Infrared Absorption Spectroscopy of Albumin Binding with Amine-Containing Plasma Polymer Coatings on Nanoporous Diamond Surfaces.

Nanocrystalline diamond (NCD) layers functionalized with amine-containing functional groups have generated considerable interest as biocompatible substrates for attachment of biomolecules and cells with a view to biosensor and tissue engineering applications. Here we prepare nanoporous diamond layers with the surfaces modified by hydrogen plasma, oxygen plasma, and conformal 7 nm amine-containing plasma polymer (PP). Immobilization of bovine serum albumin (BSA) molecules is characterized on such surfaces. Grazing angle reflectance infrared spectroscopy as well as X-ray photoelectron spectroscopy show that concentration of amine-containing bonds after BSA exposure depends on the type of NCD surface modification. AFM measurements reveal that BSA proteins are physisorbed on H- and O-terminated diamond surfaces in different thicknesses and morphology. When the diamond layers are coated with the amine-containing PP, BSA molecules assume similar thickness and morphology, and their adhesion is significantly increased on both types of the diamond surfaces.

Nanostructured diamond layers enhance the infrared spectroscopy of biomolecules.

We report on the fabrication and practical use of high-quality optical elements based on Au mirrors coated with diamond layers with flat, nanocolumnar, and nanoporous morphologies. Diamond layers (100 nm thickness) are grown at low temperatures (about 300 °C) from a methane, carbon dioxide, and hydrogen gas mixture by a pulsed microwave plasma system with linear antennas. Using grazing angle reflectance (GAR) Fourier transform infrared spectroscopy with p-polarized light, we compare the IR spectra of fetal bovine serum proteins adsorbed on diamond layers with oxidized (hydrophilic) surfaces. We show that the nanoporous diamond layers provide IR spectra with a signal gain of about 600% and a significantly improved sensitivity limit. This is attributed to its enhanced internal surface area. The improved sensitivity enabled us to distinguish weak infrared absorption peaks of <10-nm-thick protein layers and thereby to analyze the intimate diamond-molecule interface.

High-yield fabrication and properties of 1.4 nm nanodiamonds with narrow size distribution.

Detonation nanodiamonds (DNDs) with a typical size of 5 nm have attracted broad interest in science and technology. Further size reduction of DNDs would bring these nanoparticles to the molecular-size level and open new prospects for research and applications in various fields, ranging from quantum physics to biomedicine. Here we show a controllable size reduction of the DND mean size down to 1.4 nm without significant particle loss and with additional disintegration of DND core agglutinates by air annealing, leading to a significantly narrowed size distribution (±0.7 nm). This process is scalable to large quantities. Such molecular-sized DNDs keep their diamond structure and characteristic DND features as shown by Raman spectroscopy, infrared spectroscopy, STEM and EELS. The size of 1 nm is identified as a limit, below which the DNDs become amorphous.

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.

Sensitivity of bacteria to diamond nanoparticles of various size differs in gram-positive and gram-negative cells.

In this study, the influence of the size and surface termination of diamond nanoparticles (DNPs) on their antibacterial activity against Escherichia coli and Bacillus subtilis was assessed. The average size and distribution of DNPs were determined by dynamic light scattering and X-ray diffraction techniques. The chemical composition of the DNPs studied by X-ray photoelectron spectroscopy showed that DNPs > 5 nm and oxidized particles have a higher oxygen content. The antibacterial potential of DNPs was assessed by the viable count method. In general, E. coli exhibited a higher sensitivity to DNPs than B. subtilis. However, in the presence of all the DNPs tested, the B. subtilis colonies exhibited altered size and morphology. Antibacterial activity was influenced not only by DNP concentration but also by DNP size and form. Whereas untreated 5-nm DNPs were the most effective against E. coli, the antibacterial activity of 18-50-nm DNPs was higher against B. subtilis. Transmission electron microscopy showed that DNPs interact with the bacterial surface, probably affecting vital cell functions. We propose that DNPs interfere with the permeability of the bacterial cell wall and/or membrane and hinder B. subtilis colony spreading.

Superhydrophilic polystyrene nanofiber materials generating O2((1)Δ(g)): postprocessing surface modifications toward efficient antibacterial effect.

The surfaces of electrospun polystyrene (PS) nanofiber materials with encapsulated 1% w/w 5,10,15,20-tetraphenylporphyrin (TPP) photosensitizer were modified through sulfonation, radio frequency (RF) oxygen plasma treatment, and polydopamine coating. The nanofiber materials exhibited efficient photogeneration of singlet oxygen. The postprocessing modifications strongly increased the wettability of the pristine hydrophobic PS nanofibers without causing damage to the nanofibers, leakage of the photosensitizer, or any substantial change in the oxygen permeability of the inner bulk of the polymer nanofiber. The increase in the surface wettability yielded a significant increase in the photo-oxidation of external polar substrates and in the antibacterial activity of the nanofibers in aqueous surroundings. The results reveal the crucial role played by surface hydrophilicity/wettability in achieving the efficient photo-oxidation of a chemical substrate/biological target at the surface of a material generating O2((1)Δg) with a short diffusion length.

Polylactide nanofibers with hydroxyapatite as growth substrates for osteoblast-like cells.

Various types of nanofibers are increasingly used in tissue engineering, mainly for their ability to mimic the architecture of tissue at the nanoscale. We evaluated the adhesion, growth, viability, and differentiation of human osteoblast-like MG 63 cells on polylactide (PLA) nanofibers prepared by needle-less electrospinning and loaded with 5 or 15 wt % of hydroxyapatite (HA) nanoparticles. On day 7 after seeding, the cell number was the highest on samples with 15 wt % of HA. This result was confirmed by the XTT test, especially after dynamic cultivation, when the number of metabolically active cells on these samples was even higher than on control polystyrene. Staining with a live/dead kit showed that the viability of cells on all nanofibrous scaffolds was very high and comparable to that on control polystyrene dishes. An enzyme-linked immunosorbent assay revealed that the concentration of osteocalcin was also higher in cells on samples with 15 wt % of HA. There was no immune activation of cells (measured by production of TNF-alpha), associated with the incorporation of HA. Moreover, the addition of HA suppressed the creep behavior of the scaffolds in their dry state. Thus, nanofibrous PLA scaffolds have potential for bone tissue engineering, particularly those with 15 wt % of HA.