Novel contact probing method using single fiber optical trapping probe

A novel contact probing method for microdevices with high aspect ratio or biological samples is proposed. In this technique, a dielectric microsphere is optically trapped by an optical fiber and used as a touch probe. In the simulations, the finite difference time domain (FDTD) method and Maxwell stress theory are applied to obtain a suitable shape for the tip of the optical fiber. The results show that it is possible to trap the microsphere by using a single optical fiber. In experiments, single fiber optical trapping is successfully demonstrated by considering the simulation results. In order to use the trapped microsphere in the touch probe, the intensity of the reentered beam that is reflected from the surface of the microsphere is monitored. When the probe is in contact with the surface of the object, the intensity of the beam changes and this change is used as the contact signal. Because the probe is trapped optically and the trapping force is very small, this system can be used in a low invasive method.     

A simple dynamic optical manipulation technique for label-free detection of biological cells

A dynamic optical tweezers system is employed for generation of an optical trap in continuous rotation for manipulating a biological cell in an aqueous solution. When the rotating speed is increased, the trapped cell experiences an augmented viscous drag force, and eventually it escapes from the trap at the critical rotating speed: when the drag force is greater than the trapping force. With experimental verifications, the method can easily be employed to differentiate cells in terms of trapping forces due to different refractive indices. The proposed method is a simple, robust, accurate and noninvasive label-free technique for cell detection.     

小型化矩形离子阱捕获能力的仿真研究

基于SIMION 7.0离子光学仿真软件对设计的矩形离子阱（RIT）的离子捕获效率进行了仿真,研究了离子初始位置和射频电压、频率对离子捕获效率的影响。仿真结果表明,只有初始位置靠近RIT中心的离子才能被有效捕获到。针对常见毒品及爆炸物所在的质量范围,对于内建电场空间尺寸为10mm×8.4mm×44mm（x,y,z）的RIT,选择捕获射频电压为50V0-p～100V0-p、频率1MHz时,既能保证较高的离子捕获效率,同时也降低了对电路系统指标的要求。     

Infrared multiphoton dissociation tandem charge detection-mass spectrometry of single megadalton electrosprayed ions

This work presents the implementation of tandem mass spectrometry for experiments on single electrosprayed ions from compounds of megadalton (MDa) molecular weight, using two charge detection devices. The first mass spectrometry stage (first charge detection device) combined with an ion gate allows both mass-to-charge ratio and charge selections of the megadalton ion of interest. The second stage is based on an electrostatic ion trap and consists of an image charge detection tube mounted between two ion mirrors. Single MDa ions can be stored for several dozen milliseconds. During the trapping time, single ions can be irradiated by a continuous wavelength CO(2) laser. We observe stepwise changes in the charge of a single trapped ion owing to multiphoton activation. Illustration of infrared multiphoton dissociation tandem mass spectrometry are given for single megadalton ions of poly(ethylene oxide)s and DNAs.     

用于钙离子全光囚禁的离子囚禁装置研究

随着离子光钟技术的飞速发展,由离子光钟中用来囚禁离子的射频场带来的微运动效应对其性能的影响也越来越不可 忽略。 为彻底消除这一效应,提出了全光囚禁离子光钟的实验方案。 针对这一实验方案,设计并搭建了用于钙离子全光囚禁的 离子囚禁装置。 该装置是采用刀片型离子阱设计,能够实现剩余力仅有 10 -20 N 量级的高精度的杂散电场补偿;具备 6 mm 的通 关孔径,很好满足了全光囚禁实验中偶极囚禁激光的通过需求;基于改良的螺旋谐振器设计搭建的射频系统能够实现在 9. 33(1) MHz 较低射频频率下的稳定耦合;结合高达 10 -9 Pa 的真空制备和装配导电玻窗的真空腔体,可以实现长时间的离子 囚禁。 为全光囚禁钙离子提供了实验基础,对光学囚禁离子光钟的实现具有重大意义。     

多局域空心光阱及其光场调控

本文通过一种产生多局域空心光阱的光学系统,研究了光阱位置与反射镜偏转角度的关系.基于衍射积分和矩阵光学的理论,分析并计算了入射光源经过光学元件后的光场分布,通过调控反射镜的偏转角度,可以实现光阱位置的任意变换,达到精确捕获和囚禁微粒的目的.当两个反射镜偏转角度的关系为θ1-θ2=90°时,变换的光阱位置在一条倾斜的直线...     

