Gated Raman spectroscopy (GRAS): A new experimental approach for the measurement of Raman signals of particles in suspension

Abstract

A new technique for the measurement of Raman spectra of small particles in suspension, such as biological cells, is described. The particles flow through a rectangular glass capillary mounted at the sample position of a laser Raman microspectrometer. The measuring volume inside the glass capillary is comparable to the volume of the particles. The elastic forward light scattering of the laser beam by the particles is used to monitor the presence of a particle in the measuring volume. Photon pulses from the Raman detector are counted only when a particle is inside the measuring volume. In this way the background signal caused by the suspending medium is suppressed, thus allowing measurement at very low particle concentrations. The technique, which is called gated Raman spectroscopy (GRAS) combines features such as: efficient light collection, suppression of background, and the possibility to use high laser powers. A great advantage is that this technique can be used for the study of (living) biological cells under physiological conditions. The GRAS technique is demonstrated with polystyrene particles and with unicellular algae chlorella vulgaris.