We demonstrate that second-harmonic radiation imaging probes are efficient biomarkers for imaging in living tissue. We show that 100 nm and 300 nm BaTiO3 nanoparticles used as contrast markers could be detected through 50 mu m and 120 mu m of mouse tail tissue in vitro or in vivo. Experimental results and Monte-Carlo simulations are in good agreement. (C) 2011 Optical Society of America