Excellent Anti-interference Property Research Articles

Amidoxime-grafted cotton fibers with anti-microbial sludge for efficient uranium recovery

Uranium as a nuclear fuel, its source and aftertreatment has been a hot topic of debate for developers. In this paper, amidoxime and guanidino-modified cotton fibers (DC-AO-PHMG) were synthesized by the two-step functionalization approach, which exhibited remarkable antimicrobial and high uranium recovery property. Adsorption tests revealed that DC-AO-PHMG had excellent selectivity and anti-interference properties, the maximum adsorption capacity of 609.75 mg/g.More than 85 % adsorption capacity could still be kept after 10 adsorption-desorption cycles, and it conformed to the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model as a spontaneous heat-absorbing chemical monolayer process. FT-IR, EDS and XPS analyses speculated that the amidoxime and amino synergistically increased the uranium uptake. The inhibitory activities of DC-AO-PHMG against three aquatic bacteria, BEY, BEL (from Yellow River water and lake bottom silt, respectively) and B. subtilis were significantly stronger, and the uranium adsorption was not impacted by the high bacteria content. Most importantly, DC-AO-PHMG removed up to 94 % of uranium in simulated seawater and extracted up to 4.65 mg/g of uranium from Salt Lake water, which demonstrated its great potential in the field of uranium resource recovery.

Electrochemical high sensitive detection of hydrogen peroxide based on platinum-palladium nano-enzyme modified microelectrode

Hydrogen peroxide (H2O2) is widely distributed in living organisms and the environment, and its concentration is closely associated with human health. Therefore, the development of an efficient and sensitive detection method for H2O2 is imperative. In this study, a PtPd nano-enzyme composite was electrodeposited onto a platinum wire microelectrode (ME) using a one-step electrochemical deposition method to fabricate an H2O2 electrochemical sensor (PtPd/ME) with exceptional performance. The successful modification of PtPd on the electrode surface was confirmed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Chronoamperometry (i-t) was employed to investigate various technical parameters including sensitivity, detection limit, detection range, reproducibility, and anti-interference capability. The results demonstrate that the sensor exhibits a sensitivity of 11.94 mA M-1 cm-2 with a detection limit of 0.034 μM and a wide linear range from 31.25 μM to 4.15 mM while also demonstrating excellent anti-interference properties. These superior performances can be attributed to the strong catalytic activity towards H2O2 provided by PtPd nanoparticles as well as the fast electron transfer rate facilitated by microelectrodes. Furthermore, this sensor effectively enables real-time monitoring of H2O2 released by ascorbic acid-stimulated vascular endothelial cells and demonstrates its potential for detecting H2O2 in contact lens care solutions. These findings provide valuable insights for food and drug testing, and demonstrate great potential for monitoring key pathological processes within living cells.

A europium(III) metal-organic framework as effective fluorescence sensor for detection of ofloxacin antibiotic

Antibiotic overuse, a critical global concern, poses significant threats to both the eco-environment and human health. Thus, selective and sensitive detection of antibiotics is an extremely important issue. Herein, a europium(III) metal-organic framework Eu2(FA)3(H2O)4·2DMAC (1) (FA = fumaric acid, DMAC = dimethylacetamide) was synthesized by solvothermal strategy. Single-crystal structural analyses indicate that Eu3+ ions are double-bridged by carboxylate groups of fumarate ligands to create one-dimensional (1D) infinite chains, which further form a 3D pillared-layer framework. 1 exhibits superior fluorescence detection performance toward ofloxacin (OFLX) with a high quenching efficiency Ksv of 4.1 × 104 M−1 and low detection limit of 2.4 × 10−6 M, and demonstrates excellent anti-interference properties and durability. Furthermore, the mechanism of fluorescence quenching was mainly attributed to static quenching process and internal filtration effect.

