Refractive index mapping of single cells with a graphene-based optical sensor

Graphene-based optical sensors exhibit good performance in cell refractive index (RI) measurements, with high resolution and large detection depths. In this manuscript, we report an RI mapping method based on the polarization-sensitive light absorption of graphene, in focused scanning mode. Several RI mapping images of normal and cancerous human colonic cells have been obtained. A high-numerical-aperture microscope objective is used to minimize the focusing spot size. Under optimized conditions, the experimental spatial resolution reaches 2.34 μm. A ring-shaped perfect optical vortex beam with a tunable diameter is generated to control the incident angles, and the experimental RI resolution is 9.3 × 10−4 refractive index units. The large longitudinal penetration depth of the graphene evanescent field allows the recognition of RI difference between two individual cancer cells. The RI distribution and morphology of the cells can be determined, and different carcinogenesis stages can also be concluded from the image. This method has potential in biomedical sciences, especially in cell imaging, differentiation, and sorting.