Correction: Label free localization of nanoparticles in live cancer cells using spectroscopic microscopy.

Correction for 'Label free localization of nanoparticles in live cancer cells using spectroscopic microscopy' by Graham L. C. Spicer et al., Nanoscale, 2018, 10, 19125-19130, https://doi.org/10.1039/C8NR07481J.

Inferring broken detailed balance in the absence of observable currents.

Identifying dissipation is essential for understanding the physical mechanisms underlying nonequilibrium processes. In living systems, for example, the dissipation is directly related to the hydrolysis of fuel molecules such as adenosine triphosphate (ATP). Nevertheless, detecting broken time-reversal symmetry, which is the hallmark of dissipative processes, remains a challenge in the absence of observable directed motion, flows, or fluxes. Furthermore, quantifying the entropy production in a complex system requires detailed information about its dynamics and internal degrees of freedom. Here we introduce a novel approach to detect time irreversibility and estimate the entropy production from time-series measurements, even in the absence of observable currents. We apply our technique to two different physical systems, namely, a partially hidden network and a molecular motor. Our method does not require complete information about the system dynamics and thus provides a new tool for studying nonequilibrium phenomena.

Reconstruction for Complex Oromandibular Facial Defects: The Fibula Free Flap and Pectoralis Major Flap Combination.

BACKGROUND: Extensive through-and-through oromandibular defects after advanced oral carcinoma excision pose a reconstructive challenge for the head and neck surgeon. These complex oromandibular wounds often involve the mandible, oral and/or aerodigestive mucosa, and the external skin. As a result, these defects are often not amenable to reconstruction with a single flap due to the volume of soft tissue needed and the three-dimensional reconstructive requirement. The use of two free flaps has often been suggested to overcome this reconstructive challenge. A simpler and less technically demanding way to deal with this may involve the use of a free flap in combination with a pedicled regional flap. We present our experience of the use of a simultaneous microvascular fibula free flap (FFF) with a pectoralis major myocutaneous flap (PMMC) for addressing these defects. METHODS: A retrospective chart review was performed of patients treated with a FFF and PMMC combination for the reconstruction of oromandibular defects at the University of Mississippi Medical Center (Jackson, MS) between October 2013 and February 2016. A minimum follow-up of 12 months was required. Data collected included the extent and location of tumor involvement, size of the postablative defect, tumor histology, clinical and pathological staging, length of follow-up, functional outcomes, and associated complications. RESULTS: A total of three patients were identified to have been treated with the above technique. Defects repaired involved through-and-through mandibular defects with associated oral mucosa and external skin defects. In all cases, the FFF was used for restoring bony continuity with the skin paddle used to reconstruct the intraoral lining. The PMMC was used for reconstruction of the external skin defect and for providing soft tissue bulk. The average size of the fibula skin paddle used for intraoral reconstruction was 7.7 cm × 11.7 cm. The average size of the PMMC paddle was 7.3 × 9 cm. The mean follow-up was 21.7 months. Both the FFF and PMMC survived in all cases, although postoperative wound healing complications occurred in two of the three patients. There was one partial flap loss. Two patients regained good oral intake while one patient tolerated oral intake but was PEG tube-dependent. CONCLUSIONS: The combination of pectoralis major myocutaneous flap and a vascularized free fibular flap is a viable option for the reconstruction of complex through-and-through oromandibular defects. This technique may be useful when a single microvascular free flap is not sufficient for reconstruction of such defects.

Label free localization of nanoparticles in live cancer cells using spectroscopic microscopy.

