Silicon photonic biosensors using SiNx/SiO2 waveguides fabricated in a commercial CMOS process are read out with an
integrated polysilicon photodetector array buried under the waveguide. Increased surface refractive index, such as that
generated by the specific binding of target molecules, locally decreases evanescent coupling to the detector array
resulting in reduced photocurrent from elements under the higher index region. The operating principle of this local
evanescent array coupled (LEAC) sensor differs from those of other waveguide sensors and has been explored using
numerical simulations. Experimental studies have been performed using adsorbed bovine serum albumin (BSA)
nanofilms as well as antigen-antibody pairs.