Bohuslav Rezek

Optically active color centers in diamonds have been intensively studied due to their potential in photonics, energy harvesting, biosensing, and quantum computing. Silicon vacancy (SiV) center offers an advantage of suitable emission wavelength and narrow zero‐phonon line at room temperature. Measurement of surface potential and photovoltage can provide better understanding of the physics and control of SiV light emission, such as charge states and charging effects. Herein, optoelectronic properties of nanocrystalline diamond films with SiV centers at different layer thicknesses (10–200 nm, controlled by the growth time) under ambient conditions are studied. Time‐dependent measurements are performed in the light–dark–light cycle. Positive photovoltage arises on samples with SiV layer thicknesses below 55 nm on both H‐ and O‐terminated surfaces. Above 55 nm the photovoltage switches to negative …

Heterostructures of graphene and hexagonal boron nitride (G/h-BN) have been widely studied for controlling and utilizing graphene electronic properties. Here we characterize specific optical and electronic properties of G/h-BN heterostructures made of a high-quality single layer chemical vapor deposition (CVD) graphene laid over h-BN flakes, with focus on plasmonic effects. We compare the G/h-BN properties on Si and SiO2 substrates by micro-Raman spectroscopy mapping, Kelvin probe force microscopy, optical and atomic force microscopy. We observe highly enhanced Raman intensity (up to 280 %) from Si as well as graphene along the G/h-BN edge. It is attributed to localized concentration of electrons in graphene and suitable perpendicular orientation of plasmonic vibrations at the edge. The plasmonic Raman enhancement occurs under a visible light excitation (532 nm) and the effect can be tuned by the …

Prostate cancer (PCa) is the second most common cancer. In this paper, the isolation and properties of exosomes as potential novel liquid biopsy markers for early PCa liquid biopsy diagnosis are investigated using two prostate human cell lines, i.e., benign (control) cell line RWPE1 and carcinoma cell line 22Rv1. Exosomes produced by both cell lines are characterised by various methods including nanoparticle-tracking analysis, dynamic light scattering, scanning electron microscopy and atomic force microscopy. In addition, surface plasmon resonance (SPR) is used to study three different receptors on the exosomal surface (CD63, CD81 and prostate-specific membrane antigen-PMSA), implementing monoclonal antibodies and identifying the type of glycans present on the surface of exosomes using lectins (glycan-recognising proteins). Electrochemical analysis is used to understand the interfacial properties of exosomes. The results indicate that cancerous exosomes are smaller, are produced at higher concentrations, and exhibit more nega tive zeta potential than the control exosomes. The SPR experiments confirm that negatively charged α-2,3- and α-2,6-sialic acid-containing glycans are found in greater abundance on carcinoma exosomes, whereas bisecting and branched glycans are more abundant in the control exosomes. The SPR results also show that a sandwich antibody/exosomes/lectins configuration could be constructed for effective glycoprofiling of exosomes as a novel liquid biopsy marker.

Detection of UV radiation is becoming increasingly important for many applications. Here we present novel UV sensor construction on the basis of standard Si detector modification. Wavelength shifting mechanism is achieved by the luminescence effect of perovskite quantum dots embedded in polymer layers. We comprehensively characterize these composite materials, various sensor modification routes and the optical properties of UV-enhanced visible sensors. Modified S1227-16 BG silicon photodiodes and S13360-1375 CS MPPC photodetectors with the enhanced UV response are successively manufactured.

Hydrogenated nanodiamonds (NDs) get increasing attention as promising nanomaterial in biology as well as optoelectronics. This study shows how the ND synthesis process and ND size are reflected in their different colloidal/hydration and electronic properties. We employ three different ND types: detonation ND (DND), top-down high-pressure high-temperature ND (TD_HPHT ND) prepared by milling of HPHT monocrystals, and bottom-up high-pressure high-temperature ND (BU_HPHT ND) prepared by HPHT synthesis from chloroadamantane. Zeta potential measurements and Fourier transform infrared spectroscopy analysis (FTIR) reveal the best colloidal stability in neutral to basic pH and the strongest affinity to water for DND. Electrical and FTIR measurements connected with an annealing treatment show a steep increase of electrical conductivity in BU_HPHT ND above 2 nm and reveal different contribution …

