In a study published in the journal ACS Applied Materials & Interfaces, a novel flask-like nanomotor possessing a photo-triggered switching mechanism between bubble propulsion and non-ionic self-diffusiophoresis has been proposed.
Study: Interfacial Superassembly of Light-Responsive Mechanism-Switchable Nanomotors with Tunable Mobility and Directionality. Image Credit:Comaniciu Dan/Shutterstock.com
What are Nanomotors?
Nanomotors, which are also referred to as nanorobots, can move autonomously by producing kinetic energy for themselves from various types of ambient energy via energy conversion. Thus far, nanomotors with various operating modes, including bubble propulsion, magnetic field propulsion, self-electrophoresis, self-diffusiophoresis, self-acoustophoresis, self-thermophoresis have been conceived and manufactured.
Nanomotors have shown remarkable promise in healthcare applications, ecological cleanup, and microscale synthesis due to their tiny size (usually from 100 nm to 1 μm) and self-propelling characteristics.
Current Limitations of Nanomotors
While several propulsive systems for actuating nanomotors have been presented, and the swift advancement of nanomotors has permitted the extension of studies into many innovative sectors, the majority of the nanomotors generated so far demonstrate just a singular operating mechanism.
Hybridized nanomotors, on the other hand, that combine various propulsive mechanisms into a unified system, particularly mechanism-switching nanomotors that can autonomously modify their propulsive method in accordance with extrinsic inputs, are hardly ever described. This scenario greatly limits the uses of nanomotors since each distinct operating method has intrinsic constraints and hence has a limited field of uses.
Among the most common propulsive techniques, for instance, is the catalytic breakdown of hydrogen peroxide to produce oxygen, and based on whether or not bubbles will develop on the nanomotor, the produced oxygen may move the nanomotor using bubble propulsion or non-ionic self-diffusiophoresis.
The nanomotor displays good movement using bubble propulsion, but its fairly brief lifetime and limited biological compliance limit use within the healthcare sector. The nanomotor typically displays excellent biological compatibility for non-ionic self-diffusiophoresis, but its modest propulsive strength renders it an unsuitable contender for a variety of uses.
A nanomotor with changeable propulsive techniques of non-ionic self-diffusiophoresis and bubble propulsion that may reprogram its functioning as need be, based on objectives or changing environmental circumstances, is projected to be more adaptable in such situations.
Advantages of Mechanism-Switchable Nanomotors
A mode-switching nanomotor may provide synergistic benefits while avoiding the constraints of particular modes, resulting in broader application. However, the low motion control of nanomotors due to a singular propulsive mechanism has restricted their usability in complicated jobs or volatile conditions. Based on this struggle, seeing as non-ionic self-diffusiophoresis and bubble propulsion show intrinsically varying movement and direction of movement, the swap among these operating techniques may also be used to control the propulsive effectiveness of nanomotors, opening up a new aspect for sophisticated nanomotor movement control.
Key Findings of the Study
In this study, the team produced a flask-like nanomotor with a photo-triggered transition among bubble propulsion and self-diffusiophoresis. The oxygen produced by catalytically breaking down hydrogen peroxide powers this nanomotor. Fatty acids present in the nanomotor cavities, which experience a phase shift from solid to liquid state when exposed to a 980 nm laser, act as a light sensitive trigger.
Prior to laser treatment, the nanomotor displays bottom-forward bubble propulsion with comparatively poor movement, but after laser treatment, the nanomotor shows opening-forward self-diffusiophoresis with comparatively greater movement. Bubble propulsion has superior orientability than self-diffusiophoresis owing to the counter force of nanoscale bubbles on self-rotation. According to the FEA computation findings, the transition from self-diffusiophoresis to bubble propulsion was caused by the cavity's containment function, which enhances the nucleation of nanobubbles.
It should be noted that, while the migratory route may be changed from opening-forward to bottom-forward, the nanomotor's paths are frequently randomized by temperature variation. As a result, supplementary guiding solutions, like magnetic field aid or topographic steering, are preferred for achieving millimetric scale guided movement. Nevertheless, this change in migratory route is still significant as it allows for the transition between positive and negative taxis along the exterior guide (magnetic field, chemical gradient, and physical boundaries).
This mode-switching nanomotor with excellent flexibility and extensive utility is predicted to have a vast spectrum of uses. Furthermore, this study may shed light on the interaction among nanostructures, basic propulsive processes, and evident movement effectiveness, as well as give a novel technique for regulating movement and direction, which is useful for the development as well as the use of nanomotors.
Liu, T., Xie, L. et al. (2022). Interfacial Superassembly of Light-Responsive Mechanism-Switchable Nanomotors with Tunable Mobility and Directionality. ACS Applied Materials & Interfaces. Available at: https://pubs.acs.org/doi/10.1021/acsami.1c25204