Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications

NIR-emissive Alkynylplatinum(II) Terpyridyl Complex as a turn-on selective probe for heparin quantification by induced helical self-assembly behaviour

The extent of self-assembly viametal–metal and π-π stacking interactions, induced by the polyanionic biopolymers, enables the class of alkynylplatinum(II) terpyridyl complexes to be applicable for the sensing of important biomacromolecules through the monitoring of spectral changes. Strong demand arises for the design of selective and practical detection techniques for the quantification of heparin, a highly negative-charged polysaccharidethat can function as anticoagulant, due to the prevention of hemorrhagic complications upon overdose usage.Aconvenient sensing protocol for the detection of UFH and LMWH, two common forms of heparins in clinical use, in buffer and biological medium has been demonstrated with the spectral changes associated with the induced self-assembly of a NIR-emissive platinum(II) complex. The detection range has been demonstrated to cover clinical dosage levels and the structurally similar analogues can be effectively differentiated based on their anionic charge density and the formation of supramolecular helical assembly of the platinum(II) complex with them ...postprin

Amphiphilic Anionic Pt(II) Complexes: from spectroscopic to morphological changes

A new class of amphiphilic anionic platinum(II) bzimpy complexes has been demonstrated to show aggregation in water through PtfflfflfflPt and π–π stacking interactions. An interesting aggregation–partial deaggregation–aggregation process and a morphological transformation from vesicles to nanofibers have been demonstrated. These changes can be systematically controlled by the variation of solvent composition and could readily be probed by UV-vis absorption, emission, NMR, transmission electron microscopy and even with our naked eyes ...postprin

Induced self-assembly and Förster Resonance Energy Transfer Studies of Alkynylplatinum(II) Terpyridine Complex through interaction with water-soluble Poly(phenylene ethynylene sulfonate) and the proof-of-principle demonstration of this two-component ensemble for selective label-free detection of Human Serum Albumin (HSA)

The interaction of conjugated polyelectrolyte, PPE-SO3−, with platinum(II) complexes, [Pt(tpy)(C≡CC6H4CH2NMe3-4)](OTf)2 (1) and [Pt(tpy)(C≡C–CH2NMe3)](OTf)2 (2), has been studied by UV–vis, and steady-state and time-resolved emission spectroscopy. A unique FRET from PPE-SO3−to the aggregated complex 1on the polymer chain with PtfflfflfflPt interactionhas been demonstrated, resulting in the growth of triplet metal-metal-to-ligand charge transfer (3MMLCT) emission ...postprin

Effect of Gold Nanorods on the Performance of Polymer:Fullerene Organic Solar Cells

This research is an experimental investigation on the effect of inserting gold nanorods in various locations of conjugated polymer solar cells that comprise poly(3-hexylthiophene-2,5-diyl) as the electron donor, and [6,6]-phenyl-C61-butyric-acid-methyl-ester as the electron acceptor, on the cells performance. Since gold nanorods support at least two major plasmonic modes associated with metallic nanoparticles, incorporating such nanoparticles into thin films of polymer solar cells is supposed to trap light inside the cells in a broad wavelength range, leading to increasing absorptivity as well as power conversion efficiency. First, several experiments were performed to manufacture devices with a good and reproducible efficiency by optimizing the fabrication conditions, particularly the lithium fluoride thickness as well as the annealing process. This optimization succeeded in producing reproducible devices with an enhanced power conversion efficiency from 0.36% to 1.67%. Secondly, various approaches were used to introduce gold nanorods in our devices. Rods were deposited in contact with either the cells’ front electrode, or the rear one. They were also blended with the solution of the anodic buffer layer, or the one of the photoactive layer. We compared the photovoltaic parameters extracted from completed devices made with/without gold nanorods, as well as their spectroscopic and structure properties. We found that for each location of rods in our devices there was an optimal concentration of the rods to produce enhancement in the devices’ performance. Based on theoretical considerations, devices enhancement was related to either the far field or near field effect induced by the presence of rods. It was found that increasing or decreasing the rods density from the optimal one reduced the overall efficiency of resulting devices. We experimentally verified that there was a relationship between the enhancement in the devices efficiency and the multi-mode excitations associated with gold nanorods. We also found that the influence of plasmonics on absorption of the devices depended on the thickness of the devices’ photoactive layers. Using the rod shape of gold nanoparticles to increase the device performance is indeed a promising approach since a fairly low density of the rods in the layer succeeded in increasing remarkably the devices efficiency by up to 21.3 %