Utilization and value-adding of waste: Fabrication of porous material from chitosan for phosphate capture and energy storage

Efficient removal and recycling of phosphorus from complex water matrices using environmentally friendly and sustainable materials is essential yet challenging. To this end, a novel bio-based adsorbent (DX-FcA-CS) was developed by coupling oxidized dextran-crosslinked chitosan with ferrocene carboxylic acid (FcA). Detailed characterization revealed that the incorporation of FcA reduced the total pore area of DX-FcA-CS to 7.21 m2·g−1, one-third of ferrocene-free DX-CS (21.71 m2·g−1), while enhancing thermal stability and PO43− adsorption performance. Adsorption kinetics and isotherm studies demonstrated that the interaction between DX-FcA-CS and PO43− followed a pseudo-second-order kinetic model and Langmuir model, indicating chemical and monolayered adsorption mechanisms, respectively. Moreover, DX-FcA-CS exhibited excellent anti-interference properties against concentrated co-existing inorganic ions and humic acid, along with high recyclability. The maximum adsorption capacity reached 1285.35 mg·g−1 (∼428.45 mg P g−1), three times that of DX-CS and surpassing many other adsorbents. PO43−-loaded DX-FcA-CS could be further carbonized into electrode material due to its rich content of phosphorus and nitrogen, transforming waste into a valuable resource. These outstanding characteristics position DX-FcA-CS as a promising alternative for phosphate capture and recycling. Overall, this study presents a viable approach to designing environmentally friendly, recyclable, and cost-effective biomaterial for wastewater phosphate removal and value-added applications.

Metal-organic-framework-confined quantum dots enhance photocurrent signals: A molecularly imprinted photoelectrochemical cathodic sensor for rapid and sensitive tetracycline detection

BackgroundTetracycline (TC), a cost-effective broad-spectrum antibacterial drug, has been excessively utilized in the livestock and poultry industry, leading to a serious overabundance of TC in livestock wastewater. However, conventional analytical methods such as liquid chromatography and gas chromatography face challenges in achieving sensitive detection of trace amounts of TC in complex substrates. Therefore, it is imperative to develop a highly sensitive and anti-interference analytical method for the detection of tetracycline in livestock wastewater. ResultsA porphyrin-based MOF (PCN-224)-confined carbon dots (CDs) material (CDs@PCN-224) was synthesized by a “bottle-around-ship” strategy. The reduced carrier migration distance is conducive to the separation of electron-hole pairs and enhanced the photocurrent signal due to the tight coupling of CDs and PCN-224. Further, molecularly imprinted polymer (MIP) was synthesized by rapid in-situ UV-polymerization and employed as a recognition element. The specific recognition of the target by imprinted cavities blocks electron transfer, resulting in a “turn off” response signal, thus realizing the selective detection of TC. Under optimal conditions, the constructed MIP-PEC cathodic sensor detected 1.00 × 10−12 M to 1.00 × 10−7 M of TC sensitively, with a limit of detection of 3.72 × 10−13 M. In addition, the proposed MIP-PEC sensor demonstrated good TC detection performance in actual livestock wastewater. SignificanceThe strategy based on MOF pore-confined quantum dots can effectively enhance the photocurrent response of the photosensitive substrate. Simultaneously, the MIP constructed by in-situ rapid UV-polymerization showed excellent anti-interference and reusable properties. This work provides a promising MIP-PEC cathodic sensing method for the rapid and sensitive detection of antibiotics in complex-matrix environmental samples.

A recyclable Eu3+-functionalized dual-emissive metal-organic framework for portable, rapid detection and efficient removal of malachite green.

A europium-functionalized, dual-emissive, metal-organic framework-based fluorescence sensor (EuUCNDA) was constructed via post-synthetic modification of an UiO-66-type precursor through coordination interactions. EuUCNDA exhibited extremely high selectivity and sensitivity for malachite green (MG) with a low detection limit of 13.01 nM, a wide linear concentration range (0.05-50 μM), excellent anti-interference properties, a rapid response (<1 min), and the possibility of recycling. The good sensing performance of EuUCNDA enables the practical detection of MG in fish pond water and grass carp with good recoveries. Moreover, EuUCNDA can be reused for sensing MG and over 90% of fluorescence intensity can be restored after 7 cycles. Furthermore, EuUCNDA-embedded paper-based sensors combined with smartphone imaging afford portable and visual monitoring of MG in real samples. Notably, besides good sensing performance, EuUCNDA could efficiently remove MG from water. Hence, this work provides a recyclable and sensitive fluorescence sensor for portable, visual, rapid detection and efficient removal of MG.

