Optimization of silica silanization by 3-aminopropyltriethoxysilane

Detecting Selective Protein Binding Inside Plasmonic Nanopores: Toward a Mimic of the Nuclear Pore Complex

Biosensors based on plasmonic nanostructures offer label-free and real-time monitoring of biomolecular interactions. However, so do many other surface sensitive techniques with equal or better resolution in terms of surface coverage. Yet, plasmonic nanostructures offer unique possibilities to study effects associated with nanoscale geometry. In this work we use plasmonic nanopores with double gold films and detect binding of proteins inside them. By thiol and trietoxysilane chemistry, receptors are selectively positioned on the silicon nitride interior walls. Larger (~150 nm) nanopores are used detect binding of averaged sized proteins (~60 kg/mol) with high signal to noise (>100). Further, we fabricate pores that approach the size of the nuclear pore complex (diameter down to 50 nm) and graft disordered phenylalanine-glycine nucleoporin domains to the walls, followed by titration of karyopherinβ1 transport receptors. The interactions are shown to occur with similar affinity as determined by conventional surface plasmon resonance on planar surfaces. Our work illustrates another unique application of plasmonic nanostructures, namely the possibility to mimic the geometry of a biological nanomachine with integrated optical sensing capabilities.

Control of Probe Density at DNA Biosensor Surfaces Using Poly(l-lysine) with Appended Reactive Groups

Biosensors and materials for biomedical applications generally require chemical functionalization to bestow their surfaces with desired properties, such as specific molecular recognition and antifouling properties. The use of modified poly(l-lysine) (PLL) polymers with appended oligo(ethylene glycol) (OEG) and thiol-reactive maleimide (Mal) moieties (PLL-OEG-Mal) offers control over the presentation of functional groups. These reactive groups can readily be conjugated to, for example, probes for DNA detection. Here we demonstrate the reliable conjugation of thiol-functionalized peptide nucleic acid (PNA) probes onto predeposited layers of PLL-OEG-Mal and the control over their surface density in the preceding synthetic step of the PLL modification with Mal groups. By monitoring the quartz crystal microbalance (QCM) frequency shifts of the binding of complementary DNA versus the density of Mal moieties grafted to the PLL, a linear relationship between probe density and PLL grafting density was found. Cyclic voltammetry experiments using Methylene Blue-functionalized DNA were performed to establish the absolute probe density values at the biosensor surfaces. These data provided a density of 1.2 × 10¹² probes per cm² per % of grafted Mal, thus confirming the validity of the density control in the synthetic PLL modification step without the need of further surface characterization.

Solvent-Dependent Adhesion Strength of Electroless Deposited Ni-P Layer on an Amino-Terminated Silane Compound-Modified Si Wafer

Amino-terminated silane compound modification was wet-processed on a silicon wafer using four different solvents to investigate the property of the self-assembled monolayer (SAM) and its influence on the adhesion of electroless deposited nickel-phosphorus (Ni-P) films. Analyzed by various tools including dynamic light scattering, the atomic force microscope, X-ray photoelectron spectroscopy, inductively coupled plasma with mass spectroscopy, a proper link between the processing solvent and SAM quality is established. It is found that at least the chemical compatibility, the polarity, and the acidity of solvents can affect the final morphology of the resultant SAM. Unlike toluene and ethanol that are most frequently chosen in literature, we conclude that isopropyl alcohol (IPA) is a superior solvent for amino-terminated silane compounds. Owing to the good SAM quality formed in IPA, the adhesion of electroless deposited Ni-P films is largely strengthened, even as high as the bulk strength of silicon wafers.

A swarm of slippery micropropellers penetrates the vitreous body of the eye

The intravitreal delivery of therapeutic agents promises major benefits in the field of ocular medicine. Traditional delivery methods rely on the random, passive diffusion of molecules, which do not allow for the rapid delivery of a concentrated cargo to a defined region at the posterior pole of the eye. The use of particles promises targeted delivery but faces the challenge that most tissues including the vitreous have a tight macromolecular matrix that acts as a barrier and prevents its penetration. Here, we demonstrate novel intravitreal delivery microvehicles-slippery micropropellers-that can be actively propelled through the vitreous humor to reach the retina. The propulsion is achieved by helical magnetic micropropellers that have a liquid layer coating to minimize adhesion to the surrounding biopolymeric network. The submicrometer diameter of the propellers enables the penetration of the biopolymeric network and the propulsion through the porcine vitreous body of the eye over centimeter distances. Clinical optical coherence tomography is used to monitor the movement of the propellers and confirm their arrival on the retina near the optic disc. Overcoming the adhesion forces and actively navigating a swarm of micropropellers in the dense vitreous humor promise practical applications in ophthalmology.

