Device for use in the detection of binding affinities, the device comprising a substrate devoid of a waveguide, the substrate comprising a planar surface having arranged thereon a plurality of binding sites capable of binding with a target molecule, the device further comprising a predetermined beam generation location, a predetermined detection location and a beam stop which is arranged on the surface of the substrate, to, in operation, prevent propagation of non-diffracted portions of a beam of coherent light of a predetermined wavelength generated at the beam generation location and incident on the binding sites with the bound target molecule to the predetermined detection location, characterized in that the binding sites are arranged on the planar surface along a plurality of adjacently arranged curved lines which are spaced from one another by a distance to, in operation, cause the beam of coherent light of the predetermined wavelength generated at the predetermined beam generation location relative to the plurality of adjacently arranged curved lines and incident on the binding sites with the bound target molecule to be diffracted at the binding sites with the bound target molecule in a manner such that diffracted portions of the incident beam of coherent light interfere at the predetermined detection location relative to the plurality of adjacently arranged curved lines with a difference in optical path length which is a multiple integer of the predetermined wavelength of the coherent light to provide a signal representative of the binding affinity of the binding sites and the target molecule, in that the device further comprises a carrier having the predetermined beam generation location and the predetermined detection location arranged thereon, the carrier being arranged with respect to the substrate such that the predetermined beam generation location and the predetermined detection location are arranged in a common plane which is parallel to the planar surface of the substrate, and in that each line of the plurality of curved lines is arranged on the planar surface of the substrate such that the total path length of the incident coherent light from the predetermined beam generation location to the binding sites arranged on the respective same curved line plus the diffracted portion of the coherent light from the binding sites on the same curved line to the predetermined detection location is constant for all binding sites on the same curved line, with the curved lines being geometrically defined in an x,y-plane at the planar surface of the substrate by the following equation: y j 2 = j 0 + j λ 2 n s 2 + 2 n s ξ x j j 0 + j λ 2 − f 2 + ξ 2 + x j 2 wherein j 0, j is an integer, λ is the predetermined vacuum wavelength of the coherent light, n s is the refractive index of the substrate, ξ is half distance between the beam generation location and the detection location and is non-zero, and f is a number which corresponds to the distance between the center of the curved lines and the detection location. j 0, j is an integer, λ is the predetermined vacuum wavelength of the coherent light, n s is the refractive index of the substrate, ξ is half distance between the beam generation location and the detection location and is non-zero, and f is a number which corresponds to the distance between the center of the curved lines and the detection location.