A novel self-assembled dual-emissive ratiometric fluorescent nanoprobe for alkaline phosphatase sensing

BackgroundAlkaline phosphatase (ALP) is widely found in various organs and tissues of the human body which could assist in the verification of the presence of various diseases through its content in the blood. In the past few years, many analytical methods for ALP activity assays have been explored. However, a simple and economical method with high sensitivity and specificity also remains great challenge. Therefore, the development of sensitive and efficient approach for ALP analysis is of great significance in biomedical studies. ResultsHerein, we constructed a highly sensitive and label-free ratiometric fluorometric biosensing platform for the determination of ALP activity, which utilizing lysozyme(Ly)-functionalized 5-methyl-2-thiouracil(MTU)-modified gold nanoclusters (MTU-Ly@Au NC) and poly-dopamine (PDA) as signal indicators. Dopamine (DA) can self-polymerizes to form PDA under alkaline conditions that can further quenched the fluorescence of MTU-Ly@Au NC at 525nm due to fluorescence resonance energy transfer (FRET) and absorption competition quenching (ACQ) effects. In this process, the PDA fluorescence intensity at 325nm was nearly unchanged. After the addition of ALP, ascorbic acid (AA) which can alleviate the self-polymerization process of DA was generated from the substrate ascorbic acid 2-phosphate (AAP), thus changing ratiometric fluorescence intensity of I525/I325. Hence, by monitoring the fluorescence ratio (I525/I325), a ratiometric fluorescence biosensing platform for ALP was established with the linear calibration in the range of 0.5–8 U L−1 and the limit of detection of 0.157 U L−1. SignificanceThis work not only synthesized a novel fluorescence probe with simple preparation and low cost for ALP which has excellent anti-interference properties and selectivity. Furthermore, this biosensing platform was successfully applied for the determination of ALP activity in human serum samples. This work provided a potential tool for biomedical diagnostics in the future.

Optical frequency comb assisted reconfigurable broadband spread spectrum signal generation.

A photonic-assisted scheme for spread spectrum communication signals generation is proposed and demonstrated in this article. The spreading sequence and the baseband data codes are modulated on the photonic link by electro-optic modulators, and the spread spectrum process is completed through stream processing on the analog microwave photonic link. By combining optical frequency comb and injection locking technologies, the carrier frequency of the communication signals can be tuned over an ultra-broadband range of 3-39 GHz. In the proof-of-concept experiments, spread spectrum signals at 3 GHz and 6 GHz are obtained with a spread factor of 31. The analysis results indicate that the generated signals possess excellent reconfiguration, anti-interference, and anti-interception properties. Overall, our proposed scheme offers a flexible photonic architecture with significant potential in the application of ultra-broadband covert communication systems.

An electrochemical sensor based on the composite UiO-66-NH2/rGO for trace detection of Pb(II) and Cu(II)

Pb(II) and Cu(II) can cause serious harm to human health. Therefore, it is of great significance to develop highly sensitive detection methods. Herein, the composite UiO-66-NH2/rGO was prepared by in-situ growth method. The UiO-66-NH2/rGO showed high sensitivity with Pb(II) of 6.27 μA/μM and Cu(II) of 6.83 μA/μM. Additionally, the UiO-66-NH2/rGO exhibits excellent repeatability, reproducibility, anti-interference properties and practical application potential. These results indicate that UiO-66-NH2/rGO is an excellent electrode modification material. The composite has the advantages of high sensitivity and good practical application effect. This work provides a strategy for the application of UiO-66-NH2 in the field of electrochemical sensing.

A 3,5-dinitropyridin-2yl Substituted Flavonol-based Fluorescent Probe for Rapid Detection of H2S in Water, Foodstuff Samples and Living Cells.

A novel flavonol-based fluorescent probe, Fla-DNT, has been synthesized for the rapid and specific detection of H2S. Fla-DNT exhibits excellent selectivity and anti-interference properties, a short response time (4min), large Stokes shift (138nm), and low detection limit (1.357 µM). Upon exposure to H2S, Fla-DNT displays a remarkable increase in fluorescence intensity at 542nm. Meanwhile, the recognizing site of H2S was predicted through Electrostatic potential and ADCH charges calculations, while the sensing mechanism of H2S was determined via HRMS analysis and DFT calculation. More importantly, the probe owes multiple applications, such as a recovery rate ranging from 92.00 to 102.10% for detecting H2S in water samples, and it can be fabricated into fluorescent strips to track H2S production during food spoilage by tracking color changes, thereby enabling real-time monitoring of food freshness. The bioimaging experiments demonstrate the capability of Fla-DNT to detect both endogenous and exogenous H2S in living cells. These results provide a reliable method and idea for H2S detection in complex environments.

