Low-cost fabrication of graphene based field effect transistor sensors for the detection of arsenic in potable water

Arsenic, an element that exists naturally in the Earth's crust, can become airborne or contaminate groundwater and food. Exposure to arsenic can cause serious health problem and more than 200 million people, worldwide, are at risk for unsafe arsenic exposure. In this study, a graphene field effect transistor (GFET) composed of electrodes and a functionalized graphene layer was used to detect the presence of arsenic at the point of care. When a ramp voltage is applied to a reference electrode positioned near the graphene layer, a uniform electric field normal to the graphene surface is produced. Voltage gate, drain, and source electrodes configurations were studied numerically using EMS Solidworks simulations for uniformity optimization. Electrodes on the chip measure charge mobility in vicinity of Dirac point where the energy dispersion relation behaves linearly. Any change in the electrical current of the underlying graphene layer in response to the interaction of arsenic molecules with an attached active layer then is measured by an in-house curve tracer system. Concentrations of arsenic studied range from 0 to 200 ppb with linear detection sensitivity between 10ppb-100ppb of arsenic in the form of arsine gas. Repeatability studies have been performed to show the consistency of the results. The main measurement for chemical detection was the change in slope for the drain resistance within the first minute of arsine gas encountering the chip. The chip is meant to be used in tandem with a cartridge, allowing for introduction of a water sample via a port. Different types of graphene functionalization, such as dip-coating and reservoir methods were studied. Active layer coatings such as mercuric bromide and zinc bromide were also investigated. Accuracy of the system was tested by an off the shelf test kit with a sensitivity of 5ppb. In parallel, an intensive study has been performed on water quality of Boston suburbs and one New Hampshire area. The water samples were measured for their arsenic content and have been stored as sample bank for further studies.--Author's abstract