Mapping heterogeneous polarity in multicompartment nanoparticles (original) (raw)
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Using a novel method developed to quantify the polarizability of photoluminescent nanoparticles in water, we present experimental observations of the extraordinary polarizability exhibited by nanoparticles of commensurate size with the Debye screening length, confirming previously reported theory. Semiconductor quantum dots (QDs) are ideal model nanoparticles to demonstrate this assay, due to their tunable size and bright photoluminescence. This assay is based upon microfluidic chambers with microelectrodes that generate trapping potentials that are weaker than thermal energy. By comparing the local electric field strength and variations in QD concentration, their polarizability was computed and found to agree with estimates based upon the hydrodynamic diameter found using light scattering. Strikingly, the polarizability of the nanoparticles increased 30-fold in low salt conditions compared to high salt conditions due to the increased thickness of the Debye layer relative to the particle radius. In addition to providing evidence that corroborates theoretical work studying direct solutions to the Poisson−Nernst− Planck equations, these observations provide an explanation for the previously observed conductivity dependence of biomolecule polarizability. As the polarizability of nanoparticles is of high importance to the electrically directed assembly of particles, as well as their interactions with other materials in complex environments, we anticipate that these results will be highly relevant to ongoing efforts in materials by design and nanomedicine.
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Photochem
The study of local polarity at the nanoscale is of crucial importance for the development of smart drug delivery systems and photonic materials and is frequently accomplished with the use of luminescent tracer dyes. Nile Red is often used for this purpose, owing to its polarity-sensitive internal charge transfer transition, but its performance is affected by specific solute-solvent interactions that prevent its widespread applicability. Herein, we develop a new 1,8-naphthalimide dye with a strong charge-transfer transition that results in a large dipole moment change upon excitation. This leads to luminescence properties with high sensitivity to solvent polarity, that are independent of specific or inductive interactions. These properties are explored to probe the polarity of biocompatible nanocarriers. This dye was effective in probing the properties of polymeric nanoparticles, allowing the accurate calculation of polarity descriptors and dielectric constants.
Chemistry - A European Journal, 2003
Azamethine dyes of the merocyanine type [4-(N,N-din -butylamino)-2-methylphenyl]{2,4-di-keto-3-[N'-(n-hexyl)]-5-cyano-6-methyl-3-pyridin-io}-1-azamethine (1) and [4-(N,N-diethylamino)-2-(N'-tert-butylcarboxy)amidophenyl]-{2,4-diketo-3-[N''-(n-hexyl)]-5-cyano-6-methyl-3-pyridinio}-1azamethine (2) have been used as surface-polarity indicators for gold-clusterfunctionalized silica particles. Their UV/ Vis absorption maxima range from about l 600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold (l % 520 ± 540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet ± Taft solvent polarity parameters a and p*. They are mainly sensitive to the dipolarity/polarizability (p* term; 70 ± 75 %) and HBD (hydrogen-bond donating) acidity (a term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2dichloroethane or cyclohexane. The surface polarities of gold-cluster-functionalized silica particles, with and without co-adsorbed l-cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum-chemical calculations by using the AM1 and PM3 methods.
Mapping the Distribution of an Individual Chromophore Interacting with Silica-Based Nanomaterials
Journal of the American Chemical Society, 2010
Exploring the interactions of molecules with silica-based mesoporous and nanoparticle materials at the atomic level and understanding of the forces that govern such H-bonds and electrostatic interactions are of fundamental importance to nanocatalysis, nanomedicine, and nanophotonics. In our approach, we studied in single-molecule time and spectral domains a proton-transfer chromophore complexed (by diffusion) and covalently bonded to MCM-41 mesoporous nanomaterial and silica particles. The results reveal strong dependence of the distribution and behavior of the interacting single molecule with the nanopores on the mode of sample preparation and nature of the involved interaction. The change at the single molecule level results in an up to 126 nm (∼4650 cm-1) spectral shift (from 462 to 588 nm) and almost two times longer lifetime. Furthermore, a change in the electronic charges of the mesoporous framework results in significant narrowing in the emission band of the guest. The results are explained in terms of electronic nanoconfinement but at a single-molecular level.
Nile-Red–Nanoclay Hybrids: Red Emissive Optical Probes for Use in Aqueous Dispersion
Langmuir, 2013
Water-dispersible and (bio)functionalizable nanoclays have a considerable potential as inexpensive carriers for organic molecules like drugs and fluorophores. Aiming at simple design strategies for redemissive optical probes for the life sciences from commercial precursors with minimum synthetic effort, we systematically studied the dye loading behavior and stability of differently functionalized laponites. Here, we present a comprehensive study of the absorption and emission properties of the red emissive hydrophobic and neutral dye Nile Red, a well known polarity probe, which is almost insoluble and nonemissive in water. Adsorption of this probe onto disk-shaped nanoclays was studied in aqueous dispersion as function of dye concentration, in the absence and presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) assisting dye loading, and as a function of pH. This laponite
Macromolecules, 2012
We systematically assessed the loading behavior of coremultishell nanoparticles (CMS NPs) for the solvatochromic dyes Coumarin 153 and Nile Red and studied the influence of the guest and its concentration on CMS NP aggregation using steady state absorption and fluorescence spectroscopy and dynamic light scattering (DLS). These measurements revealed the strong fluorescence of dye-loaded CMS NPs and formation of nonemissive dye aggregates in the outer CMS layer at higher loading concentrations of Nile Red, whereas in the case of Coumarin 153, a new species with red-shifted absorption and blue-shifted emission appeared. Moreover, dye loading triggers an aggregation of CMS NPs which have a hydrodynamic radius of 8 nm, thereby leading to CMS aggregates with a radius of 100−120 nm. These results underline the need for systematic studies of the influence of the guest and its loading concentration on CMS NP size for cellular uptake and in vivo imaging studies and the rational design of CMS NPs with improved transport and targeting abilities.