In Situ Microfluidic SERS Chip for Ultrasensitive Hg²⁺ Sensing Based on I^–-Functionalized Silver Aggregates

Mercury(II) ions are causing serious environmental pollution and health damage. Developing a simple, rapid, and sensitive sensor for Hg2+ detection is of great significance. Herein, we demonstrate an I–-functionalized surface-enhanced Raman scattering (SERS) substrate for rapid and sensitive Hg2+ sensing on a highly integrated microfluidic platform. Based on the combination reaction between I– and Hg2+, the Hg2+ sensing is achieved via the SERS intensity “turn-off” strategy, where HgI2 precipitation is formed on an SERS substrate interface, dissociating the Raman reporters that coadsorbed with I–. Owing to the strong binding constant between I– and Hg2+, our I–-functionalized substrate demonstrates a very fast sensing response (∼150 s). Through reliable in situ SERS detection, a robust calibration curve between the “turn-off” signal and “lgC” is obtained in a broad concentration range of 10–9 to 10–13 M. Additionally, the detectable Hg2+ concentration can be as low as 1 fM. The good selectivity toward Hg2+ is also verified by testing about a dozen common metal ions in water, such as K+, Na+, Ca2+, Mg2+, and so forth. Furthermore, we apply the SERS sensor for real tap and lake water sample detection, and good recoveries of 113, 97, and 107% are obtained. With its advantages of high integration, simple preparation, fast response, high sensitivity, and reliability, the proposed I–-functionalized SERS sensor microfluidic chip can be a promising platform for real-time and on-site Hg2+ detection in natural water.