Cristian A. Strassert

Silicon(IV) Phthalocyanine-Decorated Cyclodextrin Vesicles as a Self-Assembled Phototherapeutic Agent against MRSA.

The host-guest complexation of a tailored Si(IV) phthalocyanine with supramolecular β-cyclodextrin vesicles (CDV) was studied, revealing a reduced aggregation of the photoactive center upon binding to the CDV, even in aqueous environments. For this purpose, a photosensitizing unit axially decorated with one adamantyl group and one pyridinium moiety on the other side was obtained by two successive click reactions on a bis-azido-functionalized derivative of Si(IV) phthalocyanine. To evaluate its potential as a photosensitizer against antibiotic-resistant bacteria, comparative studies of the photophysical properties including absorption and emission spectroscopy, lifetimes as well as fluorescence and singlet oxygen quantum yields were determined for the Si(IV) phthalocyanine alone and upon self-assembly on the CDV surface. In vitro phototoxicity against the methicillin-resistant Staphylococcus aureus (MRSA) USA300 was evaluated, showing an almost complete inactivation.

Aromatic Thioethers as Novel Luminophores with Aggregation‐Induced Fluorescence and Phosphorescence

Here we report on a novel system based on aromatic thioethers with unique luminescence properties. Fifteen different compounds were investigated in detail on their luminescence properties using UV/Vis absorption and steady-state and time-resolved luminescence spectroscopy. Excited state lifetimes as well as quantum yields were determined, and the toxicity towards HeLa cells was investigated. Besides X-ray analyses also quantum chemical calculations were performed to gain deeper insights in the unique behavior of this facile system. The studied compounds reveal remarkable fluorescence emission ranging from 437 to 588 nm as well as phosphorescence (up to 5 μs).

Labeling and Selective Inactivation of Gram‐Positive Bacteria Employing Bimodal Photoprobes with Dual Readouts

Carbohydrate-conjugated silicon(IV) phthalocyanines with bimodal photoactivity were developed as probes with both fluorescent labeling and photosensitizing capabilities, and the concomitant fluorescent labeling and photoinduced inactivation of Gram-positive and Gram-negative models was explored. The maltohexaose-conjugated photoprobe provides a dual readout to distinguish between both groups of pathogens, as only the Gram-positive species was inactivated, even though both appeared labeled with near-infrared luminescence. Antibiotic resistance did not hinder the phototoxic effect, as even the methicillin-resistant pathogen Staphylococcus aureus (MRSA) was completely photoinactivated. Time-resolved confocal fluorescence microscopy analysis suggests that the photoprobe sticks onto the outer rim of the microorganisms, explaining the resistance of Gram-negative species on the basis of their membrane constitution. The mannose-conjugated photoprobe yields a different readout because it is able to label and to inactivate only the Gram-positive strain.

Facile surface engineering of CuInS2/ZnS quantum dots for LED down-converters

We present a facile one-pot synthesis and simple surface modification strategies to prepare ternary CuInS2/ZnS quantum dots (CIS/ZnS QDs) functionalized with alkyl-, carboxyl- and hydroxyl-terminated ligands. Photoluminescence quantum yields (PLQY) up to 60% can be achieved for CIS/ZnS QDs synthesized on a gram scale. Aqueous mercaptopropionic acid (MPA) capped QDs are used as a base for further surface modification. On the one hand ligand–solvent interactions have been found to play a major role in the luminescence quenching mechanism of aqueous CIS/ZnS QDs. On the other hand, solvent extraction, immobilization in a polymer matrix or phase transfer greatly enhances the photoluminescence. Quantum yields in solution and in solid matrices differ greatly in the case of aqueous QDs both in polymers and in sol–gel silica. Surface engineered QDs are assessed for their usefulness in LED down-conversion experiments. We demonstrate that down-converter layer properties are not only dependent on the QD type and PLQY, but also on the matrix and the type of ligand shell. Despite significant (up to a factor of two) differences in PLQY between the hydrophobic and hydrophilic dots, their LED conversion efficiencies are comparable and up to 49% and 46% for hydrophobic and for hydrophilic QDs, respectively. Additionally, sol–gel nanocomposites incorporating CuInS2/ZnS QDs with OH-terminated ligands that can withstand 200 h high power blue LED irradiation are presented for the first time.

Agglutination of bacteria using polyvalent nanoparticles of aggregation-induced emissive thiophthalonitrile dyes

A novel class of aggregation-induced emissive bis(phenylthio)phthalonitrile dyes were synthesized. These dyes assembled into nanoparticles that were equipped with mannose units. The nanoparticles underwent selective interactions with lectins and bacteria. The bright fluorescent aggregates aid in the visualization of the agglutination of bacteria.

Effect of the C(3)-Substituent in Verdazyl Radicals on their Profluorescent Behavior.

