Raman spectroscopy is widely used in analytical sciences to identify molecules via their structural fingerprint. In the biological context the Raman response provides a valuable label-free specific contrast that allows distinguishing different cellular and tissue contents. Unfortunately, spontaneous Raman scattering is very weak, over ten orders of magnitude weaker than fluorescence. Unsurprisingly, fluorescence microscopy is often the preferred choice for applications such as live cell imaging. Luckily, Raman can be enhanced dramatically on metal surfaces or in metallic nanogaps and this surface enhanced Raman scattering (SERS) can even overcome the fluorescence response. Nanometric SERS probes are thus promising candidates for biological sensing applications, preserving the intrinsic molecular specificity. Still, the effectiveness of SERS probes depends critically on the particle size, stability and brightness, and, so far, SERS-probe based imaging is rarely applied.