Fluorescent responsive membrane based on terbium coordination polymer and carbon dots with AIE effect for rapid and visual detection of fluoroquinolone

In this study, based on aggregation-induced emission (AIE) effect and antenna effect, a novel portable fluorescent responsive membrane was constructed with red carbon dots (R-CDs) as reference signal and terbium coordination polymer (Tb-AMP CPs) as response signal for visual, instrument-free, and sensitive detection of fluoroquinolones (FQs). Specifically, the fluorescent responsive membrane (R-T membrane) was prepared by physically depositing R-CDs with AIE property and Tb-AMP CPs on the surface of polyvinylidene fluoride filter membranes at ambient temperature. In the presence of FQs, Tb3+ in the Tb-AMP CPs of the prepared membrane coordinated with the β-diketone structure of FQs, which turned on the yellow-green fluorescence through the "antenna effect". As the concentration of FQs increased, the R-T membrane achieved a fluorescent color transition from bright pink to yellow-green. Its visual detection sensitivity for three FQs, including ciprofloxacin, difloxacin, and enrofloxacin, was 0.01 μM, and the detection limits were 7.4 nM, 7.8 nM, and 9.2 nM, respectively, by analyzing the color parameter green. In the residue analysis of FQs in real samples, the constructed membrane also exhibited remarkable anti-interference and reliability, which is of great significance for ensuring the safety of animal-derived food.

An electrochemiluminescence sensor based on lanthanide bimetallic MOFs with a "cascade sensitization mechanism" for the sensitive detection of CA242

Lanthanide metal-organic frameworks (Ln-MOFs) broaden the optical sensing applications of lanthanide ions due to the antenna effect between organic ligands and metals. However, the sensitization ability of the ligand to metal ions is limited, and maximizing the sensitization of the electrochemiluminescence behavior of Eu3+ is still a challenge for the application of Ln-MOFs. Therefore, under the guidance of the "cascade sensitization mechanism" based on the antenna effect sensitizing the electrochemiluminescence of bimetallic Ln-MOFs, we proposed Eu/Tb-MOFs with high luminescence intensity as a signal probe. According to the antenna effect, the conjugated structure and high extinction coefficient of the benzene ring of 2-amino terephthalic acid (NH2-BDC) can enhance the ECL luminescence intensity of Eu/Tb-MOFs. Tb3+ can act as an energy bridge between NH2-BDC and Eu3+, buffering the energy gap. The bimetallic sensitization is formed between Tb3+ and Eu3+, which can inhibit the reverse internal flow of energy and ensure the high luminous efficiency of Eu3+. In addition, the nanosphere mixed valence Fe3O4 as a co-reactant accelerator promotes the formation of transient free radical SO4•- through the valence change of Fe2+/Fe3+. The ECL immunosensor constructed by luminophores Eu/Tb-MOFs and nanosphere Fe3O4 provided a new explanation for the ECL self-luminous of Eu/Tb-MOFs.

Sensitive electrochemiluminescence immunosensor based on a novel luminescent europium metal-organic framework and antenna effect for detecting pro-gastrin-releasing peptide

Sensitive detection of pro-gastrin-releasing peptide (Pro-GRP) is crucial because it is a highly sensitive and specific tumor marker for small cell lung cancer. Herein, we synthesized an efficient luminescent europium metal-organic framework and developed a sandwich ECL immunosensor for the sensitive detection of Pro-GRP, which used Eu3+ as the central ion and 2,4,6-tri (4-carboxyphenyl)-1,3,5-triazine (H3TATB) as the organic ligand. H3TATB acted as a strong absorbing reagent and transferred its energy to Eu3+ via the antenna effect to enhance the ECL response signal of Eu3+. As per calculations, the ECL efficiency of Eu-TATB, which was a promising ECL luminophore, was up to 130 %. The Cu2O cube worked as a substrate to assist the electron transfer and was used as a co-reaction accelerator to catalyze S2O82- to produce more SO4•- and then enhance the ECL intensity of Eu-TATB. Under optimal experimental conditions, the ECL immunosensor had a linear range of 5 fg mL-1-50 ng mL-1 for detecting Pro-GRP with a detection limit of 1.6 fg mL-1; moreover, it demonstrated excellent stability and specificity and has been successfully applied for detecting Pro-GRP in the human serum.

Fluorescent and smartphone imaging detection of tetracycline residues based on luminescent europium ion-functionalized the regular octahedral UiO-66-NH2

Antibiotic residues cause extensive damage to food security, thus arousing serious concerns. Hence, rapid and sensitive detection of antibiotic residues is crucial to food safety. This study aimed to propose a portable, visual, intelligent and rapid method for tetracycline detection. We developed a ratiometric fluorescent sensor based on the Eu3+-functionalized regular octahedral UiO-66-NH2 material. The developed sensor could quantify tetracycline in the concentration range of 0.5-200 μM with a detection limit as low as 0.2 μM under the optimum conditions. Furthermore, the analytical results obtained using the designed sensor in the actual samples were basically consistent with those obtained using high-performance liquid chromatography. Based on these achievements, a smartphone application-integrated fluorescent testing paper was designed for facile, intelligent, and visual detection of tetracycline. The integrated portable sensor not only saved cost and time for testing but also provided a forward-looking approach to fast, sensitive detection of antibiotic residues.

