Plasmonic biosensors: An integrated view of refractometric detection
The book presents an integrated view of plasmonic biosensors that operate by refractometric detection. This means that analyte binding to the sensor surface induces a local change in refractive index, which alters the far field spectrum, as detected by optical spectroscopy. Other plasmonic biosensors such as those based on coupling between suspended nanoparticles or surface enhanced Raman scattering are not discussed in detail. All aspects of refractometric detection are considered in an integrated view. It is described how efficient surface functionalization becomes critical for specificity in order to reduce nonspecific interactions while preserving high affinity for the analyte. It is also shown how the influence from binding kinetics and mass transport limitations severely affects the applicability of these types of sensors. Some basic optics related to plasmonics is introduced. Nanoparticle plasmons and surface plasmons are described in depth. Plasmons in nanohole arrays as well as near field optics of plasmonic nanostructures are also presented. Throughout the book, analytical formula are given, although no expression is explicitly derived. It is emphasized under which assumptions the formulas hold and their validity is discussed. Numerical methods for plasmonics are not described in detail. Later chapters discuss experimental plasmon spectroscopy and spectral analysis, including the challenge of quantitative interpretation of the response. In particular, it is shown that the refractometric sensing performance of a plasmonic nanostructure is best evaluated in terms of relative intensity changes with liquid refractive index. The extension of the sensitivity into the liquid environment is shown to be another critical factor. Towards the end of the book, the theoretical framework is combined into an integrated view of sensor performance. Among other conclusions, it is suggested that novel nanoplasmonic sensors offer very few advatanges over the established methodology of surface plasmon resonance biosensing. As a final outlook, examples of combinations of plasmonic biosensors with other signal transduction mechanisms are presented.