Diatom Silica for Biomedical Applications: Recent Progress and Advances

Diatoms are unicellular photosynthetic algae enclosed in porous 3D nanopatterned silica enclosures called "frustules." The diatom frustules are made from biosilica self-assembled into intricate porous shells that feature unique properties including high specific surface area, biocompatibility, tailorable surface chemistry, thermal stability, and high mechanical and chemical resistance. The ability to cultivate diatoms in artificial environments and their abundant availability of diatom frustules as mineable fossilized mineral deposits (diatomite or diatomaceous earth; DE) make diatom silica a promising natural alternative to synthetic porous silica for a broad range of biomedical, environmental, agricultural, and energy applications. This review article provides a comprehensive and current account of the use of natural DE silica materials in biomedical applications focused mainly on drug delivery with some highlights on biosensing, tissue engineering, and clotting agents. The article also covers some basic physical and chemical aspects of DE material such as purification, surface chemical functionalization, biocompatibility, and cellular uptake that are critical for the development of an efficient drug carrier.

Compact dual-fiber surface-enhanced Raman scattering sensor with monolayer gold nanoparticles self-assembled on optical fiber

Employing a self-assembly method and dual-fiber structure, a compact, low-cost, highly sensitive, fast surface-enhanced Raman scattering (SERS) optical fiber sensor was realized. Through detecting a SERS signal of 10 ppm rhodamine B analyte, sensor parameters such as coupling angle, fiber types, and corresponding glass substrate structure were optimized. The ratio of the SERS signal intensity to excitation light residual peak intensity was used as a significant parameter during the optimization process. Sensor characteristics such as the SERS signal dependence on excitation power, stability related to excitation time, and reusability were studied. Its compatibility in size with microfluidic structure would make it a prospective candidate for integrating into a microfluidic chip.

Silane Deposition via Gas-Phase Evaporation and High-Resolution Surface Characterization of the Ultrathin Siloxane Coatings

Siloxane coatings for surfaces are essential in many scientific and industrial applications. We describe a straightforward gas-phase evaporation technique in inert atmosphere and introduce a practical and reliable silanization protocol adaptable to different silane types. The primary aim of depositing ultrathin siloxane films on surfaces is to enable a reproducible and homogenous surface functionalization without agglomeration effects during the layer formation. To realize high-quality and large-area coatings, it is fundamental to understand the reaction conditions of the silanes, the process of the siloxane layer formation, and the possible influence of the substrate morphology. We used three typical silane types to exemplify the potential and versatility of our process: aminopropyltriethoxysilane, glycidoxypropyltrimethoxysilane, and 1 H,1 H,2 H,2 H-perfluorooctyl-trichlorosilane. The ultrathin siloxane layers, which are generally difficult to characterize, were precisely investigated with high-resolution surface-characterization methods to verify our concept in terms of reproducibility and coating quality. Our results show that this gas-phase evaporation protocol is easily adaptable to all three, widely used silane types also enabling a large-area upscale.

Covalent Immobilization of Proteins for the Single Molecule Force Spectroscopy

In recent years, atomic force microscopy (AFM) based single molecule force spectroscopy (SMFS) extended our understanding of molecular properties and functions. It gave us the opportunity to explore a multiplicity of biophysical mechanisms, e.g., how bacterial adhesins bind to host surface receptors in more detail. Among other factors, the success of SMFS experiments depends on the functional and native immobilization of the biomolecules of interest on solid surfaces and AFM tips. Here, we describe a straightforward protocol for the covalent coupling of proteins to silicon surfaces using silane-PEG-carboxyls and the well-established N-hydroxysuccinimid/1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimid (EDC/NHS) chemistry in order to explore the interaction of pilus-1 adhesin RrgA from the Gram-positive bacterium Streptococcus pneumoniae (S. pneumoniae) with the extracellular matrix protein fibronectin (Fn). Our results show that the surface functionalization leads to a homogenous distribution of Fn on the glass surface and to an appropriate concentration of RrgA on the AFM cantilever tip, apparent by the target value of up to 20% of interaction events during SMFS measurements and revealed that RrgA binds to Fn with a mean force of 52 pN. The protocol can be adjusted to couple via site specific free thiol groups. This results in a predefined protein or molecule orientation and is suitable for other biophysical applications besides the SMFS.

