Label-free detection using a whispering-gallery mode biosensor in a micro fluidic channel is simulated. The analyte transport in the solution is controlled by applied electric potentials and diffusion. The finite element method is employed for solving the charged species transportation equations, the Poisson equation, the equations of conservation of momentum and energy, and the Helmholtz equations for electromagnetic waves. The adsorption process of analyte on the micro resonator surface is monitored by the resonance wavelength shift in the sensor. Shift caused by temperature variation due to Joule heating is found to be negligible compared to that induced by analyte deposition. The deposition induced shifts behave in a manner similar to Langmuir-like adsorption kinetics. A linear correlation between the frequency shift and the analyte concentration in the solution is obtained. The applied voltage is found to affect the adsorption capability; and thus, the sensor sensitivity. Detection of very low concentration to the sub-ppm level using the sensor is demonstrated.