Layered rare-earth hydroxide (LRH, R = Tb, Y) composites with fluorescein: delamination, tunable luminescence and application in chemosensoring for detecting Fe(iii) ions

A smartphone-intergrated dual-emission fluorescent nanoprobe for visual and ratiometric detection of anthrax biomarkers

A novel dual-emission fluorescent nanoprobe based on rare-earth nanosheets was fabricated to detect 2,6-pyridine dicarboxylic acid (DPA), which is the biomarker of Bacillus anthracis. 2-amino terephthalic acid (BDC-NH2) and surfactant sodium dodecyl sulfate (SDS) were co-intercalated into layered europium hydroxide (LEuH) to prepare the organic/inorganic composite, which was delaminated to obtain the rare-earth nanosheets. The ratio detection of DPA is possible due to the antenna effect between DPA and Eu3+. The nanoprobe shows high accuracy and sensitivity due to the large specific surface area of the rare-earth nanosheets. The limit of detection (LOD) is 4.4 nM for DPA in the range of 0-20 μM. In addition, a more convenient and faster smartphone-based visual detection platform was established based on the obvious color change. This work offers an effective way for developing visual sensing platforms, which opens a new path for designing fluorescent probes with superior sensing capabilities.

Layered Gadolinium-Europium-Terbium Hydroxides Sensitised with 4-Sulfobenzoate as All Solid-State Luminescent Thermometers

Ternary layered gadolinium-europium-terbium basic chlorides were synthesised using a facile hydrothermal-microwave technique. A continuous series of solid solutions was obtained in a full range of rare earth concentrations. To sensitise the luminescence of Eu3+ and Tb3+, a 4-sulfobenzoate anion was intercalated in the ternary layered rare earth hydroxides using one of two methods—a high-temperature ion exchange or a single-stage synthesis. The luminescent colour of the materials was governed by the gadolinium content: at low and medium gadolinium concentrations (0–70%), layered Gd-Eu-Tb basic sulfobenzoate exhibited a bright red europium luminescence; at high gadolinium content (70–90%), a bright green terbium luminescence was observed. The colour coordinates of layered Gd-Eu-Tb basic sulfobenzoate luminescence depended on the temperature in the physiological range (20–50 °C). The relative thermal sensitivity of the obtained materials was up to 2.9%·K−1.

Spectroscopic properties and fluorescent recognition of dye sensitized layered lutetium-terbium hydroxides

The layered rare earth hydroxides have attracted increasing interests due to their diverse chemical composition and tunable spectroscopic properties. In this paper, a novel Tb³⁺ activated layered lutetium hydroxide (LLuH:Tb) was fabricated, in which the inorganic NO₃^- ions were ion-exchanged with organic (ibuprofen or dodecylsulfonate) anions. After the ion-exchange reaction, the organic anions intercalated LLuH:Tb showed the distinct lamellar structure with the interlayer distance of about 2.56 nm, confirming the formation of inorganic/organic hybrid assembly. The dye ibuprofen-intercalated hybrid effectively promoted the characteristic ⁵D₄ → ⁷F₅ green emission of Tb³⁺ in the host but failed to be exfoliated into nanosheet colloid. On the contrary, the dodecylsulfonate-intercalated hybrid was readily to be exfoliated into nanosheet colloid by dissolving in formamide solvent, but the green emission of Tb³⁺ was too weak to be observed. To take advantage of their respective merits and explore the practical uses, certain amounts of dye ibuprofen were directly added to the dodecylsulfonate-intercalated hybrid colloid. Excited with the ultraviolet light, the characteristic green fluorescence of Tb³⁺ was dramatically enhanced, indicating that the dye was a superior light-harvesting antenna to sensitize the activator Tb³⁺. The dye sensitized hybrid colloid was very stable at ambient temperature and exhibited excellent fluorescent recognition for Cu²⁺ ions over other metal ions in aqueous solution due to the large fluorescence quenching. The detection limit for Cu²⁺ ion reaches 7.63 × 10^-7 mol/L, which is far lower than the limitation of Cu²⁺ in drinking water recommended by the World Health Organization (1.57 × 10^-5 mol/L). The fluorescence enhanced/quenched sensor with excellent stability exhibits a high potential for the detection of Cu²⁺ in routine environmental water.