A single-fluorophore-based self-calibrating supramolecular sensor for the fast and ratiometric detection of permethrin

Permethrin (PMT) is a broad-spectrum synthetic pyrethroid insecticide widely used for treatment of insects in agriculture. Yet the massive use of PMT comes at the cost of its residue ubiquitous in the environment thereby causing a significant risk to human health. Therefore, development of an analytical method for accurate detection of PMT at the point-of-care is of great importance. In this study, we report a novel single-fluorophore-based supramolecular sensor with dual emissions as ratiometric output signals, successfully realizing the fast detection of PMT with the self-calibrating feature. This sensor exhibited several advantages for PMT detection, such as fast response, high sensitivity, high specificity, and excellent anti-interference property. Notably, this sensor could be used for on-site monitoring of PMT residues on the food surface without the help of complicated testing facilities. To our best knowledge, this is the first promising fluorescent method for the fast and ratiometric determination of PMT.

Efficient detection of nitrite in water based on an Au/NiO/Rh trimetallic composite modified laser-induced graphene electrode prepared by one-step electrodeposition

In this study, we employed a straightforward and rapid one-step electrodeposition method to enhance modify an Au/NiO/Rh composite on laser-induced graphene (LIG) for nitrite (NO2–) detection. We extensively characterized and tested the morphological composition and electrochemical properties of the electrode using scanning electron microscopy and other characterization techniques. To compare the electrochemical active surface areas of the electrode before and after modification, we conducted cyclic voltammetry experiments. Additionally, we confirmed the changes in electron transfer performance and adsorption energy of the modified electrode through by density functional theory calculations. The experimental results demonstrate that the combined modification of LIG with rhodium nanoparticles (RhNPs) and gold nanoparticles (AuNPs) improves electron transport ability at the electrode interface and enhances the electrode's electrocatalytic performance. The incorporation of nickel oxide (NiO) also provides a larger reaction area and more active sites for NO2– detection. The synergistic effects of these three modified components significantly enhance NO2– detection at the electrode, surpassing the performance of the bimetallic modified electrode. Under optimized experimental conditions, the sensor exhibits a linear range of 1 μmol/L to 1 mmol/L and a detection limit of 0.3 μmol/L. Furthermore, the sensor demonstrates excellent anti-interference and repeatability properties. We successfully applied the sensor for determination of NO2– in tap water, yielding satisfactory results. This research presents a promising strategy for the portable, sensitive, and in-situ detection of NO2– in water environments using metal-based electrochemical sensors.

Fluorescence determination of the total amount of tetracyclines by a flavonol-based supramolecular sensor

Tetracyclines (TCs) are a group of broad-spectrum antibiotics against multiplying microorganisms yet with several adverse effects on humans. Since all types of TCs have the similar chemical skeleton and mechanism of action, quantification of total amount of TCs in the environment was of particular importance. To date, dozens of fluorescent probes have been reported for TCs detection, but only very few of them enabled detection of total TCs. In this study, we report a novel supramolecular sensor constructed by human serum albumin as the recognition moiety and a flavonol fluorophore as the indicator. Under the 370 nm UV excitation, this sensor exhibits the rapid response (5 s), acceptable sensitivity (limit of detection ∼ 0.58 μM), long dynamic detection range (0–20 μM), prominent specificity, and excellent anti-interference properties for analysis of total TCs. The mechanism was carefully validated using 1H NMR, fluorescence titration experiments, molecular docking, and mass spectrometry. We expect this work can inspire more sensor design for TCs quantification.