We characterize gallium-doped zinc oxide (ZnO:Ga) after exposure to hydrogen or oxygen plasma for potential use as a novel antibacterial and photocatalytic material. ZnO:Ga were composed of smooth rods with a thick central portion and tapered nanometre-sized ends alongside clusters of thin disk particles. Plasma treatment removed material from the rod surface and introduced features such as small holes or pits that increased the surface roughness and reduced the zinc ion concentration measured from colloidal suspensions. The surface charge of ZnO:Ga was influenced by plasma treatment: hydrogen plasma induced a positive surface charge whereas oxygen plasma resulted in a negative surface charge. However, electrostatic interactions with negatively charged bacteria were not the predominant mechanism underlying the antibacterial effect of ZnO:Ga. Treatment with oxygen or hydrogen plasma …

Research investigating the interface between biological organisms and nanomaterials nowadays requires multi-faceted microscopic methods to elucidate the interaction mechanisms and effects. Here we describe a novel approach and methodology correlating data from an atomic force microscope inside a scanning electron microscope (AFM-in-SEM). This approach is demonstrated on bacteria-diamond-metal nanocomposite samples relevant in current life science research. We describe a procedure for preparing such multi-component test samples containing E. coli bacteria and chitosan-coated hydrogenated nanodiamonds decorated with silver nanoparticles on a carbon-coated gold grid. Microscopic topography information (AFM) is combined with chemical, material, and morphological information (SEM using SE and BSE at varied acceleration voltages) from the same region of interest and processed to create …

Diamond nanoparticles so‐called nanodiamonds (NDs) have recently experienced raising scientific interest due to interesting optical and electronic properties, nontoxicity, biocompatibility, and large surface area. Another significant feature of NDs is the versatility of the surface chemistry, where various functional groups can be attached. This provides an excellent platform for adjusting NDs properties and functions for many applications including in photovoltaic devices. Herein, high‐pressure high‐temperature (HPHT) NDs are tested as charge extraction material in organic solar cells using various surface chemistries: as‐received (HPHT ND‐ar), oxidized (HPHT ND‐O), and hydrogenated (HPHT ND‐O‐H) NDs. Despite the high work function values (≈5.3 eV) of HPHT ND‐ar and HPHT ND‐O, which make these materials normally suitable for hole extraction, devices made with them failed. In contrast, the work …

A unique set of undoped and Er-doped ZnO nanorods that are grown by a hydrothermal method under exactly the same conditions in the form of 2D nanoarrays on the SiO2/ZnO substrate or in a free-standing form on random nucleation seeds in solution were investigated. Their optoelectronic properties are characterized by photo-, radio-, and cathodoluminescence in correlation with scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron paramagnetic resonance spectroscopy, resonance Raman spectroscopy, and theoretical computing by using density functional theory. We demonstrate that erbium is incorporated at a regular zinc site in the 2D arrays and as additional nucleation seeds in the free-standing nanorods. The deposited nanorods contain a larger number of shallow donors (by about 2 orders of magnitude) and a larger number of free carriers (by about 1 order of magnitude) as …

Nanoscale Page 1 Nanoscale rsc.li/nanoscale The Royal Society of Chemistry is the world's leading chemistry community. Through our high impact journals and publications we connect the world with the chemical sciences and invest the profits back into the chemistry community. IN THIS ISSUE ISSN 2040-3372 CODEN NANOHL 15(23) 9881–10178 (2023) Cover See Jun Maruyama et al., pp. 9954–9963. Image reproduced by permission of Jun Maruyama from Nanoscale, 2023, 15, 9954. REVIEWS 9891 Recent progress in energy, environment, and electronic applications of MXene nanomaterials Ruhan E. Ustad, Somnath S. Kundale, Kasturi A. Rokade, Snehal L. Patil, Vijay D. Chavan, Kalyani D. Kadam, Harshada S. Patil, Sarita P. Patil, Rajanish K. Kamat, Deok-kee Kim* and Tukaram D. Dongale* 9927 Organ-on-chip systems as a model for nanomedicine Marios Stavrou, Ngan Phung, Jan Grimm and …

