We present a detailed study of coupled-resonator optical waveguide (CROW) based sensors for biochemical sensing. The sensitivity dependence on the CROW structure parameters, such as intercavity distance and cavity type, is investigated for the effects in the THz region of the EM spectrum of introducing small quantities of molecules, such as DNA, in the holes. Introducing the absorptive material into the low-index medium greatly affects the shape of the propagating modes of the CROW and the transmitted E-field. The shift of the resonant frequency also depends linearly on the refractive index changes for off-resonant case (dispersive effect). (c) 2005 American Institute of Physics.