Deducing Shape of Anisotropic Particles in Solution from Light Scattering: Spindles and Nanorods

Depolarized Dynamic light scattering (DDLS) enables to measure in situ rotational and translational diffusion of nanoparticles suspended in solution. Their size, shape, diffusion, and intermolecular interactions can be interred then from DDLS data using various models of diffusion. Incorporating DDLS to analyze the dimensions of easily imaged elongated particles, such as Iron (III) oxyhydroxide Spindles (FeOOH) and gold coated Nanorods, will allow a deeper understanding between rotational/translational diffusion and size distribution of hard-to-image anisotropic wet systems such as micelles, microgels, and protein complexes. The emphasis of this study was to look at the aged FeOOH Spindle sample, and explore the size distribution and modeling of the Nanorod particles. The light scattering results obtained from the basic model of non-interacting prolate ellipsoids offered dimensions similar (within 15%) to the size distribution from the Scanning Electron Microscope (SEM). The results, however, were somewhat different from the original particle size possibly due to sample aging and agglomeration of the FeOOH Spindles. Conversely, the Nanorod dimensions obtained from the Prolate Ellipsoid Model differed by a factor 1.2-2 from the values obtained by Transmission Electron Microscopy and SEM. The significant difference between DDLS and imaging results is due to the nature of the modeling employed (ellipsoid was used to model cylindrically shaped particles with spherical caps).https://engagedscholarship.csuohio.edu/u_poster_2015/1032/thumbnail.jp

Light Scattering Characterization of Elastin-Like Polypeptide Trimer Micelles

Elastin-Like Polypeptides (ELP) can be used to form thermo-reversible vehicles for drug delivery systems. The ELP nanoparticles are composed of three-armed star polypeptides. Each of the three arms extending from the negatively charged foldon domain includes 20 repeats of the (GVGVP) amino acid sequence. The ELP polymer chains are soluble at room temperature and become insoluble at the transition temperature (close to 50 oC), forming micelles. The size and shape of the micelle is dependent on the temperature and the pH of solution, along with the concentration of the Phosphate Buffered Saline (PBS) solvent. The technique of Depolarized Dynamic Light Scattering (DDLS) was employed to study the structure and dynamics of micelles at 62 oC; the solution was maintained at an approximate pH level of 7.3 - 7.5, while varying the concentration of the solvent (PBS). At low salt concentrations (\u3c 15 mM), the micellar size is not very reproducible due to unstable pH levels, arising from low buffer concentration. At intermediate salt concentrations (15 - 60 mM), the system formed spherically-shaped micelles exhibiting a steady growth in the hydrodynamic radius (Rh) from 10 to 21 nm, with increasing PBS concentration. Interestingly, higher salt concentrations (\u3e 60 mM) displayed an apparent elongation of the micelles evident by a significant VH signal, along with a surge in the apparent Rh. A model of micelle growth (and potentially elongation) with increase in salt concentration is considered.https://engagedscholarship.csuohio.edu/u_poster_2016/1038/thumbnail.jp

Light Scattering Study of Mixed Micelles Made from Elastin-Like Polypeptide Linear Chains and Trimers

Temperature sensitive nanoparticles (E20F) were generated from a construct of three chains of Elastin- Like Polypeptides (ELP) linked to a negatively charged foldon domain. This ELP system was mixed at different ratios with a single linear chain of ELP (H40L) which was deprived of the foldon domain. The mixed system is soluble at room temperature and at a transition temperature will form swollen micelles with the hydrophobic linear chains hidden inside. This system was studied using Depolarized Dynamic Light Scattering (DDLS) and Static Light Scattering (SLS) to model the size, shape, and internal structure of the mixed micelles. The mixed micelle in equal parts of E20F and H40L show a constant apparent hydrodynamic radius of 40-45 nm at the concentration window from 25:25 to 60:60 μM (1:1 ratio). At a fixed 50 μM concentration of the E20F with varying H40L concentrations from 5 to 80 μM, a linear growth in the hydrodynamic radius is seen from about 11 to about 62 nm, along with a 1000-fold increase in VH signal. A possible simple model explaining the growth of the mixed micelles is considered. Lastly, the VH signal can indicate elongation in the geometry of the particle or could possibly be a result from anisotropic properties from the core of the micelle. Static Light Scattering was used to study the molecular weight, and the radius of gyration of the micelle to help identify the structure and morphology of mixed micelles and the tangible cause of the VH signal.https://engagedscholarship.csuohio.edu/u_poster_2016/1039/thumbnail.jp

P2: Light Scattering Study of the Size and Shape of Mixed Elastin-Like Polypeptide Micelles

Elastin-Like Polypeptides (ELP) can be used to form thermoreversible vehicles for drug delivery systems. The ELP nanoparticles are composed of three-armed star polypeptides. Each of the three arms extending from the negatively charged foldon domain include 20 repeats of the (GVGVP) amino acid sequence. In addition, linear constructs composed of 40 repeats of the same (GVGVP) sequence are introduced into the system. The mixed ELP polymer system is soluble at room temperature and becomes insoluble at the transition temperature (~ 50°C) forming micelles with the foldons on the exterior and linear constructs at the core. Above the transition, the size and shape of the mixed micelles are dependent on the pH of the solution, concentration of the PBS solvent, and the ratio of the linear to foldon concentration. The technique of Depolarized Dynamic Light Scattering (DDLS) was employed to study the structure and dynamics of the mixed micelles at 62oC and maintained at an approximate pH level of 7.3 - 7.5. The ELP foldon micelles have a radius of 10 nm; the introduction of the linear concentration leads to a growth of mixed micelles at a linear rate, when the PBS and foldon concentrations are fixed. A model explaining this linear growth was developed utilizing the molar volumes of the mixed system. Static Light Scattering results seemingly support this model. However, the apparent VH signal found can indicate elongation in the geometry of the particles or anisotropic properties of the core of the mixed micelle.https://engagedscholarship.csuohio.edu/u_poster_2017/1046/thumbnail.jp

