Dye-loaded Zeolite Research Articles

Selective detection of α4β1 integrin (VLA-4)-expressing cells using peptide-functionalized nanostructured materials mimicking endothelial surfaces adjacent to inflammatory sites.

Persistent accumulation of immune cells mediated by α4β1 integrin (VLA-4) is a hallmark of the inflammatory diseases and of chronic inflammation observed in the affected tissues of autoimmune diseases. Aiming at exploring new methods for monitoring the course of the inflammatory processes, we designed the first peptide-functionalized nanostructured devices capable to mimic the high-density multivalency binding between the α4β1 integrin-expressing cells and the ligands overexpressed on the endothelial surfaces, in the proximity of the sites of inflammation. Specifically, we describe the first examples of monolayers constituted by dye-loaded zeolite L crystals, coated with α4β1 integrin peptide ligands, and we analyze the adhesion of model Jurkat cells in comparison to non-α4β1 integrin-expressing cells. In particular, the peptidomimetic diphenylurea-Leu-Asp-Val-diamine allows significant and selective detection of α4β1 integrin-expressing Jurkat cells, after very rapid incubation time, supporting the possible implementation in a diagnostic device capable to detect the desired cells from biological fluids, obtainable from patients in a noninvasive way.

Assembly of linear chains consisting of alternating silica beads and zeolite L crystals by nitroxide exchange reactions

Mild surface nitroxide exchange reactions are applied to build up linear assemblies of dye-loaded zeolite L crystals using diradical linker moieties as connecting entities. In addition, the preparation of mixed hybrid chains consisting of alternating zeolite L crystals and silica beads by applying a similar methodology is reported.

Reuse of Spent Natural Zeolite for Methylene Blue Adsorption by Microwave Irradiation

Microwave heating was efficient and the regeneration time was shortened compared to conventional thermal heating. Experiments were conducted to demonstrate that spent zeolite can be regenerated for reuse by microwave irradiation. The spent zeolite tested was prepared from the aqueous solutions of methylene blue. The effects of microwave irradiation time, microwave power on the regeneration efficiency were presented. The results show that microwave irradiation time and microwave power played significant role on the regeneration efficiency. It was concluded that microwave irradiation may be effective method for dye-loaded zeolite reuse.

Self-organized patterns of microparticles in polymer films

A simple method to create self-organized patterns of microparticles in polymer films is demonstrated. Dye-loaded zeolite crystals are used as model microparticles, allowing convenient imaging of the patterns by fluorescence microscopy. The pattern formation can be interpreted within the general framework of the model of local self-activation and lateral inhibition. Two starting parameters, namely the polymer concentration and the wet film thickness, control the size and shape of the particle aggregates in the patterns, as well as their spacing. The size of the aggregates ranges from 50 to 340μm.

Dye-loaded zeolite L @silica core-shell composite functionalized with europium(III) complexes for dipicolinic acid detection

Novel core-shell composites have been developed by immobilization of non-luminescent europium(III) complexes onto the surface of silica shells that are coated on the surface of luminescent dye-loaded zeolite L nano-crystals. The obtained core-shell composites were used for the ratiometric detection of dipicolinic acid (DPA) molecules. The dyes located in the channels of the zeolite L host are protected from any interaction with the environment of the particles and therefore provide a stable reference signal which can eliminate the need for instrument-specific calibration curves for DPA quantification in an analyte.

Weak forces at work in dye-loaded zeolite materials: spectroscopic investigation on cation–sulfur interactions

The interaction between sulfur-containing chromophores and cationic species (K(+)) has been investigated in dye-loaded zeolite materials by means of photoluminescence spectroscopy. A red-shift in the emission spectra of the host-guest compounds (HGCs) has been detected and unambiguously connected to the close proximity between a conjugated moiety and nearby free charges, suggesting a specific role played by sulfur lone pair electrons. Quantum-chemical calculations on model compounds have been performed to support this hypothesis.

