Highly sensitive and selective two-photon sensing of cartap using Au@Ag core-shell nanoparticles

A highly sensitive and selective two-photon sensing scheme for detection of cartap was developed by using Au@Ag bimetallic core-shell nanoparticles. Cartap was found to induce the aggregation of Au@Ag nanoparticles and up to 700-fold enhancement in two-photon photoluminescence. Huge enhancement in two-photon photoluminescence allows achieving a detection limit of as low as 0.0062 mg/kg, which is better than the conventional colorimetric methods. This two-photon sensing scheme has a broad dynamic range and displays excellent selectivity in detection of cartap against over other ten kinds of commonly used insecticides.     

Sub-ppt level voltammetric sensor for Hg2+ detection based on nafion stabilized l-cysteine-capped Au@Ag core-shell nanoparticles

Journal of Solid State Electrochemistry - Bimetallic nanoparticles (BMNPs) have received considerable attention due to their distinctive properties when compared to the corresponding monometallic...     

Enhanced oxygen sensing properties of Pt(II) complex and dye entrapped core-shell silica nanoparticles embedded in sol-gel matrix

This paper presents a highly sensitive oxygen sensor that comprises an optical fiber coated at one end with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core-shell silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity (I₀/I₁₀₀) of 166. The response time was 1.3 s when switching from pure nitrogen to pure oxygen, and 18.6 s when switching in the reverse direction. The experimental results show that compared to oxygen sensors based on PtTFPP, PtOEP, or Ru(dpp)₃²⁺ dyes, the proposed optical fiber oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the dye entrapped in the core of silica nanoparticles also increases the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The dye entrapped core-shell nanoparticles is more prone to oxygen quenching.     

Ratiometric sensing of mercury(II) based on a FRET process on silica core-shell nanoparticles acting as vehicles

We report on a fluorescence resonance energy transfer (FRET)-based ratiometric sensor for the detection of Hg(II) ion. First, silica nanoparticles were labeled with a hydrophobic fluorescent nitrobenzoxadiazolyl dye which acts as a FRET donor. A spirolactam rhodamine was then covalently linked to the surface of the silica particles. Exposure of the nanoparticles to Hg(II) in water induced a ring-opening reaction of the spirolactam rhodamine moieties, leading to the formation of a fluorescent derivative that can serve as the FRET acceptor. Ratiometric sensing of Hg(II) was accomplished by ratioing the fluorescence intensities at 520 nm and 578 nm. The average decay time for the donor decreases from 9.09 ns to 7.37 ns upon addition of Hg(II), which proves the occurrence of a FRET process. The detection limit of the assay is 100 nM (ca. 20 ppb). The sensor also exhibits a large Stokes shift (>150 nm) which can eliminate backscattering effects of excitation light.

Novel thionin-functionalised core shell magnetic nanoparticles for dispersive solid-phase extraction of Hg(II) in food and water samples

To develop an accurate and precise method for separation and pre-concentration of Hg(II), a novel thionin functionalised core shell structure magnetic material has been prepared and characterised. The extraction ability of the material was evaluated by magnetic solid-phase extraction coupled with inductively coupled plasma mass spectrometry determination of Hg(II) in food and water samples. Combining the advantages of magnetic separation with selective extraction of thionin towards Hg(II), the material exhibits enhanced enrich selectivity and efficiency for Hg(II). The experimental parameters influencing Hg(II) extraction efficiency, including pH of the aqueous solution, the dosage of the adsorbent, extraction time and sample volume, were systematically investigated. Under the optimised conditions, concentration of Hg(II) at 1.0 μg L^?1 can be successfully enriched by the material without the interference of the common co-existing ions. The enrichment factor and adsorption capacity were 250 and 75.2 mg g^?1, and precise of the method was confirmed by analysing the spiked food, water samples and standard water reference samples with the recoveries of 92.5–101.8%.     

Fluorescent nanoparticles for chemical and biological sensing

Fluorescent nanoparticles (NPs), including quantum dots (QDs), dye-doped NPs, and rare earth-based NPs, etc., have been a major focus of research and development during the past decade. The impetus behind such endeavors can be attributed to their unique chemical and optical properties, such as bright fluorescence, high photostability, large Stocks shift and flexible processability. The introduction of fluorescent NPs into analytical chemistry has opened up new venues for fluorescent analysis. In this review...     

Gold nanoparticles decorated carbon fiber mat as a novel sensing platform for sensitive detection of Hg(II)

The three-dimensional fibril-like carbon fiber mat electrode (CFME) decorated with Au nanoparticles (AuNPs) was employed to construct Hg(II) sensing platform for the first time. The highly porous feature of CFME combining the high affinity of AuNPs for mercury endowed the sensing platform with high sensitivity and good reproducibility. Under optimal conditions, the prepared AuNPs/CFME was capable of sensing Hg(II) with a detection limit of 0.1 μg L^− 1 (S/N = 3) using differential pulse anodic stripping voltammetry (DPASV). Finally, the AuNPs/CFME was successfully demonstrated for the determination of Hg(II) in real water samples with satisfactory results.     

