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Gene expression within cells can be altered through gene delivery approaches, which have tremendous potential for gene therapy, tissue engineering, and diagnostics. Substrate-mediated gene delivery describes the delivery of plasmid DNA or DNA complexed with nonviral vectors to cells from a surface, with the DNA immobilized to a substrate through specific or nonspecific interactions. In this work, DNA-nanoparticle (DNA–NP) adsorption to substrates is evaluated using combinatorial, in situ spectroscopic ellipsometry and quartz crystal microbalance with dissipation (SE/QCM-D), to evaluate the basic dynamic processes involved in the adsorption and immobilization of DNA–NP complexes to substrates. The concentration of DNA–NP solutions influences the adsorbed DNA–NP surface mass, which increases by a factor of approximately 6 (detected by SE) and approximately 4.5-fold (detected by QCM-D), as the DNA concentration increases from 1.5 μg/mL to 15 μg/mL, with an increase in layer porosity. In addition, SE/QCM-D analysis indicates that DNA–NP adsorption rates, surface coverage densities, and volume fractions are dependent on the type of substrate: gold (Au) and silicon dioxide substrates, protein-coated and uncoated substrates, and surfaces modified with alkanethiol self assembled monolayers (SAMs). These studies also demonstrate that the influence of an adsorbed protein layer on resulting DNA–NP immobilization efficiency is substrate dependent. For example, Au surfaces coated with fetal bovine serum (FBS) resulted in two-fold greater mass of adsorbed DNA–NPs, compared to DNA–NP adsorption to FBS-coated SAM substrates. This investigation offers insights into dynamic DNA–NP surface adsorption processes, characteristics of the immobilized DNA–NP layer, and demonstrates substrate-dependent DNA–NP adsorption.

Self-assembled monolayers (SAMs) formed via chemisorption are important for a variety of surface enhancement and biological applications. We demonstrate that combinatorial spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) provides dynamic, in-situ characterization of the chemisorption process. In agreement with other studies, we find there are two steps for 1-decanethiol, an example alkanethiol SAM, chemisorption onto gold, which are a brief, fast phase followed by one that is long but slower. By using both the optical (SE) and mechanical (QCM-D) techniques, we show that the SAM porosity decreases during the second phase as the coupled ethanol solvent in the disorganized layer is replaced by more alkanethiol.

Analysis techniques are needed to determine the quantity and structure of materials composing an organic layer that is below an ultra-thin film limit and in a liquid environment. Neither optical nor acoustical techniques can independently distinguish between thickness and porosity of ultra-thin films due to parameter correlation. A combined optical and acoustical approach yields sufficient information to determine both thickness and porosity. We describe application of the combinatorial approach to measure single or multiple organic layers when the total layer thickness is small compared to the wavelength of the probing light. The instrumental setup allows for simultaneous in situ spectroscopic ellipsometry and quartz crystal microbalance dynamic measurements, and it is combined with a multiple-inlet fluid control system for different liquid solutions to be introduced during experiments. A virtual separation approach is implemented into our analysis scheme, differentiated by whether or not the organic adsorbate and liquid ambient densities are equal. The analysis scheme requires that the film be assumed transparent and rigid (non-viscoelastic). We present and discuss applications of our approach to studies of organic surfactant adsorption, self-assembled monolayer chemisorption, and multiple-layer target DNA sensor preparation and performance testing.

A combined setup of quartz crystal microbalance and generalized ellipsometry can be used to comprehensively investigate complex functional coatings comprising stimuli-responsive polymer brushes and 3D nanostructures in a dynamic, noninvasive in situ measurement. While the quartz crystal microbalance detects the overall change in areal mass, for instance, during a swelling or adsorption process, the generalized ellipsometry data can be evaluated in terms of a layered model to distinguish between processes occurring within the intercolumnar space or on top of the anisotropic nanocolumns. Silicon films with anisotropic nanocolumnar morphology were prepared by the glancing angle deposition technique and further functionalized by grafting of poly-(acrylic acid) or poly-(N- isopropylacrylamide) chains. Investigations of the thermoresponsive swelling of the poly-(N-isopropylacrylamide) brush on the Si nanocolumns proved the successful preparation of a stimuli-responsive coating. Furthermore, the potential of these novel coatings in the field of biotechnology was explored by investigation of the adsorption of the model protein bovine serum albumin. Adsorption, retention, and desorption triggered by a change in the pH value is observed using poly-(acrylic acid) functionalized nanostructures, although generalized ellipsometry data revealed that this process occurs only on top of the nanostructures. Poly-(N-isopropylacrylamide) is found to render the nanostructures non-fouling properties.

We apply generalized ellipsometry, well-known to be sensitive to the optical properties of anisotropic materials, to determine the amount of fibronectin protein that adsorbs onto a Ti slanted columnar thin film from solution. We find that the anisotropic optical properties of the thin film change upon organic adsorption. An optical model for ellipsometry data analysis incorporates an anisotropic Bruggeman effective medium approximation. We find that differences in experimental data from before and after fibronectin adsorption can be solely attributable to the uptake of fibronectin within the slanted columnar thin film. Simultaneous, in-situ generalized ellipsometry and quartz crystal microbalance measurements show excellent agreement on the amount and rate of fibronectin adsorption. Quantitative characterization of organic materials within three-dimensional, optically anisotropic slanted columnar thin films could permit their use in optical sensor applications.