Adsorption mechanisms of l-Glutathione on Au and controlled nano-patterning through Dip Pen Nanolithography

Ultrastructure and Surface Composition of Glutathione-Terminated Ultrasmall Silver, Gold, Platinum, and Alloyed Silver-Platinum Nanoparticles (2 nm)

Alloyed ultrasmall silver-platinum nanoparticles (molar ratio Ag:Pt = 50:50) were prepared and compared to pure silver, platinum, and gold nanoparticles, all with a metallic core diameter of 2 nm. They were surface-stabilized by a layer of glutathione (GSH). A comprehensive characterization by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), differential centrifugal sedimentation (DCS), and UV spectroscopy showed their size both in the dry and in the water-dispersed state (hydrodynamic diameter). Solution NMR spectroscopy (1H, 13C, COSY, HSQC, HMBC, and DOSY) showed the nature of the glutathione shell including the number of GSH ligands on each nanoparticle (about 200 with a molecular footprint of 0.063 nm2 each). It furthermore showed that there are at least two different positions for the GSH ligand on the gold nanoparticle surface. Platinum strongly reduced the resolution of the NMR spectra compared to silver and gold, also in the alloyed nanoparticles. X-ray photoelectron spectroscopy (XPS) showed that silver, platinum, and silver-platinum particles were at least partially oxidized to Ag(+I) and Pt(+II), whereas the gold nanoparticles showed no sign of oxidation. Platinum and gold nanoparticles were well crystalline but twinned (fcc lattice) despite the small particle size. Silver was crystalline in electron diffraction but not in X-ray diffraction. Alloyed silver-platinum nanoparticles were almost fully amorphous by both methods, indicating a considerable internal disorder.

A novel electrochemical conducting polymer sensor for the rapid, selective and sensitive detection of biothiols

A rapid, selective and sensitive, novel conducting-polymer sensing platform for the detection and analysis of biothiols.

Pathways for Oral and Rectal Delivery of Gold Nanoparticles (1.7 nm) and Gold Nanoclusters into the Colon: Enteric-Coated Capsules and Suppositories

Two ways to deliver ultrasmall gold nanoparticles and gold-bovine serum albumin (BSA) nanoclusters to the colon were developed. First, oral administration is possible by incorporation into gelatin capsules that were coated with an enteric polymer. These permit the transfer across the stomach whose acidic environment damages many drugs. The enteric coating dissolves due to the neutral pH of the colon and releases the capsule's cargo. Second, rectal administration is possible by incorporation into hard-fat suppositories that melt in the colon and then release the nanocarriers. The feasibility of the two concepts was demonstrated by in-vitro release studies and cell culture studies that showed the easy redispersibility after dissolution of the respective transport system. This clears a pathway for therapeutic applications of drug-loaded nanoparticles to address colon diseases, such as chronic inflammation and cancer.

Controlled surface functionalization of Ni-S nanostructures for pH-responsive selective and superior pollutants adsorption

Herein, we developed a synthetic strategy to functionalize Ni-S nanostructures (NS) using a facile precipitation method at moderate temperature. The surface functionality of NS is controlled by varying amount of mixed surfactants to achieve the pH-responsive selective adsorption of anionic and cationic dyes and the adsorption of ciprofloxacin (CIP) and tetracycline (TC) antibiotics. Powder XRD diffraction pattern revealed the phase of NS was changed from α-NiS to mixed phases after functionalization. The surface area of functionalized NS was significantly enhanced by ~5 times of that unfunctionalized NS as 6.6 m²g^-1 to 30.3 m²g^-1. The NS selectively adsorbed methyl orange (MO) at pH 4.5 and methylene blue (MB) at pH 11.5 with separation efficiency values of 94.2% and 97.9% respectively. The maximum adsorption capacity for MO, MB, TC and CIP are obtained as 1526.3, 1031.2, 1540.8 and 632.4 mg g^-1, respectively. The electrostatic interaction is predominantly involved in the adsorption of dyes whereas adsorption of antibiotics changed to hydrogen bonding and metal coordination. Thermodynamics parameters indicated exothermic and spontaneous adsorption of dyes. The optimized adsorbent is easily recyclable. Thus, the developed strategy of functionalization of nanostructures unveils a practical approach towards selective and efficient adsorption of organic pollutants.

