Handbook of Surface Plasmon Resonance: Rsc - Hardcover

Hardcover

ISBN 10: 0854042679 ISBN 13: 9780854042678

Publisher: Royal Society of Chemistry, 2008

Synopsis

Surface plasmon resonance (SPR) plays a dominant role in real-time interaction sensing of biomolecular binding events.The book is intended as a hands-on guide for all interested in SPR

About this title

About the Author

Richard B.M. Schasfoort is currently head of the Biochip Group at the University of Twente (UT), the Netherlands, as well as director of the BioMultianalyte Detection program, strategic research orientation at MESA+ UT. He earned his MSc in biotechnology from the University of Groningen, the Netherlands and his PhD in biosensors. His research interest is focused on the coupling of lab-on-a-chip liquid handling to bio- and chemical sensors for the determination of multiple analytes in complex matrices. Relevant application areas include disease monitoring, biomarkers and food safety. Richard Schasfoort is founder of IBIS Technologies BV that has committed itself to SPR imaging technology. Richard B.M. Schasfoort has (co-)authored about 60 peer reviewed articles and 15 patent applications and was in 2002 awarded a grant for young scientists (vernieuwingsimpuls) by Netherlands Organisation for Scientific Research (NWO). Dr Tudos was senior scientist at the Biochip Group, University of Twente and now Shell Global Solutions International BV, P.O. Box 38000, 1030 BN Amsterdam, the Netherlands, She earned her PhD at the University of Amsterdam in analytical chemistry. Her post doctoral study at Iowa State University focused on electrochemical detection in miniaturized devices. Her major interest is translating scientific concepts, like SPR-based sensors or lab-on-a-chip devices into products for example for application in the food, health or defence industry. Dr Tudos is member of the editorial board of Food Chemistry (Elsevier) and head of the Analytical Chemistry Section of the Royal Dutch Society of Chemists.

From the Back Cover

Surface plasmon resonance (SPR) plays a dominant role in real-time interaction sensing of biomolecular binding events. Although the last decades have seen the birth of various books on sensors and biosensors with some mention of surface plasmon resonance, such a comprehensive work on SPR covering the issues relevant for the interested student or the practicing researcher has long been awaited. The Handbook of Surface Plasmon Resonance covers all relevant aspects of present technology spanning a bridge between theory, instrumentation and applications. The book provides a thorough theoretical introduction, including kinetic models of biomolecular interactions as well as a practical guide for assay development. The book describes the instrumentation of SPR in terms of optics, fluidics, surface chemistries and kinetics with an easy-to-follow guide of how to use the technique providing relevant applications. The history of SPR, new trends, and a vision of future developments and needs of the SPR market are given. The potential of SPR is revealed by showing highly exciting and unique opportunities for unraveling the functional relationships of complex biological processes. The book is a comprehensive source of information with easy to use, stand-alone chapters, and will be essential for scientists in industry and academia working with or affiliated to the technology. Intended for a wide audience, The Handbook of Surface Plasmon Resonance is also students aspiring to use the technology, and the wide public interested in SPR as a phenomenon and in its applications.

Excerpt. © Reprinted by permission. All rights reserved.

Handbook of Surface Plasmon Resonance

By R.B.M. Schasfoort

The Royal Society of Chemistry

Copyright © 2008 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85404-267-8

Contents

Chapter 1 Introduction to Surface Plasmon Resonance Anna J. Tudos and Richard B.M. Schasfoort, 
Chapter 2 Physics of Surface Plasmon Resonance Rob P.H. Kooyman, 
Chapter 3 SPR Instrumentation Richard B.M. Schasfoort and Alan McWhirter, 
Chapter 4 Kinetic Models Describing Biomolecular Interactions at Surfaces Damien Hall, 
Chapter 5 Kinetic and Thermodynamic Analysis of Ligand-Receptor Interactions: SPR Applications in Drug Development Nico J. de Mol and Marcel J.E. Fischer, 
Chapter 6 Surface Chemistry in SPR Technology Erk T. Gedig, 
Chapter 7 Measurement of the Analysis Cycle: Scanning SPR Microarray Imaging of Autoimmune Diseases Richard B.M. Schasfoort, Angelique M.C. Lokate, J. Bianca Beusink, Ger J.M. Pruijn and Gerard H.M. Engbers, 
Chapter 8 Advanced Methods for SPR Imaging Biosensing Alastair W. Wark, Hye Jin Lee and Robert M. Corn, 
Chapter 9 Surface Plasmon Fluorescence Techniques for Bioaffinity Studies Wolfgang Knoll, Amal Kasry, Jing Liu, Thomas Neumann, Lifang Niu, Hyeyoung Park, Harald Paulsen, Rudolf Robelek, Danfeng Yao and Fang Yu, 
Chapter 10 SPR Imaging for Clinical Diagnostics Elain Fu, Timothy Chinowsky, Kjell Nelson and Paul Yager, 
Chapter 11 The Benefits and Scope of Surface Plasmon Resonance-based Biosensors in Food Analysis Alan McWhirter and Lennart Wahlström, 
Chapter 12 Future Trends in SPR Technology Richard B.M. Schasfoort and Peter Schuck, 
Subject Index, 395, 

