Axial Optical Traps: A New Direction for Optical Tweezers

Optical tweezers have revolutionized our understanding of the microscopic world. Axial optical tweezers, which apply force to a surface-tethered molecule by directly moving either the trap or the stage along the laser beam axis, offer several potential benefits when studying a range of novel biophysical phenomena. This geometry, although it is conceptually straightforward, suffers from aberrations that result in variation of the trap stiffness when the distance between the microscope coverslip and the trap focus is being changed. Many standard techniques, such as back-focal-plane interferometry, are difficult to employ in this geometry due to back-scattered light between the bead and the coverslip, whereas the noise inherent in a surface-tethered assay can severely limit the resolution of an experiment. Because of these complications, precision force spectroscopy measurements have adapted alternative geometries such as the highly successful dumbbell traps. In recent years, however, most of the difficulties inherent in constructing a precision axial optical tweezers have been solved. This review article aims to inform the reader about recent progress in axial optical trapping, as well as the potential for these devices to perform innovative biophysical measurements.     

Melanin Granule Models for the Processes of Laser-Induced Thermal Damage in Pigmented Retinal Tissues. I. Modeling of Laser-Induced Heating of Melanosomes and Selective Thermal Processes in Retinal Tissues

The computer modeling was applied for investigation of the processes of laser-induced tissue damage. The melanin granule models for the processes of laser-induced thermal damage and the results of computer modeling of the optical, thermophysical, and thermochemical processes during selective laser interaction with melanoprotein granules (melanosomes) in retinal pigment epithelium are presented in this paper. Physical-mathematical model and system of equations are formulated which describe thermal interaction processes for “short” laser pulses of duration t _p<10⁻⁶ s and for “ long’ pulses of duration t _p10⁻⁶ s. Results of numerical simulation of the processes give the space–time distributions of temperature and degrees of thermodenaturation of the protein molecules inside and around melanosomes and in the volume of irradiated tissues. Energy absorption, heat transfer and thermochemical (thermodenaturation, coagulation) processes occurring during the interaction of laser pulses with pigmented spherical and spheroidal granules in heterogeneous tissues are theoretically investigated. The possibility for selective interaction of short laser pulses with pigmented granules is discussed which results in the formation of denaturation microregions inside and near the pigmented granules (granular thermodenaturation) without origination of a continuous macroscopic thermodenaturation lesion in tissue. Analytical model of heating of single spherical and spheroidal granule under laser pulse is presented. Simple equations for time dependencies of particle temperature are obtained. The presented results are of essential interest for laser applications in and can be used for investigation of laser interaction with pigmented tissues in different fields of laser medicine.     

性信息素水盆诱捕器和黑光灯诱捕棉铃虫成虫数量的比较

棉铃虫 (Ｈｅｌｉｃｏｖｅｒｐａａｒｍｉｇｅｒａ(Ｈ櫣ｂｎｅｒ) )已成为我国头号害虫 ,1 992年在华北棉区暴发 ,造成直接经济损失 1 0 0亿元 ,此后种群水平居高不下 ,严重威胁我国棉花的正常生产。为避免大面积防治失效 ,标准化测报是重要前提[1 ,2 ] 。根据目前我国棉铃虫测报标准化方法 ,黑光灯 ( 2 0Ｗ)诱蛾是成虫种群动态监测的主要手段 ,对越冬代更是唯一手段[3] 。然而 ,近年报道黑光灯在气温低时诱效低 ,前期诱蛾少 ,对防治指导性差[4] ,而全季性信息素(性诱剂 )水盆诱捕器的诱蛾效率均高于黑光灯[5] 。为进一步明确性信息素的监测…     

Nanoscale Probing of Thermal,Stress, and Optical Fields under Near-Field Laser Heating

Micro/nanoparticle induced near-field laser ultra-focusing and heating has been widely used in laser-assisted nanopatterning and nanolithography to pattern nanoscale features on a large-area substrate. Knowledge of the temperature and stress in the nanoscale near-field heating region is critical for process control and optimization. At present, probing of the nanoscale temperature, stress, and optical fields remains a great challenge since the heating area is very small (∼100 nm or less) and not immediately accessible for sensing. In this work, we report the first experimental study on nanoscale mapping of particle-induced thermal, stress, and optical fields by using a single laser for both near-field excitation and Raman probing. The mapping results based on Raman intensity variation, wavenumber shift, and linewidth broadening all give consistent conjugated thermal, stress, and near-field focusing effects at a 20 nm resolution (<λ/26, λ = 32 nm). Nanoscale mapping of near-field effects of particles from 1210 down to 160 nm demonstrates the strong capacity of such a technique. By developing a new strategy for physical analysis, we have de-conjugated the effects of temperature, stress, and near-field focusing from the Raman mapping. The temperature rise and stress in the nanoscale heating region is evaluated at different energy levels. High-fidelity electromagnetic and temperature field simulation is conducted to accurately interpret the experimental results.     