Physisorption and chemisorption of T4 bacteriophages on amino functionalized silica particles

Bacteriophages, or phages, are receiving increasing interest as recognition tools for the design of bioactive surfaces. However, to maintain the activity of surface-bound phages, the immobilization strategy must provide the right orientation and not compromise the phages' integrity. The objectives of this study were to characterize the phage sorption capacity and the immobilized phage activity for aminated silica particles functionalized with T4 phages. Two functionalization strategies were compared; physisorption, based on electrostatic adhesion, and chemisorption, where the phage and the particle are coupled using a carbodiimide cross-linker. We report that chemisorption, at maximum adsorption conditions on 1 µm particles, yielded 16 functional phages per particle, which is 2.5 times more than by the physisorption method. Particle diameter is shown to have an important impact on phage attachment and 1.8 µm particles were found to have ∼4 times more phages per surface area than 0.5 µm particles. Higher surface coverage is attributed to the lower steric hindrance on bigger particles. These findings provide important guidelines for the design of phage-functionalized particles for environmental, biomedical, or sensing applications.

Charge-Storage Aromatic Amino Compounds for Nonvolatile Organic Transistor Memory Devices

Here, charge-storage nonvolatile organic field-effect transistor (OFET) memory devices based on interfacial self-assembled molecules are proposed. The functional molecules contain various aromatic amino moieties (N-phenyl-N-pyridyl amino- (PyPN), N-phenyl amino- (PN), and N,N-diphenyl amino- (DPN)) which are linked by a propyl chain to a triethoxysilyl anchor group and act as the interface modifiers and the charge-storage elements. The PyPN-containing pentacene-based memory device (denoted as PyPN device) presents the memory window of 48.43 V, while PN and DPN devices show the memory windows of 24.88 and 8.34 V, respectively. The memory characteristic of the PyPN device can remain stable along with 150 continuous write-read-erase-read cycles. The morphology analysis confirms that three interfacial layers show aggregation due to the N atomic self-catalysis and hydrogen bonding effects. The large aggregate-covered PyPN layer has the full contact area with the pentacene molecules, leading to the high memory performance. In addition, the energy level matching between PyPN molecules and pentacene creates the smallest tunneling barrier and facilitates the injection of the hole carriers from pentacene to the PyPN layer. The experimental memory characteristics are well in agreement with the computational calculation.

Effect of divalent versus monovalent cations on the MS2 retention capacity of amino-functionalized ceramic filters

Ceramic capillary membranes conditioned for virus filtration via functionalization with n-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) are analyzed with respect to their virus retention capacity when using feed solutions based on monovalent and divalent salts (NaCl, MgCl2). The log reduction value (LRV) by operating in dead-end mode using the model bacteriophage MS2 with a diameter of 25 nm and an IEP of 3.9 is as high as 9.6 when using feeds containing MgCl2. In contrast, a lesser LRV of 6.4 is observed for feed solutions based on NaCl. The TPDA functionalized surface is simulated at the atomistic scale using explicit-solvent molecular dynamics in the presence of either Na+ or Mg2+ ions. Computational prediction of the binding free energy reveals that the Mg2+ ions remain preferentially adsorbed at the surface, whereas Na+ ions form a weakly bound dissolved ionic layer. The charge shielding between surface and amino groups by the adsorbed Mg2+ ions leads to an upright orientation of the TPDA molecules as opposed to a more tilted orientation in the presence of Na+ ions. The resulting better accessibility of the TPDA molecules is very likely responsible for the enhanced virus retention capacity using a feed solution with Mg2+ ions.

Methodology for sample preparation and size measurement of commercial ZnO nanoparticles

This study discusses the strategies on sample preparation to acquire images with sufficient quality for size characterization by scanning electron microscope (SEM) using two commercial ZnO nanoparticles of different surface properties as a demonstration. The central idea is that micrometer sized aggregates of ZnO in powdered forms need to firstly be broken down to nanosized particles through an appropriate process to generate nanoparticle dispersion before being deposited on a flat surface for SEM observation. Analytical tools such as contact angle, dynamic light scattering and zeta potential have been utilized to optimize the procedure for sample preparation and to check the quality of the results. Meanwhile, measurements of zeta potential values on flat surfaces also provide critical information and save lots of time and efforts in selection of suitable substrate for particles of different properties to be attracted and kept on the surface without further aggregation. This simple, low-cost methodology can be generally applied on size characterization of commercial ZnO nanoparticles with limited information from vendors.

