  Photonic crystal-based biosensors hold great promise as valid and low-cost
devices for real-time monitoring of a variety of biotargets. Given the high
processability and easiness of read-out even for unskilled operators, these
systems can be highly appealing for the detection of bacterial contaminants in
food and water. Here, we propose a novel hybrid plasmonic/photonic device that
is responsive to Escherichia coli, which is one of the most hazardous
pathogenic bacterium. Our system consists of a thin layer of silver, a metal
that exhibits both a plasmonic behavior and a well-known biocidal activity, on
top of a solution processed 1D photonic crystal. We attribute the
bio-responsivity to the modification of the dielectric properties of the silver
film upon bacterial contamination, an effect that likely stems from the
formation of polarization charges at the Ag/bacterium interface within a sort
of bio-doping mechanism. Interestingly, this triggers a blue-shift in the
photonic response. This work demonstrates that our hybrid plasmonic/photonic
device can be a low-cost and portable platform for the detection of common
contaminants in food and water.
