For the first time Bragg diffraction at a thick light grating has been shown for polyatomic organic molecules, in particular the dye phthalocyanine and the antibiotic ciprofloxacin. The resulting diffraction pattern shows a strong angular dependence and an asymmetric distribution of diffraction intensities. For detection of the interference pattern fluorescence microscopy has been used. As an alternative approach a detector currently under development made out of bacteria is presented. In

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... st to all matter wave interference experiments done so far, the spatially-resolved detection is done using living organisms. The detection mechanism is based on the biological activity of the antibiotic in bacteria. Crucially for the success of this approach is the survival of the bacteria in vacuum and their immobilization, both in vacuum and during later growth. By fixing them onto a 150 µm thick dried film of agar with a probability of surviving vacuum of about 35 % both goals could be met.