The research of zinc oxide tetrapods is a promising direction in the nano- and micro-materials field due to their unique properties. Firstly, the shape of tetrapods prevents their aggregation which is shortcomings of spherical and rod nanostructures. Secondly, zinc oxide is a non-toxic and biocompatible material. It makes zinc oxide structures are well suited for environmental, energy, and biomedical applications. Photocatalysis is one of zinc oxide’s key applications because of the high efficiency of reactive oxygen species (ROS) generation, i.e. superoxide radicals and hydroxyl radicals. Surface passivation of zinc oxide tetrapods with magnetic nanoparticles can increase their photoactivity due to effective charge separation which is useful in photocatalysis. Moreover, induced magnetic properties can be used for magnetic separation. In this work, magnetite nanoparticles were chosen as the magnetic component since they have high magnetic susceptibility, demonstrate biocompatibility and low toxicity. Various approaches to a simple formation method of such structures are considered. The composites are obtained by mixing components in water in combination with: (i) ultrasound, (ii) magnetic stirring, (iii) vortex. The samples are studied using scanning electron microscopy, absorption and luminescence spectroscopy. The results confirm that magnetite nanoparticles bind to the zinc oxide tetrapods surface in all three approaches. The photocatalytic activity of the composites is investigated using methylene blue and methyl orange as ROS indicators under light irradiation and is compared with one of the pure zinc oxide tetrapods.
Composites based on nanomaterials are becoming more popular, especially for the creation of Förster Resonant Energy Transfer systems. Here, well-established zinc oxide tetrapods and a new carbon dot material were used to create a hybrid composite. The influence of the alkalinity of the medium on the formation of the composite was studied. The morphology and optical properties were studied in detail to confirm the formation of the composite. The measurement of photoluminescence lifetimes of carbon dots/zinc oxide tetrapods composites demonstrated nonradiative energy transfer. The efficiency of Förster Resonant Energy Transfer was theoretically calculated and the rate constants of this process, as well as reabsorption, were found. Consequently, the new composite based on carbon dots and zinc oxide tetrapods can find many applications, for example, in optical sensors.
Magneto-luminescent nanocomposites can be used as agents for efficient targeted drug delivery. Here, we created a Fe3O4-based magneto-luminescent Fe3O4@SiO2-CdTe quantum dots nanocomposites and studied PL kinetics and magneto-luminescent properties of nanocomposites in biocompatible solvents. We showed that welding a shell of mesoporous SiO2 onto spherical Fe3O4 nanoparticles prevents oxidation of Fe3O4 and saves their magnetic properties.
The impact of prolonged irradiation of SPIONs/CdSe/ZnS nanocomposites by visible light on nanocomposite luminescence has been studied. It has been shown that prolonged irradiation of the nanocomposites with 405 nm laser can triple their photoluminescence quantum yield. It has been demonstrated that the efficiency of photoinduced processes on the nanocomposite surface correlates very well with the concentration of the nanocomposite surface ligand in our samples. We have also found that the quantum sized CdSe shell of SPIONs/CdSe/ZnS nanocomposites demonstrates the QD-like dependence of photoluminescence quantum yield on visible light dose and this nanocomposite property can be efficiently used to brighten their photoluminescence.
The tetrapyrrole chlorin e6 (Ce6) is actively used in photodynamic therapy (PDT) and as a test drug for sonodynamic therapy due to its ability to generate singlet oxygen. In this work, we have analyzed the absorption, photoluminescence (PL), and PL excitation spectra of Ce6 molecules in a nutrient medium and inside the melanoma cells. An analysis of the results shows that Ce6 inside the cancer cells with a low pH remains in monomeric form. A photodynamic test has also been conducted that confirmed the photodynamic effect produced by Ce6 in cancer cells by changing the signals from Ce6 and cells in the absorption and PL spectra.