Measurement of probe displacement to the thermal resolution limit in photonic force microscopy using a miniature quadrant photodetector

A photonic force microscope comprises of an optically trapped micro-probe and a position detection system to track the motion of the probe. Signal collection for motion detection is often carried out using the backscattered light off the probe-however, this mode has problems of low S/N due to the small backscattering cross sections of the micro-probes typically used. The position sensors often used in these cases are quadrant photodetectors. To ensure maximum sensitivity of such detectors, it would help if the detector size matched with the detection beam radius after the condenser lens (which for backscattered detection would be the trapping objective itself). To suit this condition, we have used a miniature displacement sensor whose dimensions makes it ideal to work with 1:1 images of micrometer-sized trapped probes in the backscattering detection mode. The detector is based on the quadrant photo-integrated chip in the optical pick-up head of a compact disc player. Using this detector, we measured absolute displacements of an optically trapped 1.1 μm probe with a resolution of ～10 nm for a bandwidth of 10 Hz at 95% significance without any sample or laser stabilization. We characterized our optical trap for different sized probes by measuring the power spectrum for each probe to 1% accuracy, and found that for 1.1 μm diameter probes, the noise in our position measurement matched the thermal resolution limit for averaging times up to 10 ms. We also achieved a linear response range of around 385 nm with cross talk between axes ?4% for 1.1 μm diameter probes. The detector has extremely high bandwidth (few MHz) and low optical power threshold-other factors that can lead to its widespread use in photonic force microscopy.     

基于辐射压力控制的微型元件的加工与检测

We have been developing new fabrication tools based on optical radiation pressur e and related phenomena to develop aflexible and accurate microfabrication tec hnology. In this paper, the laser trapping probe for the nano-CMM for assessment, in addition to micromachining technique using a small particle controlled by optical radiation pressure and laser aggregation technique are discussed. As the positional detection probe for the nano-CMM, an optically trapped silica particle with 8 mm diameter in forced oscillation state is used. A probe sphere retains a stable position when applied with trapping force by Nd:YAG laser light formed an nu lar and is forced to oscillate by the driving force changed by modulating the in tensity of LD emission. Experintal results show that this vibrational microprobe h as the possibility to achieve positional sensing accuracy of less than 25 nm. As a new micromachining technique, nano-removal process using an optically trapped micro-grain is proposed. The laser trapping force enables not only to stably trap the diamond grain with asymmetrical shape but also to freely control the positi on with spinning. Using this micro machining tool, the machining experiments of h ydrocarbon film are performed. AFM observation confirmed that the fine groove wi th depths of about 3～4 nm can be fabricated. As an additive process based on ra diation pressure, a laser microstructure fabrication using laser agglomeration p h enomena of colloidal particles aided by radiation pressure is investigated. By c ontrolling laser beam scanning in slurry containing KOH solution and SiO₂ par ticles with a diameter of 140 nm, colloidal particles are aggregated and adhered firmly to a silicon wafer substrate. Using this laser agglomerating process, two-dimensional grid microstructures at the pitch of 5 mm can be fabricated.     

A single gold particle as a probe for apertureless scanning near-field optical microscopy

We report on the fabrication, characterization and application of a probe consisting of a single gold nanoparticle for apertureless scanning near-field optical microscopy. Particles with diameters of 100 nm have been successfully and reproducibly mounted at the end of sharp glass fibre tips. We present the first optical images taken with such a probe. We have also recorded plasmon resonances of gold particles and discuss schemes for exploiting the wavelength dependence of their scattering cross-section for a novel form of apertureless scanning near-field optical microscopy.     

Multidepth, multiparticle tracking for active microrheology using a smart camera

The quantitative measurement of particle motion in optical tweezers is an important tool in the study of microrheology and can be used in a variety of scientific and industrial applications. Active microheology, in which the response of optically trapped particles to external driving forces is measured, is particularly useful in probing nonlinear viscoelastic behavior in complex fluids. Currently such experiments typically require independent measurements of the driving force and the trapped particle's response to be carefully synchronized, and therefore the experiments normally require analog equipment. In this paper we describe both a specialized camera and an imaging technique which make high-speed video microscopy a suitable tool for performing such measurements, without the need for separate measurement systems and synchronization. The use of a high-speed tracking camera based on a field programmable gate array to simultaneously track multiple particles is reported. By using this camera to simultaneously track one microsphere fixed to the wall of a driven sample chamber and another held in an optical trap, we demonstrate simultaneous optical measurement of the driving motion and the trapped probe particle response using a single instrument. Our technique is verified experimentally by active viscosity measurements on water-ethylene glycol mixtures using a phase-shift technique.     