Gold nanoparticles (GNPs) have become essential tools used in nanobiotechnology due to their tunable plasmonic properties and low toxicity in biological samples. Among the available approaches for imaging GNPs internalized by cells, hyperspectral techniques stand out due to their ability to simultaneously image and perform spectral analysis of GNPs. Here, we present a study utilizing a recently introduced hyperspectral imaging technique, live-cell PWS, for the imaging, tracking, and spectral analysis of GNPs in live cancer cells. Using principal components analysis, the extracellular or intracellular localization of the GNPs can be determined without the use of exogenous labels. This technique uses wide-field white light, assuring minimal toxicity and suitable signal-to-noise ratio for spectral and temporal resolution of backscattered signal from GNPs and local cellular structures. The application of live-cell PWS introduced here could make a great impact in nanomedicine and nanotechnology by giving new insights into GNP internalization and intracellular trafficking.

Arcsine Laws in Stochastic Thermodynamics.

We show that the fraction of time that a thermodynamic current spends above its average value follows the arcsine law, a prominent result obtained by Lévy for Brownian motion. Stochastic currents with long streaks above or below their average are much more likely than those that spend similar fractions of time above and below their average. Our result is confirmed with experimental data from a Brownian Carnot engine. We also conjecture that two other random times associated with currents obey the arcsine law: the time a current reaches its maximum value and the last time a current crosses its average value. These results apply to, inter alia, molecular motors, quantum dots, and colloidal systems.

Engineered Swift Equilibration of a Brownian particle.

A fundamental and intrinsic property of any device or natural system is its relaxation time relax, which is the time it takes to return to equilibrium after the sudden change of a control parameter [1]. Reducing τrelax, is frequently necessary, and is often obtained by a complex feedback process. To overcome the limitations of such an approach, alternative methods based on driving have been recently demonstrated [2, 3], for isolated quantum and classical systems [4-9]. Their extension to open systems in contact with a thermostat is a stumbling block for applications. Here, we design a protocol, named Engineered Swift Equilibration (ESE), that shortcuts time-consuming relaxations, and we apply it to a Brownian particle trapped in an optical potential whose properties can be controlled in time. We implement the process experimentally, showing that it allows the system to reach equilibrium times faster than the natural equilibration rate. We also estimate the increase of the dissipated energy needed to get such a time reduction. The method paves the way for applications in micro and nano devices, where the reduction of operation time represents as substantial a challenge as miniaturization [10].

Colloidal heat engines: a review.

Stochastic heat engines can be built using colloidal particles trapped using optical tweezers. Here we review recent experimental realizations of microscopic heat engines. We first revisit the theoretical framework of stochastic thermodynamics that allows to describe the fluctuating behavior of the energy fluxes that occur at mesoscopic scales, and then discuss recent implementations of the colloidal equivalents to the macroscopic Stirling, Carnot and steam engines. These small-scale motors exhibit unique features in terms of power and efficiency fluctuations that have no equivalent in the macroscopic world. We also consider a second pathway for work extraction from colloidal engines operating between active bacterial reservoirs at different temperatures, which could significantly boost the performance of passive heat engines at the mesoscale. Finally, we provide some guidance on how the work extracted from colloidal heat engines can be used to generate net particle or energy currents, proposing a new generation of experiments with colloidal systems.

Adiabatic processes realized with a trapped Brownian particle.

The ability to implement adiabatic processes in the mesoscale is of key importance in the study of artificial or biological micro- and nanoengines. Microadiabatic processes have been elusive to experimental implementation due to the difficulty in isolating Brownian particles from their fluctuating environment. Here we report on the experimental realization of a microscopic quasistatic adiabatic process employing a trapped Brownian particle. We circumvent the complete isolation of the Brownian particle by designing a protocol where both characteristic volume and temperature of the system are changed in such a way that the entropy of the system is conserved along the process. We compare the protocols that follow from either the overdamped or underdamped descriptions, demonstrating that the latter is mandatory in order to obtain a vanishing average heat flux to the particle. We provide analytical expressions for the distributions of the fluctuating heat and entropy and verify them experimentally. Our protocols could serve to implement the first microscopic engine that is able to attain the fundamental limit for the efficiency set by Carnot.

Realization of nonequilibrium thermodynamic processes using external colored noise.

