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, with increasing global travel and trade increasing the risk of rapid disease spread to pandemic levels. [1] This is exemplified by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic from 2019. One specific issue that has been highlighted by the pandemic is the need for methods to achieve rapid, accurate diagnostics for infectious diseases, not just for coronaviruses, but for other major diseases as well. Rapid diagnostics and onsite testing will therefore play a critical role in facilitating early intervention and treatment [2] of diseases. Large-scale testing and rapid onsite diagnostic decisions are crucial for surveillance monitoring of disease outbreaks and infection spread. In future, this data will enable swift decision-making and management to help prevent the spread of epidemic and pandemic infectious disease outbreaks. [1,3,4] In this work, we use the chronic hepatitis C virus (HCV) as a model infectious disease to demonstrate a viral detection platform sensor. HCV is still endemic in populations around the world and is a major cause of liver cirrhosis and hepatocellular carcinoma, affecting around 71 million people worldwide. [5] HCV deaths exceed annual deaths due to HIV, malaria, and tuberculosis. [6] Consequently, the World Health Organization (WHO) aims to eliminate HCV by 2030, [7,8] with a strategy to target an increase in HCV

Recently, the miniaturisation of immunoassay platforms has meant an enormous push towards point-of-care (POC) sensor devices. POC sensors have wide applications but are especially beneficial in resource-limited settings. Furthermore, infectious diseases such as hepatitis have become endemic in populations worldwide. Therefore, there are strong drivers to develop sensitive, cheap and portable diagnostic devices to diagnose such infections. Although multiple sensor formats have been examined, graphene has emerged as a material to impart the high sensitivity required for POC diagnostics. Affinity biosensors based on a graphene field-effect transistor (GFET) or resistor design utilise graphene’s exceptional electrical properties. Therefore, it is critical when designing these sensors that the electrical properties of graphene are maintained throughout the functionalisation process. To that end, noncovalent functionalisation may be preferred over covalent modification. Therefore, graphitic surfaces were functionalised noncovalently via a drop-cast method. Successful modification of graphene with 1,5 Diaminonaphthalene (DAN) via a drop-cast technique was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and real-time resistance measurements. Furthermore, an investigation into the effect of sequential wash steps, which are required in biosensor manufacture, confirmed that the functional layer was not removed, even after multiple solvent exposures. Although highly desirable, the high sensitivity of graphene means it is also susceptible to high background signals from the sample media; the signal-to-background ratio can potentially be improved by using signal enhancements. These enhancements may enable the sensitivity needed to provide one-stop diagnosis and commencement of treatment for resource-limited settings. A hybrid biosensor based on a graphene resistor functionalised with self-assembled graphene-AuNPs (Gold Nanoparticles) is demonstrated for the real-time detection of hepatitis B surface antigen (HBsAg). 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 the potential to be applied to any biomarker of interest. Towards the realisation of POC sensors for resource-limited settings and one-stop diagnosis, compatibility of the sensors with fingerstick (FS) sample collection will be highly desirable. A graphene-gold nanoparticle hybrid sensor platform technology is reported in this work that demonstrates the real-time detection of viral proteins utilising low volume samples (5 µL). Hepatitis C Virus (HCV) is still an endemic problem worldwide and is used as an example here to demonstrate the platform viral detection sensor technology. Real-time resistance measurements were performed for various concentrations of HCVcAg, showing a linear concentration dependence in the concentration range of 100 -750 pg/mL.