A sensor platform for use in sample analysis comprises a substrate (30) of
refractive index (n.sub.1) and a thin, optically transparent layer (32) of
refractive index (n.sub.2) on the substrate, (n.sub.2) is greater than
(n.sub.1). The platform incorporates one or multiple corrugated structures
in the form of periodic grooves (31), (33), which defines one or more
sensing areas each for one or more capture elements. The grooves are so
profiled, dimensioned and oriented that when coherent light is incident on
the platform it is diffracted into individual beams or diffraction order
resulting in reduction of the transmitted beam and an abnormal high
reflection of the incident light thereby creates an enhanced evanescent
field at the surface of the or each sensing area. The amplitude of this
field at the resonant condition is greater by an order of approximately
100 than the field of prior art platforms so that the luminescence
intensity created from samples on the platform is also increased by a
factor of 100. Also disclosed are an apparatus incorporating the platform
and a method of using the platform. Further increases of amplitude have
been detected by using light having a linear component which gives rise to
TM excitation and/or irradiating the platform from the substrate side.
