A self-assembled monolayers based conductometric algal whole cell biosensor for water monitoring

This work describes the design of a conductometric biosensor intended to monitor aquatic environments. The biosensor is based on the measurement of Alkaline Phosphatase Activity (APA) of the microalgae Chlorella vulgaris. This activity is inhibited in the presence of heavy metals. The purpose of this article is to obtain a tool for detection of heavy metals through inhibition of APA. The biosensor is composed of two parts: two platinum interdigitated electrodes which form the transducer, and the microalgae, the bioreceptor. The microalgae were immobilized on self-assembled monolayers (SAMs) of alkanethiolate. The change in the local conductivity of the electrodes following the addition of the substrate allowed us to measure alkaline phosphatase activity of Chlorella vulgaris. Good repeatability (RSD < 5%) and reproducibility between different biosensors (RSD < 10%) were obtained. Lifetime is estimated to be 17 days. The originality of this work consists in the immobilization of algal cells on self-assembled monolayers. The advantage of the SAMs is that they do not form a physical barrier between the algae and the constituents of the reaction medium (whether the reaction substrate, or the toxic components are to be detected). In addition, these sensors permit to obtain good measurement repeatability. Detection limit of cadmium reaches ppb levels.