Preface

Rapid advances are being made in the development of smart materials for detection science, from simple dry-strip colour-changing indicators to electronic biosensors and, more recently, using nanoparticle-based systems. Any reliable device needs to respond selectively to a target molecule or compound. Biology has helped in a big way here with enzymes and antibodies which show unrivalled specificity for molecular recognition. Bio-inspired materials are gaining popularity and capturing the imagination of scientific and lay audience alike, in the quest for synthetic materials to mimic biological function. The latter biomimics offer the promise of inexpensive and more stable alternatives to their biological counterparts. In some cases a fusion of materials chemistry and biochemistry is necessary to realise new and advanced functional materials. Consider, for example, that for proper function of antibodies or DNA in a biosensor detection strategy, molecular orientation is important and can be controlled with self-assembling chemistries.

The bedrock of most sensor strategies is getting the target molecule of interest to bind with a suitable complement, resulting in a measurable physical or chemical change. Of course, biological systems have had millennia to develop such strategies. Whereas materials chemistry is playing catch-up with biology, there have been significant strides in the past 20–30 years in developing advanced synthetic systems, such as complexing agents for the selective binding of small organic molecules and ions. Research in molecularly imprinted polymers has evolved from the development of materials for selective extraction of low molecular weight organics to the selective binding of large biomolecular systems such as proteins, DNA and viruses. The latter is heralding the era of functional plastic antibodies.

Nanomaterials have seen a surge in interest in the past 15–20 years, with research in carbon nanotubes, quantum dot semiconducting materials and gold nanoparticles for developing detection strategies. Their application to biosensing has met with variable successes and it is important to address the use of such materials in detection strategies and their fitness for purpose.

Where target molecule specificity is not achievable, or desirable for that matter, complex biological systems have developed natural intelligent algorithms to identify mixtures of compounds all in one sample, whether it be a liquid or gas. The ability of the human nose or tongue to discriminate between a variety of odours and flavours relies on receptors which have broad band selectivity. There have been significant efforts to mimic these systems in the laboratory with the development of electronic nose and electronic tongues.

The one overwhelming drawback in any strategy when interfacing the synthetic material world with the biological world is the lack of appreciation or, dare I say it, respect for the compatibility between the two. The issue of biocompatibility is important to address as there are many stumbling blocks en route to developing a reliable biosensor or detector, the most important being an understanding of the surface chemistry of the new material and being aware of the chemical composition and matrix effects therein of the interfacing biological sample. There are notable successes in improving the biocompatibility at the bio/sensor interface through rational design of polymeric materials that can withstand the harsh conditions presented by, for example, blood and thereby controlling bio-fouling, but at the same time the material must not elicit an adverse biological immune response. There is a lot we can learn from biology in this regard.

This book gives an introduction to bio-inspired materials in medicine in Chapter 1. Chapter 2 takes a more comprehensive and critical look at how biomimetic materials have been applied in various biosensor strategies. While the latter are important considerations for long-term exposure of a synthetic material to a bio-environment, there has been extensive research in developing extremely reliable ‘single-use and dispose’ devices. Chapter 3 focuses on the recent advances in molecularly imprinted polymers (MIPs) for imprinting of biological molecules (namely, proteins, viruses and DNA). Improvements in preparation of such antibody mimics could eventually see MIPs replacing biological antibodies in bioassays. We also review some established and new chemistries for the development of smart detectors finding applications in medicine, food and the environment. Chapter 4 gives a review of nanoparticle technologies that have been used in biosensor development and highlights some of the challenges of going down to the nanoscale. Chapter 5 explores some of the history of dry-strip colour-changing indicators and some of the more recent developments in smart indicators capable of responding to changes in their environment, with apparent applications in food packaging and biowarfare agent detection. Chapter 6 gives some of the physical chemistry and characterization techniques used to develop novel macrocyclic ligands based on calixpyrrole research for the selective binding of a range of ions. Chapter 7 gives a tutorial in pattern recognition and use of multivariate techniques and reviews the significant developments in electronic tongue research.

We have tried to capture a thread in this book that will hopefully weave a fabric of understanding and vision for potential new developments in advanced synthetic smart materials, endeavouring to bring the synthetic and biological worlds closer together to solve analysis and detection problems. Finally, I would like to thank the Royal Society of Chemistry publishing team for their support and chivvying along which has helped see this book come to completion.

Dr Subrayal Medapati Reddy

University of Surrey

Guildford, Surrey, UK