Paolo Andrich, Benjamín J. Alemán, Jonathan C. Lee, Kenichi Ohno, Charles F. de las Casas, F. Joseph Heremans, Evelyn L. Hu, and David D. Awschalom
The nitrogen-vacancy (NV) center in diamond is an attractive platform for quantum information and sensing applications because of its room temperature operation and optical addressability. A major research effort focuses on improving the quantum coherence of this defect in engineered micro- and nanoscale diamond particles (DPs), which could prove useful for high-resolution sensing in fluidic environments. In this work we fabricate cylindrical diamonds particles with finely tuned and highly reproducible sizes (diameter and height ranging from 100 to 700 and 500 nm to 2 μm, respectively) using high-purity, single-crystal diamond membranes with shallow-doped NV centers. We show that the spin coherence time of the NV centers in these particles exceeds 700 μs, opening the possibility for the creation of ultrahigh sensitivity micro- and nanoscale sensors. Moreover, these particles can be efficiently transferred into a water suspension and delivered to the region to probe. In particular, we introduce a DP suspension inside a microfluidic circuit and control position and orientation of the particles using an optical trapping apparatus. We demonstrate a DC magnetic sensitivity of 9 μT/√Hz in fluid as well as long-term trapping stability (>30 h), which paves the way toward the use of high-sensitivity pulse techniques on contactless probes manipulated within biological settings.
DOI
Friday, August 8, 2014
Optical Printing of Electrodynamically Coupled Metallic Nanoparticle Arrays
Ying Bao , Zijie Yan , and Norbert F. Scherer
Optical forces acting on metallic nanoparticles can be used to organize mesoscale arrays for various applications. Here, we show that silver nanoparticles can be deposited as ordered arrays and chains on chemically modified substrates using a simple and facile optical trapping approach that we term “optical printing”. The deposited patterns show preferred separations between nanoparticles resulting from their electrodynamic coupling (i.e., optical binding) in the electromagnetic field of the optical trapping beam. Centrosymmetric optical traps readily allow simultaneous deposition of nanoparticle pairs and triples maintaining the interparticle geometries present in solution. Repositioning an optical line trap with small intercolumn separations allows selectively sampling low and high energy parts of the interparticle potentials. We find that the preferred particle arrangements controllably change from rectangular and triangular to near-field aggregates as one forces the separation to be small. The separation affects the interactions. Interpretation of the results is facilitated by electrodynamic simulations of optical forces. This optical printing approach, which enables efficient fabrication of dense nanoparticle arrays with nanoscale positional precision, is being employed for quantum optics and enhanced sensing measurements.
DOI
Optical forces acting on metallic nanoparticles can be used to organize mesoscale arrays for various applications. Here, we show that silver nanoparticles can be deposited as ordered arrays and chains on chemically modified substrates using a simple and facile optical trapping approach that we term “optical printing”. The deposited patterns show preferred separations between nanoparticles resulting from their electrodynamic coupling (i.e., optical binding) in the electromagnetic field of the optical trapping beam. Centrosymmetric optical traps readily allow simultaneous deposition of nanoparticle pairs and triples maintaining the interparticle geometries present in solution. Repositioning an optical line trap with small intercolumn separations allows selectively sampling low and high energy parts of the interparticle potentials. We find that the preferred particle arrangements controllably change from rectangular and triangular to near-field aggregates as one forces the separation to be small. The separation affects the interactions. Interpretation of the results is facilitated by electrodynamic simulations of optical forces. This optical printing approach, which enables efficient fabrication of dense nanoparticle arrays with nanoscale positional precision, is being employed for quantum optics and enhanced sensing measurements.
