Fluorescent bicolour sensor for low-background neutrinoless double β decay experiments

Demonstration of event position reconstruction based on diffusion in the NEXT-white detector

Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from 83mKr calibration electron captures (E ∼ 45  keV), the position of origin of low-energy events is determined to 2 cm precision with bias < 1 mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E ≥ 1.5  MeV), from radiogenic electrons, yielding a precision of 3 cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Qββ in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.

Preparation and mechanism study of hydrogen bond induced enhanced composited gelatin microsphere probe

Fluorescent probes offer rapid and efficient detection of metal ions. However, their properties, including high biotoxicity and low detection limits, often limit their utility in biological systems. In this study, we used a microfluidic approach to fabricate photocrosslinked gelatin microspheres with a micropore, providing a straightforward method for loading fluorescent probes into these microspheres based on the adsorption effect and hydrogen bonding interaction. The gelatin microsphere loaded probes, GelMA/TPA-DAP and GelMA/TPA-ISO-HNO were designed and obtained. The results show that these probes exhibit obviously low biotoxicity compared to the original molecular probes TPA-DAP and TPA-ISO-HNO. Simultaneously, it is found that GelMA/TPA-DAP and GelMA/TPA-ISO-HNO have better detection sensitivity, the detection limits are 35.4 nM for Cu2+, 16.5 nM for Co2+ and 20.5 nM for Ni2+ for GelMA/TPA-DAP probe. Compared to the original TPA-DAP they are improved by 37.2 %, 26.3 % and 22.6 % respectively. The corresponding coordination constants were 10.8 × 105, 4.11×105 and 6.04×105, which is larger than homologous TPA-DAP. Similar results were also verified in the GelMA/TPA-ISO-HNO probe. The mechanism was investigated in detail by theoretical simulations and advanced spectral analysis. The density functional theory (DFT) simulations show that the probes are anchored inside the microspheres and the molecular structure is modified due to the hydrogen bonding interaction between the microsphere and the molecular probe, which makes GelMA/TPA-DAP exhibit stronger coordination capacity with metal ions than homologous TPA-DAP. In addition, the adsorption effect also provided some synergistic enhancement contribution. Meanwhile, cellular experiments have also shown that the composite microspheres can improve the biocompatibility of the probe and will provide a wider range of applications towards bioassay. This simple and effective method will provide a convenient way to improve the performance of fluorescent probes and their biological applications.

Selective and pH-Independent Detection of Ba2+ in Water by a Benzo-21-crown-7-Functionalized BODIPY

Herein, we report on highly Ba2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo-21-crown-7 as a Ba2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba2+ induced fluorescence enhancement (FE) by a factor of 12±1 independently of the pH value and a high Ba2+ sensitivity with a limit of detection (LOD) of (17.2±0.3) μM. Moreover, a second fluorescent probe consisting of the same BODIPY fluorophore, but a benzo-18-crown-6 as a cation-responsive binding moiety, showed an even higher FE upon Ba2+ complexation by a factor of 85±3 and a lower LOD of (13±3) μM albeit a lower Ba2+ selectivity. The fluorescence sensing mechanism of Ba2+ was further investigated by time-resolved fluorescence as well as transient absorption spectroscopy (TAS) and it turned out that within these probes a blocking of a photoinduced electron transfer (PET) by Ba2+ is very likely responsible for the FE.

Synthesis of a novel triphenylamine-based multifunctional fluorescent probe for continuous recognition application

In this paper, a novel fluorescent probe, TPA-PAT, with continuous recognition based on triphenylamine was designed, synthesized, and characterized by NMR, IR, and fluorescence spectrophotometry techniques.

Ba+2 ion trapping using organic submonolayer for ultra-low background neutrinoless double beta detector

If neutrinos are their own antiparticles the otherwise-forbidden nuclear reaction known as neutrinoless double beta decay can occur. The very long lifetime expected for these exceptional events makes its detection a daunting task. In order to conduct an almost background-free experiment, the NEXT collaboration is investigating novel synthetic molecular sensors that may capture the Ba dication produced in the decay of certain Xe isotopes in a high-pressure gas experiment. The use of such molecular detectors immobilized on surfaces must be explored in the ultra-dry environment of a xenon gas chamber. Here, using a combination of highly sensitive surface science techniques in ultra-high vacuum, we demonstrate the possibility of employing the so-called Fluorescent Bicolor Indicator as the molecular component of the sensor. We unravel the ion capture process for these molecular indicators immobilized on a surface and explain the origin of the emission fluorescence shift associated to the ion trapping.

