To date, the integration of plasmonics with non-linear optics (NLO) has primarily focused on lithographically fabricated two-dimensional structures. However, several applications such as biomedical labeling and imaging demand scalable syntheses of large quantities of colloidal nanoparticles (NPs). A viable approach is to synthesize plasmonic NPs coated by a NLO thin shell, in which the second or third harmonics of the shell are, both spatially and spectrally, overlapping with the LSPR of the core to further enhance the intrinsically weak non-linear optical signals.