The optimization and production of stable homogeneous amine enriched surfaces with characterized nanotopographical properties for enhanced osteoinduction of mesenchymal stem cells

Silane modification has been proposed as a powerful biomaterial surface modification tool. This is the first comprehensive investigation into the effect of silane chain length on the resultant properties of -NH₂ silane monolayers and the associated osteoinductive properties of the surface. A range of -NH₂ presenting silanes, chain length 3-11, were introduced to glass coverslips and characterized using water contact angles, atomic force microscopy, X-ray photoelectron spectroscopy, and Ninhydrin assays. The ability of the variation in chain length to form a homogenous layer across the entirety of the surfaces was also assessed. The osteoinductive potential of the resultant surfaces was evaluated by real-time polymerase chain reaction, immunocytochemistry, and von Kossa staining. Control of surface chemistry and topography was directly associated with changes in chain length. This resulted in the identification of a specific, chain length 11 (CL11) which significantly increased the osteoinductive properties of the modified materials. Only CL11 surfaces had a highly regular nano-topography/roughness which resulted in the formation of an appetite-like layer on the surface that induced a significantly enhanced osteoinductive response (increased expression of osteocalcin, CBFA1, sclerostin, and the production of a calcified matrix) across the entirety of the surface. © 2018 The Authors Journal of Biomedical Materials Research Part A Published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1862-1877, 2018.

Uranium adsorption from sulfuric acid media using silica materials functionalised with amide and phosphorous ligands

Identification of functional groups grafted onto silica supports to provide a promising uranium extraction capacity and a high selectivity versus iron.

Analysis of epoxy functionalized layers synthesized by plasma polymerization of allyl glycidyl ether

The deposition of epoxide groups by plasma polymerization opens new horizons for robust and quick immobilization of biomolecules on any type of substrate.

Modification of TiO2 nanotubes with 3-aminopropyl triethoxysilane and its performances in nanocomposite coatings

Improved thermal, mechanical and anticorrosion characteristics of epoxy-based coatings.

Nanomechanical sensors for direct and rapid characterization of sperm motility based on nanoscale vibrations

Infertility, whether of male or female origin, is a critical challenge facing the low birth rate and aging population throughout the world, and semen analysis is a cornerstone of the diagnostic evaluation of the male contribution to infertility. This means that tools which can characterize sperm properties in an effective manner are very much needed. The conventional approaches are essentially image-based, which have a limited value for analyzing sperm properties. Here, we show that an assay using nanomechanical sensors can detect sperm motility based on nanomotion. We use microcantilever sensors to directly characterize the mechanical response of the sperm based on the fluctuations of microcantilevers. We applied this methodology to sperms exposed to different chemical or physical agents. Real-time nanomechanical fluctuations showed that living sperms produced smaller fluctuations after treatment with inhibitory chemicals, and larger fluctuations after treatment with stimulatory chemicals. Our preliminary experiments suggest that the frequency of fluctuation is associated with sperm motility. This technique offers a brand-new perspective in the characterization of the sperm. By combining conventional measurements, reproductive medicine doctors and researchers should now be able to achieve unprecedented depth in the sperm properties.

Encapsulation-Stabilized, Europium Containing Nanoparticle as a Probe for Time-Resolved luminescence Detection of Cardiac Troponin I

The use of a robust optical signaling probe with a high signal-to-noise ratio is important in the development of immunoassays. Lanthanide chelates are a promising material for this purpose, which provide time-resolved luminescence (TRL) due to their large Stokes shift and long luminescence lifetime. From this, they have attracted considerable interest in the in vitro diagnostics field. However, the direct use of lanthanide chelates is limited because their luminescent signal can be easily affected by various quenchers. To overcome this drawback, strategies that rely on the entrapment of lanthanide chelates inside nanoparticles, thereby enabling the protection of the lanthanide chelate from water, have been reported. However, the poor stability of the lanthanide-entrapped nanoparticles results in a significant fluctuation in TRL signal intensity, and this still remains a challenging issue. To address this, we have developed a Lanthanide chelate-Encapsulated Silica Nano Particle (LESNP) as a new immunosensing probe. In this approach, the lanthanide chelate is covalently crosslinked within the silane monomer during the silica nanoparticle formation. The resulting LESNP is physically stable and retains TRL properties of the parent lanthanide chelate. Using the probe, a highly sensitive, sandwich-based TRL immunoassay for the cardiac troponin I was conducted, exhibiting a limit of detection of 48 pg/mL. On the basis of the features of the LESNP such as TRL signaling capability, stability, and the ease of biofunctionalization, we expect that the LESNP can be widely applied in the development of TRL-based immunosensing.

