In some instances, an apparatus can include a light sensitive imaging sensor having a surface to receive a fluid sample, a body to be moved relative to the light sensitive imaging sensor and having a surface to touch a portion of the fluid sample, and a carrier to move the body toward the surface of the light sensitive imaging sensor to cause the surface of the body to touch the portion of the fluid sample, so that as the surface of the body touches the portion of the fluid, the surface of the body (i) is parallel to the surface of the light sensitive imaging sensor, and (ii) settles on top of the fluid sample independently of motion of the carrier.