Multiplexed detection of heavy metal ions by single plasmonic nanosensors

Detection of multiple analytes simultaneously in small liquid samples with high efficiency and precision is highly important to the fields like water quality monitoring. In this letter, we present a multiplexed nanosensors with position-encoded aptamer functionalized gold nanorods for heavy metal ions detection. The individual gold nanorods respond specifically to two different heavy metal ions (Pb²⁺ and Hg²⁺) with a spectral shift in the scattering spectrum. We used a home-built spectral imaging dark-field microscope to measure the response of thousands of single plasmonic nanosensors with relatively high time resolution and precision. To explore the performance and limit of detection (LOD) of our nanosensor and setup, we recorded the concentration-dependent response of our position-encoded nanosensors with a series of mixture solutions that contain different concentrations of Hg²⁺ and Pb²⁺ ions. The LOD levels of our system are around 5 nM for Pb²⁺ ions and 1 nM for Hg²⁺ ions. Our method and results demostrate the nanomolar sensitivity and the potential to detect more different heavy metal ions.