Biotechnological applications of nanostructured hybrids of polyamine carbon quantum dots and iron oxide nanoparticles.

The combination of different nanomaterials has been investigated during the past few decades and represents an exciting challenge for the unexpected emerging properties of the resulting nano-hybrids. Spermidine (Spd), a biogenic polyamine, has emerged as a useful functional monomer for the development of carbon quantum dots (CQDs). Herein, an electrostatically stabilized ternary hybrid, constituted of iron oxide-DNA (the core) and spermidine carbon quantum dots (CQDSpds, the shell), was self-assembled and fully characterized. The as-obtained nano-hybrid was tested on HeLa cells to evaluate its biocompatibility as well as cellular uptake. Most importantly, besides being endowed by the magnetic features of the core, it displayed drastically enhanced fluorescence properties in comparison with parent CQDSpds and it is efficiently internalized by HeLa cells. This novel ternary nano-hybrid with multifaceted properties, ranging from fluorescence to superparamagnetism, represents an interesting option for cell tracking.

Electrostatically stabilized hybrids of carbon and maghemite nanoparticles: electrochemical study and application.

Binary hybrids have been investigated for the past few decades due to the emerging properties of nanoparticle composites. Electrostatically stabilized core-shell nanostructures composed of surface active magnetic nanoparticles (SAMNs) and differently charged carbon nanomaterials display specific electrochemical properties. In this work, a set of binary hybrids that include a new class of magnetic nanoparticles is presented and the electrochemical features of the hybrids are reported. Gallic acid derived carbon dots (GA-CDs), PEG derived graphene dots (PEG-GDs), and quaternized carbon dots (Q-CDs) characterized by different charged groups were used for the preparation of different complexes with SAMNs. Thus, a set of six binary nanomaterials was obtained, and characterized by electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry, demonstrating significant differences in the charge transfer resistance, capacitive current, electrochemical performance, and reversibility with respect to the isolated subunits. Among them, the combination of Q-CDs with an excess of SAMNs led to a Q-CD@SAMN hybrid, which displayed peculiar electrocatalytic properties attributable to the influence of the strong electrostatic interactions exerted by Q-CDs on the SAMN surface. Notwithstanding their small fraction (around 1% w/w), Q-CDs oriented the electrocatalysis of SAMNs toward the selective electro-oxidation of polyphenols at low applied potentials (+0.1 V vs. SCE). Finally, the Q-CD@SAMN hybrid was used for the development of a coulometric sensor for polyphenols, composed of a simple carbon paste electrode in a small volume electrochemical flow cell (1 µL), and used for the complete direct electro-oxidation of polyphenols from plant extracts.

Surface decoration of amine-rich carbon nitride with iron nanoparticles for arsenite (As(III)) uptake: The evolution of the Fe-phases under ambient conditions.

A novel hybrid material (gC3N4-rFe) consisting of amine-rich graphitic carbon nitride (gC3N4), decorated with reduced iron nanoparticles (rFe) is presented. XRD and TEM show that gC3N4-rFe bears aggregation-free Fe-nanoparticles (10nm) uniformly dispersed over the gC3N4 surface. In contrast, non-supported iron nanoparticles are strongly aggregated, with non-uniform size distribution (20-100nm). (57)Fe-Mössbauer spectroscopy, dual-mode electron paramagnetic resonance (EPR) and magnetization measurements, allow a detailed mapping of the evolution of the Fe-phases after exposure to ambient O2. The as-prepared gC3N4-rFe bears Fe(2+) and Fe° phases, however only after long exposure to ambient O2, a Fe-oxide layer is formed around the Fe° core. In this [Fe°/Fe-oxide] core-shell configuration, the gC3N4-rFe hybrid shows enhanced As(III) uptake capacity of 76.5mgg(-1), i.e., ca 90% higher than the unmodified carbonaceous support, and 300% higher than the non-supported Fe-nanoparticles. gC3N4-rFe is a superior As(III) sorbent i.e., compared to its single counterparts or vs. graphite/graphite oxide or activated carbon analogues (11-36mgg(-1)). The present results demonstrate that the gC3N4 matrix is not simply a net that holds the particles, but rather an active component that determines particle formation dynamics and ultimately their redox profile, size and surface dispersion homogeneity.

Adsorption and photocatalysis of nanocrystalline TiO2 particles for Reactive Red 195 removal: effect of humic acids, anions and scavengers.

In the present study, the coupling of adsorption capacity and photocatalytic efficiency of two different industrially produced titania catalysts was investigated and compared. The azo dye Reactive Red 195 was selected as a model compound. The tested catalysts, PK-10 and PK-180, exhibited different adsorption capacities due to their significant difference in their specific surface, but both have proven to be effective photocatalysts for photodegradation of the studied dye. PK-10 exhibited strong adsorption of the studied dye due to its high specific surface area, while the second studied catalyst, PK-180, demonstrated negligible adsorption of Reactive Red 195. The effect of the pH, the concentration of the catalyst and the initial concentration of the dye appear to affect the photocatalytic rate. The effect of the presence of humic acids and inorganic ions was also examined, while the contribution of various reactive species was indirectly evaluated through the addition of various scavengers. To evaluate the extent of mineralisation of the studied dye, total organic carbon (TOC) measurements during the experiment were also conducted. Besides total colour removal, evident reduction of TOC was also achieved using both catalysts.

