Matthew C. D. Carter

Deswelling Kinetics of Color Tunable Poly(N-Isopropylacrylamide) Microgel-Based Etalons

Poly(N-isopropylacrylamide) (pNIPAm) microgel-based etalons are optical materials fabricated by depositing a monolithic layer of microgels on a semitransparent Au film adhered to a glass coverslip, followed by the deposition of a second semitransparent Au layer over the microgel layer (overlayer). These materials exhibit characteristic colors and multipeak reflectance spectra, both of which depend on the distance between the Au surfaces (mediated by the microgel diameter) and the refractive index of the microgel layer. In this submission, the deswelling kinetics of pNIPAm microgel-based etalons are investigated by inducing microgel deswelling through exposure to a 30% methanol/H(2)O solution. Exposed to this solvent system, the transition temperature of the microgels is lowered to a temperature below the experimental temperature and the microgels comprising the etalon collapse. This collapse induces an etalon color change, which is observed as a blue shift in the reflectance spectrum. The kinetics of deswelling were shown to be strongly dependent on the thickness of the Au overlayer, e.g., thicker overlayers slow the solvent exchange and the resultant deswelling kinetics. Additionally, for thicker overlayers, the rate of deswelling increases with decreasing etalon size. Taken together, these results suggest that the kinetics depend strongly on the ability of the solvent to exchange from/to the microgel layer. For example, if the Au overlayer is thin, more solvent can exchange through the overlayer in a given amount of time compared to an etalon composed of a thick overlayer. Likewise, etalons of smaller dimensions have faster deswelling kinetics due to the shorter distance the solvent needs to travel laterally through the microgel layer to exchange. The results from this study are of fundamental importance but will be used to develop sensors with fast response times for point-of-care diagnostics.

Synthetic Mimics of Bacterial Lipid A Trigger Optical Transitions in Liquid Crystal Microdroplets at Ultralow Picogram-per-Milliliter Concentrations

We report synthetic six-tailed mimics of the bacterial glycolipid Lipid A that trigger changes in the internal ordering of water-dispersed liquid crystal (LC) microdroplets at ultralow (picogram-per-milliliter) concentrations. These molecules represent the first class of synthetic amphiphiles to mimic the ability of Lipid A and bacterial endotoxins to trigger optical responses in LC droplets at these ultralow concentrations. This behavior stands in contrast to all previously reported synthetic surfactants and lipids, which require near-complete monolayer coverage at the LC droplet surface to trigger ordering transitions. Surface-pressure measurements and SAXS experiments reveal these six-tailed synthetic amphiphiles to mimic key aspects of the self-assembly of Lipid A at aqueous interfaces and in solution. These and other results suggest that these amphiphiles trigger orientational transitions at ultralow concentrations through a unique mechanism that is similar to that of Lipid A and involves formation of inverted self-associated nanostructures at topological defects in the LC droplets.

Controlling the surface‐mediated release of DNA using ‘mixed multilayers’

Abstract We report the design of erodible ‘mixed multilayer’ coatings fabricated using plasmid DNA and combinations of both hydrolytically degradable and charge‐shifting cationic polymer building blocks. Films fabricated layer‐by‐layer using combinations of a model poly(β‐amino ester) (polymer 1) and a model charge‐shifting polymer (polymer 2) exhibited DNA release profiles that were substantially different than those assembled using DNA and either polymer 1 or polymer 2 alone. In addition, the order in which layers of these two cationic polymers were deposited during assembly had a profound impact on DNA release profiles when these materials were incubated in physiological buffer. Mixed multilayers ∼225 nm thick fabricated by depositing layers of polymer 1/DNA onto films composed of polymer 2/DNA released DNA into solution over ∼60 days, with multi‐phase release profiles intermediate to and exhibiting some general features of polymer 1/DNA or polymer 2/DNA films (e.g., a period of rapid release, followed by a more extended phase). In sharp contrast, ‘inverted’ mixed multilayers fabricated by depositing layers of polymer 2/DNA onto films composed of polymer 1/DNA exhibited release profiles that were almost completely linear over ∼60‐80 days. These and other results are consistent with substantial interdiffusion and commingling (or mixing) among the individual components of these compound materials. Our results reveal this mixing to lead to new, unanticipated, and useful release profiles and provide guidance for the design of polymer‐based coatings for the local, surface‐mediated delivery of DNA from the surfaces of topologically complex interventional devices, such as intravascular stents, with predictable long‐term release profiles.

Parallel DNA Synthesis on Poly(ethylene terephthalate)

The fabrication of DNA arrays directly on aminolyzed sheets of poly(ethylene terephthalate) (PET) is described. Array surfaces typically employ bifunctional linkers or layers of covalently attached polymers to provide substrate hydroxy groups as synthesis attachment points. An amine treatment is used here to expose hydroxy groups on films of PET. These hydroxy groups can then be used to couple phosphoramidites and initiate the array synthesis without further functionalization steps. Arrays fabricated on these substrates with a maskless array synthesizer are tolerant of the high number of chemical exposure steps required to synthesize relatively long oligonucleotides. The results might be of the greatest use to the synthetic biology community, for whom a flexible and robust substrate could enable new strategies to enhance the throughput of oligonucleotide synthesis.