The impedance spectroscopy method (AC f = 4–8 MHz at a constant amplitude of 1 V) and Pt-IDE sensors were used to detect and monitor different concentrations (103, 106, and 109 CFU/mL) of both live and dead bacteria cells (Escherichia coli and Staphylococcus aureus). The analysis of the impedance spectra shows the differences in resistance with increasing concentrations for both types of bacteria and the presence of characteristic changes in the frequency range 10–100 kHz. The presence of live bacteria led to a decrease in the impedance value compared to dead cells, and the value of Rs + Rct decreased about two times.

Fully aromatic helicenes are attractive building blocks for the construction of inherently chiral π-conjugated macrocyclic nanocarbons. These hitherto rare molecular architectures are envisaged to exhibit remarkable (chir)optical properties, self-assembly, charge/spin transport, induced ring current or a fascinating Möbius topology. Here the synthesis of helically chiral macrocycles that combine angular dibenzo[5]helicene units as corners and linear trans-stilbene-4,4′-diyl linkers as edges is reported. By subjecting a racemic or enantiopure divinyl derivative of dibenzo[5]helicene to olefin metathesis, which was catalysed by a 2nd generation Piers catalyst under kinetic control, a π-conjugated helicene cyclic trimer (33%) and a tetramer (22%) were obtained, which were separated by GPC. Combining racemic/asymmetric synthesis with the resolution of enantiomers/diastereomers by SFC/HPLC on a chiral column, both …

The interaction between protoporphyrin molecules (donor) and Si nanocrystals (acceptor) up to 2.5 nm for varying distances and orientations is studied by DFT, semi‐empirical and TDDFT methods. Simulations show an effect on electronic structure, indicative of electron charge transfer in parallel orientation and small distances and nonelectron energy transfer for different orientations and larger distances. An absorption‐emission spectral overlap is observed. The calculations of coupling and energy transfer rates show a distance dependence typical of fluorescence resonance energy transfer (FRET) in the long range, while in the short and ultra‐short range the distance dependence indicates electron transfer in addition to FRET. The Si NCs with the smallest size yield larger couplings than the larger nanocrystals. The PPIX/Si NC coupling was enhanced by adding a plasmon nanoparticle as a bridge in the donor …

Atomic force microscopy (AFM) is nowadays indispensable versatile scanning probe method widely employed for fundamental and applied research in physics, chemistry, biology as well as industrial metrology. Conventional AFM systems can operate in various environments such as ultra-high vacuum, electrolyte solutions, or controlled gas atmosphere. Measurements in ambient air are prevalent due to their technical simplicity; however, there are drawbacks such as formation of water meniscus that greatly increases attractive interaction (adhesion) between the tip and the sample, reduced spatial resolution, and too strong interactions leading to tip and/or sample modifications. Here we show how the attractive forces in AFM under ambient conditions can be used with advantage to probe surface properties in a very sensitive way even on highly mobile molecules and nanoparticles. We introduce a stable non-contact …

For sustainable energy technologies, MXenes offer unique properties such as high electrical conductivity, hydrophilicity, excellent thermal stability, large interlayer spacing, easily tunable structure, high surface area, and microporous structure that facilitate faster ion transfer. To address limitations of aqueous MXene suspension, Ti3C2-type MXene thin films are prepared from non-aqueous suspensions in N,N-dimethyl formamide (DMF) and N-methyl-2-pyrrolidone (NMP) using solvent exchange method followed by spin coating or drop casting on gold interdigitated electrodes (IDE) and ceramic substrates and their electrical properties are compared. Electrical properties investigated by impedance spectroscopy (4 Hz to 8 MHz) and four-point probe (FPP) measurements show that DMF-MXene layers exhibit higher electrical conductivity than MXene deposited from NMP. The material technology and electrical …