NZVI modified magnetic filter paper with high redox and catalytic activities for advanced water treatment technologies.

The in situ synthesis of air-stable zero-valent iron nanoparticles (NZVI) embedded in cellulose fibers leads to the assembly of highly reactive magnetic filter papers. These engineered materials display a wide range of applications in the treatment of wastewater and drinking water, including chromium removal, phenol degradation, environmental bioremediation, and catalysis.

Field emission scanning electron microscopy (FE-SEM) as an approach for nanoparticle detection inside cells.

When developing new nanoparticles for bio-applications, it is important to fully characterize the nanoparticle's behavior in biological systems. The most common techniques employed for mapping nanoparticles inside cells include transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These techniques entail passing an electron beam through a thin specimen. STEM or TEM imaging is often used for the detection of nanoparticles inside cellular organelles. However, lengthy sample preparation is required (i.e., fixation, dehydration, drying, resin embedding, and cutting). In the present work, a new matrix (FTO glass) for biological samples was used and characterized by field emission scanning electron microscopy (FE-SEM) to generate images comparable to those obtained by TEM. Using FE-SEM, nanoparticle images were acquired inside endo/lysosomes without disruption of the cellular shape. Furthermore, the initial steps of nanoparticle incorporation into the cells were captured. In addition, the conductive FTO glass endowed the sample with high stability under the required accelerating voltage. Owing to these features of the sample, further analyses could be performed (material contrast and energy-dispersive X-ray spectroscopy (EDS)), which confirmed the presence of nanoparticles inside the cells. The results showed that FE-SEM can enable detailed characterization of nanoparticles in endosomes without the need for contrast staining or metal coating of the sample. Images showing the intracellular distribution of nanoparticles together with cellular morphology can give important information on the biocompatibility and demonstrate the potential of nanoparticle utilization in medicine.

Quaternized carbon dot-modified graphene oxide for selective cell labelling--controlled nucleus and cytoplasm imaging.

Cationic quaternized carbon dots (QCDs) and anionic graphene oxide sheets (GO) are combined via non-covalent interactions following a self-assembly pathway to form highly biocompatible and fluorescent hybrid materials. These hybrids act as selective probes with controlled labelling of the cell nucleus or cytoplasm depending on the QCD loading.

Fluoro-graphene: nonlinear optical properties.

In the present work, we report on the investigation of the third-order nonlinear optical response of graphene fluoride dispersed in DMF and also of fluorosurfactant-stabilized graphene fluoride dispersed in water under visible (532 nm) and infrared (1064 nm), picosecond and nanosecond laser excitation. Both graphene derivatives were found to exhibit large nonlinear optical response, while significant differences on their nonlinear optical response have been observed (e.g. different sign of nonlinear refraction and absorption). These findings highlight the important role of the degree of fluorination of the graphene sheets on their optical and electronic properties. Furthermore, DMF dispersed graphene fluoride was found to exhibit important broadband optical limiting action under nanosecond laser excitation, making it promising candidate for optical limiting applications.

Thermostable trypsin conjugates immobilized to biogenic magnetite show a high operational stability and remarkable reusability for protein digestion.

In this work, magnetosomes produced by microorganisms were chosen as a suitable magnetic carrier for covalent immobilization of thermostable trypsin conjugates with an expected applicability for efficient and rapid digestion of proteins at elevated temperatures. First, a biogenic magnetite was isolated from Magnetospirillum gryphiswaldense and its free surface was coated with the natural polysaccharide chitosan containing free amino and hydroxy groups. Prior to covalent immobilization, bovine trypsin was modified by conjugating with α-, ß- and γ-cyclodextrin. Modified trypsin was bound to the magnetic carriers via amino groups using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide as coupling reagents. The magnetic biomaterial was characterized by magnetometric analysis and electron microscopy. With regard to their biochemical properties, the immobilized trypsin conjugates showed an increased resistance to elevated temperatures, eliminated autolysis, had an unchanged pH optimum and a significant storage stability and reusability. Considering these parameters, the presented enzymatic system exhibits properties that are superior to those of trypsin forms obtained by other frequently used approaches. The proteolytic performance was demonstrated during in-solution digestion of model proteins (horseradish peroxidase, bovine serum albumin and hen egg white lysozyme) followed by mass spectrometry. It is shown that both magnetic immobilization and chemical modification enhance the characteristics of trypsin making it a promising tool for protein digestion.

Electric field gradient in FeTiO3 by nuclear magnetic resonance and ab initio calculations.

Temperature dependence of nuclear magnetic resonance (NMR) spectra of (47)Ti and (49)Ti in polycrystalline ilmenite FeTiO(3) was measured in the range from 5 to 300 K under an external magnetic field of 9.401 T. NMR spectra collected between 300 and 77 K exhibit a resolved quadrupole splitting. The electric field gradient (EFG) tensor was evaluated for Ti nuclei and the ratio of (47)Ti and (49)Ti nuclear quadrupole moments was refined during the fitting procedure. Below 77 K, the fine structure of quadrupole splitting disappears due to the enormous increase of anisotropy. As a counterpart, ab initio calculations were performed using full potential augmented plane waves + local orbitals. The calculated EFG tensors for Ti and Fe were compared to the experimental ones evaluated from NMR and the Mössbauer spectroscopy experiments.

One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites.

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240 °C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20 nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature Mössbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.