Sub-diffraction limited morphology characterization in single noble metal nanoparticles and single conjugated polymer chains using optical microscopy techniques

At the nanoscale, materials exhibit special properties not present in the bulk, which may be exploited in diverse applications that include catalysis, sensing, and energy harvest and transfer. Due to their small size, nanoscale materials also present a characterization challenge, because optical microscopy techniques cannot resolve images of structural features smaller than finite lenses may focus visible light. Optical images of nanoparticles or single molecules show diffraction-limited spots with radii of approximately half the wavelength of the light used to interrogate them, and the underlying structure of the nanoscale object is not obvious to the eye. Fortunately, manipulation of excitation conditions and image processing techniques can tease out information about the morphology of nanomaterials investigated. The first example presented in this dissertation shows how an asymmetric excitation geometry and polarization spectroscopy elucidate the orientation of single silver triangular nanoprisms in the plane of an optical microscope’s stage. Characterizing this orientation using optical microscopy techniques opens possibilities for post-characterization nanoparticle functionalization and improved amplification of surface-enhanced spectroscopy signals. Electron microscopy may characterize single noble metal nanoparticles if one is unconcerned with those benefits, but electron microscopy investigations are more challenging for soft matter samples, so optical characterization becomes even more appealing for polymer studies. Bias-induced centroid (BIC) spectroscopy, correlated with polarization spectroscopy, reports not only on the distance over which highly ordered single poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) chains transfer energy, but also that the rod-like structures these polymers are believed to adopt are likely to transfer this energy along their longitudinal axes. BIC relies on observable changes in the position of the fluorescence centroid, but when the bias-induced hole-injection partially quenching the fluorescence occurs symmetrically, the displacement of the fluorescence centroid is small, and defining the displacement direction becomes difficult. In this event, analysis of the ellipticity of the diffraction-limited images of the MEH-PPV fluorescence also supports the conclusion that the polymer transfers energy in the direction of the longitudinal axis of the rod-like structure. Taken together, these wide-field optical techniques allow simultaneous morphological characterization of many single nanoparticles or single polymer chains without appealing to scanning probe or electron microscopies, which can damage the sample or prevent post-characterization modification.Chemistr

Nanostructured Materials for Solar Cell Applications

The use of nanomaterials in technologies for photovoltaic applications continues to represent an important area of research. There are numerous mechanisms by which the incorporation of nanomaterials can improve device performance. We invited authors to contribute articles covering the most recent progress and new developments in the design and utilization of nanomaterials for highly efficient, novel devices relevant to solar cell applications. This book covers a broad range of subjects, from nanomaterials synthesis to the design and characterization of photovoltaic devices and technologies with nanomaterial integration

Synthesis of poly(3-hexylthiophene) active layer with ZnO nanorods and AU nanoparticles for the fabrication of hybrid plasmonic solar cells

Purpose and method of study: In the present study, zinc oxide nanobars were synthesized by electrochemical method and poly(3-hexylthiophene) by template-assisted method, as well as gold nanoparticles by microwave. The three components were incorporated as part of a hybrid plasmonic solar cell, in two configurations: inverted ITO/ZnO/P3HT/Au and conventional ITO/P3HT/ZnO/Au. The nanobars and nanoparticles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, UV-Vis spectroscopy and dynamic light scattering. The solar cells were characterized with the use of a solar simulator and a picoammeter. Conclusions and contributions: A methodology was developed to adhere polymer nanorods, vertically aligned, on ITO glass; subsequently, ZnO nanobars were formed on the polymer matrix. Two hybrid plasmonic solar cells were fabricated in which gold nanoparticles were used as cathode; the nanoparticles were incorporated into the hybrid layer of ZnO and P3HT by electrophoretic deposition, which is presented as an alternative to the deposit of conductive metals by thermal evaporation. The basic parameters of the conventional solar cell were Voc = 200 mV, Jsc = 1.09x10-7 mA/cm2 , FF of 30%, while those of the inverted solar cell were Voc = 400 mV, Jsc = 6.95x10- 8 mA/cm2 , FF of 28%, however, the efficiencies of both were null (in the order of 10-7), due to the little contact between the different components of the cell

Gold nanorods functionalized with DNA oligonucleotide probes for biosensing and plasmon-enhanced fluorescence detection