Highly luminescent, stable, transparent and flexible perovskite quantum dot gels towards light-emitting diodes

By controlling the hydrolysis of alkoxysilanes, highly luminescent, transparent and flexible perovskite quantum dot (QD) gels were synthesized. The gels could maintain the structure without shrinking and exhibited excellent stability comparing to the QDs in solution. This in situ fabrication can be easily scaled up for large-area/volume gels. The gels integrated the merits of the polymer matrices to avoid the non-uniformity of light output, making it convenient for practical LED applications. Monochrome and white LEDs were fabricated using these QD gels; the LEDs exhibited broader color gamut, demonstrating better property in the backlight display application.

Depth profiling of APTES self-assembled monolayers using surface-enhanced confocal Raman microspectroscopy

The internal structure of self-assembled monolayers (SAMs) such as 3-aminopropyltriethoxysilane (APTES) fabricated on a glass substrate is difficult to characterize and analyze at nanometer level. In this study, we employed surface-enhanced Raman spectroscopy (SERS) to study the internal molecular structure of APTES SAMs. The sample APTES SAMs were deposited with Ag nanoparticles to enhance the Raman signal and to obtain subtler structure information, which were supported by density functional theory calculations. In addition, in order to carry out high-resolution analysis, especially for vertical direction, a fine piezo electric positioner was used to control the depth scanning with a step of 0.1nm. We measured and distinguished the vertical Raman intensity variations of specific groups in APTES, such as Ag/NH₂, CH₂, and SiO, with high resolution. The interfacial bond at the two interfaces of Ag-APTES and APTES-SiO₂ was identified. Moreover, APTES molecule orientation was demonstrated to be inhomogeneous from frequency shift.

Controlled Engineering of Oxide Surfaces for Bioelectronics Applications Using Organic Mixed Monolayers

Modifying the surfaces of oxides using self-assembled monolayers offers an exciting possibility to tailor their surface properties for various applications ranging from organic electronics to bioelectronics applications. The simultaneous use of different molecules in particular can extend this approach because the surface properties can be tuned via the ratio of the chosen molecules. This requires the composition and quality of the monolayers to be controlled on an organic level, that is, on the nanoscale. In this paper, we present a method of modifying the surface and surface properties of silicon oxide by growing self-assembled monolayers comprising various compositions of two different molecules, (3-aminopropyl)-triethoxysilane and (3-glycidyloxypropyl)-trimethoxysilane, by means of in situ controlled gas-phase deposition. The properties of the resulting mixed molecular monolayers (e.g., effective thickness, hydrophobicity, and surface potential) exhibit a perfect linear dependence on the composition of the molecular layer. Finally, coating the mixed layer with poly(l-lysine) proves that the density of proteins can be controlled by the composition as well. This indicates that the method might be an ideal way to optimize inorganic surfaces for bioelectronics applications.

Modular approach for bimodal antibacterial surfaces combining photo-switchable activity and sustained biocidal release

Photo-responsive antibacterial surfaces combining both on-demand photo-switchable activity and sustained biocidal release were prepared using sequential chemical grafting of nano-objects with different geometries and functions. The multi-layered coating developed incorporates a monolayer of near-infrared active silica-coated gold nanostars (GNS) decorated by silver nanoparticles (AgNP). This modular approach also enables us to unravel static and photo-activated contributions to the overall antibacterial performance of the surfaces, demonstrating a remarkable synergy between these two mechanisms. Complementary microbiological and imaging evaluations on both planktonic and surface-attached bacteria provided new insights on these distinct but cooperative effects.