High-sorption terpyridine-graphene oxide hybrid for the efficient removal of heavy metal ions from wastewater

Pollution of wastewater with heavy metal-ions represents one of the most severe environmental problems associated with societal development. To overcome this issue, the design of new, highly efficient systems capable of removing such toxic species, hence to purify water, is of paramount importance for public health and environmental protection. In this work, novel sorption hybrid materials were developed to enable high-performance adsorption of heavy metal ions. Towards this end, graphene oxide (GO) exhibiting various C/O ratios has been functionalized with ad hoc receptors, i.e. terpyridine ligands. The maximum adsorption capacity of highly oxidized/terpyridine hybrids towards Ni(ii), Zn(ii) and Co(ii) was achieved at pH = 6 and 25 °C reaching values of 462, 421 and 336 mg g-1, respectively, being the highest reported in the literature for pristine GO and GO-based sorbents. Moreover, the uptake experiments showed that heavy metal ion adsorption on GO-Tpy and GOh-Tpy is strongly dependent on pH in the range from 2 to 10, as a result of the modulation of interactions at the supramolecular level. Moreover, the ionic strength was found to be independent of heavy metal ion adsorption on GO-Tpy and GOh-Tpy. Under ambient conditions, adsorption capacity values increase with the degree of oxidation of GO because dipolar oxygen units can both interact with heavy-metal ions via dipole-dipole and/or ionic interactions and enable bonding of more covalently anchored terpyridine units. Both adsorption isotherms and kinetics studies revealed that the uptake of the heavy metal ions occurs at a monolayer coverage, mostly controlled by the strong surface complexation with the oxygen of GO and nitrogen-containing groups of terpyridine. Furthermore, selectivity of the hybrid was confirmed by selective sorption of the above heavy metal ions from mixtures involving alkali (Na(i), K(i)) and alkaline Earth (Mg(ii), Ca(ii)) metal ions due to the chelating properties of the terpyridine subunits, as demonstrated with municipal drinking (tap) water samples. Our findings provide unambiguous evidence for the potential of chemical tailoring of GO-based materials with N-heterocyclic ligands as sorbent materials for highly efficient wastewater purification.

Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)

Ultrasmall silver nanoparticles were prepared by reduction with NaBH₄ and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with ¹³C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ ¹H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL^-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag_∼250GSH_∼155.

A highly sensitive poly(chrysoidine G)-gold nanoparticle composite based nitrite sensor for food safety applications

This work demonstrated the development of conducting poly(chrysoidine G) (PCG)-gold nanoparticle (AuNP)-modified fluorine-doped tin oxide (F : SnO₂, FTO) film-coated glass electrodes for the sensitive electrochemical detection of nitrite (NO₂^-). The homogeneously distributed PCG nanoparticle layer was deposited onto the FTO electrode by cyclic voltammetry sweeping. AuNPs were then anchored onto the PCG/FTO electrode by the chemical reduction of pre-adsorbed Au³⁺ ions. The as-prepared AuNP/PCG/FTO electrode exhibited excellent electrocatalytic activity for the oxidation of NO₂^- with high sensitivity (approximately 0.63 μA cm^-2μM^-1) and a low limit of detection (0.095 μM), which is relevant within the normal concentration range of NO₂^- in human bodily fluids. The AuNP/PCG/FTO sensor showed sufficient reproducibility, repeatability, low interference, and strong recovery for NO₂^- detection in food samples. These results indicate that the AuNP/PCG nanocomposites have immense potential for the electrochemical detection of other biologically important compounds.

Efficient Method for the Concentration Determination of Fmoc Groups Incorporated in the Core-Shell Materials by Fmoc-Glycine

