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1.  Design of Aerosol Particle Coating: Thickness, Texture and Efficiency 
Chemical engineering science  2010;65(20):5471-5481.
Core-shell particles preserve the performance (e.g. magnetic, plasmonic or opacifying) of a core material while modifying its surface with a shell that facilitates (e.g. by blocking its reactivity) their incorporation into a host liquid or polymer matrix. Here coating of titania (core) aerosol particles with thin silica shells (films or layers) is investigated at non-isothermal conditions by a trimodal aerosol dynamics model, accounting for SiO2 generation by gas phase and surface oxidation of hexamethyldisiloxane (HMDSO) vapor, coagulation and sintering. After TiO2 particles have reached their final primary particle size (e.g. upon completion of sintering during their flame synthesis), coating starts by uniformly mixing them with HMDSO vapor that is oxidized either in the gas phase or on the particles’ surface resulting in SiO2 aerosols or deposits, respectively. Sintering of SiO2 deposited onto the core TiO2 particles takes place transforming rough into smooth coating shells depending on process conditions. The core-shell characteristics (thickness, texture and efficiency) are calculated for two limiting cases of coating shells: perfectly smooth (e.g. hermetic) and fractal-like. At constant TiO2 core particle production rate, the influence of coating weight fraction, surface oxidation and core particle size on coating shell characteristics is investigated and compared to pertinent experimental data through coating diagrams. With an optimal temperature profile for complete precursor conversion, the TiO2 aerosol and SiO2-precursor (HMDSO) vapor concentrations have the strongest influence on product coating shell characteristics.
doi:10.1016/j.ces.2010.07.011
PMCID: PMC3666159  PMID: 23729833
particle formation; hermetic layering; population balance; condensation; nanoparticle encapsulation; powder technology
2.  Evaluation of Complexation Ability Using a Sensor Electrode Chip Equipped with a Wireless Screening System 
Sensors (Basel, Switzerland)  2012;12(6):8405-8425.
We fabricated an electrode chip with a structure coated by an insulation layer that contains dispersed SiO2 adsorbent particles modified by an amino-group on a source-drain electrode. Voltage changes caused by chelate molecule adsorption onto electrode surfaces and by specific cation interactions were investigated. The detection of specific cations without the presence of chelate molecules on the free electrode was also examined. By comparing both sets of results the complexation ability of the studied chelate molecules onto the electrode was evaluated. Five pairs of source-drain electrodes(×8 arrays) were fabricated on a glass substrate of 20 × 30mm in size. The individual Au/Cr (1.0/0.1μm thickness) electrodes had widths of 50 μm and an inter-electrode interval of 100μm.The fabricated source-drain electrodes were further coated with an insulation layer comprising a porous SiO2 particle modified amino-group to adsorb the chelate molecules. The electrode chip was equipped with a handy-type sensor signal analyzer that was mounted on an amplifier circuit using a Miniship™ or a system in a packaged LSI device. For electrode surfaces containing different adsorbed chelate molecules an increase in the sensor voltage depended on a combination of host-guest reactions and generally decreased in the following order:5,10,15,20-tetrakis(N-methylpyridinium-4-yl)-21H,23H-porphine, tetrakis(p-toluenesulfonate) (TMPyP)as a Cu2+chelator and Cu2+>2-nitroso-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol(nitroso-PSAP) as an Fe2+chelator and Fe2+>4,7-diphenyl-1,10-phenanthrolinedisulfonic acid, disodium salt (BPDSA) as an Fe2+chelatorand Fe2+>3-[3-(2,4-dimethylphenylcarbamoyl)-2-hydroxynaphthalene-1-yl-azo]-4-hydroxybenzenesulfonic acid, sodium salt (XB-1) as a Mg2+chelator and Mg2+>2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolinedisulfonic acid, disodium salt (BCIDSA) as a Cu2+chelator and Cu2+, respectively. In contrast, for the electrode surfaces with adsorbed O,O′-bis(2-aminoethyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid (GEDTA) or O,O′-bis(2-aminophenyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid, tetrapotassium salt, hydrate (BAPTA) as a Ca2+chelator no increase in the detection voltage was found for all the electrode tests conducted in the presence of Ca2+.To determine the differences in electrode detection, molecular orbital (MO) calculations of the chelate molecules and surface molecular modeling of the adsorbents were carried out. In accordance with frontier orbital theory, the lowest unoccupied MO (LUMO) of the chelate molecules can accept two lone pair electrons at the highest occupied MO (HOMO) of the amino group on the model surface structure of the SiO2 particle. As a result, a good correlation was obtained between the LUMO-HOMO difference and the ion response of all the electrodes tested. Based on the results obtained, the order of adsorbed chelate molecules on adsorption particles reflects the different metal ion detection abilities of the electrode chips.
doi:10.3390/s120608405
PMCID: PMC3436036  PMID: 22969407
chemical adsorption; electrode; chelate; metal ion
3.  Thermodynamic Properties of Supported and Embedded Metallic Nanocrystals: Gold on/in SiO2 
Nanoscale Research Letters  2008;3(11):454-460.
