The self-assembled monolayer modification of electrodes - some recent advances in biological application

The modification of an electrode surface at the molecular level using the technique of depositing self-assembled monolayers (SAM) is a typical example of the techniques used in nanotechnology, from the process &quot;bottom up&quot;, which is to create a nanostructure by successive additions of molecular or atomic entities on a surface. This article presents some recent advances in the field, with examples: the development of systems Sat hybridized with biomolecules, nanoparticles or nanotubes in bioelectronics, the use of switchable electrodes to study the adhesion and migration of biological cells , and the integration of molecular son in the SAM to recognize and allow the transduction of a biological response allowing the practice of electrochemistry in a complex biological environment.<br /

Direct-laser writing for subnanometer focusing and single-molecule imaging

Two-photon direct laser writing is an additive fabrication process that utilizes two-photon absorption of tightly focused femtosecond laser pulses to implement spatially controlled polymerization of a liquid-phase photoresist. Two-photon direct laser writing is capable of nanofabricating arbitrary three-dimensional structures with nanometer accuracy. Here, we explore direct laser writing for high-resolution optical microscopy by fabricating unique 3D optical fiducials for single-molecule tracking and 3D single-molecule localization microscopy. By having control over the position and three-dimensional architecture of the fiducials, we improve axial discrimination and demonstrate isotropic subnanometer 3D focusing (<0.8 nm) over tens of micrometers using a standard inverted microscope. We perform 3D single-molecule acquisitions over cellular volumes, unsupervised data acquisition and live-cell single-particle tracking with nanometer accuracy

Ultrafast generation of highly crystalline graphene quantum dots from graphite paper via laser writing

Graphene quantum dots (GQDs) are attractive fluorescent nanoparticles that have wide applicability, are inexpensive, nontoxic, photostable, water-dispersible, biocompatible and environmental-friendly. Various strategies for the synthesis of GQDs have been reported. However, simple and efficient methods of producing GQDs with control over the size of the GQDs, and hence their optical properties, are sorely needed. Herein, an ultra-fast and efficient laser writing technique is presented as a means to produce GQDs with homogeneous size from graphene produced by the instantaneous photothermal gasification and recrystallization mechanism. Controlling the laser scan speed and output power, the yield of GQDs can reach to be about 31.458 mg/s, which shows promising potential for large-scale production. The entire process eliminates the need for chemical solvents or any other reagents. Notably, the prepared laser writing produced GQDs (LWP-GQDs) exhibit blue fluorescence under UV irradiation of 365 nm and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates is measured at (0.1721, 0.123). Overall, this method exhibits superior advantages over the complex procedures and low yields required by other existing methods, and thus has great potential for the commercial applications

TagPaint: Covalent labelling of genetically encoded protein tags for DNA-PAINT imaging

Recently, DNA-PAINT single-molecule localization microscopy (SMLM) has shown great promise for quantitative imaging; however, labelling strategies thus far have relied on multivalent and affinity-based approaches. Here, the covalent labelling of expressed protein tags (SNAP tag and Halo tag) with single DNA-docking strands and application of SMLM via DNA-PAINT is demonstrated. tagPAINT is then used for T-cell receptor signalling proteins at the immune synapse as a proof of principle

How Do Cells Make Decisions: Engineering Micro- and Nanoenvironments for Cell Migration

Cell migration contributes to cancer metastasis and involves cell adhesion to the extracellular matrix (ECM), force generation through the cell's cytoskeletal, and finally cell detachment. Both adhesive cues from the ECM and soluble cues from neighbouring cells and tissue trigger intracellular signalling pathways that are essential for cell migration. While the machinery of many signalling pathways is relatively well understood, how hierarchies of different and conflicting signals are established is a new area of cellular cancer research. We examine the recent advances in microfabrication, microfluidics, and nanotechnology that can be utilized to engineer micro- and nanoscaled cellular environments. Controlling both adhesive and soluble cues for migration may allow us to decipher how cells become motile, choose the direction for migration, and how oncogenic transformations influences these decision-making processes

Light Activated Electrochemistry: Light Intensity and pH Dependence on Electrochemical Performance of Anthraquinone Derivatized Silicon

We seek to understand how the thermodynamics and kinetics of anthraquinone-containing self-assembled monolayer on silicon electrodes are affected by two key experimental variables: the intensity of the light assisting the anthraquinone/anthrahydroquinone redox process and the local solution environment. The substrates are chemically passivated poorly doped p-type silicon electrodes. The study presents a strategy for the selective modulation of either the anodic or the cathodic process occurring at the interface. Cyclic voltammetry studies showed that unlike for a proton-coupled electron transfer process performed at metallic electrodes, for the redox reaction of the anthraquinone unit on a silicon electrode it becomes possible to (i) selectively facilitate only the oxidation process by increasing the electrolyte pH or (ii) at a given pH value to increase the illumination intensity to anodically shift the onset of the reduction step only but leave the oxidation process thermodynamic unchanged. A model concerning the proton coupled electron transfer mechanism was proposed, where the electron transfer is the rate-determining step for the anthraquinone reduction while a deprotonation step is the rate-determining event for the anthrahydroquinone oxidation on poorly doped illuminated p-type silicon

