Abstract: The invention relates to the field of chemistry and diagnosis, more in particular to diagnosis of current and/or past and/or symptomless infections or of a history of exposure to a gram-negative-bacterium (such as an enterobacteriaceae or a legionella). Even more in particular, the invention relates to the screening of animals or animal products for the presence of un-wanted/undesired microorganisms. The invention further relates to a method for screening samples for the presence of antibodies directed against unwanted/undesired microorganisms and preferably such a method is performed with help of a biosensor. The invention also relates to a method for immobilising polysaccharides to solid surfaces. The invention furthermore provides solid surfaces with immobilised polysaccharides as well as applications of such surfaces.