Silane-based Self-assembled Monolayer Research Articles

Silanization Strategies for Tailoring Peptide Functionalization on Silicon Surfaces: Implications for Enhancing Stem Cell Adhesion.

Biomaterial surface engineering and the integration of cell-adhesive ligands are crucial in biological research and biotechnological applications. The interplay between cells and their microenvironment, influenced by chemical and physical cues, impacts cellular behavior. Surface modification of biomaterials profoundly affects cellular responses, especially at the cell-surface interface. This work focuses on enhancing cellular activities through material manipulation, emphasizing silanization for further functionalization with bioactive molecules such as RGD peptides to improve cell adhesion. The grafting of three distinct silanes onto silicon wafers using both spin coating and immersion methods was investigated. This study sheds light on the effects of different alkyl chain lengths and protecting groups on cellular behavior, providing valuable insights into optimizing silane-based self-assembled monolayers (SAMs) before peptide or protein grafting for the first time. Specifically, it challenges the common use of APTES molecules in this context. These findings advance our understanding of surface modification strategies, paving the way for tailoring biomaterial surfaces to modulate the cellular behavior for diverse biotechnological applications.

Silane-Based SAMs Deposited by Spin Coating as a Versatile Alternative Process to Solution Immersion.

Functionalization of silica surfaces with silane-based self-assembled monolayers (SAMs) is widely used in material sciences to tune surface properties and introduce terminal functional groups enabling subsequent chemical surface reactions and immobilization of (bio)molecules. Here, we report on the synthesis of four organotrimethoxysilanes with various molecular structures and we compare their grafting by spin coating with the one performed by the conventional solution immersion method. Strikingly, this study clearly demonstrates that the spin coating technique is a versatile, fast, and more convenient alternative process to prepare robust, smooth, and homogeneous SAMs with similar properties and quality as those deposited via immersion. SAMs were characterized by PM-IRRAS, AFM, and wettability measurements. SAMs can undergo several chemical surface modifications, and the reactivity of amine-terminated SAM was confirmed by PM-IRRAS and fluorescence measurements.

Saliva and Serum Protein Adsorption on Chemically Modified Silica Surfaces

Biomaterials, once inserted in the oral cavity, become immediately covered by a layer of adsorbed proteins that consists mostly of salivary proteins but also of plasma proteins if the biomaterial is placed close to the gingival margin or if it becomes implanted into tissue and bone. It is often this protein layer, rather than the pristine biomaterial surface, that is subsequently encountered by colonizing bacteria or attaching tissue cells. Thus, to study this important initial protein adsorption from human saliva and serum and how it might be influenced through chemical modification of the biomaterial surface, we have measured the amount of protein adsorbed and analyzed the composition of the adsorbed protein layer using gel electrophoresis and western blotting. Here, we have developed an in vitro model system based on silica surfaces, chemically modified with 7 silane-based self-assembled monolayers that span a broad range of physicochemical properties, from hydrophilic to hydrophobic surfaces (water contact angles from 15° to 115°), low to high surface free energy (12 to 57 mN/m), and negative to positive surface charge (zeta potentials from –120 to +40 mV at physiologic pH). We found that the chemical surface functionalities exerted a substantial effect on the total amounts of proteins adsorbed; however, no linear correlation of the adsorbed amounts with the physicochemical surface parameters was observed. Only the adsorption behavior of a few singular protein components, from which physicochemical data are available, seems to follow physicochemical expectations. Examples are albumin in serum and lysozyme in saliva; in both, adsorption was favored on countercharged surfaces. We conclude from these findings that in complex biofluids such as saliva and serum, adsorption behavior is dominated by the overall protein-binding capacity of the surface rather than by specific physicochemical interactions of single protein entities with the surface.

Remote Doping Effects of Indium-Gallium-Zinc Oxide Thin-Film Transistors by Silane-Based Self-Assembled Monolayers.

