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The development of highly sensitive and selective fluorescent sensors toward Cu2+ has gained considerable attention in view of its application of environmental and biological fields. However, the strategy of sensing by the fluorescence "turn-on" mode at a longer wavelength has not been well explored until now. In the present study, we report a novel green-emitting Cu2+-targeted fluorescent sensor, PIA(OH)-Py, with an improved Stokes' shift (182 nm), synergistically operated by the multi-mechanism based on the excited state intramolecular proton transfer (ESIPT) process combined with the aggregation-induced emission (AIE) phenomenon. A moderate fluorescence of PIA(OH)-Py was first fabricated with the effect of ESIPT-on as well as AIE-on. In the presence of Cu2+, the strong emission of the in situ complex PIA(OH)-Py–Cu2+ was obtained by the impact of further AIE-on accompanied by ESIPT-off as a fluorescence "turn on" response. In addition, the chelation-enhanced fluorescence (CHEF) mechanism was also partly responsible for the fluorescence increment due to the formation of the complex PIA(OH)-Py–Cu2+. Further study revealed that PIA(OH)-Py could respond to Cu2+ in living cells by the green light channel and determine the concentration of Cu2+ in real blood samples. [ABSTRACT FROM AUTHOR]

The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1−14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1−14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g−1). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption–desorption cycling process. [ABSTRACT FROM AUTHOR]

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g−1) at a low Li+ concentration of 12 mmol L−1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent. [ABSTRACT FROM AUTHOR]

Accurate fabrication of fluorescence probes to efficiently monitor and detect H2S levels in the fields of foodstuffs and physiology is crucial. Herein, we report two isomeric phenanthro[9,10-d]imidazole benzene sulfonamide-derived fluorescence probes (PI-2-SA and PI-4-SA), both of which display remarkable responses toward H2S over other analytes. The spectral characteristics of the two probes were investigated and are discussed in detail. By comparison, PI-2-SA was specific, sensitive (the limit of detection was ca. 12.3 nM), rapid (within ≤3 min) and dynamic (the rate constant was 0.02 s−1). Significantly, PI-2-SA was proved to be effective in monitoring the shelf-time progress of egg samples in real time as well as in the imaging of exogenous and endogenous H2S in HeLa cells. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP), an extraordinary enzyme, can catalyze the dephosphorylation of small molecules, proteins and nucleic acids. ALP has been confirmed as a crucial serum diagnostic indicator, since the abnormal level of ALP is closely related to a variety of pathological processes, especially in the early diagnosis and screening of cancer. Herein, we designed a "turn-on" sensor to detect ALP and ascorbic acid (AA) based on the redox reaction between manganese dioxide (MnO2) coated upconversion nanoparticles (UCNPs) and AA. Firstly, 2 nm sized NaYF4:Yb3+,Tm3+ UCNPs were synthesized by a facile one-pot hydrothermal method. Then MnO2 coated UCNPs were prepared via electrostatic interactions between MnO2 nanosheets and UCNPs. MnO2 nanosheets could absorb blue light emitted by UCNPs near 471 nm under laser excitation at 980 nm, and so the luminescence of UCNPs was quenched based on luminescence energy transfer (LET). In the presence of AA, the luminescence was recovered again by the redox reaction between AA and MnO2 coated UCNPs. MnO2 nanosheets were reduced to Mn2+ and UCNPs were released. Furthermore, the "turn-on" sensor was applied to monitor ALP since the phosphate group of 2-phospho- L -ascorbic acid (AAP) was removed by ALP to yield AA. The bio-assay showed a good linear relationship between the restored luminescence intensities (ΔI = I − I0) and ALP concentrations ranging from 0.25 to 150 mU mL−1 with a limit of detection (LOD) of 0.045 mU mL−1 and between ΔI and AA concentrations ranging from 0.5 to 250 μM with an LOD of 0.29 μM. The luminescent sensor was also successfully applied for detection of ALP and AA in human serum samples with recoveries from 94.9% to 104.6% and 99.4% to 104.9%. [ABSTRACT FROM AUTHOR]

