This paper describes a layer‐by‐layer (LBL) electrostatic self‐assembly process for fabricating highly efficient antimicrobial nanocoatings on a natural cellulose substrate. The composite materials comprise a chemically modified cotton substrate and a layer of sub‐5 nm copper‐based nanoparticles. The LBL process involves a chemical preconditioning step to impart high negative surface charge on the cotton substrate for chelation controlled binding of cupric ions (Cu2+), followed by chemical reduction to yield nanostructured coatings on cotton fibers. These model wound dressings exhibit rapid and efficient killing of a multidrug resistant bacterial wound pathogen, A. baumannii, where an 8‐log reduction in bacterial growth can be achieved in as little as 10 min of contact. Comparative silver‐based nanocoated wound dressings–a more conventional antimicrobial composite material–exhibit much lower antimicrobial efficiencies; a 5‐log reduction in A. baumannii growth is possible after 24 h exposure times to silver nanoparticle‐coated cotton substrates. The copper nanoparticle–cotton composites described herein also resist leaching of copper species in the presence of buffer, and exhibit an order of magnitude higher killing efficiency using 20 times less total metal when compared to tests using soluble Cu2+. Together these data suggest that copper‐based nanoparticle‐coated cotton materials have facile antimicrobial properties in the presence of A. baumannii through a process that may be associated with contact killing, and not simply due to enhanced release of metal ion. The biocompatibility of these copper‐cotton composites toward embryonic fibroblast stem cells in vitro suggests their potential as a new paradigm in metal‐based wound care and combating pathogenic bacterial infections.

Surface-enhanced Raman scattering (SERS) was used for the detection of carbendazim using gold nanorods derivatized with a beta-cyclodextrin derivative to bind this fungicide. Gold nanorods were synthesized with an aspect ratio of 3.3 to match the 785 nm excitation wavelength used in the SERS studies. A thiolated cyclodextrin-based sensor molecule was synthesized, and its inclusion complex with carbendazim was formed and studied using SERS spectroscopy. SERS analysis of the inclusion complex at different concentrations in the presence of gold nanorods afforded good quality Raman spectra of carbendazim at micromolar concentrations. Quantitative analysis was preformed using partial least-squares (PLS), and a calibration plot for these data was generated. Results suggest that carbendazim concentrations as low as 50 microM can be accurately detected using the described SERS assay.

No abstract

Genomics provides a comprehensive view of the complete genetic makeup of an organism. Individual sequence variations, as manifested by single nucleotide polymorphisms (SNPs), can provide insight into the basis for a large number of phenotypes and diseases including cancer. The ability rapidly screen for SNPs will have a profound impact on a number of applications, most notably personalized medicine. Here we demonstrate a new approach to SNP detection through the application of surfaceenhanced Raman scattering (SERS) to the ligase detection reaction (LDR). The reaction uses two LDR primers, one of which contains a Raman enhancer and the other a reporter dye. In LDR, one of the primers is designed to interrogate the SNP. When the SNP being interrogated matches the discriminating primer sequence, the primers are ligated and the enhancer and dye are brought into close proximity enabling the dye's Raman signature to be detected. By detecting the Raman signature of the dye rather than its fluorescence emission, our technique avoids the problem of spectral overlap which limits number of reactions which can be carried out in parallel by existing systems. We demonstrate the LDR-SERS reaction for the detection of point mutations in the human K-ras oncogene. The reaction is implemented in an electrokinetically active microfluidic device that enables physical concentration of the reaction products for enhanced detection sensitivity and quantization. We report a limit of detection of 20 pM of target DNA with the anticipated specificity engendered by the LDR platform.

A single-step LbL procedure to functionalize CTAB-capped GNRs via electrostatic self-assembly is reported. This approach allows for consistent biomolecule/GNR coupling using standard carboxyl-amine conjugation chemistry. The focus is on cancer-targeting biomolecule/GNR conjugates and selective photothermal destruction of cancer cells by GNR-mediated hyperthermia and NIR light. GNRs were conjugated to a single-chain antibody selective for colorectal carcinoma cells and used as probes to demonstrate photothermal therapy. Selective targeting and GNR uptake in antigen-expressing SW 1222 cells were observed using fluorescence microscopy. Selective photothermal therapy is demonstrated using SW 1222 cells, where >62% cell death was observed after cells are treated with targeted A33scFv-GNRs.

Single nucleotide polymorphisms (SNPs) are one of the key diagnostic markers for genetic disease, cancer progression, and pharmcogenomics. The ligase detection reaction (LDR) is an excellent method to identify SNPs, combining low detection limits and high specificity. We present the first multiplex LDR-surface enhanced Raman spectroscopy (SERS) SNP genotyping scheme. The platform has the advantage in that the diagnostic peaks of Raman are more distinct than fluorescence, and in theory, a clinically significant number of markers can be multiplexed in a single sample using different SERS reporters. Here we report LDR-SERS multiplex SNP genotyping of K-Ras oncogene alleles at 10 pM detection levels, optimization of DNA labeling as well as Raman conditions, and the linear correlation of diagnostic peak intensity to SNP target concentration in heterozygous samples. Genomic DNA from typed cells lines was obtained and scored for the K-Ras genotype. These advances are significant as we have further developed our new SNP genotyping platform and have demonstrated the ability to correlate genotype ratios directly to diagnostic Raman peak signal intensity.

This paper describes the development and preparation of a new class of materials for surface-enhanced Raman scattering (SERS) consisting of gold nanoparticles coated onto hollow, buoyant silica microspheres. These materials allow for a new type of molecular assay designated as a lab-on-a-bubble (LoB). LoB materials serve as a convenient platform for the detection of analytes in solution and offer several advantages over traditional colloidal gold and planar SERS substrates, such as the ability to localize and concentrate analytes for detection. An example assay is presented using the LoB method and cyanide detection. Cyanide binds to SERS-active, gold-coated LoBs and is detected directly from the corresponding SERS signal. The abilities of LoBs and a gold colloid to detect cyanide are compared, and in both cases, a detection limit of ~170 ppt was determined. Differences in measurement error using LoBs versus gold colloid are also described, as well as an assay for 5,5'-dithiobis(2-nitrobenzoic acid) that shows the benefit of using LoBs over SERS analyses in colloids, which are often plagued by particle aggregation.

S-Layer proteins are an example of bionanostructures that can be exploited in nanofabrication. In addition to their ordered structure, the ability to self-assembly is a key feature that makes them a promising technological tool. Here, in vitro self-assembly kinetics of SpbA was investigated, and found that it occurs at a rate that is dependent on temperature, its concentration, and the concentration of calcium ions and sodium chloride. The activation enthalpy (120.81 kJ . mol(-1)) and entropy (129.34 J . mol(-1) . K(-1)) obtained infers that the incorporation of monomers incurs in a net loss of hydrophobic surface. By understanding how the protein monomers drive the self-assembly at different conditions, the rational optimization of this process was feasible.