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1.
Nano Lett ; 2022 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-36450036

RESUMO

Relaxor ferroelectrics have been intensely studied for decades based on their unique electromechanical responses which arise from local structural heterogeneity involving polar nanoregions or domains. Here, we report first studies of the ultrafast dynamics and reconfigurability of the polarization in freestanding films of the prototypical relaxor 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 (PMN-0.32PT) by probing its atomic-scale response via femtosecond-resolution, electron-scattering approaches. By combining these structural measurements with dynamic phase-field simulations, we show that femtosecond light pulses drive a change in both the magnitude and direction of the polarization vector within polar nanodomains on few-picosecond time scales. This study defines new opportunities for dynamic reconfigurable control of the polarization in nanoscale relaxor ferroelectrics.

2.
Adv Mater ; : e2202841, 2022 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-36189841

RESUMO

Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi2 Te4 , a topological insulator with intrinsic antiferromagnetism. This is achieved by optically exciting Bi-Te p states comprising the bulk topological bands and interrogating the consequent Mn 3d spin dynamics, using a multimodal ultrafast approach. Ultrafast electron scattering and magneto-optic measurements show that the p states demagnetize via electron-phonon scattering at picosecond timescales. Despite being energetically decoupled from the optical excitation, the Mn 3d spins, probed by resonant X-ray scattering, are observed to disorder concurrently with the p spins. Together with atomistic simulations, this reveals that the exchange coupling between localized spins and the topological bands is at least 100 times larger than the superexchange interaction, implying an optimal exchange gap of at least 25 meV in the surface states. By quantifying this exchange coupling, this study validates the materials-by-design strategy of utilizing localized magnetic order to manipulate topological phases, spanning static to ultrafast timescales.

3.
Mol Neurobiol ; 59(10): 6228-6244, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-35904715

RESUMO

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by the accumulation of amyloid-ß (Aß) aggregates in the brain. Clusterin (CLU), also known as apolipoprotein J, is a potent risk factor associated with AD pathogenesis, in which Aß aggregation is essentially involved. We observed close colocalization of CLU and Aß(1-42) (Aß42) in parenchymal amyloid plaques or vascular amyloid deposits in the brains of human amyloid precursor protein (hAPP)-transgenic Tg2576 mice. Therefore, to elucidate the binding interaction between CLU and Aß42 and its impact on amyloid aggregation and toxicity, the two synthetic proteins were incubated together under physiological conditions, and their structural and morphological variations were investigated using biochemical, biophysical, and microscopic analyses. Synthetic CLU spontaneously bound to different possible variants of Aß42 aggregates with very high affinity (Kd = 2.647 nM) in vitro to form solid CLU-Aß42 complexes. This CLU binding prevented further aggregation of Aß42 into larger oligomers or fibrils, enriching the population of smaller Aß42 oligomers and protofibrils and monomers. CLU either alleviated or augmented Aß42-induced cytotoxicity and apoptosis in the neuroblastoma-derived SH-SY5Y and N2a cells, depending on the incubation period and the molar ratio of CLU:Aß42 involved in the reaction before addition to the cells. Thus, the effects of CLU on Aß42-induced cytotoxicity were likely determined by the extent to which it bound and sequestered toxic Aß42 oligomers or protofibrils. These findings suggest that CLU could influence amyloid neurotoxicity and pathogenesis by modulating Aß aggregation.


Assuntos
Doença de Alzheimer , Neuroblastoma , Síndromes Neurotóxicas , Doença de Alzheimer/patologia , Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismo , Animais , Clusterina , Humanos , Camundongos , Camundongos Transgênicos , Fragmentos de Peptídeos/metabolismo , Fragmentos de Peptídeos/toxicidade
4.
Small ; 18(20): e2201248, 2022 May.
Artigo em Inglês | MEDLINE | ID: mdl-35388971