Oxide thin-film transistors (TFTs), including indium–gallium–zinc oxide (IGZO) TFTs, have been widely investigated because of their excellent properties, such as compatibility with flexible substrates, high carrier mobility, and easy-to-fabricate TFT processes. However, to increase the use of oxide semiconductors in electronic products, an effective doping method that can control the electrical characteristics of oxide TFTs is required. Here, we comprehensively investigate the effect of silane-based self-assembled monolayer (SAM) doping on IGZO TFTs. Instead of a complex doping process, the electrical performance can be enhanced by anchoring silane-based SAMs on the IGZO surface. Furthermore, differences in the doping effect based on the structure of SAMs were analyzed; the analysis offers a systematic guideline for effective electrical characteristic control in IGZO TFTs.

Mixed Silane‐based Self‐assembled Monolayers Deposited on Fluorine Doped Tin Oxide as Model System for Development of Biosensors for Toxin Detection

AbstractIn this work mixed hybrid phospholipid bilayers (mhBLM) were deposited on fluorine doped tin oxide (FTO) films. Two component silane‐based self‐assembled monolayers (SAMs) formed on FTO surface trigger vesicle fusion and formation of mhBLMs which are stable, can be easily regenerated, and therefore, used for multiple experiments. We found that certain chemical and physical conditions under which mixed SAMs are fabricated translate into functional properties of mhBLMs. In all cases we observed interaction of melittin with mhBLMs demonstrating biological relevance of these biomimetic surface constructs and their possible application in biosensors for toxin detection.

Enhanced output performance and stability of triboelectric nanogenerators by employing silane-based self-assembled monolayers

A promising strategy to simultaneously enhance the performance and stability of TENGs is developed by using silane-based self-assembled monolayers.

Silane-based self-assembled monolayer deposited on fluorine doped tin oxide as model system for pharmaceutical and biomedical analysis

Recently, self-assembled monolayers (SAMs) are gaining a lot of interest due to their simplicity of preparation and wide applicability in the development of model systems used in pharmaceutical and biomedical analysis. The most efficient methods used for the investigation of SAM-based structures usually include cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electrochemical microscopy (SECM) could be also used as an alternative method for SAM investigations, because this method enables to map modified surface. In this work, the surface of fluorine doped tin oxide (FTO) was modified with octadeciltrichlorosilane (OTS) based SAM and investigated using SECM. Measurements, which were carried out by SECM, lead to conclusion that highly heterogeneous and distributed monolayer has been formed on FTO surface.

Study of carbon nanotube-rich impedimetric recognition electrode for ultra-low determination of polycyclic aromatic hydrocarbons in water.

Carbon nanotubes (CNTs) have been studied as an electrochemical recognition element for the impedimetric determination of priority polycyclic aromatic hydrocarbons (PAHs) in water, using hexocyanoferrate as a redox probe. For this goal, an indium tin oxide (ITO) electrode functionalized with a silane-based self-assembled monolayer carrying CNTs has been engineered. The electroanalytical method, which is similar to an antibody-antigen assay, is straightforward and exploits the high CNT-PAH affinity obtained via π-interactions. After optimizing the experimental conditions, the resulting CNT-based impedimetric recognition platform exhibits ultra-low detection limits (1.75 ± 0.04ng·L-1) for the sum of PAHs tested, which was also validated byusing a certified reference PAH mixture. Graphical abstract Schematic of an indium-tin-oxide (ITO) electrode functionalized with a silane-based self-assembled monolayer carrying carbon nanotubes (CNTs) as arecognition platform for the ultra-low determination of totalpolycyclic aromatic hydrocarbons (PAHs) in water via π-interactions using Electrochemical Impedance Spectroscopy (EIS).

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory–Huggins parameter (χ ∼ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Enhancing the Thermal Conductance of Polymer and Sapphire Interface via Self-Assembled Monolayer.

