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We present a portable and easy-to-use biosensor platform, allowing for label-free detection of diagnostic markers in undiluted animal serum. Exemplarily, this is shown for the detection of anti-Salmonella antibodies. 1-lambda-Reflectometry was used as detection method, making the new biosensor platform portable, cheap, and robust. As recognition elements, lipopolysaccharides (LPSs) from Salmonella typhimurium bacteria were immobilized as sensitive layer on the transducer to carry out serological tests via a direct assay format. For this purpose, a new surface preparation protocol has been worked out allowing for immobilization of the LPS via hydrophobic interactions. It has been shown that results obtained by 1-lambda-Reflectometry are equivalent to those obtained by the non-portable Reflectometric Interference Spectroscopy setup. The new sensor platform was calibrated in both matrices, buffer and undiluted serum. Good sensitivity, selectivity and intra chip reproducibility have been observed. Furthermore, inter chip reproducibility was examined and recovery rates were found to be between 99 and 117% in undiluted serum.

A novel combined procedure for estrogen-affinity purification and labelling of estrogen receptor alpha ligand-binding domain with Cy 5.5 cystein reactive dye was established. By using this procedure, mainly functional proteins are recovered. It can be easily adapted to a large variety of other proteins for which ligand-coated affinity materials are available. The labelled receptor was used in a total internal reflection fluorescence-based binding inhibition assay for determination of the impact of pollutants in river water on the receptor. The great advantage compared to conventional methods is that the total effect on the receptor is measured instead of concentrations of single compounds and that even currently unknown ligands are found as well. Therefore, the obtained signal is related to the response of the organism, which is exposed to the water. The limit of detection was found to be 0.139 nM of estradiol equivalents. The assay also provides a highly sensitive tool for pharmaceutical research and can be adapted to diagnostic applications.