Luminescence of Tris(2,2‘-bipyridine)ruthenium(II) Cations ([Ru(bpy)3]2+) Adsorbed in Mesoporous Silicas Modified with Sulfonated Phenethyl Group

Multi-stimuli Photo and Redox-active Nanostructured Mesoporous Silica Films on Transparent Electrodes

Silica matrices hosting transition metal guest complexes may offer remarkable platforms for the development of advanced functional devices. We report here the elaboration of ordered and vertically oriented mesoporous silica thin films containing covalently attached tris(bipyridine)iron derivatives using a combination of electrochemically assisted self-assembly (EASA) method and Huisgen cycloaddition reaction. Such a versatile approach is primarily used to bind nitrogen-based chelating ligands such as (4-[(2-propyn-1-yloxy)]4'-methyl-2,2'-bypiridine, bpy') inside the nanochannels. Further derivatization of the bpy'-functionalized silica thin films is then achieved via a subsequent in-situ complexation step to generate [Fe(bpy)₂ (bpy')]²⁺ inside the mesopore channels. After giving spectroscopic evidences for the presence of such complexes in the functionalized film, electrochemistry is used to transform the confined diamagnetic (S=0) F e L S b p y 2 b p y ' 2 + species to paramagnetic (S=1/2) oxidized F e L S b p y 2 b p y ' 3 + species in a reversible way, while blue light irradiation (λ=470 nm) enables populating the short-lived paramagnetic (S=2) F e H S b p y 2 b p y ' 2 + excited state. [Fe(bpy)₂ (bpy')]²⁺ -functionalized ordered films are therefore both electro- and photo-active through the manipulation of the oxidation state and spin state of the confined complexes, paving the way for their integration in optoelectronic devices.

Ru(bpy)32+ -Loaded Mesoporous Silica Nanoparticles as Electrochemiluminescent Probes of a Lateral Flow Immunosensor for Highly Sensitive and Quantitative Detection of Troponin I

The lateral flow immunosensor (LFI) is a widely used diagnostic tool for biomarker detection; however, its sensitivity is often insufficient for analyzing targets at low concentrations. Here, an electrochemiluminescent LFI (ECL-LFI) is developed for highly sensitive detection of troponin I (TnI) using Ru(bpy)₃²⁺ -loaded mesoporous silica nanoparticles (RMSNs). A large amount of Ru(bpy)₃²⁺ is successfully loaded into the mesoporous silica nanoparticles with excellent loading capacity and shows strong ECL signals in reaction to tripropylamine. Antibody-immobilized RMSNs are applied to detect TnI by fluorescence and ECL analysis after a sandwich immunoassay on the ECL-LFI strip. The ECL-LFI enables the highly sensitive detection of TnI-spiked human serum within 20 min at femtomolar levels (≈0.81 pg mL^-1 ) and with a wide dynamic range (0.001-100 ng mL^-1 ), significantly outperforming conventional fluorescence detection (>3 orders of magnitude). Furthermore, TnI concentrations in 35 clinical serum samples across a low range (0.01-48.31 ng mL^-1 ) are successfully quantified with an excellent linear correlation (R²  = 0.9915) using a clinical immunoassay analyzer. These results demonstrate the efficacy of this system as a high-performance sensing strategy capable of capitalizing on future point-of-care testing markets for biomolecule detection.

Spatial distribution of organic functional groups supported on mesoporous silica nanoparticles (2): a study by 1H triple-quantum fast-MAS solid-state NMR

The distribution of organic functional groups attached to the surface of mesoporous silica nanoparticles (MSNs) via co-condensation was scrutinized using 1D and 2D 1H solid-state NMR, including the triple-quantum/single-quantum (TQ/SQ) homonuclear correlation technique. The excellent sensitivity of 1H NMR and high resolution provided by fast magic angle spinning (MAS) allowed us to study surfaces with very low concentrations of aminopropyl functional groups. The sequential process, in which the injection of tetraethyl orthosilicate (TEOS) into the aqueous mother liquor was followed by dropwise addition of the organosilane precursor, resulted in deployment of organic groups on the surface, which were highly clustered even in a sample with a very low loading of ∼0.1 mmol g-1. The underlying mechanism responsible for clustering could involve fast aggregation of the aminopropyltrimethoxysilane (APTMS) precursor within the liquid phase, and/or co-condensation of the silica-bound molecules. Understanding the deposition process and the resulting topology of surface functionalities with atomic-scale resolution, can help to develop novel approaches to the synthesis of complex inorganic-organic hybrid materials.