Eu3+ doped ethylenediamine functionalized UiO-66 probe for fluorescence sensing of formaldehyde

The development of probes with selectivity and prompt detection of aldehydes molecules is of great importance for protecting human health and public security. Herein, a system based on ethylenediamine (EDA) functionalized and Eu3+-doped UiO-66, namely EDA-Eu3+@UiO-66, was designed to detect formaldehyde molecules. Based on the "antenna effect" of lanthanide elements, UiO-66 transfers the absorbed energy to Eu3+ ions and emits characteristic fluorescence belonging to Eu3+. By using the fluorescence peaks of UiO-66 and Eu3+ respectively, a ratiometric fluorescence sensing probe can be constructed. Formaldehyde molecules react with the -NH2 on the surface of EDA-Eu3+@UiO-66 through an aldehyde-amine condensation reaction and connect to the functionalized surface of UiO-66. Due to the absorption of excitation light energy by formaldehyde molecules, the energy transfer efficiency from UiO-66 to Eu3+ ions is reduced, resulting in the fluorescence quenching of EDA-Eu3+@UiO-66, thus achieving selective detection of formaldehyde. The fabricated sensing platform successfully detected residual formaldehyde in frozen shrimp tail samples. The system was also used to respond to formaldehyde vapor, and a significant fluorescence quenching effect was observed. This strategy provides a sensitive, selective, and reliable method for the visual sensing of formaldehyde.

Double-emitting lanthanide metal-organic frameworks composed of Eu/Tb doping and ratiometric fluorescence detection of nitrofurazone

Lanthanide metal-organic frameworks (LnMOFs) have substantial potential in luminescence due to their unique antenna effect. Nevertheless, the single emission is susceptible to pseudo-signals caused by external environmental conditions, which significantly threaten the accurate measurement of the concentration. In this case, we prepared a dual-emission fluorescent probe {EuxTb1-x(NH2-BDC)3(DMF)4·2DMF}∞ (NH2-BDC = Diaminoterephthalic acid, DMF = N,N-dimethylformamide). The stable dual-emission signal provides a superior signal output for detecting nitrofurazone (NFZ), which is detected by the probe with excellent fluorescence for 0-10 μM NFZ. In the investigation of the detection mechanism, it is speculated that NFZ incorporates with probe to generate a novel complex. Furthermore, The UV absorption curves of the novel complexes and NFZ overlap extensively with those of the probe. The addition of NFZ attenuates the characteristic luminescence of Eu and Tb by competing for the absorption of the excitation light of the probe. The probe has exhibits rapid response, excellent sensitivity, visual detection and a meagre detection limit (LOD = 0.013 μM) for the detection of NFZ. This work not only broadens the application of LnMOFs in the field of ratiometric detection but also provides a favorable fluorescent probe for the quantitative detection of NFZ.

Eu-MOF based fluorescence probe for ratiometric and visualization detection of Cu2

Water contamination caused by heavy metals represents an urgent global issue. Cu2+, a potential trace heavy metal pollutant, can accumulate in the human body through the food chain, leading to excessive levels that give rise to diverse health complications. Hence, in this investigation, a novel and efficacious fluorescent probe named Eu-BTB was developed for the detection of Cu2+, employing 1,3,5-triphenyl(4-carboxyphenyl) (H3BTB) as the ligand and Eu3+ as the metallic framework. The probe demonstrates exceptional fluorescence characteristics. The interaction between the probe ligand BTB and Eu3+ triggers an antenna effect, heightening the emission efficiency of Eu3+ while preserving its intrinsic emission. The introduction of Cu2+ competes with BTB for binding, thus quelling the antenna effect and inducing a fluorescence alteration. Within the concentration range of 0.05-10 μM, the fluorescence intensity-to-Cu2+ concentration ratio exhibits a robust linear correlation, with a remarkably low detection limit of 10 nM and a rapid response time of 3 min. The fluorescent probe has been effectively deployed for the detection of copper ions in water across diverse environmental conditions, with the obtained outcomes being validated via the conventional approach of inductively coupled plasma mass spectrometry (ICP-MS). The Eu-BTB probe showcases the advantages of simplicity, swiftness, and broad applicability, thus affirming its potential for the prompt and accurate detection of Cu2+ in diverse environmental water samples.

