This paper describes a new class of thin-film mechanical sensor based on metallic nanoislands on graphene. These composite films are formed by exploiting the characteristic of graphene known as wetting transparency. That is, a thin film formed by an evaporated flux of metal atoms impinging on a graphene surface will adopt a morphology that is largely determined (at nominal thicknesses below approximately 20 nm) by the identity and surface energy of the material supporting the graphene. This control permits the formation of several technologically useful morphologies, among them are disconnected highly crystalline nanoislands that are separated from each other by gaps smaller than 10 nm. The electrical current through these films can be modulated by mechanical strain, which through mechanisms ranging from quantum tunneling at low applied strains to fracture of the graphene at higher strains can exhibit gauge factors over 1000. This sensitivity permits detection of strains ≤0.001%. This talk will describe our efforts to understand the mechanism of formation of these nanoisland-graphene sensors using atomistic dynamics simulations, and the detailed mechanism by which strain modulates the electrical resistance over a large dynamic range, from 0.001% to 10% strain. These sensors can be used to detect the pulse pressure waveform in the radial artery and contractions of stem-cell derived human cardiomyocytes. Moreover, functionalization of the metallic nanoislands with a monolayer of benzene thiolate permits us to measure a strain-modulated SERS signal. That is, tensile deformation increases the spacing between nanoislands and attenuates the SERS intensity. This optical mode of sensing can be used to generate spatially and temporally resolved maps of both the magnitude and direction of mechanical strain for structural deformation. In particular, myoblasts can be adhered to the graphene-nanoisland-polymer films and stimulated electrically. The deformations can then be optically detected in an orthogonal manner. The sensors can also be incorporated into the sidewalls of microfluidic channels for optics-free, label-free cytometry and measurements of cell stiffness.

Metallic nanoislands on graphene as sensors for measuring cell stiffness and electrophysiology

256th National Meeting (2018)

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