Chemically grafted carbon nanotube surface coverage gradients

Two approaches to producing gradients of vertically aligned single-walled carbon nanotubes (SWCNTs) on silicon surfaces by chemical grafting are presented here. The first approach involves the use of a porous silicon (pSi) substrate featuring a pore size gradient, which is functionalized with 3-aminopropyltriethoxysilane (APTES). Carboxylated SWCNTs are then immobilized on the topography gradient via carbodiimide coupling. Our results show that as the pSi pore size and porosity increase across the substrate the SWCNT coverage decreases concurrently. In contrast, the second gradient is an amine-functionality gradient produced by means of vapor-phase diffusion of APTES from a reservoir onto a silicon wafer where APTES attachment changes as a function of distance from the APTES reservoir. Carboxylated SWCNTs are then immobilized via carbodiimide coupling to the amine-terminated silicon gradient. Our observations confirm that with decreasing APTES density on the surface the coverage of the attached SWCNTs also decreases. These gradient platforms pave the way for the time-efficient optimization of SWCNT coverage for applications ranging from field emission to water filtration to drug delivery.     

Preparation of porous n-type silicon sample plates for desorption/ionization on silicon mass spectrometry (DIOS-MS)

This study focuses on porous silicon (pSi) fabrication methods and properties for desorption ionization on silicon mass spectrometry (DIOS-MS). PSi was prepared using electrochemical etching of n-type silicon in HF-ethanol solution. Porous areas were defined by a double-sided illumination arrangement: front-side porous areas were masked by a stencil mask, eliminating the need for standard photolithography, and backside illumination was used for the backside ohmic contact. Backside illumination improved the uniformity of the porosified areas. Porosification conditions, surface derivatizations and storage conditions were explored to optimize pSi area, pore size and pore depth. Chemical derivatization of the pSi surfaces improved the DIOS-MS performance providing better ionization efficiency and signal stability with lower laser energy. Droplet spreading and drying patterns on pSi were also examined. Pore sizes of 50-200 nm were found to be optimal for droplet evaporation and pore filling with the sample liquid, as measured by DIOS efficiency. With DIOS, significantly better detection sensitivity was obtained (e.g. 150 fmol for midazolam) than with desorption ionization from a standard MALDI steel plate without matrix addition (30 pmol for midazolam). Also the noise that disturbs the detection of low-molecular weight compounds at m/z < 500 with MALDI could be clearly reduced with DIOS. Low background MS spectra and good detection sensitivity at the 100-150 fmol level for pharmaceutical compounds were achieved with DIOS-MS.     

Stimulus-responsiveness and drug release from porous silicon films ATRP-grafted with poly(N-isopropylacrylamide)

In this report, we employ surface-initiated atom transfer radical polymerization (SI-ATRP) to graft a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), of controlled thickness from porous silicon (pSi) films to produce a stimulus-responsive inorganic-organic composite material. The optical properties of this material are studied using interferometric reflectance spectroscopy (IRS) above and below the lower critical solution temperature (LCST) of the PNIPAM graft polymer with regard to variation of pore sizes and thickness of the pSi layer (using discrete samples and pSi gradients) and also the thickness of the PNIPAM coatings. Our investigations of the composite's thermal switching properties show that pore size, pSi layer thickness, and PNIPAM coating thickness critically influence the material's thermoresponsiveness. This composite material has considerable potential for a range of applications including temperature sensors and feedback controlled drug release. Indeed, we demonstrate that modulation of the temperature around the LCST significantly alters the rate of release of the fluorescent anticancer drug camptothecin from the pSi-PNIPAM composite films.     

Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry

To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin‐printed 20 hydrophobic and hydrophilic ionic liquids onto as‐prepared, hydrogen‐passivated porous silicon (ap‐pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap‐pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox‐pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap‐pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower.     

Dual silane surface functionalization for the selective attachment of human neuronal cells to porous silicon

Porous silicon (pSi) surfaces were chemically micropatterned through a combination of photolithography and surface silanization reactions. This patterning technique produces discretely defined regions on a pSi surface functionalized with a specific chemical functionality, and the surrounding surface displays a completely different functionality. The generated chemical patterns were characterized by a combination of IR microscopy and the conjugation of two different fluorescent organic dyes. Finally, the chemically patterned pSi surface was used to direct the attachment of neuronal cells to the surface. This patterning strategy will be useful for the development of high-throughput platforms for investigating cell behavior.     