Antenna effect of perylene-sensitized up-conversion luminescent material amplifies the signal of electrochemiluminescence biosensor platform for the ultra-sensitive detection of enrofloxacin

Recently, up-conversion luminescent (UCL) materials have caught extensive sight on account of their excellent biocompatibility and weak automatic fluorescence background, but the low optical signal makes researchers shy away. Organic dye-sensitized UCL materials can improve the low optical signal drawback of UCL and rejuvenate it with adjustable optical properties and unique antenna effects. In this work, an efficient, simple and selective electrochemiluminescence (ECL) sensing platform was developed for determination of enrofloxacin (ENR). 3,4,9,10-perylene tetracarboxylic acid (PTCA) was successfully used as an "antenna" to improve the ECL performance of the UCL nanoparticles (PEI-NaYF4: Yb, Er) due to its appropriate excitation spectrum position and superior electron transfer rate. The specific recognition function of the aptamer enabled the sensor to eliminate the interference from conspecific impurity. In the presence of ENR, the specific combination of ENR with aptamer made the aptamer fall from surface of the electrode, thus we could see a considerable enhancement of signal. Under the most favourable conditions, the aptasensor based on antenna effect displayed a wide detection range (1.0 × 10-14∼1.0 × 10-6 M), low limit of detection (LOD = 3.0 × 10-15 M) and receivable recoveries (96.0%-102.4%) during water samples analysis. At this point, antenna effect provides a powerful strategy to expand the application of UCL in the field of ECL biosensing.

Development of water-dispersible Dy(III)-based organic framework as a fluorescent and electrochemical probe for quantitative detection of tannic acid in real alcoholic and fruit beverages

Tannic acid (TA) is a water-soluble polyphenol and used in beverages, medical fields as clarifying and additive agents. In daily life, TA is unavoidable, and excessive consumption of tannin containing foods can harm health. Thus, rapid and sensitive quantification is highly necessary. Herein, an eco-friendly fluorometric and electrochemical sensing of TA was developed based on a dysprosium(III)-metal-organic framework (Dy(III)-MOF). An aqueous dispersion of Dy(III)-MOF exhibits strong dual emissions at 479 and 572 nm with an excitation at 272 nm, due to the 4f-4f electronic transition and "antenna effect". Chromophore site of the functional ligand, and Dy(III) ion could potentially serve as a sensing probe for TA via quenching (fluorescence). The fluorometric sensor worked well in a wide linear range concentrations from 0.02 to 25 μM with a limit of detection (LOD) of 0.0053 μM. Secondly, the cyclic voltammetric of TA at Dy(III)-MOF modified screen-printed carbon electrode (SPCE) has been investigated. The Dy(III)-MOF/SPCE showed an anodic peak signal at +0.22 V with a five-fold stronger current than the control electrode surface. Under optimized sensing parameters, the Dy(III)-MOF/SPCE delivered wide linear concentrations from 0.01 to 200 μM with a LOD of 0.0023 μM (S/N = 3). Accessibility of real practical samples in alcoholic and juice-based beverages were quantified, resulting in superior recovery rates (98.13-99.53%), F-test, and t-test confirmed high reliability (<95% confidence level (n = 3)). Finally, practicability result of the electrochemical method was validated by fluorometric with a relative standard deviation (RSD) of 0.18-0.46 ± 0.17% (n = 3). The designed probe has proven to be a key candidate for the accurate analysis of TA in beverage samples to ensure food quality.

Two birds with one stone: Ratiometric sensing platform overcoming cross-interference for multiple-scenario detection and accurate discrimination of tetracycline analogs

Environmental pollution caused by tetracycline antibiotics (TCs) is a major concern for public health worldwide. Trace detection and reliable discrimination of tetracycline and its analogs are consequently essential to determine the distribution characteristics of various tetracycline family members. Here, a dual-response sensor was constructed by integrating the fluorescence emission of fluorescein isothiocyanate (FITC) doped SiO2 and Eu3+. A portable Lab-on-Paper device is further fabricated through probe immobilization, which allows convenient visual detection of tetracycline using a smartphone. In addition, for the coexistence of multiple tetracycline analogs, dimensionality reduction via principal component analysis is applied to the spectra, realizing accurate differentiation of the four most widely used tetracycline analogs (tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC), and doxycycline (DOX)). The dual-response nanoplatform enabled a wide-gamut color variation crossing from green to red, with limit of detection (LOD) of 2.9 nM and 89.8 nM for spectrometer- and paper-based sensors, respectively. Analytical performance was examined in multiple real samples, including food, environmental, and biological settings, confirming robust environmental adaptability and resistance. Compared to previous TC sensors, this method has several notable improvements, including improved ecological safety, accessibility, reproducibility, practicality, and anti-cross-interference capacity. These results highlight the potential of the proposed "two birds with one stone" strategy, providing an integrated methodology for synchronous quantitative detection and derivative identification toward environmental contaminants.