Field-Assessed Injury to Wolves Captured in Rubber-Padded Traps

Abstract: Minimizing and understanding the causes of capture-related injury should be a goal of every project that catches animals. We investigated the influence of age, weight, and sex on the field-assessed foot injury of 96 wolves (Canis lupus) captured in rubber-padded foothold traps. We then compared our results with those of 6 other types of wolf traps as reported in the literature. Injury from rubber-padded traps was lower than that of other traps, and age, weight, or sex did not influence foot damage. Rubber-padded foothold traps appear to be humane, and managers should consider their use for live capture of wolves.     

Localized Traps Limited Recombination in Lead Bromide Perovskites

Traps exert an omnipotent influence over the performance of halide perovskite optoelectronic devices. A clear understanding of the origin and nature of the traps in halide perovskites is the key to controlling them and realizing optimal devices. Herein, the role of localized traps on the optical properties of lead bromide perovskite films is investigated. In the low‐temperature orthorhombic phase of CH₃NH₃PbBr₃ perovskite, band‐edge carrier dynamics exhibit a power‐law decay due to the presence of structural‐disorder‐induced localized traps, which has a depth of ≈40 meV. The continuous distribution of these localized traps gives rise to a broad sub‐band‐gap emission that becomes more prominent in thicker films with a larger trap density. The presence of this emission only from the hybrid organic–inorganic perovskites points to the vital role of organic dipoles in localized trap states formation. This study explicates the nature of these localized traps as well as their nontrivial role in carrier recombination kinetics, which is of fundamental importance in perovskites optoelectronics.     

中性粒细胞胞外诱捕网和血栓形成的研究进展

中性粒细胞胞外诱捕网是由DNA骨架、组蛋白、颗粒成分以及胞浆蛋白组成的网状物,它通过捕获致病微生物,抑制其扩散、灭活毒力因子以及清除病原体来发挥抗菌活性,中性粒细胞这种与其经典的趋化、吞噬作用不同的胞外杀菌方式发挥着重要的固有免疫应答作用。然而,中性粒细胞胞外诱捕网的产生是一把双刃剑。近年来有研究表明它可以导致凝血异常、刺激血栓形成并为其提供支架,但这一过程的机制并不十分清楚,可能与中性粒细胞胞外诱捕网的促凝活性以及凝血级联反应的激活有关。本文将就中性粒细胞胞外诱捕网及其与血栓形成之间关系的研究进展做一综述。     

Castoreum and Steel Traps in Eastern North America

Historians and anthropologists have credited the invention of trapping beaver with castoreum bait and steel traps to the Indians of southeastern Canada in the 1790s. However, English trappers in Virginia used this technique before 1728, and the Indians of southeastern Canada were using it by 1756. It is suggested that the widespread adoption of castoreum and steel traps by Northeastern Indians in the 1790's was due to the collapse of the world fur market after the French Revolution.     

Real-Time Optical Diagnosis of the Rat Brain Exposed to a Laser-Induced Shock Wave: Observation of Spreading Depolarization,Vasoconstriction and Hypoxemia-Oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3–4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.     

Synthesis and Evaluation of DMPO-Type Spin Traps

The spin traps substituted with some groups at the 4-position of dimethyl-1-pyrroline N-oxide(DMPO) were compared with DMPO itself regarding their abilities as spin traps and their physical properties. 4,5,5-Trimethyl-l-pyroHine N-oxide (4MDMPO) and 5,5-dimethyl- 4-phenyl-l-pyrolline N-oxide (4PDMPO) were synthesized by the Bonnett method, and 5,5-dimethyl-4-hydroxymethyl-l-pyrolline N-oxide (4HMDMPO) was made by a unique method from 2(5H)-furanone. The melting points of 4MDMPO, 4PDMPO and 4HMDMPO were higher than that of DMPO. The magnitude of hydrophilicity was in the order of 4HMDMPO, DMPO, 4MDMPO, and 4PDMPO based on the partition coefficient experiments in a 1-octanol-water system. Several radicals, O₂, HO-, -CH₃, -CH₂OH, -CH(CH₃)OH, (CH₃)₃ CO and H radicals, were trapped with these DMPO derivatives for comparison with the trapping by DMPO itself. Spin adducts of O J with the three DMPO derivatives showed ESR spectra similar to that of DMPO. In spite of the formation of diastereomers arising from spin trapping, the line-width enlargement was very small. The intensities and the decay rates of the spectra of 4MDMPO-O₂^-, 4PDMPO-O₂^- 4HMDMPO-O₂^- and DMPO-O₂^- were almost equal. In the trapping of the OH radical by 4MDMPO, 4PDMPO and 4HMDMPO, the eight-line ESR spectra observed were different from the well-known four-line spectrum of DMPO-OH.     

