Ultrasensitive Detection of Aqueous Uranyl Based on Uranyl-Triggered Protein Photocleavage

Highly sensitive and specific uranyl ion detection by a fluorescent sensor containing uranyl-specific recognition sites

Uranium pollution has become a serious threat to human health and environmental safety, making the detection of environmental uranium contamination of great importance. The sensitive and specific detection of uranyl ions, which are the dominant form of uranium in the environment, depends on the specific recognition of uranyl ions by chemical groups. In this study, a novel fluorescent sensor containing a highly specific uranyl ion recognition group is synthesized via the reaction of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and 1,1,2,2-tetra(4-carboxylphenyl)ethylene (TPE-(COOH)4). Owing to the effects of aggregation-induced emission (AIE) and intramolecular charge transfer (ICT), the fluorescent sensor, named TPE-EDC, exhibits significant fluorescent properties in aqueous environments. The binding of uranyl ions by specific recognition groups in TPE-EDC leads to a decrease in the ICT effect, thus causing a significant reduction in the emission intensity of TPE-EDC. The attenuation of the fluorescence intensity of TPE-EDC shows an excellent linear relationship with an increase in uranyl ion concentration. TPE-EDC exhibits ultra-sensitive and ultra-selective detection ability for uranyl ions with an ultra-low detection limit of 69 pmol/L and an ultrashort response time of 30 s. These high detection performances render the fluorescent sensor TPE-EDC a promising candidate for early warning of uranium pollution.

Ultrasensitive optical detection of strontium ions by specific nanosensor with ultrahigh binding affinity

The release and escape of radioactive materials has posed tremendous threats to the global environment. Among various radioactive elements, 90Sr has attracted growing attention due to its long half-life and its tendency to accumulate in bone tissue. Nonetheless, the concentration of 90Sr in radioactive waste is exceedingly low, far below the detection limits of currently available strontium-targeting chemical sensors. Herein, we propose an optical nanosensor (Sr2+-nanosensor) that exhibits an ultra-low detection limit of 0.5 nM, surpassing the 90Sr in the treated radioactive water from the Fukushima. The sensor offers wide sensing range of eight orders of magnitude, rapid response of less than 10 s, and high selectivity against 31 common ions. These excellent performances are attributed to a specific ligand (Sr2+-ligand) for Sr2+ recognition. The Sr2+ is found to be bound by six oxygen atoms from the Sr2+-ligand with a stability constant at least two orders higher than that of other traditional ligands. This study offers invaluable insights for the design of Sr2+-sensing methodologies as well as a technique for detecting trace amounts of environmental radioactive pollution.

Field Detection of Uranyl in Coastal Water of China Using a Portable Device via DNA Photocleavage

The urgent need for field detection of uranium in seawater is 2-fold: to provide prompt guidance for uranium extraction and to prevent human exposure to nuclear radiation. However, current methods for this purpose are largely hindered by bulky instrumentation, high costs of developed materials, and severe matrix interferences, which limit their further application in the field. Herein, we demonstrated a portable and label-free strategy for the field detection of uranyl in seawater based on the efficient photocleavage of DNA. Further experiments confirmed the generation of ultraviolet (UV) light-induced reactive oxygen species (ROS), such as O2•- and •OH, which fragmented oligomeric DNA in the presence of uranyl and UV light. Detailed studies showed that DNA significantly enhances uranyl absorption in the UV-visible region, leading to the generation of more ROS. A fluorescence system for the selective detection of uranyl in seawater was established by immobilizing two complementary oligonucleotides with the fluorescent dye SYBR Green I. The strategy of UV-induced photocleavage offers high selectivity, excellent interference immunity, and high sensitivity for uranyl, with a detection limit of 6.8 nM. Additionally, the fluorescence can be visually detected using a 3D-printed miniaturized device integrated with a smartphone. This method has been successfully applied to the on-site detection of uranyl in seawater in 18 Chinese coastal cities and along the coast of Hainan Island within 3 min for a single sample. The sample testing and field analysis results indicate that this strategy has promising potential for real-time monitoring of trace uranyl in China's coastal waters. It is expected to be utilized for the rapid assessment of nuclear contamination and nuclear engineering construction.

