Selective detection of ionic liquid fluorescence probes for visual colorimetry of different metal ions.

At present, the fast distinction of different metal ions in pure water media is not only a great challenge, but also drives the protection of water quality in environmental water bodies. In this paper, a novel ionic liquid fluorescent probe Glycolic Acid-L-Arginine (GA-L-Arg) was rationally created and designed through an in-depth study of ionic liquids. It is also used as an innovative multi-ion fluorescent probe for colorimetric detection and separate identification of Fe3+ and Co2+ in aqueous solutions of various metal ions. GA-L-Arg has excellent water solubility due to the strong hydrophilicity of Glycolic Acid and L-Arginine. The probe showed high sensitivity, extremely significant selectivity, and great pH stability for Fe3+ and Co2+ in pure water. The GA-L-Arg structure and the mechanism of Fe3+ and Co2+ detection were analyzed by infrared spectroscopic characterization and quantum chemical calculations. More importantly, the distinct colorimetric partitioning of Fe3+ and Co2+ was performed by the unique extraction of Fe3+ in the presence of the fluorescent probe and buffer solution.

The Selective Detection of Cyantraniliprole Insecticides Using Molecularly Imprinted Polymers Coupled with an Acetylcholinesterase Inhibition-Based Biosensor.

Cyantraniliprole is one of the anthranilic diamide insecticides widely used in the agriculture sector. Due to its low toxicity and relatively fast degradation, there is need for a sensitive determination method for its residues. Nowadays, there is growing interest in the development of enzyme-based biosensors. The major drawback is the non-specific binding of many insecticides to the enzyme. This work employs Molecularly imprinted polymers (MIPs) to increase enzyme specificity and eliminate the organic solvent effect on the enzyme activity. The synthesized Cyan-Molecularly imprinted polymers (Cyan-MIP) possesses high affinity and selectivity toward cyantraniliprole. Acetylcholinesterase assay characteristics including enzyme concentration, substrate concentration, DTNB concentration, and acetonitrile concentration were optimized. Under optimal experimental conditions, the developed MIP-Acetylcholinesterase (MIP-AchE) inhibition-based sensor provides better precision than the AchE inhibition-based sensor with a wide linear range (15-50 ppm), limit of detection (LOD) 4.1 ppm, and limit of quantitation (LOQ) 12.6 ppm. The sensor was successfully applied for cyantraniliprole determination in spiked melon, giving satisfactory recoveries.

Self-assembly flexible SERS imprinted membrane based on Ag nanocubes for selective detection of microcystin-LR.

Silver nanocubes monolayer-modified polydimethylsiloxane (Ag NC/PDMS) flexible SERS substrates have been prepared by a three-phase interface self-assembly procedure. The combination of this method with membrane technology brings nanoparticles in close proximity, densely, and regularly arranged in monolayers over a large area, leading to excellent SERS properties. Considering the complexity of practical detection, molecular imprinted polymers (MIPs) were anchored on the surface of SERS substrate and applied to selective detection of microcystin-LR (MC-LR). It is worth mentioning that the SERS imprinted membranes (AP-MIMs) were still clearly detected at a concentration of 0.1 µg·L-1 of MC-LR in drinking water, and the detection limit was as low as 0.0067 µg·L-1. The substrate exhibited excellent uniformity with a relative standard deviation (RSD) of 6.1%. In the presence of interference molecules, AP-MIMs exhibited excellent selectivity for MC-LR. Furthermore, in the spiking and recovery tests of practical lake water samples, the method showed excellent recoveries ranging from 96.47 to 105.31%. It has been demonstrated that the prepared AP-MIMs can be applied to sensitive and specific detection of trace amounts of MC-LR in drinking water.

A New Fluorescent Probe for Hydrogen Sulfide Detection in Solution and Living Cells.

Since Hydrogen Sulfide (H2S) was recognized as a gas transmitter, its detection and quantification have become a hot research topic among chemists and biologists. In this area, fluorescent probes have shown great advantages: fast and strong response, low detection limit and easy manipulation. Here we developed a new fluorescent probe that detected H2S selectively among various bioactive and inorganic salts. This probe was based on the core structure of fluorescein and reacted with H2S through azide-reduction. Great linearity was achieved correlating fluorescence intensity and H2S concentrations in solution. The detection of H2S in cancer cells was also achieved.

Unfolding the Role of Building Units of MOFs with Mechanistic Insight Towards Selective Metal Ions Detection in Water.

