Neural interface with a silicon neural probe in the advancement of microtechnology

In this paper we describe the status of a silicon-based microelectrode for neural recording and an advanced neural interface. We have developed a silicon neural probe, using a combination of plasma and wet etching techniques. This process enables the probe thickness to be controlled precisely. To enhance the CMOS compatibility in the fabrication process, we investigated the feasibility of the site material of the doped polycrystalline silicon with small grains of around 50 nm in size. This silicon electrode demonstrated a favorable performance with respect to impedance spectra, surface topography and acute neural recording. These results showed that the silicon neural probe can be used as an advanced microelectrode for neurological applications.     

Conjugation of the photoluminescent silicon nanoparticles to streptavidin

We have covalently attached multiple photoluminescent silicon nanoparticles (SNs) to streptavidin molecules. Conjugation of SNs to a target protein is achieved using the multistage photoassisted procedure. In a first step, the terminal hydrogen in the freshly prepared SNs is substituted with an alkane monolayer that serves as a platform for chemical linkage to a heterobifunctional cross-linker: 4-azido-2,3,5,6-tetrafluorobenzoic acid, succinimidyl ester. A resulting surface coating stabilizes nanoparticles against oxidation and aggregation. Next, an open end of bifunctional cross-linker-diazirine succinimidyl ester is reacted with carboxyl moieties of streptavidin and forms an amide bond. Gel and capillary electrophoresis of the SN-streptavidin complex demonstrated separate elution of the conjugation product and unreacted protein. Then, the number of SNs per protein molecule was determined by measuring complex charge variation by capillary electrophoresis. Conjugate functionality was tested by allowing it to interact with biotinylated polystyrene microbeads. Intense photoluminescence at carefully washed microbeads demonstrated selective binding of silicon nanoparticle bearing streptavidin to biotinylated microbeads. The high quantum yield of streptavidin-SN conjugate in combination with the small size and biocompatibility of silicon nanoparticles presents an attractive platform for the fluorescence labeling in diverse bioassays.     

Evaluation of the Adherence of Candida Species to Urinary Catheters

Catheter-associated urinary tract infections (CAUTIs) are the most common kind of nosocomial infection. Recent years have seen a significant increase in numbers of infections caused by yeasts of the genus Candida. The adherence of a microorganism to the host surface is a decisive factor in the success of colonization and the pathogenesis of infection. The objective of this work was to evaluate the adherence of species of the genus Candida to urinary catheters. In vitro adherence to the sections of latex and silicon catheters of Candida albicans and Candida parapsilosis were studied. Adherence was measured by counting the number of adhering viable cells and the results were expressed as Colonies Forming Units per mL. The results demonstrated that the latex catheter facilitated adherence more than the silicon catheter (p < 0.01). The adherence of the C. albicans was significantly greater than C. parapsilosis on latex, but it was similar on silicon.     

Solution‐Based Silicon in Thin‐Film Solar Cells

Solution‐based semiconductors give rise to the next generation of thin‐film electronics. Solution‐based silicon as a starting material is of particular interest because of its favorable properties, which are already vastly used in conventional electronics. Here, the application of a silicon precursor based on neopentasilane for the preparation of thin‐film solar cells is reported for the first time, and, for the first time, a performance similar to conventional fabrication methods is demonstrated. Because three different functional layers, n‐type contact layer, intrinsic absorber, and p‐type contact layer, have to be stacked on top of each other, such a device is a very demanding benchmark test of performance of solution‐based semiconductors. Complete amorphous silicon n‐i‐p solar cells with an efficiency of 3.5% are demonstrated, which significantly exceeds previously reported values.     

