Surface functionalization of silica particles for their efficient fluorescence and stereo selective modification

Silanization of 3D-Printed Silica Fibers and Monoliths

Surface functionalization of complex three-dimensional (3D) porous architectures has not been widely investigated despite their potential in different application domains. In this work, silanization was performed in silica 3D-printed porous structures, and the homogeneity of functional groups within the architecture was investigated by comparing the extent of the functionalization in the walls and core of the monolith. A silica ink was used for direct ink writing (DIW) to shape fibers and monoliths with different architectures and stacking designs. The surfaces of the fibers and monoliths were functionalized with 3-aminopropyl(triethoxysilane) (APTES) using different reaction conditions. The nature of the functional groups on the surface and the presence of RSiO_1.5 bonds were identified by solid-state ¹³C-NMR, ²⁹Si-NMR, and by ξ-potential measurements. Elemental analysis was used to quantify the concentration of bonded APTES in the core and walls of the monolith. The availability and hydrolytic stability of the introduced amine group on fibers were evaluated using the adsorption of PdCl₄^2- ions within the pH range of 2-5. The study found that geometries with interfiber distances above 250 μm are homogeneously functionalized with amine groups. As the interfiber distance of the monolith decreases, a significantly lower density of amine groups is detected in the core of the monolith. The determination of the homogeneity of 3D-printed monoliths makes this work relevant as it provides the limits of functionalization carried out in stirred batch reactors for geometrically defined structures produced from a 3D-printing process.

Gelation of amphiphilic janus particles in an apolar medium

HYPOTHESIS

The anisotropic nature of colloidal particles results in orientation-dependent interactions that organize the particles into peculiar structures different from those formed by isotropic colloids. Particles with a hydrophilic hemisphere are expected to assemble in hydrophobic solvents due to the contribution of hydrophobic interactions as observed for molecular amphiphiles.

EXPERIMENTS

Asymmetrically decorated silica-based Janus particles are dispersed in an apolar solvent, chloroform, and their structure and dynamics are studied by light scattering and compared with computer simulations.

FINDINGS

Gelation of amphiphilic Janus particles with asymmetric surface decoration is observed in a hydrophobic medium. The influence of particle asymmetry on gel structure and dynamics is discussed. Unlike particles with long-range repulsive interactions in water, these systems rapidly form rather compact structures that are nevertheless more ramified than those made of isotropic hydrophobic particles. Comparison with computer simulations allows visualization of the gel and reveals a contribution of asymmetric short-range attractions and cross-term repulsions to the net effective interaction potential.

Polystyrene Microparticles with Convergently Grown Mesoporous Silica Shells as a Promising Tool for Multiplexed Bioanalytical Assays

Functional core/shell particles are highly sought after in analytical chemistry, especially in methods suitable for single-particle analysis such as flow cytometry because they allow for facile multiplexed detection of several analytes in a single run. Aiming to develop a powerful bead platform of which the core particle can be doped in a straightforward manner while the shell offers the highest possible sensitivity when functionalized with (bio)chemical binders, polystyrene particles were coated with different kinds of mesoporous silica shells in a convergent growth approach. Mesoporous shells allow us to obtain distinctly higher surface areas in comparison with conventional nonporous shells. While assessing the potential of narrow- as well as wide-pore silicas such as Mobil composition of matter no. 41 (MCM-41) and Santa Barbara amorphous material no. 15 (SBA-15), especially the synthesis of the latter shells that are much more suitable for biomolecule anchoring was optimized by altering the pH and both, the amount and type of the mediator salt. Our studies showed that the best performing material resulted from a synthesis using neutral conditions and MgSO₄ as an ionic mediator. The analytical potential of the particles was investigated in flow cytometric DNA assays after their respective functionalization for individual and multiplexed detection of short oligonucleotide strands. These experiments revealed that a two-step modification of the silica surface with amino silane and succinic anhydride prior to coupling of an amino-terminated capture DNA (c-DNA) strand is superior to coupling carboxylic acid-terminated c-DNA to aminated core/shell particles, yielding limits of detection (LOD) down to 5 pM for a hybridization assay, using labeled complementary single-stranded target DNA (t-DNA) 15mers. The potential of the use of the particles in multiplexed analysis was shown with the aid of dye-doped core particles carrying a respective SBA-15 shell. Characteristic genomic sequences of human papillomaviruses (HPV) were chosen as the t-DNA analytes here, since their high relevance as carcinogens and the high number of different pathogens is a relevant model case. The title particles showed a promising performance and allowed us to unequivocally detect the different high- and low-risk HPV types in a single experimental run.

Measurement of the capillary interaction force between Janus colloidal particles trapped at a flat air/water interface

The capillary interaction force between spherical Janus particles trapped at the air-water interface is measured using a time-sharing optical tweezer (bond number ≪ 1). One face of the particles is hydrophilic, and the other one, hydrophobic. Measured force goes from almost pure quadrupolar to almost pure hexapolar interaction due to the three-phase contact line corrugation. Measured force curves are modeled as a sum of power laws, Ar^-α + Br^-β + Cr^-γ, obtained from an expansion in capillary multipoles. The mean values for the exponents of particle pairs of 3 μm are 〈α〉 = 5.05 ± 0.12, 〈β〉 = 7.02 ± 0.03, and 〈γ〉 = 5.96 ± 0.03. For particles pairs of 5 μm, we find 〈α〉 = 5.02 ± 0.04, 〈β〉 = 6.94 ± 0.06, and 〈γ〉 = 5.80 ± 0.05. In both cases, A < 0, B < 0, and C > 0.