Solvent-polarity reconfigurable fluorescent 4-piperazino-N-aryl-1,8-naphthalimide crown ether logic gates

Four compounds 1-4 were designed and synthesised, comprising a 4-amino-N-aryl-1,8-naphthalimide fluorophore, a piperazine receptor, and an aryl group, as fluorescent logic gates. At the imide position, the substituent is phenyl (1), 1,2-dimethoxyphenyl (2), benzo-15-crown-5 (3), or benzo-18-crown-6 (4). Molecules 1 and 2 are constructed according to a fluorophore-spacer-receptor format, while 3 and 4 are engineered according to a receptor1-spacer1-fluorophore-spacer2-receptor2 format based on photoinduced electron transfer and internal charge transfer mechanisms. The compounds were studied in water, water/methanol mixtures of different ratios, and methanol by UV-visible absorption and steady-state fluorescence spectroscopy, as a function of pH, metal ions and solvent polarity. The excited state of 1-4 is 8.4 ± 0.2 in water, 7.6 ± 0.1 in 1 : 1 (v/v) water/methanol, and 7.1 ± 0.3 in methanol. The of 3 in water is 0.92 and the and of 4 in water are 2.3 and 2.9. 1H NMR data in D2O and CD3OD confirm H+ interaction at the piperazine moiety, and Na+ and Ba2+ binding at the benzo-15-crown-5 and benzo-18-crown-6 moieties of 3 and 4. By altering the solvent polarity, the fluorescent logic gates can be reconfigured between TRANSFER logic and AND logic. Molecules with polarity reconfigurable logic could be useful tools for probing the microenvironment of cellular membranes and protein interfaces.

Bicolour fluorescent molecular sensors for cations: design and experimental validation

Molecular entities whose fluorescence spectra are different when they bind metal cations are termed bicolour fluorescent molecular sensors. The basic design criteria of this kind of compound are presented and the different fluorescent responses are discussed in terms of their chemical behaviour and electronic features. These latter elements include intramolecular charge transfer (ICT), formation of intramolecular and intermolecular excimer/exciplex complexes and Förster resonance energy transfer (FRET). Changes in the electronic properties of the fluorophore based on the decoupling between its constitutive units upon metal binding are also discussed. The possibility of generating fluorescent bicolour indicators that can capture metal cations in the gas phase and at solid-gas interfaces is also discussed.

Preparation and properties of a dual-function cellulose nanofiber-based bionic biosensor for detecting silver ions and acetylcholinesterase

A dual-function cellulose nanofiber (CNF)-based bionic biosensor with good biocompatibility was developed for detecting Ag⁺ and acetylcholinesterase (AChE) by grafting deoxyribonucleic acid (DNA) onto CNF. The Ag⁺ ions captured by the biosensor acted as recognition sites for the detection of AChE. The CNF-based bionic biosensor (CNF-DNA) could detect Ag⁺ concentrations as low as 10^-6 nM in the presence of interference metal ions (Hg²⁺, Ba²⁺, Cd²⁺, Mg²⁺, Mn²⁺, Pb²⁺, and Zn²⁺). DNA-template silver nanoclusters (DNA-AgNCs) were formed on the surface of CNF-DNA during the detection of Ag⁺ (CNF-DNA-AgNCs). This new strategy yielded CNF-DNA-AgNCs through the adsorption of Ag⁺ ions onto the cytosine base of the single-stranded DNA in CNF-DNA without the use of any additional reducer. Meanwhile, the CNF-DNA-AgNCs exhibited excellent sensitivity and selectivity for trace levels (0.053 mU/mL) of AChE in the presence of interference reagents. The novel strategy proposed in this paper may establish a foundation for further research on DNA-template AgNCs for developing biosensors and biomarkers for in vivo and in vitro detection.

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

Single-molecule fluorescence imaging (SMFI) of gas-phase ions has been proposed for "barium tagging," a burgeoning area of research in particle physics to detect individual barium daughter ions. This has potential to significantly enhance the sensitivity of searches for neutrinoless double-beta decay (0νββ) that is obscured by background radiation events. The chemistry required to make such sensitive detection of Ba²⁺ by SMFI in dry Xe gas at solid interfaces has implications for solid-phase detection methods but has not been demonstrated. Here, we synthesized simple, robust, and effective Ba²⁺-selective chemosensors capable of function within ultrapure high-pressure ¹³⁶Xe gas. Turn-on fluorescent naphthalimide-(di)azacrown ether chemosensors were Ba²⁺-selective and achieved SMFI in a polyacrylamide matrix. Fluorescence and NMR experiments supported a photoinduced electron transfer mechanism for turn-on sensing. Ba²⁺ selectivity was achieved with computational calculations correctly predicting the fluorescence responses of sensors to barium, mercury, and potassium ions. With these molecules, dry-phase single-Ba²⁺ ion imaging with turn-on fluorescence was realized using an oil-free microscopy technique for the first time-a significant advance toward single-Ba²⁺ ion detection within large volumes of ¹³⁶Xe, plausibly enabling a background-independent technique to search for the hypothetical process of 0νββ.

Cosmogenic Activation in Double Beta Decay Experiments

Double beta decay is a very rare nuclear process and, therefore, experiments intended to detect it must be operated deep underground and in ultra-low background conditions. Long-lived radioisotopes produced by the previous exposure of materials to cosmic rays on the Earth’s surface or even underground can become problematic for the required sensitivity. Here, the studies developed to quantify and reduce the activation yields in detectors and materials used in the set-up of these experiments will be reviewed, considering target materials like germanium, tellurium and xenon together with other ones commonly used like copper, lead, stainless steel or argon. Calculations following very different approaches and measurements from irradiation experiments using beams or directly cosmic rays will be considered for relevant radioisotopes. The effect of cosmogenic activation in present and future double beta decay projects based on different types of detectors will be analyzed too.