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The properties of substrates and extracellular matrices (ECM) are important factors governing the functions and fates of mammalian adherent cells. For example, substrate stiffness often affects cell differentiation. At focal adhesions, clustered-integrin bindings link cells mechanically to the ECM. In order to quantitate the affinity between cell and substrate, the cell adhesion force must be measured for single cells. In this study, forcible detachment of a single cell in the vertical direction using AFM was carried out, allowing breakage of the integrin-substrate bindings. An AFM tip was fabricated into an arrowhead shape to detach the cell from the substrate. Peak force observed in the recorded force curve during probe retraction was defined as the adhesion force, and was analyzed for various types of cells. Some of the cell types adhered so strongly that they could not be picked up because of plasma membrane breakage by the arrowhead probe. To address this problem, a technique to reinforce the cellular membrane with layer-by-layer nanofilms composed of fibronectin and gelatin helped to improve insertion efficiency and to prevent cell membrane rupture during the detachment process, allowing successful detachment of the cells. This method for detaching cells, involving cellular membrane reinforcement, may be beneficial for evaluating true cell adhesion forces in various cell types., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Magnetic tweezers (MTW) enable highly accurate forces to be transduced to molecules to study mechanotransduction at the molecular or cellular level. We review recent MTW studies in single molecule and cell biophysics that demonstrate the flexibility of this technique. We also discuss technical advances in the method on several fronts, i.e., from novel approaches for the measurement of torque to multiplexed biophysical assays. Finally, we describe multi-component nanorods with enhanced optical and magnetic properties and discuss their potential as future MTW probes.

In biology, nucleic acids are carriers of molecular information: DNA's base sequence stores and imparts genetic instructions, while RNA's sequence plays the role of a messenger and a regulator of gene expression. As biopolymers, nucleic acids also have exciting physicochemical properties, which can be rationally influenced by the base sequence in myriad ways. Consequently, in recent years nucleic acids have also become important building blocks for bottom-up nanotechnology: as molecules for the self-assembly of molecular nanostructures and also as a material for building machinelike nanodevices. In this Review we will cover the most important developments in this growing field of nucleic acid nanodevices. We also provide an overview of the biochemical and biophysical background of this field and the major "historical" influences that shaped its development. Particular emphasis is laid on DNA molecular motors, molecular robotics, molecular information processing, and applications of nucleic acid nanodevices in biology., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Bionanotechnology blends the areas of nanotechnology and biological sciences. This article surveys the area of nanoscale biosensor development and the application of state-of-the-art biophysical techniques to elucidate fundamental membrane and surfactant biochemistry undertaken at the University of Waterloo (Canada). The Waterloo Institute for Nanotechnology (WIN), coordinates various cutting-edge nanotechnology research areas at the University of Waterloo. One focus is the area of biosensor research and fundamental biophysics in bionanotechnology. This is Part 2 of a contribution from the WIN initiative.

Solid-state nanopores can be employed to detect and study local structure along single molecules by voltage driven translocation through the nanopore. Their sensitivity and versatility can be augmented by combining them with a direct force probe, for example, optical tweezers. Such a tool could potentially be used to directly probe RNA secondary structure through the sequential unfolding of duplex regions. Here, we demonstrate the first application of such a system to the study of RNA by directly measuring the net force on individual double-stranded RNA (dsRNA) molecules. We have probed the force on dsRNA over a large range of nanopore sizes from 35 nm down to 3.5 nm and find that it decreases as the pore size is increased, in accordance with numerical calculations. Furthermore, we find that the force is independent of the distance between the optical trap and the nanopore surface, permitting force measurement on quite short molecules. By comparison with dsDNA molecules trapped in the same nanopores, we find that the force on dsRNA is on the order of, but slightly lower than, that on dsDNA. With these measurements, we expand the possibilities of the nanopore-optical tweezers to the study of RNA molecules with potential applications to the detection of RNA-bound proteins, the determination of RNA secondary structure, and the processing of RNA by molecular motors.

Molecular interaction is a key concept in our understanding of the biological mechanisms of life. Two physical properties change when one molecular partner binds to another. Firstly, the masses combine and secondly, the structure of at least one binding partner is altered, mechanically transducing the binding into subsequent biological reactions. Here we present a nanomechanical micro-array technique for bio-medical research, which not only monitors the binding of effector molecules to their target but also the subsequent effect on a biological system in vitro. This label-free and real-time method directly and simultaneously tracks mass and nanomechanical changes at the sensor interface using micro-cantilever technology. To prove the concept we measured lipid vesicle (approximately 748*10(6) Da) adsorption on the sensor interface followed by subsequent binding of the bee venom peptide melittin (2840 Da) to the vesicles. The results show the high dynamic range of the instrument and that measuring the mass and structural changes simultaneously allow a comprehensive discussion of molecular interactions.