硅对PCR过程的抑制作用研究

探讨不同氧化程度的硅材料对PCR扩增的抑制作用及其机理。将不同氧化程度的硅纳米颗粒加入PCR反应液中,使其与Taq酶、模板等充分接触,通过离心将硅纳米颗粒沉降在管壁上,取出上清或保留硅纳米颗粒上机扩增,扩增产物采用凝胶电泳法检测。结果表明,随着硅材料表面面积与PCR反应液体积之比的增大,核酸扩增效率将明显下降,并且在所研究的范围内,氧化程度高的硅材料对PCR过程抑制作用更强;通过对抑制作用机理进行初步的实验研究,表明硅材料对PCR反应液中的Taq酶的吸附是导致抑制现象产生的主要原因,而对模板的吸附影响较小;并且,反应管内是否保留硅材料对核酸扩增影响较小,硅材料没有明显的直接化学抑制作用。     

Regular consumption of a silicic acid-rich water prevents aluminium-induced alterations of nitrergic neurons in mouse brain: histochemical and immunohistochemical studies

Silicon is not generally considered an essential nutrient for mammals and, to date, whether it has a biological role or beneficial effects in humans is not known. The results of a number of studies suggest that dietary silicon supplementation might have a protective effect both for limiting aluminium absorption across the gut and for the removal of systemic aluminium via the urine, hence, preventing potential accumulation of aluminium in the brain. Since our previous studies demonstrated that aluminium exposure reduces the number of nitrergic neurons, the aim of the present study was to compare the distribution and the morphology of NO-containing neurons in brain cortex of mice exposed to aluminium sulphate dissolved in silicic acid-rich or poor drinking water to assess the potential protective role of silicon against aluminium toxicity in the brain. NADPH-d histochemistry and nNOS immunohistochemistry showed that high concentrations of silicon in drinking water were able to minimize the impairment of the function of nitrergic neurons induced by aluminium administration. We found that silicon protected against aluminium-induced damage to the nitrergic system: in particular, we demonstrated that silicon maintains the number of nitrergic neurons and their expression of nitrergic enzymes at physiological levels, even after a 12 and 15 month exposure to aluminium.     

Silicon chip-based patch-clamp electrodes integrated with PDMS microfluidics

We report on a silicon wafer-based device that can be used for recording macroscopic ion channel protein activities across a diverse group of cell-types. Gigaohm seals were achieved for CHO-K1 and RIN m5F cells, and both cell-attached and whole-cell mode configurations were also demonstrated. Two distinct intrinsic potassium ion channels were recorded in whole-cell mode for HIT-T15 and RAW 264.7 cells. Polydimethylsiloxane (PDMS) microfluidics were also coupled with the micromachined silicon chips in order to demonstrate that a single cell could be selectively directed to a micropore, and membrane protein currents could subsequently be recorded. These silicon chip-based devices have significant advantages over traditional micropipette approaches, and may serve as combinatorial tools for investigating membrane biophysics, pharmaceutical screening, and other bio-sensing tasks.     

Interactive effects of dietary silicon, copper, and zinc in the rat

A factorial rat experiment using two dietary concentrations each of copper, zinc, and silicon was conducted to identify areas in which interrelationships involving silicon may exist. The concentrations used were (mg/kg of diet): copper, 1 and 5; zinc, 2 and 12; and silicon, 5 and 270. An antagonism between silicon and zinc, whereby increases in dietary levels of either one resulted in a reduction in blood plasma concentrations of the other, was demonstrated. The depressing effect of silicon on plasma concentrations of zinc and on alkaline phosphatase occurred only in zinc-deficient rats. However, silicon had no effect on growth. Effects on aortic composition, interpreted as beneficial, accompanied increases in the silicon content of copper-deficient diets. Silicon-dependent increases in the chloroform-methanol extractable fraction of aorta closely approximated a similar response to copper. High dietary silicon increased aortic elastin in copper-deficient rats when dietary zinc was adequate. The aortic effects of silicon, while mimicking the gross effects of copper, occurred in the absence of any silicon-related changes in blood copper concentrations. Interrelationships of silicon with other elements, particularly copper and zinc, may warrant consideration in future nutritional and metabolic studies.     

