We developed metamaterial mesh sensors (MM sensors) for the detection of whole cells, such as tumor cells. In this study, we were able to capture HeLa cells (a tumor cell model) in diluted bovine blood by filtration through an MM sensor with a mesh aperture of 1.8 micro meter. Subsequently, we could detect the cells with high sensitivity from band shifts of the infrared transmittance. The surface of an MM sensor made of nickel was coated with gold (Au) using a sputtering process, resulting in enhancement of surface wetting properties and transmittance band selectivity. This treatment reduced nonspecific attachment of cells on the surface, thereby improving the size selectivity of filtration. For example, due to its small size, Escherichia coli was not captured by the mesh aperture. Moreover, erythrocytes were not captured on the mesh, even though their average size is larger than the mesh aperture. On the other, HeLa cells were selectively captured from a mixture containing excess amounts of erythrocytes. These features may be beneficial for the detection of circulating tumor cells (CTCs) from patient blood samples. This improved MM sensor, which has unique optical properties that would be useful for label-free detection, could be used as a simple device for fractionating mixtures of whole cells.