We report on the calculations of the cohesive energy, melting temperature and vacancy formation energy for Au nanocrystals with different size supported on and embedded in SiO2. The calculations are performed crossing our previous data on the surface free energy of the supported and embedded nanocrystals with the theoretical surface-area-difference model developed by W. H. Qi for the description of the size-dependent thermodynamics properties of low-dimensional solid-state systems. Such calculations are employed as a function of the nanocrystals size and surface energy. For nanocrystals supported on SiO2, as results of the calculations, we obtain, for a fixed nanocrystal size, an almost constant cohesive energy, melting temperature and vacancy formation energy as a function of their surface energy; instead, for those embedded in SiO2, they decreases when the nanocrystal surface free energy increases. Furthermore, the cohesive energy, melting temperature and vacancy formation energy increase when the nanocrystal size increases: for the nanocrystals on SiO2, they tend to the values of the bulk Au; for the nanocrystals in SiO2 in correspondence to sufficiently small values of their surface energy, they are greater than the bulk values. In the case of the melting temperature, this phenomenon corresponds to the experimentally well-known superheating process.
doi:10.1007/s11671-008-9180-y
PMCID: PMC3244952  PMID: 21752308
Nanocrystal; Surface energy; Gold; SiO2; Cohesive energy; Melting temperature; Vacancy formation energy
4.  A Safer Formulation Concept for Flame-Generated Engineered Nanomaterials 
The likely success or failure of the nanotechnology industry depends on the environmental health and safety of engineered nanomaterials (ENMs). While efforts toward engineering safer ENMs are sparse, such efforts are considered crucial to the sustainability of the nanotech industry. A promising approach in this regard is to coat potentially toxic nanomaterials with a biologically inert layer of amorphous SiO2. Core-shell particles exhibit the surface properties of their amorphous SiO2 shell while maintaining specific functional properties of their core material. A major challenge in the development of functional core-shell particles is the design of scalable high-yield processes that can meet large-scale industrial demand. Here, we present a safer formulation concept for flame-generated ENMs based on a one-step, in flight SiO2 encapsulation process, which was recently introduced by the authors as a means for a scalable manufacturing of SiO2 coated ENMs. Firstly, the versatility of the SiO2-coating process is demonstrated by applying it to four ENMs (CeO2, ZnO, Fe2O3, Ag) marked by their prevalence in consumer products as well as their range in toxicity. The ENM-dependent coating fundamentals are assessed and process parameters are optimized for each ENM investigated. The effects of the SiO2-coating on core material structure, composition and morphology, as well as the coating efficiency on each nanostructured material, are evaluated using state-of-the-art analytical methods (XRD, N2 adsorption, TEM, XPS, isopropanol chemisorption). Finally, the biological interactions of SiO2-coated vs. uncoated ENMs are evaluated using cellular bioassays, providing valuable evidence for reduced toxicity for the SiO2-coated ENMs. Results indicate that the proposed ‘safer by design’ concept bears great promise for scaled-up application in industry in order to reduce the toxicological profile of ENMs for certain applications.
doi:10.1021/sc300152f
PMCID: PMC3745221  PMID: 23961338
safer nano-formulations; flame generated nanomaterials; nanotechnology; nanotoxicology; core-shell particles
5.  Integration of solid-state nanopores in a 0.5 μm cmos foundry process 
Nanotechnology  2013;24(15):155501.
High-bandwidth and low-noise nanopore sensor and detection electronics are crucial in achieving single-DNA base resolution. A potential way to accomplish this goal is to integrate solid-state nanopores within a CMOS platform, in close proximity to the biasing electrodes and custom-designed amplifier electronics. Here we report the integration of solid-state nanopore devices in a commercial complementary metal-oxide semiconductor (CMOS) potentiostat chip implemented in On-Semiconductor’s 0.5 μm technology. Nanopore membranes incorporating electrodes are fabricated by post-CMOS micromachining utilizing the N+ polysilicon/SiO2/N+ polysilicon capacitor structure available in the aforementioned process. Nanopores are created in the CMOS process by drilling in a transmission electron microscope and shrinking by atomic layer deposition. We also describe a batch fabrication method to process a large of number of electrode-embedded nanopores with sub-10 nm diameter across CMOS-compatible wafers by electron beam lithography and atomic layer deposition. The CMOS-compatibility of our fabrication process is verified by testing the electrical functionality of on-chip circuitry. We observe high current leakage with the CMOS nanopore devices due to the ionic diffusion through the SiO2 membrane. To prevent this leakage, we coat the membrane with Al2O3 which acts as an efficient diffusion barrier against alkali ions. The resulting nanopore devices also exhibit higher robustness and lower 1/f noise as compared to SiO2 and SiNx. Furthermore, we propose a theoretical model for our low-capacitance CMOS nanopore devices, showing good agreement with the experimental value. In addition, experiments and theoretical models of translocation studies are presented using 48.5 kbp λ-DNA in order to prove the functionality of on-chip pores coated with Al2O3.
doi:10.1088/0957-4484/24/15/155501
PMCID: PMC3672232  PMID: 23519330
6.  Sustained Release of a Monoclonal Antibody from Electrochemically Prepared Mesoporous Silicon Oxide 
Advanced functional materials  2010;20(23):4168-4174.
