Facile Functionalization of Polymer Surfaces in Aqueous and Polar Organic Solvents via 3-Mercaptopropylsilatrane

Aggregation-Enabled Electrochemistry in Confined Nanopore Capable of Complementary Faradaic and Non-Faradaic Detection

Electrochemistry that empowers innovative nanoscopic analysis has long been pursued. Here, the concept of aggregation-enabled electrochemistry (AEE) in a confined nanopore is proposed and devised by reactive oxygen species (ROS)-responsive aggregation of CdS quantum dots (QDs) within a functional nanopipette. Complementary Faradaic and non-Faradaic operations of the CdS QDs aggregate could be conducted to simultaneously induce the signal-on of the photocurrents and the signal-off of the ionic signals. Such a rationale permits the cross-checking of the mutually corroborated signals and thus delivers more reliable results for single-cell ROS analysis. Combined with the rich biomatter-light interplay, the concept of AEE can be extended to other stimuli-responsive aggregations for electrochemical innovations.

Competitive Assay for the Ultrasensitive Detection of Organophosphate Pesticides Based on a Fiber-Optic Particle Plasmon Resonance Biosensor and an Acetylcholinesterase Binding Peptide

An acetylcholinesterase (AChE) binding-based biosensor was developed for the ultrasensitive detection of organophosphate (OP) pesticides. The biosensor integrates the technique based on fiber-optic particle plasmon resonance detection and a synthetic AChE binding peptide conjugated with gold nanoparticles on the optical fiber surface via an AChE competitive binding assay. The OP pesticides present in the solution hinder the binding of AChE to the peptide on the biosensor by competing for the binding sites present in AChE. The limit of detection obtained for parathion using this method was observed to be 0.66 ppt (2.3 pM). This method shows a wide linear dynamic range of 6 orders. Furthermore, the use of the AChE binding peptide in the biosensor can better discriminate OPs against carbamates by using only a single biosensor. The practical application of this method was tested using spiked samples, which yielded good recovery and reproducibility. The spiked sample required minimal pretreatment before analysis; hence, this biosensor may also be used in the field.

3-Aminopropylsilatrane and Its Derivatives: A Variety of Applications

Silatranes arouse much research interest owing to their unique structure, unusual physical–chemical properties, and diverse biological activity. The application of some silatranes and their analogues has been discussed in several works. Meanwhile, a comprehensive review of the wide practical usage of silatranes is still absent in the literature. The ability of silatranes to mildly control hydrolysis allows them to form extremely stable and smooth siloxane monolayers almost on any surface. The high physiological activity of silatranes makes them prospective drug candidates. In the present review, based on the results of numerous previous studies, using the commercially available 3-aminopropylsilatrane and its hybrid derivatives, we have demonstrated the high potential of 1-organylsilatranes in various fields, including chemistry, biology, pharmaceuticals, medicine, agriculture, and industry. For example, these compounds can be employed as plant growth biostimulants, drugs, optical, catalytic, sorption, and special polymeric materials, as well as modern high-tech devices.

Substrate-independent adsorption of nanoparticles as anti-biofilm coatings

Healthcare-associated infections are common causes of morbidity and mortality. Advanced nanotechnology provides a means of overcoming this problem, but it remains challenging to develop universal coating strategies for decorating antimicrobial nanomaterials onto various clinical devices. In this paper, we propose a general silane-based method for immobilizing monolayer metal nanoparticle (NP) arrays onto any type of substrate surface-especially for a diverse range of clinical implantable devices. The surface silanization was achieved simply through the adsorption of N¹-(3-trimethoxysilylpropyl)diethylenetriamine (TMS), regardless of the material (polymer, metal, oxide) or morphology (flat, curved, textured) of the substrate, with no need for pretreatment or expensive instrumentation. Monolayers of various nanostructures (Ag, Au, and hollow Au NPs) were then decorated rapidly onto the TMS-treated substrates, thereby further functionalizing their surfaces. In particular, immobilization of the Ag NPs resulted in excellent anti-biofilm efficacy against three clinically life-threatening pathogens: Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus. Sustained release of Ag⁺ ions led to durable inhibition of bacterial attachment for up to 28 days. Studies with NIH3T3 fibroblasts revealed that the Ag NP arrays displayed no cytotoxicity toward mammalian cells. Overall, this universal coating process appears to be an innovative method for the surface-functionalization of diverse materials and devices employed in the fields of energy, sensing, and medicine-especially to prevent healthcare-associated infections arising from the use of clinical implantable devices in hospitals.