Rare-Earth hydroxide nanosheets based ratio fluorescence nanoprobe for dipicolinic acid detection

We demonstrate a novel ratio fluorescence nanoprobe for dipicolinic acid (DPA) as an anthrax biomarker based on layered rare-earth hydroxide (LRH). 3-Amino-benzenesulfonic acid (AS) was intercalated into layered terbium hydroxide to form composite and then delaminated into nanosheets in formamide. The monolayer nanosheets were beneficial to expose the Ln³⁺ luminescence centers to the environment more completely, contributing a high sensitive detection to the environment. With the increase of DPA concentration, the emission intensity of AS kept constant which worked as a stable internal reference, while the fluorescence of Tb³⁺ was enhanced obviously due to the antenna effect. In the 0.05-5.0 μM concentration range, the I₅₄₄/I₃₆₀ fluorescence ratio changed with the DPA concentration, which exhibited a good linear relationship (R² = 0.999) and an ultralow detection limit of 3.8 nM. In addition, the probe showed high selectivity and sensitivity to the DPA detection as an anthrax biomarker, which can be applied in real tap water with good performances. This work could extend the applications of LRH nanosheets in detection and offer an extremely effective and easy technique for detecting DPA.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Recent Advances in Layered Double Hydroxide-Based Electrochemical and Optical Sensors

Layered double hydroxides (LDHs) have attracted considerable attention as promising materials for electrochemical and optical sensors owing to their excellent catalytic properties, facile synthesis strategies, highly tunable morphology, and versatile hosting ability. LDH-based electrochemical sensors are affordable alternatives to traditional precious-metal-based sensors, as LDHs can be synthesized from abundant inorganic precursors. LDH-modified probes can directly catalyze or host catalytic compounds that facilitate analyte redox reactions, detected as changes in the probe's current, voltage, or resistance. The porous and lamellar structure of LDHs allows rapid analyte diffusion and abundant active sites for enhanced sensor sensitivity. LDHs can be composed of conductive materials such as reduced graphene oxide (rGO) or metal nanoparticles for improved catalytic activity and analyte selectivity. As optical sensors, LDHs provide a spacious, stable structure for synergistic guest-host interactions. LDHs can immobilize fluorophores, chemiluminescence reactants, and other spectroscopically active materials to reduce the aggregation and dissolution of the embedded sensor molecules, yielding enhanced optical responses and increased probe reusability. This review discusses standard LDH synthesis methods and overviews the different electrochemical and optical analysis techniques. Furthermore, the designs and modifications of exemplary LDHs and LDH composite materials are analyzed, focusing on the analytical performance of LDH-based sensors for key biomarkers and pollutants, including glucose, dopamine (DA), H2O2, metal ions, nitrogen-based toxins, and other organic compounds.

A Novel Turn on Fluorescence Sensor for Determination Enoxaparin, a Low Molecular Weight Heparin

A sensor system was designed for the detection of Enoxaparin (Enox), a low molecular weight heparin (LMWH) that was run over the fluorescence quenching mechanism of fluorescein (FL) dye. At nanomolar concentrations, FL probe was subjected to fluorescence quenching by Fe(III). Fluorescence quenching mechanism of FL by Fe(III) was examined using various analytical techniques such as UV-vis absorption, fluorescence, and Fourier transform Infrared spectroscopy techniques, as well as with scanning electron microscope. The results indicated that photoinduced electron transfer process occurred between FL and Fe and that FL was quenched both statically and dynamically. Thermodynamic parameters showed that the interactions between them were predominantly hydrophobic interactions. Enox caused FL to recover its lost fluorescence properties and an increase was observed in the intensity of the fluorescence. Enox was detected successfully with the turn on fluorescence sensor. The developed Enox biosensor exhibited linearity in the range of 0-1.1 μg/ml. For Enox detection, the limit of detection was measured as 255 ng/mL. Enox biosensor was presented as a practical, simple, and applicable sensor system with high sensitivity and good selectivity. Enox is a medication usually monitored indirectly over anticoagulation. This study was presented as an alternative method for monitoring Enox directly. HIGHLIGHTS: Fluorescence quenching of Fluorescein dye by Fe(III) was studied in detail. The presence of enoxaparin enhanced the fluorescence properties of the fluorescein dye. A sensitive, simple and effective sensor system for determination of Enoxaparin, a low molecular weight heparin was shaped in the aqueous media. It was presented as a new method for Enoxaparin to be followed directly.

