One way to successfully enhance light harvesting of excitonic solar cells is the integration of optical elements that
increase the photon path length in the light absorbing layer. Device architectures which incorporate structural
order in form of one- or three-dimensional refractive index lattices can lead to the localization of light in specific
parts of the spectrum, while retaining the cell's transparency in others. Herein, we present two routes for the
integration of photonic crystals (PCs) into dye-sensitized solar cells (DSCs). In both cases, the self-assembly of
soft matter plays a key role in the fabrication process of the TiO2 electrode. One approach relies on a combination
of colloidal self-assembly and the self-assembly of block copolymers, resulting in a double layer dye-sensitized
solar cell with increased light absorption from the 3D PC element. An alternative route is based on the fact
that the refractive index of the mesoporous layer can be finely tuned by the interplay between block copolymer
self-assembly and hydrolytic TiO2 sol-gel chemistry. Alternating deposition of high and low refractive index
layers enables the integration of a 1D PC into a DSC.
Mesoporous distributed Bragg re
ectors (MDBRs) exhibit porosity on the sub-optical length scale. This makes
them ideally suited as sensing platforms in biology and chemistry as well as for light management in optoelectronic
devices. Here we present a new fast forward route for the fabrication of MDBRs which relies on the self-assembling
properties of the block copolymer poly(isoprene-block-ethylene oxide) (PI-b-PEO) in combination with sol-gel
chemistry. The interplay between structure directing organic host and co-assembled inorganic guest allows the
ne tuning of refractive index in the outcome material. The refractive index dierence between the high and low
porosity layer can be as high as 0.4, with the optical interfaces being well dened. Following a 30 min annealing
protocol after each layer deposition enables the fast and reliable stacking of MDBRs which exhibit a continuous
TiO2 network with large accessible pores and high optical quality.
Progress in biomedical imaging depends on the development of probes that combine low toxicity with high sensitivity, resolution, and stability. Toward that end, a new class of highly fluorescent core-shell silica nanoparticles with narrow size distributions and enhanced photostability, known as C dots, provide an appealing alternative to quantum dots. Here, C dots are evaluated with a particular emphasis on in-vivo applications in cancer biology. It is established that C dots are nontoxic at biologically relevant concentrations, and can be used in a broad range of imaging applications including intravital visualization of capillaries and macrophages, sentinel lymph node mapping, and peptide-mediated multicolor cell labeling for real-time imaging of tumor metastasis and tracking of injected bone marrow cells in mice. These results demonstrate that fluorescent core-shell silica nanoparticles represent a powerful novel imaging tool within the emerging field of nanomedicine.
We report the successful fabrication of layers of functionalized nanoparticles using a novel infrared, laser-based
deposition technique. A frozen suspension of nanoparticles was ablated with a laser tuned to a vibrational mode of the
solvent, resulting in the disruption of the matrix and ejection of the nanoparticles. The solvent was pumped away and
the nanoparticles collected by a receiving substrate in a conformal process. Photoluminescence measurements of
nanoparticles containing two common dyes showed no significant change to the emission properties of either dye,
suggesting that no damage occurred during the laser ablation process. The process is generally applicable to particles of
various sizes, shapes, and chemistries provided that an appropriate solvent is chosen. Deposition through shadow masks
turned out to be straightforward using this technique, suggesting its potential utility in preparing designer sensor
structures using functionalized nanoparticles.
We report on monodisperse fluorescent core-shell silica nanoparticles (C dots) with enhanced brightness and photostability as compared to parent free dye in aqueous solution. Dots containing either tetramethylrhodamine or 7-nitrobenz-2-oxa-1,3-diazole dyes with diameters ranging from tens of nanometers to microns are discussed. The benefits of the core-shell architecture are described in terms of enhanced fluorescent yield of the fluorophores in the quasi-solid-state environment within the particle as compared with parent free dye in water. Several applications of these particles in the fields of photonics and the life sciences are discussed. Specifically, fluorescent core-shell silica nanoparticles are investigated as an active medium for photonic building blocks assembled on zinc sulfide-based seed particles. Initial assembly results for these composite raspberry structures are shown. Finally, applications in the life sciences are explored, including targeting of specific antibody receptors using these single-emission nanoparticles. We expand on single-emission core-shell architecture to incorporate environmentally-sensitive fluorophores to create quantitative ratiometric nanoscale sensors capable of interrogating chemical concentrations on the sub-cellular to molecular levels and demonstrate initial results of intracellular pH imaging. The concept of a single particle laboratory (SPL) is introduced as an active investigator of its environment.
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