Despite the importance of thiorphan as a small molecule with vital biological roles, its interactions with zinc oxide (ZnO) nanomaterials that are prospective in drug delivery and theranostic applications have not yet been sufficiently explored. Here the impact of surface polarity of different ZnO facets on thiorphan adsorption is studied both experimentally by atomic force microscopy (AFM) and angle resolved X-ray photoelectron spectroscopy (XPS) and theoretically by force field molecular dynamics (FFMD) and density functional tight binding simulations (DFTB). Polar ZnO surfaces cause the formation of thiorphan nanodots, where the size of the nanodots depends on the direction of dipoles: small (4 nm) nanodots are formed on Zn-face ZnO, while large (25 nm) nanodots are formed on O-face ZnO. Nonpolar ZnO surfaces cause self-assembly into layered nanoislands with characteristic 4 nm layer thickness, which …

Solely light-induced water splitting represents a promising avenue for a carbon-free energy future, based on reliable energy sources. Such processes can be performed using coupled semiconductor materials (the so-called direct Z-scheme design) that facilitate spatial separation of (photo)excited electrons and holes, prevent their recombination, and allow water-splitting half-reactions proceeding at each corresponding semiconductor side. In this work, we proposed and prepared a specific structure, based on WO3g–x/CdWO4/CdS coupled semiconductors, created by annealing of a common WO3/CdS direct Z-scheme. WO3–x/CdWO4/CdS flakes were further combined with a plasmon-active grating for the creation of the so-called artificial leaf design, making possible complete utilization of the sunlight spectrum. The proposed structure enables water splitting with high production of stoichiometric amounts of oxygen …

The use of impedance spectroscopy (IS) to detect and study bacterial growth has increased significantly in recent decades due to the availability of inexpensive and easy-to-use impedance sensors. In general, there is insufficient of information in the literature on impedance studies of bacterial sensors regarding the relationship between the components of the equivalent electrical circuit and the processes occurring on the sensor surface. To increase the sensitivity of measurement methods and sensor parameters, a deep understanding of the sensor response mechanism and its impact on impedance is required. IS method (AC f= 4 Hz-8 MHz at a constant amplitude of 1 V) and Au/Pt IDE sensors were used to detect and monitor different concentrations (10 3, 10 6, 10 9 CFU/ml) of both live and dead bacterial cells (E. coli and S. aureus) prepared in deionized water (DH 2 O) and bacteria growth liquid (Mueller Hinton …

Hydrogenation of the surface can provide specific and unique properties to nanodiamonds. In this study, a series of high-pressure high-temperature nanodiamonds (HPHT NDs) with varying levels of hydrogenation and sp2 carbon content is prepared and characterized in terms of optical properties, structure, surface chemistry, particle size distribution, and zeta potential. The higher the surface sp2-C content and level of hydrogenation the better dispersibility in acidic to neutral pH and higher isoelectric points are achieved. We further evaluated the interaction of hydrogenated HPHT NDs with chitosan by infrared spectroscopy and atomic force microscopy. We have found that chitosan is electrostatically attracted to the hydrogenated HPHT NDs, it improves the dispersibility of the HPHT NDs with a lower level of hydrogenation, and it provides colloidal stability in the broad pH range 2–11 to all hydrogenated HPHT NDs …

Fully aromatic helicenes are fascinating building blocks for the construction of inherently chiral macrocyclic nanocarbons. Such helicene-based non-planar macrocycles interact with each other and underlying substrate and form various 2D crystals. However, the role of their chirality remains unknown. In Atomic Force Microscopy (AFM) the macrocycles show stripes with six-fold symmetry but only faintly visible internal structure that is not sufficient to see individual adsorbed molecules and identify their chirality. Here, AFM data of self-assembled helicene-based 2D molecular crystals are analyzed by a new computational method that combines various information from AFM image and expected molecular shape taken from molecular dynamic simulations. Possible molecule arrangements are thereby computed and four basic structural elements (dimers) with the smallest deviation from AFM topography image are found …