We have developed a simple, colorimetric iron telluride (FeTe) nanorods (NRs) based system for the detection of mercury, mainly based on the cation exchange reaction between FeTe NRs and Hg(2+). FeTe NRs (length, 105±21nm) react with Hg(2+) to form HgTe NRs (length, 112±26nm) and consequently release Fe(2+) ions that catalyzes the oxidation between a peroxidase substrate 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) and H(2)O(2). The concentration of Fe(2+) and thereby Hg(2+) can be determined by measuring the absorbance of the ABTS oxidized product at 418nm. This approach allows the detection of Hg(2+), with a limit of detection of 1.31nM at a signal-to-noise ratio 3 and a linear range 5-100nM (R(2)=0.99). The low-cost, simple, sensitive, and reproducible assay has been validated for the detection of Hg(2+) in a blood sample (SRM 955c), with the result being in good agreement with that provided by National Institute of Standards and Technology.