In this paper, we described the synthesis procedure of TiO₂@SiO₂ core-shell modified with 3-(aminopropyl)trimethoxysilane (APTMS). The chemical attachment of Fmoc-glycine (Fmoc-Gly-OH) at the surface of the core-shell structure was performed to determine the amount of active amino groups on the basis of the amount of Fmoc group calculation. We characterized nanostructures using various methods: transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) to confirm the modification effectiveness. The ultraviolet-visible spectroscopy (UV-vis) measurement was adopted for the quantitative determination of amino groups present on the TiO₂@SiO₂ core-shell surface by determination of Fmoc substitution. The nanomaterials were functionalized by Fmoc-Gly-OH and then the fluorenylmethyloxycarbonyl (Fmoc) group was cleaved using 20% (v/v) solution of piperidine in DMF. This reaction led to the formation of a dibenzofulvene-piperidine adduct enabling the estimation of free Fmoc groups by measurement the maximum absorption at 289 and 301 nm using UV-vis spectroscopy. The calculations of Fmoc loading on core-shell materials was performed using different molar absorption coefficient: 5800 and 6089 dm³ × mol^-1 × cm^-1 for λ = 289 nm and both 7800 and 8021 dm³ × mol^-1 × cm^-1 for λ = 301 nm. The obtained results indicate that amount of Fmoc groups present on TiO₂@SiO₂-(CH₂)₃-NH₂ was calculated at 6 to 9 µmol/g. Furthermore, all measurements were compared with Fmoc-Gly-OH used as the model sample.

A two-step approach for improved exfoliation and cutting of boron nitride into boron nitride nanodisks with covalent functionalizations

The synthesis of boron nitride nanodisks (BNNDs) with reducing the size and having fewer disk layers, and low optical band gap (E g) is essential for practical applications in electronics and optoelectronic devices. So far, the large-scale preparation of hydroxyl (-OH) and hydroperoxyl (-OOH) functionalized boron nitride nanosheets and BNNDs with reduced E g is still a challenge. This research demonstrates the scalable and solution process synthesis of hydroxyl (-OH) and hydroperoxyl (-OOH) functionalization of BNNDs at the edges and basal planes from pristine hexagonal boron nitride (h-BN) by the combination of modified Hummer's method and Fenton's chemistry. Modified Hummer's method induces exfoliation and cutting of the h-BN into BNNDs with a low percentage of -OH functionalization (6.90%), which is further exfoliated and cut by Fenton's reagent with improved -OH and -OOH functionalization (ca. 17.25%). The combination of these two methods allows us to reduce the size of the OH/OOH-BNNDs to ca. 200 nm with the number of disk layers in the range from ca. 6-11. Concurrently, the E g of h-BN was decreased from ca. 5.10 to ca. 3.58 eV for OH/OOH-BNNDs, which enables the possible application of OH/OOH-BNNDs in semiconductor electronics. The high percentage of -OH and -OOH functionalizations in the OH/OOH-BNNDs enablesg them to disperse in various solvents with high long-term stability.

Pivotal role of N and Bi doping in CQD/Mn3O4 composite structure with outstanding visible photoactivity

The roles of N and Bi doped CQDs have been checked. N-doping resulted in exclusive optical and electronic properties in the CQDs while preserving their intrinsic properties such as quantum size effect, surface area and compatibility.

Stability of di-butyl-dichalcogenide-capped gold nanoparticles: experimental data and theoretical insights

Metals capped with organochalcogenides have attracted considerable interest due to their practical applications, which include catalysis, sensing, and biosensing, due to their optical, magnetic, electrochemical, adhesive, lubrication, and antibacterial properties. There are numerous reports of metals capped with organothiol molecules; however, there are few studies on metals capped with organoselenium or organotellurium. Thus, there is a gap to be filled regarding the properties of organochalcogenide systems which can be improved by replacing sulfur with selenium or tellurium. In the last decade, there has been significant development in the synthesis of selenium and tellurium compounds; however, it is difficult to find commercial applications of these compounds because there are few studies showing the feasibility of their synthesis and their advantages compared to organothiol compounds. Stability against oxidation by molecular oxygen under ambient conditions is one of the properties which can be improved by choosing the correct organochalcogenide; this can confer important advantages for many more suitable applications. This paper reports the successful synthesis and characterization of gold nanoparticles functionalized with organochalcogenide molecules (dibutyl-disulfide, dibutyl-diselenide and dibutyl-ditelluride) and evaluates the oxidation stability of the organochalcogenides. Spherical gold nanoparticles with diameters of 24 nm were capped with organochalcogenides and were investigated using X-ray photoelectron spectroscopy (XPS) to show the improved stability of organoselenium compared with organothiol and organotellurium. The results suggest that the organoselenium is a promising candidate to replace organothiol because of its enhanced stability towards oxidation by molecular oxygen under ambient conditions and its slow oxidation rate. The observed difference in the oxidation processes, as discussed, is also in agreement with theoretical calculations.

This study presents the improved stability against oxidation by molecular oxygen under ambient conditions of organoselenium compared with organothiol, and organotellurium.