We combine two-photon lithography and optical tweezers to investigate the Brownian fluctuations and propeller characteristics of a microfabricated helix. From the analysis of mean squared displacements and time correlation functions we recover the components of the full mobility tensor. We find that Brownian motion displays correlations between angular and translational fluctuations from which we can directly measure the hydrodynamic coupling coefficient that is responsible for thrust generation. By varying the distance of the microhelices from a no-slip boundary we can systematically measure the effects of a nearby wall on the resistance matrix. Our results indicate that a rotated helix moves faster when a nearby no-slip boundary is present, providing a quantitative insight on thrust enhancement in confined geometries for both synthetic and biological microswimmers.Many organism such as E. coli 1 or C. crescentus 2 spin one or more helix-shaped flagella to propel themselves. The combination of drag anisotropy in slender bodies and a chiral shape gives rise to a net hydrodynamic thrust on helical bodies that rotate around their axis 3 . Such a biologically evolved way of propulsion has recently inspired the development of artificial helical microrobots 4 that are being perfected for targeted drug delivery 5-7 . The characterization of the thrust force of a rotating helix has been the subject of numerous theoretical 8,9 and experimental studies 10-12 in the field of low Reynolds number hydrodynamics. The absence of inertial effects is a very important ingredient in the description of dynamical phenomena at the micron scale, but what is really peculiar of the microscopic world is the unavoidable presence of Brownian fluctuations. In this respect very little has been done for chiral objects: Brownian diffusion of colloidal particles with regular shapes such as spheres, ellipsoids or rods, has been largely studied [13][14][15][16][17][18] . The study of more complex shapes has been limited to close packed clusters of spherical colloids [19][20][21][22] or L-shaped quasi 2D microstructures 23 . Although roto-translational couplings may be present in non-chiral objects, they are not essential and disappear when we place the object's origin on the center of hydrodynamic resistance 24 . On the contrary, helices are chiral objects with an intrinsic roto-traslational coupling that is responsible for the appearance of correlations in the Brownian fluctuations of rotational and translational degrees of freedom. These intrinsic correlations in chiral colloids have never been observed in experiments. The bacterium Leptospira interrogans is a natural colloidal helix whose Brownian motion over a solid substrate has been studied although without addressing the issue of roto-translational couplings 25,26 .In this work we study the full Brownian dynamics of a micro-fabricated 27 helix that is suspended in a fluid using optical tweezers. By a detailed analysis of fluctuations in translational and rotational coordinates we recover th...

Biohybrid microbots integrate biological actuators and sensors into synthetic chassis with the aim of providing the building blocks of next‐generation micro‐robotics. One of the main challenges is the development of self‐assembled systems with consistent behavior and such that they can be controlled independently to perform complex tasks. Herein, it is shown that, using light‐driven bacteria as propellers, 3D printed microbots can be steered by unbalancing light intensity over different microbot parts. An optimal feedback loop is designed in which a central computer projects onto each microbot a tailor‐made light pattern, calculated from its position and orientation. In this way, multiple microbots can be independently guided through a series of spatially distributed checkpoints. By exploiting a natural light‐driven proton pump, these bio‐hybrid microbots are able to extract mechanical energy from light with such high efficiency that, in principle, hundreds of these systems can be controlled simultaneously with a total optical power of just a few milliwatts.

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