RESUMO

Heterostructures obtained from layered assembly of 2D materials such as graphene and hexagonal boron nitride have potential in the development of new electronic devices. Whereas various materials techniques can now produce macroscopic scale graphene, the construction of similar size heterostructures with atomically clean interfaces is still unrealized. A primary barrier has been the inability to remove polymeric residues from the interfaces that arise between layers when fabricating heterostructures. Here, the interface cleaning problem of polymer-contaminated heterostructures is experimentally studied from an energy viewpoint. With this approach, it is established that the interface cleaning mechanism involves a combination of thermally activated polymer residue mobilization and their mechanical actuation. This framework allows a systematic approach for fabricating record large-area clean heterostructures from polymer-contaminated graphene. These heterostructures provide state-of-the-art electronic performance. This study opens new strategies for the scalable production of layered materials heterostructures.

5.
Bioact Mater ; 18: 433-445, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-35415304

RESUMO

All-in-one treatments represent a paradigm shift in future medicine. For example, inflammatory bowel disease (IBD) is mainly diagnosed by endoscopy, which could be applied for not only on-site monitoring but also the intestinal lesion-targeted spray of injectable hydrogels. Furthermore, molecular conjugation to the hydrogels would program both lesion-specific adhesion and drug-free therapy. This study validated this concept of all-in-one treatment by first utilizing a well-known injectable hydrogel that underwent efficient solution-to-gel transition and nanomicelle formation as a translatable component. These properties enabled spraying of the hydrogel onto the intestinal walls during endoscopy. Next, peptide conjugation to the hydrogel guided endoscopic monitoring of IBD progress upon adhesive gelation with subsequent moisturization of inflammatory lesions, specifically by nanomicelles. The peptide was designed to mimic the major component that mediates intestinal interaction with Bacillus subtilis flagellin during IBD initiation. Hence, the peptide-guided efficient adhesion of the hydrogel nanomicelles onto Toll-like receptor 5 (TLR5) as the main target of flagellin binding and Notch-1. The peptide binding potently suppressed inflammatory signaling without drug loading, where TLR5 and Notch-1 operated collaboratively through downstream actions of tumor necrosis factor-alpha. The results were produced using a human colorectal cell line, clinical IBD patient cells, gut-on-a-chip, a mouse IBD model, and pig experiments to validate the translational utility.

6.
Phys Rev Lett ; 127(22): 227401, 2021 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-34889631

RESUMO

Engineering novel states of matter with light is at the forefront of materials research. An intensely studied direction is to realize broken-symmetry phases that are "hidden" under equilibrium conditions but can be unleashed by an ultrashort laser pulse. Despite a plethora of experimental discoveries, the nature of these orders and how they transiently appear remain unclear. To this end, we investigate a nonequilibrium charge density wave (CDW) in rare-earth tritellurides, which is suppressed in equilibrium but emerges after photoexcitation. Using a pump-pump-probe protocol implemented in ultrafast electron diffraction, we demonstrate that the light-induced CDW consists solely of order parameter fluctuations, which bear striking similarities to critical fluctuations in equilibrium despite differences in the length scale. By calculating the dynamics of CDW fluctuations in a nonperturbative model, we further show that the strength of the light-induced order is governed by the amplitude of equilibrium fluctuations. These findings highlight photoinduced fluctuations as an important ingredient for the emergence of transient orders out of equilibrium. Our results further suggest that materials with strong fluctuations in equilibrium are promising platforms to host hidden orders after laser excitation.

7.
Nature ; 592(7854): 376-380, 2021 04.
Artigo em Inglês | MEDLINE | ID: mdl-33854251

RESUMO

The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

8.
Nat Commun ; 12(1): 1860, 2021 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-33767138

RESUMO

Nonradiative processes limit optoelectronic functionality of nanocrystals and curb their device performance. Nevertheless, the dynamic structural origins of nonradiative relaxations in such materials are not understood. Here, femtosecond electron diffraction measurements corroborated by atomistic simulations uncover transient lattice deformations accompanying radiationless electronic processes in colloidal semiconductor nanocrystals. Investigation of the excitation energy dependence in a core/shell system shows that hot carriers created by a photon energy considerably larger than the bandgap induce structural distortions at nanocrystal surfaces on few picosecond timescales associated with the localization of trapped holes. On the other hand, carriers created by a photon energy close to the bandgap of the core in the same system result in transient lattice heating that occurs on a much longer 200 picosecond timescale, dominated by an Auger heating mechanism. Elucidation of the structural deformations associated with the surface trapping of hot holes provides atomic-scale insights into the mechanisms deteriorating optoelectronic performance and a pathway towards minimizing these losses in nanocrystal devices.