Rationally designing porous materials with excellent hydrophilic performance for the selective removal of contaminants from wastewaters before discharge into the environment is highly desirable but still faces challenges. Herein, to address the shuttle issue, a hydrophilic covalent organic framework (BTA-BDSA-COF) was synthesized by introducing multi-sulfonated groups into a covalent framework structure and its potential applications in cationic dye capture have been evaluated in detail. Topological modulation and structural characteristics reveal the following: (1) a regular single-pore (SP) framework of BTA-BDSA-COF is constructed which is distinguishable from most reported COFs, with a condensation of D2h symmetry and ditopic linear diamine building blocks. (2) BTA-BDSA-COF undergoing excellent hydrophilicity outperforms other studied COFs functioned with sulfonated groups. Furthermore, dye sorption selectivity and kinetic studies clearly state the following: (1) the hydrophilic feature of anionic BTA-BDSA-COF is a significant driving force to ameliorate the adsorption ability of cationic dyes. (2) The degree of match between the size of the BTA-BDSA-COF pore aperture and the volume of dye molecule is intimately related to the dye adsorption properties. Therefore, BTA-BDSA-COF exhibits an impressive MLB adsorptive capacity of 1280 mg g−1 and a quick adsorption equilibrium of 30 min, owing to the moderately hydrophilic pore environment of BTA-BDSA-COF. Successful application in real water samples suggests that BTA-BDSA-COF with moderate hydrophilicity would be a promising adsorbent candidate for practical cationic dye capture. [ABSTRACT FROM AUTHOR]

Research on functionalized covalent organic framework (COF) materials with good hydrophilic characteristics is significant on account of their application in the removal of dyes in wastewater. In this work, two anionic COF materials (TFPB-Pa-SO3H COF and TFPB-BDSA COF) were successfully synthesized with sulfonated modification as dyestuff sorbents to be used for the adsorption of cationic dyes. The two prepared COF materials exhibited predominant hydrophilicity with lower water contact angles (35° and 27°) than reported COF materials. The sulfonated groups on the COFs can efficiently adsorb cationic dyes via electrostatic interaction, which can moderately ameliorate their adsorptive capacity toward hydrosoluble dyes. TFPB-Pa-SO3H COF and TFPB-BDSA COF showed superfast adsorption equilibrium with methylene blue (1 and 2 min) and high adsorption uptakes of crystal violet (1559 and 1288 mg g−1), which manifested that the adsorption rate may be closely related to the solubilities of the host COF materials as well as the guest dye molecule in aqueous solution. Meanwhile, the adsorption stability between the COF materials and dye molecule adsorbed on the COF skeleton accounted for the highly effective adsorption of the target dye in a large quantity. In addition, TFPB-Pa-SO3H COF as an adsorbing material was successfully applied for the removal of dye molecules in real water samples. [ABSTRACT FROM AUTHOR]

Cannabidiol (CBD), a natural phenolic compound, has many promising biological activities, but its use in food or other fields is restricted owing to inferior water solubility. So hydroxypropyl-β-cyclodextrin (HP-β-CD) was selected to form the inclusion complex (IC) of CBD to improve its solubility. The results showed CBD/HP-β-CD IC was formed at a 1 : 1 molar ratio. The complexation was spontaneous, endothermic, and entropy-driven. The loading efficiency (LE) and complexation efficiency (CE) were 16.2% and 95.1%, respectively. NMR revealed CBD/HP-β-CD IC was formed through incorporating the benzene ring of CBD into the HP-β-CD cavity. The water solubility was greatly enhanced to 9.4 μg mL−1. About 80% of CBD molecules in the IC were released in simulated intestinal juice. The permeability, radical scavenging ability, and in vitro cytotoxicity of CBD were enhanced significantly after complexation. And the radical scavenging ability of digested IC was less potent compared with undigested IC but still stronger than that of CBD. [ABSTRACT FROM AUTHOR]

