Biosensors for detection of Hepatitis markers
Authors:   , Walters Ffion 
Published: February 2023

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.