# Progress toward Barium Tagging in High Pressure Xenon Gas with Single Molecule Fluorescence Imaging

## TL;DR

This paper reports progress in developing single molecule fluorescence imaging techniques for barium ion tagging in high pressure xenon gas, aiming to enable background-free neutrinoless double beta decay detection.

## Contribution

Introduction of new custom fluorescent dyes and dry-phase chemosensors significantly improving barium ion detection in xenon gas.

## Key findings

- Demonstrated single barium dication sensitivity with SMFI.
- Developed dyes with stronger barium response than commercial calcium sensors.
- First dry-phase chemosensor for barium ions in this context.

## Abstract

We present an update on the development of techniques to adapt Single Molecule Fluorescent Imaging for the tagging of individual barium ions in high pressure xenon gas detectors, with the goal of realizing a background-free neutrinoless double beta decay technology. Previously reported progress is reviewed, including the recent demonstration of single barium dication sensitivity using SMFI. We then describe two important advances: 1) the development of a new class of custom barium sensing fluorescent dyes, which exhibit a significantly stronger response to barium than commercial calcium sensing compounds in aqueous solution; 2) the first demonstration of a dry-phase chemosensor for barium ions. This proceeding documents work presented at the 9th Symposium on Large TPCs for Rare Event Detection in Paris, France.