Nanofluidics: Nanoscience and Nanotechnology (Nanoscience, Volume 6) 1st Edition by Joshua Edel (PDF)

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“In his now celebrated lecture at the 1959 meeting of the American Physical Society, Richard Feynman pondered the potential of miniaturization in the physical sciences. His vision, based on known technology, examined the limits set by physical principles and proposed a variety of new nano-tools including the concept of “”atom-by-atom”” fabrication. In the intervening decades, many of these predictions have become reality. In particular, the development and application of nanofluidics is becoming a competitive and exciting field of research. These nanoscale analytical instruments employ micromachined features and are able to manipulate fluid samples with high precision and efficiency. In a fundamental sense, chip-based analytical systems have been shown to have many advantages over their conventional (larger) analogues. Despite the growth of this field, there are surprisingly few books dedicated to nanofluidics. This book will fill the gap in the literature for a text focusing on bioanalytical applications. Written at a level accessible to experts and non-experts alike, it has the potential to become a mainstream text book for advanced nanobiotechnology courses within academic institutions.”

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Editorial Reviews: Review Going with the flowNanofluidics: nanoscience and nanotechnologyJoshua B. Edel and Andrew J. de Mello (Eds.)RSC Publishing, Cambridge, UK, 2009, 198 pp, (HB) ISBN 9780854041473 Reviewed by Sally PeymanThis book is the latest addition to the RSC’s Nanoscience and Nanotechnology series dealing specifically with the growing interest in the field of nanofluidics, which involves the flow of fluids through channels fabricated on the nanometre scale.The use of lab-on-a-chip devices in the micrometre scale has already been established and nanofluidics is described within these pages as the natural progression from microfluidics.The content is well balanced and the authors have successfully covered a broad field including motivations for nanofluidic research, fabrication, fundamental physical characteristics of the nanochannel environment, fluid dynamics, and flow behaviour. It also covers the application of nanofluidics to the controlled manipulation and detection of single molecules and polymers such as DNA.Each chapter is written by researchers active in a specific area of the field and addresses the subject with an introduction and a thorough theory section, which is complemented by supportive experimental data taken from the literature. Each chapter also takes a detailed look into current research and recent advances within each area.The content is multi-disciplinary and is aimed towards an audience with a good background knowledge of microfluidics and fluid dynamics, rather than an undergraduate student or the general scientific readership.Overall, the book is a comprehensive overview of the theory and recent advancements in nanofluidic technology and would benefit any researcher interested in the physical and analytical advantages of miniaturisation.Chemistry World, 2009, 6(7), p. 63 From the Back Cover “In his now celebrated lecture at the 1959 meeting of the American Physical Society, Richard Feynman pondered the potential of miniaturization in the physical sciences. His vision, based on known technology, examined the limits set by physical principles and proposed a variety of new nano-tools including the concept of “”atom-by-atom”” fabrication. In the intervening decades, many of these predictions have become reality. In particular, the development and application of nanofluidics is becoming a competitive and exciting field of research. These nanoscale analytical instruments employ micromachined features and are able to manipulate fluid samples with high precision and efficiency. In a fundamental sense, chip-based analytical systems have been shown to have many advantages over their conventional (larger) analogues. Despite the growth of this field, there are surprisingly few books dedicated to nanofluidics. This book will fill the gap in the literature for a text focusing on bioanalytical applications. Written at a level accessible to experts and non-experts alike, it has the potential to become a mainstream text book for advanced nanobiotechnology courses within academic institutions.” About the Author “Joshua B. Edel received his PhD in physical chemistry at Imperial College London in 2004. His thesis focused on the development of single molecule detection within microfluidic systems. He then moved to Cornell University for postdoctoral training in nanobiotechnology. In 2005, Dr Edel was