Nanostructured mesoporous silica (SiO2) films are used to load and release the monoclonal antibody bevacizumab (Avastin) in vitro. A biocompatible and biodegradable form of mesoporous SiO2 is prepared by electrochemical etching of single crystalline Si, followed by thermal oxidation in air at 800 °C. Porous SiO2 exhibits a negative surface charge at physiological pH (7.4), allowing it to spontaneously adsorb the positively charged antibody from an aqueous phosphate buffered saline solution. This electrostatic adsorption allows bevacizumab to be concentrated by >100× (300 mg bevacziumab per gram of porous SiO2 when loaded from a 1 mg mL−1 solution of bevacziumab). Drug loading is monitored by optical interferometric measurements of the thin porous film. A two-component Bruggeman effective medium model is employed to calculate percent porosity and film thickness, and is further used to determine the extent of drug loading into the porous SiO2 film. In vitro drug release profiles are characterized by an enzyme-linked immunosorbent assay (ELISA), which confirms that the antibody is released in its active, VEGF-binding form. The nanostructured delivery system described here provides a sustained release of the monoclonal antibody where approximately 98% of drug is released over a period of one month.
doi:10.1002/adfm.201000907
PMCID: PMC3026353  PMID: 21274422
7.  Biogenic Hierarchical TiO2/SiO2 Derived from Rice Husk and Enhanced Photocatalytic Properties for Dye Degradation 
PLoS ONE  2011;6(9):e24788.
Background
Rice husk, an agricultural bioresource, is utilized as a non-metallic bio-precursor to synthesize biogenic hierarchical TiO2/SiO2 (BH-TiO2/SiO2) and the products are applied to dye degradation.
Methodology/Principal Findings
The as-prepared BH-TiO2/SiO2 samples are characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), nitrogen-adsorption measurement, UV-vis spectroscopy and electronic paramagnetic resonance (EPR). The results show that BH-TiO2/SiO2 possesses both anatase and rutile phases with amorphous SiO2 as background, which contains mesopore structure, and nitrogen derived from original rice husk is self-doped into the lattice. Besides, the light-harvesting within the visible-light range of BH-TiO2/SiO2 has been enhanced. Moreover, the catalytic activity of BH-TiO2/SiO2 has been proven by EPR, and both the photocatalytic activity and stability of BH-TiO2/SiO2 are improved as well, which has been illustrated by cycled degradation of methylene blue dye under irradiation.
Conclusions/Significance
This work provides a good way to combine natural hierarchical porous structure with synthetic material chemistry based on available biomass in the vast natural environment for the sustainable development of human society, and extends potentials of biomass in applications such as photocatalysts, sunlight splitting water and so forth.
doi:10.1371/journal.pone.0024788
PMCID: PMC3170388  PMID: 21931853
8.  Macroscale adhesion of gecko setae reflects nanoscale differences in subsurface composition 
Surface energies are commonly used to determine the adhesion forces between materials. However, the component of surface energy derived from long-range forces, such as van der Waals forces, depends on the material's structure below the outermost atomic layers. Previous theoretical results and indirect experimental evidence suggest that the van der Waals energies of subsurface layers will influence interfacial adhesion forces. We discovered that nanometre-scale differences in the oxide layer thickness of silicon wafers result in significant macroscale differences in the adhesion of isolated gecko setal arrays. Si/SiO2 bilayer materials exhibited stronger adhesion when the SiO2 layer is thin (approx. 2 nm). To further explore how layered materials influence adhesion, we functionalized similar substrates with an octadecyltrichlorosilane monolayer and again identified a significant influence of the SiO2 layer thickness on adhesion. Our theoretical calculations describe how variation in the SiO2 layer thickness produces differences in the van der Waals interaction potential, and these differences are reflected in the adhesion mechanics. Setal arrays used as tribological probes provide the first empirical evidence that the ‘subsurface energy’ of inhomogeneous materials influences the macroscopic surface forces.
doi:10.1098/rsif.2012.0587
PMCID: PMC3565786  PMID: 22993246
van der Waals forces; gecko adhesion; surface energy
9.  Uptake and fate of surface modified silica nanoparticles in head and neck squamous cell carcinoma 
Background
Head and neck squamous cell carcinoma (HNSCC) is currently the eighth leading cause of cancer death worldwide. The often severe side effects, functional impairments and unfavorable cosmetic outcome of conventional therapies for HNSCC have prompted the quest for novel treatment strategies, including the evaluation of nanotechnology to improve e.g. drug delivery and cancer imaging. Although silica nanoparticles hold great promise for biomedical applications, they have not yet been investigated in the context of HNSCC. In the present in-vitro study we thus analyzed the cytotoxicity, uptake and intracellular fate of 200-300 nm core-shell silica nanoparticles encapsulating fluorescent dye tris(bipyridine)ruthenium(II) dichloride with hydroxyl-, aminopropyl- or PEGylated surface modifications (Ru@SiO2-OH, Ru@SiO2-NH2, Ru@SiO2-PEG) in the human HNSCC cell line UMB-SCC 745.
Results
We found that at concentrations of 0.125 mg/ml, none of the nanoparticles used had a statistically significant effect on proliferation rates of UMB-SCC 745. Confocal and transmission electron microscopy showed an intracellular appearance of Ru@SiO2-OH and Ru@SiO2-NH2 within 30 min. They were internalized both as single nanoparticles (presumably via clathrin-coated pits) or in clusters and always localized to cytoplasmic membrane-bounded vesicles. Immunocytochemical co-localization studies indicated that only a fraction of these nanoparticles were transferred to early endosomes, while the majority accumulated in large organelles. Ru@SiO2-OH and Ru@SiO2-NH2 nanoparticles had never been observed to traffic to the lysosomal compartment and were rather propagated at cell division. Intracellular persistence of Ru@SiO2-OH and Ru@SiO2-NH2 was thus traceable over 5 cell passages, but did not result in apparent changes in cell morphology and vitality. In contrast to Ru@SiO2-OH and Ru@SiO2-NH2 uptake of Ru@SiO2-PEG was minimal even after 24 h.
