Demonstration of Selective Single-Barium Ion Detection with Dry Diazacrown Ether Naphthalimide Turn-on Chemosensors

Abstract

Single molecule fluorescence detection of barium is investigated for enhancing the sensitivity and robustness of a neutrinoless double beta decay (0νββ) search in 136 Xe, the discovery of which would alter our understanding of the nature of neutrinos and the early history of the Universe. A key developmental step is the synthesis of bariumselective chemosensors capable of incorporation into ongoing experiments in high-pressure 136 Xe gas. Here we report turn-on fluorescent naphthalimide chemosensors containing monoaza-and diaza-crown ethers as agents for single Ba 2+ detection. Monoaza-18-crown-6 ether naphthalimide sensors showed sensitivity primarily to Ba 2+ and Hg 2+ , whereas two diaza-18-crown-6 ether naphthalimides revealed a desirable selectivity toward Ba 2+ . Solution-phase fluorescence and NMR experiments support a photoinduced electron transfer mechanism enabling turn-on fluorescence sensing in the presence of barium ions. Changes in ion-receptor interactions enable effective selectivity between competitive barium, mercury, and potassium ions, with detailed calculations correctly predicting fluorescence responses. With these molecules, dry-phase single Ba 2+ ion imaging with turnon fluorescence is realized using oil-free microscopy techniques. This represents a significant advance toward a practical method of single Ba 2+ detection within large volumes of 136 Xe, plausibly enabling a background-free technique to search for the hypothetical process of 0νββ.

The Dynamics of Ions on Phased Radio-frequency Carpets in High Pressure Gases and Application for Barium Tagging in Xenon Gas Time Projection Chambers

“…sensitivity though dramatic reduction of backgrounds from radiogenic and cosmogenic activity. Barium tagging is an area of intense R&D within the neutrinoless double beta decay community [16,17,18,19,20,21,22,23,24,25,26,27,28], and several techniques have now been demonstrated for single barium ion imaging in xenon [29,20,22]. Ion collection and extraction from a ton to multi-ton scale volume of liquid or high pressure gas remains major unsolved problem, however [28,30].…”

Bicolour fluorescent molecular sensors for cations: design and experimental validation

“…31,32 A promising "wet" barium tagging experiment has been reported as a proof of concept. 33 In order to reproduce the required "dry" conditions imposed by these experiments, several interesting barium-tagging sensors have been reported so far, 34,35 all of them based on PET off-on fluorescent emission, which poses issues in terms of background noise. Therefore, the development of suitable on-on' bicolour fluorescent sensors would generate suitable barium-tagging devices.…”

Preparation and properties of a novel polystyrene solid-phase fluorescence pH sensor based on a naphthalimide derivative

“…13 Naphthalimide and its derivatives have high fluorescence quantum yields, large Stokes shifts, and good stability, making them suitable as fluorescence sensors. 14 The naphthalimide structure is a well-known building block that is often employed for the formation of luminescent sensors based on photoinduced electron transfer (PET) design. These molecules are very sensitive to substitution at the 4-position of the naphthalimide ring due to the "push-pull" nature of the internal charge transfer excited state, giving rise to a charge separated excited state.…”