Continuum and Particle methods were employed to simulate ion channels to study their characteristic properties like ion permeation and selectivity in order to demonstrate ion channels as biosensors. Fast, efficient and accurate simulators for modeling the conduction, selectivity and sensitivity of ionic channels have been developed. The continuum simulators were based on 3-D Poisson-Nernst-Planck (PNP) theories and stochastic dynamics. The transport coefficients and parameters (such as mobility, diffusivity, permittivity, etc.) were extracted from molecular dynamic simulations and from experimentation. The continuum theories are being tested by extensive experimentation to establish the range of validity of the PNP theories.