Approaches to Quantifying and Visualizing Polyelectrolyte Multilayer Film Formation on Particles

Abstract

Colloidal particles prepared by using the layer-by-layer technique are increasingly finding application in diagnostics, drug delivery, and sensing. Herein, we outline methods for applying three established techniques, confocal laser scanning microscopy (CLSM), flow cytometry, and differential interference contrast (DIC) microscopy, to characterize ultrathin films of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) assembled on silica particles. Both CLSM and flow cytometry require the use of fluorescently labeled polyelectrolytes (PEs). The film homogeneity can be assessed using CLSM, while flow cytometry allows analysis at unparalleled speed (thousands of particles per second) with unprecedented sensitivity (<0.5 fg of adsorbed polymer) of polydispersed particles of different size ( approximately 300 nm to tens of micrometers). Using CLSM and flow cytometry measurements, in conjunction with quartz crystal microgravimetry measurements on planar supports, allows quantification of PSS/PAH layer buildup on the particles. Furthermore, flow cytometry and DIC microscopy were used to unequivocally distinguish between silica-core PSS/PAH-shell particles and hollow PSS/PAH capsules obtained following core removal. The techniques outlined here are not limited to measuring PE deposition on solid particles but, in principle, are equally applicable to quantifying the adsorption of other materials (such as DNA, proteins, or nanoparticles) on a variety of particulate systems, including hollow capsules, emulsions, and cells.

Assembly of erodible, DNA-containing thin films on the surfaces of polymer microparticles: Toward a layer-by-layer approach to the delivery of DNA to antigen-presenting cells

“…Although the zeta potential profile in Figure 2A is consistent with layer-by-layer film growth, we note that these results could also arise from the iterative displacement (or stripping) of adsorbed layers of polymer or DNA from particle surfaces by an oppositely charged species upon exposure to each subsequent polyelectrolyte solution [56]. To further confirm layer-by-layer film growth, we characterized increases in the fluorescence intensities of film-coated particles during the assembly of films fabricated using fluorescently labeled DNA.…”

“…These techniques cannot generally be used to characterize the growth of films assembled on the surfaces of colloidal microparticles [56]. However, past studies have demonstrated that changes in the zeta potentials of particles (e.g., as should occur after the adsorption of a negatively charged polymer or a positively charged polymer to the surface of a microparticle) can be used to characterize film growth and assembly [43, 56–59]. Figure 2A shows representative changes in the zeta potentials of particles during the fabrication of a polymer/DNA film 2.5 bilayers thick.…”

Basic Law Controlling the Growth Regime of Layer‐by‐Layer Assembled Polyelectrolyte Multilayers

“…The permeability of the film is low [42] and the mass of the multilayer increases linearly with the number of bilayers. [43] In PDDA/PSS system, the grooves and holes spread on the surface of film and the multilayer is loose. It is favorable for the permeation of polyelectrolyte molecules and the formation of an exponentially-growing multilayer, through the polyelectrolyte diffusing ''in'' and ''out of'' the film.…”

Comparison of New and Legacy TATBs

“…In some instances it is possible to distinguish inter-crystalline interfaces due to differences in refractive indices between crystals. [31][32][33] Photomicrographs, shown in Figure 8, were taken at the highest magnification (~1000x) and the 20 μm bar in the lower left micrograph is representative for all photos. At the highest pressures, usually TATB crystals are no longer identifiable due to surface damage and flow.…”