  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.
