Golden Vaterite as a Mesoscopic Metamaterial for Biophotonic Applications

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