Interfacial thermal conductance (ITC) receives enormous consideration because of its significance in determining thermal performance of hybrid materials, such as polymer based nanocomposites. In this study, the ITC between sapphire and polystyrene (PS) was systematically investigated by time domain thermoreflectance (TDTR) method. Silane based self-assembled monolayers (SAMs) with varying end groups, -NH2, -Cl, -SH and -H, were introduced into sapphire/PS interface, and their effects on ITC were investigated. The ITC was found to be enhanced up by a factor of 7 through functionalizing the sapphire surface with SAM, which ends with a chloride group (-Cl). The results show that the enhancement of the thermal transport across the SAM-functionalized interface comes from both strong covalent bonding between sapphire and silane-based SAM, and the high compatibility between the SAM and PS. Among the SAMs studied in this work, we found that the ITC almost linearly depends on solubility parameters, which could be the dominant factor influencing on the ITC compared with wettability and adhesion. The SAMs serve as an intermediate layer that bridges the sapphire and PS. Such a feature can be applied to ceramic-polymer immiscible interfaces by functionalizing the ceramic surface with molecules that are miscible with the polymer materials. This research provides guidance on the design of critical-heat transfer materials such as composites and nanofluids for thermal management.

Filamentous Phages Displaying Multivalent Peptide Motives With Specific Affinity To Anodic Alumina Surfaces

In this work, we report for the first time on the successful selection and identification of peptide motives that exhibit a specific affinity to anodic alumina surfaces when multivalently displayed on a filamentous phage. It was also demonstrated that, for a selected phage clone, a chemical functionalisation (biotinylation) of the bacteriophage does not deteriorate its specific affinity to anodic alumina. Moreover, such biotinylated bacteriophages, after being immobilised onto an anodic alumina surface, have been shown to allow for the quantitative detection of streptavidine using an ELISA protocol. These results are believed to pave the way for shifting the surface design of integrated biosensing devices from traditional, chemically modified synthetic surfaces, like silane-based self-assembled monolayers, towards molecular linkers based on genetically engineered polypeptides.

Nanomechanical Actuation of a Silicon Cantilever Using an Azo Dye, Self-Assembled Monolayer

The emerging fields of nanomotors and optomechanics are based on the harnessing of light to generate force. However, our ability to detect small surface stresses is limited by temperature drift, environmental noise, and low-frequency flicker electronic noise. To address these limitations, we functionalized microfabricated silicon cantilevers with an azo dye, silane-based self-assembled monolayer and modulated the surface stress by exciting the optical switch with a 405-nm laser. Atomic force microscopy, contact angle analysis, ellipsometry, and X-ray photoelectron spectroscopy verified successful assembly of molecules on the cantilever. Ultraviolet and visible spectra demonstrate optical switching of the synthesized molecule in solution. By turning the laser on and off at a specific rate (e.g., 1 Hz), the cantilever deflection can be measured via Fourier techniques, thus separating the signal of interest from the noise. This technique empowers the design of highly sensitive surface stress measurements.

Functionalization of electropolished titanium surfaces with silane-based self-assembled monolayers and their application in drug delivery

This work reports a novel and reproducible route for the successful modification of the surface of titanium (Ti) with self-assembled monolayers (SAMs). By electropolishing the surface of Ti, suitable physical/chemical surface properties were obtained for adequate growth of OctadecylTrichloroSilane (OTS) based SAM. Optimum conditions to achieve a well-organized and densely packed OTS film were also determined by monitoring the effect of different parameters including time, concentration, and temperature for OTS adsorption. The optimum conditions for the formation of an OTS–SAM were found to be upon immersion of the electropolished Ti substrate in a 10mM OTS solution at 10°C for 24h. Furthermore, multiple growth regimes for the formation of OTS–SAM on electropolished Ti surface were observed. The kinetics for the self-assembly were fast at the beginning of OTS adsorption, but rapidly slowed down after 10h of immersion, i.e. during the densification process of the film at the surface of Ti. In addition, the growth behavior was found to be random as opposed to the island growth behavior usually observed with OTS at the surface of silica. The successful implementation of OTS–SAM was further investigated through the immobilization and delivery of a model drug and the OTS monolayer showed clear abilities in drug delivery with an initial burst release up to 5days followed by a sustained release up to 26days.

