Refillable Fuel-Loading Microshell Motors for Persistent Motion in a Fuel-Free Environment

Abstract

Artificial micro-/nanomotors that harvest environmental energy to move require energy surroundings; thus, their motion generally occurs in fuel solutions or under the real-time stimuli of external energy sources. Herein, inspired by vehicles, a refillable fuel-loading micromotor is proposed based on a 2 μm hemispherical multimetallic shell using catalase or platinum on its concave surface as the engine and the bowl structure as the fuel tank. H2O2 fuel is drawn into the microbowl by capillary action and restricted inside the bowl space through a self-generated O2 bubble cap on the microshell mouth. The periodic growth and burst of the O2 cap cause the enhanced diffusion motion of micromotors. This motion behavior can last for at least 30 min in a fuel-free environment with one H2O2 fueling. Additionally, the micromotor can be refilled repeatedly to achieve permanent motion. This demonstration of a refillable fuel-loading micromotor provides a model design of an energy built-in micromotor.

Enzyme-powered micro- and nano-motors: key parameters for an application-oriented design

“…1C). Enzymatic motors built solely with metals used gold (Au), 42 iron oxide (Fe 3 O 4 ), 43 or a combination of different layered metals 44 like titanium with gold (Ti-Au), 45 titania with cadmium sulde (TiO 2 -CdS), 46 gold with silver (Au-Ag-Au), 47,48 and gold with nickel and silver (Au-Ni-Ag). 49 Metals are combined with silica and metals thanks to their appealing properties, such as responsiveness to light or magnetic elds, or high conductivity.…”

“…2I) but with one of the lowest representations in the eld. [47][48][49]100 Other examples of shapes are rectangular prisms with enzymes attached under the structure to propel at the interface, 12 as well as structures fully covered by enzymes like cubelike particles, 111 elongated cucurbits that produce higher spontaneous asymmetry than spheres, 31 2D sheets that increase the accessible area of the substrate for enzymes, 108,129 zeta pentomino shapes, 123 3-and 4-arm crosses, 124 brush-shaped structures, 67 or random organization of clusters, 42 all of them with an inherent asymmetry of the product release.…”

“…Since EDC reacts with two different chemical groups crosslinking is avoided and although enzyme orientation is not nely controlled it gives the possibility to use either the amino or carboxyl groups of the enzyme. Most of the motors using this attachment method force an asymmetric distribution of the product by forming Janus structures 17,18,47,48,[50][51][52]67,69,77,95,101,104 or releasing the product through a hole, 45,[53][54][55][56][57][58]98 some of which use DNAmediated attachment 49 and show enhanced motion by applying a multilayer of enzymes. 64 Surprisingly, fully coated motors functionalized with this method showed self-propulsion.…”

“…Catalase is the most common enzymatic engine, with 38% of motors using it (Fig. 4B) because of its high turnover number and the capacity to consume hydrogen peroxide (H 2 O 2 ) and produce water (H 2 O) and oxygen bubbles (O 2 ) that drive a jetlike motion mechanism [16][17][18][19][28][29][30]38,45,48,49,[53][54][55][57][58][59]61,63,64,66,77,85,108,115,[122][123][124]126,127 or a buoyancy effect mechanism. 102,114,125 Due to this powerful bubble propulsion, faster motion and micromixing of the uid are desired for sensing [17][18][19]43,49,55,57,58,64,77,126 and water 38,42,44,…”

“…5D). These sizes are useful because more enzymes t in the structure and their motion trajectory becomes clearly visible, showing a directional propulsive behavior that is suitable for fundamental studies 14,15,26,29,35,36,44,48,[51][52][53]68,[81][82][83][84][85][86][87][89][90][91]100,103,107,118,131 and applications that take place outside the body, such as sensing, 17,43,50,77 water remediation, [54][55][56]108,126 and bacteria killing. 78,93 However, in certain situations these sizes are also intended to be used for biomedical applications 16,21,22,57,111,112,114,120 that need faster motion for a stronger micromixing or a clearly visible pro...…”