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Register a new userOptical disassembly of cellular clusters by tunable tug-of-war tweezers
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Bacterial biofilms underlie many persistent infections, posing major hurdles in antibiotic treatment. Here, we design and demonstrate tug-of-war optical tweezers that can facilitate assessment of cell-cell adhesion - a key contributing factor to biofilm development, thanks to the combined actions of optical scattering and gradient forces. With a customized optical landscape distinct from that of conventional tweezers, not only can such tug-of-war tweezers stably trap and stretch a rod-shaped bacterium in the observing plane, but, more importantly, they can also impose a tunable lateral force that pulls apart cellular clusters without any tethering or mechanical movement. As a proof of principle, we examined a Sinorhizobium meliloti strain that forms robust biofilms and found that the strength of intercellular adhesion depends on the growth medium. This technique may herald new photonic tools for optical manipulation and biofilm study, as well as other biological applications.
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We simulate a tug-of-war (TOW) scenario for a model double-stranded DNA threading through a double nanopore (DNP) system. The DNA, simultaneously captured at both pores is subject to two equal and opposite forces $-vec{f}_L= vec{f}_R$ (TOW), where $vec{f}_L$ and $vec{f}_R$ are the forces applied to the left and the right pore respectively. Even though the net force on the DNA polymer $Delta vec{f}_{LR}=vec{f}_L+ vec{f}_R=0$, the mean first passage time (MFPT) $langle tau rangle$ depends on the magnitude of the TOW forces $ left | f_L right | = left |f_R right | = f_{LR}$. We qualitatively explain this dependence of $langle tau rangle$ on $f_{LR}$ from the known results for the single-pore translocation of a triblock copolymer. We demonstrate that the time of flight (TOF) of a monomer with index $m$ ($langle tau_{LR}(m) rangle$) from one pore to the other exhibits quasi-periodic structure commensurate with the distance between the pores $d_{LR}$. Finally, we study the case $Delta vec{f}_{LR}=vec{f}_L+ vec{f}_R e 0$, and qualitatively reproduce the experimental result of the dependence of the MFPT on $Deltavec{f}_{LR}$. For a moderate bias, the MFPT for the DNP system for a chain length $N$ follows the same scaling ansatz as that of for the single nanopore, $langle tau rangle = left( AN^{1+ u} + eta_{pore}N right) left(Delta f_{LR}right)^{-1}$, where $eta_{pore}$ is the pore friction, which enables us to estimate $langle tau rangle $ for a long chain. Our Brownian dynamics simulation studies provide fundamental insights and valuable information about the details of the translocation speed obtained from $langle tau_{LR}(m) rangle$, and accuracy of the translation of the data obtained in the time-domain to units of genomic distances.
We propose a simple channel-allocation method based on tug-of-war (TOW) dynamics, combined with the time scheduling based on nonlinear oscillator synchronization to efficiently use of the space (channel) and time resources in wireless communications. This study demonstrates that synchronization groups, where each node selects a different channel, are non-uniformly distributed in phase space such that every distance between groups is larger than the area of influence. New type of self-organized spatiotemporal patterns can be formed for resource allocation according to channel rewards.
Optical resonant microcavities with ultra high quality factors are widely used for biosensing. Until now, the primary method of detection has been based upon tracking the resonant wavelength shift as a function of biodetection events. One of the sources of noise in all resonant-wavelength shift measurements is the noise due to intensity fluctuations of the laser source. An alternative approach is to track the change in the quality factor of the optical cavity by using phase shift cavity ring down spectroscopy, a technique which is insensitive to the intensity fluctuations of the laser source. Here, using biotinylated microtoroid resonant cavities, we show simultaneous measurement of the quality factor and the wavelength shift by using phase shift cavity ring down spectroscopy. These measurements were performed for disassociation phase of biotin-streptavidin reaction. We found that the disassociation curves are in good agreement with the previously published results. Hence, we demonstrate not only the application of phase shift cavity ring down spectroscopy to microcavities in the liquid phase but also simultaneous measurement of the quality factor and the wavelength shift for the microcavity biosensors in the application of kinetics measurements.
This is a preprint of Chapter 2 in the following work: Marta Lewicka, A Course on Tug-of-War Games with Random Noise, 2020, Springer, reproduced with permission of Springer Nature Switzerland AG. We present the basic relation between the linear potential theory and random walks. This fundamental connection, developed by Ito, Doob, Levy and others, relies on the observation that harmonic functions and martingales share a common cancellation property, expressed via mean value properties. It turns out that, with appropriate modifications, a similar observation and approach can be applied also in the nonlinear case, which is of main interest in our Course Notes. Thus, the present Chapter serves as a stepping stone towards gaining familiarity with more complex nonlinear constructions. After recalling the equivalent defining properties of harmonic functions, we introduce the ball walk. This is an infinite horizon discrete process, in which at each step the particle, initially placed at some point $x_0$ in the open, bounded domain $mathcal{D}subsetmathbb{R}^N$, is randomly advanced to a new position, uniformly distributed within the following open ball: centered at the current placement, and with radius equal to the minimum of the parameter $epsilon$ and the distance from the boundary $partialmathcal{D}$. With probability one, such process accumulates on $partialmathcal{D}$ and $u^epsilon(x_0)$ is then defined as the expected value of the given boundary data $F$ at the process limiting position. Each function $u^epsilon$ is harmonic, and if $partialmathcal{D}$ is regular, then each $u^epsilon$ coincides with the unique harmonic extension of $F$ in $mathcal{D}$. One sufficient condition for regularity is the exterior cone condition.
We show that the optical force field in optical tweezers with elliptically polarized beams has the opposite handedness for a wide range of particle sizes and for the most common configurations. Our method is based on the direct observation of the particle equilibrium position under the effect of a transverse Stokes drag force, and its rotation around the optical axis by the mechanical effect of the optical torque. We find overall agreement with theory, with no fitting, provided that astigmatism, which is characterized separately, is included in the theoretical description. Our work opens the way for characterization of the trapping parameters, such as the microsphere complex refractive index and the astigmatism of the optical system, from measurements of the microsphere rotation angle.
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