9.
Electrochim Acta ; 3902021 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-34483347

RESUMO

In this study, we demonstrated the unique capability of carbon-based ion-selective electrode (ISE) to perform highly sensitive square wave anodic stripping voltammetry, while maintaining all the properties of an ISE, in terms of sensitivity, detection limit, response time and selectivity. Square wave anodic stripping voltammetry involves deposition and dissolution steps of metal ions, which means adsorption and desorption of metal ions on the conductive ion-selective membrane without losing its ion-sensing property. To demonstrate this capability, we chose a Ca2+ ion-selective microelectrode (µISE) as a potentiometric method and Cu2+-stripping voltammetry as an amperometric method. The carbon-based ISE surface is capable of quantifying nanomolar to micromolar Cu2+ in both a standard acetate buffer and a complex water sample. The Ca2+-µISE also showed a Nernstian slope of 29 mV / log [Ca2+] and a detection limit of 1 µM within the linear range of 1 µM to 10 mM. It thus opens an opportunity to use the low detection limit of anodic stripping voltammetry and the high selectivity of ISE-based potentiometry.

10.
Nutrients ; 13(9)2021 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-34578957

RESUMO

Kaempferol, a bioflavonoid present in fruits and vegetables, has a variety of antioxidant and anti-inflammatory capacities, but the functional role of kaempferol in oxidative skin dermal damage has yet to be well studied. In this study, we examine the role of kaempferol during the inflammation and cell death caused by 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal human dermal fibroblasts (NHDF). TPA (5 µM) significantly induced cytotoxicity of NHDF, where a robust increase in the interleukin (IL)-1ß mRNA among the various pro-inflammatory cytokines. The skin fibroblastic cytotoxicity and IL-1ß expression induced by TPA were significantly ameliorated by a treatment with 100 nM of kaempferol. Kaempferol blocked the production of the intracellular reactive oxygen species (ROS) responsible for the phosphorylation of c-Jun N-terminal kinase (JNK) induced by TPA. Interestingly, we found that kaempferol inhibited the phosphorylation of nuclear factor-kappa B (NF-κB) and the inhibitor NF-κB (IκBα), which are necessary for the expression of cleaved caspase-3 and the IL-1ß secretion in TPA-treated NHDF. These results suggest that kaempferol is a functional agent that blocks the signaling cascade of the skin fibroblastic inflammatory response and cytotoxicity triggered by TPA.


Assuntos
Fármacos Dermatológicos/farmacologia , Fibroblastos/efeitos dos fármacos , Interleucina-1beta/metabolismo , Proteínas Quinases JNK Ativadas por Mitógeno/antagonistas & inibidores , Quempferóis/farmacologia , Pele/efeitos dos fármacos , Acetato de Tetradecanoilforbol/farmacologia , Western Blotting , Linhagem Celular , Ensaio de Imunoadsorção Enzimática , Fibroblastos/metabolismo , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Pele/metabolismo
11.
Analyst ; 146(23): 7109-7117, 2021 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-34591042