Behavior of Phrynocephalus frontalis to Avoid Traps

Previous studies have shown that reptiles are capable of spatial learning and learn to locate important environmental resources so that they can return to those locations at a future time,when needed.Lizards improve their adaptability and survival by learning the position of their shelter in a complex environment.This behavior raises the question,whether lizards can sense danger,such as a trap,in their surroundings,by determining the location of the trap and avoiding it.In the present study,we used a pitfall trap to test if steppe toad-headed agama,Phrynocephalus frontalis,can learn to recognize the position of the trap and avoid it.Our results revealed that the percentage of activity time in the trap area was significantly reduced(P 0.001) and the time of drop trap was also significantly reduced(P = 0.00631).The number of burrows dug by lizards distributed in the trap area was the least.Reduced activity time in the trap area was observed to have no obvious relationship with the drop in the number of burrows.The present study,therefore,demonstrates that P.frontalis are capable of learning the avoidance of a trap by locating its position.The findings offer significant insight in the understanding of reptilian behavior,which is important in the study of the role of reptiles in global ecology,especially because they are often very sensitive to environmental changes.     

Optimising Camera Traps for Monitoring Small Mammals

Practical techniques are required to monitor invasive animals, which are often cryptic and occur at low density. Camera traps have potential for this purpose, but may have problems detecting and identifying small species. A further challenge is how to standardise the size of each camera’s field of view so capture rates are comparable between different places and times. We investigated the optimal specifications for a low-cost camera trap for small mammals. The factors tested were 1) trigger speed, 2) passive infrared vs. microwave sensor, 3) white vs. infrared flash, and 4) still photographs vs. video. We also tested a new approach to standardise each camera’s field of view. We compared the success rates of four camera trap designs in detecting and taking recognisable photographs of captive stoats ( Mustela erminea ), feral cats (Felis catus) and hedgehogs ( Erinaceus europaeus ). Trigger speeds of 0.2–2.1 s captured photographs of all three target species unless the animal was running at high speed. The camera with a microwave sensor was prone to false triggers, and often failed to trigger when an animal moved in front of it. A white flash produced photographs that were more readily identified to species than those obtained under infrared light. However, a white flash may be more likely to frighten target animals, potentially affecting detection probabilities. Video footage achieved similar success rates to still cameras but required more processing time and computer memory. Placing two camera traps side by side achieved a higher success rate than using a single camera. Camera traps show considerable promise for monitoring invasive mammal control operations. Further research should address how best to standardise the size of each camera’s field of view, maximise the probability that an animal encountering a camera trap will be detected, and eliminate visible or audible cues emitted by camera traps.     

Application of Spin Traps to Biological Systems

Since 1971. when nitroxides were first reported to be bioreduced, several cellular enzymes, in addition to ascorbic acid. have been found to catalyze the reduction of nitroxides to their corresponding hydroxylami-nes. Numerous studies have demonstrated that cellular bioreduction of nitroxides are both dependent upon the structure of the nitroxide and cell type. For example, pyrrolidinyloxyls are considerably more resistant to bioreduction than their corresponding piperidinyloxyls. In addition, cellular levels of reductases present in freshly isolated rat hepatocytes are considerably greater than concentrations found in freshly isolated rat enterocytes. Thus, through the proper selection of a cell type and an appropriate nitroxide. one can study cellular-mediated free radical processes.

With the discovery that α-hydrogen-containing nitroxides, including 2, Z-dimethyl-S-hydroxy-l-pyrrolidinyloxyl (DMPO-OH) decompose rapidly in the presence of superoxide and thiols, the ability to determine if hydroxyl radical is generated during stimulation of human neutrophils, is in doubt. To explore the limits of spin trapping in this context. we have studied the effect of varying the rates of superoxide production. in the presence and absence of thiols, on the decomposition of DMPO-OH. In parallel studies, we have found that t-butyl α-methyl-4-pyridinyl-N-oxide nitroxide (4-POBN-CH₃) will not degrade in the presence of superoxide and a thiol. From these studies. we have determined that if hydroxyl radicals were generated as an isolated event in the presence of a continual flow of superoxide. spin trapping might not be able to detect its formation. Otherwise. spin trapping should be able to measure hydroxyl radicals. if continually generated, during activation of human neutrophils.