Novel AIEE pillar[5]arene-fluorene fluorescent copolymer for selective recognition of paraquat by forming polypseudorotaxane

A novel conjugated polymer (Co-P[5]Flu) was synthesized by copolymerizing a difunctionalized pillar[5]arene and a fluorene derivative monomer. Co-P[5]Flu displayed an aggregation-induced emission enhancement (AIEE) effect because of the restricted intramolecular rotations of the pillar[5]arene unit. Co-P[5]Flu exhibited high selectivity and sensitivity towards the pesticide paraquat (PQ) with excellent anti-interference properties. It presented fluorescence quenching response (1–I/I0=96.6%) only towards paraquat and not towards other competitive guests. The fluorescence titration experiments revealed that the detection limit (LOD) for paraquat was as low as 1.69×10−8 M, and the Stern-Volmer constant (KSV) was determined to be 2.11×104 M−1. The recognition mechanism was studied using both 1H NMR titration and theoretical calculations. The Co-P[5]Flu showed fluorescence quenching for PQ due to the synergistic effect of polypseudorotaxane formation and photoinduced electron transfer (PET). Additionally, the polymer chemosensor demonstrated potential for the detection of paraquat in practical samples.

Bimetallic copper-cobalt MOFs anchored carbon nanofibers hybrid mat based electrode for simultaneous determination of dopamine and tyramine

Early monitoring of histamine and tyramine levels in foodstuffs could protect against several diseases. In the present study, a self-standing copper-cobalt(2-methylimidazole) MOF anchored carbon nanofiber hybrid mat (Cu-Co(2-Meim)MOF@CNF) was prepared for the simultaneous detection and quantification of dopamine and tyramine in cheese and banana samples. As-prepared Cu-Co(2-Meim)MOF@CNF hybrid mats are highly porous with a large surface area, and also possess excellent hydrophilicity, which allows the analyte molecules to easily access the redox-active metal sites of the MOF matrix and subsequently enhance the sensitivity. The functional groups within the MOF matrix can also function as active adsorption sites during electrocatalysis. At the acidic condition (pH = 5.0), the Cu-Co(2-Meim)MOF@CNF exhibited improved catalytic activity and strong electrochemical sensitivity toward dopamine (DA) and tyramine (TY) with faster electron transfer kinetics and significant fouling resistance. The oxidation reactions of dopamine and tyramine at the hybrid electrode were irreversible and diffusion-controlled. The Cu-Co(2-Meim)MOF@CNF/GCE sensor demonstrated a broad linear range from 5 to 800 µM along with a low LOD of 44.2 nM and 52.7 nM for dopamine and tyramine, respectively. The hybrid sensor exhibited excellent anti-interference properties and long-term storage stability for up to 30 days. It is noteworthy that the Cu-Co(2-Meim)MOF@CNF/GCE sensor has demonstrated the capability of detecting dopamine and tyramine in cheese and banana samples, respectively, which would be helpful for food analysis and food safety.

Fast and sensitive detection of nitroxynil using a chalcone-based supramolecular fluorescent sensor

Nitroxynil as a veterinary drug has been widely used for treatment of parasitic worms in food-producing sheep and cattle. However, the residual nitroxynil in edible animal products can lead to severe adverse effects on human health. Thus, development of an effective analytical tool for nitroxynil is of great significance. In the present study, we designed and synthesized a novel albumin-based fluorescent sensor, which was capable of detecting nitroxynil with the fast response (<10 s), high sensitivity (limit of detection ∼8.7 ppb), high selectivity, and excellent anti-interference property. The sensing mechanism was clarified by using the molecular docking technique and mass spectra. Moreover, this sensor showed the detection accuracy comparable to standard HPLC method, and meanwhile exhibited much shorter response time and higher sensitivity. All the results demonstrated that this novel fluorescent senor could serve as a practical analytical tool for determination of nitroxynil in real food samples.

Development of a novel sensor based on Bi2O3 and carbonized UIO-66-NH2 nanocomposite for efficient detection of Pb(Ⅱ) ion in water environment

Development of an efficient monitoring technology for rapid detection of toxic Pb(Ⅱ) ion in water environments is extremely important. Here, a novel and highly sensitive sensor was prepared using one-step calcination technique, based on Bi2O3 nanoparticles and carbonized metal–organic framework (MOF) nanocomposite. Scanning electron microscopy, transmission electron microscopy, contact angle and X-ray photoelectron spectroscopy characterization methods were used to analyze the morphology and structure of the prepared materials. Based on the electrical double-layer capacitance theory and Raman spectroscopy, changes to the active sites of different modified materials were investigated. Besides, differential charge densities and adsorption energies of the different modified materials in Zr-O clusters were calculated using density functional theory (DFT). A Bi2O3 and carbonized UIO-66-NH2 (Bi2O3/C-UIO-66-NH2) -modified glassy carbon electrode was used to detect Pb(Ⅱ) by differential pulse anodic stripping voltammetry. Under optimal experimental parameters, the developed electrochemical sensor has a wide linear range (2–130 μg/L) and a low detection limit (0.05 μg/L). Meanwhile, the sensor has excellent stability, repeatability, and anti-interference properties and has been successfully applied to detect Pb(Ⅱ) in actual water samples. The results of this paper show that our developed sensor an efficient and rapid sensor technology for monitoring lead in water environment.

