A whole cell based amperometric biosensor was fabricated using unicellular microalgae Chlorella sp. as the biocatalyst, entrapped in a polymeric membrane directly interfaced to the surface of a platinum electrode for the detection of bioavailable heavy metal ions like zinc, copper, cadmium, cobalt and nickel with a life time of 7 days. The proposed system is sensitive to a lower concentration range of 10⁻⁹ M of nickel ions, 10⁻¹⁰ M of cadmium and cobalt ions, 10⁻¹¹ M of copper and zinc ions. The amperometric biosensor responds to heavy metal ions with a relative selectivity in the order: Zn²⁺ > Cu²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺. The proposed analytical method has been validated with atomic absorption spectroscopy for heavy metal detection in real time samples.