Novel biosensing platform based on self-assembled supramolecular hydrogel

The supramolecular hydrogel self-assembled from α-cyclodextrin (α-CD) and an amphiphilic triblock copolymer was used for the first time as a biosensing platform by the in-situ incorporation of horseradish peroxidase and polyaniline (PANI) nanoparticles. It was found that the used triblock copolymer could disperse well PANI nanoparticles in aqueous system and then interact with α-CD in the presence of horseradish peroxidase for the formation of supramolecular hydrogel composite. The content of PANI nanoparticles was found to affect the gelation time and gel strength. The circular dichroism analyses showed that the entrapped horseradish peroxidase could retain its native conformation. By electrochemical experiments, the incorporated PANI nanoparticles were confirmed to improve the current response and enzymatic activity, and the fabricated biosensor was found to provide a fast amperometric response to hydrogen peroxide.     

Achieving chiral resolution in self-assembled supramolecular structures through kinetic pathways

Chiral phase transitions were studied in a self-assembled 2,6-dibromoanthraquinones supramolecular system prepared on Au(111) using scanning tunneling microscopy. As the molecules were deposited at about 150?K, they formed heterochiral chevron structures (a racemate) consisting of two alternating prochiral molecular rows. When the as-deposited sample was warmed to 300?K followed by cooling to 80?K, phase-separated homochiral structures (a conglomerate), as well as the chevron structures, were observed. We propose molecular models for the structures that are in good agreement with ab?initio studies and can be explained by hydrogen bonds and halogen bonds. We found that heterochiral chevron structures were more stable than homochiral structures due to two additional [Formula: see text] halogen bonds per molecule. We considered kinetic pathways for the phase transitions that were made possible via a disordered liquid phase entropically stabilized at 300?K. We show how chiral resolution can be achieved by exploiting kinetic paths allowed in supramolecular systems.     

Platelet and leukocyte adhesion to albumin binding self-assembled monolayers

This study reports the use of tetraethylene glycol-terminated self-assembled monolayers (EG₄ SAMs) as a background non-fouling surface to study the effect of an 18 carbon ligand (C18) on albumin selective and reversible adsorption and subsequent platelet and leukocyte adhesion. Surface characterization techniques revealed an efficient immobilization of different levels of C18 ligand on EG₄ SAMs and an increase of surface thickness and hydrophobicity with the increase of C18 ligands. Albumin adsorption increased as the percentage of C18 ligands on the surface increased, but only 2.5%C18 SAMs adsorbed albumin in a selective and reversible way. Adherent platelets also increased with the amount of immobilized C18. Pre-immersion of samples in albumin before contact with platelets demonstrated an 80% decrease in platelet adhesion. Pre-immersion in plasma was only relevant for 2.5%C18 SAMs since this was the only surface to have less platelet adhesion compared to buffer pre-immersion. EG₄ SAMs adhered negligible amounts of leukocytes, but surfaces with C18 ligands have some adherent leukocytes. Except for 10%C18 SAMs, which increased leukocyte adhesion after albumin pre-adhesion, protein pre-immersion did not influence leukocyte adhesion. It has been shown that a surface with a specific surface concentration of albumin-binding ligands (2.5%C18 SAMs) can recruit albumin selectively and reversibly and minimize the adhesion of platelets, despite still adhering some leukocytes.     

A digital microfluidic droplet generator produces self-assembled supramolecular nanoparticles for targeted cell imaging

Controlling the size distribution of polymer-based nanoparticles is a challenging task due to their flexible core and surface structures. To accomplish such as task requires very precise control at the molecular level. Here we demonstrate a new approach whereby uniform-sized supramolecular nanoparticles (SNPs) can be reliably generated using a digital microfluidic droplet generator (DMDG) chip. A microfluidic environment enabled precise control over the processing parameters, and therefore high batch-to-batch reproducibility and robust production of SNPs with a very narrow size distribution could be realized. Digitally adjustment of the mixing ratios of the building blocks on the DMDG chip allowed us to rapidly scan a variety of synthesis conditions without consuming significant amounts of reagents. Nearly uniform SNPs with sizes ranging from 35 to 350?nm were obtained and characterized by transmission electron microscopy and dynamic light scattering. In addition, we could fine-tune the surface chemistry of the SNPs by incorporating an additional building block functionalized with specific ligands for targeting cells. The sizes and surface properties of these SNPs correlated strongly with their cell uptake efficiencies. This study showed a feasible method for microfluidic-assisted SNP production and provided a great means for preparing size-controlled SNPs with desired surface ligand coverage.     

