The chemically exfoliated 2D-MoS2 has a mixture of 1T (metallic) and 2H (semiconducting) phases.

Suspensions of micro/nano particles made of Polystyrene, Poly(methyl methacrylate), Silicon dioxide etc. have been a standard model system to understand colloidal physics. These systems have proved useful insights into phenomena such as self-assembly. Colloidal model systems are also extensively used to simulate many condensed matter phenomena such as dynamics in a quenched disordered system and glass transition. A precise control of particles using optical or holographic tweezers is essential for such studies. However, studies of collective phenomena such as jamming and flocking behaviour in a disordered space are limited due to the low throughput of the optical trapping techniques. In this article, we present a technique where we trap and pin polystyrene microspheres ~10 μm over ‘triangular crest’ shaped microstructures in a microfluidic environment. Trapping/Pinning occurs due to the combined effect of hydrodynamic interaction and non-specific adhesion forces. This method allows trapping and pinning of microspheres in any arbitrary pattern with a high degree of spatial accuracy which can be useful in studying fundamentals of various collective phenomena as well as in applications such as bead detachment assay based biosensors.

In a classic paper, Edward Purcell analysed the dynamics of flagellated bacterial swimmers and derived a geometrical relationship which optimizes the propulsion efficiency. Experimental measurements for wild-type bacterial species E. coli have revealed that they closely satisfy this geometric optimality. However, the dependence of the flagellar motor speed on the load and more generally the role of the torque-speed characteristics of the flagellar motor is not considered in Purcell's original analysis. Here we derive a tuned condition representing a match between the flagella geometry and the torque-speed characteristics of the flagellar motor to maximize the bacterial swimming speed for a given load. This condition is independent of the geometric optimality condition derived by Purcell and interestingly this condition is not satisfied by wild-type E. coli which swim 2-3 times slower than the maximum possible speed given the amount of available motor torque. Our analysis also reveals the existence of an anomalous propulsion regime, where the swim-speed increases with increasing load (drag). Finally, we present experimental data which supports our analysis.Here, A, D are the translational and rotational drag coefficients and V, ω are the translation and angular speed of the flagella. The constant, B, couples the rotational motion of helical flagella to the translation motion of bacterium.Purcell in his landmark paper on helical swimming considered the optimal geometry of the flagella which will maximize the propulsion efficiency η, defined as η =where Ω is the rotational speed of the flagellar motor, for a given size of cell body. Purcell showed that η is maximised when the translational drag coefficient of the flagella is matched to that of the cell body, i.e. A = A 0 . The propulsion matrix elements in Eq. (1) and (2) have been explicitly measured for the bacterial species E. coli and A and A 0 are found to be quite close to each other (1.48 × 10 −8 N. s. m −1 and 1.4 × 10 −8 N. s. m −1 respectively) [5] in agreement with Purcell's result. Equations (1) and (2) can be solved to obtain the swim-speed V and the torque τ produced by the flagellar motor in terms of the flagellar motor speed Ω m = Ω + ω (see Sec. 1 of the Supplemental Material (SM)) for the detailed derivation).

Fluorescence recovery after photobleaching (FRAP) is a widely used technique to study the transport of molecules in biological systems. Recently, FRAP has been used to study molecular transport in polyelectrolyte multilayers (PEMs). Through numerical simulations verified by experiments, it is shown that the FRAP behavior of PEM films in an aqueous medium differs significantly from that in previously explored systems such as single cells. This is because fluorescence recovery can take place through the aqueous medium surrounding the PEM film. The simulations show the critical role of the time scale of the different processes, namely, diffusion through PEM, diffusion through surrounding medium, and the unbinding rate of fluorophore‐labeled species in the interpretation of FRAP data. An important conclusion from the numerical and experimental study is that, for ultrathin PEM films with ≈100 nm thicknesses, recovery is dominated through the solution medium and hence, classical FRAP analysis is not sufficient to probe diffusion in PEM. The numerical study reveals several aspects of the FRAP phenomena in thin polymer films that are critical for the proper interpretation of experimental data.

Burgeoning interest in the area of bacteria-powered micro robotic systems prompted us to study the dynamics of cargo transport by single bacteria. In this paper, we have studied the swimming...