Biosensing with Back-gated Graphene Field Effect Transistors

Abstract

The widespread existence of the heavy metal lead in the environment is a severe threat to the health of humans. Lead is a neurotoxin that accumulates over time in the body restricting the cognitive, behavioural and psychological development of children. Since water is one exposure route for chemical hazards like Pb2+ it is envisioned that monitoring drinking water sources with low-cost, sensitive and field-suitable devices is one way that human exposure can be limited. Herein presents graphene field effect transistors (GFETs) functionalised with aptamers as bioreceptors, for the specific detection of Pb2+ ions in water. Functionalising GFETs with bioreceptors facilitates the specific detection of target analytes. Traditionally antibodies have been used to do this but owing to their poor stability, high expense and batch to batch variability the recent trend in biosensing technologies has focussed on the functionalisation of short-base single stranded DNA chains called aptamers. Herein, their immobilisation on sensor surfaces is demonstrated in two ways; indirectly, using the intermediary bi-directional molecule 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE) and directly, exploiting aptamers modified with pyrene groups able to stack directly on the graphene surface. This work provides an evaluation of these two immobilisation strategies for the detection of Pb2+. Alongside the development of these sensors, this contribution presents robust characterisation and testing strategies for the GFET devices in order to improve the confidence in the conclusions made about metrics describing their essential features. Open-source, customisable and innovative data analysis packages are also introduced in this work which facilitate the rapid, facile and detailed manipulation of large data sets arising from characterisation techniques. These tools dramatically decrease the time between data acquisition and analysis allowing new insights into how the GFETs are working to be uncovered.