Construction of nanostructures for selective lithium ion conduction using self-assembled molecular arrays in supramolecular solids

Abstract

In the development of innovative molecule-based materials, the identification of the structural features in supramolecular solids and the understanding of the correlation between structure and function are important factors. The author investigated the development of supramolecular solid electrolytes by constructing ion conduction paths using a supramolecular hierarchical structure in molecular crystals because the ion conduction path is an attractive key structure due to its ability to generate solid-state ion diffusivity. The obtained molecular crystals exhibited selective lithium ion diffusion via conduction paths consisting of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and small molecules such as ether or amine compounds. In the present review, the correlation between the crystal structure and ion conductivity of the obtained molecular crystals is addressed based on the systematic structural control of the ionic conduction paths through the modification of the component molecules. The relationship between the crystal structure and ion conductivity of the molecular crystals provides a guideline for the development of solid electrolytes based on supramolecular solids exhibiting rapid and selective lithium ion conduction.     

Viscoelastic winding and unwinding mechanics

Abstract

In this paper a viscoelastic analysis of tape systems in winding/ unwinding process is presented. An analytical model is developed to predict stress and displacement fields in the tape system for any winding speed. A three‐parameter solid is used as an illustrated example. Results show that tape velocity is greater than 762 or less than 0.0762 cm/sec, the elastic solutions are applicaple. If the tape velocity is between 0.0762 and 762 cm/sec, the viscoelastic results are applicable.     

Quantitative microfluidic separation of DNA in self-assembled magnetic matrixes

We present an experimental study of the microfluidic electrophoresis of long DNA in self-assembling matrixes of magnetic bead columns. Results are presented for the rapid separation of lambda-phage, 2lambda-DNA, and bacteriophage T4 DNA, where separation resolutions greater than 2 between lambda and T4 are achieved in times as short as 150 s. The use of a computer-piloted flow control system and injection results in high reproducibility between separations. We compare the experimentally measured mobility and dispersion with an exactly solvable lattice Monte Carlo model. The theory predicts that the mean velocity scales linearly with the field, the band broadening scales with the inverse of the field, and the resolution is independent of the field for intermediate fields-all of which are in accord with the experimental results. Moreover, reasonable quantitative agreement is achieved for band broadening for longer DNA (2lambda and T4) when the average postengagement time is measured experimentally. This work demonstrates the possibility of achieving fast microfluidic separation of large DNA on a routine basis.     

Periodic square-like gold nanoparticle arrays templated by self-assembled 2D DNA Nanogrids on a surface

We report the use of a self-assembled two-dimensional (2D) DNA nanogrid as a template to organize 5-nm gold nanoparticles (Au NPs) into periodic square lattices. Each particle sits on only a single DNA tile. The center-to-center interparticle spacing between neighboring particles is controlled to be approximately 38 nm. These evenly distributed Au NP arrangements with accurate control of interparticle spacing may find applications in nanoelectronic and nanophotonic devices.     