Surface chemical modification to control molecular interactions with porous silicon

Interactions between porous silicon (pSi) particles and probe molecules were evaluated to determine the effect of pSi and probe molecule chemistry on adsorption. Methylene blue, ethyl violet and orange G dyes were chosen for investigation as they possess distinct functionalities and charges. Several distinct pSi surface species were produced via thermal oxidation at 200-800 °C and their effect on adsorption investigated. The adsorption mechanisms were elucidated from equilibrium adsorption and desorption isotherms. Methylene blue adsorption was attributed to electrostatic attraction where a gradual increase in adsorption with oxidation temperature was observed. Significant methylene blue desorption was observed at pH 3, confirming adsorption occurs via electrostatic attraction. Ethyl violet demonstrated an increase in plateau adsorption capacity and affinity with increased oxidation temperatures and adsorption was initially attributed to electrostatic attraction, however desorption of ethyl violet was not observed, thus indicating potential chemisorption. Orange G exhibited high affinity adsorption for Si(y)SiH(x) terminated surfaces but no orange G desorption was detected, indicating a chemisorption adsorption mechanism. It has been successfully demonstrated that the surface modification of pSi enabled the manipulation of molecular interactions. By interacting probe molecules with similar functionalities to drug molecule with pSi, greater understanding of drug-pSi interactions can be ascertained which are of great importance. pSi surface chemistry can be tailored to enable control over molecular interactions and ultimately dictate loading, encapsulation and release behavior.     

Image‐Contrast Technology Based on the Electrochemiluminescence of Porous Silicon and Its Application in Fingerprint Visualization

The electrochemiluminescence (ECL) of porous silicon (pSi) has attracted great interest for its potential application in display technology and chemical sensors. In this study, we found that pSi with a different surface chemistry displayed an apparently different dynamic ECL process. An image‐contrast technology was established on the basis of the intrinsic mechanism of the ECL dynamic process. As a proof of principle, the visualization of latent fingerprints (LFPs) and in situ detection of TNT in fingerprints was demonstrated by using the ECL‐based image‐contrast technology.     

Membrane-less and mediator-free enzymatic biofuel cell using carbon nanotube/porous silicon electrodes

Membrane-less and mediator-free direct electron transfer enzymatic biofuel cells (BFCs) with bioelectrodes comprised of single wall carbon nanotubes (SWNTs) deposited by two methods on porous silicon (pSi) substrates, are reported. In one method the SWNTs were grown by chemical vapor deposition (CVD) and then functionalized with carboxylic groups, and in the second method, pre-synthesized carboxylated SWNTs (c-SWNTs) were electrophoretically deposited on gold-coated pSi. Anodic glucose oxidase (GOx) and cathodic laccase (Lac) were immobilized on the pSi/SWNT substrates to form BFCs in pH 7 phosphate buffer solution. A peak power density of 1.38 μW/cm² (with a lifetime of 24 h) down to 0.3 μW/cm² was obtained for a BFC comprised of c-SWNT/enzyme electrodes in 4 mM glucose solution as fuel, corresponding to normal blood sugar concentration, and air as oxidant. BFCs of this relatively simple architecture have the potential for further optimization of power output and lifetime.     

Preparation and characterization of pore-wall modification gradients generated on porous silicon photonic crystals using diazonium salts

One-dimensional photonic crystals (rugate filters) constructed from porous silicon were modified by the chemical hydrosilylation of terminal alkenes (decyl, 10-carboxydecyl, and 10-hydroxydecyl) in the presence of a concentration gradient of diazonium salt initiators. The concentration gradient was generated by vertically orienting the Si wafer containing the porous Si layer in an alkene solution and then introducing the diazonium salt at the bottom edge of the wafer. Slow diffusion of the salt led to a varying density of grafted alkene across the surface of the porous layer. The modified surfaces were end-capped with methyl groups by electrochemical grafting to impart improved stability and greater hydrophobicity. The surface modified with 10-carboxydecyl species was ionized by deprotonation of the carboxy groups to increase the hydrophilicity of this porous silicon surface. The pore-wall modification gradients were characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The more hydrophilic portion of the gradient changes color when water infiltrates the porous nanostructure because of a shift in the stop band of the photonic crystal. The more hydrophobic portion of the gradient excludes water, although mixtures of water and ethanol will infiltrate this region, depending on the concentration of ethanol in the mixture. A simple visual sensor for small quantities of ethanol in water, capable of detecting ethanol concentrations of between 0 and 8% with a resolution of 1% is demonstrated.     

