Stabilizing nanoparticles on surfaces, such as graphene, is a growing field of research. Thereby, iron particle stabilization on carbon materials is attractive and finds applications in charge-storage devices, catalysis, and others. In this work, we describe the discovery of iron nanoparticles with the face-centered cubic structure that was postulated not to exist at ambient conditions. In bulk, the γ-iron phase is formed only above 917 °C, and transforms back to the thermodynamically favored α-phase upon cooling. Here, with X-ray diffraction and Mössbauer spectroscopy we unambiguously demonstrate the unexpected room-temperature stability of the γ-phase of iron in the form of the austenitic nanoparticles with low carbon content from 0.60% through 0.93%. The nanoparticles have controllable diameter range from 30 nm through 200 nm. They are stabilized by a layer of Fe/C solid solution on the surface, serving as the buffer controlling carbon content in the core, and by a few-layer graphene as an outermost shell.

Early-stage pancreatic cancer remains challenging to detect, leading to a poor five-year patient survival rate. This obstacle necessitates the development of early detection approaches based on novel technologies and materials. In this work, the presence of a specific pancreatic cancer-derived miRNA (pre-miR-132) is detected using the fluorescence properties of biocompatible nitrogen-doped graphene quantum dots (NGQDs) synthesized using a bottom-up approach from a single glucosamine precursor. The sensor platform is comprised of slightly positively charged (1.14 ± 0.36 mV) NGQDs bound via π−π stacking and/or electrostatic interactions to the negatively charged (−22.4 ± 6.00 mV) bait ssDNA; together, they form a complex with a 20 nm average size. The NGQDs’ fluorescence distinguishes specific single-stranded DNA sequences due to bait–target complementarity, discriminating them from random control sequences with sensitivity in the micromolar range. Furthermore, this targetability can also detect the stem and loop portions of pre-miR-132, adding to the practicality of the biosensor. This non-invasive approach allows cancer-specific miRNA detection to facilitate early diagnosis of various forms of cancer.

In this study, we report the properties of the epoxy polymer composites, comprising reduced graphene oxide (RGO) in the form of the single-atomic-layer sheets. This structure is different from composites comprising multilayer RGO flakes and RGO aggregates, typically described in the literature. Viscosity of the uncured liquid resin increases by 390% after introducing 0.4% GO and increases by 4700% after its subsequent in situ reduction. The latter is explained by the reorganization of the original liquid crystalline structure of the GO-epoxy formulations with GO reduction. At the filling fractions >0.1%, the single-atomic-layer RGO flakes are assembled into clusters, where they alternate with a thin resin layer. This structure is also responsible for very unusual dielectric behavior of the cured solid composites. From one side, the real part of the complex permittivity reaches relatively high values at extremely low filling fractions: 14 at 0.1% and 60 at 0.4% RGO content. At the same time, the permittivity dispersion is accompanied with the well-pronounced symmetrical loss peaks on the imaginary part functions, which is typical for low permittivity materials. Such dielectric behavior is difficult to interpret in the frames of any single existing model. The high permittivity values strongly evidence for the Maxwell-Wagner interfacial polarization, even though the shape of the loss peaks would be better interpreted by αand/or β-relaxation in neat solid polymers. The single-atomiclayer character of RGO affords a high interfacial area, which, in turn, translates to high capacitance and high permittivity. The relaxation time and activation energy, calculated from the temperature dependence experiments, suggest that the RGO clusters, but not individual RGO flakes, serve as conductive inclusions. The extremely long relaxation times are due to the charge transfer between the individual RGO flakes within the clusters. The striking difference between the newly prepared composites and control samples comprising multilayer RGO particles exemplifies the unique structure of our materials.

Sonography offers many advantages over standard methods of diagnostic imaging due to its non-invasiveness, substantial tissue penetration depth, and low cost. The benefits of ultrasound imaging call for the development of ultrasound-trackable drug delivery vehicles that can address a variety of therapeutic targets. One disadvantage of the technique is the lack of highprecision imaging, which can be circumvented by complementing ultrasound contrast agents with visible and, especially, near-infrared (NIR) fluorophores. In this work, we, for the first time, develop a variety of lightly metal-doped (iron oxide, silver, thulium, neodymium, cerium oxide, cerium chloride, and molybdenum disulfide) nitrogen-containing graphene quantum dots (NGQDs) that demonstrate high-contrast properties in the ultrasound brightness mode and exhibit visible and/or near-infrared fluorescence imaging capabilities. NGQDs synthesized from glucosamine precursors with only a few percent metal doping do not introduce additional toxicity in vitro, yielding over 80% cell viability up to 2 mg/mL doses. Their small (<50 nm) sizes warrant effective cell internalization, while oxygen-containing surface functional groups decorating their surfaces render NGQDs water soluble and allow for the attachment of therapeutics and targeting agents. Utilizing visible and/or NIR fluorescence, we demonstrate that metal-doped NGQDs experience maximum accumulation within the HEK-293 cells 6−12 h after treatment. The successful 10-fold ultrasound signal enhancement is observed at 0.5−1.6 mg/mL for most metal-doped NGQDs in the vascular phantom, agarose gel, and animal tissue. A combination of non-invasive ultrasound imaging with capabilities of high-precision fluorescence tracking makes these metal-doped NGQDs a viable agent for a variety of theragnostic applications.