Evaluating the binding affinities of NF-kappaB protein to the single-nucleotide mismatch DNA binding sites by using double-stranded DNA microarray

Protein-DNA sequence-specific interaction plays an essential role in many biological processes. Here we immobilized a series of double-stranded DNA probes on an agarose coated slide to investigate the binding affinity of NF-kappaB p50 homodimer to the single-nucleotide mismatches (G<-->A or T<-->C) of the 10 base pair (bp) protein binding sites. The results demonstrated that the nucleotides at different positions contribute differently to the p50p50/DNA binding interaction. Within the 10 bp binding sites, the 5tG or 6cA mismatch has less effect on the protein-DNA binding affinity. Even the 5tG mismatch may have the ability to enhance the protein-DNA interaction (5t/w = 1.07). On the other hand, the 7cA or 10tG mismatch blocked the protein-DNA interaction more significantly than other six single-nucleotide mismatches. (7c/W = 0.37, 10t/W = 0.35). It also indicated that the duplex DNA probes immobilized on the agarose-coated surface were apt to be recognized by DNA-binding proteins, and this method would provide a reliable method for exploring the binding affinities of DNA-binding proteins with a larger number of DNA targets.     

Application of supramolecular nanostamping to the replication of DNA nanoarrays

The rapid development of molecular biology is creating a pressing need for arrays of biomolecules that are able to detect smaller and smaller volumes of analytes. This goal can be achieved by shrinking the average size and spacing of the arrays' constituent features. While bioarrays with dot size and spacing on the nanometer scale have been successfully fabricated via scanning probe microscopy-based techniques, such fabrication methods are serial in nature and consequently slow and expensive. Additionally, the development of truly small arrays able to analyze scarce volumes of liquids is hindered by the present use of optical detection, which sets the minimum dot spacing on the order of roughly half the excitation wavelength. Here, we show that supramolecular nanostamping, a recently introduced truly parallel method for the stamping of DNA features, can efficiently reproduce DNA arrays with features as small as 14 +/- 2 nm spaced 77 +/- 10 nm. Moreover, we demonstrate that hybridization of these nanoarrays can be detected using atomic force microscopy in a simple and scaleable way that additionally does not require labeling of the DNA strands.     

Macroscopic 2D networks self-assembled from nanometer-sized protein/DNA complexes

We demonstrate the self-assembly of DNA and DNA binding proteins into two-dimensional networks that are then addressable by sending a second protein to a specific recognition site on the DNA network. These networks cover centimeters in area but can be addressed with nanometer precision. This hierarchical self-assembly of specific DNA protein complexes will be the basis for complex positioning of single molecules in two and three dimensions.     

Co-delivery of drugs and DNA from cationic core-shell nanoparticles self-assembled from a biodegradable copolymer

Non-viral gene-delivery systems are safer to use and easier to produce than viral vectors, but their comparatively low transfection efficiency has limited their applications. Co-delivery of drugs and DNA has been proposed to enhance gene expression or to achieve the synergistic/combined effect of drug and gene therapies. Attempts have been made to deliver drugs and DNA simultaneously using liposomes. Here we report cationic core-shell nanoparticles that were self-assembled from a biodegradable amphiphilic copolymer. These nanoparticles offer advantages over liposomes, as they are easier to fabricate, and are more readily subject to modulation of their size and degree of positive charge. More importantly, they achieve high gene-transfection efficiency and the possibility of co-delivering drugs and genes to the same cells. Enhanced gene transfection with the co-delivery of paclitaxel has been demonstrated by in vitro and in vivo studies. In particular, the co-delivery of paclitaxel with an interleukin-12-encoded plasmid using these nanoparticles suppressed cancer growth more efficiently than the delivery of either paclitaxel or the plasmid in a 4T1 mouse breast cancer model. Moreover, the co-delivery of paclitaxel with Bcl-2-targeted small interfering RNA (siRNA) increased cytotoxicity in MDA-MB-231 human breast cancer cells.     

