Spectroscopy of Individual Ion in Liquid Environments

Understanding individual ions in solution is critical to advancing our knowledge of complex chemical systems; however, detecting and tracking ions at the single-ion level in liquid environments remains challenging. Here, we present a novel strategy to visualize and differentiate ions in liquids using optically active point defects in hexagonal boron nitride (h-BN) as sensitive ion sensors. Interactions between ions and these point defects alter their emission properties, enabling real-time detection and visualization of single ions. Using Li+ ions in organic electrolytes as a demonstration, we observed spectral shifts exceeding 10 nm upon addition of Li+, and over 50 nm under applied electric fields, attributed to interactions between Li+ and h-BN defects. We further successfully differentiated multiple ion types (Na+, Zn2+, Al3+) in aqueous solutions. Each ion’s unique electronic structure induces characteristic spectroscopic signatures upon interaction with h-BN defects. This sensing approach enables direct, spectroscopic visualization and differentiation of single ions, providing valuable insights into ion dynamics and chemical reactions. The platform holds significant potential for diverse applications in battery technologies, environmental monitoring, and beyond.