A hybrid biosensor based on a graphene resistor functionalized with self-assembled Graphene-AuNPs (Gold Nanoparticles) is demonstrated for the real-time detection of hepatitis B surface antigen (HBsAg). The hybrid biosensor consists of a ssDNA sequence attached to a graphene resistor device via π–π stacking interactions in combination with a ssDNA functionalized AuNP. The ssDNA has complementary sequences which through hybridization, yield the graphene-AuNP hybrid biosensor. Real-time 2-point resistance measurements, performed using varying concentrations of HBsAg, show a linear dependence of resistance change against the logarithm of HBsAg concentration (log[HBsAg]). A limit of detection of 50 pg ml⁻¹ was observed. Moreover, the hybrid biosensor platform has potential to be applied to any biomarker of interest.

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene’s exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

A real-time sensor for the detection of amyl butyrate (AB) utilising human olfactory receptor 2AG1 (OR2AG1), a G-protein coupled receptor (GPCR) consisting of seven transmembrane domains, immobilized onto a graphene resistor is demonstrated. Using CVD graphene as the sensor platform, allows greater potential for more sensitive detection than similar sensors based on carbon nanotubes, gold or graphene oxide platforms. A specific graphene resistor sensor was fabricated and modified via non-covalent π–π stacking of 1,5 diaminonaphthalene (DAN) onto the graphene channel, and subsequent anchoring of the OR2AG1 receptor to the DAN molecule using glutaraldehyde coupling. Binding between the target odorant, amyl butyrate, and the OR2AG1 receptor protein generated a change in resistance of the graphene resistor sensor. The functionalized graphene resistor sensors exhibited a linear sensor response between 0.1–500 pM and high selectively towards amyl butyrate, with a sensitivity as low as 500 fM, whilst control measurements using non-specific esters, produced a negligible sensor response. The approach described here provides an alternative sensing platform that can be used in bioelectronic nose applications.

Infectious disease outbreaks remain an ever‐prevalent global issue. The associated demand for rapid diagnostics and onsite testing will play an increasing and critical role in disease surveillance, prevention of the spread of infection, as well as timely commencement of treatment. Reported here is a graphene–gold nanoparticle hybrid sensor platform technology that is demonstrated for the real‐time detection of viral proteins utilizing low volume samples (5 μL). Hepatitis C virus (HCV) is still an endemic problem worldwide and is used as an exemplar system here to demonstrate the capability of the platform viral detection sensor technology. Hepatitis C virus core antigen (HCVcAg) is a promising marker for point‐of‐care (POC) diagnostic testing for active HCV infection, with the potential to provide a one‐stop diagnosis and trigger for the commencement of treatment. Real‐time electrical resistance measurements are performed using various concentrations of HCVcAg with linear concentration dependence of resistance on HCVcAg concentration over the range of 100–750 pg mL⁻¹.