Laser speckle spectroscopy—a new method for using small swimming organisms as biomonitors

A novel method has been devised for the study of swimming organisms by using speckle patterns produced by their scattering of coherent laser light. The speckle patterns show fluctuations in space and time which may be correlated with the activity of the organisms. The fluctuations give an immediate indication of mobility and a more detailed analysis of the frequency spectrum of the speckle fluctuations shows characteristic resonance-like features which are specific to the organism. The speckle patterns produced by several protozoans, including Paramecium bursaria, Entosiphon sulcatum, and by the alga Chlamydomonas reinhardii and the rotifer Brachionus calyciflorus have been studied. Laser speckle spectroscopy (LSS) allows a rapid non-invasive monitoring of the activity of the organisms and could find application in ecotoxicity studies and environmental biomonitoring. The results presented here are the first reports of LSS and its use in this way and demonstrate its viability and potential for further development.