  If neutrinos are their own antiparticles, the otherwise-forbidden nuclear
reaction known as neutrinoless double beta decay ($\beta\beta 0\nu$) can occur,
with a characteristic lifetime which is expected to be very long, making the
suppression of backgrounds a daunting task. It has been shown that detecting
(``tagging'') the Ba$^{+2}$ dication produced in the double beta decay
${}^{136}\mathrm{Xe} \rightarrow {}^{136}$Ba$^{+2}+ 2 e + (2 \nu)$ in a high
pressure gas experiment, could lead to a virtually background free experiment.
To identify these \Bapp, chemical sensors are being explored as a key tool by
the NEXT collaboration . Although used in many fields, the application of such
chemosensors to the field of particle physics is totally novel and requires
experimental demonstration of their suitability in the ultra-dry environment of
a xenon gas chamber. Here we use a combination of complementary surface science
techniques to unambiguously show that Ba$^{+2}$ ions can be trapped (chelated)
in vacuum by an organic molecule, the so-called fluorescent bicolour indicator
(FBI) (one of the chemosensors developed by NEXT), immobilized on a surface. We
unravel the ion capture mechanism once the molecules are immobilised on Au(111)
surface and explain the origin of the emission fluorescence shift associated to
the trapping of different ions. Moreover, we prove that chelation also takes
place on a technologically relevant substrate, as such, demonstrating the
feasibility of using FBI indicators as building blocks of a Ba$^{+2}$ detector.
