Professor Owen Guy, Director of Swansea University's Centre for Nanohealth, spoke to AZoNano about his research into graphene biosensors; which hold the promise of the rapid and accurate detection of disease in it's early stages.
Could you provide our readers with an overview of your current research interests at Swansea University?
I am based at the Centre for NanoHealth at Swansea University, which is a collaboration between medicine and engineering. The general focus of our research is to apply nanotechnology solutions to healthcare. As part of our research we are working on graphene sensors, particularly graphene biosensors, to develop point of care early diagnosis sensors for diseases such as cancer, dementia and stroke.
We also develop microfluidic technology, such as micro-channels and micro-needles, and we are working on linking the sensor and microfluidics technology together in a complete packaged device.
Could you explain what a biological sensor (biosensor) is and how they work?
In basic terms a bio sensor is a sensor, or transducer element, which is able to detect a particular bio marker. Ideally you want this detection to be sensitive and selective. You want it to be sensitive to clinically relevant concentrations and you want it to be specific, so you only detect the molecule of interest. You don't want any interference from other molecules that are present in complex solutions such as blood, saliva, or urine.
What is a biomarker? Image Credits: CADET Manchester YouTube
In terms of how a sensor works, there are many different types of sensor and they can rely on electrochemical, electrical or optical detection. Our sensors are based on electrochemical detection where the interaction of a bio marker with a bio receptor, which is attached to the sensor surface, produces a change in the electrical resistance of the sensor.
What are the main types of graphene sensors currently available?
There are graphene-based gas sensors which can detect single molecules, so they are very sensitive. There are also a lot of printed sensor technologies using various types of graphene inks or nano-graphite particle inks, which are similar to carbon nanotube based printed sensors.
These are in the format screen printed electrodes, which are three electrode printed systems. They are relatively cheap to produce and buy, but they don't offer the same kind of performance as, for example, the high-end gas sensors that people are producing in physics laboratories.
People are now developing lithography based graphene sensors or patterned graphene sensors using CVD graphene or epitaxial graphene. Methods like this will probably produce sensors that perform better. A ChemFET type (chemical field-effect transistor) sensor, would be able to go down to single molecule detection potentially.
That is an overview of what is currently available. At the moment I don't think there are too many commercial sensors for disease applications, but they are being developed.
What are the advantages of choosing graphene as a material to use when creating a biosensor?
Graphene is a wonder material and it is widely reported for its exceptional properties. Obviously the high surface area to volume ratio of graphene is very important. Any interaction of the surface is amplified by this very high surface to volume ratio. Also graphene has extremely good electrical properties, so any changes on a graphene sensors surface can produce a strong effect.
Graphene is a single-layered, extended, 2D carbon lattice. Image Credits: Mopic/shutterstock.com
Graphene is also inert when compared to structures containing silicon meaning it does not degrade over time, it doesn’t oxidize, so it should produce a much more stable sensor performance. It also has a range of surface chemistry's which can be used to modify the graphene surface and make it amenable to detecting different bio markers.
Could you provide some examples of diseases and conditions which graphene biosensors can/could be used to diagnose?
We have been developing prototype sensors for a range of diseases. The biosensors could be potentially used for future cancer diagnostics. We have looked at oxidative stress markers related to prostate cancer. We are now looking at markers related to stroke, deep vein thrombosis and blood clotting disorders.
We have done some preliminary work on cardiac disease using molecules like troponins as markers. We currently have a big project looking at dementia markers, such as those for Alzheimer's disease. Our method could then be used in a wider context for the detection of drugs or their metabolites, for example, in a cannabis sensor, or for pharmaceutical drugs - so a very broad range of applications from diseases to drugs sensors and the detection of markers related to wellbeing and health.
Why is the early diagnosis and monitoring of diseases and conditions so vitally important?
It is all about better treatment with early diagnosis. If you can detect early, then you can treat early, intervene and provide a better therapeutic outcome and successful treatment outcomes. That is what it is all about, early detection and rapid diagnosis, giving a higher chance of success of therapies.
How can the surface chemistry of graphene be functionalised in order to create a biosensor device?
There are a lot of surface chemistries available for graphene. These are reasonably well known because they have been developed for graphite and carbon nanotubes. So those technologies are translatable to graphene. A lot of work has been done on graphene oxide. We don't work on graphene oxide though and only focus on graphene, as graphene oxide doesn't have the same conductivity as graphene.
We are looking to functionalize pristine graphene and we can achieve this with amino silane chemistry. It is a common method using a molecule called an APTES, where the amino silane molecule directly functionalizes graphene. We can also use diazonium chemistry and plasma chemistry as well, where we treat the graphene surface with an excited ammonia plasma gas.
The aim of these methods is to connect an amino group to the graphene surface, which can then be used to recognise and attach to biomolecules. We’ve used amino chemistry but you can also use carboxy chemistry to achieve this. Carboxylic acid groups on the graphene surface are also capable of recognising and binding to biomolecules.
How do the surface and electrical properties of graphene change after functionalisation?
In general terms, when you perform a covalent functionalization, you are introducing sp3, diamond-type, bonds into graphene. Whereas in pristine graphene, carbon atoms are sp2 hybridised, meaning they have graphite-like bonds. When you covalently functionalize graphene you remove sp2 bonding character which results in a reduction in the electrical conductivity.
You need to be careful that you don't destroy the conductivity of graphene during the functionalization process. There is a bit of a trade-off between the degree of functionalization and the maintenance of graphene’s electrical performance.