Electrochemical Detection of Hydrogen Peroxide Based on Ag-Deposited Carbon Nanosphere Composites

Hydrogen peroxide (H2O2) is closely related to our daily life and health, so it is urgent to accurately detect and analyze its content. Herein, a non-enzymatic H2O2 electrochemical sensor was successfully constructed based on electrodeposited silver nanoparticles (Ag NPs) on carbon nanospheres (CNs). Electrochemical characterization results showed that Ag NPs/CNs/GCE displayed good electrocatalytic performance for H2O2. The diffusion coefficient (D) and heterogeneous rate constant (k0) of hydrogen peroxide were calculated separately. In addition, the sensor had a wide linear range of 4.98 × 10−9 ∼ 7.29 × 10−3 M and a low detection limit of 1.66 × 10−9 M. It also presented excellent anti-interference properties in the presence of various substances. The content of hydrogen peroxide was further detected in real samples of makeup remover, milk and disinfectant with satisfactory recovery rates, confirming its application potential in routine detection.

Impedimetric-type NO2 sensor based on the p-NiO/n-NiNb2O6 heterojunction sensing electrode

Development of high-performance NO2 gas sensors with good sensitivity and long-term stability at high temperatures is expected for exhaust gas monitoring. The sensor performance mainly depends on sensing material. In this work, p-NiO/n-NiNb2O6 heterojunction material is successfully synthesized and an impedimetric NO2 sensor was assembled using the above material as sensing electrode (SE) and gadolinia-doped ceria (CGO) with a dense/porous bilayer structure as a solid electrolyte. Introduction of SE to the CGO porous layer by screen printing followed by cold isostatic pressing treatment before calcination allows SE to successfully enter inside the porous layer and greatly increases the area of the three-phase boundary (TPB) and improves the long-term stability of the sensor. Using NiO/NiNb2O6 heterojunction SE can effectively improve the modulus (|Z|) response value (S|Z| = (|Z|air - |Z|gas)/|Z|air) of the sensor. Among the sensors, 90NiO/10NiNb2O6 (the mass ratio of NiO to Nb2O5 is 9:1) based NO2 sensor exhibits the best response performance and the highest sensitivity (0.34/ppm at 500 °C). The sensor also shows an excellent anti-interference property. Introduction of 300 ppm CO2, CH4, NO, CO, or H2 into 300 ppm NO2 makes response signal change below 3 % and 300 ppm NH3 only leads to signal reduction by 8.9 %, which is relatively low in a similar sensing system. The sensor response toward NO2 is slightly affected by O2 concentration change in 5–21 %. The superior performance of the sensor can be principally attributed to the heterojunction effect, which promotes the charge transfer and the adsorption capacity for NO2.

2-Methylimidazole-doped nanozymes with enhanced laccase activity for the (+)-catechins detection in dairy products

In this work, 2-methylimidazole (MI) was doped into the Bpy-Cu nanozyme as a second ligand to form a novel laccase-mimicking enzyme (MI-Bpy-Cu). By comparison, MI-Bpy-Cu nanozyme was identified to have excellent laccase-mimicking activity, high stability and catalytic kinetic properties. It may be that the incorporation of 2-methylimidazole helped the nanozymes to build a structure closer to natural laccase and accelerate the electron transfer rate, thereby achieving the purpose of enhancing the activity. Furthermore, we observed that MI-Bpy-Cu nanozymes could oxidize the colorless (+)-Catechin to generate a yellow radical product, and a novel colorimetric sensing strategy for (+)-Catechin was successfully developed. The method had excellent selectivity and anti-interference properties, and also had good application in the analysis of (+)-Catechin in dairy products.