A novel cell-penetrating Janus nanoprobe for ratiometric fluorescence detection of pH in living cells

pH regulates the function of many organelles and plays a pivotal role in requiring multitud cellular behaviors. Compared with single fluorescent probes, ratio fluorescent probes have higher sensitivity and immunity to interference. Herein, a novel Janus ratio nanoprobe was developed for intracellular pH detection. Modified rhodamine B probe and fluorescein isothiocyanate (FITC) were individually encapsulated in the independent hemispheres of Janus microparticles fabricated via Pickering emulsion. Moreover, it exhibits a satasified ratiometric detection of pH compared to the previous core-shell structure and organic small molecule probe. Accordingly, the Janus nanoprobe possesses many important features as an attractive sensor, including high anti-jamming capability, excellent stability, good reversibility and low cytotoxicity. Variations of the two fluorescence intensities (Fgreen/Fred) resulted in a ratiometric pH fluorescent sensor, which can respond to wide range of pH values from 3 to 8. To be more specific, with a single excitation wavelength of 488 nm, there are dual emission bands centered at 538 nm and 590 nm. Also the Janus nanoprobe displays a excellent linear relationship in the physiologically relevant pH range of 4.0-6.0. Consequently, detecting of pH and imaging was successfully achieved in living cells, which provides a simple and reliable method for detecting intracelluar pH and other similar substances.

Binary colloidal crystals (BCCs): Interactions, fabrication, and applications

The organization of matter into hierarchical structures is a fundamental characteristic of functional materials and living organisms. Binary colloidal crystal (BCC) systems present a diversified range of nanotopographic structures where large and small colloidal particles simultaneously self-assemble into either 2D monolayer or 3D hierarchical crystal lattices. More importantly, understanding how BCCs form opens up the possibility to fabricate more complex systems such as ternary or quaternary colloidal crystals. Monolayer BCCs can also offer the possibility to achieve surface micro- and nano-topographies with heterogeneous chemistries, which can be challenging to achieve with other traditional fabrication tools. A number of fabrication methods have been reported that enable generation of BCC structures offering high accuracy in growth with controllable stoichiometries; however, it is still a challenge to make uniform BCC structures over large surface areas. Therefore, fully understand the mechanism of binary colloidal self-assembly is crucial and new/combinational methods are needed. In this review, we summarize the recent advances in BCC fabrication using particles made of different materials, shapes, and dispersion medium. Depending on the potential application, the degree of order and efficiency of crystal formation has to be determined in order to induce variability in the intended lattice structures. The mechanisms involved in the formation of highly ordered lattice structures from binary colloidal suspensions and applications are discussed. The generation of BCCs can be controlled by manipulation of their extensive phase behavior, which facilitates a wide range potential applications in the fields of both material and biointerfacial sciences including photonics, biosensors, chromatography, antifouling surfaces, biomedical devices, and cell culture tools.

Bilayers of Janus and homogeneous particle mixtures trapped at an air/water interface

We study mixtures of amphiphilic Janus and homogeneous hydrophobic particles trapped at an air/water interface. In contrast to an expected monolayer formation, bilayers of colloidal particles are produced. Despite their strong interfacial adsorption, Janus particles form the upper layer. They are not placed on top of the other particles but rather shifted about one-third of the particle diameter. To understand the mechanism of bilayer formation, particle behaviour at the surface and in the bulk of the spreading solvent is considered. The vertical shift and the bilayer formation are assisted by the momentous formation of two interfaces during spreading.

Synthesis of silica nanoparticles using biomimetic mineralization with polyallylamine hydrochloride

To synthesize silica particles under mild conditions, we proposed a biomimetic synthesis method. The synthesis process was carried out based on a biphasic sol-gel synthesis method using TEOS (tetraethyl orthosilicate) as a silica source and PAH (polyallylamine) as a substitute for proteins of marine microorganisms for biosilicification. The function and activity of the PAH, used as a replacement for bioactive substances, were confirmed through comparisons between control experiments and designed experiments. The PAH exhibited the ability accelerate condensation with hydrolyzed TEOS in aqueous solutions. The PAH also exhibited high condensation activity in acidic and neutral conditions to produce silica particles. Moreover, PAH also created the nuclei of the silica particles, and the number of nuclei could be controlled by the concentration of PAH. In addition to exhibiting these unique capabilities, PAH did not generate any complexes or composites with the silica species. Depending on the synthesis conditions, the synthesized silica particles exhibited various shapes, such as sponge-like, self-assembled, irregular spherical and completely spherical shapes. The sizes of the primary particles were diverse, with a range from 10nm to 50nm. In particular, by adjusting the PAH concentration, it was possible to obtain nearly perfect spherical-shaped silica nanoparticles with uniform sizes, which has rarely been reported. Above all, using this paper, we can get closer to understanding the principles of silica formation using PAH as a replacement for the bioactive proteins of microorganisms.