The effect of integration time on fluctuation measurements: calibrating an optical trap in the presence of motion blur

Dynamical instrument limitations, such as finite detection bandwidth, do not simply add statistical errors to fluctuation measurements, but can create significant systematic biases that affect the measurement of steady-state properties. Such effects must be considered when calibrating ultra-sensitive force probes by analyzing the observed Brownian fluctuations. In this article, we present a novel method for extracting the true spring constant and diffusion coefficient of a harmonically confined Brownian particle that extends the standard equipartition and power spectrum techniques to account for video-image motion blur. These results are confirmed both numerically with a Brownian dynamics simulation, and experimentally with laser optical tweezers.Comment: 12 pages, 6 figures, revtex4; published in Optics Express. http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-25-1251

Sun-Tracking Solar-Powered LED Street Light

Street lighting is an essential utility especially in urban and industrialized areas because it provides illumination and safety for vehicles and pedestrians throughout the night. However, street lights are relatively inefficient; they consume large amounts of power from electrical grids and have predetermined operation times that are often non-optimal for the surrounding environment. The Sun-Tracking Solar-Powered LED Street Lamp is a self-sustaining device, built to replace the current lighting sources. The device features sun-tracking capabilities for maximum energy gathering and darkness recognition to establish optimal operation times. The project provides a reliable and enhanced alternative to current street lighting systems

Binary DNA Nanostructures for Data Encryption

We present a simple and secure system for encrypting and decrypting information using DNA self-assembly. Binary data is encoded in the geometry of DNA nanostructures with two distinct conformations. Removing or leaving out a single component reduces these structures to an encrypted solution of ssDNA, whereas adding back this missing “decryption key” causes the spontaneous formation of the message through self-assembly, enabling rapid read out via gel electrophoresis. Applications include authentication, secure messaging, and barcoding

Beyond the frame rate: Measuring high-frequency fluctuations with light intensity modulation

Power spectral density measurements of any sampled signal are typically restricted by both acquisition rate and frequency response limitations of instruments, which can be particularly prohibitive for video-based measurements. We have developed a new method called Intensity Modulation Spectral Analysis (IMSA) that circumvents these limitations, dramatically extending the effective detection bandwidth. We demonstrate this by video-tracking an optically-trapped microsphere while oscillating an LED illumination source. This approach allows us to quantify fluctuations of the microsphere at frequencies over 10 times higher than the Nyquist frequency, mimicking a significantly higher frame rate.Comment: 4 pages, 2 figure

Massively parallel single-molecule manipulation using centrifugal force

Precise manipulation of single molecules has already led to remarkable insights in physics, chemistry, biology and medicine. However, widespread adoption of single-molecule techniques has been impeded by equipment cost and the laborious nature of making measurements one molecule at a time. We have solved these issues with a new approach: massively parallel single-molecule force measurements using centrifugal force. This approach is realized in a novel instrument that we call the Centrifuge Force Microscope (CFM), in which objects in an orbiting sample are subjected to a calibration-free, macroscopically uniform force-field while their micro-to-nanoscopic motions are observed. We demonstrate high-throughput single-molecule force spectroscopy with this technique by performing thousands of rupture experiments in parallel, characterizing force-dependent unbinding kinetics of an antibody-antigen pair in minutes rather than days. Additionally, we verify the force accuracy of the instrument by measuring the well-established DNA overstretching transition at 66 $\pm$ 3 pN. With significant benefits in efficiency, cost, simplicity, and versatility, "single-molecule centrifugation" has the potential to revolutionize single-molecule experimentation, and open access to a wider range of researchers and experimental systems.Comment: 5 pages, 3 figure

