Richard Superfine

Controlled manipulation of molecular samples with the nanoManipulator

The nanoManipulator system adds a virtual-reality interface to an atomic-force microscope (AFM), thus providing a tool that can be used by scientists to image and manipulate nanometer-sized molecular structures in a controlled manner. As the AFM tip scans the sample, the tip-sample interaction forces are monitored, which, in turn, can yield information about the frictional, mechanical, material, and topological properties of the sample. Computer graphics are used to reconstruct the surface for the user, with color or contours overlaid to indicate additional data sets. Moreover, a force feedback stylus, which is connected to the tip via software, allows the user to directly interact with the macromolecules. This system is being used to investigate carbon nanotubes, DNA, fibrin, adeno- and tobacco mosaic virus. It is now also possible to insert this system into a scanning electron microscope which provides the user with continuous images of the sample, even while the AFM tip is being used for manipulations.

Fabrication of nanometer-scale mechanical devices incorporating individual multiwalled carbon nanotubes as torsional springs

We report on the fabrication of nanometer-scale mechanical devices incorporating multiwalled carbon nanotubes (MWNTs) as the torsional spring elements. We have employed electron beam lithography to pattern device elements directly onto individual MWNTs on a silicon dioxide substrate. The structures were suspended by etching the substrate and subsequent critical-point drying of the sample. We also briefly present characterization of the torsional properties of an individual MWNT. The techniques described are applicable to other nanometer-scale rod-like objects.

Thermally actuated untethered impact-driven locomotive microdevices

The authors have developed steerable locomotive devices as small as 30μm using the inertial impact drive as the thrust method. The devices consist of three-legged, thin-metal-film bimorphs designed to rest on three sharp tips with the device body curved up off the surface. Rapid, thermally induced curvature of one leg leads to stepwise translation on a low friction surface. A focused laser was used to supply energy and its parameters controlled the velocity and direction of motion of the device.

Thin-foil magnetic force system for high-numerical-aperture microscopy

Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 mum paramagnetic particle and 13 nN on a 4.5 mum paramagnetic particle, forces over the full 4pi sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 mum xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function.

Evidence of commensurate contact and rolling motion: AFM manipulation studies of carbon nanotubes on HOPG

We report on experiments in which multiwall carbon nanotubes (CNTs) are manipulated with AFM on a graphite (HOPG) substrate. We find certain discrete orientations in which the lateral force of manipulation dramatically increases as we rotate the CNT in the plane of the HOPG surface with the AFM tip. The three-fold symmetry of these discrete orientations indicates commensurate contact of the hexagonal graphene surfaces of the HOPG and CNT. As the CNT moves into commensurate contact, we observe the motion change from sliding/rotating in-plane to stick–roll motion.

High throughput system for magnetic manipulation of cells, polymers, and biomaterials

In the past decade, high throughput screening (HTS) has changed the way biochemical assays are performed, but manipulation and mechanical measurement of micro- and nanoscale systems have not benefited from this trend. Techniques using microbeads (particles approximately 0.1-10 mum) show promise for enabling high throughput mechanical measurements of microscopic systems. We demonstrate instrumentation to magnetically drive microbeads in a biocompatible, multiwell magnetic force system. It is based on commercial HTS standards and is scalable to 96 wells. Cells can be cultured in this magnetic high throughput system (MHTS). The MHTS can apply independently controlled forces to 16 specimen wells. Force calibrations demonstrate forces in excess of 1 nN, predicted force saturation as a function of pole material, and powerlaw dependence of F approximately r(-2.7+/-0.1). We employ this system to measure the stiffness of SR2+ Drosophila cells. MHTS technology is a key step toward a high throughput screening system for micro- and nanoscale biophysical experiments.

Hands-on tools for nanotechnology

We describe some mechanical and electrical measurements on carbon nanotubes. We discuss electron beam lithography techniques to form metal wire contacts to the as-found nanometer structures. Starting from a unique collaborative perspective, we suggest some improved design and alignment methods.

In situ imaging of polymer melt spreading with a high-temperature atomic force microscope

We have developed a method of imaging at high temperatures with atomic force microscopy using a laser to deliver heat to an area localized around the AFM tip–sample junction. We couple approximately 75 mW from an argon-ion laser into the active region to raise the temperature of a 100 nm gold film to around 225 °C. As a sample, we use 1.2 μm polystyrene spheres adsorbed onto the film. We image the flow of these spheres, in situ, over the course of an hour. The dynamics of the polymer spreading is shown to be consistent with the dry spreading of a precursor film.

Highly responsive core-shell microactuator arrays for use in viscous and viscoelastic fluids

We present a new fabrication method to produce arrays of highly responsive polymer-metal core-shell magnetic microactuators. The core-shell fabrication method decouples the elastic and magnetic structural components such that the actuator response can be optimized by adjusting the core-shell geometry. Our microstructures are 10 μm long, 550 nm in diameter, and electrochemically fabricated in particle track-etched membranes, comprising a poly(dimethylsiloxane) core with a 100 nm Ni shell surrounding the upper 3-8 μm. The structures can achieve deflections of nearly 90° with moderate magnetic fields and are capable of driving fluid flow in a fluid 550 times more viscous than water.

Mechanics of nanotubes and nanotube‐based devices

We discuss the mechanical properties of carbon nanotubes and devices incorporating carbon nanotubes. We demonstrate novel measurement and force application techniques using an atomic force microscope coupled to a unique computing environment that simplifies manipulations. We report on results from measurements of the mechanical and electronic interactions between nanotubes and graphite surfaces. We also fabricate nanometer‐scale electromechanical devices which incorporate nanotubes as springs, and discover a remarkable stiffening behavior of the nanotubes.