Softly softly approach to analysis

German researchers have developed an improved probe for use in the surface enhanced Raman spectroscopy (SERS) of sensitive biological samples. The probe has been tested in the field to measure traces of pesticides and fungicides on the surfaces of mint, vine leaves and citrus fruits.

Jurgen Popp at the Institut f?r Physikalische Chemie in Jena, has led the development, which cuts the laser power needed for experiments in half and is far less destructive than conventional techniques.

Traditionally, biological samples are extracted, separated and then analysed by chromatography. Raman spectroscopy has the advantage of being performed directly on the sample and the effects of any water present in the sample are reduced. Analysis can be conducted on limited material and this affects the rapid identification of microorganisms since time consuming cultivation of microbes is avoided.

SERS uses an electrochemically roughened silver surface as a substrate to enhance the Raman signal. The most commonly used substrate is colloidal silver. Unfortunately silver can modify or destroy the biological samples electrochemically making it desirable to minimise any contact between sample and substrate.

Popp and colleagues have developed a glass fibre probe with a specially treated tip onto which a SERS active layer is applied. The fibre tip’s small diameter means that the laser and active silver layer make only minimal interaction with the sample. This reduces the likelihood of sensitive material decomposing.

Field measurements taken with this new system also reduce the possibility of the sample degrading when it is transported from its natural environment to the laboratory.

Suzanne Abbott