In the frame of biological threat, security systems require label free biochips for rapid detection. Biosensors enable to
detect biological interactions, between probes localized at the surface of a chip, and targets present in the sample
solution. Here, we present an optical transduction, enabling 2D imaging, and consequently parallel detection of several
reactions. It is based on the absorption of biological molecules in the UV domain. Thus, it is based on an intrinsic
property of biological molecules and does not require any labelling of the biological molecules. DNA and proteins
absorb UV light at 260 and 280 nm respectively. Sensitivity is a major requirement of biosensing devices.
Configurations leading to enhancement of the interaction between light and biological molecules are of interest. For a
better sensitivity, resonant grating structures are then studied. They enable to confine the electric field close to the
biological layer. Imaging of resonant grating is not largely studied, even for visible wavelengths, but it results in good
sensitivity. The protein used in this study is the methionyl-tRNA synthetase. Its absorption is representative of protein
absorption, and it can then serve as a model for immunological detection. The best experimental contrast due to a
monolayer of proteins is 40%. With data processing currently employed for biochip imaging: average on several
acquisitions and on all the pixels imaging the biological spots, the device is able to detect a surface density of proteins in
the 10 pg/mm range.