AIEgen-sensitized lanthanide nanocrystals as luminescent probes for intracellular Fe3+ monitoring

The abnormal Fe³⁺ level is known to cause various diseases, such as heart failure, liver damage and neurodegeneration. In situ probing Fe³⁺ in living cells or organisms is highly desired for both biological research and medical diagnostics. Herein, hybrid nanocomposites NaEuF₄@TCPP were constructed by the assembly of an aggregation-induced emission luminogen (AIEgen) TCPP and NaEuF₄ nanocrystals (NCs). The anchored TCPP on the surface of NaEuF₄ NCs can reduce rotational relaxation of the excited state and efficiently transfer the energy to the Eu³⁺ ions with minimized nonradiative energy loss. Consequently, the prepared NaEuF₄@TCPP nanoparticles (NPs) exhibited an intense red emission with a 103-fold enhancement relative to that in NaEuF₄ NCs under 365 nm excitation. A selectively quenching response to Fe³⁺ ions for the NaEuF₄@TCPP NPs makes them luminescent probes for sensitive detection of Fe³⁺ ions with a low detection limit of 340 nM. Moreover, the luminescence of NaEuF₄@TCPP NPs could be recovered by the addition of iron chelators. Benefiting from their good biocompatibility and stability in living cells, together with the characteristic of the reversible luminescence response, the lipo-coated NaEuF₄@TCPP probes were successfully applied for real-time monitoring of Fe³⁺ ions in living HeLa cells. These results are expected to motivate the exploration of AIE-based lanthanide probes for sensing and biomedical applications.

Gelatinous lanthanide coordination polymer with aggregation-enhanced antenna effect for ratiometric detection of endogenous alkaline phosphatase

Aggregation-induced emission (AIE) and antenna effect (AE) are two significant behaviors that have attracted increasing attention. However, it is challenging to achieve the synergistic effect of AIE and AE in luminescent materials for more extensive applications. Here, four gelatinous Ln³⁺ coordination polymers (Ln-CPs) are synthesized by self-assembly of ciprofloxacin (CIP), adenosine monophosphate (AMP), and Ln³⁺ ions in aqueous medium. Encouragingly, a remarkable increase in the characteristic fluorescence of Ln³⁺ and a significant decrease in CIP are observed along with increasing concentration of Ln-CPs, which is attributed to the large aggregates formed by self-assembly that strictly constrain the intramolecular motions of antenna ligands, thereby achieving the aggregation-enhanced AE. More meaningfully, Eu-CP not only shows a rice-like morphology at high aggregation state, but also provides an opportunity for the selective detection of alkaline phosphatase (ALP). A new flower-like polymer is formed upon incubating Eu-CP with ALP, accompanied by the fluorescence quenching of Eu³⁺ and recovery of CIP, a ratiometric determination of ALP in the range of 0.1-6.0 U·L^-1 is thus achieved. Additionally, ALP assay in human serum and bioimaging in living cells have been successfully performed. This research opens a new horizon for the fabrication of Ln³⁺-based luminescent materials with promising applications.

A comparative study of conventional FRET and light harvesting properties of Rh-110/Rh-6G and Rh-19/Rh-B organic dye pairs impregnated in sol-gel glasses

Two different pairs of laser dyes, Rhodamine-110 (Rh-110)/Rhodamine-6G (Rh-6G) and Rhodamine-19 (Rh-19)/Rhodamine-B (Rh-B) (the first dye in each pair as a donor and the second as an acceptor) were impregnated in silica samples prepared by the sol-gel method and spectroscopically studied using absorption and steady-state fluorescence techniques. The critical transfer distance (R0), actual distance (r) between the donor and acceptor, overlap integral [J(ῡ)], FRET (fluorescence resonance energy transfer) efficiency (E), and antenna effect efficiency (AE) were investigated in detail based on the variation in acceptor concentration. The FRET efficiency, antenna effect efficiency, and actual donor-acceptor distance for Rh-110/Rh-6G and Rh-19/Rh-B dye pairs corresponding to acceptor concentration ranges (3.83 to 7.65)×10-5 M/L and (3.71 to 8.34)×10-5 M/L, respectively, were found to be in the ranges of 57.38% to 74.89%, 36.97% to 24.13%, 5.44 nm to 4.77 nm, and 77.01%. Furthermore, maximum FRET efficiencies of 85.68% and 87.63% and antenna effect efficiencies of 36.97% and 40.95% for Rh-110/Rh-6G and Rh-19/Rh-B, respectively, were also reported. Our results demonstrate the superior FRET efficiency of Rh-19/Rh-B over Rh-110/Rh-6G dye pair in sol-gel glasses, while the antenna effect efficiency of Rh-110/Rh-6G is higher than that of Rh-19/Rh-B for the same donor to acceptor (D/A) ratio. Finally, Rh-110/Rh-6G is a better energy harvester than the Rh-19/Rh-B dye pair at the common D/A ratio. These results are explained in terms of molecular structure similarity, polarity, and rigidity of donor and acceptor.