RESUMO

We have designed and synthesized a multifunctional dendritic molecular probe that selectively detects Cu2+ ions via potentiometric and fluorometric techniques with low detection limits (3.5 µM in potentiometry, 15 nM in fluorometry). The selective and reversible binding of the molecule with the Cu2+ ion was used to make a solid-state microsensor (diameter of 25 µm) by incorporating the molecular probe into the carbon-based membrane as an ionophore for Cu(II). The Cu(II) microelectrode has a broad linear range of 10 µM to 1 mM with a near Nernstian slope of 30 mV/log [aCu2+] and detection limit of 3.5 µM. The Cu(II) microsensor has a fast response time (1.5 s), and it has a broad working pH range from 3.5 to 6.0. The incorporation of the hydrophobic dendritic moiety makes the ionophore less prone to leaching in an aqueous matrix for potentiometric measurement. The cinnamaldehyde component of the molecule helps detection of Cu2+ ions fluorometrically, as indicated by a change in fluorescence upon selective and reversible binding of the molecular probe to the Cu2+ ions. The strategic design of the molecular probe allows us to detect Cu2+ ions in drinking water by using this novel dendritic fluoroionophore and solid-state Cu2+ - ion-selective microelectrode.


Assuntos
Água Potável , Sondas Moleculares , Fluorometria , Íons , Potenciometria
12.
ACS Nano ; 14(7): 8449-8458, 2020 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-32538617

RESUMO

The inspection of Friedel's law in ultrafast electron diffraction (UED) is important to gain a comprehensive understanding of material atomic structure and its dynamic response. Here, monoclinic gallium telluride (GaTe), as a low-symmetry, layered crystal in contrast to many other 2D materials, is investigated by mega-electronvolt UED. Strong out-of-phase oscillations of Bragg peak intensities are observed for Friedel pairs, which does not obey Friedel's law. As evidenced by the preserved mirror symmetry and supported by both kinematic and dynamic scattering simulations, the intensity oscillations are provoked by the lowest-order longitudinal acoustic breathing phonon. Our results provide a generalized understanding of Friedel's law in UED and demonstrate that by designed misalignment of surface normal and primitive lattice vectors, coherent lattice wobbling and effective shear strain can be generated in crystal films by laser pulse excitation, which is otherwise hard to achieve and can be further utilized to dynamically tune and switch material properties.

13.
Science ; 368(6493): 885-889, 2020 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-32439793

RESUMO

Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

14.
ACS Nano ; 14(4): 4792-4804, 2020 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-32208676

RESUMO

Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.

15.
Int J Mol Sci ; 21(3)2020 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-31991844

RESUMO

Zinc and apolipoprotein E (apoE) are reportedly involved in the pathology of Alzheimer's disease. To investigate the associative interaction among zinc, apoE, and amyloid-ß (Aß) and its role in amyloid pathogenesis, we performed various biochemical and immunoreactive analyses using brain tissues of Tg2576 mice and synthetic Aß and apoE peptides. On amyloid plaques or in brain lysates of Tg2576 mice, apoE and Aß immunoreactivities increased after zinc chelation and were restored by its subsequent replacement. Zinc depletion dissociated apoE/Aß complexes or larger-molecular sizes of Aß oligomers/aggregates into smaller-molecular sizes of apoE and/or Aß monomers/complexes. In the presence of zinc, synthetic apoE and/or Aß peptides aggregated into larger-molecular sizes of oligomers or complexes. Endogenous proteases or plasmin in brain lysates degraded apoE and/or Aß complexes, and their proteolytic activity increased with zinc depletion. These biochemical findings suggest that zinc associates with apoE and Aß to encourage the formation of apoE/Aß complexes or large aggregates, raising the deposition of zinc-rich amyloid plaques. In turn, the presence of abundant zinc around and within apoE/Aß complexes may block the access or activity of Aß-degrading antibodies or proteases. These results support the plausibility of chelation strategy aiming at reducing amyloid pathology in Alzheimer's disease.


