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

An Unprecedented Metal Distribution in Silica Nanoparticles Determined by Single-Particle Inductively Coupled Plasma Mass Spectrometry

Metal-containing nanoparticles are now common in applications ranging from catalysts to biomarkers. However, little research has focused on per-particle metal content in multicomponent nanoparticles. In this work, we used single-particle inductively coupled plasma mass spectrometry (ICP-MS) to determine the per-particle metal content of silica nanoparticles doped with tris(2,2'-bipyridyl)ruthenium(II). Monodispersed silica nanoparticles with varied Ru doping levels were prepared using a water-in-oil microemulsion method. These nanoparticles were characterized using common bulk-sample methods such as absorbance spectroscopy and conventional ICP-MS, and also with single-particle ICP-MS. The results showed that averaged concentrations of metal dopant measured per-particle by single-particle ICP-MS were consistent with the bulk-sample methods over a wide range of dopant levels. However, the per-particle amount of metal varied greatly and did not adhere to the usual Gaussian distribution encountered with one-component nanoparticles, such as gold or silver. Instead, the amount of metal dopant per silica particle showed an unexpected geometric distribution regardless of the prepared doping levels. The results indicate that an unusual metal dispersal mechanism is taking place during the microemulsion synthesis, and they challenge a common assumption that doped silica nanoparticles have the same metal content as the average measured by bulk-sample methods.

Graphene Oxide/Cholesterol-Substituted Zinc Phthalocyanine Composites with Enhanced Photodynamic Therapy Properties

In the present work, cholesterol (Chol)-substituted zinc phthalocyanine (Chol-ZnPc) and its composite with graphene oxide (GO) were prepared for photodynamic therapy (PDT) applications. Briefly, Chol-substituted phthalonitrile (Chol-phthalonitrile) was synthesized first through the substitution of Chol to the phthalonitrile group over the oxygen bridge. Then, Chol-ZnPc was synthesized by a tetramerization reaction of Chol-phthalonitrile with ZnCl2 in a basic medium. Following this, GO was introduced to Chol-ZnPc, and the successful preparation of the samples was verified through FT-IR, UV-Vis, 1H-NMR, MALDI-TOF MS, SEM, and elemental analysis. Regarding PDT properties, we report that Chol-ZnPc exhibited a singlet oxygen quantum yield (Φ∆) of 0.54, which is slightly lower than unsubstituted ZnPc. Upon introduction of GO, the GO/Chol-ZnPc composite exhibited a higher Φ∆, about 0.78, than that of unsubstituted ZnPc. Moreover, this enhancement was realized with a simultaneous improvement in fluorescence quantum yield (ΦF) to 0.36. In addition, DPPH results suggest low antioxidant activity in the composite despite the presence of GO. Overall, GO/Chol-ZnPc might provide combined benefits for PDT, particularly in terms of image guidance and singlet oxygen generation.

A plasmonic fluorescent ratiometric temperature sensor for self-limiting hyperthermic applications utilizing FRET enhancement in the plasmonic field

Nanoparticle mediated photo-induced hyperthermia holds much promise as a therapeutic solution for the management of diseases like cancer. The conventional methods of temperature measurements do not measure the actual temperature generated in the vicinity of the nanoparticles during illumination. In contrast, nano temperature sensors built on hyperthermic nanoparticles can relay local temperatures around the nanoparticles during thermal induction. In this study, we present a core shell construct consisting of a plasmonic core and a silica shell encapsulating a FRET pair of organic dyes for such application. The plasmonic core imparts photo-induced hyperthermic properties to the nanoconstruct, while the fluorescent shell enables ratiometric sensing of temperature. We see that even at a low dye encapsulation concentration, the shell displays a linear ratiometric fluorescence response to temperature and high energy transfer between the dye pair. Interestingly, Monte Carlo simulations, without considering the plasmonic core, show that the energy transfer in the system should be much smaller than that observed, confirming plasmon enhancement in the FRET energy transfer. We also show the ratiometric temperature measurement using these particles during photoinduced hyperthermia. This study suggests the use of plasmonic nanoparticles in the next generation "self-limiting" photothermal therapy.