Exploration of the Direct Use of Anodized Alumina as a Mold for Nanoimprint Lithography to Fabricate Magnetic Nanostructure over Large Area

We have explored the direct use of anodized alumina (AAO) fabricated on an Si wafer as a mold for the nanoimprint lithography (NIL). The AAO mold has been fabricated over more than 10 cm2area with two different pore diameters of163±24 nm and73±7 nm. One of the key challenges of the lack of bonding between the antisticking self-assembled monolayer (SAM) and the AAO has been overcome by modifying the surface chemistry of the fabricated AAO mold by coating it with thin SiO2layer. Then we have applied the commonly used silane-based self-assembled monolayer (SAM) on these SiO2-coated AAO molds and achieved successful imprinting of resist pillars with feature size of172±25 nm by using the mold with a pore diameter of163±24 nm. Finally, we have achieved (001) oriented L10FePt patterned structure with a dot diameter of42±4 nm by using a AAO mold with a pore diameter of73±7 nm. The perpendicularHcof the unpatterned and patterned FePt is about 3.3 kOe and 12 kOe, respectively. These results indicate that AAO mold can potentially be used in NIL for fabricating patterned nanostructures over large area.

Monitoring and Mapping Imperfections in Silane-Based Self-Assembled Monolayers by Chemical Amplification

This paper describes an innovative and simple technique for analyzing defects in silane-based self-assembled monolayers. The assembly of monolayers is a simple method for chemically modifying surfaces, which can be important for resisting chemical attack or adhesion of biomolecules. Measuring the molecular scale properties of monolayers and the reproducibility of their ability to uniformly modify a surface requires tools that provide limits of detection at the level of at least a few atoms per million with specificity to the top couple nanometers of the surface. To achieve this level of sensitivity a new technique is developed that combines spectroscopy and microscopy techniques (particularly atomic force microscopy) with chemical amplification of exposed silicon in self-assembled monolayers of silane molecules. This development is an important achievement for monitoring the quality of monolayers as a function of modifications to the method(s) used to deposit the silane molecules. Techniques presented here could be easily extended to assessing the molecular scale quality of other surface modifications.

Drop-On-Demand Inkjet Printing of SU-8 Polymer

This paper presents drop-on-demand inkjet printing of SU-8 on functionalized surfaces for direct printing of computer controlled polymer patterns. The high viscosity of SU-8 required an in-depth investigation of the print parameters such as pulse amplitude, pulse length and temperature in the piezo-actuated nozzle. The results show that the optimal drop velocity to obtain a stable printing is 2 ms-1 which corresponds to pulse amplitude and length of 220 V and 70-80 μs, respectively. The diameter of the SU-8 drop was reduced from 117 μm on non-treated silicon to 58 μm on a surface terminated by a silane-based self-assembled monolayer.

Interface Control by Surface-Initiated Deposition Polymerization and Its Application to Organic Light-Emitting Devices

Surface-initiated deposition polymerization was applied to the preparation of a hole transport layer (HTL) on an indium–tin oxide (ITO) electrode. A silane-based self-assembled monolayer (SAM) that has an azo terminal group was prepared on an ITO surface on which a vinyl monomer of carbazole (CPA) or tetraphenyldiaminobiphenyl (vTPD) was deposited by physical vapor deposition. The polymerization of the HTL was achieved by electron-assisted deposition. UV irradiation, as well as conventional evaporation, was not capable of growing polymer films on the SAM. Organic light-emitting diodes (OLEDs) were prepared by depositing tris(8-quinolinolato) aluminum (Alq3) on the HTL. The surface-initiated deposition polymerization was effective in markedly increasing device current flow and reducing turn-on voltage. However, luminescence efficiency was not improved by this method owing to improper carrier balance under excessive hole injection. Nevertheless, surface-initiated deposition polymerization was effective in improving film morphology, stability, and hole injection characteristics.

Deposition of Self-Assembled Monolayers in Mesoporous Silica from Supercritical Fluids

Deposition of silane-based self-assembled monolayers onto mesoporous ceramic substrates has been found to be substantially faster from supercritical fluids than from typical condensed phase solutions. In addition, the monolayers so prepared display higher silane population density (6.5 vs 4.6 silanes/nm2), fewer defects, and greater stability than those prepared via standard solution methods. A mechanistic rationale for the pressure-induced rate enhancement and reduced defect density is presented.