CHAPTER 1

Introduction to Surface Plasmon Resonance

ANNA J. TUDOS AND RICHARD B.M. SCHASFOORT

1.1 What is Surface Plasmon Resonance?

Since its first observation by Wood in 1902, the physical phenomenon of surface plasmon resonance (SPR) has found its way into practical applications in sensitive detectors, capable of detecting sub-monomolecular coverage. What is surface plasmon resonance? Wood observed a pattern of "anomalous" dark and light bands in the reflected light, when he shone polarized light on a mirror with a diffraction grating on its surface. Physical interpretation of the phenomenon was initiated by Lord Rayleigh, and further refined by Fano, but a complete explanation of the phenomenon was not possible until 1968, when Otto and in the same year Kretschmann and Raether reported the excitation of surface plasmons. Application of SPR-based sensors to biomolecular interaction monitoring was first demonstrated in 1983 by Liedberg et al. A historical overview of the use of the phenomenon for biosensor applications is given in Section 1.3 of this chapter. To understand the excitation of surface plasmons, let us start with a simple experiment.

1.1.1 A Simple Experiment

Consider the experimental set-up depicted in Figure 1.1. When polarized light is shone through a prism on a sensor chip with a thin metal film on top, the light will be reflected by the metal film acting as a mirror. On changing the angle of incidence, and monitoring the intensity of the reflected light, the intensity of the reflected light passes through a minimum (Figure 1.1, line A). At this angle of incidence, the light will excite surface plasmons, inducing surface plasmon resonance, causing a dip in the intensity of the reflected light. Photons of p-polarized light can interact with the free electrons of the metal layer, inducing a wave-like oscillation of the free electrons and thereby reducing the reflected light intensity.

The angle at which the maximum loss of the reflected light intensity occurs is called resonance angle or SPR angle. The SPR angle is dependent on the optical characteristics of the system, e.g. on the refractive indices of the media at both sides of the metal, usually gold. While the refractive index at the prism side is not changing, the refractive index in the immediate vicinity of the metal surface will change when accumulated mass (e.g. proteins) adsorb on it. Hence the surface plasmon resonance conditions are changing and the shift of the SPR angle is suited to provide information on the kinetics of e.g. protein adsorption on the surface.

1.1.2 From Dip to Real-time Measurement

Surface plasmon resonance is an excellent method to monitor changes of the refractive index in the near vicinity of the metal surface. When the refractive index changes, the angle at which the intensity minimum is observed will shift as indicated in Figure 1.2, where (A) depicts the original plot of reflected light intensity vs. incident angle and (B) indicates the plot after the change in refractive index. Surface plasmon resonance is not only suited to measure the difference between these two states, but can also monitor the change in time, if one follows in time the shift of the resonance angle at which the dip is observed. Figure 1.2 depicts the shift of the dip in time, a so-called sensorgram. If this change is due to a biomolecular interaction, the kinetics of the interaction can be studied in real time.

SPR sensors investigate only a very limited vicinity or fixed volume at the metal surface. The penetration depth of the electromagnetic field (so-called evanescent field) at which a signal is observed typically does not exceed a few hundred nanometers, decaying exponentially with the distance from the metal layer at the sensor surface. The penetration depth of the evanescent field is a function of the wavelength of the incident light, as explained in Chapter 2.

SPR sensors lack intrinsic selectivity: all refractive index changes in the evanescent field will be reflected in a change of the signal. These changes can be due to refractive index difference of the medium, e.g. a change in the buffer composition or concentration; also, adsorption of material on the sensor surface can cause refractive index changes. The amount of adsorbed species can be determined after injection of the original baseline buffer, as shown in Figure 1.2. To permit selective detection at an SPR sensor, its surface needs to be modified with ligands suited for selective capturing of the target compounds but which are not prone to adsorbing any other components present in the sample or buffer media.

1.2 How to Construct an SPR Assay?

Now we have a basic understanding of the surface plasmon resonance signal and how to measure it in time. We know that the sensor surface needs to be modified to allow selective capturing and thus selective measurement of a target compound. In the following, we are going to learn more about an SPR measurement. First, the steps of an SPR assay will be discussed from immobilization through analysis to regeneration in a measurement cycle. Next, we get acquainted with a typical calibration curve, followed by examples of assay formats. Finally, a short outlook is provided on the basics of the instrumentation.

