A cholesterol biosensor based on gold nanoparticles decorated functionalized graphene nanoplatelets

The fabrication of a cholesterol biosensor using gold nanoparticles decorated graphene nanoplatelets has been reported. Thermally exfoliated graphene nanoplatelets act as a suitable support for the deposition of Au nanoparticles. Cholesterol biosensor electrodes have been constructed with nafion solubilized functionalized graphene nanoplatelets (f-G) as well as Au nanoparticles decorated f-G, immobilized over glassy carbon electrode. f-G and Au/f-G thin film deposited glassy carbon electrodes were further functionalized with cholesterol oxidase by physical adsorption. Au nanoparticles dispersed over f-G demonstrate the ability to substantially raise the response current. The fabricated electrodes have been tested for their electrochemical performance at a potential of 0.2 V. The fabricated Au/f-G based cholesterol biosensor exhibits sensitivity of 314 nA/μM cm² for the detection of cholesterol with a linear response up to 135 μM. Furthermore, it has been observed that the biosensor exhibits a good anti-interference ability and favorable stability over a month's period.     

SiO2/Si(111)表面Ge量子点的生长研究

Si衬底用化学方法清洗后,表面大约残余1.0 nm厚SiO2薄膜.利用原子力显微镜(AFM)和反射高能电子衍射(RHEED)来研究温度和Ge蒸发厚度对在SiO2薄膜表面生长的Ge量子点的影响.实验结果表明,当衬底温度超过500 ℃时,SiO2开始与Ge原子发生化学反应,并形成与Si(111)表面直接外延的Ge量子点.在650 ℃时,只有Ge的厚度达到0.5nm时,Ge量子点才开始形成.     

Growth of two-dimensional arrays of uncapped gold nanoparticles on silicon substrates

A method of preparing large area patterned 2D arrays of uncapped gold (Au) nanoparticles has been developed. The pattern has been formed using self-assembly of uncapped Au nanoparticles. The Au nanoparticles were synthesized via toluene/water two phase systems using a reducing agent and colloidal solution of Au nanoparticles was produced. These nanoparticles have been prepared without using any kind of capping agent. Analysis by TEM showed discrete Au nanoparticles of 4 nm average diameter. AFM analysis also showed similar result. The TEM studies showed that these nanoparticles formed self-assembled coherent patterns with dimensions exceeding 500 nm. Spin coating on silicon substrate by suitably adjusting the speed can self-assemble these nanoparticles to lengths exceeding 1 μm.     

Ion-induced self-organized dot and ripple patterns on Si surfaces

The evolution of the surface topography during low-energy Ar⁺ ion beam erosion of silicon surfaces is studied. Depending on ion-beam parameters, a variety of nanostructured patterns with a very narrow size distribution can be developed on the surface. By rotating the sample, ordered nanodots are formed for ion energies ?300 eV at normal and oblique ion incidence angles with respect to the surface normal. Dots evolving at oblique ion incidence of 75° show a very high degree of ordering with a mean dot size λ∼30 nm. Without sample rotation at near normal ion incidence angle (∼15°), remarkably ordered ripple structures develop with a wavelength λ∼45 nm. The degree of ordering and size homogeneity of these nanostructures increases with erosion time eventually leading to the most ordered self-organized patterns on Si surfaces reported so far.     

Preparation of carbon nanotube/chitosan/gold nanoparticle composite microspheres

The electrostatic layer-by-layer (LbL) assembly of acid-modified multi-walled carbon nanotubes (MWNTs) and biopolymer chitosan (CHIT) is realized on planar substrates and polystyrene (PS) microsphere templates, respectively. The successful stepwise growing process of the composite films on planar substrates is investigated and confirmed by scanning electron microscopy and UV-vis spectroscopy. The transfer of the LbL assembly of MWNTs and CHIT to spherical PS microspheres leads to novel (MWNT/CHIT)PS core-shell structure, on which the gold nanoparticles (GNPs) are deposited to fabricate GNP(MWNT/CHIT)PS composite microspheres. The glass carbon electrodes modified with such (MWNT/CHIT)PS or GNP(MWNT/CHIT)PS composites exhibit satisfactory electrocatalytic activities for biomolecule dopamine.     