Quantitative measurements of C-reactive protein using silicon nanowire arrays

A silicon nanowire-based sensor for biological application showed highly desirable electrical responses to either pH changes or receptor-ligand interactions such as protein disease markers, viruses, and DNA hybridization. Furthermore, because the silicon nanowire can display results in real-time, it may possess superior characteristics for biosensing than those demonstrated in previously studied methods. However, despite its promising potential and advantages, certain process-related limitations of the device, due to its size and material characteristics, need to be addressed. In this article, we suggest possible solutions. We fabricated silicon nanowire using a top-down and low cost micromachining method, and evaluate the sensing of molecules after transfer and surface modifications. Our newly designed method can be used to attach highly ordered nanowires to various substrates, to form a nanowire array device, which needs to follow a series of repetitive steps in conventional fabrication technology based on a vapor-liquid-solid (VLS) method. For evaluation, we demonstrated that our newly fabricated silicon nanowire arrays could detect pH changes as well as streptavidin-biotin binding events. As well as the initial proof-of-principle studies, C-reactive protein binding was measured: electrical signals were changed in a linear fashion with the concentration (1 fM to 1 nM) in PBS containing 1.37 mM of salts. Finally, to address the effects of Debye length, silicon nanowires coupled with antigen proteins underwent electrical signal changes as the salt concentration changed.     

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures¹. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.     

Structural and functional imaging with carbon nanotube AFM probes

Atomic force microscopy (AFM) has great potential as a tool for structural biology, a field in which there is increasing demand to characterize larger and more complex biomolecular systems. However, the poorly characterized silicon and silicon nitride probe tips currently employed in AFM limit its biological applications. Carbon nanotubes represent ideal AFM tip materials due to their small diameter, high aspect ratio, large Young's modulus, mechanical robustness, well-defined structure, and unique chemical properties. Nanotube probes were first fabricated by manual assembly, but more recent methods based on chemical vapor deposition provide higher resolution probes and are geared towards mass production, including recent developments that enable quantitative preparation of individual single-walled carbon nanotube tips [J. Phys. Chem. B 105 (2001) 743]. The high-resolution imaging capabilities of these nanotube AFM probes have been demonstrated on gold nanoparticles and well-characterized biomolecules such as IgG and GroES. Using the nanotube probes, new biological structures have been investigated in the areas of amyloid-beta protein aggregation and chromatin remodeling, and new biotechnologies have been developed such as AFM-based haplotyping. In addition to measuring topography, chemically functionalized AFM probes can measure the spatial arrangement of chemical functional groups in a sample. However, standard silicon and silicon nitride tips, once functionalized, do not yield sufficient resolution to allow combined structural and functional imaging of biomolecules. The unique end-group chemistry of carbon nanotubes, which can be arbitrarily modified by established chemical methods, has been exploited for chemical force microscopy, allowing single-molecule measurements with well-defined functionalized tips.     

The potential use of silicon compounds as oxygen carriers for free and immobilized cells containing l-amino acid oxidase

Summary The relatively low solubility of oxygen in water presents a problem in particular when immobilized cells are used or enzymes are applied for oxygen dependent reactions. The other main purpose is the requirement of oxygen for the increase of biomass. In this investigation the usefulness of silicon emulsions as oxygen carriers is demonstrated.In case of l-amino acid oxidase activity of immobilized cells, an increase by a factor of four was found in the presence of silicon emulsions. Likewise, growth medium enriched with silicon emulsions showed a significantly increased growth of cells inside alginate beads compared to normal growth medium.     

Update on the possible nutritional importance of silicon

Convincing evidence that silicon is a bioactive beneficial trace element continues to accumulate. The evidence, which has come from human, animal, and in vitro studies performed by several laboratories, indicate that silicon in nutritional and supra nutritional amounts promotes bone and connective tissue health, may have a modulating effect on the immune or inflammatory response, and has been associated with mental health. A plausible mechanism of action for the beneficial effects of silicon is the binding of hydroxyl groups of polyols such that it influences the formation and/or utilization of glycosaminoglycans, mucopolysaccharides, and collagen in connective tissue and bone. In addition, silicon may affect the absorption, retention or action of other mineral elements (e.g., aluminum, copper, magnesium). Based on findings from both animal and human experiments, an intake of silicon of near 25 mg/d would be a reasonable suggestion for an adequate intake that would assure its nutritional benefits. Increased intakes of silicon through consuming unrefined grains, certain vegetables, and beverages and cereals made from grains should be recognized as a reasonable dietary recommendation.     

Carbon Nanotube‐Silicon Solar Cells

Due to the high cost of silicon photovoltaics there is currently great interest in finding alternative semiconductor materials for light harvesting devices. Single‐walled carbon nanotubes are an allotrope of carbon with unique electrical and optical properties and are promising as future photovoltaic materials. It is thus important to investigate the methods of exploiting their properties in photovoltaic devices. In addition to already extensive research using carbon nanotubes in organic photovoltaics and photoelectrochemical cells, another way to do this is to combine them with a relatively well understood model semiconductor such as silicon. Nanotube‐silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion efficiencies of up to ～14% that may in part exploit the photoactivity of carbon nanotubes.     

