Photoacoustic spectroscopy (PAS) and its application in photosynthesis research

Abstract

Photoacoustic spectroscopy (PAS), sometimes also termed optoacoustic spectroscopy, is used to study thermal emission resulting from nonradiative de-excitation following absorption of radiation. Several reviews have already been published on the method in general [33, 35, 38, 39, 42] and its application in biology [6, 31]. The detection of the photoacoustic effect dates back to experiments of Alexander Graham Bell [8], John Tyndall, Wilhelm R6ntgen and Lord Rayleigh in 1880. For the history of PAS see [42]. It was not until 1973 that photoacoustic spectroscopy started to be used in a wide range of different applications. This "rediscovered" technique provides the following main advantages over the conventional types of spectroscopy. It allows: 1 the characterization and analysis of substances in highly light-scattering and opaque materials such as powders (drugs, insulators, metals), amorphous solids (glasses), gels (films), suspensions (bacteria, algae, cell organelles) and tissues (leaves, skin), 2 non-destructive and in vivo studies at different subsurface levels of a material (depth profile analysis), 3 studies of the optical and thermal properties of the sample, 4 gathering information about the de-excitation states of molecules (e.g. energy state, quantum yield) and about the life time of the intermediates of chemical reactions. These major advantages make PAS particularly suitable for studying biological material in vivo. In plant material PAS has been used since 1976 for the spectroscopic characterization and detection of pigments in phytoplankton [32] and tissues or cell layers including depth profile analysis [1, 13]. PAS was used for measuring photosynthetic activity by comparing the heat emission of active and inactive sample [e.g. 13, 16]. PAS in combination with