1. A method comprising: providing a first volume of a sample at a sensor surface of an imaging sensor, mixing, at the sensor surface of the imaging sensor, at least part of the sample to provide a second volume of the sample at the sensor surface, capturing an image of the first volume and an image of the second volume by lensless optical microscopy using the imaging sensor, and based on the images, deriving information related to units present in the first volume and in the second volume.