Multi-color fluorescence sensing platform for visual determination of norfloxacin based on a terbium (Ш) functionalized covalent organic framework

Sensitive and visual determination of fluoroquinolone antibiotics (FQs) is of great significance since their abuse and inappropriate handling can be problematic. Herein, we propose a lanthanide covalent organic framework fluorescence sensing system (Tb@COF-Ru) with visualization capability to determine the FQs level, where Tb@COF was employed as the sensing probe, while the red-emitting Ru(bpy)₃²⁺ serves as a constant red fluorescent background. With increasing norfloxacin concentration, the green fluorescence of Tb³⁺ is gradually enhanced, finally realizing the multicolor fluorescence change from red to green. With a smartphone for RGB analysis, visual monitoring and quantitative analysis were realized without any sophisticated instrument. Limits of detection for the fluorescence quantitative and visual mode for norfloxacin were 0.33 nM and 7.3 μM, respectively. This method was rapid (1 min) and visualized, providing a simple analysis of various food matrices (honey, milk, egg and beef) and water samples for trace FQs.

Time resolved fluorescence sensor array for discrimination of phosphate anions by using transition metal dichalcogenide quantum dots and Tb (III)

Phosphate detection has garnered widespread attention due to their biological and environmental impact. Among several optical techniques, time resolved fluorescence (TRF) provides a sensitive way for discrimination of analytes in a complex mixture as it suffers less interference from the background, thus providing a high signal to noise ratio. The sensitization of rare earth metal (REM) ions by semiconducting quantum dots (QDs) can help the former overcome the drawback of low absorption coefficient, thus allowing one to exploit the additional advantage of the REM, viz, the long-excited state lifetime. Herein, we have developed a TRF based sensor array consisting of three QDs, i.e., MoS₂ , WS₂ and MoSe₂ as energy sensitizers to Tb³⁺ ion. Different QDs possess variable energy transfer ability to Tb³⁺ ion. Hence, they can be used for discrimination of phosphates. It was also observed that CrO₄ ^2- can competitively bind to Tb³⁺ and further, enhance the efficiency of the sensor array which could discriminate six different phosphates at 200 μM concentration in aqueous as well as serum media with a detection limit of 10 μM in aqueous media. Thus, the sensitivity of the TRF based sensor array is rarely compromised in a complex mixture, which is advantageous over a fluorescence-based sensor array.

Antenna effect of pyridoxal phosphate on the fluorescence of mitoxantrone-silicon nanoparticles and its application in alkaline phosphatase assay

As a kind of sensing and imaging fluorescent probe with the merit of low toxicity, good stability, and environment-friendly, silicon nanoparticles (SiNPs) are currently attracting extensive research. In this work, we obtained mitoxantrone-SiNPs (MXT-SiNPs) with green emission by one-pot synthesis under mild temperature condition. The antenna based on pyridoxal phosphate (PLP) was designed for light-harvesting to enhance the luminescence of MXT-SiNPs and to establish a novel sensing strategy for alkaline phosphatase (ALP). PLP transfers the absorbed photon energy to MXT-SiNPs by forming Schiff base. When PLP is dephosphorized by ALP, the released free hydroxyl group reacts with aldehyde group to form internal hemiacetal, which leads to the failure of Schiff base formation. Based on the relationship between antenna formation ability and PLP hydrolysis degree, the activity of ALP can be measured. A good linear relationship was obtained from 0.2 to 3.0 U/L, with a limit of detection of 0.06 U/L. Furthermore, the sensing platform was successfully used to detect ALP in human serum with recovery of 97.6-106.2%. The rational design of antenna elements for fluorescent nanomaterials can not only provide a new pathway to manipulate the luminescence, but also provide a new direction for fluorescence sensing strategy.

Red-emitting β-diketonate Eu(III) Complexes With Substituted 1,10-phenanthroline Derivatives: Optoelectronic and Spectroscopic Analysis

A series of europium diketonate complexes with 1-phenyl-1,3-butanedione (PBD) and 1,10-phenanthroline derivatives were synthesized and explored spectroscopically. Photophysical characteristics of synthesized complexes have been investigated experimentally as well as theoretically. Photoluminescence emission spectra of complexes do not contain any peak of ligand revealing efficient transferal of energy from ligand to Eu³⁺ ion. Presence of peak at 611 nm corresponding to ⁵D₀ → ⁷F₂ transition is responsible for red emanation of ternary europium complexes. Photophysical parameters viz., Judd-Ofelt, quantum efficiency, radiative and non radiative decay rates were also estimated theoretically from LUMPAC software. Geometry optimization of complexes was done via Avogadro software. All synthesized trivalent complexes exhibit red emission which was further sustained by the position of chromaticity coordinates in CIE triangle. These red emanating materials could be utilized in designing electroluminescent display devices.

