Nanoscale Irregularities Research Articles

Physicochemical characteristics of chitosan-TiO2 biomaterial. 2. Wettability and biocompatibility

The study aimed to determine the chemical nature, energy state, and topography of chitosan and/or TiO 2 thin layers, which were transferred from different aqueous solutions or dispersions onto a solid support (mica) by a dip-coating method using the Langmuir-Blodgett trough. The surface topography was analysed using an optical profilometer. The performed wettability measurements were used to estimate changes in the total surface free energy based on the theoretical mathematical Lifshitz-van der Waals-Acid-Base model. In addition, the Langmuir technique was employed to determine the effect of Ch-TiO 2 and/or hyaluronic acid (HA) on the model membrane properties in aspect of biocompatibility. The prepared materials can be classified as high-energy, hydrophilic, with roughness in the nanometric scale. Physicochemical parameters have a significant impact on the processes that take place in the surface layer of the biomaterial being in contact with the biological environment. • Biocompatible chitosan-TiO 2 coating with nano-scale irregularities was obtained on mica. • Surface properties of novel material (Ch-HA-TiO 2 ) were characterized. • Relationship between wettability and surface microstructure was shown. • Hybrid biomaterial exhibited the high surface free energy. • Presence of the hyaluronic acid increased the biocompatibility of Ch-TiO 2 combination.

Fluorine-free superhydrophobic characterized coatings: A mini review

The scientific fraternity and coating companies have researched and developed coatings with superhydrophobic features for a wide range of applications, varying from automotive, oceanic, pharmaceutical, and thermal and power sectors, over the preceding few years. The self-cleaning features of superhydrophobic surfaces exhibit pronounced dust repelling and lower dust adhesiveness qualities, along with incomparable water repellence for maritime, automotive, and pharmaceutical applications. The advancement of super-hydrophobic surfaces for averting the accrual of impurities on surfaces is an active space of exploration globally. A lesser hysteresis of contact angle leads to drops of water sliding effortlessly on such surfaces. The solid surfaces’ surface energy can be weakened by fixing materials of lesser surface energy on the exterior, which can be performed by the following dual methods; either by fixing materials of reduced surface energy straight onto the exterior of a substrate in the form of a coating of that material, or by fixing materials of less surface energy on the exterior of nano-architectural structures and then dropping the coating of those nanoscale materials on the exterior of the substrate. The generation of nanoscale irregularities on substrates by dropping nanostructure layers on surfaces makes it an attractive option since, usually, nanomaterials have a minimum of one dimension, ranging from 1 - 100 nm. The nanostructures’ sizes unveil exceptional physical and chemical characteristics, principally owing to their greater specific surface area to volume quotient. This review encompasses the non-fluorinated superhydrophobic coatings developed to date.

Enhancement of the surface characteristics of Ti-based biomedical alloy by electropolishing in environmentally friendly deep eutectic solvent (Ethaline)

This paper reports the results of the study on electrochemical polishing of Ti-based alloy using an ecologically friendly deep eutectic solvent, Ethaline. The electropolishing treatment was performed in a potentiostatic mode (E=+3.0 V and E=+4.0 V) at the temperature of 25 °C for 30–40 min. It was shown that the electropolishing in Ethaline ensured the removal of surface defects, thereby providing surface smoothing and decreasing surface roughness. The atomic-force microscopy revealed that the electrochemical polishing of titanium alloy in Ethaline yielded formation of specific surface patterns with nanoscale irregularities in the form of prolonged hemispheres. The correlations between surface roughness coefficients and wettability parameters were established and discussed. The electrochemical processes occurring during electrochemical polishing of Ti-based alloy in Ethaline were examined. The adjustment of processing time and electrode potential of electropolishing allows controllably and flexibly tuning the surface roughness and wettability of titanium-containing alloy. It issuggested that the electropolishing of the surfaces of Ti-based alloys in deep eutectic solvent can be successfully used for the processing of different biomedical products.

Development of a Biocompatible Solid Phase Microextraction Thin Film Coating for the Sampling and Enrichment of Peptides.

