Ebook: Plasmonic Biosensors

The purpose of this book is to provide the truth about plasmonic biosensors, the whole truth, nothing but the truth, without the help of God. More specifically, I wish to provide an integrated view of the science and technology of a particular type of biosensors, namely those based on refractometric plasmonic detection. However, this does not mean that I will review every plasmonic biosensor ever constructed. Rather, it means that I attempt to write about every aspect of sensor design. This includes not only optics and the physics of plasmonics, but also other aspects related to surface sensitive detection in general, not plasmonic detection in particular. The integrated view that this book provides has its advantages and drawbacks. Most likely, every reader will find at least some important information. If you approach plasmonic biosensing as a physicist you will probably find useful information about, for instance, surface functionalization and binding kinetics. If you are a biologist, you will likely learn much from the chapters about optics and plasmonics. However, if you really want to acquire in depth knowledge about a particular topic, this book can only serve as a starting point, with possible suitable references for further reading. The broad range of topics in this book reflects the interdisciplinary nature of the research field. Working with plasmonic biosensors requires knowledge in physics, chemistry and biology. More specifically, the topics of optics, nanofabrication, materials science, surface chemistry, physical chemistry and molecular biology are all highly relevant.

This book was written with two types of readers in mind: Those who work with plasmonic biosensors and those who do not. Yes, that means all people. This book is meant to be useful for those working in the research field while being interesting also for others. If you are working with plasmonics and/or biosensors, I believe you will find that this book contains useful information, but even if you do not work with such things I still suggest you read it if you want to learn more about one or the other. Of course, due to the nature of science today, it is not possible provide all the background so that an ordinary person can understand what I am writing. As science progresses, the amount of knowledge available naturally increase, which is something good, but it is also problematic that researchers become much more specialized. It is unfortunate but unavoidable that it becomes more and more difficult for us to explain to other people exactly what we are doing. For this book, I estimate that a university degree in chemistry or physics represents suitable background knowledge for following the text.

In terms of mathematical details, this book focuses on analytical expressions, while not going much into detail about numerical methods, not even for simulating the optical properties of nanostructures. Analytical models tend to be more attractive for researchers who are not specialized in computational methods and they are useful for illustrating simple physical principles. My aim is to clearly explain the physical assumptions behind each formula and go into detail about the conditions when it is applicable. The mathematical derivations will, however, not be provided. Although long calculations can be rewarding to understand in an esthetic sense, there is no point in repeating them here. Instead, references will be provided for further reading and the space in this book will be used for other purposes. As will be shown, the analytical toolkit summarized in this book is actually sufficient for illustrating many things about plasmonic biosensors, as well as drawing important conclusions.

In my opinion, one of the most important features of good science is that researchers provide both positive and negative criticism on results and theories. It is in the very nature of the scientific method to question conclusions, both your own and those of others. If we end up in a situation where it is considered “bad behavior” to criticize and be skeptical, the whole concept of science and technological progress fails. Therefore, I will sometimes give examples of research trends that do not take all important aspects of sensor design into account. (No worries, there will be no namedropping.) I will also discuss some common misunderstandings which lead to poor or meaningless conclusions. Perhaps this will make some people angry, but I suppose that is a risk I must take.

Although I consider it highly important that researchers provide each other with criticism, I am also strongly against pointless negative criticism. Examples of destructive negative criticism are phrases like “You are stupid!” or saying “You are wrong!” without providing any further explanation. This is not the type of criticism I wish to give and I have tried to stick to this principle in this book. I hope what we all want is a factual debate with rational arguments. We do not want angry people trying to talk each other down because they must be “right”, but we also do not want a quiet “consensus” where no one dares to object or question. We can all be friends even if we do not always agree about everything. (By the way, this is the principle of getting a marriage to work.)

In fact, this is another aspect of the social game in research which worries me. We are so afraid of being wrong! I sometimes get the feeling that researchers are terribly afraid that their theories turn out to be false. This is troublesome since it most likely means we do not mention ideas or theories, just because we believe we will “look stupid” if they are not correct. In addition, it means there is a risk we end up in a situation where we desperately try to show the initial idea we had was right, even though everything currently indicates it was not. I believe we must realize there is nothing wrong about being wrong! If there really is a quiet consensus among researchers that it should be shameful to be wrong, this is extremely worrying. The opposite would be more suitable. We should applaud those who change their mind!

The problem of open criticism in research can actually be related to the topic of this book through the annual review papers by Rich & Myszka in Journal of Biomolecular Recognition. Most of us find it problematic to write truly critical reviews, although journal guidelines often encourage us to, mainly because there is a high risk the referee will not share our opinion and suggest rejection of the manuscript. However, Rich & Myszka have done exactly the opposite and written truly critical and even provocative reviews. Especially the one from 2010 [430] criticizes the surface plasmon resonance biosensor literature quite harshly. Although they are even satirical, these review articles are in principle factual and show numerous serious flaws in the biosensor literature. The authors have clearly done extensive reading. For instance, over 1000 references were “graded” in the latest review [430] (at the time of writing). This paper was a success in many ways, in particular because it was in turn both criticized [555] and praised [197; 266], which shows that a factual debate actually started and as Rich & Myszka themselves mentioned [429]: “Given the poor quality of data published in the biosensor literature, we were beginning to wonder if anyone read our reviews at all.” Apparently it took a huge amount of outright provocation to actually initiate a debate.

I could probably go on for quite some time writing about worrying problems within science, but I guess perhaps this preface is already getting out of control... I will conclude by stating that even if we, as imperfect humans, always will fail to live up to the ideal scientific methodology, we should still do our very best, because it is our job.

In the long run, science is what changes our world, for better or worse.

Please feel free to contact me if you want to discuss something in this book!

adahlin@chalmers.se

http://www.adahlin.com/research/

I actually did it! I wrote a whole book myself! But still, I want to express my gratitude to some people that helped me:

Magnus Jonsson

My loyal friend and colleague. Thanks for the pictures! Hope we can work together again in the future.

Takumi Sannomiya

The Walking Wiki. Master of MMP simulations.

Norma Graf

Provides so nice 3D images!

Fredrik Höök

This book would not exist unless you had given me the chance to become what I am.

Janos Vörös

For a nice postdoc time that offered me so much freedom to develop my research.

Sara Dahlin

For you helped me so many times, my love.

Martin Dahlin

For showing me what is important in life!

Finally I wish to thank IOS Press and the editors of this series.