The construction of a specific, label-free, bacteria biosensor using porous silicon 1-D photonic crystals will be described.
Bacteria resident on the surface of porous silicon act as scattering centers for light resonant with the photonic crystal; the
diffusely scattered light possesses the optical spectrum of the underlying photonic crystal. Using a spectrometer fitted to
a light microscope, the bacteria are imaged without using exogenous dyes or labels and are quantified by measuring the
intensity of scattered light. In order to selectively bind and identify bacteria using porous Si, we use surface
modifications to reduce nonspecific binding to the surface and to engineer bacteria specificity onto the surface. Bovine
serum albumin (BSA) was adsorbed to the porous Si surface to reduce nonspecific binding of bacteria. The coatings
were then chemically activated to immobilize polyclonal antibodies specific to <i>Escherichia coli</i>. Two <i>E. coli</i> strains were
used in our study, <i>E. coli</i> DH5α and non-pathogenic enterohemorrhagic <i>Escherichia coli</i> (EHEC) strain. The nonpathogenic
<i>Vibrio cholerae</i> O1 strain was used to test for antibody specificity. Successful attachment of antibodies was
measured using fluorescence microscopy and the scattering method was used to test for bacteria binding specificity.