Conclusions
Our study is the first to provide evidence that silica-based nanoparticles may serve as useful tools for the development of novel treatment options in HNSCC. Their long intracellular persistence could be of advantage for e.g. chronic therapeutic modalities. However, their complex endocytotic pathways require further investigations.
doi:10.1186/1477-3155-9-32
PMCID: PMC3164619  PMID: 21834958
nanoparticles; silica dioxide; surface properties; tumor cell line; uptake; endocytosis; cellular fate
10.  Plasma enhanced chemical vapour deposition of silica onto Ti: Analysis of surface chemistry, morphology and functional hydroxyl groups 
Surface science  2008;602(14):2402-2411.
Previously, we have developed and characterised a procedure for the deposition of thin silica films by a plasma enhanced chemical vapour deposition (PECVD) procedure using tetraethoxysilane (TEOS) as the main precursor. We have used the silica coatings for improving the corrosion resistance of metals and for enhancing the bioactivity of biomedical metallic implants. Recently, we have been fine-tuning the PECVD method for producing high quality and reproducible PECVD-silica (PECVD-Si) coatings on metals, primarily for biomaterial applications. In order to understand the interaction of the PECVD-Si coatings with biological species (such as proteins and cells), it is important to first analyse the properties of the silica films deposited using the optimised parameters. Therefore, this current investigation was carried out to analyse the characteristic features of PECVD-Si deposited on Ti substrates (PECVD-Si-Ti). We determined that the PECVD-Si coatings on Ti were conformal to the substrate surface, strongly adhered to the underlying substrate and were resistant to delamination. The PECVD-Si surface was composed of stoichiometric SiO2, showed a low carbon content (below 10 at.%) and was very hydrophilic (contact angle <10°). Finally, we also showed that the PECVD-Si coatings contain functional hydroxyl groups.
doi:10.1016/j.susc.2008.05.027
PMCID: PMC2757315  PMID: 19809536
Biomaterial; Hydroxyl groups; Plasma enhanced chemical vapour deposition; Silica films
11.  Effect of molecular weight of polyethyleneimine on loading of CpG oligodeoxynucleotides onto flake-shell silica nanoparticles for enhanced TLR9-mediated induction of interferon-α 
Background
Class B CpG oligodeoxynucleotides primarily interact with Toll-like receptor 9 (TLR9) in B cells and enhance the immune system through induction of various interleukins including interleukin-6 in these immune cells. Although free class B CpG oligodeoxynucleotides do not induce interferon (IFN)-α production, CpG oligodeoxynucleotide molecules have been reported to induce IFN-α when loaded onto nanoparticles. Here, we investigated the in vitro induction of IFN-α by a nanocarrier delivery system for class B CpG oligodeoxynucleotide molecules.
Methods
For improving the capacity to load CpG oligodeoxynucleotide molecules, flake-shell SiO2 nanoparticles with a specific surface area approximately 83-fold higher than that of smooth-surfaced SiO2 nanoparticles were prepared by coating SiO2 nanoparticles with polyethyleneimine (PEI) of three different number-average molecular weights (Mns 600, 1800, and 10,000 Da).
Results
The capacity of the flake-shell SiO2 nanoparticles to load CpG oligodeoxynucleotides was observed to be 5.8-fold to 6.7-fold higher than that of smooth-surfaced SiO2 nanoparticles and was found to increase with an increase in the Mn of the PEI because the Mn contributed to the positive surface charge density of the nanoparticles. Further, the flake-shell SiO2 nanoparticles showed much higher levels of IFN-α induction than the smooth-surfaced SiO2 nanoparticles. The highest IFN-α induction potential was observed for CpG oligodeoxynucleotide molecules loaded onto flake-shell SiO2 nanoparticles coated with PEI of Mn 600 Da, although the CpG oligodeoxynucleotide density was lower than that on flake-shell SiO2 nanoparticles coated with PEI of Mns 1800 and 10,000 Da. Even with the same density of CpG oligodeoxynucleotides on flake-shell SiO2 nanoparticles, PEI with an Mn of 600 Da caused a markedly higher level of IFN-α induction than that with Mns of 1800 Da and 10,000 Da. The higher TLR9-mediated IFN-α induction by CpG oligodeoxynucleotides on flake-shell SiO2 nanoparticles coated with a PEI of Mn 600 Da is attributed to residence of the CpG oligodeoxynucleotide molecules in endolysosomes.
doi:10.2147/IJN.S32592
PMCID: PMC3414203  PMID: 22888224
CpG oligodeoxynucleotides; polyethyleneimine; Toll-like receptor 9; silica nanoparticles; delivery; interferon-α
12.  Development of an Interaction Assay between Single-Stranded Nucleic Acids Trapped with Silica Particles and Fluorescent Compounds 
Biopolymers are easily denatured by heating, a change in pH or chemical substances when they are immobilized on a substrate. To prevent denaturation of biopolymers, we developed a method to trap a polynucleotide on a substrate by hydrogen bonding using silica particles with surfaces modified by aminoalkyl chains ([A-AM silane]/SiO2). [A-AM silane]/SiO2 was synthesized by silane coupling reaction of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (A-AM silane) with SiO2 particles with a diameter of 5 μm at 100 °C for 20 min. The surface chemical structure of [A-AM silane]/SiO2 was characterized by Fourier transform infrared spectroscopy and molecular orbital calculations. The surface of the silica particles was modified with A-AM silane and primary amine groups were formed. [A-AM silane]/SiO2 was trapped with single-stranded nucleic acids [(Poly-X; X = A (adenine), G (guanine) and C (cytosine)] in PBS solution at 37 °C for 1 h. The single-stranded nucleic acids were trapped on the surface of the [A-AM silane]/SiO2 by hydrogen bonding to form conjugated materials. The resulting complexes were further conjugated by derivatives of acridine orange (AO) as fluorescent labels under the same conditions to form [AO:Poly-X:A-AM silane]/SiO2 complexes. Changes in the fluorescence intensity of these complexes originating from interactions between the single-stranded nucleic acid and aromatic compounds were also evaluated. The change in intensity displayed the order [AO: Poly-G: A-AM silane]/SiO2 > [AO:Poly-A:A-AM silane]/SiO2 >> [AO:Poly-C:A-AM silane]/SiO2. This suggests that the single-stranded nucleic acids conjugated with aminoalkyl chains on the surfaces of SiO2 particles and the change in fluorescence intensity reflected the molecular interaction between AO and the nucleic-acid base in a polynucleotide.
