Optical methods for observing samples and for detecting or metering chemical or biological species

A process for observing a sample, comprising the steps:

• a) providing a sample support comprising a transparent substrate (ST) on which is deposited a coating comprising at least one layer, termed contrast-amplifying layer, having a complex refractive index with an imaginary part κ greater than or equal to 0.001;
• b) placing the sample to be observed on said coating comprising the contrast-amplifying layer;
• c) directing onto said sample, through said substrate, a spatially incoherent and not polarized light beam, focused so as to form an illumination cone having an aperture half-angle θ greater than or equal to 20°;
• and
• d) observing said sample through an objective and said substrate;
• said contrast-amplifying layer being proportioned so that said sample is observed with a higher contrast than in the absence of said support,
• wherein a thickness of said contrast-amplifying layer is determined so as to optimize, for at least one illumination wavelength, the contrast integrated on said illumination cone with which would be observed a reference sample made up of a variation in thickness of said contrast-amplifying layer.