Optical Characterization of Ciprofloxacin Photolytic Degradation by UV-Pulsed Laser Radiation

Ciprofloxacin is one of the most prescribed antibiotics in treating bacterial infections, becoming an important pollutant of the wastewaters. Moreover, ciprofloxacin is hard to be destroyed by conventional water treatment processes; therefore, efficient treatments to destroy it are needed in water decontamination. This study offers insights into the performance of 266 nm laser beams on the photodegradation of ciprofloxacin. An Nd:YAG laser was used that emitted 266 nm at an energy of 6.5 mJ (power of 65 mW) and ciprofloxacin water solutions were irradiated up to 240 min. The irradiated solutions were investigated by UV-Vis and FTIR absorption spectroscopy, pH assay, and laser-induced fluorescence. An HPTLC densitometer was used to characterize the laser-induced fluorescence and fluorescence lifetime of photodegradation products. The UV-Vis absorption, FTIR, and laser-induced fluorescence spectra showed the degradation of ciprofloxacin. Moreover, HPTLC densitometry offered the fluorescence and fluorescence lifetime of ciprofloxacin and its three photoproducts as well as their relative quantification. From the FTIR spectra, the molecular structure of two out of three photoproducts was proposed. In conclusion, the laser irradiation method provided the efficient photodegradation of ciprofloxacin, whereas the analytical techniques offered the proper means to monitor the process and detect the obtained photoproducts.

S-Nitrosothiols (SNO) as light-responsive molecular activators for post-synthesis fluorescence augmentation in fluorophore-loaded nanospheres

For the first time S-nitrosothiol is engineered into fluorophore-loaded silica nanospheres for post-synthesis, light-triggered fluorescence augmentation.

Determination of berberine hydrochloride using a fluorimetric method with silica nanoparticles as a probe

The interaction of silica nanoparticles (SiO₂NPs) with berberine hydrochloride (BRH) was studied in aqueous solution at pH 9.0 and room temperature by using fluorophotometry. Based on a significant enhancement of the fluorescence intensity of the SiO₂NPs–BRH aggregates, a spectrofluorimetric method which was simple, sensitive and green was developed for the determination of BRH in aqueous solution. The linear range of the method was from 2.0–50.0 μg L⁻¹ with a detection limit of 0.73 μg L⁻¹. There was no interference from the compounds normally used to formulate pharmaceutical tablets. The proposed method was applied to the determination of BRH in tablets with satisfactory results and good consistency with the results obtained by standard methods.

A simple, green and sensitive spectrofluorimetric method was proposed for the determination of berberine hydrochloride (BRH) in aqueous solution.

Boronate Affinity Fluorescent Nanoparticles for Förster Resonance Energy Transfer Inhibition Assay of cis-Diol Biomolecules

Förster resonance energy transfer (FRET) has been essential for many applications, in which an appropriate donor-acceptor pair is the key. Traditional dye-to-dye combinations remain the working horses but are rather nonspecifically susceptive to environmental factors (such as ionic strength, pH, oxygen, etc.). Besides, to obtain desired selectivity, functionalization of the donor or acceptor is essential but usually tedious. Herein, we present fluorescent poly(m-aminophenylboronic acid) nanoparticles (poly(mAPBA) NPs) synthesized via a simple procedure and demonstrate a FRET scheme with suppressed environmental effects for the selective sensing of cis-diol biomolecules. The NPs exhibited stable fluorescence properties, resistance to environmental factors, and a Förster distance comparable size, making them ideal donor for FRET applications. By using poly(mAPBA) NPs and adenosine 5'-monophosphate modified graphene oxide (AMP-GO) as a donor and an acceptor, respectively, an environmental effects-suppressed boronate affinity-mediated FRET system was established. The fluorescence of poly(mAPBA) NPs was quenched by AMP-GO while it was restored when a competing cis-diol compounds was present. The FRET system exhibited excellent selectivity and improved sensitivity toward cis-diol compounds. Quantitative inhibition assay of glucose in human serum was demonstrated. As many cis-diol compounds such as sugars and glycoproteins are biologically and clinically significant, the FRET scheme presented herein could find more promising applications.

Highly Flexible Platform for Tuning Surface Properties of Silica Nanoparticles and Monitoring Their Biological Interaction

The following work presents a simple, reliable and scalable seeding-growth methodology to prepare silica nanoparticles (SiO2 NPs) (20, 30, 50 and 80 nm) directly in aqueous phase, both as plain- as well as fluorescent-labeled silica. The amount of fluorescent label per particle remained constant regardless of size, which facilitates measurements in terms of number-based concentrations. SiO2 NPs in dispersion were functionalized with an epoxysilane, thus providing a flexible platform for the covalent linkage of wide variety of molecules under mild experimental conditions. This approach was validated with ethylenediamine, two different amino acids and three akylamines to generate a variety of surface modifications. Accurate characterization of particle size, size distributions, morphology and surface chemistry is provided, both for as-synthesized particles and after incubation in cell culture medium. The impact of physicochemical properties of SiO2 NPs was investigated with human alveolar basal epithelial cells (A549) such as the effect in cytotoxicity, cell internalization and membrane interaction.

