**1. Introduction**

Movement is crucial for all different types of lives existing in both macroscopic and micro-/nanoscopic environments. Nature has developed smart and highefficiency biomolecular motor proteins through such many years of biological evolution and has employed them in numerous biological processes and cellular activities [1–3]. For instance, bacteria are able to propel themselves forward with the aid of rotary flagellar nanomotors, as shown in **Figure 1A** [1]. Moreover, linear biomolecular motor proteins, such as kinesin, myosin, and dynein, are capable of harvesting energy from hydrolyzing adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and phosphate (Pi) molecule for lateral motion along corresponding tracts, as shown in **Figure 1B** [2]. In addition, biological cells are equipped with intelligent biomolecular engines (ATPase), which are demanded to generate biological fuel ATP, as shown in **Figure 1C** [3].

Micro-/nanomotors are micro-/nanoscale devices, which possess the ability to convert chemical energy into mechanical force or movement [4]. Evolution bestows

Meanwhile, micro-/nanomotors have a wide variety of applications, including

*Catalytic Micro/Nanomotors: Propulsion Mechanisms, Fabrication, Control, and Applications*

Whitesides and his colleagues firstly reported the motion of a millimeter-scale object, which was composed of a piece of platinum (Pt)-coated porous glass filter mounted on a thin polydimethylsiloxane (PDMS) plate using a stainless steel pin, as shown in **Figure 2** [10]. The assembled object was immersed into hydrogen peroxide (H2O2) solution. Pt catalyzes H2O2 decomposition to generate oxygen (O2) bubbles releasing from its surface, which reversely induced a recoil force to propel the object moving forward. This is the foundation in this research field. In micro-/ nanoscale regime, only asymmetric particles can realize autonomous propulsion. Based on this, researchers focused on two aspects: shape and material compositions of micro-/nanomotors for breaking the symmetry, and various types of micro-/ nanomotors were invented. Meanwhile, there were different mechanisms proposed to explain the propulsion phenomena, depending on the shapes (e.g., wires, rods, Janus spheres, and tubular jets) and material compositions of micro-/nanomotors

In the past decades, a variety of micro-/nanomotors have been envisioned to explore the concept of self-electrophoresis propulsion, especially micro-/nanowires, rods, and Janus spheres. In self-electrophoresis, micro-/nanomotors produce a locally distributed electric field through chemical gradients and propel forward in

*(A) Schematic diagram of the propulsion of a millimeter-scale object. A thin plate (1–2 mm in thickness and 9 mm in diameter) was assembled from PDMS in a desired shape, and specified faces were rendered as hydrophilic by plasma oxidation. A 2 2 mm2 piece of porous glass filter (one side covered with Pt) was mounted on the PDMS plate by using a stainless steel pin. (B) A diagram illustrating self-assembly by capillary*

cargo towing, water cleaning, chemical sensors, biomedical applications, etc. [5, 7–9]. Advanced forms of micro-/nanomotors may stimulate and benefit other research. However, designing and powering micro-/nanomotors can be considered as a significant challenge in today's nanotechnology research. Hence, it is much beneficial for us to learn the state of the art of synthetic micro-/nanomotors and improve them in this research field. In this chapter, the reported work on the propulsion mechanisms, fabrication methods, propulsion controlling, and applications of synthetic self-propelled platinum-based micro-/nanomotors will be

presented and discussed.

[4–17].

**Figure 2.**

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*interactions. Copyright 2002, Wiley Online Library.*

**2.1 Dielectrophoresis**

**2. Propulsion mechanisms**

*DOI: http://dx.doi.org/10.5772/intechopen.90456*

#### **Figure 1.**

*(A) Schematic diagram of the architecture of the bacterial flagellar motor. (B) The twin heads of kinesin motor protein alternately bind to the microtubules so that the protein motor moves forward. (C) Schematic diagram of ATPase. Copyright 2012, Elsevier. Copyright 2004, IEEE Xplore Digital Library. Copyright 2000,The Royal society Publishing.*

biomolecular protein motors with fascinating abilities to harness energy from living environments for autonomous motion *in vivo* as described above. Inspired by the fantasy of naturally occurring motor proteins, researchers paid great attentions into synthetic micro-/nanomotors in the past decades. In particular, led by pioneering contributions of Sen and Mallouk's team and Ozin's group, current work mainly focuses on the exploration of high-efficiency and high-speed synthetic micro-/ nanomotors that are able to convert chemical energy into autonomous propulsion [4–6].

The research of synthetic self-propelled micro-/nanomotors has rapidly developed in last few decades [4–9]. Several advanced developments and excellent contributions had been made in this field. Although the bright future of this research area can be expected, some major existing challenges are still remained to be solved. The design, fabrication, and characterization of functional micro-/nanomotors require some innovative approaches and ideas to realize. Fabricating micro-/ nanomotors with individual functional parts, smartly and precisely controlling motors are still extremely challenging. Hereby, a complete understanding of the physiochemical mechanism is necessary. To realize better control of micro-/ nanomotors in the future, an industrial level of functional micro-/nanomachinery could be achieved. Despite of the significant development and advances in micro-/ nanomotors, challenges are still remained to find specific relevant applications, such as biologically compatible fuels, etc.

*Catalytic Micro/Nanomotors: Propulsion Mechanisms, Fabrication, Control, and Applications DOI: http://dx.doi.org/10.5772/intechopen.90456*

Meanwhile, micro-/nanomotors have a wide variety of applications, including cargo towing, water cleaning, chemical sensors, biomedical applications, etc. [5, 7–9]. Advanced forms of micro-/nanomotors may stimulate and benefit other research. However, designing and powering micro-/nanomotors can be considered as a significant challenge in today's nanotechnology research. Hence, it is much beneficial for us to learn the state of the art of synthetic micro-/nanomotors and improve them in this research field. In this chapter, the reported work on the propulsion mechanisms, fabrication methods, propulsion controlling, and applications of synthetic self-propelled platinum-based micro-/nanomotors will be presented and discussed.