Tracking Zone-wise perturbation during unfolding of some globular proteins using Eu(III) complex of Tetracycline as a probe exhibiting Stark splitting

Enhanced 'Antenna effect' of a suitably designed ternary complex of Eu(III), Tetracycline hydrochloride (TC) and globular proteins viz bovine serum albumin (BSA), human serum albumin (HSA) and β-lactoglobulin A (BLGA) in aqueous medium is employed to characterize the different partially unfolded states along with investigation of the micro- heterogeneous environment of the proteins during their stepwise unfolding. The zone-wise perturbation for the proteins upon denaturation by Urea and Guanidine hydrochloride (Gdn. HCl) is followed by the emission of Eu(III) through 'Antenna Effect' and that of the tryptophan (Trp) residues of the proteins as a function of denaturants both by steady state and time resolved emission study. With Gdn. HCl as denaturant, both BSA and BLGA show quenching of Eu(III) emission compared to pure protein while HSA exhibits an enhancement of antenna effect during unfolding as compared to that in its absence. In the presence of Urea, HSA and BSA show enhancement of antenna effect accompanied by Stark splitting of the ⁵D₀→⁷F₂ transition of Eu(III) although BLGA follows the similar pattern of quenching of Eu(III) emission as observed with Gdn. HCl without any Stark splitting. The proteins exhibit a two state transition with ΔG_D values of ~ 2-3 kcal mol^-1. Thus the use of Eu(III) emission as an efficient probe is advocating here to rationalize the microenvironment of the proteins during their stepwise unfolding.

An imine-linked covalent organic framework for renewable and sensitive determination of antibiotic

Lanthanide-functionalized porous organic materials have been the promising candidates in the chemical and biological sensing. Considering the superior thermal and solvent stability of covalent organic frameworks (COFs), the development of lanthanide ions-functionalized COFs based sensing platform is meaningful, while remains to be a challenge. In this work, a new imine-linked COF which provides suitable coordination sites for Tb³⁺ was constructed via the Schiff base reaction between P-phenylenediamine (Pda) and 2,6-Diformylpyridine (Dfp). Benefiting from its high signal-to-noise, the COF@Tb shows excellent ability to determinate ciprofloxacin (CIP) with a detection limit of 3.01 nM. The measurement can maintain good stability in the presence of potential interference or in actual sample. Being washed with ethanol after each measurement, COF@Tb can be recycled for five times. This work provides a novel alternative strategy for efficient construction of lanthanide-grafted COFs and may promote the development of porous organic materials based chemical sensing.

Energy transfer processes and structure of carboxymethyl cellulose-Tb/Eu nanocomplexes with color-tunable photoluminescence

A series of fluorescent nanocomplexes of carboxymethyl cellulose (CMC)/Terbium (Tb)- Europium (Eu) were successfully synthesized without introducing a second ligand. By adjusting the concentration of the coordinated ions, these nanocomplexes exhibit favorably visibly tunable luminescence properties with colors being able to change from green to red. The XPS analysis demonstrates the formation Tb(III)-O^2- and Eu(III)-O^2- between OH and COO^- in CMC and Tb³⁺ or Eu³⁺ ions, which is advantage for light absorption by UV-Vis spectroscopy and fluorescence spectroscopy. The ligand CMC plays a role in coordinating with terbium and europium ions, but also serves as an energy donor to these metal ions by antenna effect. Moreover, the energy transfer also occurred from terbium ions to europium ions in CMC matrix, which is responsible for the tunable luminescence properties of these complexes.

Ultrasensitive near-infrared electrochemiluminescence biosensor derived from Eu-MOF with antenna effect and high efficiency catalysis of specific CoS2 hollow triple shelled nanoboxes for procalcitonin

In this paper, we report a novel multiple amplification strategy for ultrasensitive near-infrared electrochemiluminescence (ECL) immunoassay in K₂S₂O₈ solution. The realization of this strategy is based on the antenna effect of Eu-MOF (EuBTC) and a high efficiency catalysis of CoS₂ hollow triple shelled nanoboxes (TSNBs). The H₃BTC ligand in the antenna effect first undergoes π-π* absorption and a singlet-singlet electronic transition. Its energy passes through the intersystem to the triplet state, next transfers from the lowest excited triplet state to the vibrational energy level of the rare earth ion, finally realizing sensitizing center ion luminescence. Moreover, ionic reaction and structural advantages endow CoS₂ TSNBs a dual signal enhancement effect. This sandwich-type ECL biosensor has a near-infrared luminescence in 800-900 nm, thus avoiding damage to the sample in the meantime. In practical diagnosis, the normal critical value of procalcitonin (PCT) (<0.5 ng/mL) is much higher than the detection limit (3.65 fg/mL) and is in the detection range (10 fg/mL-100 ng/mL), which means that the ECL biosensor has a high sensitivity in the detection of PCT and meet the requirement for diagnosis of disease completely. Therefore, the strategy provides a feasible method for efficient and stable analysis of systemic inflammatory response such as fearful bacterial infection, hepatitis B, and peritonitis.