Assuntos
Peptídeos beta-Amiloides/metabolismo , Amiloide/metabolismo , Apolipoproteínas E/metabolismo , Placa Amiloide/metabolismo , Placa Amiloide/patologia , Zinco/metabolismo , Animais , Modelos Animais de Doenças , Humanos , Camundongos , Agregados Proteicos , Agregação Patológica de Proteínas , Ligação Proteica
16.
Phys Rev Lett ; 123(9): 097601, 2019 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-31524450

RESUMO

Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound LaTe_{3}. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

17.
Nano Lett ; 19(8): 4981-4989, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31260315

RESUMO

The light-induced selective population of short-lived far-from-equilibrium vibration modes is a promising approach for controlling ultrafast and irreversible structural changes in functional nanomaterials. However, this requires a detailed understanding of the dynamics and evolution of these phonon modes and their coupling to the excited-state electronic structure. Here, we combine femtosecond mega-electronvolt electron diffraction experiments on a prototypical layered material, MoTe2, with non-adiabatic quantum molecular dynamics simulations and ab initio electronic structure calculations to show how non-radiative energy relaxation pathways for excited electrons can be tuned by controlling the optical excitation energy. We show how the dominant intravalley and intervalley scattering mechanisms for hot and band-edge electrons leads to markedly different transient phonon populations evident in electron diffraction patterns. This understanding of how tuning optical excitations affect phonon populations and atomic motion is critical for efficiently controlling light-induced structural transitions of optoelectronic devices.

18.
Brain Pathol ; 29(2): 217-231, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30295351

RESUMO

While clusterin is reportedly involved in Alzheimer's disease (AD) pathogenesis, how clusterin interacts with amyloid-ß (Aß) to cause Aß neurotoxicity remains unclear in vivo. Using 5×FAD transgenic mice, which develop robust AD pathology and memory deficits when very young, we detected interactions between clusterin and Aß in the mouse brains. The two proteins were concurrently upregulated and bound or colocalized with each other in the same complexes or in amyloid plaques. Neuropathology and cognitive performance were assessed in the progeny of clusterin-null mice crossed with 5×FAD mice, yielding clu-/- ;5×FAD and clu+/+ ;5×FAD. We found far less of the various pools of Aß proteins, most strikingly soluble Aß oligomers and amyloid plaques in clu-/- ;5×FAD mice at 5 months of age. At that age, those mice also had higher levels of neuronal and synaptic proteins and better motor coordination, spatial learning and memory than age-matched clu+/+ ;5×FAD mice. However, at 10 months of age, these differences disappeared, with Aß and plaque deposition, neuronal and synaptic proteins and impairment of behavioral and cognitive performance similar in both groups. These findings demonstrate that clusterin is necessarily involved in early stages of AD pathogenesis by enhancing toxic Aß pools to cause Aß-directed neurodegeneration and behavioral and cognitive impairments, but not in late stage.


Assuntos
Doença de Alzheimer/patologia , Clusterina/metabolismo , Clusterina/fisiologia , Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Peptídeos beta-Amiloides/fisiologia , Precursor de Proteína beta-Amiloide/metabolismo , Animais , Encéfalo/patologia , Disfunção Cognitiva/metabolismo , Modelos Animais de Doenças , Feminino , Humanos , Masculino , Transtornos da Memória/patologia , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Neurônios/patologia , Placa Amiloide/patologia , Presenilina-1/metabolismo
19.
J Nanosci Nanotechnol ; 14(12): 9268-71, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25971049

RESUMO

Titania (TiO2) powder, which is material for photoelectrode in dye-sensitized solar cells (DSSCs), was fabricated by hydrothermal synthesis process at 230 degrees C for 12 hours. The crystal structures of all the synthesized nano-structured TiO2 films exhibited anatase phase. Binder-free pastes were prepared with the change of the amount of ammonia water from 2 µl to 640 µl in order to obtain the printable viscosity. It has been known that weak inter-particle bonds in slurry of flocculated particles make the slurry more viscous than slurry of dispersed particles. The increase of the amount of ammonia water for binder-free TiO2 pastes is attributed to the improvement of the viscosity of TiO2 paste and the power conversion efficiency of DSSCs using it. The viscosity of TiO2 pastes prepared at the ammonia water of 418 µl exhibited the highest value about 109,000 cP and also, was very transparent over 84%. As a result, the power conversion efficiency of DSSC prepared with the ammonia water of 418 µl was about 3%.

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