Method for observing a sample in the infrared range

A device for observing a biological sample, comprising:

• a light source, configured to emit an incident light beam at an emission wavelength comprised between 1 μm and 20 μm;
• an image sensor, comprising pixels, the pixels of the image sensor defining a detection plane;
• a holder, configured to hold the biological sample so that the biological sample is placed between the light source and the image sensor, at a distance from the detection plane smaller than 1 mm,
• wherein
• the light source is further configured to illuminate an area of the biological sample larger than 1 mm2,
• no image-forming optics are placed between the biological sample and the image sensor, and
• the image sensor is configured to acquire an image corresponding to an area of the biological sample larger than 1 mm2, the acquired image being representative of an absorption of the incident light beam, by the biological sample, at the emission wavelength;
• and
• a processing unit, configured to determine a map of an amount of an analyte in the biological sample, on the basis of the image acquired by the image sensor at the emission wavelength, the analyte absorbing light at the emission wavelength.