Magneto-luminescent materials that do not exist in nature, can find a wide application in biomedical and environmental fields. Here we describe magneto-optical properties of core-shell-shell nanocomposites consisting of a Fe3O4 superparamagnetic iron oxide nanoparticle (SPION) covered with quantum-sized brightly luminescent CdSe layer surrounded by ZnS passivating shell. The synthesized nanocomposites demonstrate excitonic bands in their absorption and photoluminescent (PL) spectra centered at 585 nm and 603 nm, respectively. The PL quantum yield of nanocomposites has been increased by 5 times due to their passivation with ZnS shell. The analysis of magneto-optical properties of the synthesized Fe3O4/CdSe/ZnS nanocomposites has shown that their magnetic circular dichroism (MCD) spectrum is characterized with the bands centered at 430 nm, 350 nm and 303 nm corresponding to 6A1 → 4E, 4A1(4G); 6A1 → 4E(4D) and 6A1 → 4T1(4P) electronic transitions, respectively. It has been found that the synthesized core-shell SPIONs demonstrate excellent colloidal stability, magneto-optical properties typical for SPIONs and bright photoluminescence
The effect of photoinduced processes on CdSe/ZnS quantum dots surface on the functionality of TiO2 nanoparticles/quantum dots hybrid structures was investigated. It is shown that preliminary irradiation of quantum dots makes it possible to achieve a threefold increase in the efficiency of electron transfer from quantum dot to TiO2 nanoparticle in these structures. It has been demonstrated that photoinduced processes affect both the quantum yield of quantum dots luminescence and the reactive oxygen species generation by structures under visible light.
Circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) and chlorin e6 (Ce6) molecules in dimethyl sulfoxide (DMSO) and in aqueous solutions at different pH levels were investigated. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. CD spectroscopy allowed us to obtain the CD spectrum of a luminescent Ce6 dimer and to identify a nonluminescent Ce6 aggregate, which is thought to be a tetramer. The dissymmetry factor of the tetramer is 40 times larger than that of the Ce6 monomer. The analysis of the obtained data showed that in complexes with QDs Ce6 can be either in the monomer form or in the form of a nonluminescent tetramer. The interaction of the relatively unstable luminescent Ce6 dimer with QDs leads to its partial monomerization and the formation of complexes with Ce6 in the monomer form. On the basis of time-dependent density functional theory calculations, we performed a geometry model of Ce6 dimer form with corresponding calculated absorption and CD spectra, which are in a qualitative agreement with the experimental data.
Here we report our investigations of the formation conditions and photophysical properties of complexes between luminescent semiconducting nanoparticles (quantum dots, QDs) and the photosensitizer chlorin e6, which is widely used for the photodynamic therapy. In our complexes, bovine serum albumin (BSA), the most abundant protein in blood serum, was used as a linker between QDs and chlorin e6 molecules. The influence of BSA on the optical properties of Ce6 and QDs in complexes was properly examined using spectral-luminescent methods. It was found that BSA passivated QD surface and substantially QD quantum yield of luminescence was increased. In addition, BSA prevented the aggregation of chlorin e6 molecules in complexes with QDs. We demonstrated that the use of BSA as a linker allows to create functional QD-chlorin e6 complexes with effective photoexcitation energy transfer from QDs to the molecules.
A morphology and photoinduced changes of luminescence properties of two types of hybrid structures based
on TiO2 nanoparticles and CdSe/ZnS QDs were examined. A spin-coating method and a modified Langmuir-
Blodgett technique have been applied to form the multilayer hybrid structures on glass slides. It was
demonstrated that uniformity of QD surface concentration in hybrid structures depends on the method of
structure formation. A photodegradation of luminescence properties of the structures is associated with the
formation of QD aggregates. The QD aggregate concentration and their size depend on the method of the
structure formation and the concentration of TiO2 nanoparticles. A decay of luminescence of QD aggregates
in hybrid structures contains a microsecond components. An exposure of the hybrid structures with uniform
QD surface concentration by visible light resulted in a photopassivation of their surface, which is
accompanied by significant increase of luminescence quantum yield of QDs.
Photoinduced dissociation of surface complexes of CdSe/ZnS quantum dots with azo-dye 1-(2-
pyridylazo)-2-naphthol (PAN) was investigated. It was shown that the Förster resonance energy transfer contributes in
the complexes photodissociation rate, which depends on resonance condition between electronic levels of donor
(quantum dots) and acceptor (azo-dye) and donor photoluminescent quantum yield. It has allowed to estimate energy
transfer efficiency in the complexes and disclosed a new nonradiative channel that has minor contribution in the
deactivation of excited states of quantum dots in the complexes.
Photoinduced changes in luminescent and photoelectrical properties of the hybrid structure based on CdSe/ZnS QDs and
multilayer graphene nanobelts were studied. It was shown that an irradiation of the structures by 365 nm mercury line in
doses up to 23 J led to growth of QD luminescent quantum yield and photocurrent in the QD/graphene structures. This
confirms the proximity of the rates of the QD luminescence decay and energy/charge transfer from QDs to graphene, and
opens an opportunity to photoinduced control of the photoelectric response of the graphene based hybrid structures with
semiconductor quantum dots.
