— The paper proposes an improved model and its approximation for a diffusion of a biochemical agent in the air. Based on the model, a new motion control algorithm based on the Fisher Information Matrix (FIM) for detecting and localizing a biochemical source is proposed. We show that the location of the biochemical source is an equilibrium point of the system under such control. Simulations with a single moving sensor show that that the biochemical source is located with a high degree of accuracy while the trajectory of the sensor converges to the source.