The μPIVOT: an integrated particle image velocimeter and optical tweezers instrument for microenvironment investigations

A novel instrument to manipulate and characterize the mechanical environment in and around microscale objects in a fluidic environment has been developed by integrating two laser-based techniques: micron-resolution particle image velocimetry (μPIV) and optical tweezers (OT). This instrument, the μPIVOT, enables a new realm of microscale studies, yet still maintains the individual capabilities of each optical technique. This was demonstrated with individual measurements of optical trap stiffness (～70 pN μm(-1) for a 20 μm polystyrene sphere and a linear relationship between trap stiffness and laser power) and fluid velocities within 436 nm of a microchannel wall. The integrated device was validated by comparing computational flow predictions to the measured velocity profile around a trapped particle in either a uniform flow or an imposed, gravity-driven microchannel flow (R(2) = 0.988, RMS error = 13.04 μm s(-1)). Interaction between both techniques is shown to be negligible for 15 μm to 35 μm diameter trapped particles subjected to fluid velocities from 50 μm s(-1) to 500 μm s(-1) even at the highest laser power (1.45 W). The integrated techniques will provide a unique perspective toward understanding microscale phenomena including single-cell biomechanics, non-Newtonian fluid mechanics and single particle or particle-particle hydrodynamics.     

Evaluation of major historical ICR cell designs using electric field simulations

In Fourier-transform ion cyclotron resonance mass spectrometry, ions are detected by measuring image current induced in the detecting electrodes by trapped ions rotating in a magnetic field at their cyclotron frequencies. The ion trap used for this purpose is called the Penning trap. It can have various configurations of electrodes that are used to create a trapping electric field, to excite cyclotron motion, and to detect the induced signal. The evolution of this type of mass spectrometry is mainly driven by progress in the technology of superconducting magnets and in the constantly improved design of the ion cyclotron resonance (ICR) measuring cell. In this review, we focus on ICR cell designs. We consider that the driving forces of this evolution are the desire to increase resolution, mass accuracy and dynamic range, as well as to adapt new methods for creating and trapping ions.     

Optical trapping

Since their invention just over 20 years ago, optical traps have emerged as a powerful tool with broad-reaching applications in biology and physics. Capabilities have evolved from simple manipulation to the application of calibrated forces on-and the measurement of nanometer-level displacements of-optically trapped objects. We review progress in the development of optical trapping apparatus, including instrument design considerations, position detection schemes and calibration techniques, with an emphasis on recent advances. We conclude with a brief summary of innovative optical trapping configurations and applications.     

Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration

Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.     

An apparatus for immersing trapped ions into an ultracold gas of neutral atoms

We describe a hybrid vacuum system in which a single ion or a well-defined small number of trapped ions (in our case Ba(+) or Rb(+)) can be immersed into a cloud of ultracold neutral atoms (in our case Rb). This apparatus allows for the study of collisions and interactions between atoms and ions in the ultracold regime. Our setup is a combination of a Bose-Einstein condensation apparatus and a linear Paul trap. The main design feature of the apparatus is to first separate the production locations for the ion and the ultracold atoms and then to bring the two species together. This scheme has advantages in terms of stability and available access to the region where the atom-ion collision experiments are carried out. The ion and the atoms are brought together using a moving one-dimensional optical lattice transport which vertically lifts the atomic sample over a distance of 30 cm from its production chamber into the center of the Paul trap in another chamber. We present techniques to detect and control the relative position between the ion and the atom cloud.     

Micromanipulation of chloroplasts using optical tweezers

This paper describes experiments using optical tweezers to probe chloroplast arrangement, shape and consistency in cells of living leaf tissue and in suspension. Dual optical tweezers provided two-point contact on a single chloroplast or two-point contact on two adhered chloroplasts for manipulation in suspension. Alternatively, a microstirrer consisting of a birefringent particle trapped in an elliptically polarized laser trap was used to induce motion and tumbling of a selected chloroplast suspended in a solution. We demonstrate that displacement of chloroplasts inside the cell is extremely difficult, presumably due to chloroplast adhesion to the cytoskeleton and connections between organelles.  The study also confirms that the chloroplasts are very thin and extremely cup-shaped with a concave inner surface and a convex outer surface.     

