Biomolecular screening with novel organosilica microspheres

Micron-Sized Thiol-Functional Polysilsesquioxane Microspheres with Open and Interconnected Macropores: Effects of the System Composition on the Porous Structure and Particle Size of the Microspheres

Control of the porous structure and particle size is essential for improving the properties of polysilsesquioxane (PSQ) microspheres. Herein, using the strategy combining inverse suspension polymerization, two-step sol-gel- and polymerization-induced phase separation processes, micron-sized thiol-containing macroporous PSQ (TMPSQ) microspheres with controllable morphologies, adjustable particle diameters (4.9-17.3 μm), and pore sizes (40-3774 nm) were prepared. The morphology and size of the TMPSQ microspheres were characterized by SEM. The mercury intrusion method was employed to analyze the porous structure of the microspheres. The effects of the composition of the sol-gel disperse phase, the mass ratio of the sol-gel disperse phase to the oil continuous phase (WRW/O), and the Span 80 mass content in the oil continuous phase on the morphology, particle diameter and pore size of the TMPSQ microspheres were investigated. Results indicated that the composition of the sol-gel disperse phase determines the morphology and porous structure of the microspheres, and WRW/O and Span 80 content have remarkable impacts on the morphology and particle size of the microspheres. This study is beneficial to the design and fabrication of functional PSQ microspheres with desired properties and promising application prospects.

Synthetic strategies for nonporous organosilica nanoparticles from organosilanes

Organosilica nanoparticles refer to silica nanoparticles containing carbon along with organic or functional groups and can be divided into mesoporous organosilica nanoparticles and nonporous organosilica nanoparticles. During the past few decades, considerable efforts have been devoted to the development of organosilica nanoparticles directly from organosilanes. However, most of the reports have focused on mesoporous organosilica nanoparticles, while relatively few are concerned with nonporous organosilica nanoparticles. The synthesis of nonporous organosilica nanoparticles typically involves (i) self-condensation of an organosilane as the single source, (ii) co-condensation of two or more types of organosilanes, (iii) co-condensation of tetraalkoxysilane and an organosilane, and (iv) spontaneous emulsification and the subsequent radical polymerization of 3-(trimethoxysilyl)propyl methacrylate (TPM). This article aims to provide a review on the synthetic strategies of this important type of colloidal particle, followed by a brief discussion on their applications and future perspectives.

l-Arginine-Catalyzed Synthesis of Nanometric Organosilica Particles through a Waterborne Sol-Gel Process and Their Porous Structure Analysis

We report an efficient and easy-to-implement waterborne sol-gel process for the synthesis of nanometric organosilica particles. In this process, tetraethyl orthosilicate (TEOS) and 3-(methacryloxy)propyl trimethoxy silane (γ-MPS), employed as silica sources, were heterogeneously delivered in an aqueous solution of l-arginine, a basic amino acid used as a catalyst, from a top organic layer. Co-condensation of TEOS with γ-MPS led to the formation of organosilica particles with diameters between 30 and 230 nm when increasing the γ-MPS content from 0 to 10.1 mol % in the silica source. Nitrogen sorption analyses confirmed the microporous nature of the obtained particles after calcination. The Brunauer-Emmett-Teller (BET) surface areas increased from 27 (before calcination) to 684 m² g^-1 (after calcination) for the organosilica particles containing 10.1 mol % of γ-MPS. Fourier transform infrared spectroscopy and ²⁹Si NMR were employed to analyze the chemical structure of the organosilica spheres and provide insight into the mechanism of particle formation. In the second part, hybrid organosilica particles with a core-shell morphology were synthesized through the combination of Pickering emulsion and the sol-gel process. γ-MPS emulsion droplets stabilized by tiny silica particles (formed in a separate step) were first generated and used as seeds to grow a silica shell on their surface through TEOS addition from the top organic layer. Transmission electron microscopy and pore size analyses of the resulting particles after calcination revealed a unique dual-porosity structure with a mesoporous inner core and a micro/mesoporous silica shell with ink-bottle-type pores.

