  Mesoscopic photonic systems with tailored optical responses have great
potential to open new frontiers in implantable biomedical devices. However,
biocompatibility is typically a problem, as engineering of optical properties
often calls for using toxic compounds and chemicals, unsuitable for in vivo
applications. Here, we demonstrate a unique approach to biofriendly delivery of
optical resonances. We show that the controllable infusion of gold nanoseeds
into polycrystalline submicron vaterite spherulites gives rise to a variety of
electric and magnetic Mie resonances, producing a tuneable mesoscopic optical
metamaterial. The three-dimensional reconstruction of the spherulites
demonstrates the capability of controllable gold loading with volumetric
filling factors exceeding 28%. Owing to the biocompatibility of the
constitutive elements, golden vaterite paves the way to introduce designer-made
Mie resonances to cuttingedge biophotonic applications. We exemplify this
concept by showing efficient laser heating of gold-filled vaterite spherulites
at red and near-infrared wavelengths, highly desirable in photothermal therapy
and photoacoustic tomography