The effect of cysteine on electrodeposition of gold nanoparticle

The most applications of gold nanoparticles are in the photo-electronical accessories and bio-chemical sensors. Chloride solution with cysteine additive was used as electrolyte in gold nanoparticles electrodeposition. The nucleation and growing mechanism were studied by electrochemical techniques such as cyclic voltammetry and chronoamperometry, in order to obtain a suitable nano structure. The deposition mechanism was determined as instantaneous nucleation and the dimension of particles was controlled in nanometric particle size range. Atomic Force Microscope was used to evaluate the effect of cysteine on the morphology and topography of gold nanoparticles. Finally the catalytic property of gold nanoparticle electrodeposited was studied in KOH solution, where oxygen reduction on the gold nanoparticle surface was eight times greater than that on the conventional gold deposits.     

Effects of gold nanoparticles in the green and red emissions of TeO2–PbO–GeO2 glasses doped with Er–Yb

In the present work it is reported for the first time the effects of gold nanoparticles in the infrared-to-visible frequency upconversion of Er³⁺–Yb³⁺ co-doped TeO₂–PbO–GeO₂ glasses. Intense emission bands at 527, 550, and 660 nm were observed corresponding to the Er³⁺ transitions. It is shown that the combined effects of gold nanoparticles and the efficient Yb³⁺ → Er⁺³ energy transfer mechanism change the upconversion visible spectrum. It is then demonstrated that the enhanced local field contribution due to gold nanoparticles and the energy transfer processes between two different rare-earth ions can be used to control and improve the efficiency of luminescent glasses.     

Nano-structuring of sputtered gold layers on glass by annealing

The crystalline structure and surface morphology of gold nano-structures prepared by sputtering on a glass substrate are studied. The properties of the gold nano-structures were determined at room temperature and after annealing at 300 °C. XRD analysis provided information about the gold crystalline structure. Significant difference in the dependence of the lattice parameter on the sputtering time was found between the as-sputtered and annealed samples. By the XRD method the texture, crystallite size and lattice stress were also determined. With increasing sputtering time the layer thickness and the size of crystallites increased. Another rapid enlargement of the crystallites is observed after annealing. On the as-sputtered samples the value of micro-deformation depends on the structure thickness. After annealing, however, the micro-deformation is nearly constant regardless of the sputtering time. On both, the as-sputtered and the annealed samples the gold crystallites are preferentially [111] oriented. After the annealing significant changes in the structure surface morphology and a dramatic increase of the surface roughness are observed due to a structure relaxation at increased temperature.     

Self-assembled growth and magnetotransport investigations on strained Si/SiGe multilayers on vicinal (113)-Si surfaces

We have reported on the growth and magnetotransport properties of modulation p-doped Si_1−xGe_x quantum wells on strained multilayers of 2.5 nm Si_1−xGe_x/10 nm Si on vicinal (113) Si surfaces. Owing to the strong step-bunching properties of the (113) Si surface, both the Si_1−xGe_x and the Si layers exhibited a regular pattern of large steps. Low-temperature magnetotransport measurements revealed a hole density (6–9×10¹¹ cm⁻²) independent of direction, whereas a pronounced mobility anisotropy was found. The mobility (1000–2000 cm²/Vs) was approximately two times higher along the [33-2] direction compared to a perpendicular [−110] direction. This is attributed to anisotropic hole scattering caused by anisotropic shear strain which is always present in strained layers on (113) Si. No influence of the large regular steps, whose direction is given by the direction of the substrate miscut, on the mobility was found.     

Palladium nanoparticle seeded electroless metallization of Al/Al2O3 surfaces

A simple method for the formation of palladium nanoparticles on aluminum and aluminum oxide surface is demonstrated. In the present method, the palladium nanoparticles obtained directly on the solid surface by immersing the specimen in palladium(II)acetate solution followed by reduction to metallic palladium by using sodium hypophosphite. In the investigation, as-received, boiled, electropolished and anodized aluminum was used as substrate. Additionally, the method is combined with the electroless nickel plating, which facilitates two steps metallization technique on the respective surfaces. In these cases, specimens were first immersed in palladium(II)acetate solution followed by immersion in electroless nickel plating solution, where, palladium reduced on the specimen surface providing catalytic site for the subsequent electroless nickel deposition. Using the technique, about 6 to 8.5 µm thick Ni-P metallic layer was deposited on the specimen surface.     