1.2.1 The Steps of an Assay

In the simplest case of an SPR measurement, a target component or analyte is captured by the capturing element or so-called ligand (Figure 1.3). The ligand is permanently immobilized on the sensor surface previous to the measurement. Various sensor surfaces with immobilized ligands are commercially available, and many more can be custom-made, as explained in Chapters 6 and 7.

In the simplest case, the event of capturing the analyte by the ligand gives rise to a measurable signal, this is called direct detection. Figure 1.4 shows the sensor signal step-by-step in the measurement cycle with direct detection.

Each measurement starts with conditioning the sensor surface with a suitable buffer solution (1). It is of vital relevance to have a reliable baseline before the capturing event starts. At this point, the sensor surface contains the active ligands, ready to capture the target analytes. On injecting the solution containing the analytes (2), they are captured on the surface. Also other components of the sample might adhere to the sensor surface; without a suitable selection of the ligand, this adherence will be non-specific, and thus easy to break. At this step, adsorption kinetics of the analyte molecule can be determined in a real-time measurement. Next, buffer is injected on to the sensor and the non-specifically bound components are flushed off (3). As indicated in the figure, the accumulated mass can be obtained from the SPR response (ΔR). Also in this step, dissociation of the analyte starts, enabling the kinetics of the dissociation process to be studied. Finally, a regeneration solution is injected, which breaks the specific binding between analyte and ligand (4). If properly anchored to the sensor surface, the ligands remain on the sensor, whereas the target analytes are quantitatively removed. It is vital in order to perform multiple tests with the same sensor chip to use a regeneration solution which leaves the activity of the ligands intact, as the analysis cycle is required to take place repeatedly for hundreds, sometimes even thousands of times. Again, buffer is injected to condition the surface for the next analysis cycle. If the regeneration is incomplete, remaining accumulated mass causes the baseline level to be increased.

Often SPR measurements are carried out to determine the kinetics of a binding process. For realistic results it is vital to prevent immobilization from changing the ligand in a way that would influence its strength or affinity towards the target component. In addition, kinetic experiments can provide information on the thermodynamics, e.g. on the binding energy of processes. A description of the kinetic theory can be found in Chapter 4 and examples of kinetic studies in Chapter 5.

1.2.2 Calibration Curve

Apart from kinetic and thermodynamic studies, SPR measurements can also be used for the determination of the concentration of the analyte in a sample (quantitative analysis). In this case, first different concentrations of the analyte are applied in separate analysis cycles. The sensorgrams measured at different concentrations give an overlay plot similar to that depicted in Figure 1.5, with the plateaus of the association step increasing at increasing analyte concentration.

A calibration curve can be constructed by plotting the response (ΔR) after a certain time interval (t1) versus concentration.

When analyzing samples with an unknown concentration of the analyte, usually multiple dilutions are made, for example 10, 100 and 1000 times, or for more accurate determinations serial dilutions by a factor of 2. If the concentration of the analyte in the sample is very high, the undiluted sample will yield results on the upper plateau range of the calibration curve. The diluted solutions, however, might yield points along the lower, concentration-dependent sections of the calibration curve and the concentration of the analyte can be determined.

As mentioned above, SPR sensing means detection of refractive index changes at the sensor surface, which in practice translates to the amount of mass deposited at the sensor surface. Direct detection is only possible if the capturing event of the analyte brings about measurable refractive index changes. This is easier to achieve if the molecular weight of the analyte is high (i.e. around 1000 Da or higher). However, for small molecules to produce a measurable refractive index change, large numbers would be required, making the analysis intrinsically less sensitive. If the analyte is a small molecule (MW< 1000Da), often direct detection is not viable.

Detection of small molecules can be carried out using a different strategy. Most often, small molecules are detected in a sandwich, competition or inhibition assay format. In all assay formats, not only the lower detectable concentration is limited, but also the physical number of immobilized elements on the sensor surface, which provides a maximum limiting value. Discussion of the different assay formats can be found in Chapter 7 and other methods for concentration determination are described in Chapters 4 and 5.

1.2.3 Determination of Kinetic Parameters

The most prominent benefit of direct detection using SPR biosensor technology is the determination of kinetics of (bio)molecular interactions. Reaction rate and equilibrium constants of interactions can be determined, e.g. the interaction A + B -> AB can be followed in real time with SPR technology, where A is the analyte and B is the ligand immobilized on the sensor surface.

Table 1.1 contains the most relevant kinetic parameters, the association and dissociation constants, for the simplest case A + B -> AB. The association constant is the reaction rate of complex (AB) formation, giving the number of complexes formed per time at unit concentration of A and B. As soon as the complex AB is formed, its dissociation can commence. The dissociation rate constant describing this process expresses the number of AB complexes dissociating per unit time. Note that the unit dimensions for the association and dissociation rates are different and can vary with the stoichiometry of the complex. The typical range of the association and dissociation constant shows large variations and is dependent on, among other things, the temperature.