We investigate the dynamics of single microparticles immersed in water that are driven out of equilibrium in the presence of an additional external colored noise. As a case study, we trap a single polystyrene particle in water with optical tweezers and apply an external electric field with flat spectrum but a finite bandwidth of the order of kHz. The intensity of the external noise controls the amplitude of the fluctuations of the position of the particle and therefore of its effective temperature. Here we show, in two different nonequilibrium experiments, that the fluctuations of the work done on the particle obey the Crooks fluctuation theorem at the equilibrium effective temperature, given that the sampling frequency and the noise cutoff frequency are properly chosen.

RecA protein plays a role in the chemotactic response and chemoreceptor clustering of Salmonella enterica.

The RecA protein is the main bacterial recombinase and the activator of the SOS system. In Escherichia coli and Salmonella enterica sv. Typhimurium, RecA is also essential for swarming, a flagellar-driven surface translocation mechanism widespread among bacteria. In this work, the direct interaction between RecA and the CheW coupling protein was confirmed, and the motility and chemotactic phenotype of a S. Typhimurium ΔrecA mutant was characterized through microfluidics, optical trapping, and quantitative capillary assays. The results demonstrate the tight association of RecA with the chemotaxis pathway and also its involvement in polar chemoreceptor cluster formation. RecA is therefore necessary for standard flagellar rotation switching, implying its essential role not only in swarming motility but also in the normal chemotactic response of S. Typhimurium.

A simple technique based on a single optical trap for the determination of bacterial swimming pattern.

Bacterial motility is associated to a wide range of biological processes and it plays a key role in the virulence of many pathogens. Here we describe a method to distinguish the dynamic properties of bacteria by analyzing the statistical functions derived from the trajectories of a bacterium trapped by a single optical beam. The approach is based on the model of the rotation of a solid optically trapped sphere. The technique is easily implemented in a biological laboratory, since with only a small number of optical and electronic components a simple biological microscope can be converted into the required analyzer. To illustrate the functionality of this method, we probed several Salmonella enterica serovar Typhimurium mutants that differed from the wild-type with respect to their swimming patterns. In a further application, the motility dynamics of the S. Typhimurium cheV mutant were characterized.

Back-focal-plane position detection with extended linear range for photonic force microscopy.

In photonic force microscopes, the position detection with high temporal and spatial resolution is usually implemented by a quadrant position detector placed in the back focal plane of a condenser. An objective with high numerical aperture (NA) for the optical trap has also been used to focus a detection beam. In that case the displacement of the probe at a fixed position of the detector produces a unique and linear response only in a restricted region of the probe displacement, usually several hundred nanometers. There are specific experiments where the absolute position of the probe is a relevant measure together with the probe position relative the optical trap focus. In our scheme we introduce the detection beam into the condenser with low NA through a pinhole with tunable size. This combination permits us to create a wide detection spot and to achieve the linear range of several micrometers by the probe position detection without reducing the trapping force.

Force mapping of an optical trap using an acousto-optical deflector in a time-sharing regime.

We suggest and study experimentally a time-sharing protocol for acousto-optical deflectors (AODs) that permits one to map the radial optical trapping force of optical tweezers without using a controllable flux control or an additional beam. Variations of the trapping potential due to modifications of the optical system are easily detected in terms of the force map. The protocol can be used in optical tweezers that already include an AOD without adding new elements in the existing optical system.

Colored noise in the fluctuations of an extended DNA molecule detected by optical trapping.

We studied fluctuations of an optically trapped bead connected to a single DNA molecule anchored between the bead and a cover glass or between two optically trapped beads. Power spectral densities of the bead position for different extensions of the molecule were compared with the power spectral density of the position fluctuations of the same bead without the molecule attached. Experiments showed that the fluctuations of the DNA molecule extended up to 80% by a force of 3 pN include the colored noise contribution with spectral dependence 1/f (α) with α ~ 0.75.