Multifunctional Spirulina-hybrid helical microswimmers: Imaging and photothermal efficacy enabled by intracellular gold deposition

Helical micro-/nanoswimmers have been extensively explored as a miniaturized robotic tool for advanced biomedicine in the past two decades. However, the integration of biomedical functions on the existing swimmers remains insufficient to allow further in vivo developments. We propose a chemically engineered Spirulina microalgae with biogenic gold nanoparticles deposited in its cells and magnetite nanoparticles assembled on its surface. This biohybrid helical microswimmer is naturally of many desired functions and can be easily functionalized through surface modification and/or intracellular loading. The gold-enabled digital subtraction angiography of multimodal imaging function is highlighted herein. Such imaging modality makes real-time tracking possible in deep anatomical regions, guaranteeing precise in vivo navigation of our swimmers to specific lesions. Meanwhile, the gold-enhanced photothermal efficacy is also noteworthy. It regulates swimmer degradation via controlling photothermal heat and can be harnessed to implement targeted therapy, for which the targeting process and therapeutic effect are successfully demonstrated in a fluidic chip. Furthermore, the fabrication method is straightforward and cost-effective, suitable for mass production. All these results clarify the functionalization strategy enabled by biogenic intracellular deposition and provide a multifunctional biohybrid microswimmer.