doi:10.3390/jfb3030601
PMCID: PMC4031003  PMID: 24955635
nucleic acid; polynucleotide; assay; fluorescence; cellstain-AO
13.  Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: Investigations on spherical silica particles and plane-crystal-shaped zirconia particles 
Graphical abstract
Amorphous spherical silica and plane-crystal-shaped zirconia particles were prepared and functionalized with long alkyl chain coupling agents. The effect of the nanoscopic curvature and the co-functionalization with a second coupling agent was investigated.
Highlights
► Alkyl-chain ordering on curved and plane nanoscopic surfaces. ► Disturbing self-assembled monolayer formation on nanoparticles by co-functionalization. ► Improvement of the dispersion behavior of nanoparticles by co-functionalization of their surface.
The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO2 nanoparticles and spherical SiO2 nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO2 and dodecyltrimethoxysilane for SiO2 samples. The plane ZrO2 nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO2 nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO2 nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1 molecules/nm2 through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO2 and phenyltrimethoxysilane for SiO2, resulted in a significantly lower alkyl-chain ordering for ZrO2 plane crystals and for large SiO2 spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO2 nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane.
doi:10.1016/j.jcis.2011.03.035
PMCID: PMC3115058  PMID: 21549385
Nanoparticles; Surface-functionalization; Self-assembled monolayers; Silica; Zirconia; Mixed monolayers
14.  Molecular switches from benzene derivatives adsorbed on metal surfaces 
Nature Communications  2013;4:2569.
Transient precursor states are often experimentally observed for molecules adsorbing on surfaces. However, such precursor states are typically rather short-lived, quickly yielding to more stable adsorption configurations. Here we employ first-principles calculations to systematically explore the interaction mechanism for benzene derivatives on metal surfaces, enabling us to selectively tune the stability and the barrier between two metastable adsorption states. In particular, in the case of the tetrachloropyrazine molecule, two equally stable adsorption states are identified with a moderate and conceivably reversible barrier between them. We address the feasibility of experimentally detecting the predicted bistable behaviour and discuss its potential usefulness in a molecular switch.
Short-lived precursors typically occur before molecules chemisorb on surfaces. Liu et al. predict that for benzene derivatives on metal surfaces, the precursors can be long-lived and the transition to chemisorption states can be reversible, which may be useful in molecular switch applications.
doi:10.1038/ncomms3569
PMCID: PMC3826625  PMID: 24157660
15.  Interface traps and quantum size effects on the retention time in nanoscale memory devices 
Nanoscale Research Letters  2013;8(1):369.
Based on the analysis of Poisson equation, an analytical surface potential model including interface charge density for nanocrystalline (NC) germanium (Ge) memory devices with p-type silicon substrate has been proposed. Thus, the effects of Pb defects at Si(110)/SiO2, Si(111)/SiO2, and Si(100)/SiO2 interfaces on the retention time have been calculated after quantum size effects have been considered. The results show that the interface trap density has a large effect on the electric field across the tunneling oxide layer and leakage current. This letter demonstrates that the retention time firstly increases with the decrease in diameter of NC Ge and then rapidly decreases with the diameter when it is a few nanometers. This implies that the interface defects, its energy distribution, and the NC size should be seriously considered in the aim to improve the retention time from different technological processes. The experimental data reported in the literature support the theoretical expectation.
doi:10.1186/1556-276X-8-369
PMCID: PMC3847579  PMID: 23984827
Interface trap; Nanocrystalline; Quantum-size effect; Memory; Retention time; 85.30.Tv; 85.35.-p; 73.63.-b
16.  Removal of Silicone Oil From Intraocular Lens Using Novel Surgical Materials 
Purpose
To design, fabricate, and evaluate novel materials to remove silicone oil (SiO) droplets from intraocular lenses (IOL) during vitreoretinal surgery.
Methods
Three different designs were fabricated using soft lithography of polydimethylsiloxane (PDMS), three-dimensional (3D) inverse PDMS fabrication using water dissolvable particles, and atomic layer deposition (ALD) of alumina (Al2O3) on surgical cellulose fibers. Laboratory tests included static and dynamic contact angle (CA) measurements with water and SiO, nondestructive x-ray microcomputer tomography (micro-CT), and microscopy. SiO removal was performed in vitro and ex vivo using implantable IOLs and explanted porcine eyes.
Results
All designs exhibited enhanced hydrophobicity and oleophilicity. Static CA measurements with water ranged from 131° to 160° and with SiO CA approximately 0° in 120 seconds following exposure. Nondestructive x-ray analysis of the 3D PDMS showed presence of interconnected polydispersed porosity of 100 to 300 μm in diameter. SiO removal from IOLs was achieved in vitro and ex vivo using standard 20-G vitrectomy instrumentation.
