In this paper, our present work, which aimed at investigating a novel optical fiber biochemical sensor based on long
period grating (LPG), is introduced. Biochemical sensor is one of the most attractive fields of sensor research, especially
with the development and occurrence of all kinds of novel theory and technology such as LPG. When there is a
refraction index periodic perturbation, the guiding mode and cladding mode in LPG couple with each other. This make
the LPG is sensitive to the ambient refractive index. This means it can be a novel bio-chemical sensor when it is applied
in the fields of biochemistry. After investigating the principle of coupling in LPG, where the formulas of resonance wave
length and band width are induced by 3-layer step index model, we developed an optical fiber biochemical sensor. The
structure of its probe is designed by coating some function films whose thickness is between several tens and several
hundreds nanometers on the cladding of optical fiber. Experiments of monitoring the saline separateness process of
Bovine Serum Albumin (BSA) and Mice-Immunoglobulin G (M-IgG) by using the developed LPG sensor have been
done. The monitoring indicated that for the BSA, the saline separateness occurs when the saturation is between 50% and
60%, for the M-IgG, the percentage is between 30%-40%. Besides the monitoring, the experiments could also analyze
the effects of protein type (different molecule structure), protein consistency and saline saturation to saline separateness.
The experimental results show that the optical fiber biochemical sensor based on LPG has many advantages such as
simple structure, high sensitivity and miniature. It has a promising future in many research fields and application fields.