Europium coordination polymer particles based electrospun nanofibrous film for point-of-care testing of copper (II) ions

Excess free copper in serum has been identified to induce neurodegenerative diseases such as Alzheimer's disease, thus it is very important to determine copper (II) ions (Cu²⁺) content for human health test. Herein we developed a point-of-care testing (POCT) platform through a luminescence "on-off" recognition mechanism of serum copper. Microsized europium coordination polymer particles (Eu-CPs), which was prepared with citric acid (CA) and europium nitrate hexahydrate through a hydrothermal route, were then successfully loaded with the mixture of 2,6-pyridinedicarboxylic acid (DPA) and poly(vinyl alcohol) (PVA) to form electrospun nanofibrous films (ENFFs). The as-prepared Eu-CPs/DPA/PVA ENFFs exhibited red emission at 618 nm when exciting at 280 nm, with the quantum yields of 22.2% owing to the antenna effect from DPA to Eu³⁺. Furthermore, the strong luminescence could be selectively quenched by Cu²⁺ through coordination with DPA to interrupt the antenna effect. With that, Cu²⁺ was successfully detected in the range of 2-45 μM with a detection of limit of 1.3 μM, well matching with the requirement of clinic test of excess free copper induced neurodegenerative diseases. As a proof of concept at last, this POCT platform was used to detect free copper in spiked serum samples with a recovery of 101.1%-105.2%, demonstrating that this platform provides significant potential for use in clinical test.

Regulation of light-harvesting antenna based on silver ion-enhanced emission of dye-doped coordination polymer nanoparticles

The design and construction of artificial light-harvesting systems for solar energy conversion to chemical energy has been an active research field. A variety of molecules and materials have been used to mimic the function of the light-harvesting antenna. However, the improvement or regulation of the antenna effect of the existing artificial light-harvesting systems is less explored. Coordination polymers have aroused extensive concern due to their applications in light-harvesting and energy conversion. Herein, it is found that silver ion can dramatically enhance the emission of dye encapsulated in the coordination polymer nanoparticles (CPNs). The mechanism of Ag⁺-induced fluorescence enhancement is elucidated. Taking advantage of the effect of Ag⁺ ions, the regulation of CPN-based light-harvesting system by Ag⁺ is achieved for the first time. The antenna effect could be up to 2.3 times the original value by adding Ag⁺ ions. The present work provides a new approach to regulate the antenna effect of the light-harvesting system with the advantages of convenience, rapidity, low cost, and flexibility.

Unexpected luminescent and photochemical properties of europium(III) cinnamates - Theoretical and experimental study

The luminescent and photochemical properties of europium(III) cinnamates [Eu(Cin)₃]_n (I) and Eu(Cin)₃·(phen) (II) were investigated in theoretical and experimental aspects. The high photostability of the complex I was explained. The complex II displays weak luminescence and low photostability in spite of the presence of a powerful antenna ligand 1,10-phenantroline in its coordination sphere. The unexpected luminescent and photochemical properties of europium(III) cinnamates were interpreted by the quantum chemistry methods. It was revealed that inclusion of phen molecule into Eu(Cin)₃ complex results in lengthening of Eu-Cin distances that promotes weakening of antenna effect. In the process of photoexcitation of this complex noticeable lengthening of Eu-Cin-2 bond takes place and Cin-3 ligand is detached from the molecule that is the cause of low photostability and weak luminescence of II.

Europium(III) complex with powerful antenna ligands: Interligand interaction

The luminescent properties of europium(III) trifluoroacetate [Eu(TFA)3bipy·3Н2О]∙bipy (I), where TFA - trifluoroacetate anion and bipy - 2,2'bipyridyl were investigated. Despite the presence of two efficient antenna ligands in complex (bipy1 in europium coordination sphere and bipy2 in the outer-sphere) the complex displays weak luminescence. By employing density functional theory-based methods, the luminescence, electron structure, interligand interactions and the processes of energy transfer in I were investigated. The nature of the chemical bond in I was studied by the natural bond orbital analysis. The mechanism of luminescence weakening in the complex was ascertained: competitive energy transfer from coordinated bipy1 ligand on to outer-sphere bipy2 molecule results in appreciable weakening of the antenna effect.