Multilevel Organization in Hybrid Thin Films for Optoelectronic Applications

In this work we report two simple approaches to prepare hybrid thin films displaying a high concentration of zeolite crystals that could be used as active layers in optoelectronic devices. In the first approach, in order to organize nanodimensional zeolite crystals of 40 nm diameter in an electroactive environment, we chemically modify their external surface and play on the hydrophilic/hydrophobic forces. We obtain inorganic nanocrystals that self-organize in honeycomb electroluminescent polymer structures obtained by breath figure formation. The different functionalizations of the zeolite surface result in different organizations inside the cavities of the polymeric structure. The second approach involving soft-litography techniques allows one to arrange single dye-loaded zeolite L crystals of 800 nm of length by mechanical loading into the nanocavities of a conjugated polymer. Both techniques result in the formation of thin hybrid films displaying three levels of organization: organization of the dye molecules inside the zeolite nanochannels, organization of the zeolite crystals inside the polymer cavities, and micro- or nanostructuration of the polymer.

Energy Transfer in Fluorescent Nanofibers Embedding Dye‐Loaded Zeolite L Crystals

Electroluminescent polymeric nanofibers embedding dye-loaded zeolite L crystals are prepared. By exciting the polymer nanofiber, the energy is transferred to the fluorescent dyes inside the zeolite L channels through a two-step Förster resonant energy transfer process. This study opens new perspectives in the field of low-cost fabrication technology of flexible nanoscale OLEDs.

Two‐Step Energy Transfer: Energy Transfer in Fluorescent Nanofibers Embedding Dye‐Loaded Zeolite L Crystals (Adv. Mater. 10–11/2009)

The inside cover displays a confocal image of electroluminescent polymeric nanofibers embedding dye-loaded zeolite L crystals obtained by electrospinning. Varun Vohra and co-workers show on p. 1146 that such nanofibers exhibit a two-step energy transfer (FRET) from the polymer to the dye molecule inside the zeolites. The stopcock molecule present at the channel entrances is the key to this two-step energy transfer.

Microcontainers with Fluorescent Anisotropic Zeolite L Cores and Isotropic Silica Shells

Multicolor fluorescent containers: A silica coating procedure has been devised for the preparation of multifluorescent dye-loaded zeolite L crystals with luminescent anisotropic cores and isotropic shells. The method comprises a combination of the polyelectrolyte layer-by-layer technique and Stöber synthesis (see scheme, TEM image, and fluorescence microscopy images).

Proton Activity Inside the Channels of Zeolite L

The proton activity inside the channels of zeolite L has been studied by investigating dye-loaded zeolite L crystals under different conditions, such as water content, nature of the counterions, and nature of the solvent. The discussion is made within the frame of three types of dye-loaded zeolite L systems, classified according to their ability to exchange matter (dyes, cations, solvent, and other small molecules) with the environment. The classification refers to dye-loaded zeolites. The term "closed" and "semi-open" characterize different possibilities of the channels to exchange small molecules, cations, and solvent molecules with the environment, but not dyes. The "open" systems also allow for dye exchange. UV-visible and fluorescence spectroscopy have been used to observe the proton activity inside the zeolite L channels. The influence of the proton activity on the luminescence of encapsulated dyes is discussed, special attention being given to luminescence quenching by excited-state protonation. Partially proton-exchanged zeolite L can be a superacid, whereas for the M-exchanged form (M: K(+), Li(+), Cs(+), Mg(2+), Ca(2+)) the pH ranges from about 2.5 to 3.5. For these last forms, the differences in pH are due to the acid-base reactions of the respective metal cations with water inside the zeolite. Finally, we describe an easy experimental procedure that can be used to tune the proton activity inside the zeolite L to a considerable extent.

