Exceptional electronic properties, surface sensitivity & selectivity, inferred by functionalisation, makes graphene ideal for sensor applications. Novel, generic, real-time monitoring sensor technology, based on chemically modified graphene transducers, will be demonstrated for food safety applications, detecting peanut (Ara h 1-9) allergens in food products. Trace quantities of nuts can be present in food processing plants at very low concentrations & can trigger an immune response in allergic individuals, ranging from hives to severe gastrointestinal & respiratory symptoms, & in serious cases - anaphylactic shock.
Where there is a possibility of cross-contamination, food producers are obliged to label products or recall incorrectly labelled products - costing industry millions (£5m/recall incidence) & producing negative publicity. Our sensor system, developed for in-situ smart monitoring of food & food processing units, would enable instant and low-cost allergen monitoring. Using chemically modified graphene, integrated into a packaged allergen sensor, for in situ monitoring would offer end-user Unilever a real breakthrough in monitoring for trace nut contaminants.
The sensor technology uses a graphene channel functionalised with a receptor molecule - capable of selective & specific detection of a particular allergen. Chemical functionalisation methods, for attaching antibodies to graphene, have already been developed by the consortium. This project will use antibodies targeted against peanut allergens as the receptors. Commercial sensor production requires large area, uniform, electronic-grade graphene - on an insulating substrate. UCAM
will develop "Transfer free" graphene on pre-patterned Ge could providing a step change in graphene electronics. In parallel, work will be performed on graphene grown on copper - transferred onto SiO2/Si wafers - mitigating risk by enabling device and functionalisation work to be completed prior to the availability of graphene/ Germanium.
Characterisation of these materials (NPL) is essential to providing uniform graphene with consistent and controlled electrical properties. NPL will analyse layer thicknesses, uniformity, defect densities and electrical performance following growth and also subsequent to chemical modification of graphene. PG will transfer existing graphene device fabrication process to large area CVD graphene on SiO2/Si & pre-patterned graphene on Ge wafers to fabricate graphene Chemical Field Effect Transistors. Chem-FETs comprise a graphene channel, patterned via lithography & subsequent oxygen plasma etch, between two metal (Ti/Au) contacts. Large area fabrication will reduce individual sensor costs. Based on current pricing wafer & processing costs of £1000 & using 4mm square chips, yields a cost of £2.22 per sensor. This could be reduced to £0.55 per chip by using a 2mm square chip. As the price of graphene comes down, this cost could be further reduced. Amine surface chemistry, developed under previous EPSRC grants [OJ Guy], will be used by PG to attach allergen-specific antibodies. Novel electrochemical diazonium functionalisation developed for antibody attachment to graphene will be used along with new plasma amine termination processes, before (a) amide coupling to the antibody & (b) blocking non-specific binding sites. Allergen binding to modified graphenes surface induces a gating effect, which can be electrically/electrochemically detected. PG and NPL will characterise functionalised graphene (XPS, I-V, CV, Raman, SKPM). PG's prototype sensors would ultimately be integrated into a model food processing unit at Unilever & used to detect trace quantities of allergens.
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