Dispersion Behaviour of Silica Nanoparticles in Biological Media and Its Influence on Cellular Uptake

Given the increasing variety of manufactured nanomaterials, suitable, robust, standardized in vitro screening methods are needed to study the mechanisms by which they can interact with biological systems. The in vitro evaluation of interactions of nanoparticles (NPs) with living cells is challenging due to the complex behaviour of NPs, which may involve dissolution, aggregation, sedimentation and formation of a protein corona. These variable parameters have an influence on the surface properties and the stability of NPs in the biological environment and therefore also on the interaction of NPs with cells. We present here a study using 30 nm and 80 nm fluorescently-labelled silicon dioxide NPs (Rubipy-SiO₂ NPs) to evaluate the NPs dispersion behaviour up to 48 hours in two different cellular media either supplemented with 10% of serum or in serum-free conditions. Size-dependent differences in dispersion behaviour were observed and the influence of the living cells on NPs stability and deposition was determined. Using flow cytometry and fluorescence microscopy techniques we studied the kinetics of the cellular uptake of Rubipy-SiO₂ NPs by A549 and CaCo-2 cells and we found a correlation between the NPs characteristics in cell media and the amount of cellular uptake. Our results emphasize how relevant and important it is to evaluate and to monitor the size and agglomeration state of nanoparticles in the biological medium, in order to interpret correctly the results of the in vitro toxicological assays.

Fluorescence detection of Fe(3+) ions in aqueous solution and living cells based on a high selectivity and sensitivity chemosensor

Although ferric ion (Fe(3+)) performs critical roles in diverse biochemical processes in living systems, its physiological and pathophysiological functions have not been fully explored due to the lack of methods for quantification of Fe(3+) ions in biological system. In this work, a highly sensitive and selective fluorescence chemosensor, L, was developed for the detection of Fe(3+) ions in aqueous solution and in living cells. L was facile synthesized by one step reaction and well characterized by NMR, API-ES, FT-IR, and elementary analysis. The prepared chemosensor displayed excellent selectivity for Fe(3+) ions detection over a wide range of tested metal ions. In the present of Fe(3+) ions, the strong green fluorescence of L was substantially quenched. The 1:1 stoichiometry of the complexation was confirmed by a Job's plot. The association constant (Ka) of L with Fe(3+) was evaluated using the Benesi-Hildebrand method and was found to be 1.36×10(4) M(-1). The MTT assay determined that L exhibits low cytotoxicity toward living cells. Confocal imaging and flow cytometry studies showed that L is readily interiorized by MDA-MB-231 cells through an energy-dependent pathway and could be used to detect of Fe(3+) ions in living cells.

Shrink-induced silica multiscale structures for enhanced fluorescence from DNA microarrays

We describe a manufacturable and scalable method for fabrication of multiscale wrinkled silica (SiO2) structures on shrink-wrap film to enhance fluorescence signals in DNA fluorescence microarrays. We are able to enhance the fluorescence signal of hybridized DNA by more than 120 fold relative to a planar glass slide. Notably, our substrate has improved detection sensitivity (280 pM) relative to planar glass slide (11 nM). Furthermore, this is accompanied by a 30-45 times improvement in the signal-to-noise ratio (SNR). Unlike metal enhanced fluorescence (MEF) based enhancements, this is a far-field and uniform effect based on surface concentration and photophysical effects from the nano- to microscale SiO2 structures. Notably, the photophysical effects contribute an almost 2.5 fold enhancement over the concentration effects alone. Therefore, this simple and robust method offers an efficient technique to enhance the detection capabilities of fluorescence based DNA microarrays.

Rhodamine B doped silica encapsulation matrices for the protection of photosynthetic organisms

An advanced encapsulation matrix that efficiently protects microalgae from harmful UV light without causing toxicity to the entrapped culture is developed based on the electrostatic adsorption of the dye Rhodamine B on silica preformed particles during sol-gel synthesis. The three microalgae (Chlorella vulgaris, Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii) were previously immobilized in alginate following the Two-step procedure. Once entrapped in the silica gel, Rhodamine B act as an inner cut-off filter, protecting the encapsulated organisms from UV radiation. This matrix allows the sterilization of encapsulation devices without affecting the viability of the entrapped microalgae cells. The condensation of Si(IV) in the presence of silica particles with adsorbed dye generates silica matrices with good mechanical stability. Furthermore; no appreciable differences in microstructure, as assessed by SAXS (Small Angle X-ray Scattering), are caused by the addition of the dye.

Silica-based nanocomposites via reverse microemulsions: classifications, preparations, and applications

Silica-based nanocomposites with amorphous silica as the matrix or carrier along with a functional component have been extensively investigated. These nanocomposites combine the advantages of both silica and the functional components, demonstrating great potential for various applications. To synthesize such composites, one of the most frequently used methods is reverse microemulsion due to its convenient control over the size, shape, and structures. The structures of the composites have a decisive significance for their properties and applications. In this review, we tried to categorize the silica-based nanocomposites via reverse microemulsions based on their structures, discussed the syntheses individually for each structure, summarized their applications, and made some perspectives based on the current progress of this field.