While currently available methods for peptide sample preparation are mostly suitable for ex situ analysis via exhaustive extraction techniques, these techniques do not allow for in situ extraction of peptides from biological samples, such as blood or plasma collected from patients for routine clinical applications. Biocompatible solid phase microextraction (Bio-SPME) has shown great potential in metabolomics for in situ extraction of metabolites including labile compounds from biological matrices in a biocompatible and non-exhaustive fashion, thus facilitating even in vivo sampling. However, the amounts of peptides extracted by such Bio-SPME chemical biopsy tools are deemed too low for quantification when porous polyacrylonitrile (PAN)-based biocompatible thin film sorbent coatings are used, since such materials have been commonly applied as means to restrict access of high molecular weight compounds such as proteins. Aiming to improve peptide extraction by the SPME sorbent while still preventing protein adsorption, thin films with nanoscale irregularities and mesopores were prepared by inclusion of the porogen lithium perchlorate in the slurries of the coatings. The novel thin film coating method significantly improved extraction of a range of angiotensins known to possess important roles in blood pressure regulation and electrolyte balance. Model low abundance peptides covering a wide range of hydrophobicities were successfully extracted from physiological buffers and human plasma using the increased porosity coating, while the SPME protocol on the tryptic digestion of a protein supported that enzymes were excluded during peptide extraction. Surface rheological analysis, which displayed mesopores on the C18/PAN coatings, confirmed that the porosity of the coating facilitated the mass transport of peptides through the PAN layer, thus enabling extraction of high amounts of peptides by the new C18/PAN coating.

Increasing the Interferogram Sensitivity by Digital Holography

This paper presents the results of experimental studies and digital methods for recording of holograms using spatial light modulators. The use of holographic interference methods for measuring nanoscale irregularities is described for the case of a nanostep (70 nm in height and 30 $$\mu$$ m in width). Examples are given of the method of increased sensitivity for nanostep measurements and the method of hooks using a digital technique. Correction of internal system distortions in the interferometer has been shown to be a workable method. The holographic interference methods with digital processing of holograms allows the sensitivity of interferograms to be increased without loss of basic information about the object and without increasing the measurement accuracy.

Development of highly reliable SERS-active photonic crystal fiber probe and its application in the detection of ovarian cancer biomarker in cyst fluid.

Conventionally Surface-enhanced Raman spectroscopy (SERS) is realized by adsorbing analytes onto nano-roughened planar substrate coated with noble metals (silver or gold) or their colloidal nanoparticles (NPs). Nanoscale irregularities in such substrates/NPs could lead to SERS sensors with poor reproducibility and repeatability. Herein, we demonstrate a suspended core photonic crystal fiber (PCF) based SERS sensor with extremely high reproducibility and repeatability in measurement with a relative SD of only 1.5% and 4.6%, respectively, which makes it more reliable than any existing SERS sensor platforms. In addition, our platform could improve the detection sensitivity owing to the increased interaction area between the guided light and the analyte, which is incorporated into the holes that runs along the length of the PCF. Numerical calculation established the significance of the interplay between light coupling efficiency and evanescent field distribution, which could eventually determine the sensitivity and reliability of the developed SERS active-PCF sensor. As a proof of concept, using this sensor, we demonstrated the detection of haptoglobin, a biomarker for ovarian cancer, contained within the ovarian cyst fluid, which facilitated in differentiating the stages of cancer. We envision that with necessary refinements, this platform could potentially be translated as a next-generation highly sensitive SERS-active opto-fluidic biopsy needle for the detection of biomarkers in body fluids.

Structural and mechanical properties of free-standing multiwalled carbon nanotube paper prepared by an aqueous mediated process

Free-standing carbon nanotube film (bucky paper) is a very important material for various applications, but its commercial production is still limited due to size, cost and properties. In the present work, different methods are used to prepare five different types of bucky papers, namely normal, pure refluxed, oxidized, oxidized refluxed and functionalized by using as-produced multiwalled carbon nanotubes (MWCNTs), refluxed MWCNTs, air-oxidized MWCNTs, oxidized refluxed MWCNTs and HNO3 functionalized MWCNTs, respectively. Morphological, physical and structural changes appeared due to different methods are analysed by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction spectroscopy and Raman spectroscopy. Changes in the relative characteristic peak ratio (i.e. IG/ID, IG′/ID and IG′/IG) as a function of MWCNTs quality are determined. It is observed that oxidized refluxed MWCNTs have an average value of IG/ID, IG′/ID and IG′/IG ratio as 4.12, 7.15 and 1.71, respectively, which is higher as compared to other samples. The mechanical properties of different bucky papers are studied by performing tensile tests. The result showed that tensile strength, Young’s modulus and toughness of oxidized refluxed MWCNTs bucky paper are 3.9 MPa, 440 MPa and 780 Jm−3, respectively, which are higher as compared to as-produced MWCNTs bucky paper. The air oxidation and back-to-back refluxing generates nanoscale irregularities within the hexagonal C-structure of a nanotube wall. This helps in improving intermolecular bonding and packing which resulted into significant improvement in the mechanical properties. These bucky papers prepared by economical ways of air oxidation and refluxing in an alkali-soluble emulsifier assisted aqueous medium are potential candidates for field emission devices, energy storage devices and structural materials.