Proximity extension of circular DNA aptamers with real-time protein detection

Multivalent circular aptamers or ‘captamers’ have recently been introduced through the merger of aptameric recognition functions with the basic principles of DNA nanotechnology. Aptamers have strong utility as protein-binding motifs for diagnostic applications, where their ease of discovery, thermal stability and low cost make them ideal components for incorporation into targeted protein assays. Here we report upon a property specific to circular DNA aptamers: their intrinsic compatibility with a highly sensitive protein detection method termed the ‘proximity extension’ assay. The circular DNA architecture facilitates the integration of multiple functional elements into a single molecule: aptameric target recognition, nucleic acid hybridization specificity and rolling circle amplification. Successful exploitation of these properties is demonstrated for the molecular analysis of thrombin, with the assay delivering a detection limit nearly three orders of magnitude below the dissociation constants of the two contributing aptamer–thrombin interactions. Real-time signal amplification and detection under isothermal conditions points towards potential clinical applications, with both fluorescent and bioelectronic methods of detection achieved. This application elaborates the pleiotropic properties of circular DNA aptamers beyond the stability, potency and multitargeting characteristics described earlier

Magnetic nanoparticles as MRI contrast agents for the diagnosis of Alzheimer’s disease

Background Nanoparticle‐based magnetic contrast agents have opened the potential for Magnetic Resonance Imaging (MRI) to be used for early non‐invasive diagnosis of Alzheimer’s disease (AD). Current methods for clinical diagnosis in the early stages of the disease, such as Positron Emission Tomography imaging of amyloid build‐up, are limited by their availability and cost. The aim of this research is to develop a novel non‐toxic amyloid targeted nanoparticle which can successfully permeate the blood brain barrier and bind amyloid plaques resulting in enhanced contrast in the MR image and improved diagnostic sensitivity. Methods Targeted iron nanoparticles were assessed using a U‐251 cell line to determine their in vitro toxicity. Transmission electron microscopy was used to determine the movement of the nanoparticles within the cell and in vitro binding to amyloid fibrils. APPSwe/PSEN1 mice were treated with increasing doses of targeted and non‐targeted nanoparticles to evaluate acute in vivo toxicity, in addition to nanoparticle biodistribution and MRI contrast enhancement. Results The novel targeted nanoparticles have demonstrated no significant in vitro toxicity and electron microscopy results show their movement through the endocytic cycle within the cell, demonstrating an effective degradation and clearance pathway (Figure). No acute toxicity was observed in the animal model. In addition, immunohistochemistry demonstrated nanoparticles to co‐localise with plaques on ex vivo brain sections. Conclusion The present work shows promising preliminary results in the development of a targeted non‐invasive method of early AD diagnosis using contrast enhanced MRI

Light-Activated Electrochemistry for the Two-Dimensional Interrogation of Electroactive Regions on a Monolithic Surface with Dramatically Improved Spatial Resolution

The concept of light-activated electrochemistry (LAE) was recently presented where faradaic electrochemistry could be spatially resolved on a monolithic silicon electrode by illuminating the specific region with light. A major implication from the previous study using illumination from the nonsolution side, or backside, is that the spatial resolution is limited by the finite thickness of silicon wafer. To overcome this restriction, and enable the further application of LAE, in combination with optical imaging for example, herein the spatial resolution of LAE using topside illumination (illumination from the solution side) is explored. The applied potential and irradiated light intensity are found to have significant effects on the spatial resolution. A spatial resolution of ~30 µm was achieved with optimal parameters, which is a 20 times improvement compared with the previously reported backside illumination design, demonstrating the potential application of the strategy including microarray patterning of silicon or for single cell analysis

A novel route to copper(ii) detection using \u27click\u27 chemistry-induced aggregation of gold nanoparticles

A simple colorimetric method for the detection of copper ions in water is described. This method is based on the \u27click\u27 copper(i)-catalyzed azide-alkyne cycloaddition reaction and its use in promoting the aggregation of azide-tagged gold nanoparticles by a dialkyne cross-linker is described. Nanoparticle cross-linking, evidenced as a colour change, is used for the detection of copper ions. The lowest detected concentration by the naked eye was 1.8 μM, with the response linear with log(concentration) between 1.8-200 μM. The selectivity relative to other potentially interfering ions was evaluated