Optical assembly of bio-hybrid micro-robots

Abstract

The combination of micro synthetic structures with bacterial flagella motors represents an actual trend for the construction of self-propelled micro-robots. The development of methods for fabrication of these bacteria-based robots is a first crucial step towards the realization of functional miniature and autonomous moving robots. We present a novel scheme based on optical trapping to fabricate living micro-robots. By using holographic optical tweezers that allow three-dimensional manipulation in real time, we are able to arrange the building blocks that constitute the micro-robot in a defined way. We demonstrate exemplarily that our method enables the controlled assembly of living micro-robots consisting of a rod-shaped prokaryotic bacterium and a single elongated zeolite L crystal, which are used as model of the biological and abiotic components, respectively. We present different proof-of-principle approaches for the site-selective attachment of the bacteria on the particle surface. The propulsion of the optically assembled micro-robot demonstrates the potential of the proposed method as a powerful strategy for the fabrication of bio-hybrid micro-robots.

Fig. 1

Sketch of the HOT system. λ/2: half wave plate; PBS: polarizing beam splitter cube; MO1,2: microscope objective; L1-L3: lenses; SLM: spatial light modulator; M: mirror; DM: dichroic mirror; F: filter; NA: numerical aperture

Fig. 2

Experimental schemes used for the assembly of the living micro-robot. a Y-shaped PDMS microchannel with an input supplying zeolite L crystals and a second input providing the bacteria in a chemotaxis buffer. b Petri dishes with two defined reservoirs containing each the bacteria and the zeolite L crystals

Fig. 3

(a-d) Schematic and (e-h) corresponding demonstrative experimental microscopy images of the steps and optical trap configurations for the fine attachment of a single bacterium on a specific area of the surface of a zeolite L crystal

Fig. 4

Schematic (a-c) and corresponding experimental microscopy images (d-g) of the steps and optical trap configurations for the coarse attachment of a single bacterium (marked with a white arrow) on a specific area of the surface of a zeolite L crystal

Fig. 5

Microscopy images illustrating a swimming micro-robot made of a single bacterium and a zeolite L crystal (red circle) and suspended zeolite L crystal (dashed blue circle). Time lapse between images is 6 s. In (b) the corresponding representative trajectories of the micro-robot and the suspended zeolite crystal are marked with black points and blue points, respectively