The present invention relates to sensitive SE(R)RS based methods for detecting analytes such as explosives and drugs, which may be present in a sample at extremely low levels. The methods may be generally carried out in situ employing novel chemistry which is compatible with flow-cell technology and with time-scales and concentrations required for rapid and informative screening of large numbers of samples. The present invention also relates to novel compounds e.g. synthons and apparatus for use with the methods disclosed.