Controllable organosilane monolayer density of surface bonding using silatranes for thiol functionalization of silica particles for liquid chromatography and validation of microanalytical method for elemental composition determination

The present work systematically investigates a new strategy for the functionalization of silica gel using alkyl silatrane chemistry instead of alkylsilanes for synthesis of chromatographic stationary phases. In this work, silica was chemically modified for further functionalization by a thiol-ene click reaction. Thus, 3-mercaptopropylsilatrane (MPS) was used which is capable to form self-assembled monolayers (SAM) on top of silanol surfaces in a controlled manner as previously shown for silicon wafers. The utility of this chemistry for stationary phase synthesis in liquid chromatography was not evaluated yet. Hence, silica surface modifications using MPS were studied in comparison to established 3-mercaptopropyltrimethoxysilane (MPTMS) chemistry. First, the employed elemental analysis method was validated and it showed excellent intra-day and inter-day precisions (typically less than 5% RSD). It could be shown that the reaction kinetics of MPS was roughly 35-times faster than with MPTMS. After 30 min reaction time with MPS, the thiol content reached 74% of the maximal coverage. Due to controlled chemistry with MPS, which does not lead to oligomeric siloxane network at the silica surface, the ligand coverage was lower. However, multiple silanization cycles with MPS led to a dense surface coverage (around 4 µmol m^-2). ²⁹Si cross polarization/magic angle spinning (CP/MAS) solid-state NMR revealed distinct T¹/T²/T³ ratios for MPS and MPTMS materials with up to 80% T³ (indicative for trifunctional siloxane linkage) for MPS and around 20% T³ for MPTMS. This indicates a more homogeneous, thinner monolayer film of MPS on the silica surface, as compared to an irregular thick oligomeric siloxane network with MPTMS. Bonding of quinine carbamate as chiral selector afforded an efficient chiral stationary phase (CSP) for chromatographic enantiomer separation. Separation factors were comparable to MPTMS-bonded CSP, however, chromatographic efficiency was much better for the MPS-bonded CSP. H/u curves indicated a reduced mass transfer resistance by roughly factor 3 for MPS- compared to MPTMS-bonded CSP. This confirms better chromatographic performance of surfaces with homogeneous monolayer compared to network structures on the silica surface which suffer from poor stationary phase mass transfer.

Biodegradable and Biocompatible Silatrane Polymers

In this study, new biodegradable and biocompatible amphiphilic polymers were obtained by modifying the peripheral hydroxyl groups of branched polyethers and polyesters with organosilicon substituents. The structures of the synthesized polymers were confirmed by NMR and GPC. Organosilicon moieties of the polymers were formed by silatranes and trimethylsilyl blocks and displayed hydrophilic and hydrophobic properties, respectively. The effect of the ratio of hydrophilic to hydrophobic organosilicon structures on the surface activity and biological activity of macromolecules was studied, together with the effect on these activities of the macromolecules’ molecular weight and chemical structure. In particular, the critical micelle concentrations were determined, the effect of the structure of the polymers on their wetting with aqueous solutions on glass and parafilm was described, and the aggregation stability of emulsions was studied. Finally, the effect of the polymer structures on their antifungal activity and seed germination stimulation was examined.

Controlled Silanization: High Molecular Regularity of Functional Thiol Groups on Siloxane Coatings

A comparative study on deposition and molecular regularity of two organosilanes, i.e., commercially available (3-mercaptopropyl)trimethoxysilane (MPTMS) and newly developed mercaptopropylsilatrane (MPS), was conducted in this work. MPTMS and MPS were applied to modify silicon surfaces to characterize their deposition kinetics, surface morphology, thickness, and elemental composition and the reactivity of thiol end groups based on gold-thiol and thiol-ene chemistries. MPS possesses a tricyclic caged structure and a transannular N → Si dative bond, making it chemically stable and controllable to avoid fast hydrolysis and aggregation in solution. The results indicate that MPS allows faster deposition and better formation of thin and homogeneous films than MPTMS. More importantly, the functional thiol groups on MPS coatings enable immobilization of a large amount of gold nanoparticles and effective thiol-ene photopolymerization with zwitterionic sulfobetaine acrylamide. Postmodification on silanized surfaces with MPS endows excellent plasmonic and antifouling properties, potentially leading to valuable applications to biosensing and biomaterials. The work demonstrated the feasibility and applicability of the functional silatrane molecule for surface silanization in a controlled manner.