The potential emergence of fluorescence-based techniques has propelled research towards developing probes that can sense trace metal ions specifically. Although luminescent metal-organic frameworks (MOFs) are well suited for this application, the role of building blocks towards detection is not fully understood. In this work, a systematic screening by varying number of Lewis basic (pyridyl-N atoms) sites is carried out in a series of isostructural, robust UiO-67 MOFs, and targeting a model metal ion-Fe3+ . All the three fluorescent MOFs are seen to present quenching response towards Fe3+ ions in water. However, UiO-67@N exhibits highly selective and sensitive response, whereas emission of both UiO-67 and UiO-67@NN is quenched by several metal ions. Detailed experimental and theoretical mechanistic investigation is carried out in addition to demonstration of UiO-67@N being able to sense trace amount of Fe3+ ions in synthetic biological water sample. Further, UiO-67@N based mixed-matrix membrane (MMM) has been prepared and employed to mimic the real time Fe3+ ions detection in water.

The selective detection of Fe3+ ions using citrate-capped gold nanoparticles.

Citrate is a ubiquitous biological molecule that functions as Fe3+ chelators in some bacteria and the blood plasma of humans. Inspired by the strong affinity between citrate and Fe3+, a colorimetric Fe3+ probe based on citrate-capped AuNPs without any additional modification was designed. Citrate-capped AuNPs with a diameter of 22 nm were applied to detect Fe3+ without other reagents' assistance. This easily-prepared and low-cost colorimetric sensor exhibited good selectivity towards Fe3+ among common metal ions, a good linear relationship in the range of 0.1-0.8 µM of Fe3+ and quick response time of 10 min.

A fluorescent molecular rotor for the selective detection of the hybrid-conformation 22AG G-Quadruplex.

G-quadruplex (G4) DNA plays a vital role in myriad biological process and is linked to several human diseases, including Alzheimer's disease. Probing G4s with fluorescent probes can provide a better understanding their mechanisms of action and of their roles in Nature. In this study we developed a quinolinium-vinylaniline molecular rotor probe, featuring a diethylaminosalicylaldehyde unit that could discriminate the hybrid-22AG G4 sequence selectively amongst other G4 sequences. This probe underwent a significant red-shift upon binding to the target G4 (broad 575 nm â†’ sharp 630 nm) with enhanced fluorescence (up to 14-fold). We suspect that the vinylaniline unit of the molecular rotor, when bound to the hybrid-22 A G4, experienced restricted rotation, thereby undergoing enhanced intramolecular charge transfer. The presence of the diethylaminosalicylaldehyde moiety appeared to play a major role in the enhanced selectivity toward the 22AG G4.

Selective gas detection of titania nanoparticles via impedance spectroscopy and capacitive measurement.

The present paper demonstrated the impedance analysis of Au/TiO2nanoparticles/Si-Al capacitive sensor for selective detection of volatile organic compounds (VOCs) at different frequency regimes. TiO2nanoparticles (NP) were synthesized through the solution process and characterized by field-emission scanning electron microscopy , x-ray diffraction analysis, photoluminescence spectroscopy, and atomic force microscopy. The gas sensitivity of Au/TiO2-NP/Si-Al was investigated, with the effect of temperature modulation (25 °C-250 °C) and dielectric variation in the vicinity of nanoparticles. Impedance spectroscopy of TiO2-NP was carried out to obtain resonant peaks over the frequency ranging from 0.05 to 225 kHz and fitted with a complex nonlinear least-squares method. The optimum sensor response of 136%, 63%, 152%, and 174% was found at resonant frequencies of 0.38 kHz, 0.22 kHz, 0.15 kHz, and 0.1 kHz for the exposure of 2-propanol, acetone, ethanol, and methanol, respectively. The fastest response time and recovery time were found to be 32/21 s, 31.2/8 s, 32.5/9 s, and 40/26 s for acetone, 2-propanol, ethanol, and methanol, respectively. Selective detection of different VOCs at various resonant frequencies has correlated with the dielectric variation of the NPs and their associated void region under gas exposure.

Hydrophilic modification of PVDF-based SERS imprinted membrane for the selective detection of L-tyrosine.