Massively parallel singlemolecule manipulation using centrifugal force

ABSTRACT Precise manipulation of single molecules has already led to remarkable insights in physics, chemistry, biology, and medicine. However, widespread adoption of single-molecule techniques has been impeded by equipment cost and the laborious nature of making measurements one molecule at a time. We have solved these issues by developing an approach that enables massively parallel single-molecule force measurements using centrifugal force. This approach is realized in an instrument that we call the centrifuge force microscope in which objects in an orbiting sample are subjected to a calibration-free, macroscopically uniform force-field while their micro-to-nanoscopic motions are observed. We demonstrate high-throughput singlemolecule force spectroscopy with this technique by performing thousands of rupture experiments in parallel, characterizing force-dependent unbinding kinetics of an antibody-antigen pair in minutes rather than days. Additionally, we verify the force accuracy of the instrument by measuring the well-established DNA overstretching transition at 66 5 3 pN. With significant benefits in efficiency, cost, simplicity, and versatility, single-molecule centrifugation has the potential to expand single-molecule experimentation to a wider range of researchers and experimental systems. Received for publication 8 January 2010 and in final form 10 March 2010. Single-molecule research has advanced greatly in the last decade, fueled in part by the development of technologies such as the atomic force microscope (AFM) and optical and magnetic tweezers, which enable precise physical manipulation of single molecular constructs (1). Remarkable studies with these instruments have already yielded new insight into such diverse areas as protein folding and unfolding dynamics, motor proteins, dynamic strength of receptor ligand interactions, enzymatic activity, and DNA mechanics (1-5). Widespread use of these powerful techniques, however, has been impeded by the laborious nature of making measurements one molecule at a time, the typically costly equipment, and the requisite technical expertise to perform these measurements. Recently these issues have received some attention with innovations such as multiplexed magnetic tweezer systems (6,7) to increase efficiency and more cost-effective designs for optical tweezers systems (8). We have developed an approach to solve these problems: massively parallel single-molecule force measurements using centrifugal force. The basic concept is that by rapidly rotating a high-resolution detection system, a centrifugal force field can be applied to an ensemble of objects while simultaneously observing their micro-to-nanoscopic motions. This is implemented in a new instrument that we call the centrifuge force microscope (CFM) The centrifugal force applied to each molecular tether can be easily determined using F ¼ mu 2 R, where m is the mass of the bead (minus the mass of the medium displaced to account for buoyancy), u is the magnitude of its angular velocity, and R is its distance from the axis of rotation. Since R is a macroscopic length much larger than the motion of the particles and the region of observation, the force field is conveniently uniform over the sample and as stable as the constancy of u. For monodisperse beads of known size and density (available commercially or by processing (11)) the centrifugal force on each particle is identical and can be calculated directly without calibration. Detection of molecular transitions, such as bond rupture or tether extension, is also straightforward. Since the force is normal to the coverslip and the whole system rotates, the beads appear relatively stationary in the field of view, but are pulled out of focus as a molecular tether stretches or detaches. Although a variety of bead detection schemes are possible, image focus provides the simplest way to determine if a bead is connected to the surface or not. For example, when measuring bond dissociation kinetics under constant force, one simply needs to measure the times at which singly tethered beads abruptly detach from the coverslip and disappear from view. We demonstrate this method by performing thousands of single-molecule measurements in parallel to characterize the force-dependent unbinding kinetics of digoxigenin and its antibody By applying various force clamps, we determined the force-dependent off-rate k off (f) ¼ k 0 exp(f/f b ) (12,13) for the interaction of digoxigenin and its antibody. We found a stress-free off-rate of k 0 ¼ 0.015 5 0.002 s À1 and a force scale of f b ¼ 4.6 5 1.3 p

Spiny Mice (\u3cem\u3eAcomys\u3c/em\u3e) Exhibit Attenuated Hallmarks of Aging and Rapid Cell Turnover after UV Exposure in the Skin Epidermis

The study of long-lived and regenerative animal models has revealed diverse protective responses to stressors such as aging and tissue injury. Spiny mice (Acomys) are a unique mammalian model of skin wound regeneration, but their response to other types of physiological skin damage has not been investigated. In this study, we examine how spiny mouse skin responds to acute UVB damage or chronological aging compared to non-regenerative C57Bl/6 mice (M. musculus). We find that, compared to M. musculus, the skin epidermis in A. cahirinus experiences a similar UVB-induced increase in basal cell proliferation but exhibits increased epidermal turnover. Notably, A. cahirinus uniquely form a suprabasal layer co-expressing Keratin 14 and Keratin 10 after UVB exposure concomitant with reduced epidermal inflammatory signaling and reduced markers of DNA damage. In the context of aging, old M. musculus animals exhibit typical hallmarks including epidermal thinning, increased inflammatory signaling and senescence. However, these age-related changes are absent in old A. cahirinus skin. Overall, we find that A. cahirinus have evolved novel responses to skin damage that reveals new aspects of its regenerative phenotype

A Dual-Stack Coaxial Magnetic Gear for a Wave Energy Conversion Generator

This paper presents the electromagnetic and mechanical design and analyses of a 7.67:1 gear ratio magnetic gear for a wave energy converter demonstrator. A 2-D and 3-D magnetostatic finite element analysis (FEA) was conducted to maximize the mass torque density. To increase torque without increasing the diameter a unique dual-stack rotor topology was used along with a twelve-segment per pole-pair inner rotor Halbach array and a four-segment per pole-pair outer rotor Halbach topology. The eddy current loss within the magnetic gear was mitigated by using laminated magnets and a low-loss electrical steel. The experimentally tested magnetic gear had a peak torque of 1796.8 N∙m which corresponds to an active region volumetric and mass torque density of 221.1 N∙m/L and 105.74 N∙m/kg, respectively. The efficiency at rated speed and maximum torque was measured to be 95%. A new in-plane eddy current loss mechanism was identified as being a primary reason for the measured electrical losses being higher than initially calculated