Pixel sensor cells, e.g., CMOS optical imagers, methods of manufacturing and design structures are provided with isolation structures that prevent carrier drift to diffusion regions. The pixel sensor cell includes a photosensitive region and a gate adjacent to the photosensitive region. The pixel sensor cell further includes a diffusion region adjacent to the gate. The pixel sensor cell further includes an isolation region located below a channel region of the gate and about the photosensitive region, which prevents electrons collected in the photosensitive region to drift to the diffusion region.