A simple bioconjugate attachment protocol for use in single molecule force spectroscopy experiments based on mixed self-assembled monolayers.

Single molecule force spectroscopy is a technique that can be used to probe the interaction force between individual biomolecular species. We focus our attention on the tip and sample coupling chemistry, which is crucial to these experiments. We utilised a novel approach of mixed self-assembled monolayers of alkanethiols in conjunction with a heterobifunctional crosslinker. The effectiveness of the protocol is demonstrated by probing the biotin-avidin interaction. We measured unbinding forces comparable to previously reported values measured at similar loading rates. Specificity tests also demonstrated a significant decrease in recognition after blocking with free avidin.

Biofunctionalization of PET/SiO2 surfaces for single molecule experiments and medical applications

PET/SiO2 layers were chemically modified to maintain immobilization of functional single molecules. GFP molecules provide an ideal system due to their stability and intrinsic fluorescence. GFP in vivo biotinylated within its NH2-terminal region and attached on the substrate via the biotinstreptavidin bond was further investigated with confocal microscopy, atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). AFM revealed monolayered donut-like structures representing assemblies of biotinstreptavidinbiotinGFP immobilized onto PET/SiO2 surfaces via mPEG. In particular, regions with an approximate height of 12 nm, which approaches the molecular dimensions of the above complex given by molecular modeling, could be detected. The dimensions of the donut-like structures suggest a close-to-each-other positioning of the GFP molecules - which, however, retain their functionality, as evidenced by confocal microscopy. © 2011 World Scientific Publishing Company.

A Bayesian approach to tracking in single molecule fluorescence microscopy

Using fluorescence microscopy with single molecule sensitivity it is now possible to follow the movement of individual fluorophore tagged molecules such as proteins and lipids in the cell membrane with nanometer precision. These experiments are important as they allow many key biological processes on the cell membrane and in the cell, such as transcription, translation and DNA replication, to be studied at new levels of detail. Computerized microscopes generate sequences of images (in the order of tens to hundreds) of the molecules diffusing and one of the challenges is to track these molecules to obtain reliable statistics such as speed distributions, diffusion patterns, intracellular positioning, etc. The data set is challenging because the molecules are tagged with a single or small number of fluorophores, which makes it difficult to distinguish them from the background, the fluorophore bleaches irreversibly over time, the number of tagged molecules are unknown and there is occasional loss of signal from the tagged molecules. All these factors make accurate tracking over long trajectories difficult. Also the experiments are technically difficulty to conduct and thus there is a pressing need to develop better algorithms to extract the maximum information from the data. For this purpose we propose a Bayesian approach and apply our technique to synthetic and a real experimental data set.

Cryogenic single-shot spectroscopy of a floating poly-silicon gate transistor

Trapped electrons, located close to the channel of a transistor, are promising as data storage elements in non-classical information processing. Cryogenic microwave spectroscopy has shown that these electrons give rise to high quality factor resonances in the drain current and a post excitation dynamic behaviour that is related to the system lifetime. Using a floating poly-silicon gate transistor, single shot spectroscopy is performed to characterise the dynamic behaviour during excitation. This behaviour is seen to be dominated by the decay of the transient component, which gives rise to oscillations around the high quality factor resonance. © 2012 American Institute of Physics.

Polychromatic single-shot spectroscopy on SOI-FET trapped electrons

The behavior of trapped electrons, in a dielectric close to the channel of a silicon SOI-FET, is studied by cryogenic microwave spectroscopy. On-resonance microwave excitation causes one of these trapped electrons to undergo spatial Rabi oscillations between widely separated trap sites. This charge displacement causes a change in the drain current of the transistor, resulting in high quality factor resonances in continuous wave spectroscopy. The potential of this effect for non-classical information processing is investigated through polychromatic single-shot spectroscopy, using on-resonance and difference frequencies. Interaction between different trapped electrons is seen in the post excitation behavior and the possibilities of quantum gate operations are discussed. © The Electrochemical Society.

Laser micromachining of thin films for optoelectronic devices and packages

Focused laser micromachining in an optical microscope system is used to prototype packages for optoelectronic devices and to investigate new materials with potential applications in packaging. Micromachined thin films are proposed as mechanical components to locate fibres and other optical and electrical components on opto-assemblies. This paper reports prototype structures which are micromachined in silicon carbide to produce beams 5 μm thick by (i) laser cutting a track in a SiC coated Si wafer, (ii) undercutting by anisotropic silicon etching using KOH in water, and (iii) trimming if necessary with the laser system. This approach has the advantage of fast turn around and proof of concept. Mechanical test data are obtained from the prototype SiC beam package structures by testing with a stylus profilometer. The Youngs modulus obtained for chemical vapour deposited silicon carbide is 360 +/- 50 GPa indicating that it is a promising material for packaging applications.

Epitaxy of III-V semiconductor nanowires towards optoelectronic devices

GaAs and InP based nanowires were grown epitaxially on GaAs or InP (111)B substrates by MOCVD via VLS mechanism. In this paper, I will give an overview of nanowire research activities in our group. © 2009 IEEE.

Measurement of the Interaction Between Recombinant I-domain from Integrin alpha 2 beta 1 and a Triple Helical Collagen Peptide with the GFOGER Binding Motif Using Molecular Force Spectroscopy.

The role of the collagen-platelet interaction is of crucial importance to the haemostatic response during both injury and pathogenesis of the blood vessel wall. Of particular interest is the high affinity interaction of the platelet transmembrane receptor, alpha 2 beta 1, responsible for firm attachment of platelets to collagen at and around injury sites. We employ single molecule force spectroscopy (SMFS) using the atomic force microscope (AFM) to study the interaction of the I-domain from integrin alpha 2 beta 1 with a synthetic collagen related triple-helical peptide containing the high-affinity integrin-binding GFOGER motif, and a control peptide lacking this sequence, referred to as GPP. By utilising synthetic peptides in this manner we are able to study at the molecular level subtleties that would otherwise be lost when considering cell-to-collagen matrix interactions using ensemble techniques. We demonstrate for the first time the complexity of this interaction as illustrated by the complex multi-peaked force spectra and confirm specificity using control blocking experiments. In addition we observe specific interaction of the GPP peptide sequence with the I-domain. We propose a model to explain these observations.