Development of an electrochemical bioassay based on the alkaline phosphatase activity of Chlamydomonas reinhardtii to assess the toxicity of heavy metals

A novel electrochemical bioassay for the rapid and sensitive evaluation of heavy metals toxicity was developed using the alkaline phosphatase activity of Chlamydomonas reinhardtii (C. reinhardtii). The inhibition of alkaline phosphatase activity caused by heavy metals was measured by quantifying the oxidation of p-aminophenol (PAP), which was produced from the enzymatic reaction of a p-aminophenyl phosphate (PAPP) substrate. The quantification of PAP oxidation was performed via cyclic voltammetry in a micro-droplet on a screen-printed carbon electrode (SPCE). The heavy metals concentrations that produced a 50% inhibition of enzymatic activity (EC₅₀) for Cu, Pb, Cd, Zn, and Hg were 8.18, 0.10, 0.27, 1.99, and 0.07 μmol L^-1, respectively. The present method was compared with a micro-scaled algal growth inhibition test (μ-AGI) whereby the obtained values of EC₅₀ were 36.2, 7.7, 8.5, 29.1, and 2.6 μmol L^-1 for Cu, Pb, Cd, Zn, and Hg, respectively. By comparison with a conventional AGI test, the proposed method was much more sensitive and faster.