SDC/OS-LDH composite for highly sensitive fluorescence detection of Fe3+ at a much lower concentration

The significantly quenched luminescence of delaminated SDC/OS-LDH when contacted with Fe³⁺ can sensitively detect trace amounts of Fe³⁺.

Luminescence Tuning of Layered Rare-Earth Hydroxides (LRHs, R = Tb, Y) Composites with 3-Hydroxy-2-naphthoic Acid and Application to the Fluorescent Detection of Al3

Tunable luminescence (quenching or blue shift) of HNA/OS-LRH composites (HNA is 3-hydroxy-2-naphthoic acid; OS is the anionic surfactant of 1-octanesulfonic acid sodium; LRHs are layered rare-earth hydroxides, R = Tb³⁺, Y³⁺) in the solid state and delaminated state is reported, which is utilized as an effective fluorescent probe for detecting metal ions. HNA/OS species are intercalated into LRH layers to generate composites of HNA _xOS_{1- x}-LTbH ( x = 0.10, 0.15, 0.20 , 0.25) and HNA _yOS_{1- y}-LYH ( y = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30). In the solid state, LYH composites exhibit green emissions (from 493 to 504 nm) with a large blue shift in comparison to the 542 nm emission of free HNA^- anions, while in the delaminated state in formamide (FM), the composites display blue emission (480 nm) relative to the green emission (512 nm) of an HNA soltuion in FM. However, LTbH composites display coquenched luminescence in both the solid state and delaminated state. Also, HNA_0.25OS_0.75-1:1-LYH, HNA_0.25OS_0.75-1:2-LYH, and HNA_0.05OS_0.95-1:1-LYH (1:1 and 1:2 are HNA:NaOH molar ratios) show significantly elongated fluorescence lifetimes of 15.35, 14.37, and 12.72 ns, respectively, in comparison with free HNA-Na (6.44 ns), and their quantum yields of 23.40%, 21.97%, and 22.31%, respectively, are much larger than that of free HNA-Na (4.86%). The LTbH composite (HNA_0.25OS_0.75-1:1-LTbH) has also a relatively higher quantum yield of 12.46%. The HNA_0.25OS_0.75-1:1-LYH colloid exhibits excellent recognition selectivity for Al³⁺ over other metal ions (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, and Hg²⁺) with distinct fluorescence sensitization. It shows an intense change in its fluorescence emission when it is bound to Al³⁺ ions, giving a lower detection limit of 6.32 × 10^-6 M. This is novel research on the fluorescence chemosensing of LRH composites.

On-off-on relay fluorescence recognition of ferric and fluoride ions based on indicator displacement in living cells

A new boronic acid derivative functionalized with a 4-(3-(4-(4,5-diphenyl-1H-imidazole-2-yl)phenyl)-1,2,4-oxadiazol-5-yl)phenyl (IOP) moiety was synthesized for use as a sequential "on-off-on"-type relay fluorescence probe for Fe³⁺ ions and F^- ions with high selectivity and sensitivity under physiological conditions. The introduction of Fe³⁺ to IOP boronic acid (IOPBA) formed an Fe³⁺IOPBA complex, which led to quenching of the blue fluorescence intensity at 458 nm. The lowest-energy conformation of IOPBA was theoretically predicted to adopt an extended structure, and the Fe³⁺ ion in the Fe³⁺IOPBA complex was coordinated to two phenyl groups to form a π-complex. Upon addition of F^- to the Fe³⁺IOPBA complex, the original fluorescence was recovered due to formation of [FeF₆]^3‒, resulting in "on-off-on"-type sensor behavior. IOPBA showed high selectivity towards Fe³⁺ among other cations. Moreover, the Fe³⁺IOPBA complex showed specific selectivity towards F^-, with other cations and anions not interfering with detection. Both sensing processes showed 1:1 stoichiometry with binding constants of 6.87 × 10⁶ and 4.49 × 10⁶ mol^-1 L for Fe³⁺ with IOPBA and F^- with Fe³⁺IOPBA, respectively. The limits of detection for Fe³⁺ and F^- were 10 and 1 nM, respectively. The proposed method was successfully applied in real water samples. Furthermore, the probe had low cytotoxicity and was successfully used as a bioimaging reagent to detect intracellular Fe³⁺ and F^- in living HeLa cells.