Study of step instability on Si surfaces

Step instabilities on Si(1 1 1) vicinal surface and Si(1 1 1) vicinal surface induced by Au adsorption were observed by reflection electron microscopy. On the Si(0 0 1) vicinal surface faceting of (0 0 1) surface due to surface reconstruction takes place and surface steps are bunching. The kinetics of mass transport of Si depends on the substrate temperature and steps are impermeable for Si adatoms at lower temperature and they are permeable at higher temperature. On the Si(1 1 1) vicinal surface the permeability of steps depends on the heating current direction. The steps are permeable for step-up current heating and are impermeable for step-down current heating. Above a critical coverage of Au (≈0.3 ML) steps are bunching irrespective of heating current direction and periodic array of extremely straight step bands is formed for the step-down current heating.     

Formation of 1D and 2D gold nanoparticle arrays by divalent DNA-gold nanoparticle conjugates

Divalent DNA-AuNP (gold nanoparticle) conjugates comprising two DNA strands at diametrically opposed positions are prepared. Highly linear 1D and tetragonal lattice-like 2D AuNP arrays are constructed using the conjugates and DNA assemblies based on T- and double-crossover motifs and the Holliday junction.     

Strategy of fabricating enriched gold nanoparticles based on electrochemical methods

In this work, we report a new and clean electrochemical pathway to prepare enriched gold nanoparticles in aqueous solutions via the aid of chitosan without addition of any other stabilizer and reductant. First, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1 N NaCl and 1 g/L chitosan from − 0.28 to + 1.22 V vs Ag/AgCl at 500 mV/s with 500 scans. Then the Au working electrode was immediately replaced by a Pt electrode, and a cathodic overpotential of 0.6 V from the open circuit potential (OCP) of ca. 0.84 V vs Ag/AgCl was applied under sonification to synthesize Au nanoparticles. Experimental results indicate the concentration and the particle sizes of prepared Au nanoparticles are ca. 50 ppm and 10 nm in diameter, respectively. No aggregation of Au nanoparticles is observed in an ambient atmosphere for at least 3 months.     

On the processing-structure-property relationship of ITO layers deposited on crystalline and amorphous Si

Indium-tin-oxide (ITO) antireflection coatings were deposited on crystalline Si (c-Si), amorphous hydrogenated Si (a-Si:H) and glass substrates at room temperature (RT), 160 °C and 230 °C by magnetron sputtering. The films were characterised using atomic force microscopy, transmission electron microscopy, angle resolved X-ray photoelectron spectroscopy, combined with resistance and transmittance measurements. The conductivity and refractive index as well as the morphology of the ITO films showed a significant dependence on the processing conditions. The films deposited on the two different Si substrates at higher temperatures have rougher surfaces compared to the RT ones due to the development of crystallinity and growth of columnar grains.     

Mimicking cell membrane-like structures on alkylated silicon surfaces by peptide amphiphiles

We present a new strategy for flexible attachment of peptide amphiphiles on functionalized silicon surfaces. This method involves the production of an alkylated surface on which a lipidated peptide can then be attached through hydrophobic interaction. We applied this to two derivatives of amphiphilic peptide molecules with the same amino acid sequence (A-A-A-A-G-G-G-E-R-G-D) but different in alkyl chain lengths (palmitic acid, undecanoic acid). The basis of this work was to develop substrates which are more biocompatible and bioactive. The ultra-thin peptide amphiphile films were characterized using electrical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (ATR-FTIR) spectroscopy. The results demonstrated that the length of the alkyl chain in the peptide amphiphile affects the packing and coverage of the peptides on the silicon surface.     

Structural and optical properties of the SiO2-P2O5 films obtained by sol-gel method

A comparative study of the sol-gel films prepared in the SiO₂-P₂O₅ system starting with triethylphosphate, triethylphosphite and phosphoric acid as P precursors was performed. The work addresses basic aspects of physics, chemistry, and engineering of oxide films for applications in microelectronics, sensing, nano-photonics, and optoelectronics by establishing the influence of different precursors on the composition, structure and optical properties of the obtained films. The influence of the type of substrate (glass and indium tin oxide coated glass) and of the thermal treatment (200 and 500 °C) on their structure and properties was studied. By spectroscopic ellipsometry, X-Ray photoemission spectroscopy and atomic force microscopy measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when P-alkoxides were used. The phosphoric acid that forms chemical bond with silica network during the sol-gel process leads to better incorporation of P in the silica network as compared to the P-alkoxides.     