Methods for the detection of reactive intermediates such as transient radicals are important in organic chemistry, polymer chemistry, biology or medicine. Along these lines we recently reported that 1,5-diphenyl-6-oxo verdazyl radicals can be used as fluorescent spin sensors. In situ generated C-centered radicals are efficiently trapped by the verdazyls, which in turn undergo transformation from a paramagnetic non-fluorescent state to a diamagnetic fluorescent state. Whereas the N-phenyl substituent in the spin probes is of high importance for obtaining profluorescent behavior, the effect of the C(3)-substituent has not been investigated to date. We herein present the synthesis and characterization of various 1,5-diphenyl-6-oxo-verdazyl radicals bearing differently hybridized C-substituents at the C(3) position. Steady-state and time-resolved fluorescence spectroscopy in solution and in the solid state along with time-dependent density functional theory (TDDFT) calculations reveal that a C(3)-aryl substituent is crucial for obtaining fluorescence after spin trapping. In addition, it is shown that the emission wavelength of the C(3)-aryl substituted verdazyl derivatives can be tuned by selective destabilization of the HOMO and the LUMO.

Formation of Silver Nanoclusters from a DNA Template Containing Ag(I)-Mediated Base Pairs

A series of DNA double helices containing different numbers of silver(I)-mediated base pairs involving the artificial nucleobases imidazole or 2-methylimidazole has been applied for the generation of DNA-templated silver nanoclusters. The original Ag(I)-containing nucleic acids as well as the resulting nanoclusters and nanoparticles have been characterized by means of UV/Vis spectroscopy, circular dichroism (CD) spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM). The results show for the first time that metal-mediated base pairs can be used for the templated growth of metal nanoclusters.

Spatiotemporally Resolved Tracking of Bacterial Responses to ROS-Mediated Damage at the Single-Cell Level with Quantitative Functional Microscopy

Herein we report on the implementation of photofunctional microparticles in combination with optical tweezers for the investigation of bacterial responses to oxidative stress by means of quantitative functional microscopy. A combination of a strongly hydrophobic axially substituted Si(IV) phthalocyanine adsorbed onto silica microparticles was developed, and the structural and photophysical characterization was carried out. The microparticles are able to produce reactive oxygen species under the fluorescence microscope upon irradiation with red light, and the behavior of individual bacteria can be consequently investigated in situ and in real time at the single cell level. For this purpose, a methodology was introduced to monitor phototriggered changes with spatiotemporal resolution. The defined distance between the photoactive particles and individual bacteria can be fixed under the microscope before the photosensitization process is started, and the photoinduced damage can be monitored by tracing the time-dependent fluorescence turn-on of a suitable marker. The results showed a distance-dependent photoinduced death time, defined as the onset of the incorporation of propidium iodide. Our methodology constitutes a new tool for the in vitro design and evaluation of photosensitizers for the treatment of cancer and infectious diseases with the aid of functional optical microscopy, as it enables a quantitative response evaluation of living systems toward oxidative stress. More generally, it provides a way to understand the response of an ensemble of living entities to reactive oxygen species by analyzing the behavior of a set of individual organisms.

Photobleaching-resistant ternary quantum dots embedded in a polymer-coated silica matrix

Herein we present the preparation of ultrastable CuInS2/ZnS-silica composites able to withstand high density irradiation for more than 100 h without degradation using a blue LED operated at 20 mA forward current. The high photostability is obtained by employing a novel polymer-infused silica/QD composite. The versatility of the (3-mercaptopropyl)trimethoxy-silane/tetraethyl orthosilicate matrix used in this study is demonstrated by incorporating QDs with positively (amine) and negatively (carboxyl) charged ligands yielding transparent and highly luminescent gels with up to 20% solid loading. Quantum yields in solution (40–50%) are retained or even slightly improved in the silica matrix further proving efficient encapsulation without damaging the nanocrystal surface. White LED fabricated from green and orange ternary QDs exhibit a luminous efficacy of 30 lm W−1 and a color rendering index of 87 as compared to a blackbody radiator with 3850 K color temperature.

CeIV -GdIII Mixed Oxides as Hosts for ErIII -Based Upconversion Phosphors

A family of ErIII and ErIII -YbIII based nanophosphors, hosted in monophasic oxidic CeIV -GdIII binary solid solutions, was prepared. The samples were formulated with a constant ErIII content as the activator, with the eventual addition of YbIII as a sensitizer. The amorphous Ce0.94-x Gdx Er0.06 (OH)CO3 ⋅H2 O and Ce0.94-x Gdx Er0.05 Yb0.01 (OH)CO3 ⋅H2 O precursors were prepared by following the urea method to obtain monodispersed spheres of tunable size ranging from 30 to 450 nm. After being decomposed at 1273 K under an atmosphere of air, the precursors of 200 nm in diameter evolved into monophasic polycrystalline particles preserving the parent shape and size. The role of the composition of the binary matrices in the emission properties was evaluated for two different excitation wavelengths (976 nm and 780 nm) based on the upconversion (UC) emission spectra and their dependence on the incident power. The yield of the UC process is discussed in the framework of established and novel alternative mechanisms. The number of vacancies and mainly the symmetry of the ErIII environment play major roles in the deactivation pathways of the UC emission mechanisms. However, the colours obtained by employing bare CeIV or GdIII hosts are preserved in the related monophasic CeIV -rich or GdIII -rich binary hosts.