Nanoelectromechanics in Engineering and Biology

Michael Pycraft Hughes

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351835091
• Edition: 1
• Topic: Medicina
• Subtopic: Biotecnologia in medicina

The success, growth, and virtually limitless applications of nanotechnology depend upon our ability to manipulate nanoscale objects, which in turn depends upon developing new insights into the interactions of electric fields, nanoparticles, and the molecules that surround them. In the first book to unite and directly address particle electrokinetics and nanotechnology, Nanoelectromechanics in Engineering and Biology provides a thorough grounding in the phenomena associated with nanoscale particle manipulation. The author delivers a wealth of application and background knowledge, from using electric fields for particle sorting in lab-on-a-chip devices to electrode fabrication, electric field simulation, and computer analysis. It also explores how electromechanics can be applied to sorting DNA molecules, examining viruses, constructing electronic devices with carbon nanotubes, and actuating nanoscale electric motors. The field of nanotechnology is inherently multidisciplinary-in its principles, in its techniques, and in its applications-and meeting its current and future challenges will require the kind of approach reflected in this book. Unmatched in its scope, Nanoelectromechanics in Engineering and Biology offers an outstanding opportunity for people in all areas of research and technology to explore the use and precise manipulation of nanoscale structures.

chapter one

Movement from electricity

1.1 Introduction

It has been known since the discovery in antiquity that electrostatic interactions between objects (such as a rubbed material picking up small items) can induce a force, either attractive or repulsive. In the intervening millennia (but mostly in the last few years) we have learned to use this force to actuate printers and hence produce the written word, to separate and sequence strands of DNA and hence diagnose diseases, to flip mirrors the size of blood cells and hence make data projectors work. The list is endless. Furthermore, as the size of the object being manipulated is decreased, so electrostatic interactions become one of the dominant forces acting on the object. This is important, since the manipulation of ever-smaller objects has increasingly become the cornerstone of technological development. Technology has only recently begun to allow mankind the ability to exert its will over particles so small they may consist of a single molecule, thus allowing us the ability to manipulate, structure, and construct, or to study, discriminate, and separate, the fabric of materials on the level of the molecules from which those materials are made, or the fundamental biological structures that make life work.

Nanoelectromechanics — from the Greek nanos (dwarf), electro (from the goddess Electra, believed in ancient times to be the source of electric charge), and mechanics (the study of forces and their effects on bodies) — is the study of forces exerted on small objects, nanometer-scale particles such as viruses, proteins, nanotubes, and DNA, by the application of electric fields. These studies occupy the space between the quantum world of atoms and the microscopic world of cells, the space that contains nanometer-scale particles, which possess complex properties in both how they work and how they interact with their environment. Moving particles with precision on such scales requires new challenges to be overcome and new insights into the physics of the interaction between electric fields, nanoparticles, and the molecules that surround them. This book will examine, in language accessible to engineers, physicists, and biologists, how these factors can be addressed to use nanodynamics both as an investigative tool, for example in studying the interiors of single viruses without harming them, or as a manipulation tool for nanoparticle separation or molecular manufacturing. This book is concerned with the application of nanomanipulation to present and future problems in nanoscale engineering, physics, chemistry, and biology. The manipulation of particles on the nanometer scale is a key technique in the exploitation of nanotechnology, and this book will study the nanodynamics of nanotechnological devices such as molecular motors and computers.

These disparate fields all need to perform the same tasks — to selectively identify, manipulate, and separate molecules and other nanoparticles from solution. This book will review the current techniques available for this purpose, presenting the range of techniques being developed but concentrating on electrostatic techniques, which dominate the field. This book describes the first major application of what is commonly referred to as nanotechnology (the precise manipulation of nanometer-scale structures) and its use in microbiology, biochemistry, and nanoelectronics. For example, many major technology companies have described the biochip market as the key technology industry of the twenty-first century. Such a market will require miniaturized, analytical methods of identifying and separating proteins, DNA, viruses, and other nanomaterial. Similarly, drug companies and forensic scientists need devices to provide rapid biochemical analysis of tiny samples. At the same time, molecular technologists require methods to position components such as nanowires and fullerenes to form molecular diodes and transistors.

