This volume is the result of the first NATO Advanced Study Institute (ASI) on the topic “Biophotonics: From Fundamental Principles to Health, Environment, Security and Defence Applications” held in Ottawa, Canada, September 29 – October 9, 2004. This ASI was particularly timely, since the field of biophotonics is rapidly emerging in both academia and industry: for example, the number of hits for “biophotonics” if it is entered in the internet search engine Google® has quadrupled in the last year. The meeting was notable for the extent of international attendance, with 116 participants from 18 different countries, including a very high representation from former Sovietbloc countries, demonstrating the intense interest in this topic. A full list of the speakers and topics covered at the ASI is given below.

What then is biophotonics? In the most general terms, it is the convergence of photonics and life sciences. Photonics – the science and technology of light generation, manipulation and measurement – has itself seen a remarkable expansion in the past 20 years, both in research and in commercialization, particularly in telecommunications. Despite, or perhaps partly because of, the downturn in this sector, there has been substantial transfer of photonic technologies in the past 5 years into biophotonics applications. Nowhere is this clearer than in the sub-surface tissue imaging technique of optical coherence tomography (discussed in the chapters by V.V. Tuchin and B.C. Wilson), in which many of the key components are taken straight from optical telecom (light sources, fiber splitters, optical circulators, etc). This technology transfer has greatly accelerated the development of biophotonic techniques and applications.

Conversely, the life sciences have an increasing need for new technologies to which photonics can make significant contributions. As biology and medicine move into the post-genomics era, it is increasingly important to have highly sensitive tools for probing cells, tissues and whole organism structure and functions. The optical spectrum (UV-visible-infrared) is well suited to this, since the quantum energy of optical photons is comparable to molecular energy levels of biomolecules, so that optical spectroscopies and imaging techniques provide rich biomolecular information. Examples are given in the chapters by J. Chan and colleagues and S. Lane et al. in biochemical analysis and in single-cell analysis, respectively, using Raman spectroscopy.

The sensitivity of modern optical techniques even allows measurements of single molecules, as discussed by T. Huser et al. Through photonic technologies such optical fibers, as discussed in the chapter by M. Ben-David and I. Gannot, and sensitive imaging detectors, these measurements can often be done in a non- or minimally-invasive way, which is tremendously valuable for clinical and remote-sensing applications. The technological elegance of photonics is illustrated both by this chapter and that by Cartwright in the domain of optical biosensors, which are becoming ubiquitous in many applications, including biomedical, environmental and bio/chemo security. This breadth of applications of specific optical techniques is well illustrated also in the chapter by V.M. Savov on chemiluminscence and bioluminescence.

At the same time, optical wavelengths are comparable to cellular/subcellular structure dimensions, so that imaging at very high spatial resolution is possible. Photonic technologies have thus revolutionized the field of optical microscopy, as illustrated in the chapters by H. Schneckenburger and by T. Huser et al.

In clinical medicine this ability to probe and image tissues is leading to a wide range of novel diagnostic methods. Examples of these techniques are given by Matthews and colleagues. In parallel, therapeutic applications of light have developed rapidly over the past 20 years, with many applications of surgical lasers operating by photothermal or photomechanical interactions with tissue. The application of photochemical interactions is presented in the chapter by B.C. Wilson on the specific technique of photodynamic therapy using light-activated drugs. The principles of photobiology that underlie these photothermal, photochemical and photomechanical effects are discussed in depth by P. Prasad. Complementing this, S. Tanev and colleagues provide an introduction to some exact modeling methods of tissue optics that determine how light energy is distributed in tissue, while V.V. Tuchin examines light propagation and interactions with blood, both theoretically and experimentally. Understanding these lighttissue interactions is key to optimizing the delivery of light to tissue, for both treatments and diagnostics.

Finally, the new field of nanotechnology is now penetrating into biophotonics. Examples include the use of nanoparticles such as metal nanospheres or rods and quantum dots for enhanced cell and tissue imaging and local light energy absorption. The chapter by C.E. Talley et al. discusses one specific implementation, namely the use of nanoparticles for enhancing Raman biospectroscopy.

As will be evident, this volume is not intended as a comprehensive text on biophotonics. Rather, it presents 'snapshots' of some of the most exciting developments, from a perspective of photonic technologies, and life-sciences applications. The editors hope that the reader will be equally excited and encouraged to pursue further in-depth reading, using the extensive references provide by the authors of each chapter.