Spreading of mouse fibroblasts on the substrate with multiple spikes

Mouse embryo fibroblasts were cultivated on special substrates with discontinuous surfaces. The substrates were silicon plates with multiple vertical (65-90 microns height) spike-like silicon microcrystals evenly distributed on the plate surfaces. It was shown that the cells were successfully spread and flattened on these substrates. The spread cells formed several discrete attachment zones at the tops and side surfaces of the spikes; these zones were separated from one another by distances considerably greater than the diameter of the unspread cell. At early stages of spreading the unspread cells attached to the tops of single spikes and extended long filopodia attached to the distant spikes. At later stages the lamellae were formed between the filopodia: probably these filopodia served as guidelines for extension of lamellae and progressive cell spreading. These experiments demonstrated that continuity of substrate surface is not a necessary condition for advanced cell spreading.     

Application of silicon improves salt tolerance through ameliorating osmotic and ionic stresses in the seedling of Sorghum bicolor

Silicon has been widely reported to have a beneficial effect on improving plant tolerance to biotic and abiotic stresses. However, the mechanisms of silicon in mediating stress responses are still poorly understood. Sorghum is classified as a silicon accumulator and is relatively sensitive to salt stress. In this study, we investigated the short-term application of silicon on growth, osmotic adjustment and ion accumulation in sorghum (Sorghum bicolor L. Moench) under salt stress. The application of silicon alone had no effects upon sorghum growth, while it partly reversed the salt-induced reduction in plant growth and photosynthesis. Meanwhile, the osmotic potential was lower and the turgor pressure was higher than that without silicon application under salt stress. The osmolytes, the sucrose and fructose levels, but not the proline, were significantly increased, as well as Na⁺ concentration was decreased in silicon-treated plants under salt stress. These results suggest that the beneficial effects of silicon on improving salt tolerance under short-term treatment are attributed to the alleviating of salt-induced osmotic stress and as well as ionic stress simultaneously.     

18 Possible extraterrestrial life: a quantum-chemical look on the silicon analogs of carbon biomolecules

The uniqueness of life on our planet has been an important topic of discussion in scientific literature for many decades. The most particular findings are in the fields of the structure of biomolecules and the mechanisms of their conformational and chemical transfers since they underlie all the biospheric processes of our planet. The compounds based on carbon are the subject of study of organic chemistry, which has an appropriate thoroughly developed classification of such substances; a number of approaches have been proposed for the analysis of composition and structure of the organic compounds, and a theoretical basis has been created, which describes the character of various chemical bonds involving carbon atoms. At the same time, since quite a while, there is a widely discussed hypothesis (Alison, 1968) concerning the possibility of existence of compounds, which are similar to organic, but are based on silicon atoms. Even in interstellar medium, among all the diversity of molecules detected, 84 are based on carbon, and 8 on silicon (Lazio, 2000), including four hybrid types, i.e. containing both silicon and carbon. According to approximate evaluations, the contents ratio of carbon to silicon in the space equals to 10:1, though the Earth’s crust consists of 87% of silicon in the form of oxides. In the Periodic Table, silicon is situated in the same group IV, like carbon. These two elements are largely similar in the structure of their valent electronic shells, and their noteworthy that previously it was stated (Lazio, 2000) that silicon-containing compounds are not as diverse in structure as carbon compounds. Despite having higher mass and radius, the atoms of silicon form double and triple covalent bonds (Wang et al., 2008). Therefore, the issue concerning the existence of silicon structures similar to carbon biomolecules, as well as the question of hypothetical “biochemical” processes involving non-carbonic analogs of aminoacids, carbohydrates, proteins, lipids, and other biomolecules, is still a matter of discussion in scientific and popular science literature. It is particularly notable that the modern methods of computational chemistry allow carrying out the estimating calculations of the structure and dynamics of such compounds, which is quite similar to the known approaches of substance modeling de novo in drug design. For instance, first by calculations (Nagase, Kudo, & Aoki, 1985), and later on experimentally (Abersfelder, White, Rzepa, & Scheschkewitz, 2010), aromaticity of cyclic carbohydrate-like derivatives of silicon was studied. In the present study, we used quantum-chemical semiempirical PM3 and ab initio B3LYP/6-311G(d,p) level of theory to investigate the peculiarities of several structural and thermodynamic parameters of molecules, which can be assumed as complete silicon analogs of carbonic L-amino acids and other biomolecules, so-called bricks of life: carbohydrates, nitrogenous bases, fatty acids, as well as vitamins and caffeine. The quantum-mechanical calculations that we made displayed that the molecules of silicon amino acids possess higher thermodynamic stability compared to carbon analogs. Thereby, silicon amino acids have a similar conformation freedom, increased values of dipole moment, as well as more pronounced electron-donor characteristics. Silicon analogs of carbohydrates, fatty acids, and nitrogenous bases are as well considered as heavier thermodynamically stable compounds, having special features in 3D-organization and worth further experimental study. The present work also deals with the question of the existence and stability of “alpha-helices” composed of silicon amino acids, because in the molecules of Si-analogs of aspartate and glutamate, we have discovered effective formation of intramolecular hydrogen bond (due to the side chain), which is highly important for Pauling–Corey alpha helix formation in natural L-amino acids (Kondratyev, Kabanov, & Komarov, 2010). Our estimations show that an “alpha helix” composed of 10 silicon alanine analogs is more stable in isolated state than a linear form of such macromolecule, which was not observed for a molecule of the same composition having a carbon backbone.     

