Abstract: An optical biological detector is able to bind specific targeted bacterial cells by stamping an antibody grating pattern onto a silicon surface. The antibody grating alone produces insignificant optical diffraction, but upon immunocapture of the targeted cells, the optical phase change produces a diffraction pattern. Micro-contact printing provides a method for placing the antibody grating pattern directly onto a substrate surface with no additional processes or binding chemicals. Antibodies or other biologically active material may be stamped directly onto clean native oxide silicon substrates with no other chemical surface treatments. Direct binding of the antibodies to the silicon occurs in a way that still allows them to function and selectively bind antigen. The performance of the sensor was evaluated by capturing Escherichia coli O157:H7 cells on the antibody-stamped lines and measuring the intensity of the first order diffraction beam resulting from the attachment of cells.