DNA and protein absorption at 260 and 280 nm can be used to reveal theses species on a biochip UV
image. A first study including the design and fabrication of UV reflective multilayer biochips designed for
UV contrast enhancement (factor of 4.0) together with spectrally selective AlGaN detectors demonstrated the
control of chip biological coating, or Antigen/Antibody complexation with fairly good signals for typical
probe density of 4x1012 molecules/cm2.
Detection of fractional monolayer molecular binding requires a higher contrast enhancement which
can be obtained with structured chips. Grating structures enable, at resonance, a confinement of light at the
biochip surface, and thus a large interaction between the biological molecule and the lightwave field. The
highest sensitivity obtained with grating-based biochip usually concerns a resonance shift, in wavelength or
diffraction angle. Diffraction efficiency is also affected by UV absorption, due to enhanced light-matter
interaction, and this mechanism is equally able to produce biochip images in parallel.
By adjusting grating parameters, we will see how a biochip that is highly sensitive to UV absorption
at its surface can be obtained. Based on the Ewald construction and diffraction diagram, instrumental
resolution and smarter experimental configurations are considered. Notably, in conjunction with the 2D UV-sensitive
detectors recently developed in-house, we discuss the obtainment of large contrast and good signals
in a diffraction order emerging around the sample normal.