Prospects of deep Raman spectroscopy for noninvasive detection of conjugated surface enhanced resonance Raman scattering nanoparticles buried within 25 mm of mammalian tissue.

This letter discusses the potential of deep Raman spectroscopy, surface enhanced spatially offset Raman spectroscopy (SESORS and its variants), for noninvasively detecting small, deeply buried lesions using surface enhanced resonance Raman scattering (SERRS) active nanoparticles. An experimental demonstration of this concept is performed in transmission Raman geometry. This method opens prospects for in vivo, noninvasive, specific detection of molecular changes associated with disease up to depths of several centimeters representing significant improvement over traditionally detected Raman signals by 2 orders of magnitude. The disease specific signals can be achieved using uniquely tagged nanoparticles conjugated to target molecules, e.g., antibodies for production of the SERRS signal. This provides the molecular specific signal which is many orders of magnitude greater than normal biological Raman signals and can be easily multiplexed. To date, there have been no studies demonstrating the viability of deep Raman spectroscopy coupled to surface enhanced techniques for detecting low concentrations of molecules of interest at depths of greater than 5.5 mm in tissue. Such a breakthrough would open a host of new applications in medical diagnoses. Here we propose to facilitate such capability by combining SERRS (as a probe for disease specific changes) with deep Raman spectroscopy techniques. This permits noninvasive measurement of Raman signatures from conjugated SERRS nanoparticles at clinically relevant concentrations through tissues of between 15 and 25 mm thick.