Gold nanorods display plasmon resonances that are very sensitive to the refraction index close to the particle’s surface. The site-selective functionalization of Plasmon hot-spots with bioreceptors is crucial to develop plasmonic sensors with improved response bycapturing the target species at the most sensitive regions of the particle. Firstly, we used surface immobilized biotin-functionalized gold nanorods for streptavidin sensing.The selective functionalization of the nanorods’ tips was achieved with a CTAB bilayer and using a thiol linker to attach the desired biotin functionality. The sensor performance was characterized by measuring binding kinetic assays. In the recent years, Dengue virus DENV-2 has been reported as the largest dengue epidemic type and early stage detection of this virus would save the life of many patients. Thus, a plasmonic model biosensor was designed for the detection of RNA sequences proposed as disease biomarkers for Dengue virus.For this purpose, we have functionalized gold nanorods with thiolated DNA oligonucleotide probes complementary to a RNA sequence of Dengue virus.As a signal amplification strategy, we have used biotin-labeled oligonucleotide target sequences, in order to bind streptavidin or anti-biotin antibody to increase the surface plasmon response. Plasmon-enhanced fluorescence (PEF) microscopy provides fast, high-contrast, and lowbackground detection of single molecules. The interaction between the localized surface plasmon of gold nanorods and a fluorophore in their vicinity can induce the acceleration of excitation and decay rates thus leading to substantial fluorescence enhancements. In the third part of this Thesis, it was studied the interaction between gold nanorod antennas and a weakly fluorescence dye, TMPyP porphyrin. This interaction was mediated by electrostatic attraction between the tetracationic TMPyP and the DNA oligonucleotide coating on the nanorods’ surface. Preliminary measurements of optical spectroscopy were carried out to characterize the interaction in solution of TMPyP and single or double-stranded DNA oligonucleotides complementary to a RNA sequence of Dengue virus.The apparent equilibrium constants for the complex of TMPyP with single and double-stranded DNA were determined to be Ka= 3.9×107 M-1and 4.5×107 M-1respectively. The spectral changes show a strong specific intercalation of TMPyP with ds-DNA and ss-DNA because of GC-rich sites in the selected sequences. Next, the plasmon-enhanced fluorescence of TMPyP induced by gold nanorods was investigated using confocal fluorescence lifetime microscopy to perform measurements of nanoparticle emission intensity and spectrum, fluorescence correlation spectroscopy, emission intensity time trace and fluorescence decay. The gold nanorods were immobilized on glass and functionalized with a thiolated oligonucleotide coating, while TMPyP molecules are diffusing in solution and stochastically interact with the rod’s surface. The emission intensity traces measured on single particles show strong fluorescence bursts when TMPyP molecules come into close proximity of the nanorod. We have calculated the emission enhancement factors from a comparison with the non-enhanced emission of TMPyP in the same experimental conditions and found surprisingly large enhancement factors of around 60000-fold for TMPyP’s emission.These values of enhancement are two orders of magnitude larger than our calculated highest enhanced fluorescence expected for TMPyP molecule.Os nano-bastonetes de ouro são caracterizados por plasmões de superfície com frequências de ressonância bastante sensíveis ao índice de refração na proximidade da sua superfície. A funcionalização seletiva da superfície destas nanopartículas com bio-receptores é crucial para o desenvolvimento de sensores plasmónicos com resposta melhorada, pois permite a captura de analitos nas regiões mais sensíveis da nanopartícula. Em primeiro lugar foram preparadas superfícies com nano-bastonetes de ouro que depois foram funcionalizados com recetores biotina para ensaios modelo de deteção de estreptavidina. A funcionalização seletiva das extremidades dos nano-bastonetes foi conseguida através da proteção das suas paredes laterais com uma bicamada de tensioativo CTAB e usando uma biotina derivatizada com uma função tiól. O desempenho do sensor foi caracterizado por medidas da cinética de associação biotina-estreptavidina monitorizada por espectroscopia ótica de absorção. Em anos recentes, a infeção pelo vírus do Dengue DENV-2 tem sido relatada como a maior epidemia por este tipo de vírus, e a deteção precoce desta infeção poderia salvar a vida de muitos pacientes. Deste modo, foi desenhado um sensor plasmónico modelo para a deteção de sequências de ARN propostas como bio-marcadores para a infeção pelo vírus do Dengue. Para o efeito, foram funcionalizados nano-bastonetes de ouro com cadeias de oligonucleotídos de ADN complementares a uma sequência do ARN do vírus do Dengue. Como estratégia de amplificação de sinal foram usadas cadeias de oligonucleotídos alvo marcadas com biotina, de modo a ser possível num segundo passo ligar estreptavidina ou anticorpo anti-biotina com o objetivo de aumentar a resposta do plasmão de superfície dos nano-bastonetes de ouro. A fluorescência intensificada por efeito plasmónico permite a deteção rápida e com elevado contraste de molécula única em microscopia de fluorescência. A interação entre os modos localizados de plasmão de superfície de nano-bastonetes de ouro e moléculas fluorescentes na sua proximidade pode induzir a aceleração das taxas de excitação, decaimento radiativo e não-radiativo, e conduzir a uma intensificação de fluorescência.Na terceira parte desta Dissertação, foram investigadas as interações entre nano-antenas de ouro e um cromóforo pouco fluorescente, a porfirina TMPyP. Esta interação foi mediada pela atração eletrostática entre a porfirina tetra-catiónica e o revestimento de ADN na superfície dos nano-bastonetes de ouro. Ensaios preliminares de espectroscopia ótica foram realizados para caracterizar a interação em solução da TMPyP com sequências de ADN de cadeia simples ou duplacomplementares a uma sequência do ARN do vírus do Dengue. A constante aparente de equilíbrio para o complexo da TMPyP com as sequências de ADN de cadeia simples e dupla foram determinadas como sendo Ka= 3.9×107 M-1and 4.5×107 M-1, respetivamente. As alterações dos espectros de absorção e emissão mostram uma forte interação, provavelmente intercalação, daTMPyPcom ods-DNA,etambém com o ss-DNA, devido ao elevado conteúdo em pares GC nas sequências escolhidas. Em seguida, a fluorescência intensificada por efeito plasmónico na TMPyP induzida por nano-bastonetes de ouro foi investigada por microscopia confocal de tempos-de-vida, tendo sido realizadas medidas de intensidade e espectro de emissão de nanopartículas, espectroscopia de correlação de fluorescência, traços temporais de intensidade de emissão e de decaimento de fluorescência.Os nano-bastonetes de ouro foram imobilizados em vidro e funcionalizados com um revestimento de oligonucleotídostiolados, enquanto que as moléculas de TMPyP difundem-se em solução e podem interatuar estocasticamente com a superfície da nanopartícula. Os traços de intensidade de emissão medidos em nanopartículas individuais mostram picos de fluorescência intensos quando as moléculas de TMPyP se aproximam do nano-bastonete de ouro em resultado do efeito de nano-antena.Foram calculados os fatores de emissão intensificada por comparação com a emissão não-intensificada da TMPyP nas mesmas condições experimentais e obtiveram-se valores surpreendentemente elevados de cerca de 60000 vezes para a emissão intensificada da TMPyP. Estes fatores de intensificação são duas ordens de grandeza mais elevados do que as estimativas teóricas calculadas para a intensificação da emissão da TMPyP pelos nanobastonetes de ouro

