Single-Ion Sensing in Liquid Using Fluorescent h-BN Point Defects

TL;DR

This paper introduces a novel optical sensing platform using fluorescent defects in hexagonal boron nitride to detect and distinguish single ions in liquids based on spectral shifts, enabling real-time, high-resolution analysis of ionic states.

Contribution

The study demonstrates a new method for single-ion detection in liquids using h-BN defects, with enhanced spectral shifts under electric fields, allowing chemical state analysis of various ions.

Findings

Spectral shifts >10 nm upon ion addition

Enhanced shifts >40 nm with electric field

Differentiation of ions like Na+, Mg2+, Al3+ based on spectral response

Abstract

Understanding the chemical state of individual ions in solutions is crucial for advancing knowledge of complex systems. However, sensing systems at the single-ion level in liquid environments remains a significant challenge. A strategy is introduced that leverages the optical emission properties of point defects in hexagonal boron nitride (h-BN) as single ion sensors. The interaction of optically active h-BN defects with ions in solution leads to distinct spectral shifts, enabling precise visualization and analyzing of individual ions. Using Li+ ions in organic electrolytes as a model, spectral shifts exceeding 10 nm were observed upon ion addition. Application of an external electric field further enhanced these shifts to over 40 nm, enabling real-time monitoring of electrical field induced local perturbations of Li+ ions. Through this approach, individual point defects were shown to spectroscopically distinguish ions of varying charges (e.g., Na+, Mg2+, and Al3+) based on their local electrical field, each producing a distinct spectral shift. This platform allows direct sensing of ions and their chemical states in liquid environments, providing insights into subtle interfacial changes at the single-ion level, with measurable spectral shifts detectable at millisecond temporal resolution and at concentrations down to 10 micromolar range. This capability presents potential applications in various fields involving ions in liquids that include battery technology and environmental science.