Trapping silicon surface-based radicals

The spontaneous one-electron reduction of diazonium salts on hydride-terminated porous silicon (pSi) and flat silicon produces surface radicals that can be trapped chemically. These silicon radicals react with reagents such as alkyl/arylselenoethers, alkenes, alkynes, and alkylbromide groups to generate covalently bound functionalities in a manner analogous to the chemistry of molecular-based silicon radical species, prepared via different methods. When pSi is exposed to an acetonitrile solution of any of the three diazonium salts examined in this study, aryl groups from the diazonium precursor become covalently bound and significant oxidation is noted; if, however, a reactive trapping agent is added, such as an alkyl/arylselenoether or a carbon-carbon unsaturated bond, no aryl group attachment is observed and oxidation is circumvented due to the efficiency of the trapping chemistry. The reactions proceed rapidly, in less than 3 h to maximum coverage, at room temperature. The diazonium salt-initiated radical reaction with alpha,omega-alkenes and alkynes tolerates various functional groups including aryl, diene, diyne, carboxylic acid, and hydroxyl, reacting exclusively via the carbon-carbon unsaturated bond; alpha,omega-bromoalkenes are not, however, compatible with this chemistry. A silicon-based molecule, tris(trimethylsilyl)silane, in the presence of a diazonium salt initiator and a primary alkyne does not lead to the hydrosilylation product but to tris(trimethylsilyl)silylbromide and the hydrogenated arene, derived from the diazonium. The difference in reactivity between the molecule and the surface is due to the fact that the silicon surface is a source of electrons to reduce the diazonium salts to aryl radicals, whereas a heterolytic pathway is followed in the molecular silane case.     

无序介孔硅复合纳米结构的制备与慢活化行为

通过对SiO_2纳米粒子进行镁热还原及后处理,制备了多级无序Si介孔复合纳米结构MP-Si@SiO_x@C,此结构展现出容量非衰减缓升的电化学慢活化行为,可抵消循环容量常规衰减趋势,赋予负极优良的循环稳定性.通过X射线衍射(XRD)、透射电子显微镜(TEM)、场发射扫描电子显微镜(SEM)、N_2吸附-脱附测试和孔径分布模拟分析发现,Si介孔组织包含微-窄介孔(1~5 nm)、中介孔(5~20 nm)以及大介孔-宏孔(20~100 nm)三级孔道,分别源于原初级粒子内部孔道、粒子团聚堆垛与粒内酸蚀、团聚体再堆垛;此合成装配方法有效提升了Si材料的堆积密度,电池电极能获得较高的体积比容量和储能密度.     

双金属(Sn/Ni)掺杂多孔硅微球的液相合成与电化学储锂性能

使用廉价的硅铝合金前驱体,通过简单的化学沉积方法制备了新型双金属(Sn/Ni)掺杂多孔硅微球(pSi@SnNi)。pSi@SnNi复合材料的三维多孔结构可以缓冲硅在锂化过程中的巨大体积膨胀,增加储锂活性位点。双金属(Sn/Ni)的掺杂可以提高硅的电子导电性,改进pSi的结构稳定性。由于其独特的组成和微观结构,具有适当Sn/Ni含量的pSi@SnNi复合材料显示了较大的可逆储锂容量(0.1 A·g^-1下为2 651.7 mAh·g^-1)、较高的电化学循环稳定性(1 A·g^-1下400次循环后为1 139 mAh·g^-1)和优异的倍率性能(2.5 A·g^-1下为1 235.8 mAh·g^-1)。     

碳基双电层电容器的结构、机理及研究进展

活性炭基双电层电容器是一种新型电化学能量储存装置,其储电机理是利用电极材料比较大的比表面积在电极和电解液之间形成双电层储存电荷,充放电过程中无化学反应发生。活性炭材料由于具有较大的比表面积、良好的孔结构分布、化学惰性表面等,一直是双电层电容器电极的首选材料。本文简要介绍了双电层电容器的制造工艺、应用及发展趋势。     

基于普鲁士蓝电催化的三维多孔壳聚糖膜葡萄糖生物传感器的研制

利用电沉积方法对普鲁士蓝和壳聚糖/SiO2纳米粒子复合膜进行组装,用刻蚀法除去SiO2粒子,制备出孔径大小均匀的多孔壳聚糖/普鲁士蓝膜,这种三维多孔膜具有良好的微生物环境、比表面积大、孔隙率高,有利于负载更多的葡萄糖氧化酶,从而构建了一种灵敏度高、稳定性好、响应时间短、检测范围宽的葡萄糖生物传感器。     

双金属(Sn/Ni)掺杂多孔硅微球的液相合成与电化学储锂性能

使用廉价的硅铝合金前驱体,通过简单的化学沉积方法制备了新型双金属(Sn/Ni)掺杂多孔硅微球(pSi@SnNi)。pSi@SnNi复合材料的三维多孔结构可以缓冲硅在锂化过程中的巨大体积膨胀,增加储锂活性位点。双金属(Sn/Ni)的掺杂可以提高硅的电子导电性,改进pSi的结构稳定性。由于其独特的组成和微观结构,具有适当Sn/Ni含量的pSi@SnNi复合材料显示了较大的可逆储锂容量(0.1 A·g^-1下为2 651.7 mAh·g^-1)、较高的电化学循环稳定性(1 A·g^-1下400次循环后为1 139 mAh·g^-1)和优异的倍率性能(2.5 A·g^-1下为1 235.8 mAh·g^-1)。     