awarded a research fellowship at the Rowland Institute, Harvard University to study the structure and interactions of biomolecules in their native cellular environment. In July 2006, he accepted a joint lectureship at the Institute of Biomedical Engineering and the Department of Chemistry, Imperial College London. His current research focuses on the development of nanofluidic devices to further understand biophysical systems at the single molecule level. He has published 22 research articles, 13 conference proceedings, 1 book chapter and has 5 patents and patent applications to his name. Andrew J. deMello received his PhD in molecular photophysics at Imperial College London in 1995. His post-doctoral studies at the University of California, Berkeley focused on the application of microfluidic systems for DNA analysis and resulted in the first demonstration of PCR amplification, separation and detection of DNA on an integrated microchip. He has been on the faculty of the Chemistry Department at Imperial College since 1997 and now holds the Chair of Chemical Nanosciences. His research centres on miniaturized chemical analysis systems and ultra-high sensitivity detection. More generally, studies focus on performing chemistry and biology in pico- to nanoliter volumes, high-efficiency manipulation of small liquid samples and investigating novel phenomena on the micro- and nanoscale. In 2002, he was awarded the SAC Silver Medal by the Royal Society of Chemistry for his contributions to the Analytical Sciences and in 2004 became a Fellow of the Royal Society of Chemistry.” Excerpt. © Reprinted by permission. All rights reserved. NanofluidicsNanoscience and NanotechnologyBy Joshua B. Edel, Andrew J. deMelloThe Royal Society of ChemistryCopyright © 2009 Royal Society of ChemistryAll rights reserved.ISBN: 978-0-85404-147-3ContentsChapter 1 Transport of Ions, DNA Polymers, and Microtubules in the Nanofluidic Regime Derek Stein, Martin Van Den Heuvel, and Cees Dekker, Chapter 2 Biomolecule Separation, Concentration, and Detection using Nanofluidic Channels Jongyoon Han, Chapter 3 Particle Transport in Micro and Nanostructured Arrays: Asymmetric Low Reynolds Number Flow Jason Puchella and Robert Austin, Chapter 4 Molecular Transport and Fluidic Manipulation in Three Dimensional Integrated Nanofluidic Networks T.L. King X. Jin N. Aluru and P.W. Bohn, Chapter 5 Fabrication of Silica Nanofluidic Tubing for Single Molecule Detection Miao Wang and Jun Kameoka, Chapter 6 Single Molecule Analysis Using Single Nanopores Min Jun Kim, Joseph W. F. Robertson, and John J. Kasianowicz, Chapter 7 Nanopore-Based Optofluidic Devices for Single Molecule Sensing Guillaume A. T. Chansin, Jongin Hong, Andrew J. Demello and Joshua B. Edel, Chapter 8 Ion-Current Rectification in Nanofluidic Devices Li-Jing Cheng and L. Jay Guo, Chapter 9 Nanopillars and Nanoballs for DNA Analysis Noritada Kaji, Manabu Tokeshi and Yoshinobu Baba, Subject Index, 192, CHAPTER 1Transport of Ions, DNA Polymers, and Microtubules in the Nanofluidic RegimeDEREK STEIN, MARTIN VAN DEN HEUVEL, AND CEES DEKKER1.1 INTRODUCTIONLab-on-a-chip fluidic technology takes inspiration from electronic integrated circuits, from which its name is derived. Lab-on-a-chip systems aim to improve chemical and biological analysis by using chip-based micromachining techniques to shrink the size of fluid handling systems. In this way it borrows both the fabrication technology and the “smaller, cheaper, faster” paradigm from the integrated circuit industry. For silicon-based electronics, miniaturization eventually gave rise to qualitatively different transport phenomena because the device dimensions became comparable to important physical length scales, such as the de Broglie wavelength. Nanoelectronics has consequently become nearly synonymous with quantum mechanical effects. As fluidic devices are shrunk down to the nanoscale in the quest to manipulate and study samples as minute as a single molecule, it is natural to ask, “What physical phenomena should dominate in this new regime?”As early as 1959, Richard Feynman recognized the challenges to controlling the motion of matter at the nanoscale in his famous speech, “There’s plenty of room at the bottom”. He drew attention to the friction, surface tension, and thermal forces that would become important at such small dimensions. In the earliest nanofluidics experiments, the pioneering groups of Austin and Craighead observed unusual transport properties of DNA. Channel dimensions comparable to the coil size of the polymers, called the radius of gyration, gave rise to strong entropic effects. Nanofluidics is in fact a regime where multiple physical length scales and phenomena become important, including the persistence length of a polymer, the