Spin‐assembly is an excellent method for controlling the amount and thickness of adsorbed polyelectrolyte in fabricating multilayer thin films. These films are investigated by means of ellipsometry and UV‐vis spectroscopy and their spectral properties are used to determine the effect of the polyelectrolyte concentration, the speed of rotation, and other experimental parameters on the film thickness and uniformity. Adjusting these parameters allows fine‐tuning of the multilayer thin films and provides the spin‐assembly method with a control tool for many future applications.

Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for numerous applications including energy storage, heterogeneous catalysis, and greenhouse gas adsorption. Much of the early work has focused on the bulk properties of microcrystalline ZIFs. Herein, we focus on identifying the nature of the surface of ZIF-8 by studying a supported ZIF-8 nanoparticle film using surface characterization techniques. We have experimentally identified the presence of a zinc-rich surface terminated by carbonates and water/hydroxyl groups (in addition to the expected methylimidazole terminations) using X-ray photoelectron spectroscopy (XPS). The thermal stability of ZIF-8 thin films was also investigated using scanning electron microscopy (SEM) and temperature-programmed reaction spectroscopy (TPRS). We determined the onset of decomposition of ZIF-8 thin films to be approximately 630 K using TPRS in an ultrahigh vacuum (UHV) environment. This work presents the first characterization steps needed to study the evolution of ZIF surfaces in situ using surface characterization techniques. Such techniques are capable of determining reaction products and tracking intermediates and surface evolution in gas adsorption/reaction studies of thin films.

Reversible interactions between DNA and silica are utilized in the solid phase extraction and purification of DNA from complex samples. Chaotropic salts commonly drive DNA binding to silica, but inhibit DNA polymerase amplification. We studied DNA adsorption to silica using conditions with or without chaotropic salts through bulk depletion and Quartz Crystal Microbalance (QCM) experiments. While more DNA adsorbed to silica using chaotropic salts, certain buffer conditions without chaotropic salts yielded a similar amount of eluted DNA. QCM results indicate that under stronger adsorbing conditions, the adsorbed DNA layer is initially rigid, but becomes viscoelastic within minutes. These results qualitatively agreed with a mathematical model for a multiphasic adsorption process. Buffer conditions that do not require chaotropic salts can simplify protocols for nucleic acid sample preparation. Understanding how DNA adsorbs to silica can help optimize nucleic acid sample preparation for clinical diagnostic and research applications.

Supported lipid bilayers (SLBs) are widely studied model membrane platforms that are compatible with various surface-sensitive measurement techniques. SLBs are typically formed on silica-based materials, and there are numerous possible fabrication routes involving either bottom-up molecular self-assembly or vesicle adsorption and rupture. In between these two classes of fabrication strategies lies an emerging approach based on depositing quasi-two-dimensional lamellar, bicellar disks composed of a mixture of long-chain and short-chain phospholipids to promote the formation of SLBs. This approach takes advantage of the thermodynamic preference of long-chain phospholipids to form planar SLBs, whereas short-chain phospholipids have brief residence times. Although a few studies have shown that SLBs can be formed on silica-based materials from bicellar mixtures, outstanding questions remain about the self-assembly mechanism as well as the influence of the total phospholipid concentration, ratio of the two phospholipids (termed the "q-ratio"), and process of sample preparation. Herein, we address these questions through comprehensive quartz crystal microbalance-dissipation, fluorescence microscopy, and fluorescence recovery after photobleaching experiments. Our findings identify that optimal SLB formation occurs at lower total concentrations of phospholipids than previously used as short-chain phospholipids behave like membrane-destabilizing detergents at higher concentrations. Using lower phospholipid concentrations, we also discovered that the formation of SLBs proceeds through a two-step mechanism involving a critical coverage of bicellar disks akin to vesicle fusion. In addition, the results indicate that at least one cycle of freeze-thaw-vortexing is useful during the sample preparation process to produce SLBs. Taken together, the findings in this work identify optimal routes for fabricating SLBs from bicellar mixtures and reveal mechanistic details about the bicelle-mediated SLB formation process, which will aid further exploration of bicellar mixtures as tools for model membrane fabrication.

Polyelectrolyte thin films composed of alternating layers were spin-assembled by sequentially dropping cationic and anionic aqueous solutions onto a spinning substrate. In this work, we show the applicability of our technique to multiple systems and present two methods for producing linear film growth. The polycations used were PEI (poly(ethylenimine), PDDA (poly(diallyldimethylammonium chloride), PAH (poly(allylamine hydrochloride), and two poly(propylenimine) dendrimers (generations 3.0 and 4.0). The polyanions used were PAZO (poly[1-[4-(3-carboxy-4-hydroxy-phenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt]), PSS (poly(styrenesulfonate)), and PAA (poly(acrylic acid)). Layer thicknesses for all systems were determined using single-wavelength ellipsometry. UV−vis spectroscopy was used to measure deposition amounts in films containing the chromophoric polyanions PAZO and PSS. We demonstrate the ability to spin-assemble multilayered thin films up to 50 bilayers with linear increases in deposition amount between bilayers. Additionally, we show that layers of a single polyelectrolyte species can be spin-assembled with multiple deposition cycles in which consistent amounts are deposited in each cycle. In a comparison of films built from two dendrimer generations, films incorporating generation 3.0 dendrimer and PAZO show signs of higher interpenetration between layers and a more collapsed film structure than films assembled from generation 4.0 dendrimer and PAZO. Our results also suggest that a substrate effect influences the packing density of the first few bilayers, eventually dissipating around a film thickness of 50−80 Å.