Biomimetic fabrication of gold nanoparticles on templated indole-3-acetic acid based nanofibers

Self-assembly of the phytohormone indole-3-acetic acid (IAA) was examined in aqueous solutions of varying pH values. Further, it was observed that IAA biomimetically reduced Au ions leading to the formation of Au nanoparticles at a pH range of 4-9. It was found that at a pH range of 4-7, uniform spherical gold nanoparticles in the size ranges of 20-30 nm were obtained, while under basic conditions, a high degree of aggregation was observed. In addition, we conjugated IAA with the organic linker 1,4-diaminobutane in order to enhance the attachment of Au ions to the IAA moiety via the free amino group and examined its self-assembly. In general, higher yields of nanofibers were formed upon self-assembly of the amide conjugate, with lengths in the micron range. Further, it was observed that the Au nanoparticles formed in the presence of the self-assembled amide conjugates were uniformly coated, leading to the formation of uniform gold nanowires. Thus, a new class of materials based on IAA and IAA-amide conjugates could be efficiently used for formation of gold nanoparticles using environmentally friendly mild synthetic methods in the absence of harsh reducing agents. Such materials may have potential applications in optoelectronics, bioimaging and sensing.     

Physicochemical characterization of Fe3O4/SiO2/Au multilayer nanostructure

The purpose of this research was to synthesize and characterize gold-coated Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Smaller particles were synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g⁻¹. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of 80–100 emu g⁻¹ and coercivity of 80–120 Oe for particles between 35 and 96 nm, respectively. The magnetic NPs were modified with a thin layer of silica using Stober method. Small gold colloids (1–3 nm) were synthesized using Duff method and covered the amino functionalized particle surface. Magnetic and optical properties of gold nanoshells were assessed using Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis spectrophotometer, atomic and magnetic force microscope (AFM, MFM), and transmission electron microscope (TEM). Based on the X-ray diffraction (XRD) results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of each layer of a nanoshell is also demonstrated by Fourier transform infrared (FTIR) results. The Fe₃O₄/SiO₂/Au nanostructures, with 85 nm as particle size, exhibited an absorption peak at ∼550 nm with a magnetization value of 1.3 emu g⁻¹ with a specific surface area of 71 m² g⁻¹.     

纳米SiO2/聚丙烯酸酯复合乳液的研究

试验了四种制备纳米SiO2 /聚丙烯酸酯复合乳液的方法 ,结果表明 ,以KPS NH3·H2 O引发乳液聚合和以偶联剂处理SiO2 纳米溶胶再进行乳液聚合两种方法都可以得到稳定存在的无机纳米SiO2 /有机物复合乳液 ,其性能优于全丙乳液。而用HPC或以阳离子表面活性剂 -十六烷基三甲基溴化铵 (CTAB)处理SiO2 纳米溶胶后再进行乳液聚合两种方法 ,必须要有合适孔径的超滤膜或合适的专用阳离子单体 ,才能制得稳定的复合型的高分子乳液。     

Conductive thin film multilayers of gold on glass formed by self-assembly of multiple size gold nanoparticles

Highly conductive thin films of gold have been fabricated on glass substrates by the deposition of gold nanoparticles of two different diameters. A deposition sequence, alternating between 2.6-nm and 12-nm diameter particles, was used whereby the 2.6-nm particles served to fill in the gaps created by the assembly of the larger 12-nm diameter particles. The resulting thin films, with thicknesses of less than 35 nm, displayed high conductivities, yet were fabricated in substantially fewer deposition cycles than required by previous methods. Analysis of surface morphology performed by atomic force microscopy and scanning electron microscopy showed that the high conductivity is the result of a less porous surface structure than can be achieved through the layering of a single size nanoparticle. Conductivity analysis was performed by 4-point probe with resistivities of 5.00 ± 0.4 × 10^− 6 Ω m for 5 layers and 4.49 ± 0.2 × 10^− 6 Ω m for the 6-layer films.