Selfassembly of zeolite L crystals on biological self-cleaning surfaces

An interesting phenomenon was observed when the petals of different flowers were immersed into a suspension containing dye-loaded zeolite L crystals. The zeolites align into patterns which are distinct for each flower species. On the petal of a horned pansy, for example, they align into hexagons. Polarised fluorescence microscope images show that the zeolites, to a remarkable extent, are aligned along the hexagonal pattern. We have investigated this in detail and we found that the alignment observed on the flower petals is not due to topological forces. In places which exhibit self-cleaning properties, zeolites are not adsorbed. These observations are new and intriguing. Visualisation of surface patterns by means of optical microscopy methods, which are less destructive than other tools such as electron microscopy, are attractive and may also be applied to living organisms. The phenomenon may also contribute to the application of drugs at specific places, and we can learn from these observations how to pattern a surface in order to realise self-organisation of micro or nano objects.

Inside Front Cover: Hexagonal Network Organization of Dye-Loaded Zeolite L Crystals by Surface-Tension Driven Autoassembly (Adv. Funct. Mater. 17/2006)

The two-dimensional (2D) ordering of zeolite L crystals on polydimethylsiloxane is reported in the Full Paper by Yunus et al. on p. 2213. The highly fluorescent dye-loaded zeolite L crystals are organized into a 2D hexagonal network by surface-tension-driven autoassembly. The resulting film displays a hexagonal pattern of polarized fluorescence, reflecting the properties of the dye molecules in the parallel nanochannels of the zeolite crystals. Highly fluorescent dye-loaded zeolite L crystals, approximately 1.4 μm long and 650 nm in diameter, are organized in a hexagonal network by a surface-tension-driven autoassembly process. A polydimethylsiloxane (PDMS) film presenting a trigonal ordering of spherical protuberances, including a polystyrene (PS) hexagonal network occupying their interstices, is chosen as the platform for the assembly. The overall wettability and the difference in surface tension between PDMS and PS surfaces are found to offer good conditions for ordering micrometric dye-loaded zeolite L crystals in a 2D hexagonal network. The resulting film displays a regular hexagonal pattern of polarized fluorescence, reflecting the polarization properties of the dye molecules inserted in the parallel nanochannels of the zeolites.

Hexagonal Network Organization of Dye-Loaded Zeolite L Crystals by Surface-Tension Driven Autoassembly

Highly fluorescent dye-loaded zeolite L crystals, approximately 1.4 μm long and 650 nm in diameter, are organized in a hexagonal network by a surface-tension-driven autoassembly process. A polydimethylsiloxane (PDMS) film presenting a trigonal ordering of spherical protuberances, including a polystyrene (PS) hexagonal network occupying their interstices, is chosen as the platform for the assembly. The overall wettability and the difference in surface tension between PDMS and PS surfaces are found to offer good conditions for ordering micrometric dye-loaded zeolite L crystals in a 2D hexagonal network. The resulting film displays a regular hexagonal pattern of polarized fluorescence, reflecting the polarization properties of the dye molecules inserted in the parallel nanochannels of the zeolites.

Organisation and Solubilisation of Zeolite L Crystals

Zeolite L is a versatile host material for realising functional photonic antenna systems. Energy can be transferred within dye-loaded zeolite L crystals and means have been found to transport the energy from the crystal inside to the environment or vice versa. In order to direct the energy to a target, the organisation of the zeolite crystals with respect to the environment is an important issue. Some possibilities of modifying zeolite L crystals according to specific sample requirements are summarised. Zeolite L material with interesting optical properties can be obtained by controlling the interaction between the crystals and their environment.

Fluorescent Hydroxyflavone–Zeolite Nanoparticles: Ship‐in‐a‐Bottle Synthesis and Photophysical Properties

3-Hydroxyflavone (3-OHF) was incorporated in zeolite micropores by ship-in-a-bottle synthesis. This strategy consists of constructing the molecule by reaction of small precursors within the cavity. 3-OHF molecules exhibit excited-state intramolecular proton transfer (ESIPT) and a tautomeric equilibrium between the 3-OHF-excited structures N* and T*exists. This equilibrium is strongly affected by the protic nature and polarity of the surrounding medium. The textural and spectroscopic characterization of the dye-loaded zeolite colloids enabled the study of the correlation between the optical properties of the dye and the zeolite micropore environment.