Debye screening length for electrostatics, and the charge density along a channel surface.In this chapter we review our studies of nanofluidic channels. These are the most fundamental structures in lab-on-a-chip devices, and represent the “wires” in the circuit analogy. It has therefore been natural to focus on the transport properties of nanofluidic channels, which we have investigated for small ions, DNA polymers that possess many internal degrees of freedom, and microtubules that undergo motion as part of their biological function. A recurring theme in our experiments has been the strong departure from bulk behaviour in sufficiently small channels. Different fluidic, statistical, or electrostatic effects can drive the crossover to a new regime in each case. This highlights the importance of understanding multiple interacting phenomena as new nanofluidic applications are sought.1.2 IONIC TRANSPORTIons are ubiquitous in aqueous solution, and manifestations of their motion have been the subject of inquiry for centuries. In recent years the transport of ions in nanoscale systems has attracted increasing attention because of its importance to fundamental biological processes, e.g. ion channels in cellular and sub-cellular membranes, as well as man-made porous membranes for applications such as fuel cells, and solid-state nanopores for single molecule DNA analysis. The motion of ions is also coupled to the motion of the fluid by viscosity. This gives rise to electrokinetic effects such as electro-osmotic flow (EOF), which is widely applied in lab-on-a-chip technology.In order to study the transport of ions in the nanofluidic regime in detail, we fabricated channels with highly controlled geometries that were straightforward to analyze using theoretical calculations. A typical slit-like channel is illustrated in Figure 1.1. The 4 mm long, 50 µm wide channel was lithographically patterned between two 1.5 mm x 2 mm reservoirs on a fused silica substrate. A reactive ion plasma then etched the fused silica at a rate of 30 nm/min and was timed to stop when the desired channel height, h, had been reached. The channels were sealed by bonding them to a second, flat, fused silica substrate. Bonding was achieved using either a sodium silicate adhesive layer, or by direct thermal bonding. Pre-drilled holes allowed access to the reservoirs for introducing fluids or electrical connections.1.2.1 Electrically Driven Ion TransportWe have studied the electrically driven transport of ions in our nanofluidic channels. The ionic current was measured while a DC voltage, ΔV, was applied across a channel filled with aqueous solution of a given potassium chloride (KCl) salt concentration, n. The salt dependence of the conductance is shown in Figure 1.2 for 5 channels ranging in height from h = 70 nm to h = 1050 nm. At high salt concentrations, the channel conductances scaled with the salt concentration and the channel height, just as would be expected for a bulk KCl solution. For low salt concentrations, however, the conductance saturated at a minimum value independent of the channel height, and was orders of magnitude higher than would be expected from the bulk conductivity of the fluid.The ionic conductance saturation results from the electrostatic influence of the charged channel walls on the ionic fluid. The silica surface is negative in solution at neutral pH, and therefore attracts positive counter-ions, while repelling negative co-ions. The thin region of fluid near the surface in which a net charge density is created is called the double layer. It is the transport of mobile counter-ions in the double layer that accounts for the extra conductance observed at low salt concentrations.The conductance of nanofluidic channels can be understood quantitatively. It is necessary to account for all the ions, including the double layer, and properly couple their motion to that of the fluid. We have modelled the electrostatic potential in the double layer using the nonlinear Poisson-Boltzmann (PB) equation, which is the conventional mean field theory that describes the competition between electrostatic and entropic forces on the ions:[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1.1)Here kBTψ(x)/e is the electrostatic potential at height x from the channel mid-plane, e is the electron charge, kBT is the thermal energy, 1/κ is the Debye screening length, defined by [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], and εε0 is the permittivity of water. The Debye length sets the range of electrostatic interactions in solution. It is inversely related to salt concentration, increasing from 1/κ = 1 nm at the roughly physiological salt concentration of n = 100 mM, to 1/κ = 10 nm at n = 1 mM, and to 1/κ = 1 µm in de-ionized water.The