The invention relates to a device (10) comprising a support (14) having a wave guide (42) allowing the propagation of light of at least one wavelength, generating evanescent waves outwards. According to the invention, the device comprises means for receiving a liquid sample, designed to receive the liquid sample upon contact of the wave guide (42) in such a way as to impregnate the wave guide with a portion of the liquid sample, and actuatable means for breaking the contact between the liquid sample and the wave guide (42).