Unveiling the exciton dissociation dynamics steered by built-in electric fields in conjugated microporous polymers for photoreduction of uranium (VI) from seawater

Developing highly efficient photocatalysts based on conjugated microporous polymers (CMPs) are often impeded by the intrinsically large exciton binding energy and sluggish charge transfer kinetics that result from their vulnerable driving force. Herein, a family of pyrene-based nitrogen-implanted CMPs were constructed, where the nitrogen gradient was regulated. Accordingly, the built-in electric field endowed by the nitrogen gradient dramatically accelerates the dissociation of exciton into free carriers, thereby enhancing charge separation efficiency. As a result, PyCMP-3N generated by polymerization of 1,3,6,8-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine featured an optimized built-in electric field and exhibited the highest photocatalytic removal efficiency of uranium (VI) (99.5 %). Our proposed strategy not only provides inspiration for constructing the built-in electric field by controlling nitrogen concentration gradients, but also offers an in-depth understanding the crucial role of built-in electric field in exciton dissociation and charge transfer, efficiently promoting CMPs photocatalysis.

Towards tailoring hydrophobic interaction with uranyl(VI) oxygen for C-H activation

Bovine serum albumin (BSA) has a uranyl(VI) binding hotspot where uranium is tightly bound by three carboxylates. Uranyl oxygen is "soaked" into the hydrophobic core of BSA. Isopropyl hydrogen of Val is trapped near UO22+ and upon photoexcitation, C-H bond cleavage is initiated. A unique hydrophobic contact with "yl"-oxygen, as observed here, can be used to induce C-H activation.

The construction of a stable hydrogen-bonded organic framework for the photocatalytic reduction and removal of uranium

An imidazolyl hydrogen-bonded organic framework (HOF-T) with outstanding thermal and water stability was constructed by C-H⋯N hydrogen bonding and C-H⋯π interactions. UO22+ can be selectively captured by the imidazole group of HOF-T and rapidly reduced to UO2 under visible light irradiation, realizing exceptional uranium removal with high capacity and fast kinetics.

Heavy Metal-Induced Assembly of DNA Network Biosensor from Double-Loop Hairpin Probes for Ultrasensitive Detection of UO22+ in Water and Soil Samples

The uranyl ion (UO22+) is the most stable form of uranium, which exhibits high toxicity and bioavailability posing a severe risk to human health. The construction of ultrasensitive, reliable, and robust sensing techniques for UO22+ detection in water and soil samples remains a challenge. Herein, a DNA network biosensor was fabricated for UO22+ detection using DNAzyme as the heavy metal recognition element and double-loop hairpin probes as DNA assembly materials. UO22+-activated specific cleavage of the DNAzyme will liberate the triggered DNA fragment, which can be utilized to launch a double-loop hairpin probe assembly among Hab, Hbc, and Hca. Through multiple cyclic cross-hybridization reactions, hexagonal DNA duplex nanostructures (n[Hab•Hbc•Hca]) were formed. This DNA network sensing system generates a high fluorescence response for UO22+ monitoring. The biosensor is ultrasensitive, with a detection limit of 2 pM. This sensing system also displays an excellent selectivity and robustness, enabling the DNA network biosensor to work even in complex water and soil samples with excellent accuracy and reliability. With the advantages of enzyme-free operation, outstanding specificity, and high sensitivity, our proposed DNA network biosensor provides a reliable, simple, and robust method for trace levels of UO22+ detection in environmental samples.

pH-Dependent Dual-Mode Detection toward Uranium by a Zinc-Tetraphenylethylene Fluorescent Metal-Organic Framework

An interpenetrated tetraphenylethylene-based fluorescent metal-organic framework (ECUT-180) with exceptional sensitivity, excellent selectivity, and fast response (less than 30 s) toward uranium was successfully prepared. Especially, in the prescence of uranyl, ECUT-180 displays significant fluorescence turn-on under pH 2-3, while fluorescence turn-off under pH 4-8. The corresponding detection limits were determined to be 2.92 ppb at pH 2 and 0.86 ppb at pH 8, both of which are lower than the average uranium content (3.3 ppb) in seawater. Mechanism investigation reveals that the fluorescence enhancement on the strong acid condition can be assigned to uranium adsorption, while the quenching is caused by the resonance energy transfer.

