12 research outputs found
Light controlled motility of Escherichia coli. Characterization and applications
Characterization of wild type E. coli motility in response to light stimuli. Gene editing of bacteria to implement specifc functions (e.g. photokinesis). The engineered strain has been used to demonstrate that density modulation of photokinetic bacteria can be obtained by projecting spatially structured light on the sample. Additionally these bacteria have been also used as propelling units in microfabricated structures
Invariance properties of bacterial random walks in complex structures
Motile cells often explore natural environments characterized by a high
degree of structural complexity. Moreover cell motility is also intrinsically
noisy due to spontaneous random reorientation and speed fluctuations. This
interplay of internal and external noise sources gives rise to a complex
dynamical behavior that can be strongly sensitive to details and hard to model
quantitatively. In striking contrast to this general picture we show that the
mean residence time of swimming bacteria inside artificial complex
microstructures, can be quantitatively predicted by a generalization of a
recently discovered invariance property of random walks. We find that
variations in geometry and structural disorder have a dramatic effect on the
distributions of path length while mean values are strictly constrained by the
sole free volume to surface ratio. Biological implications include the
possibility of predicting and controlling the colonization of complex natural
environments using only geometric informations
Multiple temperatures and melting of a colloidal active crystal
Thermal fluctuations constantly and evenly excite all vibrational modes in an
equilibrium crystal. As the temperature rises, these fluctuations promote the
formation of defects and eventually melting. In active solids, the
self-propulsion of "atomic" units provides another source of strong
non-equilibrium fluctuations whose effect on the melting scenario is still
largely unexplored. Here we show that when a colloidal crystal is activated by
a bath of swimming bacteria, solvent temperature and active temperature
cooperate to define dynamic and thermodynamic properties. Our system consists
of repulsive paramagnetic particles confined in two dimensions and immersed in
a bath of light-driven E. coli. The relative balance between fluctuations and
interactions can be adjusted in two ways: by changing the strength of the
magnetic field and by tuning activity with light. When the persistence time of
active fluctuations is short, a single effective temperature controls both the
amplitudes of vibrational modes and the melting transition. For more persistent
active noise, energy equipartition is broken and multiple temperatures emerge,
whereas melting occurs before the Lindemann parameter reaches its equilibrium
critical value. We show that this phenomenology is fully confirmed by numerical
simulations and can be framed within a minimal model of a single active
particle in a periodic potential
Light Controlled Biohybrid Microbots
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. © 2023 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC
This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as ab of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as ab of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics
Currents and flux-inversion in photokinetic active particles
Many active particles, both of biological and synthetic origin, can have a light controllable propulsion speed, a property that in biology is commonly referred to as photokinesis. Here we investigate directed transport of photokinetic particles by traveling light patterns. We find general expressions for the current in the cases where the motility wave, induced by light, shifts very slowly or very quickly. These asymptotic formulas are independent of the shape of the wave and are valid for a wide class of active particle models. Moreover we derive an exact solution for the one-dimensional "run and tumble" model. Our results could be used to design time-varying illumination patterns for fast and efficient spatial reconfiguration of photokinetic colloids or bacteria
3D dynamics of bacteria wall entrapment at a water–air interface
Swimming bacteria can be trapped for prolonged times at the surface of an impenetrable boundary. The subsequent surface confined motility is found to be very sensitive to the physico-chemical properties of the interfaces which determine the boundary conditions for the flow. The quantitative understanding of this complex dynamics requires detailed and systematic experimental data to validate theoretical models for both flagellar propulsion and interfacial dynamics. Using a combination of optical trapping and holographic imaging we study the 3D dynamics of wall entrapment of swimming bacteria that are sequentially released towards a surfactant-covered liquid–air interface. We find that an incompressible surfactant model for the interface quantitatively accounts for the observed normal and tangential speed of bacteria as they approach the boundary. Surprisingly we also find that, although bacteria circulate over the air phase in counterclockwise circular trajectories, typical of free-slip interfaces, the body axis is still tilted “nose down” as found for no-slip interfaces