Conclusion
Removal of SiO from IOLs can be achieved using materials with lower surface energy than that of the IOLs. This can be achieved using appropriate surface chemistry and surface topography. Three designs, with enhanced hydrophobic properties, were fabricated and tested in vitro and ex vivo. All materials remove SiO within an aqueous environment. Preliminary ex vivo results were very promising, opening new possibilities for SiO removal in vitreoretinal surgeries.
Translational Relevance
This is the first report of an instrument that can lead to successful removal of SiO from the surface of IOL. In addition to the use of this instrument/material in medicine it can also be used in the industry, for example, retrieval of oil spills from bodies of water.
doi:10.1167/tvst.3.5.4
PMCID: PMC4164073  PMID: 25237593
silicone oil; vitrectomy; retinal detachment; IOL; tamponade; ALD; PDMS; lithography; super hydrophobicity; oleophilicity
17.  A Renewable and Ultrasensitive Electrochemiluminescence Immunosenor Based on Magnetic RuL@SiO2-Au∼RuL-Ab2 Sandwich-Type Nano-Immunocomplexes 
Sensors (Basel, Switzerland)  2011;11(8):7749-7762.
An ultrasensitive and renewable electrochemiluminescence (ECL) immunosensor was developed for the detection of tumor markers by combining a newly designed trace tag and streptavidin-coated magnetic particles (SCMPs). The trace tag (RuL@SiO2-Au∼RuL-Ab2) was prepared by loading Ru(bpy)32+(RuL)-conjuged secondary antibodies (RuL-Ab2) on RuL@SiO2 (RuL-doped SiO2) doped Au (RuL@SiO2-Au). To fabricate the immunosensor, SCMPs were mixed with biotinylated AFP primary antibody (Biotin-Ab1), AFP, and RuL@SiO2-Au∼RuL-Ab2 complexes, then the resulting SCMP/Biotin-Ab1/AFP/RuL@SiO2-Au∼RuL-Ab2 (SBAR) sandwich-type immunocomplexes were absorbed on screen printed carbon electrode (SPCE) for detection. The immunocomplexes can be easily washed away from the surface of the SPCE when the magnetic field was removed, which made the immunosensor reusable. The present immunosensor showed a wide linear range of 0.05–100 ng mL−1 for detecting AFP, with a low detection limit of 0.02 ng mL−1 (defined as S/N = 3). The method takes advantage of three properties of the immunosensor: firstly, the RuL@SiO2-Au∼RuL-Ab2 composite exhibited dual amplification since SiO2 could load large amount of reporter molecules (RuL) for signal amplification. Gold particles could provide a large active surface to load more reporter molecules (RuL-Ab2). Accordingly, through the ECL response of RuL and tripropylamine (TPA), a strong ECL signal was obtained and an amplification analysis of protein interaction was achieved. Secondly, the sensor is renewable because the sandwich-type immunocomplexes can be readily absorbed or removed on the SPCE’s surface in a magnetic field. Thirdly, the SCMP modified probes can perform the rapid separation and purification of signal antibodies in a magnetic field. Thus, the present immunosensor can simultaneously realize separation, enrichment and determination. It showed potential application for the detection of AFP in human sera.
doi:10.3390/s110807749
PMCID: PMC3231728  PMID: 22164043
[Ru(bpy)3]2+@SiO2-Au; alpha-fetoprotein; sandwich-type immunoreaction; screen printed carbon electrode; electrochemiluminescence
18.  Lattice-patterned LC-polymer composites containing various nanoparticles as additives 
In this study, we show the effect of various nanoparticle additives on phase separation behavior of a lattice-patterned liquid crystal [LC]-polymer composite system and on interfacial properties between the LC and polymer. Lattice-patterned LC-polymer composites were fabricated by exposing to UV light a mixture of a prepolymer, an LC, and SiO2 nanoparticles positioned under a patterned photomask. This resulted in the formation of an LC and prepolymer region through phase separation. We found that the incorporation of SiO2 nanoparticles significantly affected the electro-optical properties of the lattice-patterned LC-polymer composites. This effect is a fundamental characteristic of flexible displays. The electro-optical properties depend on the size and surface functional groups of the SiO2 nanoparticles. Compared with untreated pristine SiO2 nanoparticles, which adversely affect the performance of LC molecules surrounded by polymer walls, SiO2 nanoparticles with surface functional groups were found to improve the electro-optical properties of the lattice-patterned LC-polymer composites by increasing the quantity of SiO2 nanoparticles. The surface functional groups of the SiO2 nanoparticles were closely related to the distribution of SiO2 nanoparticles in the LC-polymer composites, and they influenced the electro-optical properties of the LC molecules. It is clear from our work that the introduction of nanoparticles into a lattice-patterned LC-polymer composite provides a method for controlling and improving the composite's electro-optical properties. This technique can be used to produce flexible substrates for various flexible electronic devices.
doi:10.1186/1556-276X-7-46
PMCID: PMC3275447  PMID: 22222011
phase separation; nanoparticle; LC-polymer composite; photopolymerization; lattice pattern.