Phonon Transport and Scattering in Rough and Porous Silicon Nanowires

Silicon nanostructures and methods to grow them and influence their structure and morphology has recently been demonstrated to offering a useful strategy to control thermal conductivity and light-matter interactions. The transport and scattering of phonons in Si has demonstrated effective thermoelectric performance largely due to effects caused by surface roughening and nanoscale irregularities in the crystal structure that contribute to diffuse boundary scattering mechanisms. When confinement effects are introduced in crystalline materials the electron and phonon transport can be significantly due to three discrete effects: increased boundary scattering, changes in phonon dispersion, and quantization of phonon transport. Using both room-temperature and in-situ thermal Raman scattering spectroscopy the transport of phonons within Si and its nanostructures can be probed quickly and with little sample preparation. Both ambient and high temperature characteristics of the Si are examined and phonon transport changes between the b-Si and the SiNWs can be linked to scattering effects due to the different morphologies possible using metal-assisted chemical etching to form NWs with tunable porosity and surface roughness. This work demonstrates that by increasing the number of available scattering sites in nanostructured Si within the structure (not just boundary scattering at rough surfaces), the role of four phonon processes on the phonon transport within Si can be optimised. This study is important for providing information on the phonon transport within Si and its nanostructures allowing morphologies that affect phonon transport to be exploited for engineering the thermoelectric properties of future Si devices.ReferencesJ. Lim, K. Hippalgaonkar, S. C. Andrews, A. Majumdar, P. Yang, Nano Letters, 12, 2475 (2012).J. Tang, H.-T. Wang, D. H. Lee, M. Fardy, Z. Huo, T. P. Russell, P. Yang, Nano Letters, 10, 4279 (2010).A. I. Hochbaum, R. Chen, R.D. Delgado, W. Liang, E. C. Garnett, M. Najarian, A. Majumdar, P. Yang, Nature, 451, 163 (2008).A. I. Boukai, Y. Bunimovich, J. Tahir-Kheli, J. K. Yu, W. A. Goddard, J. R. Heath, Nature, 451, 168 (2008).K. Q. Peng, J. J. Hu, Y. J. Yan, Y. Wu, H. Fang, Y. Xu, S. T. Lee, J. Zhu, Advanced Functional Materials, 16, 387 (2005).

Angle- and Spectral-Dependent Light Scattering from Plasmonic Nanocups

As optical frequency nanoantennas, reduced-symmetry plasmonic nanoparticles have light-scattering properties that depend strongly on geometry, orientation, and variations in dielectric environment. Here we investigate how these factors influence the spectral and angular dependence of light scattered by Au nanocups. A simple dielectric substrate causes the axial, electric dipole mode of the nanocup to deviate substantially from its characteristic cos(2) θ free space scattering profile, while the transverse, magnetic dipole mode remains remarkably insensitive to the presence of the substrate. Nanoscale irregularities of the nanocup rim and the local substrate permittivity have a surprisingly large effect on the spectral- and angle-dependent light-scattering properties of these structures.