exact solution for ψ(x) in the slab geometry is known, which allows us to calculate the exact (mean field) distribution of ions in our channels. The solution remains valid even when the double layers from opposing channel walls overlap. Moreover, the motion of ions is coupled to the fluid flow via the Stokes equation:[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1.2)where u(x) is the fluid velocity, Δp is the pressure difference across the channel, and l is the length of the channel. We take ψ(x) to be the equilibrium distribution, which is justified as long as the applied electric field gradients are too weak to significantly distort the double layer, i.e. smaller than k BTκ. It is also conventional to apply the no-slip boundary condition at the channel surfaces.In the absence of an applied pressure gradient and taking the electrical mobility of the ions to be the bulk value, the solutions to Equations 1.1 and 1.2 can be used to calculate the total conductance of a channel. This was the approach used by Levine to calculate the ionic conductance in a narrow channel with charged walls. However in order to accurately describe our experimental conductance data, it was necessary to replace the constant surface potential boundary condition that had been commonly used. We found that a constant effective surface charge density, σ, described the data extremely well and could be imposed on our transport model using Gauss’ Law, i.e.[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1.3)Our ionic transport model described the experimental data very well, as can be seen from the theoretical fits in Figure 1.2(b). The model contains only a single fit parameter, namely σ, which was found to agree well with published values for silica surfaces obtained by chemical titration experiments.The ion transport model also provides insight into the very different behaviour that was observed in the high and the low salt regimes. At high n, the number of ions in the double layer is overwhelmed by the number in the bulk fluid. The conductance of a nanochannel at high n therefore increases with n just as the conductivity of bulk solution. At low n, by contrast, the counter-ions in the double layer dominate. Their number is fixed by the requirement of overall charge neutrality, and so the conductance of the nanochannel becomes governed by the charge density at the surfaces. The crossover between high-salt and low-salt behaviour occurs when |σ| ≈ enh for monovalent salt. It is important to note that this does not correspond to double layer overlap. The data in Figure 1.2(b) clearly show, for example, that a 380 nm high channel is in the low-salt conductance plateau at n = 10-4M, where the Debye length is only 30 nm.Solid-state nanopores and nanotubes are systems in which ion transport in the low salt regime is particularly relevant. Due to their small diameter (<10 nm typically), the onset of the conductance plateau in a nanopore occurs at salt concentrations as high as hundreds of millimolar. In addition, nanopore experiments typically involve the insertion of an individual DNA molecule, which is itself a highly charged object. The backbone of double-stranded DNA carries two electronic charges for every 3.4 Å of length. DNA insertion into a solid-state nanopore therefore entrains a high concentration of mobile counter-ions into the pore, which actually increases the measured conductance for salt concentrations below ~0.4 mM.The electrically driven transport of ions in nanochannels reveals an interesting parallel with integrated circuits. The dependence of channel conductance on the surface charge is analogous to the conductance modulations in a field effect transistor (FET) that can be induced by the charge on the gate. It is therefore possible to "gate" the conductance of a nanofluidic channel by chemically modifying its surface charge density, as we have shown in Figure 1.2(c). The conductance of an h = 87 nm channel in the low-salt regime was clearly reduced by treatments with octadecyltrichlorosilane (OTS), whose attachment to silica neutralizes the surface. Other groups have employed this phenomenon as a sensing mechanism for biological agents or reported how the surface charge density of a nanochannel can be voltage-modulated using gate electrodes to result in an "ionic transistor".1.2.2 Streaming CurrentsIons are displaced in a pressure-driven flow because of the viscous drag between them and the fluid. In bulk solution, equal densities of positive and negative ions leave the fluid neutral, so no net charge transport occurs. In the vicinity of a charged surface, however, the excess of counterions in the double layer is advected by the flow and carries an electrical current. These so-called streaming currents can become