Experimental investigation of circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS QDs
and chlorin e6 (Ce6) molecules in aqua solutions at different pH level, in methanol and in DMSO were carried out. The
changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. Application of CD
spectroscopy allowed to obtain the CD spectrum of luminescent Ce6 dimer for the first time, and to discover a nonluminescent
Ce6 aggregate, preliminary identified as a "tetramer", dissymmetry factor of which is 40 times larger than
that for its monomer. The analysis of obtained data showed that in complexes with QDs Ce6 can be either in the
monomeric form or in the form of non-luminescent tetramer. The interaction of relatively unstable luminescent Ce6
dimerwith QDs leads to its partial monomerization and formation complexes with chlorin e6 in monomeric form.
New biocompatible complexes based on manganese-doped core/shell ZnS/ZnS quantum dots (ZnS:Mn2+/ZnS) and drug "Photoditazin" were formed and compared to traditional complexes with CdSe/ZnS quantum dots. Complexes with ZnS:Mn/ZnS quantum dots show some advantages in their photophysical properties. At the same time they demonstrate evident difference in their photophysical properties that may be associated with various location of trap states in places where drug molecule bounds with quantum dot.
Photophysical properties of complexes of semiconductor quantum dots with conventional photosensitizers for photodynamic therapy (tetrapyrroles) were investigated. A luminescent study of complexes in aqueous solutions was performed using spectral- and time-resolved luminescence spectroscopy. It was found that increasing the photosensitizer relative concentration in complexes resulted in sharp drop of the nonradiative energy transfer efficiency and the quantum yield of the photosensitizer photoluminescence. This fact indicates that additional channels of nonradiative energy dissipation may take place in the complexes. Using complexes of Al(OH)-sulphophthalocyanine with CdSe/ZnS quantum dots in the aqueous solution as an typical example, we have demonstrated that new channels of the energy dissipation may arise due to aggregation of the photosensitizer molecules upon formation of the complexes with quantum dots. We also demonstrated that use of methods of complex formation preventing aggregation of photosensitizers allows to conserve the high energy transfer efficiency and quantum yield of the acceptor photoluminescence in complexes in wide range of the photosensitizer concentrations. We believe that our study allows obtaining new information about the physical mechanisms of nonradiative energy transfer in quantum dots-tetrapyrrole complexes perspective for photodynamic therapy.
KEYWORDS: Molecules, Quantum dots, Quantum efficiency, Photodynamic therapy, Energy transfer, Cancer, Fluorescence resonance energy transfer, Absorption, Spectroscopy, Molecular energy transfer
In present study complexes between non-toxic ZnSe/ZnS quantum dots and chlorin e6 molecules that are widely used as photosensitizers in photodynamic therapy were formed. It was found that in aqueous solution cationic ZnSe/ZnS quantum dots and chlorin e6 formed stable complexes that exhibit efficient photoexcitation energy transfer from quantum dots to molecules. Spectroscopic methods were applied to evaluate the energy transfer efficiency. Stoichiometry of these complexes was studied. Additionally, the photodynamic therapy efficacy of the quantum dotchlorin e6 complexes was in vitro assessed against Ehrlich ascites carcinoma cancer cell line using a trypan blue assay. We found that complex offered an improved cancer cell photodynamic destruction effect as compared to that of free chlorin e6.
We investigate electrical photoresponse of multilayer graphene decorated with CdSe/ZnS quantum dots. It was found that photoresponse of these hybrid structures depends on quantum dot photoluminescence quantum yield. We demonstrate in uence of external factors (light exposure and treatment with ammonia vapors) on photoluminescence quantum yield of quantum dots and electrical photoresponse of the hybrid structures.
KEYWORDS: Molecules, Fluorescence resonance energy transfer, Quantum dots, Positron emission tomography, Energy transfer, Molecular energy transfer, Data modeling, Semiconductors, Luminescence, Resonance energy transfer
Hybrid structures based on CdSe/ZnS quantum dots and porphyrin molecules with effective energy transfer were formed in samples of polymer track pore membrane. It was observed that energy transfer efficiency depends on quantum dot size and correlates with overlapping integral between quantum dot photoluminescence and porphyrin absorption spectra inherent for Förster Resonant Energy Transfer, FRET. However, a noticeable deviation of experimental FRET efficiency dependence on an acceptor concentration from theoretical ones was observed for all donor-acceptor pairs. A gradient of donor and acceptor concentrations in the matrix is considered as the most probable reason of this deviation. A theoretical model describing energy transfer in a rigid solution with a gradient of particle concentration is proposed.
We present technique of obtaining complex hybrid structures combining the multi-walled carbon
nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots
CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced
by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a
spatial correlation between the luminescence and Raman signals is found.
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