and a stabilizer, yielding monodispersed blue-emissive GQDs of 2–3 nm with a quantum yield of 11.26% and a fluorescence lifetime of 1.57 ns.

Why combine graphene quantum dots with gold nanostructures for biosensing?

When fluorescent GQDs and plasmonic gold nanobundles are brought into nanoscale proximity through antibody–antigen binding, light–matter interaction creates a local electric field enhancement under UV-visible illumination. This strongly amplifies the electrochemical response in a ferro/ferricyanide redox probe, enabling sensitive optoelectronic detection. The hybrid achieved an 8.75 PFU/mL detection limit for fowl adenovirus, about 100× more sensitive than ELISA.

What advantages do graphene quantum dots offer over cadmium-based quantum dots?

Graphene quantum dots are carbon-based, biocompatible, water-soluble, and environmentally friendly, avoiding the heavy-metal toxicity of cadmium-based QDs that limits their use in clinical and food-industry applications. They retain strong, stable photoluminescence due to quantum confinement, and can be functionalized with antibodies via electrostatic conjugation with poly-l-lysine, making them well suited for bioimaging, diagnostics, and theranostic applications.