The polyvinylidene difluoride (PVDF) membrane has received considerable attention as a flexible surface enhanced Raman scattering (SERS) substrate due to its excellent mechanical and physicochemical properties. However, the poor fouling resistance of PVDF membrane due to its intrinsic hydrophobic property limits its practical application. To address this, in this investigation, a SERS imprinted membrane is synthesized based on W18O49/Ag composites. Firstly, to promote hydrophilicity, N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) are copolymerized by hydrolysis condensation and linked with engineered polyvinypyrrolidone (PVP) chains exposed on the surface of membrane. Furthermore, W18O49/Ag composites are dispersed on the membrane under the assistance of polydopamine (pDA) to promote the pollution resistance. Subsequently, in order to demonstrate the practical detection property, W18O49/Ag/PVDF membrane is selected as the SERS substrate to synthesize SERS imprinted membrane by precipitation polymerization for the selective detection of L-tyrosine. The characteristic results reveal that the SERS-imprinted membrane exhibits satisfactory hydrophilicity, and it can effectively degrade the pollutant molecules absorbed on its surface under ultraviolet light illumination. It is proved from the detection results that the LOD of WADP-MIMs for L-tyrosine reached 10-9 mol L-1 when the concentration of L-tyrosine changed between 10-3-10-9 mol L-1. The correlation coefficient (R2) is 0.994 and the limit of detection is 10-9 mol L-1. Meanwhile, it can be applied for the selective detection of L-tyrosine in mixture samples. Overall, this study presents a novel approach for the hydrophilic modification and pollution resistance enhancement of PVDF-based SERS imprinted membrane, which can be effectively utilized for the selective detection of practical samples.

Integrating a Luminescent Porous Aromatic Framework into Indicator Papers for Facile, Rapid, and Selective Detection of Nitro Compounds.

Porous aromatic framework materials with high stability, sensitivity, and selectivity have great potential to provide new sensors for optoelectronic/fluorescent probe devices. In this work, a luminescent porous aromatic framework material (LNU-23) was synthesized via the palladium-catalyzed Suzuki cross-coupling reaction of tetrabromopyrene and 1,2-bisphenyldiborate pinacol ester. The resulting PAF solid exhibited strong fluorescence emission with a quantum yield of 18.31%, showing excellent light and heat stability. Because the lowest unoccupied molecular orbital (LUMO) of LNU-23 was higher than that of the nitro compounds, there was an energy transfer from the excited LNU-23 to the analyte, leading to the selective fluorescence quenching with a limit of detection (LOD) ≈ 1.47 × 10-5 M. After integrating the luminescent PAF powder on the paper by a simple dipping method, the indicator papers revealed a fast fluorescence response to gaseous nitrobenzene within 10 s, which shows great potential in outdoor fluorescence detection of nitro compounds.

Behaviour of Extractives in Norway Spruce (Picea abies) Bark during Pile Storage.

The current practices regarding the procurement chain of forest industry sidestreams, such as conifer bark, do not always lead to optimal conditions for preserving individual chemical compounds. This study investigates the standard way of storing bark in large piles in an open area. We mainly focus on the degradation of the most essential hydrophilic and hydrophobic extractives and carbohydrates. First, two large 450 m3 piles of bark from Norway spruce (Picea abies) were formed, one of which was covered with snow. The degradation of the bark extractives was monitored for 24 weeks. Samples were taken from the middle, side and top of the pile. Each sample was extracted at 120 °C with both n-hexane and water, and the extracts produced were then analysed chromatographically using gas chromatography with flame ionisation or mass selective detection and high-performance liquid chromatography. The carbohydrates were next analysed using acidic hydrolysis and acidic methanolysis, followed by chromatographic separation of the monosaccharides formed and their derivatives. The results showed that the most intensive degradation occurred during the first 4 weeks of storage. The levels of hydrophilic extractives were also found to decrease drastically (69% in normal pile and 73% in snow-covered pile) during storage, whereas the decrease in hydrophobic extractives was relatively stable (15% in normal pile and 8% in snow-covered pile). The top of the piles exhibited the most significant decrease in the total level of extractives (73% in normal and snow-covered pile), whereas the bark in the middle of the pile retained the highest amount of extractives (decreased by 51% in normal pile and 47% in snow-covered pile) after 24-week storage.

Two New Coordination Polymers: Selective Detection of Cu(II) Ion and Treatment Activity on Inner Ear Damage.