Ceramic-based microelectrode arrays: Recording surface characteristics and topographical analysis

Amperometric measurements using microelectrode arrays (MEAs) provide spatially and temporally resolved measures of neuromolecules in the central nervous system of rats, mice and non-human primates. Multi-site MEAs can be mass fabricated on ceramic (Al 2O 3) substrate using photolithographic methods, imparting a high level of precision and reproducibility in a rigid but durable recording device. Although the functional capabilities of MEAs have been previously documented for both anesthetized and freely moving paradigms, the performance enabling intrinsic physical properties of the MEA device have not heretofore been presented. In these studies, spectral analysis confirmed that the MEA recording sites were primarily composed of elemental platinum (Pt°). In keeping with the precision of the photolithographic process, scanning electron microscopy revealed that the Pt recording sites have unique microwell geometries post-fabrication. Atomic force microscopy demonstrated that the recording surfaces have nanoscale irregularities in the form of elevations and depressions, which contribute to increased current per unit area that exceeds previously reported microelectrode designs. The ceramic substrate on the back face of the MEA was characterized by low nanoscale texture and the ceramic sides consisted of an extended network of ridges and cavities. Thus, individual recording sites have a unique Pt° composition and surface profile that has not been previously observed for Pt-based microelectrodes. These features likely impact the physical chemistry of the device, which may influence adhesion of biological molecules and tissue as well as electrochemical recording performance post-implantation. This study is a necessary step towards understanding and extending the performance abilities of MEAs in vivo.

Local and average electromagnetic enhancement in surface-enhanced Raman scattering from self-affine fractal metal substrates with nanoscale irregularities

We study the electromagnetic mechanism in surface-enhanced Raman scattering (SERS) from random self-affine fractal metal substrates with nanoscale irregularities by means of the rigorous Green’s theorem integral equation formulation. The SERS enhancement factor is calculated from the numerical results for the surface electric field intensity at the pump frequency for ensembles of self-affine fractal realizations a few microns wide with decreasing lower scale cutoff. We observe a dramatic increase of the local and average SERS enhancement factors throughout the visible and near infrared when the size of surface irregularities is diminished to a few nanometers.

Ultrafast ablation with high-pulse-rate lasers. Part II: Experiments on laser deposition of amorphous carbon films

Ultrafast pulsed laser deposition is a novel technique for depositing particle-free, thin solid films using very high repetition rate lasers. The process involves evaporation of the target by low energy laser pulses focused to an optimum intensity to eliminate particles from the vapor. This results in films with very high surface quality while the very high repetition rate increases the overall deposition rate. Here we report an experimental demonstration of the process by creating ultrasmooth, thin, amorphous carbon films using high repetition rate Nd:YAG lasers. Both a 10 kHz, 120 ns Q-switched Nd:YAG laser, or a 76 MHz 60 ps mode-locked Nd:YAG laser were used in the experiments. The number of particles visible with an optical microscope on the carbon film deposited using the mode-locked laser was less than one particle per mm2. Scanning electron microscopy images demonstrated that the deposited film had a very fine surface texture with nanoscale irregularities. Atomic force microscopy surface microroughness measurements revealed a saturation-like behavior of the root-mean-square roughness at <12 nm over the whole deposited surface area for 10 kHz Q-switched laser evaporation; and almost at the atomic level (<1 nm) for the 76 MHz mode-locked laser evaporation. Raman spectroscopy of the deposited films indicated that they consisted of a mixture of sp3 and sp2 bonded amorphous carbon. The thickness of the amorphous carbon film deposited simultaneously on two 4 in. silicon wafers varied by only ±5% over an area of ∼250 cm2. The deposition rate was ∼2–6 Å/s at a distance of ∼150 mm from the target, which is 10 to 25 times higher than that achieved with conventional high energy low repetition rate nanosecond lasers.

Nanoscale study of the as-grown hydrogenated amorphous silicon surface

A scanning tunneling microscope has been used to study the topography of the as-grown surface of device-quality, intrinsic, hydrogenated amorphous silicon deposited by rf discharge from silane. The substrates were atomically flat, oxide-free, single-crystal silicon or gallium arsenide. No evidence for island formation or nanoscale irregularities was seen in studies of 100-Å-thick films on either silicon or gallium arsenide. The topography of 1000- and 4000-Å-thick films has much variation; many regions can be characterized as ‘‘rolling hills,’’ but atomically flat areas have also been observed nearby. Generally, it appears that surface diffusion plays a role in smoothing the film topography. In most regions, the observed slopes were 10% or less from horizontal, but some steep-sided valleys, indicating incipient voids, were observed. The effect of the finite size of the scanning tunneling microscope probe tip is considered; this has an effect on the observed images in some cases.