P1: Salt Concentration and pH Affect the Size of Elastin-Like Polypeptide Nanoparticles

The transport of therapeutic drugs to specific tissues in the body can be accomplished using nanoparticles that encapsulate the drugs. Elastin-like polypeptides (ELP) is a class of materials that can reversibly form such nanoparticles in response to environmental cues. FLPs transition from soluble compounds to a phase separated system under particular solution conditions and have been used to produce temperature responsive surfactants. When these ELP surfactants are above their transition temperature, they spontaneously form energetically stable spherical micelles. When the temperature drops below the transition temperature, the micelles break apart and the ELP goes into solution. The size of these micelles can change depending on the solution conditions, including pH and salt concentration. We studied how the size of the micelles are affected by these solution conditions by using dynamic light scattering to determine the diameter of the ELP micelles. When the salt concentration increased, we found that there was a region of constant size followed by a region of linear increase in diameter. Following the linear region, there is a jump in micelle size. As the pH of the solution increased from neutral pH, the diameter drastically increased. As pH decreased from neutral pH, the diameter slightly increased.https://engagedscholarship.csuohio.edu/u_poster_2017/1045/thumbnail.jp

Deducing Shape of Anisotropic Particles in Solution from Light Scattering: Spindles and Nanorods

Depolarized Dynamic light scattering (DDLS) enables to measure in situ rotational and translational diffusion of nanoparticles suspended in solution. Their size, shape, diffusion, and intermolecular interactions can be interred then from DDLS data using various models of diffusion. Incorporating DDLS to analyze the dimensions of easily imaged elongated particles, such as Iron (III) oxyhydroxide Spindles (FeOOH) and gold coated Nanorods, will allow a deeper understanding between rotational/translational diffusion and size distribution of hard-to-image anisotropic wet systems such as micelles, microgels, and protein complexes. The emphasis of this study was to look at the aged FeOOH Spindle sample, and explore the size distribution and modeling of the Nanorod particles. The light scattering results obtained from the basic model of non-interacting prolate ellipsoids offered dimensions similar (within 15%) to the size distribution from the Scanning Electron Microscope (SEM). The results, however, were somewhat different from the original particle size possibly due to sample aging and agglomeration of the FeOOH Spindles. Conversely, the Nanorod dimensions obtained from the Prolate Ellipsoid Model differed by a factor 1.2-2 from the values obtained by Transmission Electron Microscopy and SEM. The significant difference between DDLS and imaging results is due to the nature of the modeling employed (ellipsoid was used to model cylindrically shaped particles with spherical caps).https://engagedscholarship.csuohio.edu/u_poster_2015/1032/thumbnail.jp

P2: Light Scattering Study of the Size and Shape of Mixed Elastin-Like Polypeptide Micelles

Elastin-Like Polypeptides (ELP) can be used to form thermoreversible vehicles for drug delivery systems. The ELP nanoparticles are composed of three-armed star polypeptides. Each of the three arms extending from the negatively charged foldon domain include 20 repeats of the (GVGVP) amino acid sequence. In addition, linear constructs composed of 40 repeats of the same (GVGVP) sequence are introduced into the system. The mixed ELP polymer system is soluble at room temperature and becomes insoluble at the transition temperature (~ 50°C) forming micelles with the foldons on the exterior and linear constructs at the core. Above the transition, the size and shape of the mixed micelles are dependent on the pH of the solution, concentration of the PBS solvent, and the ratio of the linear to foldon concentration. The technique of Depolarized Dynamic Light Scattering (DDLS) was employed to study the structure and dynamics of the mixed micelles at 62oC and maintained at an approximate pH level of 7.3 - 7.5. The ELP foldon micelles have a radius of 10 nm; the introduction of the linear concentration leads to a growth of mixed micelles at a linear rate, when the PBS and foldon concentrations are fixed. A model explaining this linear growth was developed utilizing the molar volumes of the mixed system. Static Light Scattering results seemingly support this model. However, the apparent VH signal found can indicate elongation in the geometry of the particles or anisotropic properties of the core of the mixed micelle.https://engagedscholarship.csuohio.edu/u_poster_2017/1046/thumbnail.jp

P1: Salt Concentration and pH Affect the Size of Elastin-Like Polypeptide Nanoparticles

The transport of therapeutic drugs to specific tissues in the body can be accomplished using nanoparticles that encapsulate the drugs. Elastin-like polypeptides (ELP) is a class of materials that can reversibly form such nanoparticles in response to environmental cues. FLPs transition from soluble compounds to a phase separated system under particular solution conditions and have been used to produce temperature responsive surfactants. When these ELP surfactants are above their transition temperature, they spontaneously form energetically stable spherical micelles. When the temperature drops below the transition temperature, the micelles break apart and the ELP goes into solution. The size of these micelles can change depending on the solution conditions, including pH and salt concentration. We studied how the size of the micelles are affected by these solution conditions by using dynamic light scattering to determine the diameter of the ELP micelles. When the salt concentration increased, we found that there was a region of constant size followed by a region of linear increase in diameter. Following the linear region, there is a jump in micelle size. As the pH of the solution increased from neutral pH, the diameter drastically increased. As pH decreased from neutral pH, the diameter slightly increased.https://engagedscholarship.csuohio.edu/u_poster_2017/1045/thumbnail.jp

La Atalaya : diario de la mañana: Año XXII Número 8327 - 1914 septiembre 30

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte. Subdirección General de Coordinación Bibliotecaria, 201