Aggregation enhanced FRET: A simple but efficient strategy for the ratiometric detection of uranyl ion

Uranium is one of the most important radionuclides but could also cause potential health risks to human beings due to its radioactive and chemical toxicity. It is an urgent task to develop a simple but efficient sensing platform for UO₂²⁺, the main existing form of uranium in environment. Herein, a rhodamine-functionalized carbon dots (o-CDs-Rho) was synthesized and applied for UO₂²⁺ sensing through a simple but novel aggregation-enhanced FRET strategy. The weak FRET efficiency (16.2%) of o-CDs-Rho in dispersed solution is significantly enhanced (>77.2%) after UO₂²⁺ triggered aggregation due to the increased number of rhodamine acceptors around each CDs from dispersed 80 to aggregated 2800. This is the first ratiometric fluorescence sensor with an inverse change of fluorescence intensity at dual emission wavelengths under single-wavelength excitation for UO₂²⁺. Under optimized experiment conditions, o-CDs-Rho nanosensor shows a low detection limit of 53 nM and excellent selectivity. Meanwhile, the as-prepared nanosensor also shows high reliability and stability. These excellent properties make it successful in detecting uranium content in real samples.

Ultrafast extraction of uranium from seawater using photosensitized biohybrid system with bioinspired cascaded strategy

The highly effective utilization of uranium resources in global seawater is a viable method to satisfy the rising demands for fueling nuclear energy industry. Herein, inspired by the multi-mechanisms of the marine bacteria for uranium immobilization, CdS nanoparticles are deposited on the cell of marine bacterial strain Bacillus velezensis UUS-1 to create a photosensitized biohybrid system UUS-1/CdS. This system achieves high uranium extraction efficiency using a cascaded strategy, where the bacterial cells guarantee high extraction selectivity and the photosensitive CdS nanoparticles realize cascading photoreduction of high soluble U(VI) to low soluble U(IV) to enhance extraction capacity. As one of the fastest-acting adsorbents in natural seawater, a high extraction capacity for uranium of 7.03 mg g^-1 is achieved with an ultrafast extraction speed of 4.69 mg g^-1 d^-1. The cascaded strategy promisingly improves uranium extraction performance and pioneers a new direction for the design of adsorbents to extract uranium from seawater.

Novel biocompatible and sensitive visual sensor based on aggregation-induced emission for on-site detection of radioactive uranium in water and live cell imaging

In consideration of the severe hazards of radioactive uranium pollution, the rapid assessment of uranium in field and in vivo are urgently needed. In this work a novel biocompatible and sensitive visual fluorescent sensor based on aggregation-induced emission (AIE) was designed for onsite detection of UO₂²⁺ in complex environmental samples, including wastewater from Uranium Plant, river water and living cell. The AIE-active sensor (named as TPA-SP) was prepared with a "bottom-up" strategy by introducing a trianiline group (TPA) with a single-bond rotatable helix structure into the salicylaldehyde Schiff-base molecule. The photophysical properties, cytotoxicity test, recognition mechanism and the analytical performance for the detection of UO₂²⁺ in actual water samples and cell imaging were systematically investigated. TPA-SP exhibited high sensitivity and selectivity toward UO₂²⁺ as well as outstanding anti-interference ability against large equivalent of different ions in a wide effective pH range. A good linear relationship in the UO₂²⁺ concentration range of 0.05-1 μM was obtained with a low limit of detection (LOD) of 39.4 nM (9.38 ppb) for uranium detection. The prepared visual sensor showed great potential for fast risk assessment of uranium pollution in environmental systems. In addition, our results also indicated that the TPA-SP exhibited very low cytotoxicity in cells and demonstrated great potential for uranium detection in vivo.

Halogen hydrogen-bonded organic framework (XHOF) constructed by singlet open-shell diradical for efficient photoreduction of U(VI)

Synthesis of framework materials possessing specific spatial structures or containing functional ligands has attracted tremendous attention. Herein, a halogen hydrogen-bonded organic framework (XHOF) is fabricated by using Cl- ions as central connection nodes to connect organic ligands, 7,7,8,8-tetraaminoquinodimethane (TAQ), by forming a Cl-···H3 hydrogen bond structure. Unlike metallic node-linked MOFs, covalent bond-linked COFs, and intermolecular hydrogen bond-linked HOFs, XHOFs represent a different kind of crystalline framework. The electron-withdrawing effect of Cl- combined with the electron-rich property of the organic ligand TAQ strengthens the hydrogen bonds and endows XHOF-TAQ with high stability. Due to the production of excited electrons by TAQ under light irradiation, XHOF-TAQ can efficiently catalyze the reduction of soluble U(VI) to insoluble U(IV) with a capacity of 1708 mg-U g-1-material. This study fabricates a material for uranium immobilization for the sustainability of the environment and opens up a new direction for synthesizing crystalline framework materials.