Zwitterionic Silane Copolymer for Ultra-Stable and Bright Biomolecular Probes Based on Fluorescent Quantum Dot Nanoclusters

Fluorescent semiconductor quantum dots (QDs) exhibit several unique properties that make them suitable candidates for biomolecular sensing, including high brightness, photostability, broad excitation, and narrow emission spectra. Assembling these QDs into robust and functionalizable nanosized clusters (QD-NSCs) can provide fluorescent probes that are several orders of magnitude brighter than individual QDs, thus allowing an even greater sensitivity of detection with simplified instrumentation. However, the formation of compact, antifouling, functionalizable, and stable QD-NSCs remains a challenging task, especially for a use at ultralow concentrations for single-molecule detection. Here, we describe the development of fluorescent QD-NSCs envisioned as a tool for fast and sensitive biomolecular recognition. First, QDs were assembled into very compact 100-150 nm diameter spherical aggregates; the final QD-NSCs were obtained by growing a cross-linked silica shell around these aggregates. Hydrolytic stability in several concentration and pH conditions is a key requirement for a potential and efficient single-molecule detection tool. However, the hydrolysis of Si-O-Si bonds leads to desorption of monosilane-based surface groups at very low silica concentrations or in a slightly basic medium. Thus, we designed a novel multidentate copolymer composed of multiple silane as well as zwitterionic monomers. Coating silica beads with this multidentate copolymer provided a robust surface chemistry that was demonstrated to be stable against hydrolysis, even at low concentrations. Copolymer-coated silica beads also showed low fouling properties and high colloidal stability in saline solutions. Furthermore, incorporation of additional azido-monomers enabled easy functionalization of QD-NSCs using copper-free bio-orthogonal cyclooctyne-azide click chemistry, as demonstrated by a biotin-streptavidin affinity test.

Organofunctional Silane Modification of Aluminum-Doped Zinc Oxide Surfaces as a Route to Stabilization

Aluminum-doped zinc oxide (AZO) is a low-temperature processed transparent conductive oxide (TCO) made of earth abundant elements; its applications are currently limited by instability to heat, moisture, and acidic conditions. We demonstrate that the application of an organofunctional silane modifier mitigates AZO degradation and explore the interplay between performance and material composition and morphology. Specifically, we evaluate degradation of bare AZO and APTES (3-aminopropyltriethoxysilane)-modified AZO in response to damp heat (DH, 85 °C, 85% relative humidity) exposure over 1000 h and then demonstrate how surface modification impacts changes in electrical and optical properties and chemical composition in one of the most thorough studies to date. Hall measurements show that the resistivity of AZO increases due to a decrease in electron mobility, with no commensurate change in carrier concentration. APTES decelerates this electrical degradation, without affecting AZO optical properties. Percent transmission and yellowness index of an ensemble of bare and modified AZO are stable upon DH exposure, but haze increases slightly for a discrete sample of modified AZO. Atomic force microscopy (AFM) and optical profilometer (OP) measurements do not show evidence of pitting or delamination after 1000 h DH exposure but indicate a slight increase in surface roughness on both the nanometer and micrometer length scales. X-ray photoelectron spectroscopy data (XPS) reveal that the surface composition of bare and silanized AZO is stable over this time frame; oxygen vacancies, as measured by XPS, are also stable with DH exposure, which, together with transmission and Hall measurements, indicate stable carrier concentrations. However, after 1500 h of DH exposure, only bare AZO shows signs of catastrophic destruction. Comparison of the data presented herein to previous reports indicates that the initial AZO composition and microstructure dictate the degradation profile. This work demonstrates that surface modification slows the bulk degradation of AZO and provides insight into how the material can be more widely used as a transparent electrode in the next generation of optoelectronic devices.

Surface Chemistry and Humidity in Powder Electrostatics: A Comparative Study between Tribocharging and Corona Discharge

In the present study, the correlation between surface chemical groups and the electrostatic properties of particulate materials was studied. Glass beads were modified to produce OH-, NH₂-, CN-, and F-functionalized materials. The materials were charged separately both by friction and by conventional corona charging, and the results were compared. The results obtained from both methods indicated that the electrostatic properties are directly related to the surface functional group chemistry, with hydrophobic groups accumulating greater quantities of charge than hydrophilic groups. The fluorine-rich surface accumulated 5.89 times greater charge upon tribocharging with stainless steel than the hydroxyl-rich surface. However, in contrast to the tribocharging method, the charge polarity could not be determined when corona charging was used. Moreover, discharge profiles at different humidity levels (25% RH, 50% RH, and 75% RH) were obtained for each modified surface, which showed that higher humidity facilitates faster charge decay; however, this enhancement is surface chemistry-dependent. By increasing the humidity from 25% RH to 75% RH, the charge relaxation times can be accelerated 1.6 times for fluorine and 12.2 times for the cyano group. These data confirm that surface functional groups may dictate powder electrostatic behavior and account for observed charge accumulation and discharge phenomena.