In the current study, on the basis of 1,3,5-tris(2-methylimidazol-1-yl)benzene (timb), a designed tripodal connector, two new transition metal coordination polymers (CPs), {[Cu4(timb)2(Br-IPA)4]·5H2O}n (1) and {[Zn(timb)0.5(NH2-IPA)]·4H2O}n (2) have been generated with the mixed ligand method by the reaction between the timb and corresponding metal salts in the existence of dissimilar functional isophthalic acid (H2IPA) ligands. Furthermore, the Zn(II)-based complex 2 displays high sensitivity in the detection of Cu(II) ion in water. The neural stem cells proliferation after treated via compounds was detected with Cell Counting Kit-8 detection assay. And the real time reverse transcription polymerase chain reaction was carried out for the investigation of the differentiation function of the neural stem cells after the compound 1 treatment and compound 2 treatment. Further, molecular docking simulations confirmed that the biological activity that has been observed from experiments were from the carboxyl group on the Cu complex, in contrast, the imidazole groups were only used for binding with the Cu metal ion to retain the complex structure.

FeIII -Salen-Based Probes for the Selective and Sensitive Detection of E450 in Foodstuff.

Inorganic pyrophosphate (PPi) is considered as a diagnostic marker for various diseases such as cancer and vascular calcification. PPi also plays an important preservative role as an additive E450 in foodstuff. In this work, a selective FeIII -salen-based probe for PPi is described; this probe disassembles in the presence of the target analyte into its molecular blocks, 1,2-propanediamine and 3-chloro-5-formyl-4-hydroxybenzenesulfonic acid. The latter signaling unit leads to a fluorometric response. Compared with a related prototype, the new complex shows a 2.3-times stronger emission at 500 nm and a 155-times better selectivity of PPi over adenosine triphosphate (ATP). Importantly, the new probe was successfully applied for detecting E450 in foodstuff.

Detection of Organophosphorous Chemical Agents with CuO-Nanorod-Modified Microcantilevers.

Microcantilevers are really promising sensitive sensors despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper oxide (CuO) nanorods. The synthesis of the nanostructure consists of the oxidation of a copper layer deposited beforehand on the surface of the sample. The oxidation is performed in an alkaline solution containing a mixture of Na(OH) and (NH4)2S2O8. The synthesis procedure was first optimized on a silicon wafer, then transferred to optical cantilever-based sensors. This transfer requires specific synthesis modifications in order to cover all the cantilever with nanorods. A masking procedure was specially developed and the copper layer deposition was also optimized. These nanostructured cantilevers were engineered in order to detect vapors of organophosphorous chemical warfare agents (CWA). The nanostructured microcantilevers were exposed to various concentration of dimethyl methylphosphonate (DMMP) which is a well-known simulant of sarin (GB). The detection measurements showed that copper oxide is able to detect DMMP via hydrogen interactions. The results showed also that the increase of the microcantilever surface with the nanostructures improves the sensors efficiency. The evolution of the detection performances of the CuO nanostructured cantilevers with the DMMP concentration was also evaluated.

High Stability and Strong Fluorescence of Carbon Nanodots as Nanosensor for Hg2+ in Environmental Waters.

Pollution of toxic heavy-metal ions such as mercury ions (Hg2+) is well known to severely threaten ecological environment and human health. Correspondingly, development of a fast and sensitive method for detecting heavy-metal ions is urgently needed and has been received widespread attention in recent years. In this study, carbon nanodots (CDs) with strong blue fluorescence were synthesized by a microwave-assisted hydrothermal method. The as-prepared blue fluorescent CDs not only have excellent stability (e.g. photostability, salt stability and pH stability), but also have extremely high selectivity and sensitivity for probing Hg2+ via fluorescence quenching. Specifically, fluorescence of CDs is gradually quenched along with the increase in Hg2+ concentration, and a low concentration of Hg2+ can be identified (with low detection limit, 15 nM). Therefore, the novel fluorescent CDs could be developed for detecting Hg2+ in aqueous conditions, and have great potential for fast probing Hg2+ in environmental samples.

Modification of nanocrystalline TiO2 coatings with molecularly imprinted TiO2 for uric acid recognition.

Combining the surface modification and molecular imprinting technique, a novel piezoelectric sensing platform with excellent molecular recognition capability was established for the detection of uric acid (UA) based on the immobilization of TiO2 nanoparticles onto quartz crystal microbalance (QCM) electrode and modification of molecularly imprinted TiO2 (MIT) layer on TiO2 nanoparticles. The performance of the fabricated biosensor was evaluated, and the results indicated that the biosensor exhibited high sensitivity in UA detection, with a linear range from 0.04 to 45 µM and a limit of detection of 0.01 µM. Moreover, the biosensor presented high selectivity towards UA in comparison with other interferents. The analytical application of the UA biosensor confirmed the feasibility of UA detection in urine sample.