DOI
Precession Mechanism of Nematic Liquid Crystal Droplets under Low Power Optical Tweezers
Sorasak Phanphak, Apichart Pattanaporkratana, Jumras Limtrakul & Nattaporn Chattham
Optical tweezers is a magnificent tool for microscopic manipulation. Owing to few piconewton noninvasive trapping force, the tiny objects from micro sand beads down to living bacteria can be trapped under optical tweezers system. Liquid crystals (LC) are materials that enriched of optical properties providing various phemomena that can be applied for technology. In this report, we applied optical tweezers to nematic liquid crystal system for the optical manipulation study. 5CB (4-cyano-4’-pentylbiphenyl) was used with an appropriate surfactant to prepare nematic liquid crystal (NLC) droplets at room temperature. NLC droplets in radial and bipolar configurations can be formed. They react with light angular momentum and reveal dynamic and static changes through spinning and changing of internal configuration. Several recent articles reported spinning dynamics of NLC droplets under high power trapping (more than a few hundred milliwatts), however, high power caused disturbance in internal configuration of droplets. Dynamic changes of droplet under low power trapping (lower than 100 mW) conducting so far were reported unsuccessful. Here we report the first investigation on behaviour of radial NLC droplet under low power optical trap. The configuration of droplets was not disturbed under low power trapping. We investigated the dynamic behaviour of non-disturbed NLC droplet in low power optical trap.
DOI
Optical tweezers is a magnificent tool for microscopic manipulation. Owing to few piconewton noninvasive trapping force, the tiny objects from micro sand beads down to living bacteria can be trapped under optical tweezers system. Liquid crystals (LC) are materials that enriched of optical properties providing various phemomena that can be applied for technology. In this report, we applied optical tweezers to nematic liquid crystal system for the optical manipulation study. 5CB (4-cyano-4’-pentylbiphenyl) was used with an appropriate surfactant to prepare nematic liquid crystal (NLC) droplets at room temperature. NLC droplets in radial and bipolar configurations can be formed. They react with light angular momentum and reveal dynamic and static changes through spinning and changing of internal configuration. Several recent articles reported spinning dynamics of NLC droplets under high power trapping (more than a few hundred milliwatts), however, high power caused disturbance in internal configuration of droplets. Dynamic changes of droplet under low power trapping (lower than 100 mW) conducting so far were reported unsuccessful. Here we report the first investigation on behaviour of radial NLC droplet under low power optical trap. The configuration of droplets was not disturbed under low power trapping. We investigated the dynamic behaviour of non-disturbed NLC droplet in low power optical trap.
DOI
Optical trapping Rayleigh particles by using focused multi-Gaussian Schell-model beams
Xiayin Liu and Daomu Zhao
We numerically investigate the radiation forces of multi-Gaussian Schell-model (MGSM) beams, in which the degree of coherence is modeled by the multi-Gaussian function, exerted on the Rayleigh dielectric sphere. By simulation of the forces calculation it is found that the steepness of the edge of the intensity profile (i.e., the summation index M) and the initial coherence width of the MGSM beams play important roles in the trapping range and stability. We can increase the trapping range at the focal plane by increasing the value of M or decreasing the initial coherence of the MGSM beams. It is also found that the trapping stability becomes lower due to the increase of the value of M or the decrease of coherence. Furthermore, the trapping stability under different conditions is explicitly analyzed. The results presented here are helpful for some possible applications.
DOI
We numerically investigate the radiation forces of multi-Gaussian Schell-model (MGSM) beams, in which the degree of coherence is modeled by the multi-Gaussian function, exerted on the Rayleigh dielectric sphere. By simulation of the forces calculation it is found that the steepness of the edge of the intensity profile (i.e., the summation index M) and the initial coherence width of the MGSM beams play important roles in the trapping range and stability. We can increase the trapping range at the focal plane by increasing the value of M or decreasing the initial coherence of the MGSM beams. It is also found that the trapping stability becomes lower due to the increase of the value of M or the decrease of coherence. Furthermore, the trapping stability under different conditions is explicitly analyzed. The results presented here are helpful for some possible applications.