We report an ultra-sensitive surface-enhanced Raman scattering (SERS)-based detection system for 2,4,6-trinitrotoluene (TNT) using nano-dumbbell structures formed by the electrostatic interaction between positively and negatively charged gold nanoparticles. First, Meisenheimer complexes were produced between TNT and l-cysteine on gold substrates, and 4-mercaptopyridine (4-MPY) labeled gold nanoparticles (positively charged) were allowed to interact with the Meisenheimer complexes through the electrostatic interaction between the negatively charged aromatic ring of the complex molecules and the positively charged nanoparticles. Then, negatively charged gold nanoparticles were added in order to form nano-dumbbells. As a result, many hot junctions were generated by the dumbbell structures, and the SERS signals were greatly enhanced. Our experimental results demonstrate that the SERS-based assay system using nano-dumbbells provides an ultra-sensitive approach for the detection of TNT explosives. It also shows strong potential for broad application in detecting various explosive materials used for military purposes. [ABSTRACT FROM AUTHOR]

The pn junctions significantly affect the responsivity of photodetectors (PDs). However, the enhancement mechanism of the pn junction is still unclear. Herein, operando Raman spectroscopy was employed to study PDs with NiO/TiO2 pn junctions composed of p-NiO nanoparticles (NPs) and n-TiO2 nanotube arrays (TNAs). The results suggest that the built-in potential field of the NiO/TiO2 interface decreases the charge transfer resistance and changes the vibrational frequency of the phonon modes of TiO2, which is attributed to the electron–phonon coupling effect. Operando Raman spectroscopy is proved to be a powerful tool for manufacturing highly responsive PDs. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) as precursors to form non-noble metal containing composites for the hydrogen evolution reaction (HER) have attracted an increasing amount of research attention, as they can be structurally modified at the molecular level without undergoing any structural changes upon multi-electron transfer. Herein, a novel mixed metal 3D nanoflower POM-based composite (Co/Ni-POM) on Ni foam (denoted as Co/Ni-POM/NFs) was prepared as an electrocatalyst for the HER, with tunable synthesis parameters. The optimized Co/Ni-POM/NF sample exhibits excellent catalytic activity and high stability, manifesting in an overpotential of only 68 mV for the HER (10 mA cm−2) and a Tafel slope of 60.8 mV dec−1 in 1 M KOH. The outstanding catalytic activity of Co/Ni-POM/NF stems from the synergistic effect between the metallic elements of the Co/Ni-POM and its large specific surface area. The Co/Ni-POM tightly riveted on nickel foam during the catalytic process also shows that the as-prepared catalyst is an excellent material for use in the HER. [ABSTRACT FROM AUTHOR]

This study was performed to investigate the potential application of a chitosan (CS) and quinoa polysaccharide (QS) composite aerogel for the adsorption of dyes from water. The properties of the synthesized CSQS composite aerogel were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). Results showed that the CSQS composite aerogel possesses a porous, loose and flexible structure with a mesoporous nature and high hydrophobicity. Meanwhile, various factors such as the initial concentration, temperature, contact time, and pH have been investigated for evaluation of the optimum adsorption for the removal of Congo red (CR) and methylene blue (MB) in batch sorption experiments, and experimental results showed that the maximum adsorption capacity was found to be 342 mg g−1 for CR and 57.80 mg g−1 for MB under the optimum conditions. The adsorption kinetics of CR and MB on the CSQS composite aerogel were found to be well modeled by pseudo-second-order and pseudo-first-order kinetic models, respectively. In addition, the experimental equilibrium data were represented well by the Langmuir isotherm model. The results in this article demonstrated that the obtained aerogel is suitable for application in drinking water purification. The entire synthesis process of the CSQS aerogel is green and economical without additional need for toxic agents, which allows the process to greatly reduce the discharge of secondary pollution to the environment. The facile, scalable and general strategy presented here can be extended to the preparation of other polysaccharide-based aerogel materials, and has a good prospects for application in the removal of dyes from water. [ABSTRACT FROM AUTHOR]

An ultra-high sensitivity sensor with the function of chiral signal amplification has been proposed for the enantiomer discrimination of various amino acid enantiomers based on charge transfer (CT)-induced SERS spectroscopy. The introduced TiO2 in this sensor improves the CT behavior and discrimination efficiency distinctly and enantiomeric discrimination is realized even at low concentration. [ABSTRACT FROM AUTHOR]