19.  In Vivo Biodistribution and Pharmacokinetics of Silica Nanoparticles as a Function of Geometry, Porosity and Surface Characteristics 
The in vivo biodistribution and pharmacokinetics of silica nanoparticles (SiO2) with systematically varied geometries, porosities, and surface characteristics were investigated in immune-competent CD-1 mice via the intravenous injection. The nanoparticles were taken up extensively by the liver and spleen. Mesoporous SiO2 exhibited higher accumulation in the lung than nonporous SiO2 of similar size. This accumulation was reduced by primary amine modification of the nanoparticles. High aspect ratio, amine-modified mesoporous nanorods showed enhanced lung accumulation compared to amine-modified mesoporous nanospheres. Accumulation of the nanoparticles was mainly caused by passive entrapment in the discontinuous openings in the endothelium of the liver and spleen or in the pulmonary capillaries, and was highly dependent on nanoparticle hydrodynamic size in circulation. The SiO2 were likely internalized by the reticulo-endothelial system (RES) following physical sequestration in the liver and spleen. The nanoparticles that were transiently associated with the lung were re-distributed out of this organ without significant internalization. Pharmacokinetic analysis showed that all SiO2 were rapidly cleared from systemic circulation. Amine-modified or nonporous nanoparticles possessed a higher volume of distribution at steady state than their pristine counterparts or mesoporous SiO2. In all, surface characteristics and porosity played important roles in influencing SiO2 biodistribution and pharmacokinetics. Increasing the aspect ratio of amine-modified mesoporous SiO2 from 1 to 8 resulted in increased accumulation in the lung.
doi:10.1016/j.jconrel.2012.05.046
PMCID: PMC3476833  PMID: 22684119
silica nanoparticles; nanotoxicity; biodistribution; geometry; porosity
20.  Engineering functional protein interfaces for immunologically modified field effect transistor (ImmunoFET) by molecular genetic means 
The attachment and interactions of analyte receptor biomolecules at solid–liquid interfaces are critical to development of hybrid biological–synthetic sensor devices across all size regimes. We use protein engineering approaches to engineer the sensing interface of biochemically modified field effect transistor sensors (BioFET). To date, we have deposited analyte receptor proteins on FET sensing channels by direct adsorption, used self-assembled monolayers to tether receptor proteins to planar FET SiO2 sensing gates and demonstrated interface biochemical function and electrical function of the corresponding sensors. We have also used phage display to identify short peptides that recognize thermally grown SiO2. Our interest in these peptides is as affinity domains that can be inserted as translational fusions into receptor proteins (antibody fragments or other molecules) to drive oriented interaction with FET sensing surfaces. We have also identified single-chain fragment variables (scFvs, antibody fragments) that recognize an analyte of interest as potential sensor receptors. In addition, we have developed a protein engineering technology (scanning circular permutagenesis) that allows us to alter protein topography to manipulate the position of functional domains of the protein relative to the BioFET sensing surface.
doi:10.1098/rsif.2007.1107
PMCID: PMC2605506  PMID: 17580287
biosensors; interface engineering; surface modifications; protein engineering
21.  Area Selective Growth of Titanium Diselenide Thin Films into Micropatterned Substrates by Low-Pressure Chemical Vapor Deposition 
Chemistry of Materials  2013;25(23):4719-4724.
The neutral, distorted octahedral complex [TiCl4(SenBu2)2] (1), prepared from the reaction of TiCl4 with the neutral SenBu2 in a 1:2 ratio and characterized by IR and multinuclear (1H, 13C{1H}, 77Se{1H}) NMR spectroscopy and microanalysis, serves as an efficient single-source precursor for low-pressure chemical vapor deposition (LPCVD) of titanium diselenide, TiSe2, films onto SiO2 and TiN substrates. X-ray diffraction patterns on the deposited films are consistent with single-phase, hexagonal 1T-TiSe2 (P3̅m1), with evidence of some preferred orientation of the crystallites in thicker films. The composition and structural morphology was confirmed by scanning electron microscopy (SEM), energy dispersive X-ray, and Raman spectroscopy. SEM imaging shows hexagonal plate crystallites growing perpendicular to the substrate, but these tend to align parallel to the surface when the quantity of reagent is reduced. The resistivity of the crystalline TiSe2 films is 3.36 ± 0.05 × 10–3 Ω·cm with a carrier density of 1 × 1022 cm–3. Very highly selective film growth from the reagent was observed onto photolithographically patterned substrates, with film growth strongly preferred onto the conducting TiN surfaces of SiO2/TiN patterned substrates. TiSe2 is selectively deposited within the smallest 2 μm diameter TiN holes of the patterned TiN/SiO2 substrates. The variation in crystallite size with different diameter holes is determined by microfocus X-ray diffraction and SEM, revealing that the dimensions increase with the hole size, but that the thickness of the crystals stops increasing above ∼20 μm hole size, whereas their lengths/widths continue to increase.
doi:10.1021/cm402422e
PMCID: PMC3903341  PMID: 24489437
Selective deposition; single-source precursor; titanium selenide; chemical vapor deposition; selenoether; microfocus X-ray diffraction
22.  Enhanced Photodynamic Selectivity of Nano-Silica-Attached Porphyrins Against Breast Cancer Cells 
Journal of materials chemistry  2012;22(25):12701-12708.
