  Soft substrates decorated with micropillar arrays are known to be sensitive
to deflection due to capillary action. In this work, we demonstrate
micropillared epoxy surfaces are sensitive to single drops of bacterial
suspensions. The micropillars can show significant deformations upon
evaporation, just as capillary action does in soft substrates. The phenomenon
has been studied with five bacterial strains S. epidermidis, L. sakei, P.
aeruginosa, E. coli and B. subtilis. The results reveal that only droplets
containing motile microbes with flagella stimulate micropillar bending, which
leads to significant distortions and pillar aggregations forming dimers,
trimers, and higher order clusters. Such deformation is manifested in
characteristic patterns that are left on the microarrayed surface following
evaporation, and can be easily identified even by the naked eye. Our findings
could lay the ground for the design and fabrication of mechanically responsive
substrates, sensitive to specific types of microorganisms.
