  In this article, tip-enhanced Raman spectroscopy (TERS) is investigated as a
precise method for analysis of biological samples. Using Finite Difference Time
Domain (FDTD) simulation, it has been tried to design the required structures
for analysis of these samples. At first, by comparing different TERS structures
and considering the material, dimensions and other parameters in the
simulation, the ideal structure is introduced from a physical point of view and
considering the electric field enhancement. In the following, taking into
possibility of the effect of environmental and chemical reactions during
testing on biological samples, biocompatible materials are used as substrate
coating in the simulation, and the effect of using these materials are
investigated in comparison with the previous conditions. After performing the
simulations, we concluded that Au, Cu and Ag have the highest electric field
enhancement, respectively, and the presence of Au next to Cu, also Au and Cu
next to Ag, leads to the enhancement of the electric field in them. In the
following, we found that the material and thickness of the layer under the
coating in the substrate and tip have a great effect on the enhancement.
finally, using five biocompatible materials as a coating in the case of using
the Au tip and substrate, which creates the most electric field enhancement, we
saw that the use of biocompatible materials greatly reduces the enhancement and
the use of these five materials does not differ much from each other. Anyway,
the use of a 1 nm layer of biocompatible coating creates a much more favorable
effect on enhancement than upper thicknesses.
