For the detection of molecular interaction, a novel approach of the guided-mode resonance (GMR) spectroscopy identifies molecules via specific bindings with their ligands immobilized on the grating surface is presented. The structure of GMR device generally consists of two stages -- upper grating layer and waveguide layer. When the wide-band light illuminating, the GMR device inhibits on a specific resonant narrow-band of wavelength, and allows for other wavelength to transmit. The specific resonant narrow-band of wavelength results in the diffraction of the incident wide-band wave and the selection in the waveguide layer. This is very useful in highly sensitive measurement, especially for the variations in the refractive index of bulk media, and for the monitoring of variations in the thickness of thin film. In the simulation, one Si3N4 (n=2) GMR device is designed. When the wavelength of the illumination ranges from 1520nm to 1620nm, the resonant peak wavelength will shift 0.03nm as per
1nm bio-layer (nbio 1.3) has been attached on. Finally, on the basis of the theoretical analysis, the optimization of a spectral GMR sensor in terms of the operation wavelength has been carried out.