Charge-transfer processes of coupled semiconductor nanoparticles play an essential role in many application fields of semiconductors. It has been difficult to characterize the charge-transfer process between two semiconductor nanoparticles. Herein, we propose a new analytical tool with the chemical mechanism of Surface-Enhanced Raman Scattering (SERS) to provide information about the charge-transfer process in coupled semiconductor nanoparticle systems. In this work, two assemblies (namely, TiO2–MBA–CdS and CdS–MBA–TiO2) have been fabricated as models to explore the charge-transfer process between TiO2 and CdS nanoparticles by SERS. 4-MBA works as both the linker of these two semiconductors and the probe of SERS to reveal the charge-transfer process. Under excitations at 633 and 785 nm, which are far from the surface plasmon resonance of the CdS and TiO2 nanoparticles in the assemblies, there are some obvious changes in the peak intensities and peak shifts in the SERS spectra after introducing CdS to the TiO2/MBA system and TiO2 to the CdS/MBA system. The differences of the peak intensities in the TiO2–MBA–CdS and CdS–MBA–TiO2 assemblies show different charge-transfer processes. We have found that the dipole moment of a MBA molecule greatly influences the charge-transfer process between the TiO2 and CdS nanoparticles. [ABSTRACT FROM AUTHOR]

The illegal adulteration of natural healthcare products with chemical drugs can result in serious health risks for consumers. Thus there is an urgent need for a fast and precise detection method. In this research, sodium alginate (SA)-silver nanoparticles (AgNPs) were used as a substrate in surface-enhanced Raman scattering (SERS) for determining vardenafil and rosiglitazone maleate (ROS). Sodium alginate can not only reduce silver ions rapidly to AgNPs as reducing agents but can also protect AgNPs from aggregation by its use as a capping agent. The coffee ring effect has also been applied in this research to facilitate the separation and concentration of analytes. A prominent SERS enhancement can be obtained on the ring because of the electromagnetic mechanism. Both of the properties, including the use of SA and the coffee ring effect, make the method more sensitive in detecting the analytes compared to the classical AgNPs, SERS substrate which were produced using the reduction of silver nitrate with sodium citrate. The method displays a linear response for the determination of vardenafil and ROS in the 4.88–488 μg·mL−1 and 4.74–94.7 μg·mL−1 concentration ranges, and the limit of detection is as low as 1.63 μg·mL−1 and 2.20 μg·mL−1, respectively. The method was successfully applied to the detection of vardenafil and ROS in healthcare products, with recoveries between 91.52% to 107.1% and relative standard deviations of less than 4.31%. This method shows good potential for real applications. [ABSTRACT FROM AUTHOR]

Currently, studies are increasingly focusing on the cytotoxic effects of anticancer drugs. Such investigations urgently warrant the assessment of single-cell viability. Here, we developed a novel method for quantifying single-cell viability with high selectivity by resonance Raman scattering. We report on this powerful tool that will allow researchers to study cellular metabolism at the level of a single cell. [ABSTRACT FROM AUTHOR]