The effects of mechanical stress on the growth, differentiation, and paracrine factor production of cardiac stem cells

Stem cell therapies have been clinically employed to repair the injured heart, and cardiac stem cells are thought to be one of the most potent stem cell candidates. The beating heart is characterized by dynamic mechanical stresses, which may have a significant impact on stem cell therapy. The purpose of this study is to investigate how mechanical stress affects the growth and differentiation of cardiac stem cells and their release of paracrine factors. In this study, human cardiac stem cells were seeded in a silicon chamber and mechanical stress was then induced by cyclic stretch stimulation (60 cycles/min with 120% elongation). Cells grown in non-stretched silicon chambers were used as controls. Our result revealed that mechanical stretching significantly reduced the total number of surviving cells, decreased Ki-67-positive cells, and increased TUNEL-positive cells in the stretched group 24 hrs after stretching, as compared to the control group. Interestingly, mechanical stretching significantly increased the release of the inflammatory cytokines IL-6 and IL-1β as well as the angiogenic growth factors VEGF and bFGF from the cells in 12 hrs. Furthermore, mechanical stretching significantly reduced the percentage of c-kit-positive stem cells, but increased the expressions of cardiac troponin-I and smooth muscle actin in cells 3 days after stretching. Using a traditional stretching model, we demonstrated that mechanical stress suppressed the growth and proliferation of cardiac stem cells, enhanced their release of inflammatory cytokines and angiogenic factors, and improved their myogenic differentiation. The development of this in vitro approach may help elucidate the complex mechanisms of stem cell therapy for heart failure.     

Silicon Improves the Tolerance of Wheat Seedlings to Ultraviolet-B Stress

Enhanced ultraviolet-B (UV-B) irradiation is one of the most important abiotic stresses that could influence the growth and physiological traits of plants. In this work, we reported the effects of silicon on the growth and physiological characteristics of wheat seedlings (Triticum aestivum L. cv Hengmai5229) subject to UV-B stress. Treatments with silicon significantly increased total biomass and chlorophyll (a + b) content, and reduced malondialdehyde (MDA) content and the rate of superoxide radical (O₂⁻) production in wheat seedlings subjected to UV-B stress. Silicon treatments also induced an increased in soluble sugar, anthocyanins, and flavonoid content. Leaf silicon concentration increased with the increasing of silicon supply to soil. Positive correlations were found in leaf silicon concentration with total biomass, chlorophyll (a + b), proline, and soluble protein content, respectively. MDA content and the rate of O₂⁻ production were negatively correlated with leaf silicon concentration in seedlings. The results demonstrated that silicon alleviated the damage caused by UV-B on wheat seedlings to some extent by the increase in antioxidant compounds content and leaf silicon concentration.