DOI
Friday, August 1, 2014
DNA bridging and looping by HMO1 provides a mechanism for stabilizing nucleosome-free chromatin
Divakaran Murugesapillai, Micah J. McCauley, Ran Huo, Molly H. Nelson Holte, Armen Stepanyants, L. James Maher III, Nathan E. Israeloff and Mark C. Williams
The regulation of chromatin structure in eukaryotic cells involves abundant architectural factors such as high mobility group B (HMGB) proteins. It is not understood how these factors control the interplay between genome accessibility and compaction. In vivo, HMO1 binds the promoter and coding regions of most ribosomal RNA genes, facilitating transcription and possibly stabilizing chromatin in the absence of histones. To understand how HMO1 performs these functions, we combine single molecule stretching and atomic force microscopy (AFM). By stretching HMO1-bound DNA, we demonstrate a hierarchical organization of interactions, in which HMO1 initially compacts DNA on a timescale of seconds, followed by bridge formation and stabilization of DNA loops on a timescale of minutes. AFM experiments demonstrate DNA bridging between strands as well as looping by HMO1. Our results support a model in which HMO1 maintains the stability of nucleosome-free chromatin regions by forming complex and dynamic DNA structures mediated by protein–protein interactions.
DOI
The regulation of chromatin structure in eukaryotic cells involves abundant architectural factors such as high mobility group B (HMGB) proteins. It is not understood how these factors control the interplay between genome accessibility and compaction. In vivo, HMO1 binds the promoter and coding regions of most ribosomal RNA genes, facilitating transcription and possibly stabilizing chromatin in the absence of histones. To understand how HMO1 performs these functions, we combine single molecule stretching and atomic force microscopy (AFM). By stretching HMO1-bound DNA, we demonstrate a hierarchical organization of interactions, in which HMO1 initially compacts DNA on a timescale of seconds, followed by bridge formation and stabilization of DNA loops on a timescale of minutes. AFM experiments demonstrate DNA bridging between strands as well as looping by HMO1. Our results support a model in which HMO1 maintains the stability of nucleosome-free chromatin regions by forming complex and dynamic DNA structures mediated by protein–protein interactions.
DOI
Ceragenin Mediated Selectivity of Antimicrobial Silver Nanoparticles
Mark A Hoppens , Christopher B Sylvester , Ammar T Qureshi , Thomas Scherr , Desiree R Czapski , Randolph S Duran , Paul B Savage , and Daniel J. Hayes
The understanding that common broad spectrum antimicrobials disrupt natural microbial flora important in acquiring nutrients and preventing infection has resulted in a paradigm shift favoring more selective antimicrobials. This report explores silver nanoparticles conjugated with ceragenin, or cationic antimicrobials (CSA-SNPs), as a potential gram-positive selective antimicrobial. Herein, CSA-SNPs are characterized using TEM, DLS, zeta potential, and HPLC-ESI-TOF-MS. The antimicrobial properties are determined through MIC/MBC and time-kill studies. Spatial selectivity of the conjugate nanoparticle was evaluated using confocal imaging, MATLAB statistical analysis, and video monitored interactions between bacteria and CSA-SNPs via laser trapping techniques. Cytotoxicity is also determined by live/dead staining and flow cytometry. Average particle size as determined through TEM analysis and hydrodynamic diameter determined via DLS are 63.5 +/- 38.8 nm and 102.23 +/- 2.3 nm respectively. The zeta potential of the SNP before and after CSA attachment is -18.23 mV and -8.34 mV. MIC/MBC data suggests CSA-SNPs are eight times more effective against Staphylococcus aureus than SNPs alone. Furthermore, MATLAB analysis of confocal imaging found that 70% of CSA-SNPs are within 2 µm of S. aureus whereas this percentage falls to below 40% with respect to Escherichia coli. These results are bolstered further by laser trapping experiments demonstrating selective adherence of CSA-SNPs conjugates with bacterial strains. Cytotoxicity studies of CSA-SNPs against 3T3 fibroblasts indicate 50% cell viability at 50 ppm.
