22 research outputs found
Single molecule studies of meso/macro porous silica materials and gradient films
Doctor of PhilosophyDepartment of ChemistryDaniel A. HigginsThe preparation of mesoporous/macroporous silica materials and polarity gradient thin film are introduced in this thesis. These porous silica materials and gradient materials have the potential applications as stationary phases for chemical separations, as materials for combinatorial catalysis and as absorbent/adsorbent layers for use in chemical or biological sensors. Single molecule spectroscopy is used to probe the chemical interaction between single dye molecule and porous silica matrix. Bulk fluorescence spectroscopy is used to investigate the properties of gradient film.
In Chapter one, the applications of single molecule spectroscopic methods to sol-gel silica materials are reviewed, which covers a subset of the recent literature in this area and provided salient examples of the new information that can be obtained by single molecule studies.
In Chapter two, both the sample preparation and experiment setup are covered.
In Chapter three, the preparation of mesoporous silica film is presented. Single molecule spectroscopy is used to probe the mass transport and molecule-matrix interactions in mesoporous thin-film systems. Three different dyes of varying size, charge, and hydrophilicity are used. Silica films with/without surfactant or containing different kind surfactant are studied. The results provide new information on mass transport through the films, evidence of reversible surface adsorption, and quantitative information on variations in these phenomena with film hydration.
In Chapter four, a new model describing how to explore the actual dye concentration in single molecule experiment with considering the molecule orientation is presented, which is verified to be correct by both experimental and simulated data.
In Chapter five, the growth process of Methylsilsesquioxane (MSQ) particle is studied by single molecule spectroscopy, in which, the MSQ particle is treated as ānativeā dye molecule.
In Chapter six, silica films incorporating polarity gradients are produced by using āinfusion-withdrawal dip-coatingā method. The gradient film is characterized by bulk fluorescence spectroscopy, water contact angle and FTIR.
In Chapter seven, a brief conclusion is drawn and future directions are presented
High-intensity near-IR fluorescence in semiconducting polymer dots achieved by cascade FRET strategy
Near-IR (NIR) emitting semiconducting polymer dots (Pdots) with ultrabright fluorescence have been prepared for specific cellular targeting. A series of Ļ-conjugated polymers were synthesized to form water dispersible multicomponent Pdots by an ultrasonication-assisted co-precipitation method. By optimizing cascade energy transfer in Pdots, high-intensity NIR fluorescence (Ī¦ = 0.32) with tunable excitations, large absorptionāemission separation (up to 330 nm), and narrow emission bands (FWHM = 44 nm) have been achieved. Single-particle fluorescence imaging show that the as-prepared NIR Pdots were more than three times brighter than the commercially available Qdot705 with comparable sizes under identical conditions of excitation and detection. Because of the covalent introduction of carboxylic acid groups into polymer side chains, the bioconjugation between NIR-emitting Pdots and streptavidins can be readily completed via these functional groups on the surface of Pdots. Furthermore, through flow cytometry and confocal fluorescence microscopy the NIR-emitting Pdotāstreptavidin conjugates proved that they could effectively label EpCAM receptors on the surface of MCF-7 cells, via specific binding between streptavidin and biotin
Lyophilization of Semiconducting Polymer Dot Bioconjugates
Semiconducting
polymer dot (Pdot) bioconjugates are a new class
of ultrabright fluorescent probes. Here, we report a procedure for
lyophilizing Pdot bioconjugates so that they successfully retain their
optical properties, colloidal stability, and cell-targeting capability
during storage. We found that, when Pdot bioconjugates were lyophilized
in the presence of 10% sucrose, the rehydrated Pdot bioconjugates
did not show any signs of aggregation and exhibited the same hydrodynamic
diameters as before lyophilization. The brightness of the lyophilized
Pdots was at least as good as before lyophilization, but in some cases,
the quantum yield of lyophilized Pdots curiously showed an improvement.
Finally, using flow cytometry, we demonstrated that lyophilized Pdot
bioconjugates retained their biological targeting properties and were
able to effectively label cells; in fact, cells labeled with lyophilized
Pdot bioconjugates composed of PFBT, which were stored for 6 months
at ā80 Ā°C, were ā¼22% brighter than those labeled
with identical but unlyophilized Pdot bioconjugates. These results
indicate lyophilization may be a preferred approach for storing and
shipping Pdot bioconjugates, which is an important practical consideration
for ensuring Pdots are widely adopted in biomedical research
Importance of Having Low-Density Functional Groups for Generating High-Performance Semiconducting Polymer Dots
Semiconducting polymers with low-density side-chain carboxylic acid groups were synthesized to form stable, functionalized, and highly fluorescent polymer dots (Pdots). The influence of the molar fraction of hydrophilic side-chains on Pdot properties and performance was systematically investigated. Our results show that the density of side-chain carboxylic acid groups significantly affects Pdot stability, internal structure, fluorescence brightness, and nonspecific binding in cellular labeling. Fluorescence spectroscopy, single-particle imaging, and a dye-doping method were employed to investigate the fluorescence brightness and the internal structure of the Pdots. The results of these experiments indicate that semiconducting polymers with low density of side-chain functional groups can form stable, compact, and highly bright Pdots as compared to those with high density of hydrophilic side-chains. The functionalized polymer dots were conjugated to streptavidin (SA) by carbodiimide-catalyzed coupling and the Pdot-SA probes effectively and specifically labeled the cancer cell-surface marker Her2 in human breast cancer cells. The carboxylate-functionalized polymer could also be covalently modified with small functional molecules to generate Pdot probes for click chemistry-based bio-orthogonal labeling. This study presents a promising approach for further developing functional Pdot probes for biological applications
Hybrid Semiconducting Polymer DotāQuantum Dot with Narrow-Band Emission, Near-Infrared Fluorescence, and High Brightness
This communication describes a new class of semiconducting
polymer
nanoparticleāquantum dot hybrid with high brightness, narrow
emission, near-IR fluorescence, and excellent cellular targeting capability.
Using this approach, we circumvented the current difficulty with obtaining
narrow-band-emitting and near-IR-fluorescing semiconducting polymer
nanoparticles while combining the advantages of both semiconducting
polymer nanoparticles and quantum dots. We further demonstrated the
use of this new class of hybrid nanomaterial for effective and specific
cellular and subcellular labeling without any noticeable nonspecific
binding. This hybrid nanomaterial is anticipated to find use in a
variety of in vitro and in vivo biological applications
Single-Chain Semiconducting Polymer Dots
This
work describes the preparation and validation of single-chain
semiconducting polymer dots (<i>s</i>Pdots), which were
generated using a method based on surface immobilization, washing,
and cleavage. The <i>s</i>Pdots have an ultrasmall size
of ā¼3.0 nm as determined by atomic force microscopy, a size
that is consistent with the anticipated diameter calculated from the
molecular weight of the single-chain semiconducting polymer. <i>s</i>Pdots should find use in biology and medicine as a new
class of fluorescent probes. The FRET assay this work presents is
a simple and rapid test to ensure methods developed for preparing <i>s</i>Pdot indeed produced single-chain Pdots as designed