New surfaces for desorption electrospray ionization mass spectrometry: porous silicon and ultra-thin layer chromatography plates

The performance of nanoporous silicon (pSi) and ultra-thin layer chromatography (UTLC) plates as surfaces for desorption electrospray ionization (DESI) was compared with that of polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE), both popular surfaces in previous DESI studies. The limits of detection (LODs) and other analytical characteristics for six different test compounds were determined using all four surfaces. The LODs for the compounds were in the fmol-pmol (pg-ng) range. The LODs with the pSi surface were further improved for each of the compounds when heat was applied to the surface during sample application which gave LODs as low as or lower than those achieved with PMMA and PTFE. The UTLC plates were successfully used as a rapid means of chromatographic separation prior to DESI-MS analysis. Another advantage achieved using the newer pSi and UTLC surfaces was increased speed of analysis, associated with drying of solution-phase samples. This took place immediately at the UTLC surface and it could be achieved rapidly by gently heating the pSi surface. The presence of salts in the sample did not cause suppression of the analyte signal with any of the surfaces.     

电化学制备P型硅基二维光子晶体优化参数

利用光刻技术与碱性腐蚀等工艺预写晶格图样,采用电化学腐蚀方法在P〈100〉型硅基底制备二维大孔硅光子禁带结构.结果表明:在预写有晶格图样的P〈100〉型硅基底上由电化学阳极氧化制备的二维大孔硅,其孔洞的生长速率、深宽比及表/侧面形貌与电解质配比方案及阳极电流密度均密切相关.在优化的电化学工艺参数下得到的空气洞阵列,具有近乎完美的二维四方晶格,晶格常数为3.8μm,孔洞直径约3.0μm,孔洞深宽约90μm,深宽比达30.该方法可用于制备在中红外或近红外波段具有完全二维光子带隙的光子晶体.     

Anisotropic hydrogel thickness gradient films derivatized to yield three-dimensional composite materials

We report the preparation of in-plane density gradients of amino-terminated molecules and gold particles through derivatization of laterally varying thickness gradients of poly(acrylic acid) (PAA) or poly(acrylamide) (PAAm) films. PAA and PAAm gradients were formed by Zn(II)-catalyzed electropolymerization of acrylic acid (AA) or acrylamide (AAm) in the presence of an in-plane electrochemical potential gradient applied to Au or indium-tin-oxide (ITO) working electrodes. PAA thickness gradients were converted into density gradients of fluorocarbons or biocompatible groups by derivatizing with NH(2)CH(2)(CF(2))(6)CF(3) or an Arg-Gly-Asp (RGD)-containing peptide, respectively. X-ray photoelectron spectroscopy (XPS) and XPS imaging were used to characterize the modified PAA gradients. Transition regions as narrow as 104 mum were achieved for fluorocarbon gradients. PAAm gradients were treated with gold particles to form a density gradient of gold particles. Surface plasmon resonance imaging and scanning electron microscopy (SEM) as well as UV-visible absorption measurements were used to characterize the gold particle density gradients. It is likely that the gold particles were attached both on the surface and inside the PAAm film.     

Mesoporous carbon/sulfur composite with N-doping and tunable pore size for high-performance Li-S batteries

Mesoporous carbons (MCs) were used as the matrixes to load sulfur for lithium sulfur (Li-S) batteries, and pore sizes were tuned by heat treatment at different high temperatures. The cathode material shows the highest discharge capacity of 1158.2 mAh g^?1 at the pore size of 4.1 nm among as-prepared nitrogen-free materials with different sizes. Meanwhile, the nitrogen doping of mesoporous carbon helps to inhibit the diffusion of polysulfide species via an enhanced surface adsorption. The carbon/sulfur containing N (4.56%) shows a high initial discharge capacity of 1315.8 mAh g^?1 and retains about 939 mAh g^?1 after 100 cycles at 0.2 C. The improved electrochemical performance is ascribed to the proper pore size, surface chemical property, and conductivity of the N-doped carbon material.     

On-demand electrochemical activation of the click reaction on self-assembled monolayers on gold presenting masked acetylene groups

We report on a new surface modification method for grafting a "dynamic" property for on-demand activation of the click reaction. Our approach utilizes the acetylene group masked with dicobalt hexacarbonyl, Co(2)(CO)(6), which is not reactive toward the click reaction. Electrochemical treatment reveals the acetylene group on the selected region, which is then used as a chemical handle for surface functionalization via the click reaction with an azide-containing molecule. Electrochemical and chemical conversions on the surface were verified by cyclic voltammetry, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. We have demonstrated immobilization of an azide-modified RGD peptide and promotion of cell adhesion/migration to the region of electrochemical induction.