Formation mechanism and size control in one-pot synthesis of mercapto-silica colloidal spheres

Mercapto-silica spheres with controllable size from ∼150 nm to ∼3.5 μm and narrow size distribution have been prepared in water using a one-pot synthesis, in which 3-mercaptopropyltrimethoxysilane (MPS) was used as the sole silica source and ammonia as the base catalyst. The hydrolysis of MPS at the early stage of the reaction produces amphiphilic silicate species which initiate the self-emulsification of the system and lead to the formation of oil-in-water emulsion droplets. Further hydrolysis and condensation promote the nucleation and growth of the mercapto-silica spheres inside the emulsion droplets. These mercapto-silica spheres are both structurally and functionally different from typical silica particles prepared from silicon alkoxides. Understanding the formation mechanism allows systematic tuning of the size of mercapto-silica spheres in a wide range by changing the amount of precursor, the concentration of ammonia, the amount of additional surfactants, and the reaction time. We find that Ostwald ripening may occur quickly if the spheres are kept in the reaction solution, resulting in significant broadening of the particle size distribution. In order to obtain uniform and stable samples, it is important to quench the growth of the mercapto-silica spheres by separating them from the original reaction mixture and then storing them in solvents that can prevent further ripening.

Effect of poly(ethylene glycol) (PEG) spacers on the conformational properties of small peptides: a molecular dynamics study

Poly(ethylene glycol) (PEG) is used as an inert spacer in a wide range of biotechnological applications such as to display peptides and proteins on surfaces for diagnostic purposes. In such applications it is critical that the peptide is accessible to solvent and that the PEG does not affect the conformational properties of the peptide to which it is attached. Using molecular dynamics (MD) simulation techniques, we have investigated the influence of a commonly used PEG spacer on the conformation properties of a series of five peptides with differing physical-chemical properties (YGSLPQ, VFVVFV, GSGGSG, EEGEEG, and KKGKKG). The conformational properties of the peptides were compared (a) free in solution, (b) attached to a PEG-11 spacer in solution, and (c) constrained to a two-dimensional lattice via a (PEG-11)(3) spacer, mimicking a peptide displayed on a surface as used in microarray techniques. The simulations suggest that the PEG spacer has little effect on the conformational properties of small neutral peptides but has a significant effect on the conformational properties of small highly charged peptides. When constrained to a two-dimensional surface at peptide densities similar to those used experimentally, it was found that the peptides, in particular the polar and nonpolar peptides, aggregated strongly. The peptides also partitioned into the PEG layer. Potentially, this means that at high packing densities only a small fraction of the peptide attached to the surface would in fact be accessible to a potential interaction partner.

Development of a multiplexed bead-based assay for detection of DNA methylation in cancer-related genes

Herein we report a method for the detection of methylated CpG dinucleotides located within CpG islands in genomic DNA using multiplexed bead-based assays and standard flow cytometry instrumentation. Four CpG "clusters" were identified in the TFPI2 and SPARC CpG islands whose methylation status was highly correlated with the incidence of invasive cervical cancer in our previous studies. Eight probes in total were designed for both the methylated and unmethylated forms of each cluster and attached to different fluorescently-encoded organosilica bead sets. Probe design was investigated by changing either the length of probes whilst keeping the melting temperature constant, or changing the melting temperature and keeping the probe length constant. Asymmetric polymerase chain reaction (PCR) methods designed without methylation-specific primers were used to prepare fluorescently-labelled targets based on bisulfite-converted genomic DNA. After investigating the specificity of the probes in a model system using fluorescently-labelled synthetic oligonucleotides, cancer cell-line DNA was analysed and the constant length probe design facilitated the correct genotyping of all clusters with respect to negative controls.