White light color tuning ability of hybrid Dibenzoylmethane/YAG:Ce nanophosphor

In this study, we have considered the synthesis of a novel hybrid material consisting of cerium-doped yttrium aluminium garnet (YAG:Ce) nanophosphor surface decorated by UV/blue sensitizing Dibenzoylmethane (DBM) organic molecule. A comparative evaluation of synthesized hybrid material YAG:Ce/DBM nanophosphor and YAG:Ce nanophosphors was made using a combination of different analytical techniques like X-ray diffraction, Scanning electron microscopy, UV-Visible-Infrared absorption, Photoluminescence techniques etc. Due to the presence of organic ligand, the hybrid nanophosphor has extended excitation. We have monitored the emission spectra at excitation with 355 nm, 375 nm, 405 nm, and 465 nm. The synthesized luminescent hybrid material was characterized by various spectroscopic techniques and its photophysical properties were thoroughly investigated. The color perception of hybrid YAG:Ce/DBM nanophosphor is significantly modified due to the mixing of blue color in the green-yellow emission of YAG:Ce nanophosphor at different excitations which yield CIE coordinates (0.37, 0.59).

Mesoporous SiO2 Nanoparticles: A Unique Platform Enabling Sensitive Detection of Rare Earth Ions with Smartphone Camera

Fast and sensitive detection of dilute rare earth species still represents a challenge for an on-site survey of new resources and evaluation of the economic value. In this work, a robust and low-cost protocol has been developed to analyze the concentration of rare earth ions using a smartphone camera. The success of this protocol relies on mesoporous silica nanoparticles (MSNs) with large-area negatively charged surfaces, on which the rare earth cations (e.g., Eu³⁺) are efficiently adsorbed through electrostatic attraction to enable a "concentrating effect". The initial adsorption rate is as fast as 4025 mg (g min)^-1, and the adsorption capacity of Eu³⁺ ions in the MSNs is as high as 4730 mg g^-1 (equivalent to ~ 41.2 M) at 70 °C. The concentrated Eu³⁺ ions in the MSNs can form a complex with a light sensitizer of 1,10-phenanthroline to significantly enhance the characteristic red emission of Eu³⁺ ions due to an "antenna effect" that relies on the efficient energy transfer from the light sensitizer to the Eu³⁺ ions. The positive synergy of "concentrating effect" and "antenna effect" in the MSNs enables the analysis of rare earth ions in a wide dynamic range and with a detection limit down to ~ 80 nM even using a smartphone camera. Our results highlight the promise of the protocol in fieldwork for exploring valuable rare earth resources.

RF Heating of Gold Cup and Conductive Plastic Electrodes during Simultaneous EEG and MRI

PURPOSE

To investigate the heating of EEG electrodes during magnetic resonance imaging (MRI) scans and to better understand the underlying physical mechanisms with a focus on the antenna effect.

MATERIALS AND METHODS

Gold cup and conductive plastic electrodes were placed on small watermelons with fiberoptic probes used to measure electrode temperature changes during a variety of 1.5T and 3T MRI scans. A subset of these experiments was repeated on a healthy human volunteer.

RESULTS

The differences between gold and plastic electrodes did not appear to be practically significant. For both electrode types, we observed heating below 4°C for straight wires whose lengths were multiples of ½ the radiofrequency (RF) wavelength and stronger heating (over 15°C) for wire lengths that were odd multiples of ¼ RF wavelength, consistent with the antenna effect.

CONCLUSIONS

The antenna effect, which has received little attention so far in the context of EEG-MRI safety, can play as significant a role as the loop effect (from electromagnetic induction) in the heating of EEG electrodes, and therefore wire lengths that are odd multiples of ¼ RF wavelength should be avoided. These results have important implications for the design of EEG electrodes and MRI studies as they help to minimize the risk to patients undergoing MRI with EEG electrodes in place.

Pr(III) luminescence enhancement by chelation in solution and in sol-gel glass

Due to the weak emission of lanthanide ions in solution, it is common practice to form complexes of the lanthanide ions with organic ligands that strongly absorbs light and transfers the energy to the lanthanide ion center via the antenna effect. The organic ligands 2-6-pyridinedicarboxylate (L1) and the polytonic diazine (N-N) ligand L2 (C22H16N12O2) were used to synthesize two Pr(III) complexes, namely: Pr-L1 (Na3[Pr(C7H3NO4)3]) and Pr-L2. The prepared complexes were further encapsulated in an optically transparent sol-gel glass. The synthesized ligands and complexes were characterized by FTIR and (1)H NMR. Room temperature luminescence of Pr-L1 and Pr-L2 complexes in solution and in sol-gel glass were investigated using a spectrofluorometer. Excitation at the maximum absorption wavelength of the ligands (280nm) resulted in the typical visible luminescence (centered at around 600nm) resulting from the (1)D2→(3)H4 transition of the Pr(III) ion, which contributes to the efficient energy transfer from the absorbing ligand L1 to the chelated Pr(III) ion (an antenna effect) while the Pr(III) luminescence is not efficiently sensitized by ligand L2. The obtained emission spectra indicated that the excitation energy level for the central Pr(III) is in a slightly lower location than ligand L1 excitation triplet (T1) level and can accept the energy transfer from T1 efficiently.