Magnetic nanostirrers play a vital role in enhancing the mixing efficiency of tiny droplets, significantly accelerating chemical reactions in confined spaces. Their development can be traced through three key stages

Product Availability

The magnetic nanostirrer product developed by Professor Chen’s team is:

• Product Name: Magnetic nano-stir bars, silica coated iron oxide (II,III), 0.1 mg/mL in ethanol

• Features: High purity, consistent quality, and available in multiple packaging options

1. Magnetotactic Bacteria: Nature’s Inspiration

In 1975, Richard P. Blakemore first introduced the concept of magnetotactic bacteria. These microorganisms contain chains of iron-rich particles, known as magnetosomes, primarily composed of Fe₃O₄ and/or Fe₃S₄. This unique composition allows the bacteria to move under the influence of a magnetic field 1.

Inspired by this natural behavior, researchers began utilizing magnetotactic bacteria as magnetic nanostirring elements (MNSRs). Encapsulated within microdroplets, these biological MNSRs facilitate solution mixing, enhancing mass transfer and dramatically increasing reaction rates 2.

2. Artificial Synthesis: Overcoming Biological Limitations

Cultivating magnetotactic bacteria is time-consuming and technically demanding. To overcome this challenge, scientists developed synthetic magnetic nanostirrers. These are typically produced by assembling Fe₃O₄ particles into linear chains, then coating them with silica or polymers to stabilize the structure.

The resulting nanostirrers are:

• Small in size

• Capable of suspending in solution

• Able to generate multiple vortices during stirring for efficient mixing 3

While magnetic field-induced self-assembly is a common method for synthesizing these nanostirrers, it suffers from issues such as limited induction areas, low efficiency, complex post-processing, and batch inconsistencies.

To address these drawbacks, Professor Chen Hongyu’s team pioneered the use of electrospinning technology. This method allows for the rapid, flexible, and scalable synthesis of Fe₃O₄-based magnetic nanostirrers in various sizes 4.

3. Expanding Applications: From Stirring to Catalysis

In recent years, magnetic nanostirrers have evolved beyond mixing tools into catalyst carriers. For instance, Yang et al. developed a nanostirrer embedded with palladium nanoparticles (Fe₃O₄ NC PZS Pd) and demonstrated its superior catalytic activity in the hydrogenation of methylene blue compared to commercial Pd/C catalysts 5.

Additionally, Chen Hongyu’s group coated their Fe₃O₄ nanostirrer (NSB-4) with gold nanowires for use in the catalytic reduction of 4-nitrophenol. The reaction's progress was visibly confirmed as the yellow solution rapidly faded (Figure 1) 4.

Over more than a decade, Professor Chen Hongyu from Nanjing University of Technology has focused on the synthesis and application of magnetic nanostirrers. The Fe₃O₄ nanostirrers developed by his team are known for their uniform morphology and stable quality, making them suitable for a variety of confined-space stirring applications.

Figure 1 Magnetic nanostirr NSB-4 loaded with Au catalyst catalytically reduces 4-nitrophenol4

References

1. Blakemore R. Magnetotactic bacteriaJ. Science, 1975, 190(4212): 377-379.
2. Zhou X, Chen C, Cao C, et al. Enhancing reaction rate in a Pickering emulsion system with natural magnetotactic bacteria as nanoscale magnetic stirring barsJ. Chemical science, 2018, 9(9): 2575-2580.
3. Chong W H, Huang Y, Wong T N, et al. Magnetic nanorobots, generating vortexes inside nanoliter droplets for effective mixingJ. Advanced Materials Technologies, 2018, 3(4): 1700312.
4. Ji Q, Hu T, Chen Q, et al. Scalable and continuous preparation of nano-stirbars by electrospinningJ. Chemical Communications, 2020, 56(79): 11767-11770.
5. Yang S, Cao C, Sun Y, et al. Nanoscale magnetic stirring bars for heterogeneous catalysis in microscopic systemsJ. Angewandte Chemie International Edition, 2015, 54(9): 2661-2664.