Raman-scattered photons from a molecule can directly reveal the signature of vibrational energy states of the molecule and their intensities can be greatly enhanced by plasmonic nanostructures or surfaces of plasmonic materials,which leads to high sensitivity.Therefore,surface enhanced Raman spectroscopy(SERS)attracts more and more attentions in bioanalysis recently.The probability of spontaneous Raman scattering is directly proportionally to the photon density of state(DOS)at related frequency.Therefore,structures that can increase DOS are desired in SERS applications.Photonic crystal(PC),which has periodic nanostructures relevant to the length of light,has photonic band gaps that forbidden the propagation of light in some frequency range.