Distribution Control-Oriented Intercalation of a Cationic Metal Complex into Layered Silicates Modified with Organosulfonic-Acid Moieties

A layered sodium silicate, octosilicate (Na₂Si₈O₁₇· nH₂O), was modified with an organosulfonic-acid moiety (sulfonated propyl (SPr) group, sulfonated phenethyl (SPhE) group, or sulfonated p-trifluoromethylphenyl (STFPh) group) for use as a host material to accommodate a cationic guest, tris(2,2'-bipyridine)ruthenium(II) cation ([Ru(bpy)₃]²⁺). The organosulfonic-acid moiety was bound to the silicate layer via a reaction of an alkylammonium-exchanged octosilicate with a silane coupling agent, and subsequent treatment (oxidation or sulfonation) of the bound organosilyl groups; the surface densities of the organosulfonic-acid moiety were varied by controlling the added amount of silane coupling agents. Adsorption of [Ru(bpy)₃]²⁺ onto surface-modified octosilicates was conducted to find that some surface-modified octosilicates successfully adsorbed [Ru(bpy)₃]²⁺ in the interlayer space (intercalation), while other surface-modified octosiliates did not. In addition, the UV-vis absorption and the luminescence indicate that intercalated [Ru(bpy)₃]²⁺ diffused in the interlayer and that the distribution of the time-averaged location varied depending on the kind and amount of the organosulfonic-acid moieties. Thus, the kind and surface density of the organosulfonic-acid moiety, which correlates to the interactions between the group and the guest species, the volume of free nanospace for adsorption and motion of guests, and the swelling properties, are the key factors not only for the intercalation ability but also for the dynamics of the guest in the interlayer space.

Spatial distribution of organic functional groups supported on mesoporous silica nanoparticles: a study by conventional and DNP-enhanced 29Si solid-state NMR

DNP-enhanced solid-state NMR determined spatial distributions of organic functionalities attached to surfaces of mesoporous silica nanoparticles via co-condensation and grafting.

Host-guest chemistry of mesoporous silicas: precise design of location, density and orientation of molecular guests in mesopores

Mesoporous solids, which were prepared from inorganic-surfactant mesostructured materials, have been investigated due to their very large surface area and high porosity, pore size uniformity and variation, periodic pore arrangement and possible pore surface modification. Morphosyntheses from macroscopic morphologies such as bulk monolith and films, to nanoscopic ones, nanoparticles and their stable suspension, make mesoporous materials more attractive for applications and detailed characterization. This class of materials has been studied for such applications as adsorbents and catalysts, and later on, for optical, electronic, environmental and bio-related ones. This review summarizes the studies on the chemistry of mesoporous silica and functional guest species (host-guest chemistry) to highlight the present status and future applications of the host-guest hybrids.

The protective effect of the mesoporous host on the photo oxidation of fluorescent guests: a UV-Vis spectroscopy study

The inclusion of fluorescent molecules within the pores of an inorganic host system ensures an outstanding improvement of stability against photo oxidation under different experimental conditions.