Diagram showing how the functionalised graphene can interact with compounds and proteins in a fluid sample
Once you have initially functionalized the graphene you can then attach things like antibodies. If these are charged then they can have an additional effect on the overall conductivity meaning it can actually increase again or decrease further. This change in conductivity really depends on things like the charge and size of the molecule.
How can graphene biosensors be integrated with point of care microfluidics?
We are doing a lot of work on this at the moment. There's a big challenge in connecting the graphene chip to something like a printed circuit board. We’re trying to develop interconnects between the PCB and the graphene chip and subsequently integrate these with a microfluidic chip, which has fluid channels running over the graphene device.
There are techniques available for these processes; we are currently using techniques which were developed for producing lab on chip technology and to produce silicon semiconductor MEMS (micro electrical mechanical systems). We are using this kind of technology to integrate microfluidic channels onto the surface of the graphene chip, or indeed to produce a microfluidic chip and then bond that to a graphene chip.
At the moment it is quite a challenging area but the technologies are already available, they just need to be integrated together.
How much is the global biosensors market currently valued at and how is the market forecast to grow over the next three years?
At the moment, the global point of care market is around about fifteen billion dollars. This is set to grow at about four and a half percent per annum, and predicted to reach about nineteen billion by 2018.
When do you think graphene biosensors will be universal across the healthcare sector for the detection of common diseases and conditions?
I think over the next three years, we are going to see sensors emerging for the wellbeing markets, or sensors for non life threatening diseases, and also for health and sports applications. And then following that, we are probably going to see some sensors for drug metabolites or we could see some sensors emerge in the detection of brain injury and cardiac or stroke markers. These kinds of sensors are going to be introduced over the next three to ten years.
Where can our readers find out more information about your research on graphene biosensors?
We’ve a number of publications (below), which people might be interested in.
- "Generic Epitaxial Graphene Biosensors for Ultrasensitive Detection of Cancer Risk Biomarker" by Tehrani, Zari; Burwell, Gergory; Mohd Azmi, Mohd Azraie; Castaing, Ambroise; Rickman, Robbert; Almarashi, Jamal; Dunstan, Peter; Miran Beigi, Ali Akbar; Doak, Shareen; and Guy, Owen, 2D Materials. 2014, 1, 025004 doi:10.1088/2053-1583/1/2/025004
- “Effects of a modular two-step ozone-water and annealing process on silicon carbide graphene”, Webb, Matthew J. and Polley, Craig and Dirscherl, Kai and Burwell, Gregory and Palmgren, Pål and Niu, Yuran and Lundstedt, Anna and Zakharov, Alexei A. and Guy, Owen J. and Balasubramanian, Thiagarajan and Yakimova, Rositsa and Grennberg, Helena, Applied Physics Letters, 105, 081602 (2014), DOI:http://dx.doi.org/10.1063/1.4893781
- “Investigation of the utility of cellulose acetate butyrate in minimal residue graphene transfer, lithography, and plasma treatments”, Gregory Burwell, Nathan Smith and Owen Guy, Microelectronic Engineering 146 (2015) 81–84.
- “Chitosan/AuNPs Modified Graphene Electrochemical Sensor for Label-Free Human Chorionic Gonadotropin Detection” Teixeira, Sofia; Ferreira, Nadia S.; Conlan, Robert Steven; Guy, OJ; Sales, MGF, ELECTROANALYSIS Volume: 26 Issue: 12 Pages: 2591-2598 ( 2014).
- Teixeira, S. Conlan, S. Guy, O. & Sales, M. (2014). Label-free human chorionic gonadotropin detection at picogram levels using oriented antibodies bound to graphene screen printed electrodes. Journal of Materials Chemistry B, doi:10.1039/C3TB21235A
- Teixeira, S. Burwell, G. Castaing, A. Gonzalez, D. Conlan, R. & Guy, O. (2014). Epitaxial graphene immunosensor for human chorionic gonadotropin. Sensors and Actuators B: Chemical, 190, 723-729. doi:10.1016/j.snb.2013.09.019.
- Novel single-wall carbon nanotube screen-printed electrode as an immunosensor for human chorionic gonadotropin, Sofia Teixeira, Robert Steven Conlan, Owen J Guy, Maria Goreti Ferreira Sales, Electrochimica Acta 01/ 2014; 136(1):323-329.
About Professor Owen J Guy
Prof. Owen J Guy is a Professor at the College of Engineering, Swansea University, working in nano/micro fabrication, MNs, microfluidics, devices and silicon nanowire and graphene sensors for healthcare applications. His research is funded by the Engineering and Physical Science Research Council and Innovate UK. His primary current research areas are graphene biosensors and integration with Point of Care microfluidics and electronics technology.
OJG gained a 1st class BSc in Chemistry and the Ayling prize for highest degree in Chemistry at Swansea University in 1997. He was awarded the Leonard Hinkel prize for his PhD (Chemistry) in 2001 for work on the photodegradation of ink-jet dyes in collaboration with Zeneca. His research background also includes materials science and electronics. In 2007 he became an RCUK fellow in nanomedicine and lecturer at Swansea.
Recent projects include: the top ranked EPSRC Grand Challenge in Nanohealth EP/G061882/1 (2009-2012) - developing a micro-needle sampling / drug delivery system, an EPSRC funded project developing graphene biosensors and industry collaboration projects with partner SPTS Technologies, developing nanostructure and microneedle technology.
He is also director of Swansea’s new £21m Centre for Nanohealth (CNH); a new nano-device fabrication facility dedicated to providing nanotechnology solutions for healthcare.
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