Localized Photoactuation of Polymer Pens for Nanolithography.

Localized actuation is an important goal of nanotechnology broadly impacting applications such as programmable materials, soft robotics, and nanolithography. Despite significant recent advances, actuation with high temporal and spatial resolution remains challenging to achieve. Herein, we demonstrate strongly localized photoactuation of polymer pens made of polydimethylsiloxane (PDMS) and surface-functionalized short carbon nanotubes based on a fundamental understanding of the nanocomposite chemistry and device innovations in directing intense light with digital micromirrors to microscale domains.

Photopolymerized Features via Beam Pen Lithography as a Novel Tool for the Generation of Large Area Protein Micropatterns.

A cantilever-free scanning probe lithography (CF-SPL)-based method for the rapid polymerization of nanoscale features on a surface via crosslinking and thiol-acrylate photoreactions is described, wherein the nanoscale position, height, and diameter of each feature can be finely and independently tuned. With precise spatiotemporal control over the illumination pattern, beam pen lithography (BPL) allows for the photo-crosslinking of polymers into ultrahigh resolution features over centimeter-scale areas using massively parallel >160 000 pen arrays of individually addressable pens that guide and focus light onto the surface with sub-diffraction resolution. The photoinduced crosslinking reaction of the ink material, which is composed of photoinitiator, diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, poly(ethylene glycol) diacrylate, and thiol-modified functional binding molecules (i.

Cyclization Improves Membrane Permeation by Antimicrobial Peptoids.

The peptidomimetic approach has emerged as a powerful tool for overcoming the inherent limitations of natural antimicrobial peptides, where the therapeutic potential can be improved by increasing the selectivity and bioavailability. Restraining the conformational flexibility of a molecule may reduce the entropy loss upon its binding to the membrane. Experimental findings demonstrate that the cyclization of linear antimicrobial peptoids increases their bactericidal activity against Staphylococcus aureus while maintaining high hemolytic concentrations.

Nanopores suggest a negligible influence of CpG methylation on nucleosome packaging and stability.

Nucleosomes are the fundamental repeating units of chromatin, and dynamic regulation of their positioning along DNA governs gene accessibility in eukaryotes. Although epigenetic factors have been shown to influence nucleosome structure and dynamics, the impact of DNA methylation on nucleosome packaging remains controversial. Further, all measurements to date have been carried out under zero-force conditions.

Label-free optical detection of biomolecular translocation through nanopore arrays.

In recent years, nanopores have emerged as exceptionally promising single-molecule sensors due to their ability to detect biomolecules at subfemtomole levels in a label-free manner. Development of a high-throughput nanopore-based biosensor requires multiplexing of nanopore measurements. Electrical detection, however, poses a challenge, as each nanopore circuit must be electrically independent, which requires complex nanofluidics and embedded electrodes.

Fast, label-free force spectroscopy of histone-DNA interactions in individual nucleosomes using nanopores.

Herein we report a novel approach for fast, label-free probing of DNA-histone interactions in individual nucleosomes. We use solid-state nanopores to unravel individual DNA/histone complexes for the first time and find that the unraveling time depends on the applied electrophoretic force, and our results are in line with previous studies that employ optical tweezers. Our approach for studying nucleosomal interactions can greatly accelerate the understanding of fundamental mechanisms by which transcription, replication, and repair processes in a cell are modulated through DNA-histone interactions, as well as in diagnosis of diseases with abnormal patterns of DNA and histone modifications.

Cholesterol mediates membrane curvature during fusion events.

Biomembranes undergo extensive shape changes as they perform vital cellular functions. The mechanisms by which lipids and proteins control membrane curvature remain unclear. We use x-ray reflectivity, grazing incidence x-ray diffraction, and epifluorescence microscopy to study binding of HIV-1 glycoprotein gp41's membrane-bending domain to DPPC/cholesterol monolayers of various compositions at the air-liquid interface.

Mechanism of membrane perturbation by the HIV-1 gp41 membrane-proximal external region and its modulation by cholesterol.

Membrane-activity of the glycoprotein 41 membrane-proximal external region (MPER) is required for HIV-1 membrane fusion. Consequently, its inhibition results in viral neutralization by the antibody 4E10. Previous studies suggested that MPER might act during fusion by locally perturbing the viral membrane, i.

Membrane-proximal external HIV-1 gp41 motif adapted for destabilizing the highly rigid viral envelope.

Electron microscopy structural determinations suggest that the membrane-proximal external region (MPER) of glycoprotein 41 (gp41) may associate with the HIV-1 membrane interface. It is further proposed that MPER-induced disruption and/or deformation of the lipid bilayer ensue during viral fusion. However, it is predicted that the cholesterol content of this membrane (∼45 mol %) will act against MPER binding and restructuring activity, in agreement with alternative structural models proposing that the MPER constitutes a gp41 ectodomain component that does not insert into the viral membrane.

Cholesterol-phospholipid interactions: new insights from surface x-ray scattering data.

We report a structural study of cholesterol-DPPC (1,2-dipalmitoyl-sn-glycero-3-phophocholine) monolayers using x-ray reflectivity and grazing incidence x-ray diffraction. Reflectivity reveals that the vertical position of cholesterol relative to phospholipids strongly depends on its mole fraction (chi(CHOL)). Moreover, we find that at a broad range of chi(CHOL) cholesterol and DPPC form alloylike mixed domains of short-range order and the same stoichiometry as that of the film.

A miniature mimic of host defense peptides with systemic antibacterial efficacy.

Oligomers of acylated lysines (OAKs) are synthetic mimics of host defense peptides (HDPs) with promising antimicrobial properties. Here we challenged the OAK concept for its ability to generate both systemically efficient and economically viable lead compounds for fighting multidrug-resistant bacteria. We describe the design and characterization of a miniature OAK composed of only 3 lysyls and 2 acyls (designated C(12(omega7))K-beta(12)) that preferentially targets gram-positive species by a bacteriostatic mode of action.

A comparative study on the interactions of SMAP-29 with lipid monolayers.

This work investigates the discrimination of lipid monolayers by the ovine antimicrobial peptide SMAP-29 and compares it to that of the human LL-37 peptide. Fluid phospholipid monolayers were formed in a Langmuir trough and subsequently studied with the X-ray scattering techniques of X-ray reflectivity and grazing incidence X-ray diffraction. Any changes in the phospholipid structure after injection of peptide under the monolayer were considered to be due to interactions between the peptides and lipids.

Antibacterial properties and mode of action of a short acyl-lysyl oligomer.

We investigated the potency, selectivity, and mode of action of the oligo-acyl-lysine (OAK) NC(12)-2 beta(12), which was recently suggested to represent the shortest OAK sequence that retains nonhemolytic antibacterial properties. A growth inhibition assay against a panel of 48 bacterial strains confirmed that NC(12)-2 beta(12) exerted potent activity against gram-positive bacteria while exhibiting negligible hemolysis up to at least 100 times the MIC. Interestingly, NC(12)-2 beta(12) demonstrated a bacteriostatic mode of action, unlike previously described OAKs that were bactericidal and essentially active against gram-negative bacteria only.

Peptoids that mimic the structure, function, and mechanism of helical antimicrobial peptides.

Antimicrobial peptides (AMPs) and their mimics are emerging as promising antibiotic agents. We present a library of "ampetoids" (antimicrobial peptoid oligomers) with helical structures and biomimetic sequences, several members of which have low-micromolar antimicrobial activities, similar to cationic AMPs like pexiganan. Broad-spectrum activity against six clinically relevant BSL2 pathogens is also shown.