We investigated the CT process between a 4-mercaptobenzoic acid (4-MBA) monolayer and TiO2 NPs under high pressure using surface-enhanced Raman scattering (SERS). Employing the CT enhancement mechanism of semiconductors, we explore the CT process and explain how the pressure affects the process in the 4-MBA@TiO2 system. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were used to study the ruthenium porphyrin-catalyzed oxidation of styrene to generate an aldehyde. The results indicate that two reactive oxidants, dioxoruthenium and monooxoruthenium-superoxo porphyrins, participate in the catalytic oxidation. In the mechanism, the resultant monooxoruthenium porphyrin acts in the tandem epoxide isomerization (E-I) to selectively yield an aldehyde and generate a dioxoruthenium porphyrin, thereby triggering new oxidation reaction cycles. In this calculation, several key elements responsible for the observed oxidative ability have been established by using Frontier molecular orbital (FMO) theory, natural bond orbital (NBO) analysis, etc., which include the reaction energy, the spin exchange effect, the spin-state conversion process, and the energy level of the lowest unoccupied molecular orbitals (LUMOs) of the reactive oxidants. The comparative oxidative abilities of the ruthenium-oxo/superoxo compounds with different axial ligands are also investigated. The results suggest that the ruthenium-oxo/superoxo species featuring a chlorine axial ligand is more reactive than that substituted with oxygen. This tuneable reactivity can be understood when considering the different electronic characters of the two ligands and the effective atomic number rule (EAN). [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) on organic–inorganic hybrid perovskites is explored and for the first time the SERS activity (EF ≥ 104) of the nanostructured CH3NH3PbBr3 has been proved. Here, the SERS profile displays high similarity with the normal Raman spectra and the enhancement mechanism is discussed according to the charge transfer contribution. [ABSTRACT FROM AUTHOR]

Surface-enhanced resonance Raman scattering (SERRS) has been used to establish a rapid and quantitative assay based on the diazotization coupling reaction for thyrotropin-releasing hormone (TRH). Ultrahigh sensitivity of this approach originates from two factors: changing TRH to an azo compound and the SERRS effect with the addition of silver nanoparticles (AgNPs) at 532 nm excitation wavelength. The lowest detectable concentration of TRH was found to be as low as 1 pg mL−1, which is 10-fold lower than the lowest normal reference value in human serum reported in previous literature. The quantitative measurements in human serum based on this method were conducted, and the results showed its feasibility for detection in complex biological samples. In comparison with conventional TRH identification and quantification methodologies, radioimmunoassay (RIA) and subsequent various hyphenated techniques, the main advantages of this study are simplicity, rapidness (2 minutes), time effectiveness, no additional steps required to further characterize the immunogenic material, highest sensitivity (57.1 fg), high selectivity, practicality and reliability. Thus, this work puts forward a research tool that may be applied to the determination of TRH in practical assays. [ABSTRACT FROM AUTHOR]

We proposed a novel readout method based on a peculiar phenomenon in which the vibrational frequencies of a SERS-active probe (dimethyldithiocarbamic acid sodium salt, DASS) can be affected when there is mercury species. Compared to the SERS intensity-dependent quantitative determination method, SERS frequency-shift-based methods have several advantages: smaller standard deviation, perfect linear relationship, and higher accuracy and sensitivity. In addition, the SERS frequency-shift-based method was not affected by irreproducible aggregation of the SERS substrate and instrumental factors, which greatly improved the application prospect of SERS-based detection. The DASS-modified silver nanoparticles produced a highly sensitive sensor specific to mercury species. Upon the addition of a solution of mercury species to the chip, the mercury species specifically binds to the sulfur atoms, which induces a frequency shift of the band at 1374 cm−1. The detection limit of the proposed method for Hg2+ is as low as 10−8 M. In addition, the proposed method exhibited the same phenomenon for organic mercury. Moreover, these results suggest that the proposed platform possesses the potential for sensitive, selective, and high-throughput on-site mercury pollution monitoring in resource-constrained settings. [ABSTRACT FROM AUTHOR]

Quantitative analysis of phosphate anions was achieved by measurement of “turn-off” SERS based on the first-layer effect of a chemical mechanism. More importantly, our results demonstrate that it is possible, by means of semiconductor-enhanced Raman scattering, to enhance the SERS sensing performance including stability and reproducibility. [ABSTRACT FROM AUTHOR]

Based on bovine serum albumin (BSA)-modified Au NPs, a simple and cost-effective approach was proposed to fabricate an anti-aggregated Au NP sensing platform for the detection of metal ions. It exhibits excellent stability even under highly ionic conditions due to its electrostatic stabilization, as well as the steric stabilization. [ABSTRACT FROM AUTHOR]

We have fabricated a charge-transfer system using the self-assembly method. We find the nontotally symmetric b2modes are selectively enhanced in SERS spectroscopy and represent a laser wavelength-dependent property. [ABSTRACT FROM AUTHOR]