Layer-by-layer (LbL) assembly, a technique that alternately deposites cationic and anionic materials, has proven to be a powerful technique for assembling thin films with a variety of properties and applications. The present work incorporates the antimicrobial agent cetyltrimethylammonium bromide (CTAB) in the cationic layer and uses poly(acrylic acid) (PAA) as the anionic layer. When the films are exposed to a humid environment, these agents diffuse out of the film, inhibiting bacterial growth in neighboring regions. Film growth, microstructure, and antimicrobial efficacy are studied here, with 10-bilayer films yielding thicknesses on the order of 2 microm. Various factors are shown to influence the antimicrobial efficacy including time, temperature, secondary ingredients, and number of bilayers. As more layers are deposited, antimicrobial efficacy is increased because more CTAB is able to diffuse throughout the film, and higher amounts of antimicrobials are released. Additionally, inclusion of the cationic poly(diallyldimethylammonium chloride) (PDDA) in the cationic layer in conjunction with CTAB increases film uniformity, and as a result, antimicrobial effectiveness is enhanced. These thin films provide the ability to render a surface antimicrobial and may be useful for bandages or sterilization of disposable objects (e.g., surgical marker).

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The water solubilization of nanoparticles is key for many applications in biomedicine. Despite the importance of surface functionalization, progress has been largely empirical and very few systematic studies have been performed. Here we report on the water solubilization of QDs using lipid encapsulation. We systematically evaluate the monodispersity, zeta potential, stability, and quantum yield (QY) for QDs encapsulated with single and double acyl chain lipids, pegylated double acyl chain lipids, and single alkyl chain surfactant molecules with charged head groups. We show that charged surfactants and pegylated lipids are important to obtain monodisperse suspensions with high yield and excellent long-term stability.

Applications in nanomedicine, such as diagnostics and targeted therapeutics, rely on the detection and targeting of membrane biomarkers. In this paper we demonstrate absolute quantitative profiling, spatial mapping, and multiplexing of cancer biomarkers using functionalized quantum dots. We demonstrate highly selective targeting molecular markers for pancreatic cancer with extremely low levels of non-specific binding. We confirm that we have saturated all biomarkers on the cell surface, and, in conjunction with control experiments, extract absolute quantitative values for the biomarker density in terms of the number of molecules per square micrometer on the cell surface. We show that we can obtain quantitative spatial information of biomarker distribution on a single cell, important since tumors cell populations are inherently heterogeneous. We validate our quantitative measurements (number of molecules per square micron) using flow cytometry and demonstrate multiplexed quantitative profiling using color-coded quantum dots.

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