Transport of Electronic Excitation Energy in Dye-Loaded Zeolite L

Zeolite L is an aluminosilicate with one-dimensional channels, having an opening diameter of 7.1 Å. This allows the incorporation of different, electronically non-interacting dye molecules to build an artificial photonic antenna system. The conditions within the channels are such that the dye molecules cannot glide past each other. Hence, a consecutive incorporation leads to crystals with different compartments, where the density of one kind of dye is dominant. The photophysical processes taking place on such dye-loaded zeolite L antenna systems can be studied either on single micrometer or submicrometer sized crystals, on crystals dispersed in a solvent, orcoated as thin layers on a support. The energy transfer process that occurs is of the Förster-type and its transfer rate can be tuned, e.g. by first incorporating the acceptor dyes, in a second step consecutively incorporating different amounts of spacer molecules and then in a third step adding the donor dyes. By selectively exciting the donor, energy transfer to the unexcited acceptor as a function of the amount of spacer molecules can be observed. To make a quantitative analysis, one has to take into consideration the situation at the phase boundaries of the particular compartments. This has been done by modeling the distribution of the dye molecules and empty sites within a zeolite crystal by means of a Monte Carlo simulation.

Injecting electronic excitation energy into an artificial antenna system through an Ru2+ complex.

The Ru2+ complex [Ru(bpy)2(bpy-ph4-Si(CH3)3)]2+ can be electrostatically bound to the negatively charged channel entrances of dye-loaded zeolite L crystals where it acts as a functional stopcock molecule. Impressive electronic triplet-singlet excitation energy transfer from the Ru2+ complex to the acceptor dye oxazine 1 (Ox1) located inside the channels can be observed when the donor molecule is selectively excited. Time-resolved luminescence experiments have been performed on the separate components and on the assembled donor-acceptor material. The luminescence lifetime of the Ru2+ complex attached to the zeolite is reduced by a factor of 30 when Ox1 acceptor molecules are present. The fluorescence decay of Ox1 incorporated in zeolite L is single exponential with a lifetime of 3 ns. The much longer lifetime in zeolite L than in solution is due to the fact, that the diethyl groups are sterically restricted when the dye is inside the host.

Evaluation of methylene blue incorporated in zeolite for construction of an optical humidity sensor

A novel dye incorporated into microporous material is introduced for optical humidity sensing. Methylene blue (MB) was encapsulated into the protonated mordenite zeolite (HMOR) via ion exchange reaction. The dye molecules are strongly retained in the channels of the zeolite and take part in the protonation/deprotonation reactions reversibly. The mechanism of the sensor is based on the protonation or deprotonation of the dye molecules which are associated with the desorption or adsorption of water molecules by the zeolite, respectively. The spectral changes due to different humidity levels are probed by diffuse reflectance spectroscopy. Discs prepared from 200 mg of the dye-loaded zeolite provide a thickness of ≈0.8 mm and show good characteristics for an optical humidity sensor. They showed a linear response range from 9 to 92% relative humidity ( r 2 > 0.99), and good stability and reversibility. The sensor operates at either of the two 650 or 745 nm bands but it exhibits a higher sensitivity for the measurements performed at 650 nm. The sensor demonstrates relatively fast response and recovery times about 2 min in the direction of adsorption and about 4 min in the direction of desorption of water.

Organic–Inorganic Composites as Photonic Antenna

A photonic antenna system is an organized multi-component arrangement in which several chromophoric molecular species absorb the incident light and channel the excitation energy to a common acceptor component. Photonic antenna materials, based on dye–zeolite L composites, collect excitation energy and transport it over large distances. Fine tuning of dye-loaded zeolite L photonic antenna materials in the size range of 30–3000 nm was realized. Stationary and time-resolved luminescence experiments on an ensemble and space and time resolved luminescence measurements on single crystal antenna materials have been carried out. Coupling of the photonic antenna information to an external device is in progress.