The development of self-propelled micro- and nanoscale robots for biomedical applications holds significant promise. These devices offer advantages over conventional systems due to their autonomous motion and ability to interact specifically with biomolecules. However, many existing self-propelled systems rely on unsuitable fuels for biomedical use, such as H2O2, acidic, alkaline, Br2, or I2 solutions. This necessitates the development of biocompatible and environmentally friendly fuel sources. Water is the ideal choice, but creating water-powered micro/nanobots with advanced mobility and the capacity for complex biological functions like specific cell recognition within short timeframes remains a significant challenge. This research addresses this challenge by introducing a water-powered, self-propelled Janus nanobot capable of efficient and selective cancer cell isolation.

The paper does not explicitly detail a separate literature review section. However, the introduction section implicitly reviews existing self-propelled micro- and nano-robots and highlights their limitations, primarily their reliance on non-biocompatible fuels. This sets the stage for the proposed water-powered nanobot as a solution to these limitations.

The researchers designed and synthesized two types of Mg-Fe₃O₄-based Magneto-Fluorescent Nanorobots (MFNs): Mg-Fe₃O₄-GSH-G4-Cy5-Tf and Mg-Fe₃O₄-GSH-Cy5-Ab. These nanobots were fabricated through a series of surface modifications and conjugation chemistry. The process involved assembling multiple components onto one side of the Mg nanoparticle, creating a Janus structure. These components included: (i) EpCAM antibody/transferrin for targeting cancer cells; (ii) cyanine 5 (Cy5) dye for fluorescence imaging; (iii) fourth-generation (G4) dendrimers for multiple conjugations; and (iv) glutathione (GSH) for chemical conjugation. The synthesis involved several steps including the coating of Mg nanoparticles with Fe3O4, conjugation with GSH, conjugation with G4 dendrimers, and finally, conjugation with either EpCAM antibody or transferrin. The characterization techniques used included Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX), Dynamic Light Scattering (DLS), Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis spectroscopy, fluorescence spectroscopy, and zeta potential measurements to confirm the successful synthesis and composition of the MFNs. The propulsion performance of the MFNs was evaluated in various media (PBS, DMEM, serum) by tracking their movement and measuring their velocity. Cancer cell capture efficiency was assessed using both artificial CTC samples (HCT116 and MCF7 cells spiked into healthy blood) and clinical blood samples from epithelial cancer patients. The samples were incubated with MFNs, followed by magnetic separation and immunocytochemistry to identify and enumerate captured CTCs.

The MFNs demonstrated efficient self-propulsion in various biologically relevant media, including PBS, DMEM, and serum, driven by the spontaneous reaction between Mg and water, producing hydrogen bubbles. The Fe₃O₄ shell allowed for magnetic guidance. The nanobots exhibited exceptionally high cancer cell capture efficiency, approaching 100%, in both serum and whole blood, especially with MCF7 breast cancer cells. This high efficiency was observed even at very low CTC counts (1 cell/ml). The addition of NaHCO₃ further enhanced the propulsion speed and capture efficiency by assisting in the dissolution of the Mg(OH)₂ passive layer formed during the Mg-water reaction. Clinical validation using blood samples from five epithelial cancer patients confirmed the ability of the MFNs to capture CTCs, with counts ranging from 1 to 5 CTCs per mL of blood. The capture efficiency remained high even in the presence of other blood components. The specificity of the capture was confirmed by using nanobots without Ab and Tf, resulting in significantly lower capture efficiency.

The study successfully demonstrates a novel, water-powered self-propelled nanobot for efficient and rapid capture of CTCs. The high capture efficiency, even at low CTC concentrations, is attributed to the continuous motion of the nanobots, which enhances the interaction and binding with target cells. The use of water as fuel significantly improves the biocompatibility of the system compared to previously reported nanobots using toxic chemicals. The successful clinical validation suggests the potential of this technology for early cancer detection and prognosis. The modular design allows for easy modification with different antibodies, broadening its applicability to various types of cancer and other biomarkers.

This research successfully developed water-powered, self-propelled magnetic nanobots for highly efficient CTC capture. The nanobots demonstrated near 100% capture efficiency in blood samples, even at low CTC concentrations. The platform’s modular design allows for easy adaptation to various target cells and biomarkers. Future research could focus on in vivo testing and optimization for clinical applications.

While the study demonstrates excellent results in vitro, further in vivo studies are needed to confirm the efficacy and safety of the nanobots. The long-term stability and potential toxicity of the nanobots in vivo also need to be investigated. The current study used a limited number of clinical samples, and larger clinical trials are warranted to validate the findings.