Unexpected "Hammerlike Liquid" to Pulverize Silica Powders to Stable Sols and Its Application in the Preparation of Sub-10 nm SiO2 Hybrid Nanoparticles with Chirality

Silane coupling agents are well-known as surface modifiers for various kinds of silica (SiO2). However, in the present research, it has been found that they can also work as "hammerlike liquid" to pulverize different kinds of bulk amorphous SiO2 in aqueous systems. This new function was typically clarified by using 3-aminopropyltrimethoxysilane (APS) and bundles of chiral SiO2 nanofibers (with average diameter of ∼10 nm) as raw materials. By a simple reflux of the mixture of SiO2 nanofibers and excessive APS in pure H2O, the solid-containing mixture turned into a completely clear solution that contained sub-10 nm, amine-modified, and water-soluble hybrid SiO2 sols (HS-sols). Moreover, this solution showed blue luminescence under ultraviolet irradiation. Furthermore, the circular dichroism and vibrational circular dichroism spectra revealed that the HS-sols are optically active even though the pristine chiral SiO2 nanofibers were completely destroyed. It was considered that the chirality of SiO2 nanofibers was due to the asymmetric arrangement of Si and O atoms in chiral domains (<10 nm) on the Si-O-Si network of SiO2, and these domains are still preserved in chiral HS-sols. This green method has high potential for the recycling of rich SiO2 sources to obtain functional SiO2 nanomaterials with applications such as optical display, imaging, and chiral recognition. Also, it offers a tool for the analysis of the structural properties of SiO2 on the molecular scale.

Surface-Triggered Tandem Coupling Reactions of Cyclic Azasilanes

Cyclic azasilanes have been synthesized for the purpose of developing coupling agents appropriate for a variety of nanotechnologies including surface modification of nanoparticles, nanocrystals, mesoporous materials and substrates. N‐Methyl‐aza‐2,2,4‐trimethylsilacyclopentane is representative of this class of compounds. Preliminary data for the treatment of inorganic surfaces, including nanoparticles and oxidized silicon wafers, with cyclic azasilanes suggest high‐density monolayer deposition by a ring‐opening reaction. Cyclic azasilanes contain a cryptic amine functionality that can perform a subsequent tandem coupling reaction with functional molecules after the surface‐triggered ring‐opening reaction, allowing for a one‐pot self‐assembly route on nanostructures. Tandem coupling reactions are demonstrated via addition reactions of the cryptic amine with epoxy and acrylate systems.

Hydrolytic Stability of 3-Aminopropylsilane Coupling Agent on Silica and Silicate Surfaces at Elevated Temperatures

3-Aminopropylsilane (APS) coupling agent is widely used in industrial, biomaterial, and medical applications to improve adhesion of polymers to inorganic materials. However, during exposure to elevated humidity and temperature, the deposited APS layers can decompose, leading to reduction in coupling efficiency, thus decreasing the product quality and the mechanical strength of the polymer-inorganic material interface. Therefore, a better understanding of the chemical state and stability of APS on inorganic surfaces is needed. In this work, we investigated APS adhesion on silica wafers and compared its properties with those on complex silicate surfaces such as those used by industry (mineral fibers and fiber melt wafers). The APS was deposited from aqueous and organic (toluene) solutions and studied with surface sensitive techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), streaming potential, contact angle, and spectroscopic ellipsometry. APS configuration on a model silica surface at a range of coverages was simulated using density functional theory (DFT). We also studied the stability of adsorbed APS during aging at high humidity and elevated temperature. Our results demonstrated that APS layer formation depends on the choice of solvent and substrate used for deposition. On silica surfaces in toluene, APS formed unstable multilayers, while from aqueous solutions, thinner and more stable APS layers were produced. The chemical composition and substrate roughness influence the amount of deposited APS. More APS was deposited and its layers were more stable on fiber melt than on silica wafers. The changes in the amount of adsorbed APS can be successfully monitored by streaming potential. These results will aid in improving industrial- and laboratory-scale APS deposition methods and increasing adhesion and stability, thus increasing the quality and effectiveness of materials where APS is used as a coupling agent.