The synthesis and characterization of bare silica (4 nm in diameter) nanoparticle-attached meso-tetra(N-methyl-4-pyridyl)porphine (SiO2-TMPyP, 6 nm in diameter) are described for pH-controllable photosensitization. Distinguished from organosilanes, SiO2 nanoparticles were functionalized as a potential quencher of triplet TMPyP and/or singlet oxygen (1O2) at alkaline pH, thereby turning off sensitizer photoactivity. In weak acidic solutions, TMPyP was released from SiO2 surface for efficient production of 1O2. By monitoring 1O2 luminescence at 1270 nm, quantum yields of 1O2 production were found to be pH-dependent, dropping from ~ 0.45 in a pH range of 3–6 to 0.08 at pH 8–9, which is consistent with pH-dependent adsorption behavior of TMPyP on SiO2 surface. These features make bare SiO2-attached cationic porphyrin a promising candidate for use in PDT for cancer treatment in which efficient 1O2 production at acidic pH and sensitizer deactivation at physiological pH are desirable. The enhanced therapeutic selectivity was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests and trypan blue exclusion tests of cell viability in breast cancer cell lines. Bimolecular quenching rate constants of 1O2 by free TMPyP, SiO2 and SiO2-TMPyP nanoparticles were also determined.
doi:10.1039/C2JM30897E
PMCID: PMC3501744  PMID: 23180907
23.  Advanced Cu chemical displacement technique for SiO2-based electrochemical metallization ReRAM application 
Nanoscale Research Letters  2014;9(1):592.
This study investigates an advanced copper (Cu) chemical displacement technique (CDT) with varying the chemical displacement time for fabricating Cu/SiO2-stacked resistive random-access memory (ReRAM). Compared with other Cu deposition methods, this CDT easily controls the interface of the Cu-insulator, the switching layer thickness, and the immunity of the Cu etching process, assisting the 1-transistor-1-ReRAM (1T-1R) structure and system-on-chip integration. The modulated shape of the Cu-SiO2 interface and the thickness of the SiO2 layer obtained by CDT-based Cu deposition on SiO2 were confirmed by scanning electron microscopy and atomic force microscopy. The CDT-fabricated Cu/SiO2-stacked ReRAM exhibited lower operation voltages and more stable data retention characteristics than the control Cu/SiO2-stacked sample. As the Cu CDT processing time increased, the forming and set voltages of the CDT-fabricated Cu/SiO2-stacked ReRAM decreased. Conversely, decreasing the processing time reduced the on-state current and reset voltage while increasing the endurance switching cycle time. Therefore, the switching characteristics were easily modulated by Cu CDT, yielding a high performance electrochemical metallization (ECM)-type ReRAM.
doi:10.1186/1556-276X-9-592
PMCID: PMC4214826  PMID: 25364318
Cu CDT; SiO2; ECM; ReRAM
24.  Spectroscopic Investigation into Oxidative Degradation of Silica-Supported Amine Sorbents for CO2 Capture 
Chemsuschem  2012;5(8):1435-1442.
Oxidative degradation characteristics of silica-supported amine sorbents with varying amounts of tetraethylenepentamine (TEPA) and polyethylene glycol (PEG; P200 or P600 represents PEG with molecular weights of 200 or 600) have been studied by IR and NMR spectroscopy. Thermal treatment of the sorbents and liquid TEPA at 100 °C for 12 h changed their color from white to yellow. The CO2 capture capacity of the TEPA/SiO2 sorbents (i.e., SiO2-supported TEPA with a TEPA/SiO2 ratio of 25:75) decreased by more than 60 %. IR and NMR spectroscopy studies showed that the yellow color of the degraded sorbents resulted from the formation of imide species. The imide species, consisting of NH associated with two C—O functional groups, were produced from the oxidation of methylene groups in TEPA. Imide species on the degraded sorbent are not capable of binding CO2 due to its weak basicity. The addition of P200 and P600 to the supported amine sorbents improved both their CO2 capture capacities and oxidative degradation resistance. IR spectroscopy results also showed that TEPA was immobilized on the SiO2 surface through hydrogen bonding between amine groups and the silanol groups of SiO2. The OH groups of PEG interact with NH2/NH of TEPA through hydrogen bonding. Hydrogen bonds disperse TEPA on SiO2 and block O2 from accessing TEPA for oxidation. Oxidative degradation resistance and CO2 capture capacity of the supported amine sorbents can be optimized through adjusting the ratio of hydroxyl to amine groups in the TEPA/PEG mixture.
doi:10.1002/cssc.201100662
PMCID: PMC3561697  PMID: 22744858
adsorption; amines; imides; oxidation; polymers
25.  Surface Enhanced Electrochemiluminescence of Ru(bpy)32+ 
Scientific Reports  2015;5:7954.
Surface enhanced spectroscopy such as surface enhanced Raman spectrum (SERS) and surface enhanced fluorescence have been investigated extensively in the past two decades. Herein, we present experimental evidence to demonstrate the existence of a new surface enhanced spectroscopy, namely, surface enhanced electrochemiluminescence (SEECL). Our investigation indicates that the electrochemiluminescence (ECL) response of the Ru(bpy)32+-tri-n-propylamine (TPrA) system could be significantly enhanced when the working electrode is modified with gold nanoparticle-SiO2 core-shell nanocomposites (AuNP@SiO2). It is worth noting that comparing with a working electrode modified with pure SiO2 nanoparticles, the electrochemical responses of the two electrodes were quite similar, but the ECL signal of the AuNP@SiO2 modified electrode was ~5 times higher than that of the SiO2 nanoparticles modified electrode. Thus we infer that the localized surface plasmon resonance (LSPR) of the AuNPs could be a major contribution to the ECL enhancement. Our investigations also demonstrate that the ECL enhancement is closely related to the thickness of the SiO2 layer. As much as 10 times ECL enhancement (comparing with the ECL intensity of bare electrode) is observed under the optimal conditions. The possible mechanism of the SEECL phenomenon is also discussed.
doi:10.1038/srep07954
PMCID: PMC4302298  PMID: 25608922

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