DOI
The understanding that common broad spectrum antimicrobials disrupt natural microbial flora important in acquiring nutrients and preventing infection has resulted in a paradigm shift favoring more selective antimicrobials. This report explores silver nanoparticles conjugated with ceragenin, or cationic antimicrobials (CSA-SNPs), as a potential gram-positive selective antimicrobial. Herein, CSA-SNPs are characterized using TEM, DLS, zeta potential, and HPLC-ESI-TOF-MS. The antimicrobial properties are determined through MIC/MBC and time-kill studies. Spatial selectivity of the conjugate nanoparticle was evaluated using confocal imaging, MATLAB statistical analysis, and video monitored interactions between bacteria and CSA-SNPs via laser trapping techniques. Cytotoxicity is also determined by live/dead staining and flow cytometry. Average particle size as determined through TEM analysis and hydrodynamic diameter determined via DLS are 63.5 +/- 38.8 nm and 102.23 +/- 2.3 nm respectively. The zeta potential of the SNP before and after CSA attachment is -18.23 mV and -8.34 mV. MIC/MBC data suggests CSA-SNPs are eight times more effective against Staphylococcus aureus than SNPs alone. Furthermore, MATLAB analysis of confocal imaging found that 70% of CSA-SNPs are within 2 µm of S. aureus whereas this percentage falls to below 40% with respect to Escherichia coli. These results are bolstered further by laser trapping experiments demonstrating selective adherence of CSA-SNPs conjugates with bacterial strains. Cytotoxicity studies of CSA-SNPs against 3T3 fibroblasts indicate 50% cell viability at 50 ppm.
DOI
Channel-Facilitated Diffusion Boosted by Particle Binding at the Channel Entrance
Stefano Pagliara, Simon L. Dettmer, and Ulrich F. Keyser
We investigate single-file diffusion of Brownian particles in arrays of closely confining microchannels permeated by a variety of attractive optical potentials and connecting two baths with equal particle concentration. We simultaneously test free diffusion in the channel, diffusion in optical traps coupled in the center of the channel, and diffusion in traps extending into the baths. We found that both classes of attractive optical potentials enhance the translocation rate through the channel with respect to free diffusion. Surprisingly, for the latter class of potentials we measure a 40-fold enhancement in the translocation rate with respect to free diffusion and find a sublinear power law dependence of the translocation rate on the average number of particles in the channel. Our results reveal the function of particle binding at the channel entrances for diffusive transport and open the way to a better understanding of membrane transport and design of synthetic membranes with enhanced diffusion rate.
DOI
We investigate single-file diffusion of Brownian particles in arrays of closely confining microchannels permeated by a variety of attractive optical potentials and connecting two baths with equal particle concentration. We simultaneously test free diffusion in the channel, diffusion in optical traps coupled in the center of the channel, and diffusion in traps extending into the baths. We found that both classes of attractive optical potentials enhance the translocation rate through the channel with respect to free diffusion. Surprisingly, for the latter class of potentials we measure a 40-fold enhancement in the translocation rate with respect to free diffusion and find a sublinear power law dependence of the translocation rate on the average number of particles in the channel. Our results reveal the function of particle binding at the channel entrances for diffusive transport and open the way to a better understanding of membrane transport and design of synthetic membranes with enhanced diffusion rate.
DOI
Four-directional stereo-microscopy for 3D particle tracking with real-time error evaluation
R. F. Hay, G. M. Gibson, M. P. Lee, M. J. Padgett, and D. B. Phillips
High-speed video stereo-microscopy relies on illumination from two distinct angles to create two views of a sample from different directions. The 3D trajectory of a microscopic object can then be reconstructed using parallax to combine 2D measurements of its position in each image. In this work, we evaluate the accuracy of 3D particle tracking using this technique, by extending the number of views from two to four directions. This allows us to record two independent sets of measurements of the 3D coordinates of tracked objects, and comparison of these enables measurement and minimisation of the tracking error in all dimensions. We demonstrate the method by tracking the motion of an optically trapped microsphere of 5 μm in diameter, and find an accuracy of 2–5 nm laterally, and 5–10 nm axially, representing a relative error of less than 2.5% of its range of motion in each dimension.
