Light-propulsion wavelength-dependent microswimmer and the fuel and efficiency problem therein

Abstract

Over the past decades, scientists endeavored to develop nanorobot and envisioned that those tiny artificial machines could be used in medical treatment and material fabrication. The breakthrough in this area will motivate theranostic nanoplatforms and open the door to in-depth knowledge of diseases. The micro/nano-motor with scale comparable to a single cell is of particular interest due to its relative simple preparation and potential biological application at the cellular scale. Among all micro/nano-motors, light-driven motor is an emerging candidate due to its capability of delivering distinct communication signals via localized light field with different wavelengths. However, the existing state-of-the-art motors often relies on UV light source, which is undesirable for biomedical applications. In this thesis, a visible/near-infrared light-driven microswimmer based on the single silicon nanowire was developed. The silicon microswimmer harvests energy from incident photon and propels itself by self-electrophoresis mechanism. Due to high light harvesting efficiency, the silicon nanowire can be readily driven by visible and near-infrared illumination at low light intensity, which is highly preferred for the biomedical applications. Furthermore, our experimental study, as well as numerical simulation, shows that the detailed structure around the concentrated reaction center on the nanowire determines the migration behavior of the microswimmer. Importantly, we also demonstrated that the well-developed photonic technique could be applied to engineer the spectral response of microswimmer. Due to the optical resonance inside the silicon nanowire, the spectral response of the nanowire-based microswimmer can be readily modulated by the nanowire’s diameter which opens up a new dimension for designing the next generation light-driven nanomotor and offers tremendous opportunities for the realization of many novel functions such as multiple channels communication to nanorobot and controllable self-assembly. On the other hand, the fuel biocompatibility and efficiency problems are the critical hurdle for the next step forward. Therefore, we proposed a simple quantitative model with combining electrochemistry and solar cell to describe the microswimmer migration dependence with different fuels and light intensity and demonstrated experimentally with different fuels. The diffusion coefficient influence was also restudied and successfully verified by ferrocene derivatives. Cell toxicity measurement was employed to determine the biocompatibility of different fuels and a comparison criteria was also proposed to evaluate fuel efficiency and toxicity. Furthermore, ferrocene derivatives are demonstrated to be a fire-new biocompatible and high efficiency fuels. This fuel and efficiency principle envisions a bright future for the breakthrough of biomedical application of chemically powered micro/nano-motors.