Chiral photonic materials self-assembled by cellulose nanocrystals

Cellulose nanocrystals are natural nanomaterials with a high aspect ratio, high specific area, excellent stability, and favorable optical performances. Cellulose nanocrystals can form cholesteric liquid crystals through a left-handed spiral arrangement. The suspension liquid of cellulose nanocrystals can retain the chiral cholesteric structure in the solid film after being completely dried, leading to the appearance of Bragg reflection and bright structural color in the visible spectrum. By changing the conditions or mixing with polymers, the cellulose nanocrystals film will show different structural colors due to the change of pitch. The film can cover almost the entire visible spectrum, which can be applied to various aspects such as sensing, anti-counterfeiting, detection, and so on. In this review, we elaborated on the synthesis and properties of cellulose nanocrystals materials and introduced the mechanism of structural color formation, as well as the current research progress and applications. Cellulose nanocrystals have become a hot spot in the field of structural color, and provide more research value for providing a cheap, easy-to-obtain, green-friendly, and high-biocompatibility natural photonic material.     

Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets

Highly ordered arrays of nanoparticles exhibit many properties that are not found in their disordered counterparts. However, these nanoparticle superlattices usually form in a far-from-equilibrium dewetting process, which precludes the use of conventional patterning methods owing to a lack of control over the local dewetting dynamics. Here, we report a simple yet efficient approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their dewetting process. This approach can provide rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures with high degrees of internal order, including single-particle-width corrals, single-particle-thickness microdiscs and submicrometre-sized 'supra-crystals'. Remarkably, these features could be addressed by micropatterned electrode arrays, suggesting potential applications in bottom-up nanodevices.     

Single-molecule kinetics and super-resolution microscopy by fluorescence imaging of transient binding on DNA origami

DNA origami is a powerful method for the programmable assembly of nanoscale molecular structures. For applications of these structures as functional biomaterials, the study of reaction kinetics and dynamic processes in real time and with high spatial resolution becomes increasingly important. We present a single-molecule assay for the study of binding and unbinding kinetics on DNA origami. We find that the kinetics of hybridization to single-stranded extensions on DNA origami is similar to isolated substrate-immobilized DNA with a slight position dependence on the origami. On the basis of the knowledge of the kinetics, we exploit reversible specific binding of labeled oligonucleotides to DNA nanostructures for PAINT (points accumulation for imaging in nanoscale topography) imaging with <30 nm resolution. The method is demonstrated for flat monomeric DNA structures as well as multimeric, ribbon-like DNA structures.     

Mode of drug binding to DNA determined by optical tweezers force spectroscopy

Abstract

Optical tweezers were employed to investigate the effects of small DNA-binding molecules on the low-force (≤ 15 pN) stretching behaviour of single DNA molecules. As the canonical B-DNA helix is not perturbed in this force regime, the effects on DNA elasticity observed upon drug binding provide useful insight into how DNA-binding drugs may alter in vivo processes. In this study, the effects of agents with different DNA binding modes were analysed. DNA force—extension curves were recorded in the presence of netropsin, a purely minor groove-binding antibiotic drug, ethidium bromide, an intercalating fluorescent dye, and berenil, an antiprotozoal drug proposed to exhibit both intercalative and minor groove-binding modes. Applying an approximation of the worm-like chain model, which describes the low-force stretching behaviour, the results were analysed in terms of the DNA contour length and persistence length. From these single molecule studies it was observed that minor groove-binding and intercalating modes of DNA-binding could be distinguished based on changes to DNA elasticity.     

Inkjet printed electrode arrays for potential modulation of DNA self-assembled monolayers on gold

In this paper, we report a novel and cost-effective fabrication technique to produce electrode arrays that can be used for monitoring and electrical manipulation of the molecular orientation of DNA self-assembled monolayers (SAMs) on gold. The electrode arrays were prepared from gold coated glass sides or compact discs (CD-Rs) by using standard office inkjet printers without any hardware or software modifications. In this method, electrode arrays of varied shape and size (from submillimeter to centimeter) can be rapidly fabricated and are suitable for standard electrochemical measurements. We were able to use a dual-channel potentiostat to control the electrodes individually and a fluorescence (FL) scanner to image the electrode array simultaneously. With such an integrated modulation setup, the structural switching behavior (from "lying" to "standing" position) and the enhanced hybridization reactivity of thiolate DNA SAMs on gold under potential control have been successfully demonstrated.