Flow cytometric detection of proteolysis in peptide libraries synthesised on optically encoded supports

The concept of optically encoding particles for solid phase organic synthesis has existed in the literature for several years. However, there remains a significant challenge to producing particles that are capable of withstanding harsh solvents and reagents whilst maintaining the integrity and range of the optical encoding. In this study, a new generation of fluorescently encoded support particles was used for both solid phase peptide synthesis and on-particle analysis of proteolysis in a multiplexed, flow cytometric assay. The success of the assay was demonstrated through the use of a model protease, trypsin. Our results show that the use of solid supports with high peptide yield, high swellability in water and high penetration of the enzyme into the interior of the particle is not absolutely necessary for proteolysis assays.

Detection of unlabeled oligonucleotide targets using whispering gallery modes in single, fluorescent microspheres

The development of an inexpensive, highly sensitive, whispering gallery mode (WGM) based biosensing system is demonstrated. The system comprises a silica microsphere functionalized with a fluorophore and a dense monolayer of single-strand oligonucleotides. The adsorption of the complementary strand causes spectral shifts in the emission spectrum of the microsphere that can be registered using a conventional optical microscope and CCD detector. The system is capable of detecting low-abundance, unlabeled-oligonucleotide targets. The spectral shifts can be used to monitor both the hybridization kinetics and the denaturation of the double-strand DNA at elevated temperatures. The hybridization appears to be completely reversible. Complementary oligonucleotide probes more than 30 bases in length are most readily detected while a complete assay takes only a few minutes.

Refractometry of organosilica microspheres

The refractive index of novel organosilica (nano/micro) material is determined using two methods. The first method is based on analysis of optical extinction efficiency of organosilica beads versus wavelength, which is obtained by a standard laboratory spectrometer. The second method relies on the measurable trapping potential of these beads in the focused light beam (laser tweezers). Polystyrene beads were used to test these methods, and the determined dispersion curves of refractive-index values have been found accurate. The refractive index of organosilica beads has been determined to range from 1.60 to 1.51 over the wavelength range of 300-1100 nm.

Fluorescent organosilica micro- and nanoparticles with controllable size

This paper reports on the synthesis of uniformly dye-doped organosilica particles with narrow size distribution. The particle size can be controlled from tenths of nanometers up to several micrometers, whilst still maintaining monodispersity. Microparticles were observed to swell in various solvents up to approximately 2.5 times their original volume, suggesting the presence of a gel-like internal structure. As shown by confocal microscopy, this morphological control of particle swelling has important implications for the encoding of the nano/micro particles with organic dyes, such as rhodamine B isothiocyanate. Swelling allows the dye to penetrate the organosilica matrix and produce uniformly dye-doped nano- and microparticles. Finally, we suggest a coagulation model for the particle formation which significantly differs from conventional Stöber synthesis.

Optically Encoded Particles and Their Applications in Multiplexed Biomedical Assays

In the future, the rapid discovery of new cures, vaccines, and diagnostics for common diseases will depend on the ability of biomedical researchers to investigate complex mixtures of proteins or DNA. The need to measure the abundance of these entities, together with their level of interaction, has driven the development of new research tools that enable simultaneous analysis of multiple analytes (multiplexing). Optically encoded particles are emerging as the multiplexing tools of choice, especially for clinical research. In this Review, an overview of various new optical encoding methods will be presented, together with important biomedical applications in which particle-based assays are currently being used.

Better chemistry through ceramics: the physical bases of the outstanding chemistry of ORMOSIL

Twenty years after their invention, sol-gel organically modified silicates (ORMOSIL) are finding a number of impressive applications that range from efficient deliver of genes into mouse brains to self-ordered helices of interest to fields as diverse as optics, catalysis, molecular recognition, and chromatography. The physical bases of this mulifaceted chemistry, therefore, are of immense importance to scientists working toward new applications such as photovoltaics and catalysis that are crucially important in making sustainable global development. The purpose of this article is to provide a general picture of ORMOSIL's physical chemistry that will be useful in the creative development of new materials capable to solve a number of relevant open problems.