A number of approaches have been taken to the study of the dynamic interactions between moving objects on the molecular scale, which form the basis of the science of molecular dynamics. The work presented in this book concentrates firmly on the scale of the macromolecular and the supramolecular — larger molecules, of the orders of nanometers across and larger — and nanometer-scale objects consisting of many molecules, such as colloids, viruses, and nanowires (as shown in Figure 1.1). Similarly, there are a number of different approaches that may be taken to impart force to nanometer-scale objects with high precision. These have included the manipulation of atoms on a dry surface using atomic force microscope tips or the manipulation of molecules in suspension using a focused laser. However, one method of precision manipulation has demonstrated great potential for trapping, positioning, or studying nanometer-scale particles; this is the manipulation by controlling the electrostatic interactions between an object and its environment — a science known variously as electrokinetics, electromechanics, and the study of ponderomotive forces. From its origins in antiquity, the subject was first explored mathematically in the eighteenth century and was later described by luminaries such as James Clerk Maxwell but was the subject of significant study only in the latter part of the twentieth century for the study of micrometer particles such as biological cells — and subsequently submicrometer particles such as those described here. In particular, this book will focus on the manipulation of particles using magnitude-variant or phase-variant electric fields, generally known (since the early 1990s) as AC electrokinetics.

Figure 1.1 A diagram showing the relative sizes of a range of particles on a logarithmic scale. Particles in the nanometer range, between 1 nm and 1,000 nm, demonstrate particular properties separate from those of bulk matter (on the micrometer scale) and individual small molecules (on the atomic scale). This book is concerned with the manipulation of particles on this scale.

1.2 The promise of nanotechnology

Taniguchi¹ invented the term nanotechnology in 1974 to describe the precision machining of surfaces. Since then it has grown to encompass a vast array of different technologies and sciences. Nanotechnology first caught the attention of the general public in 1986, when K. Eric Drexler published the popular-science book Engines of Creation,² in which he described how machines, micrometers across, operating with atomic precision might one day revolutionize the world; these ideas were explored with considerable rigor in Drexler’s second work on the subject, Nanosystems: Molecular Machinery, Manufacturing and Computation.³ In fact, such ideas can be traced back to Nobel laureate Richard Feynman, who first produced these ideas in his lecture “There’s Plenty of Room at the Bottom” in 1960.⁴ In this, he considered the idea that by developing a scalable manufacturing system, a device could be made that could make a miniature replica of itself, which could in turn replicate itself in miniature, and so on down to molecular scale. He later revisited the subject in a subsequent lecture, “Infinitesimal Machinery” in 1983,⁵ in which he postulated the now-famous idea of swimming machines in the human blood stream repairing damaged tissues, an idea he attributed to A1 Hibbs.

However, since these works came to prominence, the subjects encompassed by the term nanotechnology have grown immeasurably; this is because, on many different levels, scientists have been manipulating objects on a molecular level for many years. For example, at a fundamental level, chemistry is the original nanotechnology, where custom molecules are delivered to order. Similarly, materials science often relies on molecular-scale arrangements of different materials in order to control specific properties of the ensemble. In recent years, microscopists have discovered that scanning-probe microscopes such as the atomic force microscope (AFM) can be used to push atoms around a surface.⁶ And beyond this, nature itself has over billions of years provided us with examples of what can be achieved by developing rotary motors (functionally the same as electric stepper motors) nanometers in diameter to provide locomotion to swimming bacteria, linear motors to provide the basis for our muscles, and a method of data storage and retrieval powerful enough to describe a complete living entity, but compact enough that a complete copy resides on a molecular punch tape 2-nm wide inside almost every cell in the body: DNA.

With so many applications for the term, a new definition for nanotechnology needs to be formed that encompasses them all without being so general as to be meaningless; one current definition is the study of structures with at least one dimension on the nanometer scale. Even the definition of nanometer scale (or nanoscale for short) is vague, with the threshold between micrometer scale and nanometer scale falling either at 30 nm (the halfway point between the two on a logarithmic scale) or 100 nm (where 0.1 μm is considered sufficiently submicrometer to warrant the nanoscale label); often objects with minimum dimensions of 2–300 nm are considered, especially where they form part of a family of objects that extends downward in size; for example, herpes simplex viruses are over 200 nm in diameter but are still applicable here since they represent the largest of viruses, a class of organism that extends downward in size to some examples that are only 5 nm in diameter.

Where, in a subject so broad as to contain a hundred volumes, does this book fit in? As stated previously, it is concerned with the manipulation of particles on the nanoscale using the force that is most dominant at this scale, that of electrostatics. Drexler has divided the methods for the manipulation of nanoscale particles (nanoparticles) into two categories: top down, where larger devices are used to move smaller ones, and bottom up, where small structures self-assemble into larger ones. Here we will examine the application of electrostatic interactions with particles in solution, for the manipulation and assembly (and in some cases, self-assembly) of nanoparticles. The techniques can be used either as tools for assembling particles (that is, for engineering) or for the determination of the electrical properties of the particles being investigated. Since there are many bi...