When association of A and B starts, no product is yet present at the sensing surface. At this point, the rate of the association reaction is highest and that of the dissociation reaction is lowest. As the process progresses, more and more of the AB complex is produced, enhancing the rate of dissociation. Due to decreasing A and B concentration, the rate of association might decrease. Equilibrium is reached when the rates of the association and dissociation reactions are equal; the definitions and unit dimensions are given in Table 1.2. As can be seen, the equilibrium association and dissociation constants, which represent the affinity of an interaction, have a reciprocal relationship with each other. The effect of parameters such as temperature is described in later chapters.

The rate constants (Table 1.1) and equilibrium constants (Table 1.2) of (bio)molecular interactions provide information on the strength of association and the tendency of dissociation. Various aspects of kinetics, models and calculation of affinity constants are described in Chapters 4, 5 and 9.

1.2.4 Basics of Instrumentation

Studying biomolecular interactions using SPR does not require a detailed understanding of the physical phenomena. It is sufficient to know that SPR-based instruments use an optical method to measure the refractive index near a sensor surface (within ~200 nm to the surface). SPR instruments comprise three essential units integrated in one system: optical unit, liquid handling unit and the sensor surface. The features of the sensor chip have a vital influence on the quality of the interaction measurement. The sensor chip forms a physical barrier between the optical unit (dry section) and the flow cell (wet section).

SPR instrumentation can be configured in various ways to measure the shift of the SPR-dip. In general, three different optical systems (Chapter 2) are used to excite surface plasmons: systems with prisms, gratings and optical waveguides. Most widespread are instruments with a prism coupler, also called "Kretschmann configuration". In this configuration, which is shown in Figure 1.1, a prism couples p-polarized light into the sensor coated with a thin metal film. The light is reflected on to a detector, measuring its intensity, using a photodiode or a camera. In instruments with a grating coupler, light is reflected at the lower refractive index substrate. In practice, this means that light travels through the liquid before photons generate surface plasmon waves as in ellipsometric instruments. Besides the grating couplers, some instruments apply optical waveguide couplers or measure the SPR wavelength shift as a result of the biomolecular interaction process (see Chapter 2 and ref. [13]).

All configurations share the same intrinsic phenomenon: the direct, label-free and real-time measurement of refractive index changes at the sensor surface. SPR sensors offer the capability of measuring low levels of chemical and biological compounds near the sensor surface. Sensing of a biomolecular binding event occurs when biomolecules accumulate at the sensor surface and change the refractive index by replacing the background electrolyte. Protein molecules have a higher refractive index than water molecules (Δn ≈ 10-1). The sensitivity of most SPR instruments is in the range Δn ≈ 10-5 of proteinous material. Often in real-time biosensing absolute values are not a prerequisite, only the change is monitored as a result of biospecific interaction at the sensor surface. A detailed description of commercial instruments is given in Chapter 3.

1.3 History of SPR Biosensors

The term biosensor was introduced around 1975, relating to exploiting transducer principles for the direct detection of biomolecules at surfaces. Currently the most prominent example of a biosensor is the glucose sensor, reporting glucose concentration as an electronic signal, e.g. based on a selective, enzymatic process. Some argued that all small devices capable of reporting parameters of the human body were biosensors (e.g. ion-sensitive field-effect transistors (ISFETs) measuring pH). But then, a thermometer recording fever should also be called biosensor. According to the present definition, in biosensors the recognition element (ligand) of the sensor or the analyte should originate from a biological source.

Biosensors are analytical devices comprised of a biological element (tissue, microorganism, organelle, cell receptor, enzyme, antibody) and a physicochemical transducer. Specific interaction between the target analyte and the biological material produces a physico-chemical change detected by the transducer. The transducer then yields an analog electronic signal proportional to the amount (concentration) of a specific analyte or group of analyte s.

1.3.1 Early History of SPR Biosensors

Application of SPR-based sensors to biomolecular interaction monitoring was first demonstrated in 1983 by Lundstrom's pursuit towards physical methods for label-free, real-time detection of biomolecules. The intrinsic properties of the molecules, e.g. mass, refractive index and/or charge distribution, were probed using ellipsometry, refractometry, surface plasmon resonance, photothermic detection methods and others. At the National Defense Research Laboratory of Sweden, protein-protein interactions were monitored in real time, label-free, using ellipsometry. Most importantly, the refractive index change at a light-reflecting surface was the operating transducer mechanism. Although successful in the detection of refractive index change due to the binding of biomolecules on optical transducer surfaces, a disadvantage of the ellipsometer is that light passes through the bulk of the sample solution, hence light-absorbing or particle- containing samples cannot easily be measured.

(Continues...)

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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2008
• Language: English
• ISBN 10: 0854042679
• ISBN 13: 9780854042678
• Binding: Hardcover
• Number of pages: 426