Detection of hexavalent chromium in ground water using a single microcantilever sensor

We report the detection of hexavalent chromium, Cr(VI), in ground water from the US Department of Energy Hanford site using a single microcantilever coated with a self-assembled monolayer of 4-mercaptopyridine. These experiments show that CrO₄ ^2- ions can be detected with the microcantilever sensor in the presence of significant concentrations (>1000 μg/L) of Ca²⁺, Cl^-, Mg²⁺, NO₃ ^-, K⁺, Na⁺, and SO₄ ^2-ions, as well as a variety of other ions of smaller concentrations. The chromate concentrations were also measured using the Hach spectrophotometric kit, which is widely used for chromate monitoring. The microcantilever measurements are an order of magnitude more sensitive compared to the photometric method, and may be deployed for in situ detection of chromium in ground water. The microcantilever measurements are in good agreement with the photometric measurements for the higher concentration samples. To our knowledge, this is the first reported detection of a target species in a complex matrix by a single microcantilever.