Soft Polymeric Matrix as a Macroscopic Cage for Magnetically Modulating Reversible Nanoscale Ligand Presentation

A physical, noninvasive, and reversible means of controlling the nanoscale presentation of bioactive ligands is highly desirable for regulating and investigating the time-dependent responses of cells, including stem cells. Herein we report a magnetically actuated dynamic cell culture platform consisting of a soft hydrogel substrate conjugated with RGD-bearing magnetic nanoparticle (RGD-MNP). The downward/upward magnetic attraction conceals/promotes the presentation of the RGD-MNP in/on the soft hydrogel matrix, thereby inhibiting/enhancing the cell adhesion and mechanosensing-dependent differentiation. Meanwhile, the lateral magnetic attraction promotes the unidirectional migration of cells in the opposite direction on the hydrogel. Furthermore, cyclic switching between the "Exposed" and "Hidden" conditions induces the repeated cycles of differentiation/dedifferentiation of hMSCs which significantly enhances the differentiation potential of hMSCs. Our design approach capitalizes on the bulk biomaterial matrix as the macroscopic caging structure to enable dynamic regulation of cell-matrix interactions reversibly, which is hard to achieve by using conventional cell culture systems.

Design, Synthesis, Investigation, and Application of a Macromolecule Photoswitch

Azobenzene (AZO) has attracted increasing interest due to its reversible structural change upon a light stimulus. However, poor fatigue durability and the photobleaching phenomenon restricts its further application. Herein, the AZO domain as a pendent group, was incorporated into copolymers, which was synthesized by radical copolymerization in the research. Structure-properties of synthesized copolymer can be adjusted by monomer ratios. Emphatically, responsive properties of copolymer in different solutions were investigated. In the DMSO solution, copolymer exhibited effective structural change, stable rapid responsive time (1 min) upon UV light at room temperature, stable relative acceptable recovery time (100 min) upon white light at room temperature, and good fatigue resistance property. In an aqueous solution, even more controllable responsive properties and fatigue resistance properties for copolymer were verified by results. More pervasively, the recovery process could be controlled by light density and temperature. In order to clarify reasons for the difference between the AZO molecule and the AZO domain of copolymer, energy barrier or interactions between single atoms or even structural units was calculated using the density functional theory (DFT). Furthermore, the status of copolymer was characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Finally, copolymer was further functionalized with bioactive protein (concanavalin, ConA) to reduce the cytotoxicity of the AZO molecule.

Controlled Silanization Using Functional Silatrane for Thin and Homogeneous Antifouling Coatings

Organosilicons for surface modification are gaining prominence because of their easy and rapid preparation, high availability, and effective modification for varying interfacial properties. However, their implementation has been humbled by poor control of the packing density, thickness, and molecular structures due to the uncontrollable hydrolysis and condensation. This study reports for the first time new functional silatrane chemistry for the precision deposition of a thin and homogeneous zwitterionic coating. Sulfobetaine silatrane (SBSiT) has a tricyclic caged structure and a transannular N → Si dative bond, which shows excellent chemical stability in the presence of water and an acid-modulated hydrolysis characteristic. Results from X-ray photoelectron spectroscopy indicate the progressive deposition of SBSiT on a silicon surface. Characterization using atomic force microscopy and ellipsometry shows the uniform and thin SBSiT films on silicon surfaces. The superior antifouling properties of SBSiT coatings were demonstrated by resisting bacterial and protein adsorption. More importantly, the stable and complete formation of the SBSiT coatings allows an accurate interpretation of the interfacial phenomena for sensing and nanomaterial applications.

Selective mercury ion recognition using a methyl red (MR) based silatrane sensor

A methyl red based silatrane (MR-APS) sensor has been synthesized and applied for Hg²⁺ ion recognition by UV-Visible spectrophotometery.