Development of "Liquid-like" Copolymer Nanocoatings for Reactive Oil-Repellent Surface

Here, we describe a simple method to prepare oil-repellent surfaces with inherent reactivity. Liquid-like copolymers with pendant reactive groups are covalently immobilized onto substrates via a sequential layer-by-layer method. The stable and transparent nanocoatings showed oil repellency to a broad range of organic liquids even in the presence of reactive sites. Functional molecules could be covalently immobilized onto the oil-repellent surfaces. Moreover, the liquid repellency can be maintained or finely tailored after post-chemical modification via synergically tailoring the film thickness, selection of capping molecules, and labeling degree of the capping molecules. Oil-repellent surfaces that are capable of post-functionalization would have technical implications in surface coatings, membrane separation, and biomedical and analytical technologies.

Byproduct-Free Route to Aminosiloxane Monolayers on Silicon/Silicon Dioxide

The chemisorption of N-methyl-aza-2,2,4-trimethylsilacyclopentane from either the solution or the vapor phase produces monolayer films on silicon (oxide) substrates. The formation of a covalent siloxane linkage to the surface by this adsorbate is accompanied by ring opening, which produces no byproduct. The resulting secondary amine reacts with maleic anhydride to produce a carboxylic acid-terminated surface, accompanied by the formation of a stable amide bond. These reactions and their products were characterized by a combination of optical ellipsometry, contact-angle goniometry, and X-ray photoelectron spectroscopy.

Immobilization and detection of platelet-derived extracellular vesicles on functionalized silicon substrate: cytometric and spectrometric approach

Among the various biomarkers that are used to diagnose or monitor disease, extracellular vesicles (EVs) represent one of the most promising targets in the development of new therapeutic strategies and the application of new diagnostic methods. The detection of circulating platelet-derived microvesicles (PMVs) is a considerable challenge for laboratory diagnostics, especially in the preliminary phase of a disease. In this study, we present a multistep approach to immobilizing and detecting PMVs in biological samples (microvesicles generated from activated platelets and human platelet-poor plasma) on functionalized silicon substrate. We describe the application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and spectroscopic ellipsometry methods to the detection of immobilized PMVs in the context of a novel imaging flow cytometry (ISX) technique and atomic force microscopy (AFM). This novel approach allowed us to confirm the presence of the abundant microvesicle phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE) on a surface with immobilized PMVs. Phosphatidylcholine groups (C5H12N+; C5H15PNO4+) were also detected. Moreover, we were able to show that ellipsometry permitted the immobilization of PMVs on a functionalized surface to be evaluated. The sensitivity of the ISX technique depends on the size and refractive index of the analyzed microvesicles. Graphical abstract Human platelets activated with thrombin (in concentration 1IU/mL) generate population of PMVs (platelet derived microvesicles), which can be detected and enumerated with fluorescent-label method (imaging cytometry). Alternatively, PMVs can be immobilized on the modified silicon substrate which is functionalized with a specific IgM murine monoclonal antibody against human glycoprotein IIb/IIIa complex (PAC-1). Immobilized PMVs can be subjected to label-free analyses by means ellipsometry, atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).

Biofunctional polyelectrolytes assembling on biosensors - A versatile surface coating method for protein detections

This paper reports a surface functionalization strategy for protein detections based on biotin-derivatized poly(l-lysine)-grafted oligo-ethylene glycol (PLL-g-OEG_x-Biotin) copolymers. Such strategy can be used to attach the biomolecule receptors in a reproducible way simply by incubation of the transducer element in a solution containing such copolymers which largely facilitated the sensor functionalization at an industrial scale. As the synthesized copolymers are cationic in physiology pH, surface biotinylation can be easily achieved via electrostatic adsorption on negatively charged sensor surface. Biotinylated receptors can be subsequently attached through well-defined biotin-streptavidin interaction. In this work, the bioactive sensor surfaces were applied for mouse IgG and prostate specific antigen (PSA) detections using quartz crystal microbalance (QCM), optical sensor (BioLayer Interferometry) and conventional ELISA test (colorimetry). A limit of detection (LOD) of 0.5 nM was achieved for PSA detections both in HEPES buffer and serum dilutions in ELISA tests. The synthesized PLL-g-OEG_x-Biotin copolymers with different OEG chain length were also compared for their biosensing performance. Moreover, the surface regeneration was achieved by pH stimulation to remove the copolymers and the bonded analytes, while maintaining the sensor reusability as well. Thus, the developed PLL-g-OEG_x-Biotin surface assembling strategy is believed to be a versatile surface coating method for protein detections with multi-sensor compatibility.