A Selective Turn off Fluorescence Sensor Based on Propranolol-SDS Assemblies for Fe3+ Detection.

A fluorophore modulation with sodium dodecyl sulphate (SDS) assemblies for the selective and sensitive sensing of Fe3+ ions in aqueous solution is illustrated in this work. Emission spectral characteristics of fluorescent molecule, propranolol (PPH) was intact in presence of metal ions. While on modulation with SDS assemblies, PPH was transformed into a tuneable sensor for Fe3+ ions. This sensor ensemble was not only highly sensitive towards Fe3+ ions in aqueous solution with detection limits lower than 3 µM but also possess high discriminating efficiency in presence of other metal ions like Cu2+, Pb2+, Zn2+, Ni2+, Fe2+, Cd2+, Co2+, Al3+, Mg2+, Hg2+ and Mn2+. The electrostatic interaction of the anionic group of surfactants with the metal cations significantly increases the communication between metal ions and PPH moiety which results in the quenching of PPH fluorescence. We have employed fluorescence steady state and lifetime studies to understand the metal sensing behaviour of the PPH-SDS sensor system. Principal component analysis (PCA) was used to evaluate the discriminative ability of the developed sensor system towards Fe3+ ions.

A molecularly imprinted nanoprobe incorporating Cu2O@Ag nanoparticles with different morphologies for selective SERS based detection of chlorophenols.

In a new method for the determination of trace levels of chlorophenols in river waters, detection via surface-enhanced Raman scattering (SERS) is combined with recognition by a molecularly imprinted polymer (MIP). Nanoparticles of type Cu2O@Ag were synthesized by attaching silver particles to the surface of Cu2O nanoparticles. The Cu2O@Ag were then coated with a layer of a MIP that was obtained by atom transfer radical polymerization using from methacrylic acid as monomers and 2,6-dichlorophenol as the template. The morphology of Cu2O is found to be flower-like. The Cu2O@Ag-MIPs displays a strong SERS effect. Following removal of the template by rinsing with the mixture solution of methanol/acetic acid (9/1, v/v), the material was used to selectively bind 2,6-dichlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenol. The SERS peak intensity at 1580 cm-1 increases linearly with the concentration of the various chlorophenols in the range from 10 nM to 1 mM, and the detection limit is 5.8 nM. The imprinting factor is 4.62. The method was applied to the analysis of (spiked) river water, with recoveries ranging from 91.8 to 115.4% and relative standard deviations of <4.5%. Graphical abstract.

A Porous Framework as a Variable Chemosensor: From the Response of a Specific Carcinogenic Alkyl-Aromatic to Selective Detection of Explosive Nitroaromatics.

Selective probing of one molecule from one class of similar molecules is highly challenging due to their similar chemical and physical properties. Herein, a novel metal-organic framework FJI-H15 with flexible porous cages has been designed and synthesized, which can specifically recognize ethylbenzene with ultrahigh enhancement efficiency from a series of alkyl-aromatics, in which an unusual size-dependent interaction has been found and proved. It can also selectively detect phenolic-nitroaromatics among a series of nitroaromatics based on energy transfer and electrostatic interactions. Such unusual specificity and variable mechanisms responding to different types of molecules have not yet been reported, which will provide a new strategy for the development of more effective chemosensors based on MOFs for probing small structural differences in molecules.

Flow injection gas chromatography with sulfur chemiluminescence detection for the analysis of total sulfur in complex hydrocarbon matrixes.

A fast and reliable analytical technique for the determination of total sulfur levels in complex hydrocarbon matrices is introduced. The method employed flow injection technique using a gas chromatograph as a sample introduction device and a gas phase dual-plasma sulfur chemiluminescence detector for sulfur quantification. Using the technique described, total sulfur measurement in challenging hydrocarbon matrices can be achieved in less than 10 s with sample-to-sample time <2 min. The high degree of selectivity and sensitivity toward sulfur compounds of the detector offers the ability to measure low sulfur levels with a detection limit in the range of 20 ppb w/w S. The equimolar response characteristic of the detector allows the quantitation of unknown sulfur compounds and simplifies the calibration process. Response is linear over a concentration range of five orders of magnitude, with a high degree of repeatability. The detector's lack of response to hydrocarbons enables direct analysis without the need for time-consuming sample preparation and chromatographic separation processes. This flow injection-based sulfur chemiluminescence detection technique is ideal for fast analysis or trace sulfur analysis.