Limited utility of acetoxymethyl (AM)-based intracellular delivery systems, in vivo: interference by extracellular esterases

The use of acetoxymethyl (AM) groups to deliver and trap exogenous optical probes inside cells is an established tool in cell biology/physiology, however, these probes have not been used extensively in vivo. In this study, the use of the acetoxymethyl delivery system for optical probes was evaluated, in vivo. Initial studies revealed very little trapped probe in intact tissues even when near saturating levels of probe were injected in living animals. We tested the hypothesis that extracellular esterases rapidly cleave the acetoxymethyl groups preventing the probes from entering cells, in vivo. The rates of hydrolysis of 11 acetoxymethyl probes in diluted porcine plasma revealed an essentially first order high rate dye cleavage with half times on the order of minutes or less. Studies on mice and rabbits revealed rates 10‐ to 2‐fold higher, respectively. These plasma studies suggested that the acetoxymethyl probes were being cleaved before having a chance to enter cells in tissues in vivo. This was confirmed using intravital 2‐photon excitation microscopy in muscle tissue where several acetoxymethyl probes were found to rapidly cleave in the vascular space during infusion and not be trapped in the muscle cells. Studies with succinimidyl esters that should quickly bind to proteins on cleavage also failed to enter cells, in vivo, consistent with the notion that the cleavage was occurring in the extracellular space. These data suggest that the high level of plasma and extracellular esterase activity render the classical acetoxymethyl probes ineffective for monitoring intracellular events, in vivo. Different approaches to trapping exogenous probes will need to be explored for physiological studies using intravital microscopy.     

Characterization of a new open cylindrical ion cyclotron resonance cell with unusual geometry

A new cylindrical ion cyclotron resonance cell with electrodes of different diameters is characterized. It consists of a central segmented electrode for ion trapping and detection and two planar trapping electrodes with a center bore, to which two small tube electrodes are fitted. The cell can trap either positive or negative ions or both ion polarities in the center region. For trapping both ion polarities, an unsymmetrical double well potential can be generated. Ions generated from SF(6) by electron impact or electron attachment are investigated. In depth analysis of radial excitation patterns of positive and negative ions trapped simultaneously in different stability regions reveals sharp discrimination in the extent of radial acceleration. SIMION simulations of the radial excitation show different trajectories of positive and negative ions. Axial component of radial dipolar excitation field exists in the terminal stability regions.     

Evanescent-wave scattering in near-field optical microscopy

Extended Mie theory is used to investigate the scattering and extinction of evanescent waves by small spherical particles and aggregates of such particles. Metallic, dielectric and metal-coated dielectric particles are taken into consideration. In contrast to plane-wave excitation, p- and s-polarized spectra differ in the case of evanescent waves due to the inherent asymmetry of both polarizations. Furthermore, contributions from higher multipoles are strongly enhanced, compared with plane-wave excitation, and the enhancement factors are polarization dependent. The corresponding changes in the scattering and extinction spectra are most pronounced in cases where higher multipoles exhibit resonances in the spectral range considered. This applies, for example, to morphological resonances of dielectric particles with size parameters > 1. The effect of the surface, where the evanescent wave is generated by total internal reflection, on the scattering and extinction spectra is investigated via numerical field calculations employing the multiple multipole method. In an application to apertureless near-field optical microscopy, the variation of the scattered power is calculated when a silicon particle is scanned across a silver particle in the evanescent field.     

An integrated ion trap and time-of-flight mass spectrometer for chemical and photo- reaction dynamics studies

We demonstrate the integration of a linear quadrupole trap with a simple time-of-flight mass spectrometer with medium-mass resolution (m/Δm ～ 50) geared towards the demands of atomic, molecular, and chemical physics experiments. By utilizing a novel radial ion extraction scheme from the linear quadrupole trap into the mass analyzer, a device with large trap capacity and high optical access is realized without sacrificing mass resolution. This provides the ability to address trapped ions with laser light and facilitates interactions with neutral background gases prior to analyzing the trapped ions. Here, we describe the construction and implementation of the device as well as present representative ToF spectra. We conclude by demonstrating the flexibility of the device with proof-of-principle experiments that include the observation of molecular-ion photodissociation and the measurement of trapped-ion chemical reaction rates.