Optical microscopy by near field detection belongs to the new born family of local probes. This very promising technique theoretically allows one to image periodic structures of characteristic sizes much smaller than the radiation wavelength. The present work is a generalization of this concept to local spectroscopy. Starting from a self-consistent equation, we study the near-field behavior in the vicinity of particles having an optical activity in the visible range. It will be shown that the spectral resolution depends both on the tip-surface distance and on the detector size.