Background: One of the important molecules in the human body is protein. The proteins
are incredibly complex chains of smaller molecules namely amino acids. After the invention of biosensor,
optical sensing mechanisms received considerable attention in the applications of the chemical
and biochemical sensors in various applications such as industrial process control. Photonic crystals
(PhCs) are as an attractive sensing platforms due to the control light in very small dimensions.
The photonic crystals can control and guide the photons in the periodic lattice. In this paper, an optical
biochemical sensor is presented based on photonic crystal nano-ring resonators for detection of
Methods: In biochemical sensors, the effective refractive index of sensing hole can be changed by
binding the biomolecule to the sensing hole. The resonant wavelength of the transmission spectrum
or intensity of the transmission spectrum can be shifted resulting from refractive index variations.
The proposed biochemical sensor constructed by photonic crystal nano-ring resonator using twodimensional
PhC is designed and simulated. In our design, the hexagonal lattice of air holes in the
dielectric slab is used.
Results: Two-dimensional finite-difference time-domain (2-D FDTD) method is used for simulating
the propagation of electromagnetism wave and plane-wave expansion (PWE) approach is applied to
analyze the proposed sensor. Biochemical sensor is presented for identifying small changes in the
refractive index. The detection of protein concentration from 0% to 35% as one of its applications
has been presented. The biochemical sensor structure includes a ring resonator shaped by consecutive
curves and two waveguides. By binding protein concentration into the sensing hole, the refractive
index of sensing hole is changed and the intensity of the transmission spectrum is shifted to the
lower values. The results reveal that the quality factor and the sensitivity of proposed biochemical
sensor are respectively obtained about 2960 and 925.02 a.u./RIU.
Conclusion: The biochemical sensor structure includes a ring resonator and two waveguides. The
ring resonator is shaped by consecutive curves. By binding protein concentration into the sensing
hole, the refractive index of sensing hole is changed and the intensity of the transmission spectrum is
shifted to lower values. By increasing the protein concentration of the sensing hole, the intensity of
the transmission spectrum is shifted to lower values. The normalized curve of the intensity of the
transmission spectrum shows approximately linear relationship between the protein concentration
and intensity shift.