increasingly important in nanofluidic channels, whose surface to volume ratio is particularly high.We have measured streaming currents in nanofluidic channels between h = 70 nm and h = 1147 nm. The relationship between the streaming current, Istr, and Δp was found to be linear, so we characterized a channel by its streaming conductance, Sstr, defined as the slope Istr / Δp. The salt concentration dependence of Sstr for a typical h = 140 nm channel is presented in Figure 1.3 and shows an extended plateau at low n that drops to a small fraction of the plateau value as n is increased beyond ~1 mM.Streaming currents can be analyzed within the same theoretical framework as electrophoretic ion transport. The applied pressure, Δp generates a parabolic (Poiseuille) fluid velocity profile that is maximal in the centre of the channel and stationary at the surfaces according to Equation 1.2. The distribution of ions that is described by the PB equation (Equation 1.1) is advected at the local fluid velocity. The streaming conductance is therefore highest at low n because the Debye length extends into the centre of the channel, where the fluid velocity is highest. We have found, however, that the constant σ boundary condition underestimates the streaming conductance at high n, predicting an earlier decay in Sstr than observed. This can be resolved by accounting for the chemistry of the silica channel, whose surface charge density is taken to be salt and pH dependent using a model described by Behrens and Grier. It predicts that as n increases, the double layer consists increasingly of potassium counter-ions rather than H+. This shifts the chemical equilibrium towards a more negatively charged surface and explains the extended streaming current plateau that is observed in Figure 1.3(b).At this point, we note the discrepancy between the boundary conditions that best describe pressure-driven and electrophoretic transport of ions in the same fluidic channels. This observation is not new. The Poisson-Boltzmann model can be used to interpret measurements of an object's charge by different techniques, including electrokinetic effects such as ionic conductance and streaming currents, as well as direct measurements of electrostatic forces on micron-scale surfaces using surface force apparatus and atomic force microscopy (AFM) techniques. It has been experimentally found that these techniques yield values for σ that can differ by a factor of 10 or more. These discrepancies highlight the fact that the Poisson-Boltzmann model does not accurately describe the microscopic structure of the double layer all the way down to the charged surface. As a result, it is necessary to speak of the "effective charge", which is a model-dependent parameter that characterizes a system's behaviour for a particular type of experiment. The double layer picture has been gradually refined to achieve more consistent predictions that account for the effects of non-specific adsorption (the so-called "Stern Layer"), ion correlations, and finite ion size.1.2.3 Streaming Currents as a Probe of Charge InversionStreaming currents are a sensitive probe of the surface charge and can be used to study the details of the solid-liquid interface. The current derives from charge transport in the diffuse part of double layer only, because ions in the bulk fluid carry no net charge, and it is generally accepted that the tightly bound counter-ions in the Stern layer (also called the inner Helmholtz plane) remain immobile in a pressure-driven flow. An important advantage of an electrokinetic probe of the surface charge over direct AFM force measurements is that streaming currents remain reliable even at high salt concentrations. We have used streaming currents in silica nanochannels to investigate the phenomenon of charge inversion (CI) by multivalent ions.Ions play a fundamental role in screening electrostatic interactions in liquids. Multivalent ions (where the ion valency Z exceeds 1) can exhibit counterintuitive behaviour by not only reducing the effective charge of a surface, but by actually flipping its sign (Figure 1.4(a-b)). This phenomenon has been proposed to be relevant in important biological situations such as DNA condensation, viral packaging, and drug delivery. CI, however, cannot be explained by conventional mean-field theories of screening such as the Poisson-Boltzmann model. (Continues...)Excerpted from Nanofluidics by Joshua B. Edel, Andrew J. deMello. Copyright © 2009 Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site. Read more Reviews from Amazon users which were colected at the time this book was published on the website: ⭐Not found. ⭐Not found. ⭐Not found. ⭐Not found. ⭐Not found. ⭐Not found.

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