Graphene-based materials have been the subject of interest for photothermal therapy due to their high light-to-heat conversion efficiency. Based on recent studies, graphene quantum dots (GQDs) are expected to possess advantageous photothermal properties and facilitate fluorescence image-tracking in the visible and near-infrared (NIR), while surpassing other graphene-based materials in their biocompatibility. Several GQD structures including reduced graphene quantum dots (RGQDs) derived from reduced graphene oxide via top-down oxidation and hyaluronic acid graphene quantum dots (HGQDs) hydrothermally bottom-up synthesized from molecular hyaluronic acid were employed to test these capabilities in the present work. These GQDs possess substantial NIR absorption and fluorescence throughout the visible and NIR beneficial for in vivo imaging while being biocompatible at up to 1.7 mg/mL concentrations. In aqueous suspensions, RGQDs and HGQDs irradiated with a low power (0.9 W/cm2) 808 nm NIR laser facilitate a temperature increase up to 47.0 °C, which is sufficient for cancer tumor ablation. In vitro photothermal experiments sampling multiple conditions directly in the 96-well plate were performed using an automated simultaneous irradiation/measurement system developed on the basis of a 3D printer. In this study, HGQDs and RGQDs facilitated the heating of HeLa cancer cells up to 54.5 °C, leading to the drastic inhibition of cell viability from over 80% down to 22.9%. GQD’s fluorescence in the visible and NIR traces their successful internalization into HeLa cells maximized at 20 h suggesting both extracellular and intracellular photothermal treatment capabilities. The combination of the photothermal and imaging modalities tested in vitro makes the GQDs developed in this work prospective agents for cancer theragnostics.

No abstract

Composite materials, comprising metal nanoparticles (NP) on a structural support have gained significant attention as novel systems for catalysis and energy conversion. Despite the importance of these materials for practical applications, the mechanism of the NPs formation remains elusive. Here, we investigate the seeding and the growth of Pd‐NPs on graphene oxide (GO) support in the two‐step process: impregnation and annealing. During the impregnation step, Pd2+ uniformly covers GO surface due to the strong chemical bonding with the oxygen functional groups. During the thermal annealing step, the growth of Pd‐NPs occurs via the radial in‐plane migration of Pd‐NPs along the GO surface to incorporate new Pd atoms in a way, similar to the snowball effect. The exact migration path depends on the annealing temperature, and on the Pd/GO ratio. The same two factors are responsible for the size‐distribution and the lateral density of as‐grown Pd‐NPs. At high temperatures, diffusion of the growing Pd‐NPs across the GO layers complicates the picture. The annealing temperature also influences the crystallinity, or the degree of porosity of the graphenic support. Below 500°C, carbon planes remain almost intact, while above 700°C, GO decomposes into highly porous material.

With the advent of graphene, there has been an interest in utilizing this material and its derivative, graphene oxide (GO) for novel applications in nanodevices such as bio and gas sensors, solid-state supercapacitors and solar cells. Although GO exhibits lower conductivity and structural stability, it possesses an energy band gap that enables fluorescence emission in the visible/near infrared leading to a plethora of optoelectronic applications. In order to allow fine-tuning of its optical properties in the device geometry, new physical techniques are required that, unlike existing chemical approaches, yield substantial alteration of GO structure. Such a desired new technique is one that is electronically controlled and leads to reversible changes in GO optoelectronic properties. In this work, we for the first time investigate the methods to controllably alter the optical response of GO with the electric field and provide theoretical modeling of the electric field-induced changes. Field-dependent GO emission is studied in bulk GO/polyvinylpyrrolidone films with up to 6% reversible decrease under 1.6 V µm −1 electric fields. On an individual flake level, a more substantial over 50% quenching is achieved for select GO flakes in a polymeric matrix between interdigitated microelectrodes subject to two orders of magnitude higher fields. This effect is modeled on a single exciton level by utilizing Wentzel, Kremer, and Brillouin approximation for electron escape from the exciton potential well. In an aqueous suspension at low fields, GO flakes exhibit electrophoretic migration, indicating a degree of charge separation and a possibility of manipulating GO materials on a single-flake level to assemble electric field-controlled microelectronics. As a result of this work, we suggest the potential of varying the optical and electronic properties of GO via the electric field for the advancement and control over its optoelectronic device applications.