DOI
High-speed video stereo-microscopy relies on illumination from two distinct angles to create two views of a sample from different directions. The 3D trajectory of a microscopic object can then be reconstructed using parallax to combine 2D measurements of its position in each image. In this work, we evaluate the accuracy of 3D particle tracking using this technique, by extending the number of views from two to four directions. This allows us to record two independent sets of measurements of the 3D coordinates of tracked objects, and comparison of these enables measurement and minimisation of the tracking error in all dimensions. We demonstrate the method by tracking the motion of an optically trapped microsphere of 5 μm in diameter, and find an accuracy of 2–5 nm laterally, and 5–10 nm axially, representing a relative error of less than 2.5% of its range of motion in each dimension.
DOI
Near real-time measurement of forces applied by an optical trap to a rigid cylindrical object
Joseph Glaser; David Hoeprich; Andrew Resnick
An automated data acquisition and processing system is established to measure the force applied by an optical trap to an object of unknown composition in real time. Optical traps have been in use for the past 40 years to manipulate microscopic particles, but the magnitude of applied force is often unknown and requires extensive instrument characterization. Measuring or calculating the force applied by an optical trap to nonspherical particles presents additional difficulties which are also overcome with our system. Extensive experiments and measurements using well-characterized objects were performed to verify the system performance.
DOI
DOI
Surface Charge Effects on Optical Trapping of Nanometer-Sized Lipid Vesicles
Seongmin Park, Siyoung Choi, Chaeyeon Song, MahnWon Kim and Myung Chul Choi
Optical trapping of nanometer-sized lipid vesicles has been challenging due to the low refractive index contrast of the thin lipid bilayer to the aqueous medium. Using an “optical bottle”, a recently developed technique to measure interactions of nanoparticles trapped by an infrared laser, we report, for the first time, quantitative measurements of the trapping energy of charged lipid vesicles. We found that the trapping energy increases with the relative amount of anionic lipids (DOPG) to neutral lipids (DOPC) in vesicles. Moreover, as monovalent salt is added in the exterior solution of vesicles, the trapping energy rapidly approaches zero, and this decrease in trapping energy strongly depends on the amount of anionic lipids in vesicles. A simple model with our experimental observations explains that the trapping energy of charged lipid vesicles is highly correlated with the surface charge density and electric double layer. In addition, we demonstrated selective trapping of a binary mixture of vesicles in different mole fractions of charged lipids, a strategy that has potential implications on charge selective vesicle sorting for engineering applications.
DOI
Optical trapping of nanometer-sized lipid vesicles has been challenging due to the low refractive index contrast of the thin lipid bilayer to the aqueous medium. Using an “optical bottle”, a recently developed technique to measure interactions of nanoparticles trapped by an infrared laser, we report, for the first time, quantitative measurements of the trapping energy of charged lipid vesicles. We found that the trapping energy increases with the relative amount of anionic lipids (DOPG) to neutral lipids (DOPC) in vesicles. Moreover, as monovalent salt is added in the exterior solution of vesicles, the trapping energy rapidly approaches zero, and this decrease in trapping energy strongly depends on the amount of anionic lipids in vesicles. A simple model with our experimental observations explains that the trapping energy of charged lipid vesicles is highly correlated with the surface charge density and electric double layer. In addition, we demonstrated selective trapping of a binary mixture of vesicles in different mole fractions of charged lipids, a strategy that has potential implications on charge selective vesicle sorting for engineering applications.
DOI
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