Effects of a nanoscale silica matrix on the fluorescence quantum yield of encapsulated dye molecules

The effects that nanometer-sized matrices have on the properties of molecules encapsulated within the nanomatrix are not fully understood. In this work, dye-doped silica nanoparticles were employed as a model for studying the effects of a nanomatrix on the fluorescence quantum yield of encapsulated dye molecules. Two types of dye molecules were selected based on their different responses to the surrounding media. Several factors that affect fluorescence quantum yields were investigated, including aggregation of dye molecules, diffusion of atmospheric oxygen, concentration of dye molecules, and size of the nanomatrix. The results showed that the silica nanomatrix has a varied effect on the fluorescence quantum yield of encapsulated dye molecules, including enhancement, quenching and insignificant changes. Both the properties of dye molecules and the conditions of the nanomatrix played important roles in these effects. Finally, a physical model was proposed to explain the varied nanomatrix effects on the fluorescence quantum yield of encapsulated dye molecules.

Attachment of the sulfonic acid group in the interlayer space of a layered alkali silicate, octosilicate

The surface modification of a layered alkali silicate, octosilicate (Na(2)Si(8)O(17)·nH2O), with a sulfonic acid group was conducted. The sulfonic acid group was attached to the silicate layer by the reaction of octosilicate with phenethyl(dichloro)methylsilane and the subsequent sulfonation of the attached phenethyl groups with chlorosulfonic acid. The modified octosilicate is a solid acid as indicated by the intercalation of dodecylamine. A systematic expansion of the interlayer space was observed by the ion exchange with a series of alkyltrimethylammonium ions to show the variation of the layer charge density.

Effective and selective bisphenol A synthesis on a layered silicate with spatially arranged sulfonic acid

The silylated derivatives of a layered alkali silicate, magadiite, modified with propylsulfonic or arylsulfonic acid were synthesized and used as catalysts for an acid-catalyzed condensation of phenol with acetone. The propylsulfonated magadiites with a different amount of the attached silyl group were synthesized by the silylation of the dodecylammonium-exchanged magadiite with the tuned amount of 3-(mercaptopropyl)trimethoxysilane and the subsequent oxidation of the attached thiol to sulfonic acid. The arylsulfonated magadiite was synthesized by the silylation of the dodecylammonium-exchanged magadiite with 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane and the subsequent hydrolysis of the attached sulfonyl chloride to sulfonic acid. The X-ray diffraction (XRD) patterns and elemental mappings of the products, and the photoluminescent spectra of the Eu(3+)-exchanged products suggested that propylsulfonic or arylsulfonic acid was homogeneously distributed in the interlayer space. When all the sulfonated materials were used as an acid catalyst for condensation between phenol and acetone, p,p' bisphenol A selectively formed over the o,p' isomer, and higher yield and selectivity were attained on the catalysts with larger amount of the attached sulfonic acid. When the interlayer space of the propylsulfonated magadiite was expanded by the co-attachment of octadecylsilyl group, lower selectivity was obtained. The arylsulfonated magadiite showed considerably higher p,p' bisphenol A yield than the propylsulfonated magadiites.

Swelling in water of a layered alkali silicate, octosilicate, modified with a sulfonic Acid group

A layered alkali silicate, octosilicate (Na(2)Si(8)O(17) x nH(2)O), was functionalized with sulfonic acid to impart swelling ability in water. To immobilize the sulfonic acid group on octosilicate, (3-mercaptopropyl)trimethoxysilane was attached in the interlayer space and subsequently oxidized. Surface coverage with the sulfonic acid group (0.7, 1.3, and 1.7 groups per Si(8)O(17)) was controlled by changing the added amount of the silane coupling reagent (0.7, 1.3, and 2.0 groups per Si(8)O(17)). The sulfonated octosilicates hydrated to expand the interlayer space, where the degree of expansion varied with the surface coverage of sulfonic acid. For the sulfonated octosilicate with the lowest surface coverage (0.7 group per Si(8)O(17)), the remaining interlayer silanol group was efficiently grafted with the trimethylsilyl group to expand the interlayer space further upon hydration. The effect of the electrolyte concentration on the hydration of the sulfonated octosilicates was investigated to find that with the increase in NaCl concentration the basal spacing decreased. The sulfonated and trimethylsilylated octosilicates were dispersed in water to form colloidal suspensions with varied transparency.