DFT calculations reveal pronounced HOMO-LUMO spatial separation in polypyrrole-nanodiamond systems.

The low-cost efficient generation of renewable energy and its blending with societal lifestyle is becoming increasingly pervasive. Diamond-based inorganic-organic hybrid systems may have an immense, yet still mostly unexplored, potential in photovoltaic solar cells applications. In this work, we study the interactions of polypyrrole (PPy) with diamond nanoparticles (so-called nanodiamonds, NDs) by computational density functional theory (DFT) methods. We compute the structural and electronic properties of such hybrid organic-inorganic systems. During modeling, PPy is chemisorbed and physisorbed on (111) and (100) ND edge-like surface slabs terminated with oxygen, hydroxyl, carboxyl, and anhydride functional groups, i.e., in the arrangements most commonly found in real NDs. Moreover, NDs terminated with an amorphous surface layer (a-C:H, a-C:O) are considered to approach realistic conditions even further. In a predominant number of cases, we obtain the spatial separation of HOMO and LUMO at the interface, facilitating exciton dissociation. Further, there is a favorable energy level alignment for charge transport. The theoretical results, therefore, show the promising potential of PPy-ND composites in photovoltaic applications.

Nanocrystalline diamond-based impedance sensors for real-time monitoring of adipose tissue-derived stem cells.

Cell-based impedance spectroscopy is a promising label-free method for electrical monitoring of cell activity. Here we present a diamond-based impedance sensor with built-in gold interdigitated electrodes (IDT) as a promising platform for simultaneous electrical and optical monitoring of adipose tissue-derived stem cells (ASCs). The impedance spectra were collected in a wide frequency range (from 100 Hz to 50 kHz) for 90 h of cell cultivation in chambers designed for static cultivation. Absolute impedance spectra were analyzed in terms of measured frequencies and cell properties monitored by a high-resolution digital camera. The control commercially-available impedance system, based on gold electrodes exposed to the cultivation media, and also our specially developed sensor with gold electrodes built into a diamond thin film detected three phases of cell growth, namely the phase of cell attachment and spreading, the phase of cell proliferation, and the stationary phase without significant changes in cell number. These results were confirmed by simultaneous live cell imaging. The design of the sensing electrode is discussed, pointing out its enhanced sensitivity for a certain case. The diamond-based sensor appeared to be more sensitive for detecting the cell-substrate interaction in the first phase of cell growth, while the control system was more sensitive in the second phase of cell growth.

Hydroxylation and self-assembly of colloidal hydrogenated nanodiamonds by aqueous oxygen radicals from atmospheric pressure plasma jet.

Plasma chemical surface modification of nanoparticles in gas-liquid type reactors enables a controllable, specific, low-cost, and environmentally friendly alternative to wet chemistry methods or thermal and dry plasma treatments. Here the atmospheric pressure radio-frequency microplasma jet (µ-APPJ) operating with 0.6% O2 in He is used to deliver aqueous oxygen radicals (AOR) to the surface of ∼3 nm hydrogenated detonation nanodiamonds (H-DNDs) suspended in water. The AOR-treated H-DND samples are characterized by FTIR and XPS spectroscopies and by AFM and SEM imaging. The main chemical reaction mechanism is identified as the abstraction of surface hydrogen atoms by O or OH radicals and a consequent attachment of the OH group, thereby increasing concentration of alcohols, carboxyls, and aldehydes on the DND's surface. FTIR spectra reveal also a structural re-arrangement of the surface water on the AOR-treated H-DNDs. Yet zeta-potential of AOR-treated H-DNDs still remains positive (decreases from +45 mV to +30 mV). The chemical modification gives rise to formation of nanoscale chain-like aggregates when AOR-treated H-DNDs are deposited on Si substrate.

Size and Purity Control of HPHT Nanodiamonds down to 1 nm.

High-pressure high-temperature (HPHT) nanodiamonds originate from grinding of diamond microcrystals obtained by HPHT synthesis. Here we report on a simple two-step approach to obtain as small as 1.1 nm HPHT nanodiamonds of excellent purity and crystallinity, which are among the smallest artificially prepared nanodiamonds ever shown and characterized. Moreover we provide experimental evidence of diamond stability down to 1 nm. Controlled annealing at 450 °C in air leads to efficient purification from the nondiamond carbon (shells and dots), as evidenced by X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and scanning transmission electron microscopy. Annealing at 500 °C promotes, besides of purification, also size reduction of nanodiamonds down to ∼1 nm. Comparably short (1 h) centrifugation of the nanodiamonds aqueous colloidal solution ensures separation of the sub-10 nm fraction. Calculations show that an asymmetry of Raman diamond peak of sub-10 nm HPHT nanodiamonds can be well explained by modified phonon confinement model when the actual particle size distribution is taken into account. In contrast, larger Raman peak asymmetry commonly observed in Raman spectra of detonation nanodiamonds is mainly attributed to defects rather than to the phonon confinement. Thus, the obtained characteristics reflect high material quality including nanoscale effects in sub-10 nm HPHT nanodiamonds prepared by the presented method.