Fluorescent sensing and selective Pb(II) extraction by a dansylamide ion-exchanger

The (bis)dansylated sulfonamide 1,2-C6H4(NHSO2C10H6-5-N(CH3)2)2 (1) extracted Pb(II) selectively from water into 1,2-dichloroethane via an ion-exchange mechanism and showed fluorescence quenching upon Pb(II) extraction. The distribution ratios for metal extraction (determined by ICP-MS) for Pb(II) were 133-1410 times higher than those for other metal cations [Co(II), Ni(II), Cu(II), Zn(II), and Cd(II)] under identical conditions. Fluorescence quenching was observed upon Pb(II) extraction, which was dependent on Pb(II) concentration. The monodansylated control, C6H5NHSO2C10H6-5-N(CH3)2 (2), showed neither extraction nor quenching, indicating that the fluorescence effects are a direct result of Pb coordination to 1. The observed selectivity for Pb(II) is ascribed to the formation of a low-coordinate binary Pb(II)-Sulfonamido complex in the organic phase.     

Fluorescent nanoscale zinc(II)-carboxylate coordination polymers for explosive sensing

Fluorescent nanoscale coordination polymers with cubic morphology and long range ordered structure were fabricated and exhibited efficient sensing for both nitroaromatic explosive and nitromethane due to large surface area to volume ratio and strong binding affinity to explosive molecules.     

Control of silica shell thickness and microporosity of titania-silica core-shell type nanoparticles to depress the photocatalytic activity of titania

Titania is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of its excellent UV light absorption properties. Its high photocatalytic activity, however, facilitates the generation of reactive oxygen species, which can oxidize and degrade other ingredients during its formulation, raising safety concerns. Dense coating of titania nanoparticles with a silica layer could help in depression of their photocatalytic activity by disturbing the formation of radicals produced by the reaction of oxygen and/or water with the electron-hole pair. Depression of the high photocatalytic activity of titania necessitates that the silica shell has to be thick, with minimum microporosity. Coating parameters were optimized to attain greater amounts of precipitated silica and thicker shells with lower microporosity, which in turn resulted in great depression of photocatalytic activity. Silica-coated titania nanoparticles were characterized by TEM, XPS, FT-IR, EDX, and microporosity measurements. The photocatalytic activity was evaluated for the coated powder to investigate the efficiency of the silica coating as well.     

Rhodamine thiospirolactone. Highly selective and sensitive reversible sensing of Hg(II)

A novel rhodamine thiospirolactone chemosensor was found to develop prominent absorbance and fluorescence enhancements in the presence of Hg(2+) in aqueous solution and this was suggested to result from the thiospiro ring opening induced by Hg(2+) binding.     

l-Valine-derived simple benzimidazole-based host in selective sensing of Hg(II) ions

A new and an easy-to-make simple benzimidazole-based chemosensor 1, derived from l -valine is reported. The chemosensor effectively recognises Hg²⁺ ion in the open cleft in CH₃CN containing 0.2% DMSO by exhibiting significant enhancement in fluorescence emission. In the selectivity, the steric isopropyl groups in 1 play the key role as confirmed by considering the model compound 2. The ensemble of 1.Hg²⁺, on the other hand, shows the fluorescence sensing of l -cysteine, homocysteine, and glutathione over the other amino acids with no thiol group in aq. DMSO (DMSO:H₂O = 4:1, v/v).     

Iron nanoparticles: the core-shell structure and unique properties for Ni(II) sequestration

It is demonstrated that iron nanoparticles function as a sorbent and a reductant for the sequestration of Ni(II) in water. A relatively high capacity of nickel removal is observed (0.13 g Ni/g Fe, or 4.43 mequiv Ni(II)/g), which is over 100% higher than the best inorganic sorbents available. High-resolution X-ray photoelectron spectroscopy (HR-XPS) confirms that the zerovalent iron nanoparticles have a core-shell structure and exhibit characteristics of both hydrous iron oxides (i.e., as a sorbent) and metallic iron (i.e., as a reductant). Ni(II) quickly forms a surface complex and is then reduced to metallic nickel on the nanoparticle surface. The dual properties of iron nanoparticles may offer efficient and unique solutions for the separation and transformation of metal ions and other environmental contaminants.     