Periodic semiconductor nano-structures for the enhanced photovoltaic devices

Department of Chemical EngineeringThe photovoltaic devices which convert the solar energy to the electrons or chemical materials become very important clean energy devices due to the environmental pollution from the fossil energy. The Dye-sensitized Solar cell (DSSC) which generates the electron-hole pairs using solar light and photoelectrochemical cell (PEC), one of the promising clean energy solar cells for capturing and storing solar energy by splitting water into a hydrogen and oxygen gas have received extensive attention because of high performance and low price. Enhancing optical property is the one of the fascinate strategy for the increasing the properties of photovoltaic devices. Interference lithography (IL) is a very convenient and fast method to fabricate the two/threedimensional polymer template in a submicrometer scale. By combining an IL technique and hydrothermal growth, the high crystalline periodic semiconductor nanowires such as ZnO, TiO2 and Fe2O3 can be fabricated. The 2D patterned semiconductor nanowires can be considered as a diffraction grating layer which can enhance the optical property for increasing the overall performance of photovoltaic devices such as DSSC and PEC. In this thesis, I studied on the synergetic effects of the IL technique and the hydrothermal growth method for enhancing the optical properties. The patterned nanowires with a subwavelength scale that act as the diffraction grating layer can increase the optical path in the photovoltaic devices. Especially, the absorption of visible wavelength of solar light (400nm ~ 800nm), a major source to generate the electron-hole pairs in the photovoltaic cells can be enhanced by the pattern nanowires. The outstanding properties of the 2D patterned nanowires suggest the great potential in energy-related devices such as DSSCs, PEC cells and sensor devices such as SERS.ope