Parts per trillion detection of heavy metals in as-is tap water using carbon nanotube microelectrodes

Heavy metal contamination of drinking water is a major global issue. Research reports across the globe show contamination of heavy metals higher than the set standards of the World Health Organization (WHO) and US Environmental Protection Agency (EPA). To our knowledge, no electrochemical sensor for heavy metals with parts per trillion (PPT) limits of detection (LOD) in as-is tap water has been reported or developed. Here, we report a microelectrode that consists of six highly densified carbon nanotube fiber (HD-CNTf) cross sections called rods (diameter ∼69 μm and length ∼40 μm) in a single platform for the ultra-sensitive detection of heavy metals in tap water and simulated drinking water. The HD-CNTf rods microelectrode was evaluated for the individual and simultaneous determination of trace level of heavy metal ions i.e. Cu²⁺, Pb²⁺ and Cd²⁺ in Cincinnati tap water (without supporting electrolyte) and simulated drinking water using square wave stripping voltammetry (SWSV). The microsensor exhibited a broad linear detection range with an excellent limit of detection for individual Cu²⁺, Pb²⁺ and Cd²⁺ of 6.0 nM, (376 ppt), 0.45 nM (92 ppt) and 0.24 nM (27 ppt) in tap water and 0.32 nM (20 ppt), 0.26 nM (55 ppt) and 0.25 nM (28 ppt) in simulated drinking water, respectively. The microelectrode was shown to detect Pb²⁺ ions well below the WHO and EPA limits in a broad range of water quality conditions reported for temperature and conductivity in the range of 5 °C-45 °C and 55 to 600 μS/cm, respectively.