CdS/ZnS core-shell quantum dots capped with mercaptoacetic acid as fluorescent probes for Hg(II) ions

We have synthesised water soluble CdS/ZnS core-shell quantum dots (QDs) capped with mercaptoacetic acid (MAA). They were characterised by UV–vis absorption spectroscopy, fluorescence spectroscopy, FT-IR and transmission electron microscopy. Such QDs can be used as fluorescent probes for the determination of metal ions because they quench the fluorescence of the QDs. The QDs exhibit absorption and emission bands at 345?nm and 475?nm respectively, which is more longer wavelength compared to MAA-capped CdS QDs and obviously is the result of the larger particle size. The fluorescence intensity of CdS-based QDs is strongly enhanced by coating them with a shell of ZnS. In addition, such functionalised QDs are more sensitive to Hg(II) ions. Parameters such as pH, temperature and concentration of the QDs have been optimised. A high selectivity and sensitivity toward Hg(II) ions is obtained at pH 7.4 and a concentration of 12.0?mg of QDs per L. Under optimum conditions, the fluorescence intensity of CdS/ZnS QDs is linearly proportional to the concentration of Hg(II) in the range from 2.5 to 280?nM, with a detection limit of 2.2?nM. The effect of potentially interfering cations was examined and confirmed the high selectivity of this material.

Decreasing the shell ratio of core-shell type nanoparticles with a ceria core and polymer shell by acid treatment

Core-shell type nanoparticles with a ceria core and polymer shell have good dispersibility. Some applications, such as fillers for increasing the refractive index and/or protecting resin films from ultraviolet (UV) light, i.e., UV cutting, require a smaller shell. Previous studies have decreased the shell weight by heat treatment in gas; however, the dispersibility of the treated nanoparticles was poor in water or alcohol. In this study, we investigated the efficacy of acid treatment for decreasing the shell weight and also evaluated the dispersibility of acid-treated nanoparticles. The thus-formed nanoparticles treated by acetic acid and formic acid show not only good dispersibility but also a well decreased shell thickness. The structure of the shell after acetic acid treatment was found to be the same as that of the untreated core-shell nanoparticles; moreover, acetic acid was present in the shell. Furthermore, by using the acetic-acid-treated nanoparticles, a transparent resin film without nanoparticle aggregation could be obtained.     

FRET‐based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II) and Cu(II) with Dual‐mode

A dual‐function fluorescence resonance energy transfer (FRET)‐based fluorescent and colorimetric probe was rationally fabricated from an energy donor coumarin moiety and an energy acceptor rhodamine moiety linked by a thiohydrazide arm for selective detection of Hg²⁺ and Cu²⁺. Two distinct mechanisms were used for the selective detection. Results revealed that probe 1 showed high fluorescent selectivity towards Hg²⁺ and evident colorimetric selectivity for Cu²⁺, which was suitable for ‘naked‐eye’ detection.     

Synthesis of core-shell structured dual-mesoporous silica spheres with tunable pore size and controllable shell thickness

Core-shell structured dual-mesoporous silica spheres (DMSS) that possess smaller pores (2.0 nm) in the shell and larger tunable pores (12.8-18.5 nm) in the core have been successfully synthesized by utilizing an amphiphilic block copolymer (polystyrene-b-poly (acrylic acid), PS-b-PAA) and cetyl trimethyl ammonium bromide (CTAB) as cotemplates. The thickness of the shells and the larger pore size in the core could be easily tuned by changing the amounts of TEOS and the hydrophobic block (PS) length during synthesis, respectively. By encapsulating hydrophobic magnetite nanoparticles into the cores, superparamagnetic dual-mesoporous silica spheres were obtained. Drug storage and release testing results showed that the diffusing rate of the stored drug could be efficiently controlled by changing the shell thickness of DMSS.     

Bactericidal core-shell paramagnetic nanoparticles functionalized with poly(hexamethylene biguanide)

Bactericidal paramagnetic particles were obtained either through the attachment of a conjugate of poly(ethyleneimine) (PEI) and poly(hexamethylene biguanide) (PHMBG) to the surface of magnetite (Fe(3)O(4)) particles, or via the sol-gel encapsulation of magnetite particles with a functional silane (3-glycidoxypropyl trimethoxysilane) and subsequent binding of the polysiloxane shell by the amine/imine groups of PHMBG. The encapsulated core-shell particles possess a high saturation magnetization, which is preserved for more than 10 months while in contact with air in aqueous suspensions. The minimum inhibitory concentration (MIC) of the encapsulated particles for eight types of bacteria was size-dependent, with polydisperse submillimeter particles possessing a several-fold higher MIC than analogous particles sized below 250 nm. The encapsulated particles are biocompatible and nontoxic to mammalian cells such as mouse fibroblasts. The particles efficiently bind both glycopeptide components mimicking the gram-positive bacteria membranes and whole bacteria, and possess broad-range bactericidal activity. The cell-particle complexes can be captured, manipulated, and removed by means of a magnet.     

A new bis(pyrenyl)azadiene-based probe for the colorimetric and fluorescent sensing of Cu(II) and Hg(II)

A novel colorimetric and fluorescent chemosensor 2, made up of two pyrene units connected by a 2-aza-1,3-butadiene ionophore, was designed and prepared for the selective detection of Cu²⁺ and Hg²⁺ in the presence of other metal cations. This molecular sensor exhibits substantial colour changes and fluorescence enhancement upon complexation with these metal cations in acetonitrile solutions, with detection limits in the order of 10⁻⁶ M. Job's plots revealed a 1:1 stoichiometry rationalized by theoretical DFT calculations.